Answer:

The formation of cracks is inherent in the nature of the raw material quartzite when the silicon linings are done.

They are contractions and volume changes involving breakage of the lining.

What can happen?

The vertical cracks, normally they close.

What to do?

1- Ideally working in 3 shifts and the furnace does not cool.
2- To observe the closing of the cracks putting the furnace back on track.