Oxy Acetylene Welding - Characteristics, Process and Equipment

Oxyacetylene welding:- Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. Pure oxygen, instead of air (20% oxygen/ 80% nitrogen), is used to increase the flame temperature to allow localized melting of the workpiece material (e.g. steel) in a room environment. A common propane/oxygen flame burns at about 3,5000-degree centigrade. In oxy-fuel 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 depends upon the metals to be welded.

• Welding Equipment:-

• Regulator:- The regulator is used to controlling 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.

• Gas hoses:- The hoses are specifically designed for welding and cutting. The hose is usually a double hose design, meaning 'that there are two hoses joint together'. These hoses are color-coded for visual identification and their threaded connectors are handed to avoid accidental connection, oxygen is right-handed as normal, fuel gases use a left-handed thread. These left-handed threads also have an identifying groove cut into their nuts.

• Nonreturn valve:- Between the regulator and hose, and ideally between hose and torch on both oxygen and fuel lines, a flashback arrester and/ or nonreturn valve (check valve) should be installed to prevent flame or oxygen fuel mixture from being pushed back into either cylinder and damaging the equipment or making a cylinder explode. 

• Check valve:-  A check valve lets gas flow in one direction only. Not to be confused with a flashback arrestor, a check valve is not designed to block a shock wave. The pressure wave could occur while the ball is so far from the inlet that the pressure wave gets past before the ball reaches its off position. A check valve is usually a chamber containing a ball that is pressed against one end by a spring's gas flow one way pushed 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.

• Arches:- 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.

• 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.

• Cutting torch:- A cutting torch head is used to cut materials. It is similar to a welding torch but can be identified by the oxygen blowout trigger or lever.

• Rose-bud torch:- A rosebud torch is used to heat metals for bending, straightening, etc. where a large area needs to be heated. It is called as such because the flame at the end looks like arose bud. A welding torch can also be used to heat small areas such as rusted nuts and bolts.

• Injector torch:- A typical oxy-fuel torch, called an equal pressure torch, merely mixes the two gases. In an injector torch, high-pressure oxygen comes out of a small nozzle inside the torch head so that it drags the fuel gas along with it, via venturi effects. In oxyacetylene welding, the flame is the most important tool. All the welding equipment simply serves to maintain and control the flame. The correct type of flame is essential for the production of satisfactory welds. The flame must be of the proper size, shape, and condition to operate with maximum efficiency.

• Neutral flame:- The neutral flame is the primary flame used by gas welder. A figural flame has two zones, a hotter lighter inner zone, and a cooler, darker outer zone. In a neutral flame, all of the fuel gas is being burned in the process, resulting in a clean flame. The welder uses the tip of the inner flame zone to heat the parts to be welded, as this is the hottest part of the flame.  

• Carburizing flame:- If the oxygen is reduced, a carburizing flame is created from a neutral flame. In this case, not all of the fuel gas is being burned by the flame. A carbonizing flame has three zones and is cooler than a neutral flame because the excess carbon acts as an insulator. Carbonizing flames deposit soot on the workpiece that has to be cleaned when the part is cooled, but the addition of carbon to the metal is desirable in some iron and steel welding applications.

• Oxidizing flame:- An oxidizing flame is caused by increasing the oxygen from a neutral flame. Because of the excess oxygen, this flame is hotter than neutral or carbonizing flames. Welders generally do not use an oxidizing flame, because it can increase the oxides in the base material. However, an oxidizing flame is used for bronze and brass work.