The size of the flame can be altered by varying the ratio of oxygen and acetylene. By doing so, the following three types of flames are obtained.
- Neutral flame
- Carburizing flame
- Oxidizing flame
1. Neutral Flame
The supply of equal quantities of oxygen and acetylene produces neutral flame. There are two zones in this flame- 1. Sharp and bright inner cone and 2. Bluish outer cone. The temperature of the inner cone will be around 3200°C. This neutral flame is generally used as it will not cause any chemical reaction upon the heated metal.
2. Carburizing Flame
This flame is also known as reducing flame. The supply of acetylene will be more than oxygen to produce this flame. Carburizing flame consists of three zones namely,
- Sharp inner cone
- White intermediate cone
- Bluish outer cone
Carburizing flame is useful in welding low carbon steel and alloy steels. It is also used to harden the outer surface of metal parts.
3. Oxidizing flame
Oxidizing flame is obtained by supplying more oxygen than acetylene. It consists of two zones namely bright inner cone and outer cone. This flame is useful in welding brass and bronze.