Fireclay refractory brick is the most widely used refractory brick. Fireclay refractory bricks are inferior to silica and basic refractories in resistance to slag. Dense and more aluminous bricks resist slag the best.
Fireclay refractory bricks contain 18–45 percent of alumina (Al2O3) and 50-80 percent of silica (SiO2) with minor proportion of other minerals. They are made from refractory clays and kaolinite by the addition of fireclay or, sometimes, nonplastic clay rocks and quartz. Calcined clay or grog is added to the brick mix to reduce the firing shrinkage and to give greater stability in applications. Fireclay refractory brick is a kind of acid refractories.
Fireclay refractory brick is resistant to high temperatures, having fusion points higher than 1,600 °C (2,910 °F). The fireclays are graded into super duty, high-duty, medium-duty, low-duty, and also semi-silica, depending upon their capacity to withstand high temperature before melting. The low duty fireclay can withstand temperatures between 1515 and 1615 °C (PCE 19 to28), intermediate duty fireclay up to 1650 °C (PCE 30), high duty fireclay up to 1700 °C (PCE 32) and super duty beyond 1775 °C (PCE 35).
Refractoriness and plasticity are the two main properties needed in fireclay for its suitability in the manufacture of refractory bricks. A good fireclay should have a high fusion point (greater than 1580 deg C) and good plasticity.
Fireclay refractory brick has great features: low thermal conductivity, good thermal insulation, high resistance to thermal shock, abrasion and chemical attack, easy operation and installation, broad usage or applications and cheapness, etc.
Fireclay refractory manufacturing involves five processes: raw material processing, forming, drying, firing and final processing. The variety of clays and manufacturing techniques allows the production of numerous brick types appropriate to particular applications.
Fireclay refractory brick is extensively used in almost all places of heat generation, like boiler furnaces, glass melting furnaces, chimney linings, pottery kilns, blast furnaces, and reheating furnaces.