Page 490 of 561

AC/OX CUTTING/WELDING/BRAZING The Acetylene/Oxygen Flame A correct Acetylene/Oxygen flame from a cutting nozzle or blowpipe is dependent on correct gas pressure being supplied to the torch. Inaccurate regulators or long gas hoses may result in pressure deviations that gives wrong pressure to the torch. In such cases the actual pressure at the torch connection should be checked. Too low gas pressures may give a gas flow which is slower than the flame velocity of the gas mixture. This can cause the flame to burn backwards into the nozzle opening and accelerate through the gas channels, resulting in flashback.

Too high gas pressures may cause the flame to leave the nozzle tip, starting at the distance from the tip where the gas flow has slowed down to match the flame velocity.

If the gas pressure is too high it may be difficult or impossible to ignite a flame.

The correct Acetylene/Oxygen flame shall be a quiet stable flame, burning close to the nozzle tip, but well away from the point where flashbacks may occur.

NOTE!

The Acetylene/Oxygen flame uses the oxygen supplied from the nozzle for the primary reaction taking place in the inner cone.

(C2H2+O2 → 2C0+H2+Heat). In the flame envelope a secondary reaction takes place.

(2C0+H2+O2 → +2C02+H2 0+Heat). This reaction needs as much Oxygen as the primary reaction, but the required Oxygen is taken from the surrounding air. Therefore always ensure proper ventilation when working with the Acetylene/Oxygen flame.

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 metallurgically neutral, and is used for heating, cutting and for most steel welding work.

5.01

489