Study and operation of an oxy-

acetylene gas welding machine Gas welding overview Oxyacetylene welding is a gas welding process. A coalescence or bond is produced by heating with a gas flame or flames obtained from the combustion of acetylene with oxygen, with or without the application of pressure, and with or without the use of filler metal.

2009

Sobuj SUST

12/14/2009

Gas welding operation

Name of the experiment: Study and operation of an oxy-

acetylene gas welding machine.

Objectives:

1. To be familiar with the oxy-acetylene welding machine.

2. To learn about the oxy-acetylene welding procedure.

3. To perform the oxy-acetylene welding operation.

Introduction: Oxyacetylene welding is a gas welding process. A coalescence or bond is

produced by heating with a gas flame or flames obtained from the combustion of acetylene

with oxygen, with or without the application of pressure, and with or without the use of filler

metal. A welding torch is used to mix the gases in the proper proportions and to direct the

flame against the parts to be welded. The molten edges of the parts then literally flow

together and, after cooling, form one solid piece. Usually, it is necessary to add extra material

to the joint. The correct material in rod form is dipped in and fuses with the puddle of molten

metal from the parent metal parts.

Acetylene is widely used as the combustible gas because of its high flame temperature when

mixed with oxygen. The temperature, which ranges from approximately 5,700° to 6,300°F,

is so far above the melting point of all commercial metals that it provides a means for the

rapid, localized melting essential in welding.

Gas welding operation

Types of gas welding: Gas welding involves the use of a gas-fed flame torch to

heat the metal work piece and the filler material to create a weld. The gas is generally

a mixture of a fuel gas and oxygen to create a clean, hot flame. Many different gases

can be used as fuel for gas welding, and electricity is not needed to power the welding

system, resulting in a flexible and portable fabrication method.

There are many types of gas welding some of them are:

1. Oxy-Acetylene Welding: Oxy-acetylene welding uses a mixture of acetylene gas and

oxygen gas to feed the welding torch. Oxy-acetylene welding is the most commonly used

gas welding technique. This gas mixture also provides the highest flame temperature of

available fuel gases.

2. Oxy-Gasoline Welding: Pressurized gasoline is used as a welding fuel where fabrication

costs are an issue, particularly in locations where acetylene canisters are not available.

3. MAPP Gas Welding: Methylacetylene-propadiene-petroleum (MAPP) is a gas mixture

that is much more inert than other gas mixtures, making it safer for hobbyists and

recreational welders to use and store. MAPP can also be used at very high pressures,

allowing it to be used in high-volume cutting operations.

4. Butane/Propane Welding: Butane and propane are similar gases that can be used alone

as fuel gases or mixed together. Butane and propane have a lower flame temperature than

acetylene, but are less expensive and easier to transport. Propane torches are more

frequently used for soldering, bending and heating.

5. Hydrogen Welding: Hydrogen can be used at higher pressures than other fuel gases,

making it especially useful for underwater welding processes. Some hydrogen welding

equipment works off electrolysis by splitting water into hydrogen and oxygen to be used

in the welding process. This type of electrolysis is often used for small torches, such as

those used in jewelry making processes.

Among those welding we’ve performed the 1st type of welding means oxy-acetylene

welding operation now I’ll discuss about the oxy-acetylene welding.

Oxy-acetylene welding: Oxyacetylene welding, commonly referred to as gas

welding, is a process which relies on combustion of oxygen and acetylene. When

mixed together in correct proportions within a hand-held torch or blowpipe, a

relatively hot flame is produced with a temperature of about 3,200 deg.C

Oxy-acetylene welding Advantages:

1. It's easy to learn.

2. Filler metal can be properly controlled and heat properly adjusted giving rise to a

satisfactory weld.

3. Welding power of most common metals.

4. Using ability in many jobs like repair shops.

5. The equipment is cheaper than most other types of welding rigs (e.g. TIG welding)

6. The equipment is more portable than most other types of welding rigs (e.g. TIG

welding)

7. OA equipment can also be used to "flame-cut" large pieces of material.

8. One advantage of this welding process is the control a welder can exercise over the

rate of heat input, the temperature of the weld zone, and the oxidizing or reducing

potential of the welding atmosphere.

9. Weld bead size and shape and weld puddle viscosity are also controlled in the

welding process because the filler metal is added independently of the welding heat

source.

10. OA, Oxy-Acetylene welding is ideally suited to the welding of thin sheet, tubes, and

small diameter pipe. It is also used for repair welding. Thick section welds, except for

repair work, are not economical.

11. Oxy-fuel gas welding can be used for all the types of joints and in all positions.

Disadvantages of Oxy-Acetylene (OA) Welding: 1. OA weld lines are much rougher in appearance than other kinds of welds, and require

more finishing if neatness is required.

2. OA welds have large heat affected zones (areas around the weld line that have had

their mechanical properties adversely affected by the welding process).

3. Since this type of welding is done in open atmosphere with a little protection thus the

welded zone is contaminated by the various types of impurities like oxygen, carbon,

nitrogen etc. thus poor quality welding is obtained.

4. Required time for this type of welding is very high compare to other welding

operation.

Applications:

1. Air-fuel gas is used for welding lead up to approximately 1/4 in. (6.4 mm) in

thickness. The greatest field of application in the plumbing and electrical industry.

The process is used extensively for soldering copper tubing.

2. Used in repair workshop for joining various metals.

3. It is normally used to weld thin sheets of steels and alloys with low melting

temperature.

Oxy-acetylene welding setup:

Figure: A complete oxy-acetylene welding setup

Equipments used in oxy-acetylene welding: The apparatus

used in gas welding consists basically of

1. An oxygen source.

2. A fuel gas source (usually cylinders).

3. Two pressure regulators.

4. Non-return valve.

5. Two flexible hoses (one of each for each cylinder).

6. A torch and,

7. Oxy-acetylene welding rods.

1. An oxygen source: An oxygen source supplies the necessary oxygen during

welding operation.

2. A fuel gas source: A fuel gas source supplies the necessary fuel

(i.e. acetylene) during welding operation. Commercial fuel gases have one common property: they all require

oxygen to support combustion. To be suitable for welding operations, a

fuel gas, when burned with oxygen, must have the following:

1. High flame temperature.

2. High rate of flame propagation.

3. Adequate heat content.

4. Minimum chemical reaction of the flame with base and filler

metals.

3. Regulator: The regulator is used to control pressure from the tanks to the required

pressure in the hose. The flow rate is then adjusted by the operator using needle

valves on the torch. Accurate flow control with a needle valve relies on a constant

inlet pressure to it.

Figure: Oxygen source

Figure: acetylene source

Regulator

4. Gas hoses: The hoses used are specifically designed for welding and cutting. The

hose is usually a double-hose design, meaning that there are two hoses joined

together. The oxygen hose is green and the fuel hose is red. The type of gas the hose

will be carrying is important because the connections will have different threads for

different types of gas. Fuel gases (red) will use left-hand threads and a groove cut into

the nut, while the oxygen (green) will use right-hand threads. This is a safety

precaution to prevent hoses from being hooked up the wrong way.

5. Non-return valve: Between the regulator and hose, and ideally between hose

and torch on both oxygen and fuel lines, a flashback arrestor and/or non-return valve

(check valve) should be installed to prevent flame or oxygen-fuel mixture being

pushed back into either cylinder and damaging the equipment or making a cylinder

explode.

6. Torches: A welding torch head is used to weld metals. It can be identified by

having only one or two pipes running to the nozzle and no oxygen-blast trigger and

two valve knobs at the bottom of the handle letting the operator adjust the oxygen

flow and fuel flow.

7. Oxy-acetylene welding rods: The welding rod, which is melted into

the welded joint, plays an important part in the quality of the finished weld. Good

welding rods are designed to permit free flowing metal which will unite readily with

the base metal to produce sound, clean welds of the correct composition. Welding

rods are made for various types of carbon steel, aluminum, bronze, stainless steel, and

other metals for hard surfacing.

Figure: Gas hoses

Figure: Welding torch

Figure: Welding rod or filler metal

Significant terms of Oxy-acetylene welding:

Welding Preparation:

1. Assemble all of the materials needed to make the weld. This includes parts, OA

equipment, fixturing, tools, safety mask, gloves, and filler rod.

2. Clean the parts to be welded to remove any oil, rust, or other contaminants. Use a

wire brush if needed to remove any rust.

3. Assemble and fixture the parts in place - the parts need to be stable for a good weld

line. Ceramic bricks, vise grips, pliers, and clamps are available in a file cabinet in the

weld room for fixturing.

4. Attach the nozzle to the gas feed line by hand. Don't over-torque - the nozzle and hose

fitting are both made of brass which does not stand up well to abuse. A snug, finger

tight fit is sufficient.

5. Check the pressure levels in the oxygen and acetylene tanks. There should be at least

50 psi in the acetylene tank. The oxygen tank can be used until it is completely empty.

Lighting the flame:

12. Open the main valve on the acetylene tank ~1/2 turn. This charges the pressure

regulator at the top of the tank.

13. Open the pressure regulator valve on the acetylene tank (turn clockwise to open) and

adjust the pressure in the acetylene line to 5 psi.

14. Open the acetylene pin valve on the handle of the welding tool, letting acetylene

escape. Tweak the pressure regulator valve until the regulator pressure is constant at 5

psi. Close the acetylene pin valve.

15. Open the main valve on the oxygen tank. Turn the valve until it is fully open (until it

stops turning).

16. Open the pressure regulator valve on the oxygen tank (turn clockwise to open) and

adjust the pressure in the oxygen line to 10 psi.

17. Open the oxygen pin valve on the handle of the welding tool, letting oxygen escape.

Tweak the pressure regulator valve until the regulator pressure is constant at 10 psi.

Close the oxygen pin valve.

18. Slightly open the acetylene valve (~1/8), until we can just barely hear acetylene

escaping.

Types of flame: The flame can be adjusted by varying the composition of the

ratio of oxygen and acetylene. However there are three types of flame.

1. Neutral flame.

2. Carburizing or reducing flame.

3. Oxidizing flame.

1. Neutral flame: The neutral flame has a one-to-one ratio of acetylene and

oxygen. It obtains additional oxygen from the air and provides complete combustion.

It is generally preferred for welding. The neutral flame has a clear, well-defined, or

luminous cone indicating that combustion is complete.

2. Carburizing or reducing flame: The carburizing flame has excess

acetylene; the inner cone has a feathery edge extending beyond it. This white feather

is called the acetylene feather. If the acetylene feather is twice as long as the inner

cone it is known as a 2X flame, which is a way of expressing the amount of excess

acetylene. The carburizing flame may add carbon to the weld metal.

3. Oxidizing flame: The oxidizing flame, which has an excess of oxygen, has a

shorter envelope and a small pointed white cone. The reduction in length of the inner

core is a measure of excess oxygen. This flame tends to oxidize the weld metal and is

used only for welding specific metals.

A table is given bellow to show which types of flame is used in different metal welding operation

Number Metal Types of flame used 1. Mild steel Neutral flame

2. Alloy steel Neutral

3. Lead Neutral

4. Grey cast iron Neutral, slightly oxidizing

5. Copper, bronze Neutral, slightly oxidizing

6. Aluminium Slightly carburizing

7. Nickel alloy Slightly carburizing

8. Brass Slightly oxidizing

9. High carbon steel reducing

Flame adjustment:

1. The oxyfuel gas welding torch mixes

the combustible and combustion-

supporting gases. It provides the means

for applying the flame at the desired

location. A range of tip sizes is

provided for obtaining the required

volume or size of welding flame which

may vary from a short, small diameter

needle flame to a flare 3/16 in. (4.8

mm) or more in diameter and 2 in. (51

mm) or more in length.

2. The inner cone or vivid blue flare of the burning mixture of gases issuing from the tip is

called the working flare. The closer the end of the inner cone is to the surface of the metal

being heated or welded, the more effective is the heat transfer from flame to metal. The flame

can be made soft or harsh by varying the gas flow. Too low a gas flow for a given tip size

will result in a soft, ineffective flame sensitive to backfiring. Too high a gas flow will result

in a harsh, high velocity flame that is hard to handle and will blow the molten metal from the

puddle.

3. The chemical action of the flame on a molten pool of metal can be altered by changing

the ratio of the volume of oxygen to acetylene issuing from the tip. Most oxyacetylene

welding is done with a neutral flame having approximately a 1:1 gas ratio. An oxidizing

action can be obtained by increasing the oxygen flow, and a reducing action will result

from increasing the acetylene flow. Both adjustments are valuable aids in welding.

Use of flux:

Flux is employed in the welding of such metal as cast iron. Some alloy steel and non-ferrous

metals to dissolve such as:

1. Remove impurities.

2. Control surface tension.

3. Give protection from atmosphere.

It is usually in the format paste in which the rod is dipped.

Figure: Flux

Method of welding using oxy-acetylene welding process.

1. Back hand welding: In this method, the torch precedes the welding rod, as shown

bellow.

2. Forehand welding: In this method, the welding rod precedes the torch. The torch is

held at approximately a 45 degree angle from the vertical in the direction of welding,

as shown bellow.

3. Fillet welding: The fillet weld is the most popular of all types of welds because there

is normally no preparation required.

Figure: Backhand welding

Figure: Forehand welding.

4. Horizontal position welding: In horizontal welding, the weld axis is approximately

horizontal, but the weld type dictates the complete definition. For a fillet weld,

welding is performed on the upper side of an approximately horizontal surface and

against an approximately vertical surface. For a groove weld, the face of the weld lies

in an approximately vertical plane.

5. Flat position welding: This type of welding is performed from the upper side of the

joint. The face of the weld is approximately horizontal.

Figure: Bed welding with a welding rod. Figure: Bed welding without a welding rod.

6. Vertical position welding: In vertical position welding, the axis of the weld is

approximately vertical.

7. Over head position welding: Overhead welding is performed from the underside of a

joint.

Among them we’ve performed butt weld in flat position of steel.

General Principles in Welding Steel:

1. A well balanced neutral flame is used for welding most steels. To be sure that the flame is

not oxidizing, it is sometimes used with a slight acetylene feather. A very slight excess of

acetylene may be used for welding alloys with a high carbon, chromium, or nickel content.

However, increased welding speeds are possible by using a slightly reducing flame. Avoid

excessive gas pressure because it gives a harsh flame. This often results in cold shuts or laps,

and makes molten metal control difficult.

2. The tip size and volume of flame used should be sufficient to reduce the metal to a fully

molten state and to produce complete joint penetration. Care should be taken to avoid the

formation of molten metal drip heads from the bottom of the joint. The flame should bring

the joint edges to the fusion point ahead of the puddle as the weld progresses.

3. The pool of the molten metal should progress evenly down the seam as the weld is being

made.

4. The inner cone tip of the flame should not be permitted to come in contact with the

welding rod, molten puddle, or base metal. The flame should be manipulated so that the

molten metal is protected from the atmosphere by the envelope or outer flame.

5. The end of the welding rod should be melted by placing it in the puddle under the protection

of the enveloping flame. The rod should not be melted above the puddle and allowed to drip into

it.

Performing welding operation:

We’ve performed butt weld in flat position

1. At first apply the flame to the parts to begin heating. Use the region of the flame near the

tip of the bluish inner region.

2. The metal will begin to glow. Continue heating both parts being welded until a small pool

of welded metal appears near the edge of each of the parts. We must get molten pools on

BOTH parts simultaneously to create the weld. They may require adding more heat to one

side than the other, and takes some practice.

3. After the molten pools have formed on both sides of the weld, we’ve used the flame to

gently stir the two pools together to form the weld. 4. After the two pools have joined, slowly move the flame along the weld line, lengthening

the pool using metal from both parts. A gentle, circular, swirling motion will help mix the

molten metal from both sides as the puddle is lengthened.

5. Continue this process until the entire weld line is complete. 6. Once we’ve done, turn off the flame. Close the oxygen pin valve first, and then the

acetylene valve.

Figure: Position of filler rod, flux heating area and welding

torch.

Metal pool Flux Recast metal

Flame

Welding torch

Oxy fuel mixture

Filler metal

Shutting Down and Cleaning Up:

When we’ve completely finished welding and are ready to quit for the day, we need to clean

up.

1. With the flame extinguished and the pin valves closed, close the main valve on the

oxygen tank. It should be firmly seated at the bottom.

2. Open the oxygen pin valve to bleed off all of the oxygen in the regulator and feed line.

Close the pin valve once the feed line pressure has gone to zero.

3. Fully back out the oxygen regulator valve so there is no pressure in the line. DO NOT

close the valve, as this will pressurize the line once the tank is open again. In the case of

the acetylene, if it is pressurized over 15psi. It may explode!

4. Repeat steps 1 through 3 for the acetylene line.

5. Return all of the tools to their proper storage places and coil the feed lines around the

handle on the gas cylinder cart. Note: Do not remove the nozzle from the feed line. The

feed lines should always have a nozzle attached to prevent accidental damage to the

threads used to attach the nozzle.

Operation data:

1. Types of gases used, Oxygen & Acetylene.

2. Types of weld joint, Butt.

3. Types of filler metal used, Brass.

4. Types of base metal used, Mild steel.

5. Types of flame used during operation, Carburizing.

6. Thickness of the workpiece, 2.5 mm.

7. Length of the workpiece, 4.5 mm.

8. Power density of the welding operation, watt/mm2.

9. Pressure of the oxygen cylinder,

10. Pressure of the acetylene cylinder,

11. Welding pressure of the acetylene cylinder,

12. Welding pressure of the oxygen cylinder,

Safety:

Oxyacetylene welding/cutting is not difficult, but there are a good number of subtle safety

points that should be learned such as:

More than 1/7 the capacity of the cylinder should not be used per hour. This causes

the acetone inside the acetylene cylinder to come out of the cylinder and contaminate

the hose and possibly the torch.

Acetylene is dangerous above 15 psi pressure. It is unstable and explosively

decomposes.

Proper ventilation when welding will help to avoid large chemical exposure

Correct and safe oxygas welding station

Discussion: In our 1st year 1

st semester we’ve learn many thing about gas

welding theoretically but now we’ve gotten the practical concept of gas welding

operation. Performing welding operation was a very interesting experience for all of

us. But during our operation we’ve faced many problems some of them are listed

bellow,

1. We don’t have sufficient oxygen and acetylene during our operation.

2. We’ve used carburizing flame insist of neutral flame because of the shortage

of oxygen gas.

3. We’ve used brass as the filler metal where we should use the same types of

filler metal used in base metal.

4. We don’t have any protective measurements to protect us from welding

fumes.

5. We actually didn’t join the metal workpiece but just take a concept of joining

process.

We hope our respective teacher will give priority and will take the necessary steps to resolve

those shortages. Overall the flowing operation gives us the practical concept of gas welding

operation which is very essential for our future job field.

Conclusion: Oxy-Acetylene (OA) welding is one of the types of welding

supported by the PRL. It is extremely versatile, and with enough skill and practice we

can use this type of welding for virtually any metal. In fact, the oxy-acetylene flame

burns at 6000 °F, and is the only gas flame that is hot enough to melt all commercial

metals. Oxy-acetylene welding is simple in concept - two pieces of metal are brought

together, and the touching edges are melted by the flame with or without the addition

of filler rod. The equipment used in OA is low in cost, usually portable, and versatile

enough to be used for a variety of related operations, such as bending and

straightening, preheating, postheating, and surface, braze welding, and torch brazing.

Oxy-acetylene welding carries’ a significant importance. That’s why the study of

Oxy-acetylene welding process is very useful for us.

Edited by Sobuj

SUST

Dept of Industrial & Production

Engineering

Registration No. 2008334053

k.sobuz@gmail.com