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Answer:

The slag adhered to the silicon lining carries an inefficient running of the furnace. It can be low or high melting point.

Low melting point. When the furnace works at low temperatures silicon oxide is formed and it sticks to the walls of the lining as:

Si metal + O2 -> SiO2 slag

High melting point. Slag difficult to eliminate are formed because these have higher melting point than the own lining:

2 FeO oxidized load + Si metal -> 2 Fe + Si O2 slag

Al metal-> Al2O3 + SiO2 lining -> Al2O3.SiO2 mullitic slag

What can happen?

In any of two cases the furnace loses capacity, increases the risk of cracks forming, presents an irregular melting with distinct areas of magnetic behaviour, in short the life of the furnace decreases.

What to do?

It is indispensable to analyse the reason of this regrowth.

With low point of melting slag, raise the metal level and proceed to raise the temperature up to eliminate it.

With high point of melting slag, it is indispensable to analyse the load and used additives. Often high concentrations of Si appear in FeSi causing of this problem.