FLAME ADJUSTMENT

1)To start with, when the oxyacetylene gas welding torch is ignited, it gives an acetylene flame (fig-) in which enough oxygen is drawn in from the atmosphere to burn acetylene partially.From acetylene flame excess of free carbon is released into the air. Air acetylene flame may be used to apply carbon to mold faces in the foundry, because the carbon acts as an insulator between the molten metal and the mold face.

2)As the oxygen valve in the torch is progressively opened, the flame becomes luminous.Then the luminous portion contracts towards the welding tip forming a distinct bright zone within a blue outer envelope. This is Carbonizing flame and has large excess of acetylene.

3)With further increase of oxygen content, the bright zone of the flame contracts farther and is seen to consists of two parts: a brighter inner cone and a pale green feather trailing off its end into the blue envelope. This is a reducing flame.(fig)

4)If at this stage oxygen flame is increased gradually a certain point will reach where one will notice a distinct change in the sound of the flame and a well defined white cone will appear near the tip surrounded by a bluish envelope that is faintly luminous.This is a neutral flame.There is an approximate one to one mixture of acetylene and oxygen to result a neutral flame.

5)Further increase of oxygen content into the mixture will give rise to an oxidizing flame.