Castables are made by mixing refractory aggregates and powders, adding binders and additives, and kneading. The binder generally used in castables is aluminate cement. The amount of cement added can affect the castable’s overall performance, high-temperature strength, corrosion resistance, etc. Low-cement castables are made by adjusting the formula during the production process to reduce the CaO content, improve the castable’s overall performance, and increase the lining’s service life.
What is low cement castable?
Low cement castable is a refractory castable with low cement content. Refractory castables with aluminate cement as a binder and CaO content less than 2.5% can be called low cement castables; castables with a CaO content of 1.0-2.5% can be called ultra-low cement castables. Low cement castable is a high-grade refractory castable, which is called low cement castable because of the low CaO content in cement.
Physical and chemical indicators of low cement castables
| Item | Clay | High alumina | Corundum |
| Al2O3 % | 45 | 75 | 92 |
| SiO2 % | 50 | 12 | 5 |
| CaO % | <1.8 | <1.5 | <1.5 |
| Bulk Density(110℃, 24h) g/cm3 | 2.3 | 2.6 | 3.0 |
| Cold crushing strength(110℃, 24h) Mpa | 72 | 75 | 85 |
| Linear change rate(1350℃, 3h) % | ±0.3 | ±0.5 | ±0.5 |
| Max working temperature ℃ | 1450 | 1600 | 1700 |
| Water needed % | 6.0~6.5 | 6.0~6.5 | 4~5 |
Characteristics of low cement castables
Types of low-cement refractory castables
What are the common low-cement refractory castables? Low-cement castables can be made into high-aluminum low-cement castables, corundum low-cement castables, aluminum-magnesium spinel low-cement castables, etc. according to the selected refractory raw materials.
According to the construction performance, it can be divided into self-flowing low-cement castables and vibration-type low-cement castables.
Application scope of low cement castables
Low cement castables are suitable for linings of heating furnaces, various heat treatment furnaces, electric furnace covers, vertical kilns, rotary kilns, blast furnace tapholes, ladles, iron ladles, etc.; self-flowing low cement castables are suitable for linings of high-temperature refractory components with metal anchors, such as the outer lining of water-cooled tubes of heating furnaces, integral spray gun linings for jet metallurgy, impregnation tube linings for RH and DH vacuum degassing devices, ladle gas supply components, and high-temperature wear-resistant linings of petrochemical catalytic cracking reactors, etc.; they are mostly used for construction of complex structures, which can greatly improve the overall use effect.
The raw material composition of low cement castable
Refractory aggregates: mainly include corundum, mullite, corundum mullite, aluminum-magnesium spinel, etc.
Micropowder: such as silica micropowder, is used to fill the gaps between aggregates and improve the density of castables.
Binder: usually aluminate cement or phosphate, which plays the role of bonding aggregates and micro powders.
Dispersants: such as high-molecular-weight polycarboxylate, are used to reduce the viscosity of cement castables and improve fluidity.
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