Gas welding

Gas Welding

• Gas welding is a process in which acetylene and oxygen are used to produce a high-temperature flame zone to melt the material and fuse them to produce weld bead.
• Since there is no external filler material is used to produce weld pool so it is an autogenous process

There are three types of flame produced during the combustion of acetylene and oxygen

1. Carburizing flame
2. Neutral frame 
3. Oxidizing flame

Carburizing flame

• In this process, the oxygen content is less than the acetylene in the acetylene-oxygen mixture.
• Oxygen available in the mixture of acetylene is .7 to .8 times the acetylene available in the (A-O) mixture.
• When less amount of oxygen is provided to the mixture, part of combustible acetylene is left as it is and results in reducing or carburizing flame.
• This flame is the same as the natural flame, only with the third phase in between the outer blue flame and inner white cone it is called "intermediate flame feather". 
• Its color is reddish and the flame length of the feather is an indication of the excess of acetylene present in the Acetylene-oxygen mixture.
• voiceless combustion of the mixture
• Since unburned carbon present goes into the weld metal pool, the material appears to boil this excess carbon cause the Steel to become extremely hard and brittle.

Neutral flame.

• When only a certain amount of oxygen is available in the mixture so that acetylene can completely combust and produce a high-temperature flame zone.
• In this case, the intermediate page is approximately neglected and so only 2 phase exist 

1. The inner core(white zone) Temp- 3100-degree Celcius
2. Outer blue zone(Blue zone) Temp- 1200-1800 degree Celcius

• Acetylene to Oxygen ratio is 1:1
• In oxidizing flame maximum temperature achieved is approx 3100 degree Celsius

Oxidizing flame-

• When the excess amount of oxygen is supplied to the mixture then it is known as oxidizing flame this flame is similar to the neutral flame with the exception of the inner white cone is somewhat smaller than other flames.
• Acetylene to oxygen ratio is approx 1:1.2
• In the white flame, the zone rises to the highest temperature up to 3300 degrees Celsius.
• This flame produces a roaring sound.
• This film is useful for non-ferrous alloys.
• The excess oxygen present in the acetylene oxygen mixture forms an oxidizing layer to the material which prevents the defects produced inside the weld pool.