During day to day furnace operation, the lining is subjected to various kinds of thermal stresses, mechanical loading, and metal-lining reactions. As a result, some minor or major type of lining wear does take place. There are various methods to repair the lining depending on the size and nature of wear.
Cracking: Often, small hair-like cracks are seen on the lining surface after it has been cooled to room temperature. This is natural and need not cause any problem. On cooling the lining refractory contracts, and when it cannot withstand the contraction – stresses, it develops small cracks and thereby release the stresses. Tiny cracks o this nature close themselves on reheating of the crucible during the next melt. The only care needed is to ensure that in the initial heat after cold-start the charge should not contain fine metallic particles or borings which can enter the crack and prevent from self- closing.