arc welding

Dr. N. RAMACHANDRAN, NITC 1

ARC WELDING


LIQUID STATE PROCESSPARTIAL MELTING

BY STRIKING AN ARC

AFTER THE INVENTION OF ELECTRICITY

HOW ARC STRUCK?

ARC COLUMN THEORY


• ARC WELDING ELECTRIC ARC

WITHOUT ADDITIONAL EXTERNAL SOURCE

AUTOGENEOUS NONCONSUMABLE- CONSUMABLE

CARBON ARC WELDING (CAW) - OLDEST

METALLIC ARC WELDING (MAW)

COATING MATERIALS

ARC TO BE CREATED BY ELECTRICITY

WHEN? WITH THE INVENTION OF AC DYNAMO IN 1877


BEGINNING IN 1881- TO CONNECT PLATES OF STORAGE BATTERY

1886- BUTT WELDING TECHNIQUE WAS DEVELOPED

BUTTED, CLAMPED HIGH CURRENT PASSED

AT THE JOINT, RESISTANCE OF METAL TO ELECTRIC CURRENT PRODUCES HIGH HEAT- PIECES FUSED


ARC WELDING- MELTING AND FUSING OF METAL BY ELECTRODES

1ST BY N.V. BERNADO USING CARBON ELECTRODES

CONSISTANTLY IMPROVED

1895 N.G. SLAVIANOFF USED METALLIC ELECTRODES

1905 BARE ELECTRODES COATED—SHIELDING--- (SAW)

PORTABLE AND AUTOMATIC WELDING MACHINES


ARC WELDING PROCESSES

USE OF CONSUMABLE ELECTRODES SHIELDED METAL ARC WELDING

(SMAW)• SIMPLEST AND MOST VERSATILE• ABOUT 50% OF INDUSTRIAL WELDING

BY THIS PROCESS• CURRENT- 50 TO 300 A, < 10 KW• AC/DC USED• FOR THICKNESSES UPTO 19 –20 MM

SHIELDED METAL ARC WELDING (SMAW)


•Shielded metal arc welding (SMAW), •Also known as Manual Metal Arc (MMA) welding • Informally as stick welding

is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld.

•An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined.

http://en.wikipedia.org/wiki/Arc_welding

http://en.wikipedia.org/wiki/Electrode

http://en.wikipedia.org/wiki/Flux_%28metallurgy%29

http://en.wikipedia.org/wiki/Current_%28electricity%29

http://en.wikipedia.org/wiki/Alternating_current

http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Welding_power_supply

http://en.wikipedia.org/wiki/Electric_arc

http://en.wikipedia.org/wiki/Metal

ANODE +

CATHODE -

ELECTRICAL / IONIC THEORY

IONS FROM ANODE TO CATHODE,AS METAL IONS ARE +VE CHARGED

DC

ARC COLUMN THEORY

•TOUCH AND THEN ESTABLISH A GAP TO BALANCE THE ATOMIC STRUCTURE

•IONS COLLIDE WITH GAS MOLECULES

•PRODUCES A THERMAL IONISATION LAYER

•IONISED GAS COLUMN – AS HIGH RESISTANCE CONDUCTOR

•ON STRIKING CATHODE, HEAT GENERATED•TERMED AS IONIC THEORY

•NOT COMPLETE IN EXPLAINING ARC COLUMN THEORY•THUS, ELECTRON THEORY


ANODE +

CATHODE -

ELECTRON THEORY

IONS FROM ANODE TO CATHODEAS METAL IONS ARE +VE CHARGED

-VELY CHARGED ELECTRONS DISSOCIATED FROM CATHODE MOVE OPPOSITE WITH HIGH VELOCITY

DC(MASS- 9.1x 10-28 gm)

CAUSES HEAT IN ARC COLUMNRELEASES HEAT ENERGY IN

STRIKING THE ANODE

CALLED ELECTRON IMPINGEMENT

AND IONIC BOMBARDMENT

ARC COLUMN THEORY


HIGH HEAT

MEDIUM HEAT

LOW HEAT

ANODE+

CATHODE -

ELECTRON IMPINGEMENT

IONIC BOMBARDMENT


MAGNETIC FLUX THEORY

• THE COLUMN NOT FLAIRING

DUE TO THE FLUX LINES AROUND THE ARC COLUMN.

(Right hand Thumb Rule)

THIS COMPLETES THE ARC COLUMN THEORY


POLARITYAC

1. Currents higher than those of DCRP can be employed (400 A to 500 Afor 6 mm electrode)

2. Arc cleaning of the base metal

3. Normal penetration4. Equal heat distribution

at electrode and job5. Electrode tip is colder as

compared to that in DCRP

6. Average arc voltage in argon atmosphere is 16V


DCRP 1. Currents generally less than 125 amps (upto 6 mm dia electrodes) to avoid overheating

2. 2/3rd heat at electrode and 1/3rd at the job

3. Least penetration4. Average arc voltage on

argon atmosphere is 19V

5. Chances of electrode overheating, melting and losses

6. Better arc cleaning action


DCSP1. Welding currents upto

1000 amps can be employed for 6 mm electrodes

2. 33.33% heat is generated at the electrode and 66.66% at the job.

3. Deep penetration

4. Average arc voltage in an argon atmsphere is 12 V

5. Electrode runs colder as compared to AC or DCRP

6. No arc cleaning of base metal

METALLURGY OF WELDING

During joining, localized heating occurs.

This leads to metallurgical and physical changes in materials welded.

Hence, study of:

1. Nature of welded joint2. Quality and property of welded joint3. Weldability of metals4. Methods of testing welds5. Welding design6. Process selection- important

.


(2) Fusion Zone

(1) Base Metal

Structures: (1) SMALL (2) MEDIUM (3) LARGE

Properties of (2) and (3) important

(3) Heat Affected Zone (HAZ)


• Cooling of Bead- similar to a casting in mould, which is metallic here.

Cooling is slow Hence the structure is coarse and Strength toughness and ductility low.

But use of proper electrodes improves these.

• The purpose of coating the electrode is to achieve the improved properties. If without, nitrides and oxides of base metal form and these result in weak and brittle nature.

• With coating, properties comparable with base metal achieved.


Arc column makes CRATER on striking the surface- Temperature above 1500 C

Gas shield

Flux + impurities- less dense. Floats as SLAG

Slag prevents heat loss- makes an evenly distribution of heat radiation.

Preheating to receive the molten metal at an elevated temperature and modify the structure. Not for M.S.

Locked in stresses due to heating and cooling- to be relieved by PEENING, or other heat treatment processes.


MAGNETIC ARC BLOW -- FOR AC SUPPLY.

Current through conductor- magnetic Flux lines perpendicular to current flow- apply Right hand Thumb Rule.

Three areas of magnetic field

1. Arc; 2. Electrode; 3. Work piece, when ground.

Forward pull of Arc column results, called as Magnetic Arc Blow.


EQUIPMENT

Dr. N. RAMACHANDRAN, NITC

25

PURPOSE OF COATING• Gives out inert or protective gas- shields• Stabilizes the arc- by chemicals• Low rate consumption of electrode- directs arc and

molten metal• Removes impurities and oxides as slag• Coatings act as insulators- so narrow grooves welded• Provide means to introduce alloying elements

Bare electrodes - carbon- more conductive- slow consumption in welding

Dr. N. RAMACHANDRAN, NITC

26

ELECTRODE COATING INGREDIENTS• Slag forming ingredients- silicates of sodium, potassium, Mg,

Al, iron oxide, China clay, mica etc.• Gas shielding- cellulose, wood, starch, calcium carbonate• De-oxidising elements- ferro manganese, ferro silicon- to

refine molten metal• Arc stabilizing – calcium carbonate, potassium silicate,

titanates, Mg silicate etc.• Alloying elements- ferro alloys, Mn, Mo., to impart special

properties• Iron powder- to improve arc behaviour, bead appearance• Other elements - to improve penetration, limit spatter,

improve metal deposition rates,


• As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.

• Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's most popular welding processes.

http://en.wikipedia.org/wiki/Shielding_gas


• It dominates other welding processes in the maintenance and repair industry, used extensively in the construction of steel structures and in industrial fabrication.

• The process is used primarily to weld iron and steels (including stainless steel) but aluminum, nickel and copper alloys can also be welded with this method.

• Flux-Cored Arc Welding (FCAW) , a modification to SMAW is growing in popularity

http://en.wikipedia.org/wiki/Iron

http://en.wikipedia.org/wiki/Steel

(A).BARE ELECTRODE MOLTEN METAL TRANSFER

(B). LIGHT COATED ELECTRODE ARCACTION

Dr. N. RAMACHANDRAN, NITC 30Various welding electrodes and an electrode holder


SAFETY PRECAUTIONS• Uses an open electric arc, so risk of burns – to be prevented by protective clothing in the form of heavy leather gloves and long sleeve jackets.

•The brightness of the weld area can lead arc eye, in which ultraviolet light causes the inflammation of the cornea and can burn the retinas of the eyes. •Welding helmets with dark face plates to be worn to prevent this exposure


• New helmet models have been produced that feature a face plate that self-darkens upon exposure to high amounts of UV light

• To protect bystanders, especially in industrial environments, transparent welding curtains often surround the welding area.

• These are made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.


Arc eye, also known as arc flash or welder's flash or corneal flash burns, is a painful condition sometimes experienced by welders who have failed to use adequate eye protection. It can also occur due to light from sunbeds, light reflected from snow (known as snow blindness), water or sand. The intense ultraviolet light emitted by the arc causes a superficial and painful keratitis.

Symptoms tend to occur a number of hours after exposure and typically resolve spontaneously within 36 hours. It has been described as having sand poured into the eyes.

ARC EYE


SignsIntense lacrimation Blepharospasm Photophobia Fluorescein dye staining will reveal corneal ulcers

under blue light

Management• Instill topical anaesthesia • Inspect the cornea for any foreign body • Patch the worse of the two eyes and prescribe analgesia • Topical antibiotics in the form of eye drops or eye

ointment or both should be prescribed for prophylaxis against infection

Shielded Metal Arc Welding

What Is Welding ?

Process of joining metals / alloys

The process performed by Heat with or without Pressure

Filler metal may or may not be used

The joint will be homogeneous

Classification Of Welding

1 Pressure Welding – With Heat & Pressure

2 Fusion Welding – With Heat & mostly with Filler

Pressure Welding Process

Metal parts heated to forging temperatureHeating by Oven, Oxy fuel flame or Electric ResistancePressure applied on heated parts – by Hammer, Hydraulic Press or Mechanical leverThe Parts remain permanent homogeneous joint

Types Of Pressure Welding

Forge WeldingResistance Butt / Flash Butt / Stud WeldingResistance Spot WeldingResistance Seam welding

Fusion Welding Process

Metal parts locally heated to melt along the joint.

Heating by oxy fuel flame or electric Arc.

Invariably filler metal added to molten pool.

On cooling, molten puddle solidifies to permanent homogeneous joint.

Types Of Fusion Welding

Shielded Metal Arc Welding- SMAW Gas Tungsten Arc Welding - GTAWGas Metal Arc Welding - MIG / MAGSubmerged Arc Welding – SAWGas welding – Oxy Fuel GasElectron Beam Welding - EBWThermit Welding

An electric Arc struck between electrode and base metal jointBase metal melts under arcElectrode tip melts in drops and transfers to molten pool of BMElectrode with Arc moves along the joint keeping constant arc lengthOn cooling pool solidifies

Arc

Base Metal

Flux Coating

Core Wire

Pool

SMAW Process

Equipment, Accessories & tools

Power Source

Welding Cables, Holder & Earthing Clamp

Head Screen, Hand gloves, Chipping Hammer & Wire Brush

Types Of Power Source

Inverter- DC

Thyrester – DC

Motor Generator / Diesel Generator Set -DC

Rectifier – DC

Transformer - AC

Characteristic Of Power Source

Manual welding Machine weldingDrooping – Cons. A Linear – Cons. V

V V

A A

Vertical Curve

Horizontal Curve

V1

V2

A1 A2

V1V2

A1 A2

Electrode

Consumable

Metallic Wire Coated with Flux

Conducts Current and generates Arc

Wire melts & deposited as filler in joint

Flux Coating On Electrode

Sodium ChloridePotassium ChlorideTitanium DioxideSodium SilicateFerrosilicon Iron Powder Alloying ElementsBinding Material

Function Of Flux In welding

Stabilizes ArcPrevents contamination of weld metalCleans the weld from unwanted impuritiesIncreases fluidity of molten metalGenerates inert gas shielding while metal transfers

Function Of Flux In welding

Forms slag after melting & covers weldAllows deposited metal to cool slowlyIntroduces alloying elements in the weldIncreases deposition efficiencyMinimizes the spatter generationHelps in even & uniform bead finish

CS & LAS Electrode Sizes & Recommended Currents

No

Core Wire in mm

Gage

Current

Time required

for burning in seconds

Average electrodes

consumed in 8 Hrs shift

Dia Length

1 2 300 14 40 – 60 A 50-55 ---

2 2.5 350 12 60 – 85 A 60-65 ---

3 3.15 450 10100 – 130

A80 -85 120 - 140

4 4 450 8130 – 180

A 85-90 110 - 120

5 5 450 6150 – 210

A 90-95 80 - 90

6 6.3 450 4240 – 250

A 95-100 60 -70

ASME Classification Of Electrodes

SFA 5.1 E 7018

E = Electrode 70 = UTS in 1000 psi ( 60/70/80/90/100/ 110) 1 = Position (1= all, 2= 1G, 1F & 2F, 3= 1G

& 1F) 8 = Type of coating (0,1,2,3,5,6,8)

Baking Of Basic Coated Electrodes

Bake the loose electrodes in a baking OvenBaking Temperature 250° C to 300° C Baking Time 2Hrs to 3 HrsReduce the temperature to 100° C to 150° C Hold the electrodes at this temperature till useUnused / left over electrodes to be re-baked

ELECTRODE IDENTIFICATION

Arc welding electrodes are identified using the A.W.S, (American Welding Society) numbering system and are made in sizes from 1/16 to 5/16 .

An example would be a welding rod identified as an 1/8" E6011 electrode.

The electrode is 1/8" in diameter

The "E" stands for arc welding electrode.


• Next will be either a 4 or 5 digit number stamped on the electrode. The first two numbers of a 4 digit number and the first 3 digits of a 5 digit number indicate the minimum tensile strength (in thousands of pounds per square inch) of the weld that the rod will produce, stress relieved. Examples would be as follows:

• E60xx would have a tensile strength of 60,000 psi E110XX would be 110,000 psi

• The next to last digit indicates the position the electrode can be used in.

• EXX1X is for use in all positions • EXX2X is for use in flat and horizontal positions • EXX3X is for flat welding


• The last two digits together, indicate the type of coating on the electrode and the welding current the electrode can be used with. Such as DC straight, (DC -) DC reverse (DC+) or A.C.Type of coatings of the various electrodes are explained elsewhere.

• Examples of the type current each will work with are as below.


• ELECTRODES AND CURRENTS USED• EXX10 DC+ (DC reverse or DCRP) electrode positive. • EXX11 AC or DC- (DC straight or DCSP) electrode

negative. • EXX12 AC or DC- • EXX13 AC, DC- or DC+ • EXX14 AC, DC- or DC+ • EXX15 DC+ • EXX16 AC or DC+ • EXX18 AC, DC- or DC+ • EXX20 AC ,DC- or DC+ • EXX24 AC, DC- or DC+ • EXX27 AC, DC- or DC+ • EXX28 AC or DC+


• CURRENT TYPES• SMAW is performed using either AC or

DCcurrent. Since DC current flows in one direction, DC current can be DC straight, (electrode negative) or DC reversed (electrode positive). With DC reversed,(DC+ OR DCRP) the weld penetration will be deep. DC straight (DC- OR DCSP) the weld will have a faster melt off and deposit rate. The weld will have medium penetration.Ac current changes it's polarity 120 times a second by it's self and can not be changed as can DC current.


ELECTRODE SIZE AND AMPS USEDElectrode Table

ELECTRODEDIAMETER

AMPRANGE

PLATE

1/16" 20 - 40 UP TO 3/16"

3/32" 40 - 125 UP TO 1/4"

1/8 75 - 185 OVER 1/8"

5/32" 105 - 250 OVER 1/4"

3/16" 140 - 305 OVER 3/8"

1/4" 210 - 430 OVER 3/8"

5/16" 275 - 450 OVER 1/2"

The table shown will serve as a basic guide of the amp range that can be used for different size electrodes. These ratings can be different between various electrode manufactures for the same size rod. The type coating on the electrode could effect the amperage range. Check manufacturer’s recommended amperage settings.

Note! The thicker the material to be welded, the higher the current needed and the larger the electrode needed


SOME ELECTRODE TYPES• E6010 : Used for all position welding using DCRP. It produces a deep

penetrating weld and works well on dirty,rusted, or painted metals

• E6011: Same characteristics as of the E6010, but can be used with AC

and DC currents.

• E6013: Used with AC and DC currents. It produces a medium penetrating

weld with a superior weld bead appearance.

• E7018: Known as a low hydrogen electrode and can be used with AC or

DC. The coating on the electrode has a low moisture content that reduces the introduction of hydrogen into the weld. The electrode can produce welds of x-ray quality with medium penetration.

(This electrode must be kept dry. If wet, it must be dried in a rod oven before use.)

Why Baking?

To remove the moisture (H2O) from coating to avoid possible cracking of weld

How Does Moist Electrode Generate Crack Within Weld?

Moist electrodes introduce atomic hydrogen at high temperature in weldOn cooling, atomic hydrogen try to form moleculesThe reaction results in stresses and fine cracks Cracks occur within hardened metal - HAZ Known as “Hydrogen Embrittlement” , “Under Bead Crack”, HIC, Delayed Crack

Important Terminologies used in Critical Welding Operation

PreheatingPost Heating or DehydrogenationIntermediate Stress leavingInter pass TemperaturePost Weld Heat Treatment

What Is Preheating?

Heating the base metal along the weld joint to a predetermined minimum temperature immediately before starting the weld.Heating by Oxy fuel flame or electric resistant coilHeating from opposite side of welding wherever possibleTemperature to be verified by thermo chalks prior to starting the weld

Why Preheating? Preheating eliminates possible cracking of weld and HAZ

Applicable to Hardenable low alloy steels of all thickness Carbon steels of thickness above 25 mm. Restrained welds of all thickness

Preheating temperature vary from 75°C to 200°C depending on hardenability of material, thickness & joint restraint

How does Preheating Eliminate Crack?

Preheating promotes slow cooling of weld and HAZ Slow cooling softens or prevents hardening of weld and HAZSoft material not prone to crack even in restrained condition

What Is Post Heating?

Raising the pre heating temperature of the weld joint to a predetermined temperature range (250° C to 350° C) for a minimum period of time (3 Hrs) before the weld cools down to room temperature.Post heating performed when welding is completed or terminated any time in between.Heating by Oxy fuel flame or electric resistant coilHeating from opposite side of welding wherever possibleTemperature verified by thermo chalks during the period

Why Post Heating? Post heating eliminates possible delayed cracking of weld and HAZApplicable to

Thicker hardenable low alloy steelsRestrained hardenable welds of all

thicknessPost heating temperature and duration depends on hardenability of material, thickness & joint restrain

How does Post Heating Eliminate Crack?

SMAW introduces hydrogen in weld metal

Entrapped hydrogen in weld metal induces delayed cracks unless removed before cooling to room temperature

Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld

What Is Intermediate Stress Relieving?

Heat treating a subassembly in a furnace to a predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thicknessApplicable to

Highly restrained air hardenable material

Why Intermediate Stress Relieving?

Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.

Cracks due to entrapped hydrogen and built in stress

“Intermediate stress relieving” relieves built in stresses and entrapped hydrogen making the joint free from crack prone

What Is Inter- Pass Temperature?

The temperature of a previously layed weld bead immediately before depositing the next bead over itTemperature to be verified by thermo chalk prior to starting next beadApplicable to Stainless Steel Carbon Steel & LAS with minimum impact

Why Inter Pass Temperature?

Control on inter pass temperature avoids over heating, there by Refines the weld metal with fine grains Improves the notch toughness properties Minimize the loss of alloying elements in welds Reduces the distortion

What Is Post Weld Heat Treatment?

Heat treating an assembly on completion of all applicable welding, in an enclosed furnace with controlled heating/cooling rate and soaking at a specific temperature for a specific time. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thicknessApplicable to All type of CS & LAS

Why Post Weld Heat Treatment?

Welded joints retain internal stresses within the structure HAZ of welds remains invariably hardened“Post Weld Heat Treatment” relieves internal stresses and softens HAZ. This reduces the cracking tendency of the equipment in service

Welding Terminologies used in Qualifications

Heat In Put Heat Effected Zone – HAZ Dilution Overlap In Weld Overlay Tempering Bead

What Is Heat In Put In Welding?

The extent of heat energy generated in Joules per unit length while making each weld bead. “Heat In Put” is the Function of Welding Current, Arc Voltage, And the Welding Speed It is measured in Joules -

Heat In Put In Joules / mm = (A x V x 60) ÷ Travel Speed in mm / min

Why Control On Heat in Put?

“Heat In put” controls the grain size of weld metal. Lower the Heat in put finer the grain size. Finer the Grain size Better the impact

properties

“Heat In Put” Also controls Dilution, HAZ & Geometry of Bead size

What Is Heat Affected Zone (HAZ)

A small volume of BM adjacent to weld fusion line, which is totally changed in its structure due to intense heat of each weld bead is known HAZ

Weld Zone

HAZDiluted BM

Diluted BM

Weld Zone

Fusion Line

What Is Significant Of HAZ

It is a part and parcel of weld joint It is inevitable It has properties different from BM &

Weld Metal

Weld Zone

HAZDiluted BM

Diluted BM

Weld Zone

Fusion Line

What Is Dilution In Weld

In all Fusion welding, a small portion of BM very close to the welding heat gets melted

and added to weld zone / fusion zone. Dilution is the ratio of molten base metal volume (Area) to the volume ( Area) of total fusion zone

HAZ

Diluted BM

Weld / Fusion Zone

Fusion Line

% Dilution = (Area of Diluted BM ÷ Total Fused Area) × 100

What Is Significant Of Dilution

Weld metal chemistry changes depending on the extent of dilution Chemical elements influence Physical

properties of the joint. Weld chemistry influences corrosion resistance of weld overlays

Weld Zone

HAZDiluted BM

Diluted BM

Weld Zone

Fusion Line

What Is Overlap In Weld Overlay?

The extent of covering or over lapping of previous weld bead by the adjacent bead.

40 to 50 % Over Lap

10 to 15 % Over Lap

Less Dilution More DilutionMore Thickness Less

Thickness

What Is Significant Of Overlap In Weld Overlay?

Overlap of 40 to 50% results in Less Dilution & more weld overlay Thickness per layerLess dilution results weld metal chemistry more towards filler metal chemistry

40 to 50 % Over Lap 10 to 15 % Over Lap

Less Dilution More DilutionMore Thickness Less

Thickness

What Is Temper Bead Technique?

In a multi pass groove & Fillet Welds, each bead & its HAZ are getting tempered (heat treated) by the welding heat of the next bead. Thus all beads & their HAZ, except those in last layer, are tempered. Temper beads are the specially & carefully welded temporary beads on the top of final weld reinforcement with out allowing to generate any HAZ within the BM. Temper beads are to be ground flush with the required reinforcement.

Temper Bead

Temper Bead T1 & T2 Not To Generate HAZ In BMTemper Beads To Be Ground Flush

T2T1

21

3 34 4

55

T1 & T2 To be ground Flush

HAZ

Rqd. Reinforcement

Good Engineering Practices In SMAWDo Welding with properly baked electrodes Basic coated CS electrodes to be baked to 250°C to 300°C for two hours Baked electrodes to be directly used on job or to be retained in a hold over oven at 100°C to 150°C until useUnused balance electrodes shall be returned to baking oven

Do not weld with damp ElectrodesDo not try to heat electrodes by touching the job (Short circuiting)Do not use electrodes with damaged coating Do not use electrodes with cracked coatingDo not bend the electrodes after holding it in the holder

Good Engineering Practices In SMAW

Do not weld on groove / surface with mill scale or rustingPrior to welding, clean the weld groove with power wire wheelDo not weld with unidentified electrodesDo not leave balance electrodes unattended on shop


All connections with earthing and welding cables shall be tight fittedEarthing clamp shall always be tightly connected to the jobBurn the full length of electrode till 37 mm stub length


Earthing cable shall directly connect to the job with an earthing clamp.Tacks for set up shall be minimum 5 times the electrode diameterWeaving shall be limited to three times the electrode diameter.Only trained & qualified welders shall be employed for welding


Do not direct fan or blower to welding arcRemove paint if any from the area near weldingWhile welding in open, area shall be covered to protect from rain water & breezeWeld edge preparation shall be free from serrations


Use poison plates between the job material & structural supports.Do not damage parent metal while removing temporary supports.Locations where from temporary supports are removed shall be touched up by welding / grinding and PT checked.


Remove visible defects from welds before placing the subsequent beadsDo not weld over a visible crackElectrodes kept out side more than 2 Hrs shall be returned to baking ovenMaximum 15 electrodes at a time shall be taken from oven for welding


When preheat is required, heat from opposite side of welding.Use temperature indicating crayons for checking temperatureDo not Weld more than specified weld size- Fillet / Reinforcement.


Safety Precautions in

Shielded Metal Arc Welding

Safety Precautions In SMAW

Welders shall use safety devises – Hand gloves, Head screen with right glass & Safety shoesWelders shall use full sleeve boiler suit Use welding glass-DIN 11/12 up to 250 Amps and 13 above 250 AmpsDo not look at the arc with naked eyes

Do not throw Stubs on ground. They shall be placed in stub collector.Do not keep electrode in the holder when work is not in progressDo not touch the electrode held on holder and the the job when the power source is onKeep welding cables duly wound near power source when no welding is done


Do not breath welding fumesWhen working in confined area, ensure adequate ventilation / exhaustGas cutting torch / preheating burner shall not be taken inside confined area unless the flame is lit When not in use, switch off the the power source from electric supply


Acetone / inflammable liquids (Chemical for dye penetrant test) shall not be brought near weldingGas cutting unit / fuel gas cylinders shall be away from welding area Wet safety Shoes or wet hand gloves shall not be worn while welding

……………………………………………………


arc welding

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