An Investigation of the Temperature Gradients Established in Refractory Blocks during their Firing.

JSGT 1941 V25 T310-T327

The temperature gradients set up within refractory blocks during their firing have been determined with reference to three blocks of one foot cube in size. One hand-made block was of fireclay containing 50 per cent grog, another hand-made block of sillimanite and the third slip-cast of sillimanite containing 75 per cent grog. Platinum-platinum rhodium thermocouples were inserted in the blocks, which were then individually subjected to a firing treatment comparable with commercial practice for some 200 to 300 hours in a gas-fired furnace having a total combustion space of 22 inches diameter by 31 inches depth. The time-temperature curves obtained showed that when heat is applied intermittently there is neither a smooth temperature rise, nor uniformity of temperature gradient between different parts of a block in the firing process; and these parts finally attain a temperature controlled by their location within the furnace, so that a natural temperature gradient becomes set up which prolonged soaking cannot remove. In the blocks for which data are given, the centre lagged behind the outer parts by about 6 to 8 hours in attaining a certain temperature during heating up; but at any one setting of the burners some 20 to 30 hours were necessary for stable temperature distribution to be reached, the natural gradients finally set up being 8° to 10° per inch from top to bottom of the block. The effect of these differences in thermal treatment of different parts of the block was ascertained by cutting sections from selected locations and determining their porosities and after-contractions.

Eric Preston, Ph.D., D.Sc., F.I.C., F.Inst.P., and Professor W. E. S. Turner