Heat source in the Gas welding (oxy fuel gas welding) is the flame produced by the combustion of a fuel ( Acetylene) and oxygen. Three different types of gas welding flames can be obtained by varying the oxygen–acetylene (or oxygen–fuel gas) ratio.
- Neutral Flame
- Oxidizing Flame
- Carburizing Flame
Neutral Flame: ►
Neutral flame is achieved with an approximately 1:1 ratio of oxygen and acetylene. It has two zones – a brighter (white) inner core and a bluish outer layer. Due to equal proportion of oxygen and acetylene, the reaction takes place not so much quickly and forms a bigger inner core.
◙ The inner core has a temperature of near about 3200°C and the outer layer has a temperature pf 1275°C.
◙ Neutral flame is used to weld mild steel, cast iron, stainless steel, copper and aluminum as it causes no chemical change to the metal.
Oxidizing Flame: ►
Oxidizing flame is achieved with an approximately 1.5:1 ratio of oxygen and acetylene. It has two zones – a smaller brighter (white) inner core and a bluish outer layer.
To reduce the inner core, more amount of oxygen to be supplied so that the reaction takes place very quickly and forms a smaller inner core.
◙This flame is used to weld brass, bronze and zinc and sometimes cast iron. This flame is not suitable for steels due to excess oxygen oxidizes the metal, leading to porous and brittle welds.
Carburizing Flame: ►
Carburizing flame is produced with an approximately 1:1.2 ratio of oxygen and acetylene. If acetylene is increased, the excess acetylene decomposes into carbon and hydrogen and the flame temperature as not great. So this carbon and hydrogen makes an intermediate layer (feather).This flame is also known as reducing flame. If acetylene is increased further, a smoky flame is produced.
◙ Reducing flame can be recognized by the presence of three distinct zones- whitish inner core, intermediate feather and light bluish outer envelop.
◙ Carburizing flame is used to weld nickel, Monel and certain alloys and many nonferrous alloys and satellite.