High alumina castables represent a type of refractory concrete made of refractory aggregates bound together using a high alumina cement matrix. These castable refractory mixtures find wide application as insulation lining in industrial furnaces and equipment operating at high temperatures. Here are key details about high alumina castables and their uses.

High alumina castables contain Refractory castable bound by a high alumina cement that sets and hardens to form a monolithic insulation lining for industrial furnaces and high temperature process equipment.

What are High Alumina Castables?

High alumina castable consist of:

• Refractory aggregates: Made using bauxite, mullite or chamotte to provide heat resistance. Aggregates range in size from micrometers to millimeters.
• High alumina cement: Binds aggregates together using a cementitious matrix based on aluminate phases. Provides the paste portion in castables.
• Additives: Inclusions like silica sol, zircon, graphite etc. to enhance properties for specific uses.

Through a chemical reaction between alumina in aggregates and cement, high alumina castables set and harden, forming monolithic refractory linings suited for high temperature applications. Available in dry premixed or ready mix wet formulations, high alumina castables offer insulation in lining thicknesses up to several inches.

Properties

High alumina castables offer:

• High temperature stability: Withstand temperatures up to 2900°F (1590°C) in reducing atmospheres.
• Low thermal conductivity: Rely on entrapped air in pores to impede heat flow for thermal insulation.
• Good refractoriness under load: Withstand pressure, impact and vibration at elevated temperatures.
• Chemical resistance: Remain stable when exposed to various molten slags and industrial gases.
• Abrasion resistance: Tolerate wear during service life to provide durability.
• Low creep: Minimize dimensional change at elevated temperatures for consistent insulation.

Applications

High alumina castables find key applications as:

• Lining for steel making furnaces to protect shell plates from molten metal and slags.
• Insulation lining for kilns, reheat furnaces and melting furnaces used in ceramics and glass.
• Back-up insulation in boiler combustion chambers and flues for reducing heat losses.
• Channels and walkways in industrial furnaces for operators and equipment.

Key Factors

Other factors to consider when selecting high alumina castable include:

• Aggregate shape and size: Affects castable properties like flow, permeability and strength.
• Cement content: Determines castable setting time, mechanical properties and temperature resistance.
• Castable rheology: Dry castables require addition of water while wet castables need mixing before use.
• Additives and impurities: Influence properties like thermal shock resistance, creep resistance and corrosion resistance.