Re: Red spot
There are many reasons for loss or erosion of bricks. Here are a few. (The first two are related to your question regarding silica content);-
1. Very little liquid phase (high silica ratio, >3) - Bricks are worn away by abrasion due to little or no protective coating in the burning zone.
2. Excessive liquid phase (low silica ratio, <2) - Kiln coating may be washed out, exposing bricks to both mechanical and chemical erosion, or liquid phase may penetrate and weaken bricks, which then fall out.
3. Very low liquid phase viscosity (low alumina ratio, <1.2) - Coating may be washed out, exposing bricks to erosion, or liquid phase may penetrate and weaken bricks, which then fall out.
4. Excessive alkali attack - penetration of the bricks by either gaseous or liquid alkalis causing premature weakening and spalling of the bricks.
5. Thermal shock - ie. extreme and/or sudden changes of temperature in the burning zone. (eg. power failures, sudden heavy rain, fluctuations in fuel rate, overheating, unstable kiln operation)
6. Rings or coating buildups falling out and taking attached bricks with them.
7. Age of the bricks - bricks will eventually deteriorate and weaken under normal running conditions due to liquid phase and alkali infiltration. Regular re-bricking is therefore required.
8. Badly installed bricks
9. Incorrect brick types used.