Abhimanyu pradhan B.TECH MECHANICAL (3rd YEAR)

1222240001

GAS WELDING

Gas welding is a fusion welding process.

Flame produced by the combustion of gases is employed to melt the metal

The molten metal is allowed to flow together thus forming a solid continuous joint upon cooling.

By burning pure oxygen in combination with other gases, in special torches, a flame up to 3300 degree can be attained.

During the welding, heat from the flame is concentrated on the joint edges until the metal melts and starts to flow. When the molten metal from both sides melts it starts to fuse, when the metal cools down the two parts become Permanently joined

Additional Filler Metal is fed in by hand into the weld pool, at regular intervals where it becomes molten and joins with the parent metal.

The Oxy-acetylene welding Flame

Oxidizing Excess oxygen (1.5:1) (Brasses, Bronzes, copper)

Neutral Equal acetylene & oxygen (low carbon steel, mild steels).maximum temp. is

3100 degree

Reducing or Carburizing Excess acetylene (0.9:1) (Alloy steels and aluminium alloys) . 2900 deg

Inner Cone

Secondary Combustion envelope

Acetylene feather

Max. Temp. Zone

Carburising Neutral Oxidising

The Oxy-acetylene welding Flame

Equipment used in Oxy-Acetylene welding

The oxygen and acetylene hose pipes

Gases used

Gas pressure Regulators

Flashback arrestor

Welding torch/Welding nozzle

Filler rods and fluxes

Gases used

Oxygen extracted from air and compressed into cylinders at high pressure. Cylinder is black. Oil should never be brought into contact and should not be used on fittings

Acetylene (C2H2) is a fuel gas. Cannot be compressed directly as explodes at high pressures. Cylinders are packed with porous material which is filled with acetone. Acetone absorbs acetylene. Cylinder colour coded maroon

Gas Pressure Regulators

One gauge indicates the pressure of the cylinder and the other indicates the pressure in the supply pipe to the torch.

Advantages

The equipment is inexpensive, simple and is easily portable.

Useful for welding light metals such as automobile  bodies and repair works

A large variety of material can be welded.4.Welds can be produced at reasonable cost.

Compared to electric arc welding this provides greater flexibility with respect to heat impact and cooling rates.

Disadvantages

Equipment must always be handled carefully as in certain circumstances acetylene is explosive as oxygen when used in an oily atmosphere (such as an old dirty garage floor pit).

 A high temperature flame from a hand held torch isdangerous when handled carelessly.

It is much slower than electric arc welding and does not concentrate the heat close to the weld. Thus, the heat treated area is larger, which causes more distortion

Highly skilled operators are required to produce a good weld.

If electric arc welding is available gas welding is seldom used for work over 3.2mm thick.

The process is not satisfactory for heavy sections

Defects

Cracking

Incorrect edge preparation

Craters

Under cutting

Porosity

Over welding

APPLICATIONS

In aircraft building industry

Cylinders, boilers & vessel manufacturing

Structural constructions like bridges, buildings, ships etc.

Manufacturing of furnaces, tanks, cranes, hoists, railway equipment's, steel furniture etc.

Building of automobile bodies and other parts.

WELDING-APPLICATIONS1

. In aircraft building industry.2.C

ylinders, boilers & vessel manufacturing.3. Structural constructions like bridges, buildings, shipsetc.4. Manufacture of various machineries like mechanical,food processing, agricultural, earth moving & textilemachineries.5.B

uilding of automobile bodies and other parts.6. Manufacturing of furnaces, tanks, cranes, hoists,railway equipments, steel furniture etc.39         

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