Any hot spot should in principle not be allowed to reach a temperature superior to 700°C. The reason for this is that at 730-740°C is the phase transition between pearlite and austenite. This phase transition will cause stresses and will dramatically change the mechanical properties of the steel, hence causing very quickly shell deformation.

However, for large potions of shell, this is already too much as the mechanical properties of the steel will already be lowered at this temperature. For large portion of shell, the maximum should be 450-500°C.

First response to a small hot spot should be to put a fan on it to cool down and promote coating. NEVER USE WATER to cool a hot spot (stress will be too high). Flame adjustment can also help.

For larger hot spot, better to stop the kiln.

Attention: if you have a very large hot spot (i.e. kiln shell red over a full circle), DO NOT STOP ROTATION of the kiln until it is cooled down to less than 500°C. If you stop rotation and restart it, the extra torque required for starting rotation may twist the shell.

Dear All ,

Thank you all for your replies .