Q. Describe the types of flames obtained in an oxyacetylene gas welding process giving the applications.
There are three types of flames in the gas welding on the base of the properties of oxygen and acetylene.
1. Neutral flame (Balanced flame)
At a ratio of 1 : 1 that is when there is no excess oxygen, it is
considered to be a neutral flame. In neutral flame all the acetylene present completely burnt and thus all the available heat in the acetylene is release. The temperature of the neutral flame is of the order of about 3260ºC. The neutral flame consist pf sharp brilliant inner cone extending a short distance from the tip of the torch and an outer cone or envelope. The inner cone develops heat and outer envelope protects the molten metal from oxidation, because the oxygen in the surrounding atmosphere is consumed by gases from flame.
The neutral flame is commonly used for welding most of the metals such as mild steel, stainless steel, cast iron, copper, aluminium.
2. Oxidizing flame
When the volume of oxygen supplied to the neutral flame is increased it becomes an oxidizing flame. The flame is similar to the neutral flame with the exception that the inner white cone is somewhat small, giving rise to higher tip temperatures (3300ºC). This flame is harmful especially for steels, because it oxidizes the steel. Only in the welding of copper and copper based alloy is an oxidizing flame desirable, because in those cases a thin protective layer of slag forms over the molten metal.
3. Carburizing flame
When the volume of oxygen supplied to the neutral flame is reduced. This type of flame is called carburizing flame or reducing flame.
The temperature of a reducing flame (on having excess acetylene) is lower,
so it is suitable for application requiring low heat, such as brazing, soldering and flame hardening. The carburizing flame is not suggested for general use. This flame has three zones.
(i) Inner zone
(ii) An intermediate of whitish color
(iii) The bluish outer cone.
The outer flame envelope is longer than the other flames.