Types, Formulations, and Applications of Refractory Castables
2025-11-18 10:20:23
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.