Refractory Castables: Classification and Applications

Refractory castables are classified much like refractory bricks—by material composition or by performance characteristics—and include lightweight, dense, wear-resistant, high-strength, steel-fiber-reinforced and self-flowing products. They are mainly used to line high-temperature furnaces and kilns.

Refractory castables are unshaped, unfired refractories made of properly graded granular and powdered materials plus a binder. The granular material is called aggregate, the powder is called the admixture or matrix, and the binder is called the bonding agent. Having no fixed shape, these materials can be prepared as slurry, paste or loose material, which is why they are also called bulk refractories; and because they form seamless monolithic structures, they are also called monolithic refractories.

Classification of refractory castables

Powdered refractory combined with a suitable binder and water forms a high-flow refractory mostly installed by pouring or vibration. Those made from insulating lightweight refractory materials, typically bonded with hydraulic calcium aluminate cement, are called lightweight castables.

Refractory castables are generally classified by bonding agent, refractory aggregate and porosity.

① Hydraulic bond, ② hydraulic plus coagulation bond, ③ coagulation bond, ④ chemically bonded castables; low-cement series, cement-free castables, alkali-resistant, acid-resistant, lightweight, steel-fiber, high-alumina, corundum and silicon carbide castables, etc.

Lightweight castables by service temperature

I: Low-temperature (lightweight) castables, service temperature 600–900°C.

II: Medium-temperature insulating (lightweight) castables, service temperature 900–1200°C.

III: High-temperature insulating (lightweight) castables, service temperature >1200°C.

Applications of refractory castables

Refractory castables are mainly used to build monolithic structures such as the linings of various reheating furnaces, and some grades can also be used in smelting furnaces. Aluminate cement castables, for example, are widely used in reheating furnaces and other thermal equipment free of slag and acid/alkali attack. For higher-temperature areas such as tapping spouts, steel ladles, blast furnace bodies and iron runners, high-quality castables made from high-quality granular and powdered materials bonded with low-calcium, pure high-alumina cement can be used.

Unshaped refractories generally have high cold strength and can be made into precast shapes installed on site, such as precast weirs for continuous-casting tundishes. Refractory castables are mainly used in metallurgical furnaces and are widely applied in furnaces and thermal equipment in the petroleum, chemical, building materials, power and machinery industries.

Classification and uses of refractory castables

Refractory castables are classified much like refractory bricks—by material composition or by performance characteristics—and include lightweight, dense, wear-resistant, high-strength, steel-fiber-reinforced and self-flowing products. They are mainly used to line high-temperature furnaces and kilns.