Refractory castables are a type of monolithic refractory material that does not require molding and can be directly cast on-site. Due to their ease of construction, strong integrity, and excellent high-temperature resistance, they are widely used in high-temperature industrial equipment in metallurgy, building materials, power, and petrochemical industries. To help companies and engineers better select and use castables, this article will provide a detailed introduction from three aspects: types, typical formulations, and main application areas.

I. Main Types of Refractory Castables

Based on differences in binder, material, water content, and characteristics, refractory castables can be divided into the following categories:

1. Ordinary Refractory Castables

Using cement as a binder, these have simple formulations and are easy to construct. They are commonly used in areas where temperatures do not exceed 1400℃, such as boiler refractory layers, hot air ducts, and flue linings.

Features:

Low price

High initial strength

Moderate high temperature resistance

2. Low-cement castable (LCC)

Cement content is generally 1%–3%, significantly improving refractory performance, making it one of the most widely used medium-to-high-grade castables.

Features:

High strength, strong wear resistance

Good high-temperature volume stability

Significantly better slag erosion resistance than ordinary castables

Typical applications: Ladle working layer, kiln mouth, kiln door, furnace bottom.

3. Ultra-low cement and cement-free castable (ULCC/NCC)

Cement content is less than 1%, or even completely cement-free, relying on micro-powder, gelling materials, etc. for bonding.

Advantages:

Extremely high-temperature strength

Strong erosion resistance

Good thermal shock stability

Commonly used in: Cement kiln transition zone, glass kiln regenerator, high-temperature parts of electric furnace smelting.

4. Wear-resistant Castables

Added with specific wear-resistant aggregates (such as mullite and corundum) and reinforcing agents to improve resistance to mechanical erosion.

Typical Applications:

Circulating fluidized bed boilers

Slag flushing channels in the foundry industry

Liners for tapping channels and troughs

5. Lightweight Castables (Insulating Castables)

Aggregates are lightweight materials such as perlite, cenospheres, and expanded vermiculite, with low thermal conductivity.

Suitable for:

External insulation layers for industrial furnaces

Flue insulation

Insulation linings for heat treatment furnaces

6. Acid-resistant/Alkali-resistant Castables

Designed for special chemical environments, mainly used in corrosive environments such as chemical towers and flue gas systems.

7. Steel Fiber Castables

Added with stainless steel fibers to improve crack resistance and thermal shock resistance.

Applications:

High-temperature erosion areas

Strress-bearing areas such as metallurgical furnace bottoms, furnace doors, and material inlets

II. Typical Formulation Composition of Refractory Castables

The formulation of refractory castables typically consists of the following parts:

1. Refractory Aggregates (Coarse Aggregates)

Function: Provides volume and strength, bearing the main high-temperature load.

Common Aggregates:

High-alumina Aggregates

Corundum Aggregates

Mullite Aggregates

Magnesium Aluminum Spinel Aggregates

Lightweight Aggregates (used in insulating castables)

2. Refractory Fine Powders (Matrix Part)

Function: Fills voids, improves material density and erosion resistance.

Common Fine Powders: Activated alumina, silica powder, ultrafine mullite powder, etc.

3. Binder

Different binders are selected based on the type of castable:

High-alumina cement (ordinary castables, low-cement castables)

Cementitious materials (silica sol, phosphates, aluminosilicate gel)

Chemical binders (e.g., phosphates)

Binders have a significant impact on setting time, strength, and post-firing properties.

4. Additives (Admixtures)

Common functions:

Dispersants: Improve flowability

Anti-knock agents: Prevent cracking during kiln drying

Water-reducing agents: Increase material density

Steel fibers: Improve thermal shock resistance

Appropriate additives can significantly improve the performance of castables.

5. Water Content

Generally controlled within the range of 4% to 10%.

Excessive water content reduces strength, while insufficient water content leads to construction difficulties; it is a crucial factor affecting castable performance.

III. Main Application Areas of Refractory Castables

Due to their good integrity, flexible construction, and convenient maintenance, refractory castables play a key role in many industries:

1. Metallurgical Industry

The most widespread applications include:

Blast furnace tapping troughs

Tundish working layer

Converter slag splashing protection areas

Electric arc furnace bottom and walls

Low-cement, ultra-low-cement, and steel fiber castables are particularly prominent.

2. Building Materials Industry (Cement Industry)

Cement rotary kilns and auxiliary equipment use a large amount of castables, such as:

Preheaters

Three-stage and four-stage cyclone separators

Decomposition furnace linings

High-temperature feed pipes

Kiln mouths and kiln doors

High-alumina castables, mullite castables, and corundum spinel castables show significant application results.

3. Power Industry (CFB Boilers)

Circulating fluidized bed boilers have extremely high wear resistance requirements. Commonly used materials include:

High-wear-resistant castables

Steel fiber reinforced castables

Insulating castables

Applications include the furnace, water-cooled walls, return feeders, and wear-resistant layers of air caps.

4. Petrochemical Industry

High corrosion resistance and resistance to rapid temperature changes are required. Commonly used materials include:

Cracking furnaces

Hydrogenation reactors

Flue gas desulfurization towers

Waste heat boiler linings

Acid-resistant castables and phosphate-bonded castables are the most common.

5. Waste Incineration Industry

Waste incinerators require materials that are erosion-resistant, corrosion-resistant, and thermal shock-resistant. Commonly used materials include:

High-alumina castables

Corundum castables

Steel fiber reinforced castables

Used in the upper part of the grate, secondary combustion chamber, and flue area.

IV. Conclusion

Refractory castables are diverse in type and formulation, with varying requirements for binders, aggregates, micro-powders, and additives. When selecting castables, companies should consider factors such as temperature, operating conditions, corrosivity, construction methods, and budget to achieve optimal service life and economic benefits through proper material selection.