Any small localized broken or worn out portion on the furnace lining can be easily patched up using air-setting refractory. The area should be thoroughly cleaned by removing slag and the refractory should be trowelled with pressure. After its moisture has escaped it will develop the strength.
Bottom Erosion: This can be repaired by thoroughly cleaning the eroded area and filling it with the ramming mass mixed with the binder. It is then rammed with a lat rammer. If the area to be repaired is large, it is covered after during the initial stages of the next heat.
Erosion of Bottom as well as Lower side walls: If the lower sidewalls and the bottom have eroded, these are thoroughly cleaned free of slag. The bottom is rammed by using the ramming mass mixed with the binder. A half-former is then positioned on it and the sides are carefully rammed with the ramming mass. This former is somewhat smaller in diameter than the original diameter of the lining. The next heat is followed slowly as if it is a sintering cycle. The newly rammed portion sinters itself. This kind of half-former patching is commonly practiced in large furnaces after half the normal life of lining is completed.
Slag line Erosion: Repair of slag line erosion can be done as described earlier in the repair of localized wear. It can also be done if needed, while the furnace is in operation. The melt-level is kept at the area to be repaired. Slag is removed Loose ramming mass is added on top of the melt. Through the movement of the bath, the ramming mass is drawn to the sidewalls and adheres to the wall. It is called hot patching of the lining.
MONITORING OF LINING CONDITION: Due to chemical and mechanical action of molten metal and also the slag. The lining of the furnace is continuously wearing out. So long as the lining wear is uniform and controlled, the lining life is prolonged. Once the lining has worn out to a point where its use becomes unsafe, it must be changed. The wear depends on the type of metal being melted, the operating temperature, as well as on the volume and type of slag being formed. Wear I maximum at the junction of the side-wall with the bottom, and also at the metal/slag level. Unusual wear at any other position indicates the possibility of poor lining practice. Three methods are commonly used to monitor lining condition.
- Visual observations.
- Physical measurement.
- Electrical measurement.