| While a fair reflection of the characteristics of the refractories may be obtained by the normal tests
given in various standard specifications, they are inadequate to explain the actual difference in the
durability under service conditions of apparently similar bricks supplied by different manufacturers to
meet the same specification. The service conditions bring in certain intangibles owing to the degree
of vitrification and continuation of mineralogical changes depending on the method of manufacture and
the nature of the constituents. Consequently, a proper appraisal of the refractories requires further
tests which simulate service conditions.
The aluminous refractories used in the soaking pit covers are subjected to the combined effect of
high temperature and ferruginous fumes. When these bricks failed, the nature of their failure was studied
over a period of ten years to understand the difference between the bricks.
The investigations included studies of viscous flow, plastic deformation, creep or changes
due to the advance of vitrification or recrystallisation. The service performance of the soaking pit
cover bricks has been found to depend on the degree of deformation under a constant load or drop
in porosity on refiring at about the working temperature. These properties are dependent on the presence
of comparatively low fusible ingredient contributing to the formation of glassy matrix. Better life of
the cover bricks can be expected from those with higher resistance to deformation and low drop in
porosity on refiring. |
