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GAS WELDING RODS AND FLUXES

The neutral flame

Two distinct zones may be seen in the neutral flame. The inner cone of the flame has a bright blue light and extends only a short distance from the tip. Around this inner cone is the flame envelope which is darker and less intensely blue. This flame is neutral, and is used for heating, cutting and for most steel welding work.

The carburizing flame

The carburizing flame has excess of acetylene, and is recognised by a secondary flame zone between the inner cone and the flame envelope. This zone is less bright and more white in colour than the inner cone, but is considerably brighter than the flame envelope.

When igniting an Ac/Ox torch one normally opens fully for Acetylene and only slightly for Oxygen, obtaining a strongly carburizing flame. By adding Oxygen (and if necessary reducing the Acetylene flow) the secondary zone will be reduced, and a neutral flame is obtained just as the secondary zone disappears. Reducing the Oxygen flow slightly again will give a carburizing flame with a small secondary flame zone, approximately twice as long as the inner cone. This soft flame (also called a reducing flame) is used for welding of aluminum and aluminum alloys, and for soft soldering.

The oxidising flame

By increasing the Oxygen flow slightly beyond the point where the secondary zone disappears one will obtain an oxidising flame (with excess oxygen). The flame will be shorter and sharper than the neutral flame, with a shorter, more pointed inner cone. This flame is slightly hotter than the neutral flame, and is used for welding cast iron, brass, bronze and zinc alloys, and for brazing.

Hottest spot in flame 3100°C

x Neutral flame.

3.04

Carburizing flame.

Oxidizing flame.

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