1 Experiment No.
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1.1 Objective
To investigate the effect of varying gas pressure on gas welded specimen.
1.2 Theory
1.2.1 Gas Welding
Gas welding is a fusion welding process in which the heat for welding is obtained by the combustion of
oxygen and fuel gas. The fuel gas may be acetylene, hydrogen, propane or butane. An intense gas flame
is thus produced which melts the edges of the parts to be welded. The molten metal is allowed to flow to
Solidify together and continuous joint is obtained.
Figure 1 Schematic Diagram of Gas Welding Process
1.2.2 Applications of Gas Welding
The applications of gas welding include welding and cutting metals. Below is the used gas welding:
Joining of ferrous and nonferrous metals
oxyacetylene welding can be used for joining carbon steels, alloy steels, cast iron, aluminum, and
its alloys, copper and its alloys, nickel, magnesium, etc.
Widely used in automotive and aircraft industries.
oxyacetylene welding applications are used in sheet metal fabricating plants. finally,
Can join materials that require a relatively slow rate of heating and cooling.
1.2.3 Types of Gas Welding
Following are the 5 different types of gas welding:
1) Oxy-acetylene gas welding
2) Oxy-gasoline gas welding
3) MAPP gas welding
4) Butane or propane welding
5) Hydrogen gas welding
In this experiment, we used Oxy-acetylene welding.
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1.2.4 Oxy-Acetylene Welding
Oxy-acetylene welding commonly referred to as gas welding, is a process that relies on the 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 oC. In Oxy-acetylene
welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a
temperature that produces a shared pool of molten metal. The molten pool is generally supplied with
additional metal called a filler. Filler material selection depends upon the metals to be welded.
1.2.4.1 Working Principle of Oxy-acetylene Welding
In Oxy-acetylene welding, a welding torch is used to weld metals. Welding metal results when
two pieces are heated to a temperature that produces a shared pool of molten metal. The molten
pool is generally supplied with additional metal called a filler. Filler material selection depends
upon the metals to be welded.
The fuel gas and oxygen gas are stored in pressurized steel cylinders. Regulators in the cylinder
reduce gas pressure.
Gas flows through flexible hoses, with the welder controlling the flow via the torch. The filler
rod is then melted with the base material. However, melting two pieces of metals is also possible
without the need for a filler rod.
1.2.5 Types of Flames used in Oxy-acetylene Welding
The flame has to be adjusted to appear a certain way before you can proceed with the Oxy-Acetylene
weld. Different types of flames are used to weld different types of metals.
1.2.5.1 Carburizing Flame
Carburizing flame contains an excess of acetylene gas. This type of flame is suitable for applications
where a low-heat flame is required. It is used for welding nickel, Monel metal, high-carbon steel, and a
number of non-ferrous metals. This flame is not used to weld regular steel.
1.2.5.2 Neutral Flame
Neutral flame contains equal proportions of oxygen and acetylene gases. This type of flame is used in
most welding operations since the chemical effect of this flame on heated metal is the least.
1.2.5.3 Oxidizing Flame
As you can tell by the name, an oxidizing flame has a high content of oxygen (the oxygen and acetylene
ratio being 1.5:1). This type of flame is used when welding copper and alloys of copper, such as bronze
and brass. It cannot be used to weld steel as it will oxidize it.
1.2.6 Oxy-acetylene Cutting Torch
The oxyacetylene torch is a vital component of oxyacetylene equipment. Broadly speaking, it receives
gas supply from the two gas cylinders (one for acetylene and other for oxygen), mixes them, and
delivers them to the point of flame. Robust and precise construction of the oxyacetylene welding torch is
important for obtaining a quality weld, and for safety of personnel and equipment.
1.2.6.1 Components of Cutting Torch
The cutting torch is composed of following components;
The torch is composed of a handle which the welders grips while welding.
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Two gas inlet nipples are available at the rear end, which are used to connect the gas hoses
coming from the gas cylinders.
A mixing chamber follows the handle where the acetylene and oxygen get mixed together. Two
tubes which deliver gases from the hoses to the mixing chamber.
The tip is where the flame originates.
In addition to this, two needle valves are mounted at the rear end to regulate the flow of gases to
the torch tip. These valves are used to control the volume of gases in desired proportions.
By varying the opening of these valves, the required type of flame (that is, a reducing flame,
oxidizing flame, or a neutral flame) can be achieved.
1.2.7 Welding Rods, its Types and Uses
Comes in two varieties: Bare and Flux-cored.
Use bare when brazing thin sheets, extruded-shapes and especially corner-
Aluminum
joints.
Welding Rods
Flux-cored includes non-corrosive, non-hygroscopic flux inside a tubular rod
so that you don’t need separate flux.
Used primarily for TIG and oxyacetylene welding of copper, copper-silicon
Bronze Alloy
and copper-zinc based metals to themselves, and to steel.
Welding Rods
Also useful for surfacing areas subjected to corrosion.
Multiple types available.
General Purpose for low-carbon steels, particularly when you need ductility
and machinability.
Copper Alloy
High Strength for gas brazing low carbon and low alloy steels where you need
Welding Rods
high-tensile strength.
And Low Alloy for high-speed fusion welding of pressure vessels, tanks and
piping.
Low fuming characteristics and good mechanical properties meet
requirements for gas-brazing steel, copper alloys, cast iron, nickel alloys and
Copper Alloy
stainless steel.
Welding Rods
Preheating recommended for some applications. Bronze brazing flux
required.
Hard Facing Often used to restore dimensions of worn surfaces.
Welding Rods When applied to new parts, provides protection against wear, abrasion, impact
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and corrosion.
1.2.8 Gas Welding Machine
1.2.8.1 Oxygen Cylinder
Oxygen cylinder is usually painted in black color. In this cylinder, oxygen is stored under a pressure of
1550 N/m2. The common cylinder is 1.8 m3, 3.5 m3, 7 m3, etc.,
1.2.8.2 Acetylene Cylinder
Acetylene cylinder is usually painted in maroon color. In this cylinder, acetylene is stored under a
pressure of 175 N/m2. The common cylinder is 1.6 m3, 2.8 m3, 8.4 m3, etc.,
1.2.8.3 Regulator
The regulator is used to control pressure from the tanks by reducing pressure and regulating flow rate.
1.2.8.4 Gas hoses
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.
1.2.8.5 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 should be installed to prevent flame or Oxygen-fuel mixture
being pushed back into either cylinder and damaging the equipment or making a cylinder explodes.
1.2.8.6 Check valve
A check valve lets gas flow in one direction only. A check valve is usually a chamber containing a ball
that is pressed against one end by a spring: gas flow one way pushes the ball out of the way, and no flow
or flow the other way lets the spring push the ball into the inlet, blocking it.
1.2.8.7 Torches
The torch is the part that the welder holds and manipulates to make the weld. It has a connection and
valve for the fuel gas and a connection and valve for the oxygen, a handle for the welder to grasp, a
mixing chamber (set at an angle) where the fuel gas and oxygen mix, with a tip where the flame forms.
The top torch is a welding torch and the bottom is a cutting torch
1.2.8.8 Welding torch
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.
1.2.8.9 Cutting torch
A cutting torch head is used to cut metal. It is similar to a welding torch, but can be identified by having
three pipes that go to a 90-degree nozzle and by the oxygen-blast trigger. Only iron and steel can be cut
using this method.
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1.2.8.10 Other Accessories
a) Filler rod / Welding rod: Filler rod is a metal which is used in gas welding to supply additional metal
to make the joint.
b) Flux is used in oxy-acetylene gas welding to prevent oxidation and also to remove impurities. The
flux may be either in powder or liquid form.
1.2.8.11 Safety devices
a) Goggles
b) Leather goggles
c) Apron
