WELDING Reference Text 2

JOURNEYMANPROGRAMME

ForewordMIC has produced this book for us in its Industrial Maintenance Journeyman Programme and it is specifically designed to introduce the basics of maintenance.

This book is intended for use as a reference text to be supplemented by notes and explanations and does not stand alone.

Compilation of this book was completed with standard published material, Tel-A-Train and resource personnel at MIC. No claim is made to the ownership of any material contained herein.

THIS BOOK IS NOT FOR SALE

REFERENCE TEXT USED

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TABLE OF CONTENTS

1. Occupational Safety, Health and Environment 3

2. General Workshop Safety 8

3. Oxy-Fuel and Welding Equipment 19

4. Oxy-Fuel Gas Welding and Practical Exercises 30

5. Oxy-Fuel Gas Cutting 46

6. Shielded Metal Arc Welding (S.M.A.W.) Equipment 82

7. Shielded Metal Arc Welding Fundamentals 90

8. Inspection and Quality Control 121

9. Cutting Processes (Introduction) 129

10. Welding Symbols and Blue Print Reading (Introduction) 132

11. Basic Welding Metallurgy 146

12. Basic Science of Welding 153

13. Distortion and Residual Stress 160

14. Arc Welding Electrode Classification 169

15. Shielded Metal Arc Welding Exercise 184

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OccupationalSafety,Health

AndEnvironment

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OCCUPATIONAL HEALTH AND SAFETY

WHAT IS OCCUPATIONAL HEALTH AND SAFETY?

Occupational health and safety encompasses the social, mental and physical wellbeing of workers in their oc-cupations.This will include:

i. The promotion of good working conditions.ii. The protection of workers from occupational risk.iii. The adaption of work to humans. (Ergonomics)

WHY IS OCCUPATIONAL HEALTH AND SAFETY IMPORTANT?

Occupational health and safety is very important. In that, work related accidents and diseases can be very costly both to employees and employers directly and indirectly.

Pertaining to workers, direct cost can be:

• The pain and suffering of the injury or illness.• The loss of income• The possible loss of job• Health-care costs

One of the most obvious indirect costs is the physiological effect suffered by both the worker and his/her imme-diate family.

The direct cost to employers will include:

• Payment for work not performed• Medical and compensation payments• Repair or replacement of damaged machinery and equipment• Reduction or a temporary halt in production• Increased training expenses and administration costs• Possible reduction in the quality of work• Negative effect on morale in other workers

Indirect cost will include:

• The injured/ill worker has to be replaced.• A new worker has to be trained and given time to adjust• It takes time before the new worker is producing at the rate of the original worker• Time must be devoted to obligatory investigations, to the writing of reports and filling out of forms.• Accidents often arouse the concern of fellow workers and influence Labour relations in a negative way.• Poor health and safety conditions in the workplace can also results in poor public relations.

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DEVELOPMENTS BEFORE THE INDUSTRIAL REVOLUTION

It is important for students of industrial health and safety to first study the past. Under-standing the past can help safety and health professionals examine the present and future with a sense of perspective and continuity. Modern developments in health and safety are neither isolated nor independent. Rather, they are part of the long continuum of developments in the safety and health movements.The continuum begins with days of the ancient Babylons. During that time, circa 2000 B.C., their ruler Hammu-rabi developed his Code of Hammurabi. The code encompassed all of the laws of the land at that time, showed Hammurabi to be a just ruler, and set a precedent followed by other Mesopotamian kings. The significance of the code from the perspective of safety and health is that it contained clauses dealing with injuries, allowable fees for physicians, and monetary damages assessed against those who injured others. This clause from the code illustrates Hammurabi’s concern for the proper handling of injuries: “If a man has caused the loss of a gentle-man’s eye, his own eye shall be caused to be lost.”This movement continued and emerged in later Egyptian civilization. As evidenced form the temples and pyramids that still remain, the Egyptians were an industrious people. Much of the labor was provided by slaves, and there is ample evidence that slaves were not treated well; that is, unless it suited the needs of the Egyptian taskmasters.One such case occurred during the reign of Rameses 11 (cira 1500 B.C.), who undertook a major construction project, the Ramesseum. To ensure the maintenance of a workforce sufficient to build this huge temple bearing his name, Ramesses created an industrial medical service to care for workers. They were required to bathe daily in the Nile and were given regular medical examinations. Sick workers were isolated.The Romans were vitally concerned with safety and health, as can be seen from the remains of their construc-tion projects. The Romans built aqueducts, sewerage systems, public baths, latrines, and well-ventilated houses.As civilization progressed, so did safety and health developments. In 1567, Philippus Aureolus produced a treatise on the pulmonary disease on miners. Entitled on the miners’ Sickness and Other Miners’ diseases, the treatise covered the disease of smelter workers and metallurgists and diseases associated with the handling of and exposure to mercury. Around the same time, Georgius Agricola published his treatise De Re Metallica, emphasizing the need for ventilations in mines and illustrating various devices that could be used to introduce fresh air into mines.The Eighteenth century saw the contributions of Bernardino Ramazzini, who wrote Discourse on the Diseases of Workers. Ramazzini drew conclusive parallels between diseases suffered by workers and their occupations. He related occupational diseases to the handling of harmful materials and to irregular or unnatural movements of the body. Much of what Ramazzini wrote is still relevant today.The industrial Revolution changed forever the methods of producing goods. According to LaDou, the changes in production brought about by the industrial Revolution can be summarized as follows:

• Introduction of inanimate power (i.e., steam power) to replace people and animal power• Substitution of machines for people• Introduction of new methods for converting raw materials• Organization and Specialization of work, resulting in a division of labor

These changes necessitated a greater focusing of attention on the safety and health of workers. Steam power in-creased markedly the potential for life-threatening injuries, as did machines. The new methods used for convert-ing raw materials also introduced new risks of injuries and diseases. Specialization, by increasing the likelihood of boredom and attentiveness, also made the workplace a more dangerous environment.

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MILESTONES IN THE SAFETY MOVEMENT

Just as the United States traces its roots to Great Britain, the safety movement in this country traces its roots to England. During the Industrial Revolution, child labor in factories was common. The hours were long, the work hard, and the conditions often unhealthy and unsafe. Following an outbreak of fever among children in their cotton mills, the people of Manchester, England, began demanding better working conditions in the factories. Public pressure eventually forced a government response, and in 1802 the Health and Morals o Apprentices Act was passed. This was a milestone piece of legislation: It marked the beginning of governmental involvement in workplace safety.When the industrial sector began to grow in the United States, hazardous working conditions were common-place. Following the civil war, the seeds of the safety movement were sown in this country. Factory inspection was introduced in Massachusetts in 1867. In 1868, the first barrier safeguard was patented. In 1869, the Penn-sylvania legislation passed a mine safety law requiring two exits from all mines. The Bureau of Labor Statistics (BLS) was established in 1869 to study industrial accidents and report pertinent information about those acci-dents.The following decade saw little new progress in the safety movement until 1877, when the Massachusetts legis-lative passed a law requiring safeguards for hazardous machinery. This year also saw passage of the Employer’s Liability Law, establishing the potential for employer liability in workplace accidents. In 1892, the first record-ed safety program was established in a Joliet, Illinois, steel plant in response to a scare caused when a flywheel exploded. Following the explosion, a committee of managers was formed to investigate and make recommenda-tions. The committee’s recommendations were used as the basis for the development of a safety program that is considered to be the first safety program in American industry.Around 1900, Frederick Taylor began studying efficiency in manufacturing. His purpose was to identify the im-pact of various factors on efficiency, productivity, and profitability. Although safety was not a major focus of his work, Taylor did not draw a connection between lost personnel time and management policies and procedures. This connection between safety and management represented a major step toward broad-based safety conscious-ness.In 1907, the U.S. Department of the interior created the Bureau of Mi9nes to investigated accidents, examine health hazards, and make recommendations for improvements. Mining workers definitely welcomed this devel-opment since over 3,00 of their fellow workers were killed in mining accidents in 1907 alone.

The Health and safety at Work etc. Act 1974

This act is very important. It covers the legal duties of employers, employees and self-employed persons. Health and safety are everyone’s responsibility. One of the important aims of the Act is to encourage employers and employees to work together to make a safer workplace.

General Duties of Employers

The following points are summarized from the Act.

1. It is the duty of every employer to ensure the safety, health and welfare of all employees at the work-place. This includes the maintenance of plant and the working environment, and also the provision of safe entrances to and exits from the workplace.

2. Safety and the absence of risks to health must be ensured during all handling, storage and transportation operations.

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3. Instruction, training and supervision must be provided so far as is reasonable practicable.

4. A written statement of the general policy with respect to health and safety of employees at work must be drawn up.

5. Provision is also included in the Act for the election of employees as safety representatives.

General Duties of Employees

As an employee it is your duty to take reasonable care of your own health and safety. You must not take risks or endanger others by your actions. You must also cooperate with the employer on health and safety matters.

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GeneralWorkshop

Safety

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GENERAL WORKSHOP SAFETY

Knowledge of general workshop safety is absolutely imperative to ensure control of safety hazards and reduc-tion of incidents or accidents. This knowledge will include:

i. CLOTHING AND PERSONAL SAFETY

ii. HOUSEKEEPING

iii. FIRE HAZARDS

iv. ELECTRICAL HAZARDS

v. MACHINE HAZARDS

vi. FUMES AND VENTILATION

vii. LIFTING

viii. HAZADOUS OBSTACLES

ix. HAND AND POWER TOOLS

i. CLOTHING AND PERSONAL SAFETY are subdivided into six sections:

➢ Protective clothing ➢ ➢ Leathers/Cap ➢ ➢ Welding Gloves ➢ ➢ Safety Boots ➢ ➢ Glasses/Goggles ➢ ➢ Welding Helmet

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➢ Protective Clothing

Clothing for the trainees in the welding environment should be of the appropriate type and design so as to pre-vent the occurrence of overexposure of the body to heat and radiation. Polyester and synthetic fibers are strictly forbidden as these materials ignite when exposed to intense heat or sparks. Wool or treated cotton is strongly recommended to resist the heat or sparks. The shirt or coveralls should have covered pockets and have buttons at the neck. Trousers and coveralls should not have cuffs that could catch hot metal spatter. The colour of the clothing is also very critical, in that, dark clothing is preferred to minimize the reflection of the arc rays, which could be deflected under the welding helmet.

➢ Leathers/Caps

As a welder sometimes you are required to weld in positions that are very uncomfortable (out-of-position) and the falling of hot metal or spatter become very dangerous to the welder. Therefore, the wearing of leathers and cap become extremely necessary to prevent skin and scalp burns.

Leathers are classified as:

• Leather aprons: - These are worn to the front of your body.• Split leg aprons: - These are worn similar to the leather aprons.• Sleeves and jackets: - These are worn on the shoulders to prevent burning from falling hot metal.• Spats: - These are worn over the safety boots to prevent spatter from entering the boots from top.• Caps: - The cap is worn to protect the hair from hot metal spatter.

➢ Welding Gloves

The welding gloves should be made of leather to protect hands from spattering hot metal and ultraviolet and infrared arc rays.N.B. Trainees must be instructed that the gloves are not designed to handle hot material as this action will harden and shrivel the leather.

➢ Safety Boots

Safety boots must be designed with steel-toe or tips, to protect trainees from heavy falling objects. Additionally, the height of the boots is also important a slow-top shoes are forbidden, due to the fact that sparks or spatter could fall into the shoes, causing severe burns.

➢ Glasses/Goggles

Anyone entering the welding shop or welding environment should wear goggles or approved safety glasses to protect eyes from flying debris due to grinding or any other similar exercise. Approved safety glasses/goggles are designed with impact resistance lenses and side shields to ensure maximum safety as stated by the Ameri-can Welding Society (A.W.S.). The required standard is normally Z 87.1.

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➢ Welding Helmet

The welding helmet is required once Shielded Metal Arc Welding (S.M.A.W.) is performed, as it provides pro-tection to the welder’s eye and face from dangerous arc rays. The material for the helmet is usually heat resist-ant and very light. The shades of the lens are normally chart recommended.

ii. HOUSEKEEPING

Housekeeping involves keeping floors and workbenches clean of dirt, scrap metal, grease, and oil. Combustibles such as wood, paper, rags, and flammable liquids must be kept clear off all areas where sparks or hot metal may fly. Passageways must be kept clear of hoses and electric cables, which can cause tripping accidents. Hoses and cables may be run over possibly become damaged in the process.Therefore, it is absolutely necessary that trainees maintain an environment, which is properly organized and clear of hazards.

iii. FIRE HAZARDS

Fire Hazards are caused by the exposure of combustible materials in a welding environment. Fire extinguish-ers must be employed, and the trainees, trained in the usage of such equipment. Furthermore, the knowledge of types of fires and the proper shutting down of equipment in case of fire must be taught.

iv. ELECTRICAL HAZARDS

Electrical Hazards are very dangerous and can be fatal. What must be enforced to trainees is that, all electrical equipment must be installed and repaired only by well-trained and competent technicians. Additionally, signs identifying the specific voltage of equipment and the correct procedures to follow when in use must be on dis-play.

v. MACHINERY HAZARDS

Machinery must be operated only after thorough training on how the machine operates, its safety hazards, its safety features, the correct placement of hands and feet, and the proper sequence of operation.

vi. FUMES AND GASES

Dust, Fumes and metal particles can be a hazard to health. For this reason, shops should have high ceiling for greater air volume and well-designed ventilation systems.

vii. LIFTING

Part of general workshop safety is knowing how to lift objects safely. Firstly, it involves putting on lifting belts or back brace. Furthermore, in the lifting exercise the back must be kept straight and the legs must do the lifting.

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viii. HAZARDOUS OBSTACLES

These obstacles can be divided into two hazards:

• Temporary• Permanent

Temporary hazards should be identified with signs, fences, or barriers, whereas, permanent hazards must be painted with yellow and black stripes to create high visibility.

ix. HAND AND POWER TOOLS

Before use, all hand and power tools must be examined for defects or loose parts. If some defect has been dis-covered it should be reported to the instructor as soon as possible.

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FUMES AND GASES

The presence of fumes and gases generated by Shielded Metal Arc welding (S.M.A.W.), in the Welding envi-ronment, is a matter of concern to those responsible for the well-being of welding personnel. Some constitute a potential hazard to the health of the welder, while others are merely a nuisance. The potential harm however, depends on the chemical composition of the fumes, the concentration in the breathing zone, and the length of exposure time.Fumes are particles formed by electrode and base metal constituents that are vaporized and subsequently con-densed in the welding area. Because of their small size, fume particles may remain suspended in the aerosol form for long periods. Since the particles have mass and size and are affected by air movement, electrical fields, gravity, diffusional forces, and other external forces, they trend to agglomerate into clumps that gradually settle on the floor and other surfaces. While suspended, however, all persons in the vicinity inhale them.In addition to fume particles, there are also gases formed that have toxic effects. These include ozone, oxides of nitrogen, carbon monoxide, carbon dioxide, and various specific constituents of the rods, rod coatings, and the metal themselves. Welding on steel produces oxides of nitrogen and ozone gases. Ozone is an intense-ly irritating gas produced by the action of the electric arc on the welding material.Toxic fumes may be generated if the steel has been coated with various materials or on alloys containing certain materials. Some non-toxic paints may produce toxic fumes when welded upon. For example, certain phthalic-based paints may give off extremely irritating fumes. Additionally, welding of metals coated with greases or paints containing synthetic chemical polymeric binders may emit highly toxic chemicals such as carbon monoxide, benzene, phosgene, hydrogen cyanide, polycyclic aromatic hydrocarbons and nitrogen dioxide. Fumes from metals such as copper and zinc are capable of producing metal fume fever. Apart from zinc and copper, other metals that can cause such occurrence are aluminum, antimony, iron, manganese, nickel and cad-mium. Metal fume fever is a common occupational illness among welders, caused by inhalation. Fever, chills, general malaise, joint pains, cough, sore throat, chest tightness, and fatigue usually appear four to twelve hours following exposure and last from one to two days.Diagnosis of metal fume fever is often difficult because its symptoms resemble those of a number of upper res-piratory tract illnesses. Cadmium poisoning is one of them.Cadmium poisoning is associated with the welding of cadmium and the overexposure of the welder. Further-more, it has been reported that cadmium poisoning can cause kidney damage, which is first manifested by urinary excretion of serum proteins (proteinuna). Again this occurrence depends on the duration and severity of exposure.Shielded Metal Arc welding is done with coated electrodes. Compounds, which are contained in welding electrode coating, include oxides of various metals, hydroxides, carbonates, silicates, fluorides, and organic materials. The fluorides are of the greatest significance because of their toxicity and because large amounts are released during welding.The welding of stainless steel with its coated electrodes produces fumes, which contain hexavalent chromium and nickel compounds which may be carcinogenic. (Cancerous).The welding of alloys particularly those containing beryllium can be exceptionally hazardous. Beryllium and its compounds can cause lung disease and certain skin conditions.

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RADIATION

Shielded Metal Arc welding (S.M.A.W.) process produces an arc between a base metal and a consumable flux-coated metal electrode. The arc across the gap between the metal electrode and the base metal cre-ates a temperature of approximately 6500 F – 7000 F (3600 C – 3900 C). The intensity of this light pro-duces both infrared radiation and ultraviolet radiation which, causes skin damage and “flash burn” or “welder’s flash” to the eyes of the welder.Photokeratitis (welder’s flash) is a painful inflammation of the cornea, which results from exposure to ultravio-let radiation. Symptoms do not appear until several hours after exposure. Additionally, Pterygia, membranous growths that extend across the outer eye from the conjunctiva to the cornea, are thought to be caused by overex-posure to ultraviolet radiation.“Welder’s flash” is temporary but repeated or prolonged exposure can lead to permanent injury to the eyes, such as retinal burning and the foundation of senile cataracts.

ELECTRIC SHOCK

The avoidance of electric shock in the Shielded Metal Arc Welding process is very critical to the trainee welder. Most electric shocks experienced at welding voltages have not caused severe injury; however, these voltages are sufficiently high that under certain conditions they may be lethal. Even mild shocks can produce involuntary contractions leading to injurious falls. Largely the path of the current and the amount flowing through the body determines the severity of the shock. The voltage and the contact resistance of the area of skin involved deter-mine this. Wearing clothing damp from perspiration or working in wet conditions reduces skin contact resist-ance and thus increases the risk of electric shock.The electric shock hazard, associated with arc welding may be divided into two categories, which are quite dif-ferent:

• Primary voltage shock (230-460 volts)• Secondary voltage shock (60-100 volts)

The primary voltage shock is very dangerous because it is much greater than the welder secondary voltage. You can receive a shock from the primary (input) if you touch a lead inside the machine with the power to the machine “on” while you have your body or hand on the machine case or other grounded metal. Remember that turning the machine switch “off” does not turn the power off inside the machine. The input power cord must be unplugged or the power disconnect switch turned off.A secondary voltage shock occurs when you touch a part of the electrode circuit, perhaps a bare spot on the electrode cable at the same time another part of your body is touching the metal, which you are welding.

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NOISE

Noise has been described as an unwanted and undesirable sound. In a welding environment or welding shop apart from the Shielded Metal Arc Welding process, there are other processes that can produce noise that may affect the hearing threshold shift of the welder or worker.

These processes are:

• GRINDING• CUTTING PROCESSES SUCH AS: a) Air carbon arc cutting b) Plasma arc cutting

Noise in the welding environment can pose two safety and health related problems.

i. Distractionii. Hearing Loss

Distraction is likely to happen when there is noise, and this could lead to a disruption in concentration, which can lead to accidents.Hearing loss can occur when exposure to noise exceeds the prescribed levels, and this could be described as two types.

a) Temporary hearing lossb) Permanent hearing loss

Temporary hearing loss occurs when a short time has been spent in a noisy environment without proper protec-tion. The condition is called temporary threshold shift. This means that after short exposure in a noisy envi-ronment there is a ringing in the ears and one cannot hear very well. This occurrence however, wears off if the worker is isolated from the source of noise for a short time. Permanent hearing loss occurs when the worker or welder has been exposed to excessive noise for a long time. Permanent hearing loss can never be repaired, and this may cause social problems since the worker may find it difficult to hear what other people are saying and warning signals in the workplace may also become unclear, resulting in accidents.

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TYPES OF NOISE

In the welding environment there are various types of noise:

➢ Steady wide – band noise, noise including a wide range of frequencies e.g. general machine shop noise. ➢ Steady narrow – band noise in which the sound energy is largely concentrated in a few frequencies e.g.

circular saws, planners etc. ➢ Impact noise – single, short duration impulses e.g. hammering. ➢ Repeated impact noise – riveting, fettling. ➢ Intermittent noise – traffic noise, aircraft noise.

In conclusion, it could be stated that the fundamental hazard associated with excessive noise is hearing loss. Ex-posure to excessive noise levels for an extended period of time can damage the inner ear (sensorineural loss) so that the ability to hear high-frequency sound is diminished or lost altogether. Additional exposure can increase the damage until even lower frequency sounds cannot be heard. A number of different factors affect the risk of hearing loss associated eith exposure to excessive noise.

The most important of these are;

➢ Intensity of the noise (sound pressure level) ➢ Type of noise (wide band, narrow band, or impulse) ➢ Duration of daily exposure ➢ Total duration of exposure (number of years) ➢ Age of individual ➢ Coexisting hearing disease ➢ Nature of environment in which exposure occurs ➢ Distance of the individual from the source of the noise ➢ Position of the ears relative to the sound waves.

Of these factors, the most critical are the sound level, frequency, duration, and distribution of noise.

FIGURE 1CRITICAL NOISE RISKS FACTORS

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The unprotected human ear is at risk when exposed to sound levels exceeding 115 dBA. Exposure to sound lev-els below 80 dBA is generally considered safe. Prolonged exposure to noise levels higher than 80 dBA should be minimized through the use of appropriate personal protective devices.To increase the risk of hearing loss, exposure to noise should be limited to a maximum eight hour time weighted average of 85 dBA. The following general rules should be applied for dealing with noise in the workplace:

➢ Exposure of less than 80 dBA may be considered safe for the purpose of risk assessment. ➢ A time-weighted average (threshold) of 85 dBA should be considered the maximum limit of continuous

exposure over eight hour days without protection.

The following chart gives recommended limits of noise exposure for the number of hours exposed.

FIGURE 11

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FIRE AND EXPLOSION(Fire Hazards)

The temperature associated with the Shielded Metal Arc Welding (SMAW) is very high or extreme, thus, mak-ing it imperative that the trainees be aware of the dangers as it pertains to fire hazards.

The heat of the welding arc can reach temperatures of 10,000 F, but this heat in itself is not generally a fire hazard. The danger of fire actually results from the effects of this intense heat upon your work and in the form of sparks and molten metals. Because these can spray up to 35 feet from your work, you must recognized and distance yourself from combustible materials. It is also important to be sure the work is not in contract with any combustible materials, which it may ignite when heated.

These materials fall into three categories:

➢ Liquid (gasoline, oil, paints and thinners) ➢ Solid (wood, cardboard and paper) ➢ Gaseous (acetylene and hydrogen)

Watch where the sparks and metals are falling from your work. If there are flammable materials including fuel or hydraulic lines in the work area and neither the work nor the combustible substances can be moved then a fire resistance shield should be put in place.If you are welding above the ground or off ladder, make sure that there are no combustibles underneath. Also, do not forget about your co-workers, and everybody else who may be in the work area, as they probably would not appreciate being hit with slag or sparks from your work.Particular care must be taken when welding or cutting in dusty locations. The nature of the dust may be ex-tremely volatile in the heat of the arc or in the presence of a hot spark. Fine dust particles may readily oxidize and without warning result in a flash fire or even an explosion. Additionally, welding on concrete can also be explosive due to the chemical makeup of the concrete material.

Fires are classified into four main categories, which must be known by the trainees.

They are as follows:

➢ Class A: Fires, which involve solid materials, predominantly of an organic kind, forming glowing em-bers. Examples are wood, paper, and coal.

➢ Class B: Fires, which involve liquids or liquefiable solids; they are further subdivided into: Class B 1: which involve liquids soluble in water, for example methanol. Class B 2: which involve liquids not soluble in water, such as petrol and oil.

➢ Class C: Fires, which involve gases or liquefied gases resulting from leaks or spillage, e.g. methane or butane.

➢ Class D: Fires, which involve metals such as aluminum or magnesium.

N.B. electrical fires have been removed from the category of fires, because, it has been noted that electricity is a cause of fire.

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Oxy-FuelAnd

WeldingEquipment

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SETTING UP OXYACETYLENEWELDING EQUIPMENT

OBJECTIVES

After completing this unit the student will:

• Properly set up oxyacetylene welding equipment• Observe specific safety precautions when handling oxyacetylene equipment• Be able to list the components of an oxyacetylene welding outfit and describe their functions.

The following is a list of the most important equipment for a standard welding outfit:

• Oxygen• Acetylene• Oxygen Regulator• Acetylene Regulator/Flash Back arrestors• Welding hoses• Torch (sometimes called a blow pipe)• Welding tips• Goggles• Hammer• Pliers• Striker• Tip cleaners• Table with steel or firebrick top• Twelve-inch adjustable wrench (or manufacturer’s cylinder wrenches)• Protective clothing

Oxyacetylene Processes

Oxyacetylene welding is based on the principle that, when acetylene gas is burned in the proper proportions, with oxygen gas, a flame is produced, which is hot enough to melt and fuse metals.

This proportion is approximately 1 part of acetylene to 2 ½ parts of oxygen. Oxyacetylene flame cutting uses much of the same equipment, but the principle is different. In oxyacetylene cutting a stream of oxygen is direct-ed against a piece of ferrous metal (metal which contains iron called ferrous), which has been heated to a color. This causes the metal to burn

Oxygen Cylinder

The oxygen cylinder, figure 1-1, is usually green or yellow in color, so that it can be identified. It is made from a single plate of high grade steel, which has been heat treated to develop toughness and strength. When fully charged, the oxygen bottle, as it is sometimes called, contains 244 cubic feet of oxygen at a pressure of 2,200 pounds per square inch at 70 degrees Fahrenheit. This oxygen is 99.99% pure and is colorless, odorless and tasteless. Oxygen by itself will not burn, but it does support combustion.

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CAUTION: Because of the extremely high pressure at which oxygen is stored in the cylinder, several precau-tions must be observed at all time.

• All cylinders must have Interstate Commerce Commission markings, indicating the dates of bottle pres-sure test.• Cylinders must be stored so they cannot be knocked down.• They should not be stored in an area where extreme temperature changes occur.• Oxygen cylinders must not be stored near grease, oil or electrical connections. Bringing oxygen into contact with oil or grease may cause a violent explosion.• They must never be moved without the cylinder cap in place, on top of the cylinder.• Cylinders which are defective in any way should be taken out of service and reported to the supplier.

Valve Protection cap

The valve protection cap, or bottle cap, screws onto the cylinder and completely covers the valve, figure1-2. It protects the valve from damage when the cylinder is being moved or if it is accidentally knocked over.

Oxygen Cylinder Valve

The oxygen cylinder valve, figure 1-3, is attached to the top of the oxygen cylinder. It is used to turn the flow of oxygen on or off, as needed. These valves are double seated. This means that when the valve is completely closed the flow of oxygen from the cylinder from the cylinder is shut off, and when the valve is opened all the way the valve seats and prevents leakage of oxygen around the valve stem. The valve should be opened completely when the cylinder is in use.

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A safety fuse plug and disc are installed in the oxygen cylinder valve. As the temperature of the oxygen in the cylinder increases, the pressure also increas-es. If the pressure of the gas in the bottle becomes too great, the safety plug and disc will release the pressure.

Acetylene Cylinder

The pressure in acetylene cylinders is not as high as that in oxygen cylinders. For this reason, acetylene cylin-ders are rolled to the size needed and welded at the seams, figure 1-4.Acetylene cylinders are filled with a porous material, such as fuller’s earth or balsa wood. A liquid chemical (acetone) is poured into the bottle and is absorbed by the porous material. Acetone absorbs acetylene gas.Acetylene gas, which is made by mixing water and calcium carbide ( a gray, rock-like substance), has a strong disagreeable odor, resembling garlic. It is highly flammable and, in combination with oxygen, produces the hot-test flame known (5,800 degrees – 6,300 degrees Fahrenheit). When there is not enough oxygen present it burns with a smoky, yellow flame.

CAUTION: Because acetylene gas is highly flammable and explosive, certain safety precautions must be ob-served.

• Cylinders must be tested and certified by the Interstate Commerce Commission.• Cylinders which leak or are defective in any way should be taken out of service and reported to the sup-plier.• Free acetylene gas (that which is not absorbed in acetone) must not be stored at pressure above 15 pounds per square inch. Above this pressure acetylene becomes very unstable and may explode.• If large numbers of acetylene cylinders are stored close to oxygen cylinders a fire resistant wall must be built between the two types of cylinders.• Cylinders should never be used in any position but the upright position. Liquid acetone can run into the gages and hoses if the cylinder valve is opened while the cylinder is lying on its side.• Never store acetylene cylinders where excessive heat may contact them.

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Acetylene Cylinder Valves

The acetylene cylinder valve, figure 1-5, is attached to the top of the acetylene cylinder. It is used to turn the flow of acetylene on or off as needed. Acetylene cylinder valves are not double seated, be-cause they do not have to withstand the high pressure that oxygen cylinders do.These valves are of two types. One type has a hand wheel, resem-bling that on the oxygen cylinder valve. The other has a square stem, without the wheel, and is turned on and off with a special wrench, called a key.

CAUTION: The acetylene cylinder valve should never be opened more than 1 ½ turns. In this way, it can be turned off quickly in case of fire. For the same reason, the key should always be left on the valve.

Acetylene cylinders have plugs installed in them for safety. These plugs are made of a metal which melts at a low temperature. Any excessive heat, which would cause the gas in the cylinder to reach higher pressure, melts the plugs. This allows the acetylene to escape and prevents an explosion.

Oxygen Regulators

Full oxygen cylinder pressure is 2,200 pounds per square inch. It is impossible to weld with this much pres-sure, so a regulator is installed on the cylinder, figure 1-6. This regulator allows the welder to set the pressure at reduced amounts. It has a safety device, which vents the pressure if it exceeds safe limits.

Regulators are equipped with two gauges, figure 1-7. One indicates the cylinder pressure, while the other indi-cates the working or torch pressure. Oxygen gauges are generally built to withstand 3,000 pounds per square inch of pressure. When temperature variations cause the gas in the cylinder to expand, and increase the pressure, the gauge indicates this rise in pressure.

The regulator is equipped with a nut, which screws onto the cylinder valve. The threads are conventional, right hand threads. To install the regulator, tighten the nut with the wrench supplied by the manufacturer or with an adjustable wrench.

Acetylene Regulators

Acetylene regulators are similar to oxygen regulators, with two exceptions. All acetylene fittings have left hand threads. This is important to remember, as the fittings may be damaged by attempting to turn them the wrong way. The reason for the left hand threads on acetylene fittings is to prevent them from being accidently installed on oxygen equipment.

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The second way in which they are different from oxygen regulators is that acetylene gauges have lower numbers than oxygen gauges. As a general rule, the acetylene cylinder pressure gauge registers to 500 pounds per square inch. The acetylene working pressure gauge regis-ters to a maximum of 15 pounds per square inch. Also, the numbers and graduations on the dial of oxygen gauges are normally green, while on acetylene gauges they are normally red.

Note: gauges are delicate mechanisms and through mishandling they may not register correctly. However, the regulator will hold the cor-rect pressure, even if the gauge does not indicate it correctly.

Torch

The welding torch (or blowpipe) has separate inlets for oxygen and acetylene. It transports the gases to the mixing chamber where they mix in the correct proportion for welding. The mixing is controlled by two valves on the handle, each of which may be opened and closed to regulate the flow of gases for the welding flame.The most commonly used torch is the equal pressure (or medium pressure) type, figure 1-8. In this type approximately equal amounts of oxygen and acetylene are used for welding.

• Acetylene valves should not be opened more than 1 ½ turns.• Oxygen regulators register high pressures.• Acetylene regulators are made to register lower pressures.• Oxygen equipment is identified by green markings and has right-hand threaded connections.• Acetylene equipment is identified by red color and has left-hand threaded connections, with grooves cut in the nuts.

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JOB 1: SETTING UP OXY ACETYLENE WELDING EQUIPMENT

Equipment: Oxygen bottle Acetylene bottle Oxygen regulator Acetylene regulator One set of welding hoses Torch Bottle cart Acetylene bottle key (if required) 12” adjustable wrench or manufacturer’s supplied wrenches

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PROCEDURE KEY POINTS1. Obtain full oxygen and acetylene cylinders and install them in the bottle cart, or fasten them se-curely in an upright position.2. Remove the cap from the oxygen cylinder. Store the cap on the cart.3. Open the cylinder valve slightly. Allow a small amount of oxygen to blow through the valve. Close the cylinder valve.4. Install the oxygen regulator, using a suitable wrench.5. Remove the cap from the acetylene cylinder. Store the cap.6. Open the valve on the acetylene cylinder slightly, using the cylinder key. Close valve.7. Install the acetylene regulator.8. Install the green hose on the oxygen gauge; install the red hose on the acetylene gauge.9. Open the oxygen cylinder valve slowly until a small amount registers on the gauge, then open it completely. Turn the adjustment screw on the regu-lator to the right, until a small amount of pressure shows on the low pressure gauge. This will blow the hose clean. Turn the adjustment screw to the left and release the pressure.10. Open the acetylene valve slowly until a small amount registers on the gauge. Then open it 1 ½ turns. Turn the adjustment screw on the regulator to the right, until a small amount of pressure shows on the low pressure gauge. This will blow the hose clean. Turn the adjustment screw to the left and release the pressure.11. Install the blowpipe (torch) on the open ends of the hoses.12. Be sure the torch valves are closed. Adjust the regulators so that 10 pounds of pressure shows on both the acetylene and the oxygen gauges.13. Check all connections with soapsuds. If bub-bles appear, a leak is indicated and the connections must be tightened.

1. Fasten the cylinders securely.

3. Do not stand in front of the valve. Make sure no one else is standing in front of the valve. This is called cracking the valve.4. Oxygen cylinders and regulators have right-hand threads. Tighten the nut snugly, but do not apply too much force or the threads may be stripped.

6. Caution: This gas is inflammable. No open fire!7. Left hand thread.8. Tighten fittings snugly. Over tightening will strip the threads.9. Sudden release of oxygen pressure may dam-age the gauges. Open valve very slowly until a slight pressure registers.Caution: Do not stand in front of the gauge face. Pressure may blow face outward.

10. Acetylene gas is inflammable. When releasing it into the room, be sure there is no open fire present. Do not open the acetylene valve more than 1 ½ turns.

11. Acetylene fittings have left-hand threads.

13. Caution: Do not use soap with an oil base. Oil and oxygen may cause a violent explosion. Use no oil.

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Summary: Job 1• Fasten the bottles securely in an upright position.• Crack the valves to clean any dirt from them.• Install the regulators. (Acetylene has left-hand threads)• Install the hoses.• Install the torch.• Set the regulators for 10 pounds per square inch, working pressure.• Check for leaks with soapsuds.• Reverse the procedure to disassemble the equipment.

REVIEW QUESTIONS

1. List the steps to be followed in setting up a welding outfit.2. What are the main differences between the valve on an oxygen cylinder and the valve on an acetylene cylinder?3. What is acetylene made from?4. What is the maximum safe pressure of free acetylene?5. Why are cylinder valves cracked before installing the regulators?6. Why is “Use No Oil” so strongly stressed?7. Why should the oxygen cylinder valve be opened very slowly after the regulator is attached?8. What is the purpose of a regulator?9. What is the difference between oxygen and acetylene fittings?10. Is oxygen inflammable?

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Oxy-FuelGas WeldingAnd Practical

Exercises

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SAFETY RULES

Oxygen Handling

1. Important. Use no oil or grease around oxygen. When mixed with oil or grease, oxygen can cause a vio-lent explosive.2. Do not use pipe fitting compounds on oxygen connections.3. Only hoses which are made for welding should be used.4. Do not force connections which do not fit.5. If gas cylinders are not clearly marked as to contents, do not use them.6. Do not use oxygen under high pressure without an oxygen regulator.7. Be sure that the oxygen cylinder is securely fastened so it cannot fail.8. Be sure the pressure adjusting screw is turned out (to the left) before the cylinder is opened.9. Stand to one side when opening a cylinder.

Acetylene Handling

1. Do not use pipe fitting compounds on acetylene equipment2. Always use an acetylene pressure reducing regulator.3. Never force connections which do not fit.4. Be sure the acetylene cylinder is securely fastened so it cannot fall.5. Do not release acetylene into the atmosphere when welding is being done in the area.6. Leave the bottle key on the acetylene cylinder.

General Rules

1. Always use a striker to light a torch.2. Never lay a lighted torch down.3. Before lighting the torch be sure it is not pointing at another person.4. Before lighting the torch be sure that flame will not come in contact with inflammable material.5. Make it a habit to hold your hand close to a piece of metal to see if it is lost, before picking it up.6. Never operate equipment without instruction on its use.7. Wear safety glasses or grinding shields when using a power grinder.

Oxyacetylene Welding Safety Rules

8. Be aware of the condition of the hoses on the torch. If a leak develops it should be reported immediately, and the hoses taken out of service.9. Report all burns.10. Never work with defective equipment.11. Hammers, chisels and punches wear out. Do not use them if they are defective.12. Never use any kind of fire around oxygen and acetylene cylinders. Oxygen supports combustion and acetylene will burn or explode.13. Bronze rod contains zinc. Galvanizing on some steel contains zinc. When zinc is heated it gives off a toxic vapor. Do not breathe these fumes. Be sure the ventilation is adequate.14. Avoid breathing the fumes when welding painted objects.15. Always wear goggles when cutting or welding.16. Always wear protective clothing when cutting or welding.17. Know the location of fire extinguishers, and how to use them.

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18. Some factors which contribute to accidents:

Poor lighting Improper electric outlets Poor maintenance of equipment Poor ventilation Poor housekeeping Machines without guards Poor arrangement of equipment Horseplay Slippery, dirty floors Damaged equipment Inadequate instruction

Summary: Job 1

• Fasten the bottles securely in an upright position.• Crack the valves to clean any dirt from them.• Install the regulators. (Acetylene has left-hand threads)• Install the hoses.• Install the torch.• Set the regulators for 10 pounds per square inch, working pressure.• Check for leaks with soapsuds.• Reverse the procedure to disassemble the equipment.

Review Questions

1. List the steps to be followed in setting up a welding outfit.2. What are the main differences between the valve on an oxygen cylinder and the valve on an acetylene cylinder?3. What is acetylene made from?4. What is the maximum safe pressure of free acetylene?5. Why are cylinder valves cracked before installing the regulators?6. Why is “Use No Oil” so strongly stressed?7. Why should the oxygen cylinder valve be opened very slowly after the regulator is attached?8. What is the purpose of a regulator?9. What is the difference between oxygen and acetylene fittings?10. Is oxygen inflammable?

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Lighting the Oxyacetylene Torch

OBJECTIVESThe welding student will:• Light the oxyacetylene torch following proper safety precautions.• Be able to identify oxidizing, carburizing, and neutral flames.• Adjust the torch for each of the tree types of flame.• Discuss the effect of each of the three types of flame on the metal.

FlamesThree basic flames can be made by adjusting the valves on the welding torch.• The carburizing flame.• The neutral flame.• The oxidizing flame.

Carburizing FlameA carburizing flame, figure 2-1, is the result of too much acetylene gas in the flame. This flame may be recog-nized by a long streamer of green colored gas which burns around the inner cone of the flame. This is called an acetylene feather. A carburizing flame is used to make the outside of metal hard, but is not good for a weld. The addition of the extra acetylene to the melted weld adds carbon to the metal and makes a hard, brittle weld. When this flame is used on melted parent metal, it causes the puddle to turn dark red, and gives it a boiling action.

Neutral FlameThe neutral flame, figure 2-2, is the welding flame. This flame can be recognized by a sharp inner cone and the absence of an acety-lene feather. It is made up of 2 ½ parts of oxygen and 1 part of acetylene. One part of the oxygen in the flame and one part of the acetylene come from the bottles. The other 1 ½ parts of oxygen are picked up from the air around the welding tip. A neutral flame does not add anything to or subtract anything from the parent metal (the metal being welded). The acetylene torch is adjusted for a neutral flame, for most welding jobs that require the metal to be melted and mixed together.

Oxidizing FlameAn oxidizing flame, figure 2-3, is the result of having too much oxygen in the gas mixture. This flame can be identified by a shorter inner cone and a whistling sound. It causes the molten metal to boil and spark. The additional oxygen in the flame causes the metal to burn, resulting in a brittle weld. A slightly oxidizing flame may be used for brazing, but it is not used for fusion weld-ing.

StrikerThe striker, figure 2-4, produces a spark by dragging a piece of flint across a file. A striker must always be used to light the oxyacetylene torch. The use of matches creates a hazard and may result in personal injury. The flints in most strikers may be replaced when the original one is worn out.

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GogglesGoggles are to be worn when welding. They are made in many shapes and sizes, to suit the individual welder. Welding goggles have dark lenses which filter out ultraviolet and infrared rays. For oxyacetylene welding they should be equipped with #4 or #5 filter lenses, either blue or brown. A clear glass cover lens fits over the filter lens, to protect the more expensive filter lenses from hot weld spatter.Ultraviolet rays are given off by the welding flame. These are the same invisible rays which make it dangerous for the human eye to look directly at the sun. These rays can cause severe burns and possible blindness.Infrared rays can cause a burn which looks like sunburn. The skin must be covered by clothing and the eyes protected by dark lenses to avoid the dangers of burns from infrared rays while welding.

Job 2: Lighting the Oxyacetylene TorchEquipment; Oxyacetylene outfit as assembled in Unit 1 Welding tips Goggles Gloves Striker

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1. Open the acetylene cylinder valve slightly until pressure registers on the high pressure gauge, figure 2-7, then open it ½ turn

2. Turn the adjusting screw to the right until pres-sure registers on the low pressure gauge, figure 2-8.

3. Open the acetylene needle valve on the torch handle and readjust the screw on the regulator until about 5 pounds registers, with the needle valve open. Close the needle valve on the torch.4. Open the acetylene needle valve on the torch about ½ turn. Hold the striker in the left hand (if right-handed), the torch in right hand, and strike a spark in front of the escaping gas.5. Open the needle valve on the torch until the flame jumps away from tip about 1/8”.6. As oxygen is added to the acetylene, observe the luminous cone at the tip, and the long greenish-color envelope around it. The green envelope is the excess acetylene of the carburizing flame.7. Continue to add oxygen by opening the oxygen needle valve until the feather of acetylene just disap-pears. The inner cone will now appear soft and lumi-nous. This is a neutral flame.8. If more oxygen is added now, the flame be-comes pointed and white in color. In addition, it makes a sharp whistling sound. This is an oxidizing flame.9. Practice adjusting the torch to carburizing, neutral, and oxidizing flames.10. Shut off the acetylene needle valve on the torch; shut off both cylinder valves completely; open the needle valves on the torch handle and drain the hoses. (Watch the gauges until they register 0.)11. Close the needle valves on the torch, release the pressure adjusting screws on the regulators by turning the handles to the left; coil the hoses and hang them up on the hose holder.

1. Never open the acetylene cylinder valve over ½ turn. Leave the key on the valve.

3. Set at about 5 psi.

4. Be sure the torch is not pointed toward any in-flammable material or people. Wear gloves and goggles.

5. The flame will appear turbulent, but will not smoke.6. A carburizing flame is used for hardening steel. It is generally used with the acetylene feather about 3 times as long as the inner cone.

7. The torch should make a soft, even blowing sound.

8. An oxidizing flame is harmful to the weld. It is never used for welding.

10. Shut off the acetylene first, so the escaping oxy-gen will blow any soot or impurities from tip.

11. Do not hang the hoses on the gauges. The weight may damage the gauges. Make sure no fires are burning around the work area.

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Summary: Job 2• Set up the welding equipment.• Install the tip on the torch.• Open the oxygen cylinder valve slowly.• Turn the adjusting screw on the regulator until the gauge indicates 5 psi.• Open the oxygen needle valve on the torch.• Readjust the gauge pressure to 5 psi with the valve open.• Open the acetylene cylinder valve.• Turn the adjusting screw on the regulator until the gauge indicates 5 psi.• Open the acetylene valve on the torch and light the flame.• Continue to open the acetylene needle valve until the flame jumps slightly away from the tip.• Open the oxygen needle valve on the torch and adjust the flame to neutral.• Reverse the procedures for shutting off the equipment.• Check for fires.

REVIEW QUESTIONS1. What is neutral flame?2. What is a carburizing flame?3. What is an oxidizing flame?4. Why is the pressure on the line gauges adjusted with the needle valves open?5. When shutting off the torch; which needle valve should be closed first?6. Why should the operator stand behind, or to one side of, the oxygen cylinder when opening the cylinder valve?7. What is the maximum working pressure of acetylene gas?

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OAW-OXY-ACETYLENE WELDINGOR

OFW-OXY-FUEL WELDING

In this welding process, low basic gases are employeda) Acetylene – C 2 N 2b) Oxygen – O 2 The energy for welding is created by a flame, so this process is considered to be a chemical method. Just as the heat is provided by a chemical reaction, the shielding for oxy-acetylene welding is accomplished by this flame as well. Therefore, no flux or eternal shielding is necessary.

Equipment for this process is relatively simple. It consists of several parts: Oxygen tank, acetylene tank, pres-sure regulators, torch and connecting hoses. The oxygen cylinder is a hollow, high pressure container capable of withstanding a pressure of approximately 2200 P.S.I. The acetylene cylinder on the other hand, is filled with a porous material similar to cement.

Acetylene exists in the cylinder dissolved in liquid acetone. Care must be taken since gaseous acetylene is extremely unstable at pressure exceeding 15 P.S.I. and an explosion could occur even without the oxygen. Since the acetylene cylinder contains a liquid it is important that it remains upright to prevent spillage.

Each cylinder has attached to its top a pressure regulator, which reduces the high internal tank pressure to work-ing pressures. Hoses then connect these regulators to the torch. The torch includes a mixing section where the oxygen and acetylene combine to provide the necessary mixture.These mixtures could then result into three types of flames.1) Neutral Flame2) Carburizing Flame3) Oxidizing Flame

After the gases are mixed, they flow through a detachable tip. Tips are made in a variety of sizes to allow weld-ing of different metal thickness.

Filter material used for this purpose has a quite simple identification system. Examples (RG-45 and RG-60). The “R” designates it as a rod, “G” stands for gas and the 45 and 60 relate to the minimum tensile strength of the weld deposit in thousands pounds per square inch (PSI). So 45 designates a weld deposit having a tensile strength of a least 45,000 PSI.The primary usage of OAW is the welding of thin sheet and small diameter piping. It is also applied in many maintenance situations as well.

However, as in all other processes there are advantage and disadvantages.

ADVANTAGES: i. It is relatively inexpensive and can be made very portable.ii. There is no electrical input.

DISADVANTAGES:i. The heat source produced by OAW is not as concentrate as an arc. Therefore, if a groove weld is being made, the joint penetration should exhibit a thin “feather edge” to assure that complete fusion is obtained at the root of the joint.ii. In comparison it is a slower process than S.M.A.W.iii. A substantial level of skill level is required.

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OXY-ACETYLENE WELDING

There are four key points that affects the quality of a finish weld. They are:-i. Quantity of heatii. Angle between rod and torchiii. Speed of traveliv. Distance of the cone from the puddle

i. QUANTITY OF HEATThis is determined by the size nozzle or tip. In the gas welding process if more heat is required it is recom-mended that the tip size be changed. If less heat is required the same as above is recommended. Reasons for this is that when welding a neutral flame is required and in this process the balance between Oxygen and Acetylene is equal. Oxygen readily supports combination; therefore to obtain more heat in the flame requires the addition of oxygen. If this is done it means that the balance between O2 and C2 H2 is affected. This would result in the change of the flame, thus affecting the finish weld. When less heat is required it means less oxygen, again af-fecting the two gases balance resulting in a defective weld. Backfire also occurs when this is done.

ii. ANGLE BETWEEN ROD AND TORCHThis is considered in relation to two types of weldsa) Buttb) FilletsInitially the blow pipe is held perpendicular to the plate and gradually the angle is decreased as the puddle is formed, to allow better viewing of the puddle and some ease with the filler rod may be added.

The filler rod is added after the puddle has been formed by dipping into the puddle. By maintaining an angle of 900 between the rod and torch ensures heating of this filler rod – i.e. it remains close to melting point, prior dipped into the puddle thus making melting of the rod easier.

iii. DISTANCE OF THE CONE FROM THE PUDDLEThe hottest region of the flame is the area just outside the cone, the closer this is kept to the base metal the more efficient the heating would be, also the “exposed” flame is more open to heat loses.Another reason for keeping the cone close to the puddle is to take advantage of the reducing cone.

iv. SPEED OF TRAVELFor consistent results the speed of travel must be such that the puddle be molten long enough for proper filler metal and base metal interaction.Thus the object then is to travel slowly enough to allow evolution of the gasses and ensure the puddle be of the same size throughout.

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Running a Bead with Filler Rod, Flat Position OBJECTIVES The student will:• Be able to define penetration and its importance.• Be able to describe filler rod and its use.• Be able to describe the flat position for welding.• Run a bead in the flat position using filler rod.

Penetration An oxyacetylene weld should always have 100% penetration. This means that the weld appears on the bottom of the parent metal as well as on the top. Poor penetration causes the metal to break in the weld. How-ever, too much penetration causes the molten metal to drop through and hang down below the parent metal. This condition is known as “icicles”. Excessive drop-through of molten metal cause oxidation, as the molten metal takes oxygen out of the atmosphere into the weld. This oxidation cause a brittle weld which is easily broken.

Mild Steel Steel which contains 0.30% carbon, or less, is called mild steel. It is the most commonly used steel for constructions purposes. It is also called low-carbon steel and black iron. Most of the steel used for construction purposes has a black appearance, caused by hot rolling at the steel mills, resulting of oxide on the metal.

Forehand Welding Right-handed welders usually hold the torch in the right hand and weld from right to left, adding the filler rod at the front of the flame. This procedure is called forehand welding. Left-handed operators weld from left to right, but the rod is still added at the front of the flame, since the torch is held in the left hand and the filler rod in the right.

Flat Welding Position A weld made on the topside of the parent metal and within 30 degrees of horizontal is called a flat weld. Flat welding is the most desirable position for welding, since the welder can control penetration and bead ap-pearance easily. In many welding shops, machines called positioners are used to hold the work so that it can eas-ily be turned into the flat position.

Filler Rod Filler rod is commonly called welding rod. It is added to the molten puddle to build up the cross section of weld where the penetration has forced the molten metal below the surface of the parent metal. To insure good penetration, filler rod should be added only after the puddle has been formed. The weld should have a cross sec-tion thicker than the original parent metal, so that strength is added at the point of the weld. The word convex means a rounded-up bead. Filler rods most commonly used are 1/16”,3/32” and 1/8” diameters.

Sheet Metal Metal which has been rolled in the steel mill to a thickness of 1/8” or less is commonly called sheet metal. This is the metal most commonly used with the oxyacetylene welding process, since any thickness over 1/8” is more easily jointed by electric arc welding. Sheet metal is designated by gauges. A few of the most com-mon gauges are listed below: 12-gauge .1120” approx. 1/8” thickness 14-gauge .0821” approx. 5/64” thickness 16-gauge .0635” approx. 1/16” thickness 18-gauge .0508” approx. 3/64” thickness

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Neutral Flame A neutral flame is used for welding. On an equal pressure torch, the gauges should be set at approxi-mately the same pressure, if the welding is not to be done in a confined area. Welding in a restricted area, such as a corner of the metal, uses up the atmospheric oxygen rapidly and changes the character of the flame from neutral to carburizing. More oxygen pressure may be needed for such a welding condition. In this case the oxy-gen pressure must be higher than the acetylene pressure, until the welding in the restricted area is completed. If the oxygen pressure has been increased, it must be lowered after the welding in the corner is finished.

JOB 3: RUNNING A BEAD WITH FILLER RODEquipment and Material: Standard Oxyacetylene Welding Equipment. 16-gauge mild steel sheet metal. 1/16” mild steel filler rod.

PROCEDURE

1. Place the sheet metal sample on 2 firebricks.2. Wear goggles to protect the eyes. Light the torch and adjust to a neutral flame.3. Hold the torch in the right hand, if right-hand-ed, and a piece of filler rod in the left hand.4. Hold the flame 1/16” to 1/8” above the par-ent metal at the right edge of the sample until a molten puddle is formed. Dip the end of the rod into the puddle, allowing a small amount of the rod to melt off and fuse with the base metal, figure 3-1.5. Weld across the sample, from right to left, add-ing filler rod to the molten parent metal.6. Melt enough rod into the puddle to build up the bead evenly in height and width. Alternately raise the rod as the base metal melts and dip it into the font of the puddle when penetration is completed.

7. When good penetration is obtained the under-side of the metal will look as though a bead has been run on it. Addition of the rod to the molten puddle is the key to good welding. Practice the job until the technique is mastered.

KEY POINTS

3. Grasp rod as you would a pencil, with 6” to 8” ex-tending below the left hand. 4. Do not add rod until molten puddle is formed. Keep the end of the rod in the outer end of the flame envelope to protect it from oxida-tion. The tip should be at an angle of 450 to 600 with the par-ent metal, figure 3-2.

5. This is called forehand welding.

6. Get penetration before adding the filler rod. Filler metal melted onto the sheet metal is not a weld, unless it is fused into the parent metal. A slight circular motion of the flame will make a better weld, figure 3-3.

7. The edges of the weld should be feathered smoothly into the parent metal. The rod should not be pulled up. The bead should look like fish scales overlapping each other.

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Summary: Job 3• Weld with a neutral flame.• Weld from right to left (left to right if left-handed)• The torch should be at an angle of 450 to 600 with the parent metal.• Circular motion of the flame is used to control the head and bead appearance.• If the metal becomes too hot the torch may be flashed off the weld. Momentarily direct the flame away from the puddle, but keep the puddle fluid.• When good penetration has been developed, the underside of the sheet metal will look like a bead has been run on it.

REVIEW QUESTIONS1. What is parent metal?2. Why is it necessary to get penetration before the rod is added to the weld?3. Why is the addition of filler rod necessary for a strong weld?4. What type of flame is used for welding?5. What percentage of penetration is necessary for the best weld?

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Butt Weld on Mild Steel Sheet Metal, Flat Position

OBJECTIVES The students will be able to:• List and define several terms applying to butt welding.• Discuss the effects of expansion and contraction.• Compensate for expansion and contraction in butt welding.• Make a butt weld which withstands a bend test.• Perform a bend test on a butt weld.

Gapping One of the greatest concerns the welder has in butt welding steel sheet metal is how expansion and con-traction are dealt with. When steel is heated, as in welding, it expands, or increases in size. As it cools it con-tracts, or decreases in size. When butt welding sheet metal it is a good practice to gap the metal. At the side where the weld is to begin leave about a 1/16-inch gap between the two pieces of parent metal. At the side where the weld is to end leave about a 1/8-inch gap. (These figures apply to a piece of 16-gage sheet metal 6-inches long). The extra gap at the finishing end of the weld allows for the additional heat which is absorbed by the metal as the weld moves along. Tack the pieces securely, so the gap will remain for welding. Tack welds are small completely fused welds made at several places along the line of the weld to hold the pieces in place. Attempting to weld sheet metal without gapping the butt weld will produce a scissors effect, where one piece of sheet metal will be wrapped over the top of the other.

Keyhole At the start of the weld, as the puddle is formed, the edges ahead of the weld should be melted away a small amount. This creates a place for the penetration to work though the gap. This keyhole should remain small. As it is carried along in front of the puddle, it insures 100% penetration.

Testing A good weld will bend 1800 over the bead, without breaking and will stand as much pull as the parent metal when tested for tensile strength. Most of the tests used in this text are destructive tests. They will bend the welded jobs out of shape, so the metal cannot be used again without considerable preparation.

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JOB 4: BUTT WELD IN MILD STEEL SHEET METAL, FLAT POSITIONEquipment and Material: Standard Oxyacetylene Welding Equipment 16-gauge mild steel samples, 2” wide by 6” long 1/16” or 3/32” mild steel filler rod

PROCEDURE

1. Tack weld two pieces of 16-gauge metal as shown in figure 4-1.2. Beginning at right side, from a puddle and add a little rod. Progress across the joint, alternately melt-ing the puddle and adding rod at the leading edge of the puddle.3. Get complete fusion of the mental to the bot-tom of the gap, and add filler rod so that the weld will be above the top of the parent mental.4. Practice this exercise until the butt weld is mastered.5. Test the weld. Place the welded sample in a vise with the weld at the top of the vise jaws. Bend the mental against the bead a full 1800. No cracks or tears should appear.

KEY POINTS

1. Leave a gap between the pieces.

2. Keep a keyhole ahead of the puddle at all times so that penetration is achieved before the rod is added to the puddle. 100% fusion and penetration are necessary for a strong weld.3. The weld should always be thicker than the parent metal.

5. Both good appearance and strength care necessary. Be sure the sample is cold before testing. Hot metal bends easier, but has less strength.

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REVIEW QUESTIONS1. Why is it necessary to gap a butt weld?

2. How high should the bead be built up on this type of weld?

3. What percentage of penetration should be achieved?

4. What is the keyhole?

5. What type of flame is used for this weld?

COURSE OBJECTIVES

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Oxy-FuelGas

Cutting

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Upon completion of this module, the trainee will be able to:1. Explain oxyfuel cutting safety.

2. Identify and explain oxyfuel cutting equipment.

3. Identify and explain oxyfuel flames.

4. Identify and explain backfire and flashbacks.

5. Set up oxyfuel equipment.

6. Light and adjust an oxyfuel torch.

7. Shut down oxyfuel cutting equipment.

8. Disassemble oxyfuel equipment.

9. Change empty cylinders.

10. Perform housekeeping tasks.

11. Perform oxyfuel cutting.

• Straight-line and square shapes

• Piercing and slot cutting

• Bevels

• Washing

• Gouging

This is a basic operation which the welder should correctly master as he will repeat it frequently when doing

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different jobs of oxy-acetylene welding. It consists of mastering the knowledge dealing with the functioning of the oxy-acetylene equipment so as to render it in working condition.

METHOD OF EXECUTION:

1st Step - Mount the regulators, thus: SAFETY MEASURE:THE CYLINDERS SHOULD BE IN A VERTICAL POSITION AND BE SECURED, SO AS TO PREVENT TOPPLING.

a) Remove the cover of the cylinders.

b) Slightly open and close the valve to expel the impurities.

SAFETY MEASURES:1) BEFORE OPENING THE ACETYLENE CYLINDER, MAKE SURE THAT THERE IS NO EX-POSED FLAME NEARBY.

2) WHEN HANDLING THE CLYLINDERS YOUR HANDS SHOULD BE CLEAN OF GREASE AND OIL, AS THESE MAY CAUSE EXPLOSIVE COMBUSTIONS.

c) Connect the regulators to their respective cylinders.

OBSERVATIONS:

1) The connector nut should be tightened with the spanner for the equipment.

2) The dials should remain in such a way that the operator should be able to take the pressure readings with ease.

d) Turn the pressure regulating screw which regulates the flow of gas to the gauge which indicates the working pressure.

SAFETY MEASURE:

WHEN TURNING THE PRESSURE-REGULATING SCREW, DO NOT DO SO IN AN ANTI-CLOCKWISE DIRECTION.

2nd Step - Position the hoses, thus:

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a) Connect the hoses to the regulators (fig. 2)

b) Connect the hoses to the welding torch shank (fig. 3).

OBSERVATIONS:

1) The hose that supplies acetylene is red in color and its connectors have left-handed threads.

2) The hose that supplies oxygen is blue or green in color and its connectors have right-handed threads.

3rd Step - Install the nozzle, thus: a) Adjust the nozzle manually.

b) Place the nozzle in the working position (fig. 4).

4th Step - Regulate the working pressure, thus:a) Open the cylinder valves.

b) Turn the knobs that regulate the oxygen and acetylene.

5th Step - Ignite the torch, thus:

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a) Open the acetylene valve in the torch for a ¼ turn.

b) Operate the lighter (fig. 5.)

SAFETY MEASURE:

WHEN THE TORCH IS IGNITED, AIM THE NOZZLE OVER A FREE SECTION AND MANIPULATE THE LIGHTER, WITHOUT PUTTING OUT THE FLAME, SO AS TO PREVENT ACCIDENTS.

c) Slowly open the oxygen valve of the torch until obtaining a well regulated flame, “neutral”.

OBSERVATION:

It is important that the welder be able to distinguish between the neutral, oxidizing and carburizing flames (figs. 6,7 and 8).

6th Step - Turn off the torch; thus:a) Shut off the acetylene valve in the torch.

b) Shut off the oxygen valve in the torch.

SAFETY MEASURE:

EACH TIME YOU TURN OFF THE TORCH, FIRST SHUT OFF THE AVETYLENE VALVE.

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THE CUTTING TORCHThe cutting torch carries the fuel gas and oxygen in separate tubes to the mixing chamber within the torch head or torch body. In the mixing chamber, these two gases combine. The combine gases then travel to the torch preheat orifices (holes) in the tip to produce the preheat flames. The torch must also carry the cutting oxygen to a separate orifice in the tip. As it emerges from the tip, it oxidizes the metal and blows it away to form a clean kerf (cut). The torch is usually constructed from a yellow brass body, stainless steel tubes that carry the gases, and a brass head or tip holder. All these parts are silver-soldered together.The copper tip is held into the torch head by a threaded nut. The torch is equipped with three valves.• A fuel gas valve similar to the welding torch.• An oxygen valve, similar to the welding torch.• A cutting oxygen valve, button-or leveler-operated, with an automatic spring closing device. A cutting torch may consist of an attachment that may be fastened to a welding torch body or it may be a torch designed to attach directly to the hoses.The combination welding and cutting torch is most popular in small shops where welding and cutting are auxil-iary operations to the workshop. In oxy-acetylene cutting there are two types of cutting torches:• Positive-pressure torch• Injector-type torch

POSITIVE-PRESSURE TORCH. The gases are mixed in the positive-pressure type cutting torch and are burned at the end of the torch tip. The positive-pressure torch is used with cylinder gases. Its construction necessitates that each gas be supplied under enough pressure to force it into the mixing chamber. Torches are made of various materials, including brass, aluminum, and/or stainless steel. The various parts are threaded and silver-brazed together.The hand valves are located either at the end of the torch where the hoses attach to the handle, or at the tip end of the handle. The torch valves are generally either needle-and-seat or ball-and-seat design. These hand valves are used chiefly for shutting off the gas and turning it on; however, many welders use them to throttle (make the final flow adjustment to) the gases being fed to the torch. The mixing chamber is usually located inside the torch body, although some torches incorporate the mixing chamber in the torch tube. Gases are fed to this chamber through two brass or stainless steel tubes lead-ing from the torch valves.

INJECTOR-TYPE TORCH. The injector-type (low-pressure) cutting torch has a different type internal structure than the positive-pressure torch. The chief characteristic of the injector-type torch is its constant regardless of the size tip or the thickness of the metal being cut. The mixing chamber of the injector-type cutting torch is situated in the torch tube. The oxygen line enters the mixing chamber through the jet which is surrounded by the acetylene passage. As oxygen flows from the jet, it draws (injects) the acetylene along with it. Handling the valves and the other operations of the torch is much the same as with the positive-pressure type torch. It should be noted that the oxygen pressure used in these torches is considerable higher than with the positive-pressure type torch. It should be noted that the oxy-gen pressure used in these torches is considerably higher than with the positive-pressure type torches. The mate-rials of the injector-type torch construction are usually the same as those materials used in the positive pressure torch.

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CUTTING PROCUDURES AND TECHNIQUES

OXY-FUEL GAS CUTTING:

The oxy-fuel gas process of cutting steel depends on the chemical reaction between red hot steel and oxygen – this results in the oxidation of the steel – an exothermic reaction (a reaction in which heat is liberated).

The surface of the steel is heated to a temperature termed the “KINDLING TEMPERATURE”. A stream of high pressure oxygen is then impinged on the surface of the heated steel.

The metal is oxidized – the oxides so formed have a lower melting point than the parent plate they melt and flow away – the action continuing until the cut is complete.

The heat liberated during oxidation of the steel is not enough to keep the process going. The additional heat is supplied by the use of a cutting torch.

The practical application of cutting depends on:i. Heating the steel to its ignitions or kindling temperature ii. The burning or oxidation of the metal in the path of the oxygeniii. Removal of the oxide – slag by the force of the oxygen streamiv. The continued and even movement of the blowpipe along the line of cut: This maybe:a. Free handb. Guided (free hand)c. Mechanical (machinery)These points produce the desired finish when:a. The accuracy of the cutb. The quality of the cutc. Judged wiselyThe accuracy of the cut may be obtained by correct relationship between the line of cut and the oxygen orifice.

Having an accurate and smooth cut are not the only essentials for a good cut other points are:i. Composition of parent plateii. Cleanliness of parent plateiii. Correct selection of tip-sizes and gas pressuresiv. Cleanliness of the tipv. Distance of the preheat flame from the parent platevi. Correct preheating flamevii. The deformity of speed and movement of the blowpipeviii. Freedom of operator of machine

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BEVEL CUTTING

This simply involves holding the torch head at the angel of bevel require. It should be born in mind that cutting at an angle means cutting through a greater thickness of material and therefore requires a slower speed of travel and a slightly higher gas pressure.

NOTE: Once the metal is ignited the type of fuel gas used for preheating has no influence on the cutting. From this the use of acetylene is not compulsory and other fuel-gases may be used for the following reasons:a. Greater safetyb. Economyc. Convenience

OXY-FUEL GAS CUTTING – KEY POINTS

SPEED OF TRAVEL

If the rate of travel is too slow the plate shows evidence of excessive melting and the slag is hard to remove. There is also the tendency of the oxide to “weld” back in the kerf. If the rate of travel is too fast drag lines are too long and somewhat uneven or the plate is not completely cut or there is the tendency to lose the cut at inter-vals.DIRECTION OF TRAVEL

The direction of travel is not too important except if the tip is allowed to waver, the cut will follow its path.

AMOUNT OF PREHEATIf the preheat is too great then there is much melting of the top edge and the slag is hard to remove. If the pre-heat is too little the cut is hard to maintain and the cut surface is uneven. CUTTING OXYGEN PRESSUREIf the cutting oxygen is too low the cut is hard to maintain and the surface is rough. If the pressure is too high the cut surface is gouge and does not maintain a square cut.

THE ANGLE OF TORCHIf the angle of the torch changes then the line of direction changes also.

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Oxyacetylene CuttingStraight Cutting with the Oxyacetylene Cutting Torch

OBJECTIVES The student will be able to:• Explain how an oxyacetylene flame cuts ferrous metal.• Assemble an oxyacetylene cutting outfit.• Make a clean, smooth cuts in the mild steel plate. Oxyacetylene cutting is done by directing a stream of oxygen onto the ferrous metal which has been preheated. The oxygen burns the metal. By controlling the amount of preheat and the size of the steam of oxygen, a cut may be made with clean, smooth sides. The cut is called a kerf. Oxyacetylene cutting is one of the most used oxyactylene processes. The cutting torch can be used to cut intricate shapes or to make straight, clean cuts. The cutting,and burning process does not change the chemical composition of the metal. Therefore, a ferrous metal can be welded immediatelg after it has been cut. However, slag (oxidize metal) is sometimes left at the bottom edge of the cut. This must be removed by grinding or chis-eling. If oxidized metal is included in the muddle it will contaminate the weld. Metal should always be clean before welding.

Cutting Torch The cutting torch, figure 23-1, is designed only for cutting ferrous metals. To instill the cutting torch the welding torch handle must be removed from the hoses. The cutting torch is then installed in its place. The cut-ting torch is designed for heavy cutting and performs better over long periods of time than the cutting head.

Cutting Head The cutting head, figure 23-2, is an attachment to the welding torch. By removing the tip from the welding torch the cutting head may be screwed onto the torch handle. In this manner a welding torch may be used for cutting.

Oxygen Pressure Since large amounts of oxygen are required to burn the metal, more oxygen pressure is needed for cutting than for welding. When using a cutting torch, or cutting head, the gas pressures should be regulated according to the manufacturer’s specifications for the torch being used.

Cutting Tip The cutting tip, figure 23-3, is designed especially for cutting and cannot be used for welding.

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Cutting tips are made with a hole in the center, through which the stream of oxygen is directed at the cut. A group of holes around the center hole give off a neutral flame which preheats the metal, figure 23-4. Depending on the size of the tip, there are 4, 6, 8 or 12 preheat holes. Each of these is like a miniature welding tip and when the torch is lighted, it should be adjusted so that each of the preheat holes makes a neutral flame. When the metal to be cut has been preheated to red-hot, the cutting oxygen valve is pressed. The stream of oxygen will burn (cut) the metal as long as the preheat is maintained. Oxyacetylene cutting must be done at a slow, even rate of speed. If the cut is made too rapidly, the metal may cool down and the cutting action will stop. If this happens the torch should be moved back into the kerf and the metal preheated again. The cut may then be started again.

JOB 23: OXYACETYLENE CUTTING

Equipment and Materials Oxyacetylene outfit with cutting head Straight edge Hammer Center punch Soapstone or chalk Scrap pieces of ½-inch mild steel plate

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PROCEDURE

1. Install the head on the torch handle.

2. Install the cutting tip in the position shown in figure 23-4.

3. Use the acetylene and oxygen pressures recom-mended by the manufacturer of the equipment.

4. Light the cutting torch in the same manner as the welding torch and adjust it for a neutral flame.

5. Depress the cutting oxygen valve and with the valve wide open, adjust the preheat flames to neutral.

6. Shut off the torch.

7. Mark a line ½ inch from the end of the steel plate, using the straightedge and soapstone.

8. Position the plate on a suitable table so that the marked end overhangs the edge of the table.

9. Relight the cutting torch.

10. Hold the flame about 1/8 inches above the edge of the plate.

11. Preheat the metal to a red heat.

12. Depress the oxygen lever and, as the metal burns and is blown through the kerf, move across the plate. Follow the marked line until the cut is complet-ed.

13. Practice cutting pieces from the plate until smooth, even, straight cut is achieved. 1. The procedure for using a cutting torch is the same as for cutting head.

KEY POINTS

1. The procedure for using a cutting torch is the same as for cutting head.

3. The high pressure of the cutting oxygen helps blow the kerf clear.

4. Wear gloves and goggles. All preheated flames should be neutral.

5. With the cutting oxygen valve wide open the working pressure should be adjusted to the manufacturer specifi-cations.

7. Center punch the line. Soapstone and chalk will burn off, but center punch marks can be followed after the soapstone is gone.

10. Position the torch so the tip is at the beginning of the line, but do not let it touch the plate.

11. Brace the torch by sing the bend behind the plate for support.

12. CAUTION: Stand clear of the mater when the cut is completed the material fall off. Falling sparks can ignite the cloth. DO not cut or direct the stream of oxidized material toward inflammable objects toward oxygen and acetylene containers.

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Summary: Job 23• The preheat flames must be kept neutral.

• The torch must be held at an angle of 900 with the cut so that a straight edge is made.

• Keep the oxygen trigger fully depressed so that the kerf blows clean.

• The tip must be kept clean. Use tip cleaners if the holes become plugged.

• Be sure the tip is installed for straight cutting.

• The metal must be kept red-hot, or the cutting action will stop.

REVIEW QUESTIONS

1. How does the oxyacetylene flame cut metal?

2. How is a cutting head installed on an oxyacetylene welding outfit?

3. What is the result when a cut is made too fast and the preheat is lost?

4. What is a kerf?

5. What is slag?

6. Make a sketch of the end of the cutting nozzle showing how it is installed for a straight cut.

7. Is the acetylene pressure increased when the cutting torch is used?

8. Why should a line be center-punched for cutting with the cutting torch?

9. List the safety measure which should be taken when cutting with the torch?

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Beveling Plate with the Oxyacetylene Cutting Torch

OBJECTIVES The student will be able to:• Describe the position of the cutting torch tip for cutting a bevel.• Define a land and tell why it is used.• Cut a straight, smooth bevel with the oxyacetylene torch.

Ordinarily, 100% penetration is required for an oxyacetylene weld in order to insure strength in the welded joint. Metal which is over 1/8 inch think is very difficult to melt through, so some method has to be provided to insure complete penetration. Metal 1/8 inch to 3/16 inch thick is frequently gapped for welding, but the edge of metal over 3/16 inch thick should be beveled. This is done by cutting the edge of the metal on an angle.Cutting straight through a piece of steel leaves a cross section the same width as the thickness of the original metal. However, when the edge is beveled, the cross section is increased, figure 24-1. Beveling leaves the bottom of the plate with a very thin edge, which has a tendency to melt off during weld-ing. The edge is generally ground square to a thickness of 1/16 inch, to prevent the edge from melting off. This ground shoulder is called a land. Sometimes when bevels are made, a small increase of oxygen pressure is necessary to cut the larger cross sec-tion of the bevel. To cut a bevel, the cutting tip should be turned so the holes line up as shown in figure 24-2.

JOB 24: BEVELING PLATE WITH THE OXYACETYLENE CUTTING TORCHEquipment and Materials: Standard oxyacetylene outfit with cutting head Straightedge Hammer Center punch Soapstone Scrap pieces of ½ “ thick mild steel plate

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REVIEW QUESTIONS1. Why is metal over 3/16 inch thick beveled to prepare it for a butt weld?

2. How does beveling affect the cross section of a piece of metal?

3. What is the land of a beveled plate?

4. If a piece of angle iron is used as a guide for cutting a bevel what will the angle of the bevel be?

5. Draw a sketch showing the placement of the preheat holes in a cutting tip as it is used for beveling metal.

Cutting Holes with the Oxyacetylene Cutting TorchOBJECTIVES The student will be able to:• Pierce steel plate with the oxyacetylene cutting torch.

• Cut round holes within 1/15 inch of the right diameter.

• Holes cut will have clean, straight sides and be free of slag. The oxyacetylene cutting torch is a good tool for cutting holes in steel, where precision fit is not necessary. Round, square, rectangular, ad odd-shaped holes can be cut equally well. As the cutting oxygen valve is opened, after the metal has been preheated to a red heat, the torch tip must be moved upward away from the cut. This is to keep the slag from blowing up into the tip. When the hole is burned completely through the plate, lower the torch until the preheat flames are about 1/8 inch from the surface of the metal, figure 25-1. With the hole pierced and the torch in position to keep the metal preheated, cut away from the hole to the mark and around the circle. Clean the slag from the underside when the cut is completed.

PROCEDURE

1. Mark a straight line with soapstone and center punch.

2. Preheat the edge of the plate and cut alone the mark, with the torch held at a 450 angle with the plate.|

3. Practice cutting a bevel until a smooth, regular bevel is achieved.

KEY POINTS

2. Be sure the cutting tip is installed on the torch cor-rectly for bevel cut. Keep the torch the same distance from the plate at all times. Move slowly and steadily, so the preheat is no lost. Visibility will be best if the torch is drawn toward the operator.

3. An angle iron guide may be used to main-tain a straight, even bevel, figure 24-3.

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JOB 25: CUTTING HOLES WITH THE OXYACETYLENE CUTTING TORCH

Equipment and Materials

Standard oxyacetylene cutting outfit

Soapstone

Center punch

Hammer

Scraps of 1/4 –inch or ½-inch mild steel plate.

REVIEW QUESTIONS1. What type of preheat flame is used from oxyacetylene cutting?

2. What is done to prevent the slag from blowing up into the tip as a hole is started? 3. When cutting a hole in the center of a plate, where is the cut started?

4. When making a cut, how far should the preheat flames be from the surface of the metal?

5. How can the operator tell when the metal is preheated enough to begin a cut?

SECTION 4: OXYACETYLENE CUTTING, COMPREHENSIVE REVIEW

PROCEDURE

1. Mark 1-inch and 2-inch circles on the plate, using soapstone. 2. With a neutral flame, preheat the inside of the circle. When the metal is red-hot, depress the oxygen lever.3. When the cut starts, raise the tip up about ½”. 4. When the hole has been burned through, lower the torch until the preheat flame is about 1/8” from the surface of the metal. 5. Cut outward to the punched line and follow the mark around the circle, figure 25-2.6. Practice this until a smooth, slag-free cut is achieved.

KEY POINTS

1. Center punch soapstone lines.

3. This prevents the oxide from blowing back into the tip.

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A. OXYACETYLENE FLAME CUTTING

Equipment and Materials

Standard oxyacetylene cutting outfit

Soapstone

Center punch

Hammer

¼ - inch mild steel plate

PROCEDURE:1. Mark all cuts with soapstone and center punch the marks. See oxyacetylene cutting evaluation drawing.

2. Complete all cuts slowly and carefully/

3. Remove all slag.

4. If the cuts are not acceptable, practice cutting on scrap until enough skill is developed to complete this evaluation.

CUTTING TORCH TIPS

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Just as in welding, the proper size cutting tip is very important if quality work is to be done. The preheat of flames must furnish just the right amount of heat, and the oxygen jet orifice must deliver the correct amount of oxygen at just the right pressure and velocity to produce a clean kerf. Each manufacturer has cutting tips of different designs. The orifice arrangements and the copper allow tip material are much the same among various manufacturers. The sealing surface of the tip which fits into the torch head, however, often differs in design among manufactures. Just as some cutting torches are designed to mix preheat flames in the handle (body). There are cutting tips that are designed to mix preheat gases in the tip. The tips and seats are designed and constructed to produce a good flow of gases, to keep the tips as cool as possible, and to produce leak-proof joints. The sealing areas are generally metal-to-metal between the tip and the torch head. These surfaces must be kept clean and free from damage. If these joints leak, preheat gases may mix with the oxygen or may escape to the atmosphere. It is important that the orifices and passages be kept clean and free of burrs, to permit free gas flow, and to form a well-shaped flame.

TORCH GUIDES The welder should always try to cut a smooth kerf, and to cut accurately to a dimension. Freehand cut-ting (holding the torch in your hands) makes both of these objectives very difficult. Many mechanical, electrical and electronic devices have been developed to help produce clean cuts, accurate size cuts and exact duplicate pieces.

MECHANICAL GUIDES Mechanical Guides are used to help control the position of the torch. They do not control the speed of the cutting operation. Therefore, the welder must be very skilled, otherwise rough, ragged cuts may result. To cut straight edges, a single torch guide may be assembled. A bend type clamp may be attached to the torch tip and a length of angle iron clamped to the base metal to ensure a straight cut. To cut arcs and circles, a circle guide may be used.

MOTORIZED CARRIAGES An electric motor-driven carriage and track mat be used when making long straight cuts. An oxy-fuel cutting torch is then mounted on it and it is appropriately named a profile cutter. SHIELDED METAL ARC WELDING (S.M.A.W.)

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Shielded MetalArc WeldingEquipment(S.M.A.W.)

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Shielded MetalArc Welding

Fundamentals

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Shielded metal arc welding (S.M.A.W.) sometimes called “stick welding” is the most popular form or electric arc welding. This process is done by producing an arc between the base metal and a consumable, flux-covered metal electrode. The electrode acts as an electrical conductor and filler metal. Electricity, as it arcs across the gap between the metal electrode and the work, creates a temperature or approximately 65000F to 70000F (36000C to 39000C).

However, as we are about to explore this process, various factors need to be discussed. They are:• SAFETY• MACHINES OR POWER SOURCES/EQUIPMENT CARE.• ACCESSORIES/ACCESSORIES CARE• S.M.A.W. FUND/AMENTALS.• ELECTRODES/ELECTRODES STORAGE AND CARE.• TECHNIQUES-(PRACTICAL).SAFETY: As was discussed before the chief hazards to avoid in arc welding are:• Radiation• Flying sparks and globules of molten metal.• Electric shock• Fumes • Burns MACHINES/POWER SOURCES: Arc welding power sources, also called arc welding machines, are either dc, ac or combination of ac/dc machines. They are constructed to produce either a constant current measured in amperes, or a constant voltage measured in volts. Direct current (dc) power sources are of the following types:• Transformer with a dc rectifier.• Motor-or-engine-driven generator.• Motor-or-engine-driven alternator with a dc rectifier.• Inverter.Alternating current (ac) power sources may be of the following types:• Transformer • Motor-or-engine-driven alternator.• Inverter Combination ac and dc arc welding power sources are of the following types:• Transformer with a dc rectifier.• Motor-or-engine-driven alternator with a dc rectifier• Inverter

An inverter welding power source is a transformer type machine. Inverters change incoming ac current to dc, then back to very high frequency ac current. This high-frequency ac current then passes through a very small and efficient transformer. Inverters are much smaller, lighter in weight, and more efficient than regular trans-former-type machines. Inverter power supplies can perform like either a constant current or a constant voltage machine.

As was mentioned previously, arc welding machines are designed to produce an output that could be either con-

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stant current or constant voltage. In manual arc welding however, the constant current power source is desired. Reasons being, that, if the voltage varies, and this comes about due to verying are lengths, there is little change or variation in the current and weld quality is maintained. This properly illustrated in the diagrams listed. N.B. Constant current power sources are dropper-type power sources.

DIRECT CURRENT POWER SOURCES. Direct current (dc) are welding power sources are either the transformer rectifier or the generator type. In the transformer section of the transformer-rectifier welding machine, ac is changed from ling voltage and current to an ac welding voltage and current. Line voltage supplied to the transformer is generally 220v and 440v at 60Hz (cycles). The transformer changes the high voltage to an open circuit (no load) welding voltage of 60v-80v. The current (amperage) welding is usually several hundred amps, depending on the construction of the welding machine. After leaving the transformer section, the welding current enters the rectifier. The rectifier changes the ac to dc. A dc constant current transformer-rectifier may be either a single-phase or three-phase power source. The trans-

formation of ac to dc current could only be achieved with the use of a diode in the welding machine. Alternating current flowing into the rectifier is changing direction 120 times per second. The current flows from the rectifier in one direction only and has, therefore, been converted to direct current (dc).

DIRECT CURRENT (dc) ARC WELDING FUNDAMENTALS

COMPARISON OF VARIABLE COLTAGE AND CONSTANT VOLTAGE OUTPUT

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DCEN AND DCEP FUNDAMENTALS

The welding circuit shown in figure (4) is known as a direct current electrode negative (DCENT) circuit or (DCSP). In this circuit, the electrons are flowing from the negative terminal (or pole) of the machine to the electrode. The electrons continue to travel across the arc into the base metal and to the positive terminal or pole of the machine. The welding circuit shown in figure (5) is known as a direct current electrode positive (dcep) or (dcrp). In this circuit, the electrons flow from the negative pole of the welding machine to the work. Electrons travel across the arc to the electrode and then return to the positive terminal (pole) of the machine. To achieve the reverse electron flow in the arc circuit the electrode and workpiece leads are disconnected and reverse in their positions. In some machines there is a switch that will change the circuit polarity. The decision to use any of these (DECN OR DCEP) depends on such variables as:• The depth of penetration desired. • The rate at which filler metal is deposited. • The position of the joint.• The thickness of the base metal.• The type of base metal. ALTERNATING CURRENT POWER SOURCES Alternating current (ac) power sources are of either the transformer or alternator type. The purpose of a transformer used in a welding machine is to change high-voltage, low-current electricity into the lower voltages and higher currents required for welding. Transformers are constructed of three principal electrical components. They are primary winding, a secondary winding, and an iron core.

The primary winding uses thinner wire than the secondary winding, because the primary winding carries less current. There are many more windings in the primary. When a transformer has more turns in the primary than in the secondary, it will decrease the voltage and increase the amperage from the primary to the secondary circuit. This type transformer is called a step-down transformer. A step-down transformer reduces the voltage and increases the current. In the center of both the primary and secondary winding is a laminated iron core. Its purpose is to keep the magnetic field from wandering too far from the windings.

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OBJECTIVES

Upon completion of this module, the trainee will be able to:1. Identify and explain SMAW safety.

2. Identify and explain welding electrical current.

3. Identify and explain arc welding machines.

4. Explain setting up arc welding equipment.

5. Identify and explain tools for weld cleaning.

ALTERNATING CURRENT (ac). ARC WELDING FUNDAMENTALS

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In alternating current (ac), the current reverses its direction of flow 120 times per second. It requires 1/60 of a second to complete a cycle or HERTZ (Hz). The current flow completes 60Hz (cycles) per second and is called 60Hz (cycle) current. In most parts of the world, 50Hz current is used.

Figure (8) shows what happens at the arc in one cycle of a typical ac transformer-type arc welder. The voltage at both points A and B is zero. Beginning at the left side of the graph, the voltage builds up to a maximum in one direction to point C, and then back to zero at point A. the voltage then builds up to a maximum in the other direction to point D, then back to zero again at point B. this action is repeated at the rate of 60Hz (cycle) per second.

SEE DIAGRAM BELOW

SELECTING AN ARC WELDING MACHINE Deciding whether an ac or dc welding machine is best to buy or use depends on several factors. Select-ing the type of current to use should be done after considering their individual advantages and disadvantages.Advantages of the dc constant current-type arc welding machine include.• The ability to choose direct current electrode positive (DCEP) or (DCRP).

• DCEP or DCRP produces deeper penetrating welds than DCEN. • DCEP or DCRP can be used in positions other than flat positions or downhand welding. • Electrodes designed to weld nickel, aluminum, and copper gener-ally use DCEP.• The ability to choose direct current electrode negative (DCEN) or (DCSP).• DCEN or DCSP is recommended for xx2x electrodes that have high metal deposition rates.• DCEN or DCSP can also be used in welding positions other than flat.

The disadvantage of the direct current (dc), constant current arc welding machine is that a dc arc welder is generally more expensive than an arc

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welding machine of the same quality, current output and duty cycle. Advantages of the alternating current (ac), constant current, arc welding machine includes:• Weld s made with ac arc welding machines and electrodes have moderate penetration.• Large-diameter electrodes can be used with high ac currents to obtain greater filler metal deposition rates and faster welding speeds.• Ac arc welding machines are generally less expensive than dc arc welding machines of equal quality, current output, and duty cycle rating.• Arc blow is reduced.The major disadvantage of ac welding machine is that not all S.M.A.W. electrodes can be used with alternating current. NOTE. Duty cycle is the length of time that a welding machine can be used continually at its rated output in any ten (10) minute period.NOTE. Arc Blow : Once started, the ac arc is quite stable. The dc arc, however, may have a tendency at times to wander from the weld line. The wandering, called arc blow, is usually caused by a magnetic flied of the mag-netic field around the dc electrode. All electrical conductors are surrounded by magnetic field when strong. Ac electrodes are not affected because of the constantly changing direction of the current. These reversals virtually cancel the magnetic blow effects in the ac circuit.NOTE. There are two types of arc blow. Forward arc blow, Backward arc blow.

If the arc blow is extremely strong, certain preventive or corrective measures can be taken. One or more of the following may be used to correct magnetic arc blow:• Place the ground connections as far from the weld joint as possible.• If forward arc blow is a problem, connect the work piece lead (ground) near the start of the weld. It will also help to weld toward a large tack weld. The large tack weld will give the magnetic field a place to flow. This will prevent a crowding of the magnetic field which causes arc blow.• Reduce the welding current. This will reduce the strength of the magnetic field.• Position the electrode so that the arc force counteracts the arc blow force.• Use the shortest arc that will produce a good bead. The short arc will permit the filler metal to enter the arc pool before it is blown away. A short arc will also permit the arc force to overcome the arc blow force. • Weld towards a run-off tab or heavy tack weld

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• Wrap the electrode lead around the base metal in the direction which will counteract the arc blow force. • Change to an ac welding machine and electrodes.• Use backstep method of welding.

Accessories / Care. Welding Leads: Large diameter, superflexible leads (cables) are used to carry current from the welding machine to the work and back. The lead from the machine to the electrode holder is known as the electrode lead. The lead from the work to the machine is known as the workpiece lead or ground lead. Leads are well insulated with neoprene. The leads are usually subjected to considerable wear and should be checked periodically for breaks in the insulation. The voltage carried by the leads vary between 14v and 80v.

Leads are produced in several sizes. The smaller the number, the large the diameter of the lead. The lead must be flexible to permit easy installation of the cable, and to reduce the strain on the welder’s hand when welding. The same diameter electric cable must be used on both the electrode and workpiece leads. The length of the lead has considerable effect on the size to be used for certain capacity machines.

Connections For Leads.To constantly carry the large currents used in welding, all parts of the welding circuit (including all terminals) must be of heavy duty design and construction. The leads are fastened to the welding machine and workpiece by means of insulated or uninsulated terminals. The uninsulated terminals are called lugs. These lugs are mechani-cally crimped to the leads. The lugs provide a firm means of attaching the electrode lead and the workpiece lead to the machine or worktable. These connections must be durable and must have low resistance, or the joint will overheat during welding. Less current will flow if the connections is loose.

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CABLE SIZES

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REVIEW QUESTIONS1. Why must connections on a welding machine be tight?2. What is another name for a welding electrode holder?3. What is another name for a welding helmet?4. Describe the direction of flow of electricity when using DCRP.5. Describe the direction of flow of electricity when using DCSP.6. Describe the direction of flow of electricity when using AC.7. What welding polarity releases the greatest amount of heat at the base metal?8. What is the tensile strength of a property made weld using an E-7014 electrode?9. What does the digit 1 indicate in the electrode designation E-7014?10. What are the rays, given off by the arc welding process, which are dangerous to the eyes?

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QualityControl

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1. COMMON WELD DEFECTS

2. CODES GOVERNING WELD INSPECTION

Every *country has some code for Welding Inspection or adapts to some acceptable international code e.g. DIN, BS, AWS, ASTM, Lloyds of London. The American codes and rules for welding are as follows:-

a) AWS – American Welding Society

b) ASME – American Society for Mechanical Engineers

c) ANSI – American National Standards Institute d) API – American Petroleum Institute

e) MIL – United Sates Department of Defense

f) ABS – American Bureau of Shipping

g) AWWS – American Water Works Association

h) ASNT – American Society for Non-Destructive Testing i) ASTM – American Society for Testing Materials

j) SAE – Society of Automotive Engineers All these societies require that records are kept and be made available for the Inspector. All drawings must be kept together with inspection records.

*Japan, Germany, France, British, Italy, Norwegan

It should be noted that most of these codes were first developed by private organisations and after some time were adopted by various government agencies, and eventually some because of laws governing weldments.

WELDING INSPECTION METHODS1. Macro-Inspection: Visual, low magnification x52. Micro-Inspection: High Magnification x101 - x1063. Non-Destructive- Inspection: Using aids to assist in the identification of flaws. Job must not be physically damaged during testing process.

4. Destructive Testing: To verify physical and chemical properties of the weld or for failure analysis.

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1.1 MACRO INSPECTION This method of inspection requires that the inspector be an experienced welder who is very familiar with weld-ing processes and various defects associated with the processes, preferably a coded inspector or one who has completed a welding inspection course of studies from a recognized institution, e.g. AWS, ASM, API, etc.Defects in this category of inspection requires direct observation with the eyes or the very low powered mag-nification after etching. Etching requires the use of small quantities of acids in solution alcohol, water or other solvents. Penetration, porosity, fusion zones and other phenomenon may be observed.

1.2 MICRO- INSPECTIONThis is a destructive method of testing since a sample has to be cut out from the welded member to be tested. Samples are prepared and placed under a high power microscope to observe grain structures, HAZ, and other micro defects that cannot be seen by macro-inspection. Chemical analysis also falls under the category and re-quires that small pieces of materials be removed from the job and mounted, polished and view under the optical microscope or Scanning Election Microscope (S.C.M.)

1.3 NON-DESTRUCTIVE TESTINGThere is a range of tests done on the actual job to detect surface or sub-surface flaws, the component remains completely functional after the tests.The following are NOT test commonly done on weldments: a. Liquid Penetrant Inspection (LP) b. Magnetic Particle Inspection (MP) c. Ultrasonic Inspection (UT) d. Radiographic Inspection (RI) e. Eddy-current Inspection (EI) f. Acoustic Emission Inspection (AE) g. Proof Tests (PT) h. Leak Tests (LT)

1.4 DESTRUCTIVE TESTING

There are test done to verify the physical properties and also the chemical properties of weld and base metals. This method of testing requires that the component be destroyed in order to obtain a sample for testing. The tests are done to verify:

a. Tensile strength of weld and base metal b. Impact strength of weld and base metal c. Compression strength of weld and base metal d. Shear strength of weld and base metal e. Bending strength of welded joint f. Metallographic Inspection

2.1.0 INSPECTION PERIODS 2.1.1 Before welding a. Material to be used for fabrication – scabs, seams, scales, laminations, plate dimension, tensile testing. b. After assemblies – root opening, edge preparation and other features of joint geometry. c. Checks on backing strips, run on and run off plates etc. d. Cleanliness of material and joint before welding begins.

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2.1.2 INSPECTION DURING WELDING

Among details to be checked are:

a. Welding process b. Filler metal c. Flux or shielding gas d. Pre-heat and interpass temperature/post heating and time e. Cleaning (interpass) f. Chipping, grinding or gonging g. Joint preparation for other side h. Distortion control

2.1.3 INSPECTION AFTER WELDING

a. Conformity to drawings b. Appearance of weldment c. Presence of structural discontinuities d. Any defects that may be visible

WELDING: QUALITIS, CHARACTERISTICS AND RECOMMENDATIONS

Among other things, a good weld must offer safety and quality. To attain these objectives, it is necessary that the welding beads be made with a maximum of skill, good regulation of the current and proper selection of elec-trodes.

CHARACTERISTICS OF A GOOD WELD

A good weld must have the following characteristics: a. Good penetration. b. No undercutting. c. Complete fusion. d. No porosity. e. Good appearance. f. No cracks. Good penetrationThis is obtained when the filler metal fuses the root and is extended under the surface of the welded parts.

No undercuttingA weld without undercut is obtained when near to is root (toe) there is not produced on the base metal any gig-ging which damages the workpiece.

Complete fusionA good fusion is obtained when the base metal and the filler metal form a homogenous mass.

No porosityA good weld is free of porosity, when in its inner structure there are no gas pockets nor slag inclusion.

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Good appearance A weld has good appearance, when there is seen in the whole extension of the joint an even welding bead, with-out cracks or overlapping.

No cracksA weld is considered without cracks when the finished bead has no fissures throughout its length.Following are some recommendations for producing a good weld.

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(Introduction)

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Fissures are small or moderately sized separations along grain boundaries. They are readily formed there because of the large grains. High restraint stresses case separation.

THERMAL CUTTING Process allied to welding that interest the welding inspector are oxyfuel gas cutting (OFC) and air carbon-arc cutting or gouging (AAC). A welding inspector may also encounter plasma arc cutting (PAC). These processes are being used for edge preparation, repairing welds and backgouging. Quality of cut surfaces varies with the nature of the weldment. The welding inspector should know what difficulties the welder may have with the irregularities in the cut surface. Unacceptable sizes and locations of irregularities must be marked for repair, just as defective welds are marked. Gouging grooves for welding and backgouging the root passes from the reverse side are usually done manually, but they also can be done by machine and automatic methods. The air carbon-arc process may allow carbon to dissolve in the surface of stainless steel grooves or cuts. To minimize carbide precipitation, the inspector should recommend grinding the cut stainless steel surfaces to remove the outer 0.4 mm (1.64 in.).

Oxyfuel Gas Cutting

Oxyfuel gas cutting (OFC) was at one time exclusively oxyacetylene cutting (OFC-A), but in present day practice, the inspector will encounter natural gas (OFC-N), propane (OFC-P) and a proprietary mixture of stabilized methyl acetylene and propadiene (Mapp gas). Metal powder cutting (POC) of stainless steel, alu-minum and copper alloys may also be encountered. Oxygen cutting severs ferrous metals by burning the iron in oxygen to form iron oxide. Above a kindling temperature of about 940C (1700 F) the familiar oxidation of iron (rusting) becomes a combustion, which may be confined to a narrow well-defined zone of controlled width called the kerf. The parts to be cut are heated to the kindling temperature by preheat flames disposed around the oxygen cutting jet. Torch modifications to suit each fuel gas are required. An oxygen cutting attachment for a welding torch is shown in Fig. 5-19. The lever opens the oxygen jet.

Fig. 5-19 oxygen cutting attachment on a welding torch.(Linde Division, Union Carbide)

Oxyfuel gas cutting is often applied a sa manual machine or fully automatic method of plate preparation. The quality of cut surface varies over wide limits. The skill of the operator affects all operations, because the cutting flame must be manually adjusted even for automatic cutting. Plasma arc cutting is less susceptible to this variable.

Air Carbon-Arc Cutting and Gouging

The air carbon arc (ARC-AIR) process removes metal by melting the metal with a carbon arc, then blowing out the molten metal by compressed air. A high velocity air jet, travelling parallel to the electrode and striking the puddle just behind the arc, blows the molten meat away. The principle of air carbon-arc gouging is

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shown in Fig. 5-20. The basic equipment requires a power source with suitable capacity (up to 1300 A for 16 mm or 5/8 in electrodes), compressed air at 0.55 to 0.7 MPa (80 to 100 psi), welding cables and work clamp, an air carbon arc torch and carbon electrodes. Air carbon arc gouging is performed both manually and automatically.

Plasma Arc Cutting

The greater the heat of the plasma arc (15,000 C or 27.000 F) will melt a kerf through any metal, ferrous or nonferrous, removing the molten material with its high velocity jet of hot ionized gas. The process operates on direct current electrode negative (dcent) with a constricted arc, struck between the water cooled electrode in the torch and the workpiece. The orifice, which constricts the arc, also is water cooled. The schematic view in Fig. 5-21 shows the power supply and controls, the pilot arc circuit through the workpiece and the water-cooled torch with gas inlet for ei-ther nitrogen or argon, plus 0 to 30% hydrogen. Water may be injected into the torch nozzle to further constrict the arc and square up the kerf. Plasma arc cutting is a machine or automatic process. Fig. 5-20. Schematic diagram for air carbon-are gouging.(Hobart Brothers Co.)

Mechanical Cutting

Joints are also prepared for welding either in part or entirely by mechanical means, such as milling, grinding, shaping, sawing, shearing and chipping.

Fig. 5-21. Schematic diagram for plasma-arc cutting. (Aluminum Company of America)

The inspector is frequently concerned about residues of sulfurized cutting oils used to lubricate the cut-ting tools, not only because sulfur may cause cracking in welds, but also because all oils are a source of hy-drogen. The unfused root in passes chipped or ground back from the other side to expose sound metal may be hidden by metal smeared over the unfused root of the joint by a blunt tool or a loaded wheel. On critical jobs, the inspector should have the supposedly exposed bead etched to remove such smeared metal and verify that the weld metal is revealed.

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WeldingSymbols And

Blue PrintReading

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WELDING SYMBOLS

Figure 2 – Standard Location of Elements of a Welding Symbol

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JOINT & WELD SYMBOLS – MANUAL METAL ARC WELDING

TRANING NOTES

Types of Joint

Butt Welded JointA joint where a weld is made between the ends of edges of metals.

Fillet Welded JointA weld approximately triangular in shape and external to the surface to be jointed.

Square Butt JointA joint with permanent backing strip held in place by fillet welds.

Double Lap JointA joint made by two fillet welds.

RootThe position in a prepared butt joint where the parts to be joined are near-est together. OrThe corner of the angle formed by the two fusion faces of a fillet joint.

Root FaceThe square faces at the root of prepared workpieces.

Toe of Weld The top and bottom position where the weld face joins the parent metal.Leg Length The distance from the root to the toe of the weld.Throat thickness The shortest distance from the root of the weld to the weld face in a fillet weld.

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Gap The distance between the parts to be jointed.

Included angleThe total angle between the fusion faces of the parts in position ready for welding.

Parent Metal (of workpiece)The materials and or the parts to be welded.

Penetration The depth the molten metal from the electrode penetrates the parent metal.

Reinforcement (excess weld metal)Weld metal lying outside the plane joining the toes.

Tack weld A short weld used to help assembly by holding workpieces in position during welding.

Run or PassThe molten metal deposited during the passage of the electrode.

Root Run The first run deposited in the root of a joint where there is to be more than one run.

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Filler Runs or PassesThe build up runs(s) between root and capping run(s).

Capping or Final RunsThe weld runs which make up the top layer of the joint.

Sealing RunA weld deposited on the root side of a butt or corner joint, after completion of the main weld.

Sealing WeldA weld used to make a fluid-tight joint.

Welding Terminology

The following are the meanings of some of the terms used in welding.

Angle of BevelThe angle of an edge or end which is cut or chamfered.

Arc LengthThe distance between the end of an electrode and the surface of the weld pool.

Fusion FaceThe surfaces or edges of the parent metal to be fused by welding.

Fusion ZoneThe palace where the deposited metal fuses with the workpiece.

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BasicWelding

Metallurgy

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HEAT TREATMENT

Welding inspectors normally are interested only in the left hand portion of the diagram up to about 0.35% C. it must be recognized that the ad-dition of alloying elements will cause a low carbon to harden on rapid cooling in a manner similar to high carbon steels. At this point, some of the terms relating to the iron-carbon alloy system will be reviewed.

Phases Ferrite (α–Fe). The body-centered cubic (bcc) form of pure iron, stable below 912 C (1674 F). Carbon content ranges from 0 to 0.022%. Austenite (γ-Fe). A solid solution of one or more elements in face-centered cubic (fcc) iron. Unless otherwise designated, the solute is generally assumed to be carbon, ranging in content from 0 to 2.11%. Ferrite (δ-Fe). A solid solution of one or more elements in body-centered cubic (bcc) iron. Unless other-wise designated, the solute is generally assumed to be carbon, ranging in content from 0 to 0.10%. Cementite. A compound of iron and carbon, known chemically as iron carbide and having the approxi-mate chemical formula Fe,C. It is characterized by an orthorhombic crystal structure. Graphite. Carbon in the free state occurring in several geometric forms. Alloy Carbide. A chemical compound of carbon and alloying elements that form both simple and com-plex chemical compounds with carbon, usually Fe, Mn, Cr, V, W, Mo, Cb and Ti. The microstructures that can be produced within the system as a function of cooling rate and chemical composition are listed below:Microstructures Ferrite. See definitions under Phases. Austenite. See definitions under Phases. Cementite. See definition under Phases. Pearlitic, coarse and fine. A mixture of ferrite and cementite consisting of alternate platelets with the thickness of the ferrite being about seven times the thickness of the cementite. Spheroidite. An aggregate of iron or alloy carbides if essentially spherical shape dispersed throughout a matrix of ferrite. Bainite. A decomposition product of austenite consisting of an aggregate of ferrite and carbide. In gen-eral, it forms at temperatures lower than those where very fine pearlite forms and higher than those where very fine pearlite forms and higher than those where martensite begins to form on cooling. Its appearance is feathery if formed in the upper part of the temperature range; acicular, resembling tempered martensite, if formed in the lower part. Tempered Martensite. A mixture of ferrite and cementite in which the carbides are very finely dis-persed in a submicroscopic spheroidal form. Martensite. A metastable phase of steel, formed by a transformation of austenite below the M5 (or At “) temperature. It is an interstitial supersaturated solid solution of carbon in iron having a body-centered tetrago-nal lattice. Its microstructure is characterize by an acicular, or needlelike, pattern. Graphite. See definition under Phases. Free carbon whose shape either as a flake, nodule or spheroid describes the type of cast iron, which is gray, malleable or ductile, respectively. Alloy Carbide. See definition under Phases.

Cooling rates are often described as follows: Spheroidizing. Very slow, forming spheroidized carbides and ferrite. Annealing. Furnace cool, forming lamellar carbides and ferrite. Normalizing. Air cooling, forming fine lamellar pearlite and ferrite.

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5.3.5 TTT CURVES

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HEAT TREATMENT

What is heat treatment?

Heat treatment could be describe as the changes that takes place within a material when heat is applied. This could be done in a number of ways: i. Air fuel Gas ii. Oxy-fuel Gas iii. Electrical resistance heating iv. Induction heating v. Furnace Heating

Why Heat Treatment?

All metals can be heated. Some metals are affected very little by heat treating, but some particularly most steels, are greatly affected. Heat treating may serve the following purposes. i. Develop ductility ii. Improve Machinery qualities iii. Relieve Stresses iv. Change grain size v. Increase hardness or tensile vi. Change chemical composition of metal surface as in case hardening vii. Alter magnetic properties viii. Modify electrical conduction properties ix. Include toughness x. Re-crystallize metal which has been cold worked

When heat treating, there are four factors of great importance. i. The temperature to which the metal is heated ii. The length of time that the metal is held at the temperature iii. The rate (speed) at which the metal is cooled iv. The material surrounding the metal when it is heated as in casehardening

There are several basic heat treatment. They are:- i. Annealing ii. Normalizing iii. Quenching iv. Tempering v. Preheat vi. Postheat vii. Thermal stress relief

(i). ANNEALINGAnnealing is softening treatment used to increase the metal’s ductility at the expense of its strength. This is done by heating metal into its austenitic range, where it is held for one hour and then cooled very slowly in a furnace, this cool-ing is usually done by simply turning off the furnace power and allowing the part to cool to room temperature while remaining in the furnace.

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(ii) NORMALIZINGNormalizing also softens the metal, but not as significantly as annealing. It is considered as ‘homogenizing’ heat treatment by making the metal structure very uniform throughout its cross section. This heat treatment is accomplished by raising the metals temperature into the austenitic range; holding for a short time, and then allowing it to slow cool in still air. This process however creates a faster cooling medium. Therefore, the resulting properties include slightly higher hardness and strength and possibly lower ductility as compared to annealing.

(iii) QUENCHING Quenching is accomplished by raising the metal’s temperature into the austenite range, holding for a time and rapidly cooling to room temperature by immersing the part in a quenching medium, such as water, oil or brine (salt water). This procedure produces a primarily martensite structure which has characteristically high hardness and strength and low ductility. To improve the ductility of the material, a tempering treatment is usually performed. This is done by re-heating the material to a tempera-ture below the lower transformation temperature, hold for a short time to allow the highly stressed martensite structure to relax somewhat and then cooled.

(iv) PREHEATPreheat treatments are used, to slow down the cooling rate of the base metal adjacent to the weld to allow for the formation of micro-structural constituents other than martensite. Preheat is applied prior to welding.

(v) POSTHEATPostheat treatments are used to reduce residual stresses and temper hard, brittle phases formed during cooling or quenching. Postheat is applied after the welding has been completed. Generally, Postheat temperatures are higher than those used for preheat.

(vi) THERMAL STRESS RELIEFThis heat treatment falls under the category of Postheat treatment in that, they both reduce the amount of residu-al stresses which are present following welding. Thermal stress relief is done at temperatures below the lower transformation temperature (13330F). by raising the temperature of the weld and base metal gradually and uniformly the thermal stresses created by the localized heat of welding are allowed to relax. Stress relief occurs because the strength of a metal is reduced as its tem-perature is increased, allowing the residual stress to relax and the metal to recover. This treatment helps in the reduction of distortion.

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PREHEAT AND POSTHEAT

PREHEAT

Preheating has long been known as a highly effective means of preventing weld metal and base metal cracking. Preheating is beneficial for a number of reasons. 1. Its lowers the cooling rates in the weld metal and heat affected base metal, rendering these metals inca-pable of cracking under some conditions.2. It lowers the magnitude of shrinkage stresses. The need for preheating carbon steel is based not on carbon content alone, but rather on the combination of carbon magnesium, silicon the residual alloy contents along with various aspects of joint configuration-chiefly section thickness.However, generally, neither preheating nor post heating are required when the carbon content is less than 0.25%.

Summarizing Preheating an assembly for welding is intended primarily to prevent cracking in the weld or in the heat af-fected zone. With preheating the hardness in the heat-affected zone will usually be lower, because cooling rate is slower and residual stresses and distortion will be minimized. Thus, many code governed weldments have mandatory requirements and specific conditions for preheating.

POSTHEATPostheat, is just as important as preheating. Base metal thickness and carbon content do have some influence on this procedure.Postheating may, under certain conditions prevent cracking. As simple Postheat treatment, which will prevent the formation of underbead cracking is the immediate application of heat to a completed weld so as to retard the cooling.

PEENING Peening as an adjunct to welding has, in general been beneficial in preventing weld metal cracking and in reduc-ing shrinkage stress and distortion. Peening consists of the mechanical working of a metal by the application of hammer blows.The effects of peening are obtained from plastic flow introduced at the locus of the hammer blows. As the metal is pushed laterally, the inward pull of each bead as it cools is reduced. The effectiveness of peening has been amply demonstrated by many instances in which cracking, in thick joints extremely high restraint could not be prevented without the use of peening.

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EFFECTS OF ALLOYING ELEMENTS

These are ferrous elements made by the fusion of steel with other elements such as:

Nickel (Ni) Chromium (Cr) Manganese (Mn) Tungsten (W) Molybdenum (Mo) Vanadium (Va) Silicon (Si) Cobalt (Co) Aluminium (Al)

Steel alloys are used to manufacture parts and tools which depending on their use, require in their composition the presence of one or several of the above mentioned elements. The resulting alloy receives the name of the element or elements, as the case may be, that compose it. Each one of these elements gives the following prop-erties to the steel.

NICKEL (Ni)This is one of the first metals to be used successfully in rendering certain qualities to steel. Nickel increases its resistance and toughness, raises its limit of elasticity, makes it a good conductor and increases its resistance to corrosion. Nickel steel contains 2 to 5% Ni and 0.1 to 0.5% carbon. The percentages 12 to 21% Ni and 0.1% carbon produce stainless steels which are very hard and resistant.

CHROMIUM (Cr)It also renders to the steel high resistance, hardness, high elasticity limit and good resistance to corrosion.Chromium steels contains 0.5 to 2% chromium and 0.1 to 1.5% C. the special chromium-steel (stainless type) contains 11 to 17% Chromium.

MANGANESE (Mn)Steels with 1.5 to 5% manganese are brittle. Manganese, nevertheless, when added in correct quantities, increas-es the resistance of steel to wear and shock, maintaining its ductility. Manganese steel usually contains 11 to 14% Mn and 0.8 to 1.5% carbon.

TUNGSTEN (W)It is generally added to steels with other elements. Tungsten increases hardness, the breaking point, limit of elas-ticity and resistance to heat. Steels with 3 to 18% W and 0.2 to 1.5% C are very resistant.

MOLYBDENUM (Mo)Its effects on steel is similar to that of tungsten. It is used generally, added to chromium, to produce chrome-molybdenum steel of great stress, especially under repeated stress.

VANADIUM (Va)It improves, in steels, the resistance to tension, without loss in ductility, and elevates the limits of elasticity and fatigue. Chrome-vanadium steels generally contain, 0.5 to 1.5% Cr. 0.15 to 3% Va and 0.13 to 1.1% C.

SILICON (Si)Increases the elasticity and resistance of steels. Silicon steels contain 1 to 2% Si and 0.1 to 0.4%f C. Silicon has the property of insulating or suppressing magnetism.

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COBALT (Co)It favorably influences the magnetic properties of steels. Besides, cobalt associated with tungsten increases the resistance of steels to heat.

ALUMINIUM (Al) It deoxidizes steel. In the thermos-chemical treatment process called nitriding, it is confined with nitrogen to aid informing a very hard superficial layer.

NOTES ON ENGINEERING MATERIALSGENERAL: The Physical Properties of Materials.

1. DUCTILITY: It is the property which enables a material to be drawn out to a considerable length with-out fracturing materials selected to make wire must be extremely ductile.

2. ELASTICITY: Is the ability of a material which has been deformed in some way to return to its origi-nal shape and size after the deforming force has been removed.

3. HARDNESS: Is the property of resistance to surface wear of indentation.

4. MALLEABILITY: Is the property which allows a material to be deformed by hammering, rolling or pressing, without fracturing. Heating improves malleability.

5. PLASTICITY: Is the ability of a material to flow into new shapes under pressure, and to retain its new form.

6. TENACITY: Is the property of resistance under tensile force. This property is expressed as (lbf/in2) or (Tons.f/in2) (Nm-2) Tensile strength and is of treat importance to designers.

7. TOUGHNESS: Is the property of resistance to fracture under sudden shock loads. It is usually found in a material which combines high tenacity with good ductility. Heating usually lessens toughness.

8. BRITTLENESS: Is the opposite of toughness: Brittle materials fracture cleanly under shock loads but may withstand constant pressures. The property is also referred to as shortness. A material brittle at room tem-peratures is said to be cold short and when hot, as hot short.

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DISTORTION

In welding, the metal is not heated uniformly and local contraction takes place, i.e. the joining of plates by welding, however, involves molten-metal, red-hot metal, and cold metal. The molten metal (weld metal) con-tracts as is solidifies and usually pulls the plates of alignment. This results in distortion.

TYPES OF DISTORTIONDistortion may affect a welded section or joint in four ways. Welded joitns are subject to two or more of the fol-lowing:1. Angular Distortion 2. Transverse Distortion 3. Longitudinal Distortion 4. Bucking or Bowing

1) ANGULAR DISTORTION

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2) TRANSVERSE DISTORTION

When two plates are butt-welded together, they draw together and overlap as the weld progresses.

3) LONGITUDINAL DISTORTIONWhen a weld is deposited on a strip of metal, the metal will bend upwards in the direction of the weld. This is longitudinal contraction due to the shrinkage of the weld metal as it cools. If the weld could be separated from the plates, the weld when cold would be shorter than the plates.

4) BOWING OR BUCKING If a heated section in the centre of a piece of sheet metal is heated, the heated section at-tempts to expand. The cold metal that surrounds the heated section resists the expansion, and so the heated section must expand upwards, forming a bulge in the plate.

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CAUSES OF DISTORTION

The amount of distortion maybe estimated by careful consideration of the following factors:1. More heat input results in more expansion and contraction, hence, more distortion is likely to occur.2. Existing residual stresses, due to previous forming operations tend to relieve themselves when the metal is heated thus, causing distortion.3. The amount of weld metal – more weld metal results in more contraction stresses hence more distortion.4. Relative movement of parts i.e. consideration of freedom of movement and restriction of movement by clamping etc.5. Temperature of weld and associated parts i.e. localized heating – localized contraction. Temperature of surrounding parts determines the cooling rate hence the amount of distortion.6. Physical properties of the metal i.e. coefficient of expansion, thermal conductivity.

METHOD OF MINIMIZING DISTORTION

There are several ways in which the effect of contraction forces may be controlled.Some of these are:

1. PRESETTINGPresetting is carried out prior to welding. The plated to be welded are set slightly out of alignment so that when contraction stresses occur, the plates will be pulled into the correct position. This practice is limited to simple assemblies.

2. BACKSTEPPINGThe object of this method is to put an expansion and a contraction zone next to each other and thereby cancel out the expansion and contraction forces.This could be accomplished with a skip welding technique.

3. EVEN HEAT DISTRIBUTIONThe welding sequence for a large complex structure may be planned prior to fabrication.A variation of this method is to use a welding torch to heat the side opposite to the weld. This cancels out the distortion caused by welding.

4. JIGGINGThis consist of locating, holding and in some cases backing the plates to be weld.The plates may be tacked or welded in the jig where they are held firmly, resisting shrinkage forces.

5. JOINT-DESIGN(a) Design job to avoid highly localized areas of weld i.e. avoid many welds meeting at the same place.(b) Weld about a neutral axis: Ensure penetration.

6. HEAT INPUTThe more heat used on the job, the greater the chance of distortion. The following steps can reduce the heat input.(i) Make the minimum number of weld(ii) Make the minimum number of passes(iii) Make the smallest size weld that fulfil the requirements of designHeat dissipation by use of chills. The object of this is to conduct heat away from the weld area by means of a metal conductor e.g. (CU.)

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RESIDUAL STRESSES: The strength of a welded joint depends a great deal on the way expansion and contraction of the metal are controlled during the welding operation. Whenever heat is applied to a piece of metal, expansion forces are created which tend to dis-tort the dimension of the piece. Upon cooling, the metal undergoes a change again as it attempts to resume its original shape. When free movement is restricted there is likely to occur warping or distortion if the metal is brittle, as with cast iron. If expansion is restricted in its movement the building up force will find another direction for uneven expansion in the heated area and some of the original dis-

placed metal will contract unevenly on cooling and the workpiece will become permanently distorted.

CONTROLLING RESIDUAL STRESSES: Few simple procedures will help control undue forces caused by expansion and contraction; Proper edge preparation and fit up; Reduced bevel angle with sufficient room in the joint to permit proper manipulation of the electrode. Weld joint near-est to the neutral axis first, followed by welding the unit farthest from the neutral axis. On long seams especially thin section allow 3mm per 300mm length for weld expansion during set up procedures. Preset pieces of the joint slightly out of alignment to counteract direction of distortion.

FORMS OF DISTORTION: Angular distortion in a fillet weld are caused by unrestrained plates being drawn together as the plates and weld cool. Distortion will increase as further unbalanced runs are deposited. A flat, thin plate will bend upwards as the plate and weld cool. Two butt welded plates which are free to move will be drawn together as welding takes place. Distortion may occur if the welds are made on one side of the joint. Double sided butt joints will distort less. In a T-joint the weld along the seam will bend both the upright and flat piece. Distortion is counteracted by welding to a specified

pattern given in weld procedures. This is known as balanced welding.

LIMITING DISTORTION BY WELDING SEQUENCE: Track welds are also used to hold plates in position and control undue expansion on long seams. A long longitudinal (end ways) seam is welded before a short transverse (side-ways) seam. Jigs and fixtures are used to preset and hold plates and prevent excessive movement, heavy fixture plates not only control distortion but they also serve as chill blocks to avoid excessive heat building up in the work.

Intermittent or skip weld is employed to minimize heat input by making a short weld at beginning (1) center of seam (2) end of joint (3) and repeating the cycle for completing the seam.In back – step or step – back technique instead of laying a contin-uous bead from left to right deposit off short sections of the beads from right to left to complete the pass.

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PRE-HEATING: On many work pieces, particularly alloy steel and cast iron, expansion and contraction forces can be better controlled if the entire structure or large parts of the weld area can be preheated before the welding is started. Ensure uniform temperature during welding operation and care for slow cooling.

POST HEATING (STRESS RELIEVING): Stress set up during welding may be relieved by heating the work piece for a stated temperature and period of time and cooling in controlled rate.

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PREVENTION, CONTROL AND CORRECTION OF DISTORTION

TRAINING NOTES

FixturesFixtures may be temporary or specially made for quick and correct positioning of materials to be welded.

Tack Weld A short weld used to help assembly by holding workpieces in position during welding.

Backing Bar A piece of metal tacked behind a butt or corner joint to aid the welding operation but not intended to become part of the finished joint.

Backing StripA piece of metal tacked at the root of the joint which becomes part of the joint when welding is completed.

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Bridge Pieces of metal of the same shape which are tack welded in several places around pipes to hold them in position. A bridge may be used to hold the clamp of an earth return lead close to the weld area.A short continuous weld in the root gap may also be called a bridge.

Strongback Similar to a bridge and used to hold workpieces in position for butt welding in the flat, horizontal, vertical and overhead positions.

Temporary Fixtures

1. Temporary fixtures may be tack welded to workpieces to hold materials which are to be welded. Care must be taken to ensure that the fixture does not move during welding. Dimensions should always be checked for accuracy after tacking and before starting to weld.

Tack Welded Cleats as an aid to alignment

2. Workpieces may be lap jointed in position for welding, using clamps and angle bars.

3. Cleats temporarily attached to workpieces to hold T joint in posi-tion for welding.

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4. A strongback, bolt and clamp may be attached to workpieces to hold them in position whilst a butt joint is welded.

5. A bolt, clamp and hard wood blocks may be used to hold an angle section on position during welding.

Positioners The universal balance type of positioner allows for positioning of the work-piece in any direction.

Manipulators The most widely used types of manipulators are motor driven and de-signed to rotate and move work at the required welding speed.

Manipulation and Positioning of WorkpiecesEnsure that components placed in or on a fixture, positioner or welding manipulator are properly balanced and secured.

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Arc WeldingElectrode

Classifications

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COURSE OBJECTIVES

Upon completion of this module, the trainee will be able to:1. Identify and explain AWS/ASME filler metal classification system.2. Identify and explain different types of filler metals.3. Identify and explain the relationship of filler metal classification to welding current.4. Explain considerations for selecting electrodes.5. Explain the storage and control of filler metals. 6. Explain filler metal traceability requirements7. Explain how to use applicable code requirements.

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First of all there are two types of electrodes:-i) Coated electrodes ii) Bare wire electrodes

A coated electrode could then be described as a solid metal core wire covered with a layer of granular flux held in place by some type of bonding agent. The core wire is a low carbon, rimmed steel. The flux is made up of varying alloying element, depending on its applicability.However, they do have their functions. In that, the core wire provides the molten metal to form the weld bead. Whereas, the flux has five separate functions which are listed.

1. Shielding: the coating decomposes to form a gaseous shield for the molten metal.2. Deoxidation: the coating provides a fluxing action to remove oxygen and other atmospheric gases.3. Alloying: the coating provides additional alloying ele-ments for the weld deposit.4. Ionizing: the coating improves electrical characteristics to increase arc stability.5. Insulating: the solidified slag provides an insulating blanket to slow down the weld metal cooling rate (minor ef-fect).

Since the electrode is such an important feature of the shielded metal arc welding process it is necessary to understand how the various types are identified and classified. The American Welding Society has developed a system for the identification of shielded metal arc welding electrodes. Figure 3.3 illustrates the various parts of this system. American Welding Society Specifications A5.1 and A5.5 describe the requirements for carbon and low alloy steel electrodes respectively. They describe the various classifications and characteristics of these electrodes.

Figure 3.3- SMAW Electrode Identification System

The identification consists of an “E”, which stands for electrode, followed by four or five digits. The first two, or three numbers refer to the minimum tensile strength of the deposited weld metal. These numbers state the mini-mum tensile strength in thousands of pounds per square inch. For example, “70” means that the tensile strength of the deposited well metal is at least 70,000 psi.The next number refers to the positons in which the electrode can be used a “1” indicated the electrode is suit-able for use in any position. A “2” means that the molten metal is so fluid that the electrode can only be used in the flat or horizontal fillet positions. A “4” means the electrode is suitable for welding in a downhill progression. The number “3” has no designation. The last number describes other characteristics which are determined by the compositions of the coating present on the electrode. This coating will determine its operating characteristics and recommended electrical current:

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AC (alternating current), DCEP (direct current, electrode positive) or DCEN (direct current, electrode negative). Figure 3.4 lists the significance of the last digit of the SMAW electrode identification system. It is important to note that those electrodes ending in “5”, “6”, or “8” are classified as ‘low hydrogen’ types. To maintain this low hydrogen (moisture) content, they must be stored in their original factory sealed container or an acceptable storage oven. This oven should be heated electrically and have a temperature control capability in the range of 150o to 350o F. Since this device will assist in the maintenance of a low moisture content (less than 0.2%), it must be suitably vented. Any low hydrogen electrodes which are not to be used immediately should be placed into the holding oven as soon as their airtight container is opened. Most codes require that low hydrogen electrodes be held at a minimum oven temperature of 250o F (120o C) after removal from their sealed container.However, it is important to note that electrodes other than those mentioned above may be harmed if placed in the oven. Some electrode types are designed to have a certain moisture level. If the moisture is eliminated the operating characteristics of the electrode will deteriorate significantly.

Note: iron powder percentage is based on weight of the covering Figure 3.4 - Significance of Last Digit of SMAW Identification

FACTORS TO BE CONSIDERED IN SELECTION OF AN ELECTRODE

1. Basemetal strength properties 2. Composition of the parent plate 3. Welding position4. Welding current 5. Joint design and fit-up 6. Thickness and shape of base metal 7. Service condition and specification (welds with high strength good ductility)8. Production efficiency (cost of electrode, electrode – class)

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Shielded MetalArc Welding

Exercise

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COURSE OBJECTIVES

Upon completion of this module, the trainee will be able to:

1. Weld beads on plate in the flat position using E6010 and E7018 electrodes.

2. Make fillet welds in the horizontal position using E6010 and E7018 electrodes.

3. Make fillet welds in the vertical position using E6010 and E7018 electrodes.

4. Make fillet welds in the overhead position using E60160 and E7018 electrodes.

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Striking an Arc

OBJECTIVES After completing this unit the student will be able to:• Describe the basic principles of arc welding.• Discuss reasons for welds with poor appearance of lack of penetration.• Successfully strike and maintain an arc, using standard welding electrodes and equipment.

Striking the Arc

When a ground and a wire carrying an electrical charge contact each other, an arc (continuous spark) occurs, causing intense heat and bright light. This is the principle on which arc welding operates, except that after the arc is started, the welding electrode is moved a short distance away from the parent metal. This keeps a constant arc and continuous heat. An arc length of 1/8 inch is maintained most of the time. Lengthening the arc by moving the electrode father away from the parent metal increases the heat and size of the puddle. Improper arc length can sometimes be determined by visually inspecting a completed weld. Too short an arc can cause poor fusion (fusion is the mixing of the parent metal with the weld metal), undercutting (an area where metal is missing), and porosity (pinholes). Too long an arc can cause lack of concentration of the heat, excessive splatter, poor penetration (penetration is the depth of the weld in the parent metal), and arc action which is not smooth. Holding the arc too short can also cause the electrode to stick to the parent metal. The arc may be struck by dragging the electrode across the grounded metal much as a match is struck, figure 3-1. If the electrode has a heavy flux coating, it may be necessary to break the coating away from the end of the rod before contact can be made. Another method, and one frequently used, is to bring the rod down onto the plate at a 90-degree angle, then raise it quickly to the correct distance to maintain even heat and penetration, figure 3-2.

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Welds in the Flat Position

Fig. 3-3 Electrode Angle for Filling Puddle and Welding.

After the arc is established, movement across the plate must be made in a steady forward motion, and the arc must be kept a uniform length. Too rapid progress will result in poor penetration. Right-handed welders generally progress from left to right, so that the weld puddle can be seen and the filling (or buildup) of the rod can be controlled. Left-handed welders should work from right to left. The flux coating on the shielded electrode melts and forms slag over the molten metal. This shields the weld from the action of the gases in the atmosphere. When the weld is completed and cooled, the slag may be removed from the surface of the weld by the use of a chipping hammer. The heat of the arc melts a crater into the parent metal which must then be filled with the electrode metal. As the electrode is melted into the weld, it is thorough mixed with the parent metal. It is not enough to lay a bead on the parent metal. Through penetration and fusion between parent metal and electrode metal must take place. As the electrode melts it must be gradually lowered towards the weld to maintain the correct length of the arc.

Electrode After the arc has been started, the electrode should be help away from the plate to begin the weld. A good rule to follow is to keep the arc at a distance equal to the diameter of the rod being used. The rod must be held perpendicular to the plate being welded, and tipped slightly (about 10 degrees) in the direction of travel, figure 3-3. The bead width should be approximately twice the diameter of the rod.

JOB 3: STRIKING AND MAINTAINING AN ARC

Equipment and Material: Standard AC or DC welding machine Helmet Gloves Chipping hammer Safety glasses Wire brush Protective clothing ¼” mild steel plate 1/8”, E-6011 or E-6-13 electrodes

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PROCEDURE

1. To form an arc, it is necessary to being the electrode into contact with the workpiece.

2. Place the metal workpiece in the flat position.

3. Install a 1/8-inch electrode in the electrode holder.

4. Hold the end of the electrode about ¼-inch above the workpiece, on the left edge of the plate. Practice bringing the electrode own onto the plate, tipping the head forward to bring the helmet down over the face at the same time.

5. Set the polarity switch on the machine on “Elec-trode Negative” and the current at 90 amperes.

6. Turn on the welding machine.

7. In the same manner as in No. 4 of this lesson, drop the hood over the face and strike an arc. The electrode should contact the spot the welder was watching be-fore lowering the helmet.

8. If the electrode sticks to the plate, quickly depress the lever on the electrode holder, releasing the elec-trode. Break the electrode off the plate with pliers.

9. Run a bead about ½-inch long. Raise the rod to break the arc, then repeat the operation until an arc can be struck and a weld can be run about 2inches.

10. Shift the polarity of the welding machine, alter-nating between DSCP and DCRP. Practice with both polarities. If AC is available use that also.

11. Chip the welds beads, using a slag hammer (chipping hammer), brush them with a wire brush, and show them to the instructor for comments.

KEY POINTS

1. Do not turn on the welding machine.

4. Practice this exercise until the electrode strikes the edge of the plate at the same time the helmet drops over the face to cover the eyes.\

6. Do not make contact between the end of the rod and any grounded material.7. CAUTION: Be very careful not to strike an arc with-out the colored lens of the hood in front of your eyes. Draw the electrode across the plate with a quick, whip-ping motion, as if striking a match.

8. CAUTION: The rod is hot.

9. A weld made at the correct temperature and rate of travel makes a soft, frying sound.

10. CAUTION: Do not change the polarity of a welding machine during an arc. The machine must not have any load on it when the polarity is changed.

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REVIEW QUESTIONS1. What happens when a wire carrying an electrical charge touches a ground?

2. How far away from the metal being welded should the electrode be held for arc welding?

3. List three things which can be observed on a completed weld made with the arc too short.

4. Describe one method of striking an arc with an electrode.

5. What is the reason for the flux coating on the electrode?

6. How should the width of a bead compare with the diameter of the electrode being used?

7. How does the length of the arc affect the amount of heat generated in the welding process?

8. Describe the angle at which the electrode should be held for welding a bead on a flat surface. 9. Define the term penetration, as it is used in welding.

Straight Beads, Flat Position

OBJECTIVES After completing this unit the student will be able to:• Identify at least five common welding electrodes by their AWS classification and exhibit knowledge of their specific uses.• Weld a smooth, even bead using E-6011 electrodes.• Weld a smooth, even bead using E-6013 electrodes.

Electrode Selection Welding electrodes are classified according to whether they are to be used with DC reversed polarity (DCRP), DC straight polarity (DCSP), or alternating current (AC). The electrodes used most commonly for mild steel welding are discussed here.E-6010 indicates an all-position welding rod (flat, vertical, horizontal, and overhead). It performs best when used with DCRP. Deep penetration can be achieved with this electrode which has a thin coating, and which lends itself particularly well to out-of-positioning welding.E-6011 also indicates an all-position welding rod. It is particularly suited for use with AC, but it can also be used with DCRP and DCSP. Its thin coating makes it a good electrode for out-of-position work.E-6012 is another all-position electrode, however, because of its heavier flux coating, it is slightly more difficult to make out-of position welds with this electrode. It is best suited for use with DCSP or AC.E-6013 indicates an electrode which is especially suited for deep-penetration welds in the flat position. Because of its heavier coating it is a more difficult electrode for beginners to use than are the E-6011 electrodes. This electrode can be used with all types of polarity.E-6020 electrodes have a heaving iron powder flux coating. They are used for flat and horizontal welding only. (Notice that the third digit is 2). These electrodes can be used with DCRP, DCSP, or AC. E-6030 electrodes also have a heavy iron powder flux coating. As is indicated by the third digit being 3, they are for flat position welding only. These electrodes may be used with DCRP or AC. Note: E-6020 and E-6030 electrodes are sometimes called drag rods. This is because the welder can run a bead without removing the rod from the parent metal once the arc is struck.

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Welding Currents Generally, the amperage at which the rod runs most readily is indicated by the manufacturer. Differences in rod diameter and in material used for the flux coating require differences in the current settings used.

Fig. 4-1 Current Setting for Common Electrodes

Fig. 4-1 indicates current settings which generally give satisfactory results.

Welding Coupon The welding coupon (or sample) is generally small, therefore the heat from the welding tends to concen-trate and build up in the plate. After welding is started on the practice plate the lower ranges of current should be used, and the plate cooled in water frequently. This prevents excessive heat from building up in the coupon.

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JOB 4A: STRINGER BEADS IN THE FLAT POSITION, DCRPEquipment and Material Standard AC or DC welding machine Helmet Gloves Chipping hammer Safety glasses Wire brush Necessary protective clothing ¼” mild steel plate 1/8”, E-6011 and E-6013 electrodes

PROCEDURE

1. Clamp a 1/8-inch, E-6011 electrode in the elec-trode holder.

2. Set the welding machine for reverse polarity (electrode positive).

3. Turn on the machine.

4. Strike an arc and run a smooth, even straight bead across the sample plate.

5. Shut off the machine.

6. Hang up the stinger and remove the sample from the welding job or table. Use a chipping hammer to remove all the slag from the weld.

7. Brush the weld and the plate with a wire brush and have the instructor check it.

8. Follow the procedure listen in steps 2 through 7 using a 1/8-inch E-6013 electrode.

9. Observe the difference in the way the weld is deposited by the two electrodes.

KEY POINTS

2. Check the manufacturer’s char a set the amperage for the rod being used.

3. Be careful that the rod does not come into contact with the grounded material. 4. The welder’s face should be covered by the helmet when the arc is striking an while the weld is in progress. CAUTION: The welder must have face and eye protec-tion when chipping welds.

6. Open the window in the hood but keep the hood down when chipping or brushing welds.The metal is hot. Handle it with pliers.

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JOB 4B: STRINGER BEAD IN THE FLAT POSITION, DCSPEquipment and Materials Standard arc welding equipment Protective clothing 3/16” or ¼” mild steel plate 1/8” or 5/32”, E-6011 and E-6013 electrodes

Fig.4-3 Electrode Angle for Stringer Beads in the Flast Position

PROCEDURE

1. Fasten the coupon in a jig or lay it flat on the bench.

2. Set the welding machine for straight polarity.

3. Working in a comfortable position, and begin-ning at the left side for the plate (if right-handed), deposit a stringer bead with an E-6011 electrode.

4. Remove the slag and brush the weld.

5. Run another rbead1/2 inch away from the par-allel to the first one, using an E-6013 electrode.

6. Remove the slag, brush the weld, and have it inspected by the instructor.

KEY POINTS

2. Check the current setting on a piece of scrap metal.

3. Center punch the plate if necessary to keep the weld in a straight line. The electrode should be at an angle of 90 degrees with the weld and tipped about 5 degrees in the direction of travel, figure 4-3.4. Cool the material in water before attempting to han-dle it with bare hands.

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JOB 4C: STRINGER BEAD PAD BUILDUP IN THE FLAT POSITIONEquipment and Materials Standard arc welding equipment Protective clothing 3/16” or ¼” mild steel plate 1/8”, E6013 electrodes.

PROCEDURE

1. Set the welding machine for DCSP.

2. Run the stringer beads across the plate, over-lapping each bead about one-fifth until the plate is completely covered.

3. Slag and brush the welds.

4. Weld stringer beads across the first layer, over-lapping about one-fifth, until the first welds are com-pletely covered, figure 4-4.

5. Stag and brush the welds.

6. Weld a third series of beads across the second layer, overlapping about one-fifth.

7. Slag and brush the welds.Note: Save this weldment for testing in another unit.

KEY POINTS

1. Electrode negative.

2. Right-handed welders should proceed from left to right. Concentrate on achieving penetration into the plate.

4. Concentrate on achieving penetration into the metal deposited on the first weld.

6. Concentrate on achieving penetration into the second layer.

7. The beads should appear smooth and uniform.

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REVIEW QUESTIONS

A. 1. What is the purpose of overlapping beads when they are welded close together? 2. Why should a weld be chipped and brushed before another weld is made over it? 3. For what position of welding are electrodes with heavy coatings most suited? 4. What characteristic of an electrode determines the current setting with which it should be used? 5. Describe the proper electrode angle for welding a bead on a flat surface.

B. Match the characteristics of the electrodes listed on the left with the electrode designations listed on the right.

1. __________ All-position electrode a. E-6030 Heavy coating b. E-6010 Best for AC and DCSP c. E-6012 d. E-6013 2. __________ All-position electrode e. E-6020 Heavy coating Best for AC and DCSP

3. __________ Flat-position coating Heavy iron-powder coating Best for DCRP or AC

4. __________ Used for flat and horizontal position Heavy iron-powder coating Good for DCRP, DCSP, and AC

5. __________ Flat-position deep-penetration electrode Heavy coating Good for DCRP,DCSP, and AC

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Weave Beads, Flat Position

OBJECTIVES After completing this unit the student will be able to:• Identify a weave bead.• List three reasons for the use of weave beads.• Describe the process of weaving a bead.• Weave a bead in the flat position.

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Weave Bead Weaving a bead increases the width of the deposit. It also increases the overlap. Weaving is used to widen a bead, to fill the undercut at the sides and to assist in slag formation. Weaving is generally recommended for filling poor fitting joints. A weave bead is deposited by moving the rod back and forth across the surface to be welded. Stringer beads may be run at the edges first. Several different electrode movements may be used, but weaving is gener-ally done in the first position using a semicircular motion to the left and the right, figure 6-1.

STRAIGHT ACROSS FIGURE “8” “U” Fig. 6-1 Weave Bead Techniques

Flat Position A weld made on the topside of the parent metal and within 30 degrees of horizontal is called a flat. The flat position is the most desirable position for welding, since the operator can see the work easily. In many weld-ing shops a device called a positioner is used to hold the work, so that it can easily be turned into the flat posi-tion. Flat welds can be made successfully with AC, DCRP, or DCSP.

JOB 6: WEAVE BEADS, FLAT POSITIONEquipment and Materials Standard arc welding equipment Protective clothing3/16” or ¼” mild steel plate1/8”, E-6011 electrodes

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PROCEDURE

1. Set the machine for straight polarity.

2. Weld stringer beads ½ inch apart on a plate, figure 6-2.

3. Slag and brush the stringer beads.

4. Beginning at the left side (left-handed welders being at the right side) run a weave bead between two string-ers, all the way across the plate.

5. Slag and brush the weld, then have it inspected by the instructor.

6. Repeat the procedure until the plate has three thick-ness of welded weave beads.

7. Saw through the center of the plate and smooth the cut edges with a file or grinder. Etch the cut edges with ammonium persulphate or a weak solution of nitric acid.

KEY POINTS

1. Electrode negative.

3. Welds must be cleaned between passes to prevent the slag from being trapped in the welds. 4. The current must be set high enough to make the bead edges flow together.

7. Check the weld for penetration and fusion. No slag holes or slag inclusions should be present.

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REVIEW QUESTIONS

1. Draw a sketch of the motion most frequently used for weaving a bead in the flat position.

2. Should stringer beads or weave beads be used to fill poorly fitting joints?

3. Describe the flat welding position.

4. Why the flat position is considered the most desirable position for welding?

5. What is a positioner?

6. Describe two methods which can be used to keep the sides of a weave bead in a straight line.

7. When one bead runs over the top of another, why is it necessary to clean the slag from the first bead?

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