Equipment for Oxyacetylene Welding | Types | Gas Welding | Metallurgy

The following points highlight the equipments used for oxyacetylene welding. The equipments are: 1. Welding Torch 2. Pressure Regulator 3. Hose and Fittings 4. Cylinders 5. Goggles 6. Spark Lighter 7. Apron 8. Gloves 9. Welding Rods 10. Fluxes.

Equipment # 1. Welding Torch:

It is a tool for mixing the two gases in the desired volumes and burning the mixture at the end of a tip. It has a handle to carry it and two inlet connections for gases at end. Each inlet has a valve to control the volume of oxygen or other gas. The two gases from two paths mix up in a mixer and flame is produced by igniting the mixture at the tip of the torch.

The torches are available in two types:

(1) Positive or equal pressure type (Medium pressure torch).

(2) Injector type (Low pressure torch).

In the first type, gases are delivered at pressures generally above 0.7 kg/cm². The acetylene pressure is about 0.7 to 1 kg/cm² and that of oxygen varies upto 1.7 kg/cm² depending upon tip size. In the second type, acetylene pressure is less than 0.7 kg/cm² and oxygen is at 0.7 to 2.7 kg/cm² depending upon tip size. In both the types, oxygen tends to draw in acetylene and mix with it due to high pressure.

In medium pressure blowpipe, both oxygen and acetylene enter a mixing device in approximately equal volumes. Low pressure blowpipe contains an injector through which high pressure oxygen passes sucking acetylene with it. Low pressure torch is used where acetylene is produced from a generating plant.

The gas mixer in the torch must be able to:

(i) Mix gases thoroughly before they leave out of noz­zle,

(ii) Arrest flash backs that might occur through im­proper operation,

(iii) Stop any flame from travelling farther back than the mixer,

(iv) Permit a range of tip sizes to be operated from one size of mixer.

The tip of the torch is generally made of copper alloys having high thermal conductivity and ability to withstand high temperature. All blowpipes are fitted with a flashback arrestor to avoid explosion due to backfire travelling back upto cylinder.

Equipment # 2. Pressure Regulator:

The function of pressure regulator is to reduce the pressure from the cylinder and to maintain it at constant value regardless of the pressure variations at the source. It is also used to adjust the pressure of gas to torch. Changes in the pressure can be made simply by turning the handle at the regulator. Generally there are two types of pressure regulators viz., single-stage and double-stage.

In single stage type, the pressure of the gases from the source pressure is directly reduced to the working pressure of the torch in one stage. In general, mechanism consists of a floating valve, a diaphragm and balancing springs, all enclosed in a suitable housing. In two-stage type regulators, the reduction of pressure is accomplished in two stages. It has two independent diaphragms and valve assemblies which make operation extremely efficient. This ensures much more constant delivery pressure.

Equipment # 3. Hose and Fittings:

Two hoses to carry oxygen and acetylene separately are required. They connect the regulator mounted on cylinders to the torch. Generally green colour is adopted for oxygen hose and red for acetylene. These should be strong, durable, non-porous, light and flexible. To avoid explosion, oxygen fittings should never be greased or oiled.

Special hose fittings and connections are provided for attachments to the torch and pressure regulators.

Equipment # 4. Cylinders:

The gases are generally stored at high pressure in the steel cylinders. For oxygen which is obtained commercially, cylinders are made of drawn-steel without seams and carefully heat treated so as to develop great strength and toughness.

The cylinder is also equipped with a high pressure valve and valve-protector cap. It is charged at a pressure of about 150 kg/cm² and temperature about 20°C. A safety fuse plug is also provided so as to release oxygen in case, temperature inside increases.

Acetylene cylinders are closely packed with absorbent filler, which is saturated with acetone. The compressed acetylene is dissolved in the acetone. The reason for this is that acetylene when stored under pressure may become unstable at elevate temperature.

Acetone can absorb about 25 times its own volume of acetylene per atmosphere of pressure and forms porous spongy mass, thus acetylene is prevented from being separated into its chemical constituents and avoiding any explosion.

These are also fitted with high pressure valve, valve protector cap and fusible plugs. For safety reasons, to avoid accidental mixing of gases, screwed hose and cylinder fittings are threaded with opposite hand threads. (Right hand for O₂ and left hand for acetylene).

Equipment # 5. Goggles:

These are very essential to protect eyes. These are fitted with coloured lenses that prevent harmful heat and the ultraviolet and infra-red rays.

Equipment # 6. Spark Lighter:

It provides a convenient and instant means for lighting the welding torch. It consists of a pointed stone and a rough surface which produce a spark when rubbed together.

Equipment # 7. Apron:

This protects the clothes of operator from dirt and danger and keeps him alert.

Equipment # 8. Gloves:

These are essential to protect hands.

Equipment # 9. Welding Rods:

Theoretically the composition and properties of the welding rod should match with the base metal very closely. Therefore proper welding rods should be chosen for welding various non-ferrous and ferrous metals. The materials of welding rod should flow smoothly and freely and unite readily with the base metal to produce sound and clean weld.

The welding rod coated with flux should always be stored in air conditioned rooms, otherwise the property of the flux will be deteriorated due to moisture leakage in them.

Equipment # 10. Fluxes:

In welding of certain metals, the fusion of the weld does not take place very readily particularly when the oxides of the base metal have a higher melting point than the metal itself. Thus these oxides remain on the surface and become entrapped in the solidifying metal instead of flowing from the welding zone.

This oxide can be removed from the weld location by use of certain fluxes which react chemically with the oxides of most metals and form fusible slags at welding temperature. These float at the top of molten puddle and do not interfere with the deposition of filler metal.

Besides, flux also protects the molten puddle from atmospheric oxygen and thus avoids formation of oxide on the metal surface. It may be noted that the absorption of oxygen into the molten weld-pool will result in a poor weld.

These also help to clean and protect the surfaces of the base metal. These are available in several forms, such as dry powder, paste or thick solution or in form of coating on the welding rod.

Use of flux is very essential for welding cast iron, brass, bronze, stainless steel, aluminium etc. but not for carbon steel. In the case of carbon steel, the oxide formed is lighter than the parent metal and therefore removes itself by floating to the surface of the weld in the form of a scale.