Some Observations On Reheat Expansion of Fireclay Refractories

Firebricks were made from Chittarpur fireclay with the addition of Chakla non-plastic clay grog and calcined Lohardaga bauxite. Chakla clay was calcined both in rotary as well as in intermittent kilns at temperatures around 1350°. Bricks were fired to 1350° for 4 hours and were tested for their properties. Reheat shrinkage was observed on bricks containing intermittent kiln-clay grog, and even with the addition of 25% calcined bauxite in the batch. Bricks containing 70% rotary kiln-clay grog showed slight reheat expansion. Incorporation of finer fractions of calcined bauxite increased firing expansion and reduced reheat expansion. Similar observations were made also with higher calcination temperature of the bauxite. To minimise the reheat expansion of fireclay refractories, it is desirable to avoid calcined bauxite together with rotary kiln-clay grog and to use in case of necessity, only finer fractions of high temperature calcined bauxite.