A Brief Introduction to High Performance Refractory Castables

1. Composition of Refractory Castables

Refractory castables consist of three components: binder, aggregate, and admixtures. A setting accelerator is sometimes also added.
Refractory aggregate is the main component of refractory concrete. Various refractory materials (clay, high-alumina, siliceous, magnesian, etc.), calcined clinker, or various scrap bricks crushed to a certain size can be used as refractory aggregate. Aggregate particle size significantly affects the quality of the product. Therefore, in addition to certain restrictions on aggregate particle size, there are also certain requirements for the quantity and ratio. Refractory aggregate is equivalent to the crushed stone and sand in ordinary building concrete. Aggregate generally accounts for 70% to 80% of the refractory concrete mix. Of this, coarse aggregate (5-20 mm) accounts for 35% to 45%, and fine aggregate (0.15-5 mm) accounts for 30% to 35%.
The binder acts as a cementing and hardening agent, giving the product a certain strength. Binders include ordinary Portland cement, alumina cement (high-melting cement), magnesia cement, water glass, and phosphoric acid. To ensure sufficient refractoriness in concrete (binder acts as a flux at high temperatures; the higher its amount, the lower the concrete's refractoriness) and to minimize volume shrinkage during use, the binder dosage should be kept as low as possible, generally 10% to 25%. It is also desirable that the binder and aggregate not form excessive low-melting products.

Some refractory concretes (such as phosphate refractory concrete) require the addition of a small amount of accelerator to accelerate hardening and consolidation.

To improve the properties of refractory concrete, such as increasing its strength during heating and reducing volume shrinkage, 10% to 25% of admixtures are often added. The admixtures are made from the same raw materials as the aggregates: finely ground refractory clinker powder, with 70% to 80% of the fineness below 0.088mm.

2 Classification of refractory castables:

According to the special functions of the binder and certain materials, they can be divided into the following 7 categories:

(1) Clay-bonded refractory castables;

(2) Ultrafine powder (such as silica fume, etc.) bonded refractory castables;

(3) Cement-bonded refractory castables;

(4) Chemically bonded refractory castables;

(5) ρ-Al2O3 (hydrated Al2O3) bonded refractory castables;

(6) Low-cement bonded refractory castables;

(7) Silicon, aluminum sol (sol-gel) bonded refractory castables.

Our factory mainly produces low-cement castables, ultra-low-cement castables and anhydrous castables.

3 Application of refractory castables

① Industrial kiln lining: Refractory castables are the most widely produced and used amorphous refractory materials. They are mainly used to construct various heating furnace linings and other integral structures10.

② High-temperature industrial furnaces: Refractory castables can be widely used in various high-temperature industrial furnaces, such as cement rotary kilns, glass melting furnaces, ironmaking blast furnaces, and electric furnaces.11

③ Repair materials: Phosphate refractory castables have also shown good results in repairing certain areas of metallurgical furnaces and other vessels that come into direct contact with slag and molten metal.2

④ Prefabricated components: Refractory castables can be manufactured into prefabricated components, such as the weir plates of continuous casting tundishes, which are assembled using prefabricated refractory castables.12

⑤ Other high-temperature equipment: Refractory castables can also be used in other high-temperature equipment, such as waste incinerators, petrochemical cracking furnaces, and ceramic firing kilns.