Thermal shock
The cause of thermal shock is usually due to the temperature inside the rotary kiln heating or cooling too fast. If the kiln skin comes off inside the kiln and the protection of the kiln skin is lost, the chance of causing thermal shock is even greater.
Generally, when the rotary kiln is in the heating stage, it will rotate according to the heating schedule, and the material located inside the kiln will protect the relatively cooler refractory lining at the bottom of the kiln; while the refractory lining in the upper half of the kiln will be directly heated by the flame.
However, as the kiln rotates further, the lining previously protected by the feed material is now no longer protected and is exposed to the hot flame. At this point, if the kiln is not heated and fed at the proper time, the sudden temperature change can cause the hot face of the brick to crack and spall horizontally.
Overheating loads
Excessive thermal loads occur when the temperature in the rotary kiln is too high for a long period of time and there is no proper feeding or lack of protection of the kiln skin. In these cases, the refractory lining of the kiln is subjected to flame impingement, resulting in premature destruction of the refractory material. This continuous overheating may lead to secondary sintering of the refractory, which alters the microstructure of the refractory.
As the refractory's elasticity is significantly reduced, the affected areas become more susceptible to mechanical and/or thermo-mechanical loads, and are therefore susceptible to cracking or thermal corrosion.
These are some of the common cases of thermal stress damage to refractory brick linings. In addition, there are a number of different situations that can also lead to thermal stress damage, so it is important to pay close attention to the use of refractory bricks and the operating conditions of the kiln.