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 Gasweldingoperation
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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.
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.