What is ‘Black Core’?
As the name suggests these are circular or semi-circular shaped black spots forms around the core or middle portion in non-basic refractory bricks containing good percentage of raw clay. The two reasons attributed to the formation of Black Core are:
=> Presence of Carbonaceous matters in plastic / non-plastic fire clay. Sometimes, too much carbonaceous matters have been found to occur in the fireclays which are available particularly around a Coal-belt.
=> Reducing atmosphere in the kiln during firing of bricks.
Following are the few steps to avoid the formation of Black Core in refractory bricks:
=> The firing atmosphere (kiln atmosphere) must be kept oxidizing.
=> Soaking time should be prolonged.
=> If it is not eliminated even after taking the above two steps then the raw clay has to be replaced.
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