Linear Change On Reheating Of Refractories

Refractory brick and shapes of different compositions exhibit unique permanent linear change after heating or reheating. Linear change is an important indicator of the quality of refractory. 

Linear change is also known as linear change on reheating or residual linear change. It refers to the irreversible changes of its size (length) after heated to high temperature., expressed in %. A positive value indicates expansion, called reheating linear expansion. A negative value indicates contraction, called reheating linear shrinkage. 

 

Linear change can be measured experimentally. It is tested by heating the refractory to a predetermined temperature, holding a certain time and then cooling it to room temperature. The measuring temperature and time should be chosen according to the technical standard of each product. During the use, the refractory may be subjected to further sintering and there may be further change in phase and volume. 

 

Linear change is also an aspect of high temperature volume stability. It is an important property to ensure the stability of masonry body, reduce the gap of masonry body, improve its tightness and corrosion resistance and avoid damage to the overall structure of the masonry body.  For example, if the reheating linear shrinkage of the crown is too big, the crown may collapse. For non burned products and unshaped refractories, this indicator is more important.

 

During use, for the fireclay brick, linear shrinkage always occurs, while for silica brick, linear expansion always occurs. Carbonaceous refractories have low linear change and good high temperature volume stability.