Classification Methods of Lightweight Castables

Classification Methods of Lightweight Castables

Lightweight castables can be categorized in various ways. Below are some of the main classification methods:

1. Classification by Porosity

• Dense Castables: Feature relatively low porosity, offering higher strength and density.
• Insulating Castables: Have a porosity of no less than 45%, mainly used for insulation and heat preservation to effectively reduce thermal conductivity.

2. Classification by Binder Type

• Hydraulic Bonded Castables: These harden at room temperature through hydration. Key varieties include castables made with silicate cement, ordinary calcium aluminate cement, pure calcium aluminate cement, and fused calcium aluminate cement.
• Chemically Bonded Castables: Harden at room temperature via chemical reactions initiated by additives. Common examples include castables bonded with water glass, aluminum sulfate, and phosphate.
• Cohesively Bonded Castables: Harden through sintering during the firing process. The primary example is clay-based castables.

3. Classification by Refractory Aggregate

• Clay-Based Aggregates: Contain 30%–45% alumina.
• High-Alumina Aggregates: Contain no less than 45% alumina.
• Silica-Based Aggregates: Contain no less than 85% silica and less than 10% alumina.
• Basic Aggregates: Typically include magnesia and dolomite.
• Special Aggregates: Include materials such as carbon, carbides, spinel, zircon, and nitrides.
• Insulating Aggregates: Examples include perlite, vermiculite, ceramic spheres, cenospheres, lightweight brick sand, porous clinker, and hollow alumina spheres.

4. Classification by Bulk Density

• Semi-Lightweight Refractory Castables: Have a bulk density of 1.0–1.8 g/cm³.
• Lightweight Refractory Castables: Have a bulk density of 0.4–1.0 g/cm³.
• Ultra-Lightweight Refractory Castables: Have a bulk density of less than 0.4 g/cm³.

5. Classification by Operating Temperature

• Low-Temperature Insulating Refractory Castables: Suitable for use at 600–900°C.
• Medium-Temperature Insulating Refractory Castables: Suitable for use at 900–1200°C.
• High-Temperature Insulating Refractory Castables: Suitable for use at temperatures above 1200°C.

In practical applications, lightweight castables can also be tailored to specific engineering requirements by incorporating mixed aggregates or special composite materials such as carbon fibers to achieve specific functional needs.

Conclusion

In summary, lightweight castables can be classified using diverse methods, each with unique advantages and applicable scenarios. Selecting the appropriate type of lightweight castable requires consideration of the specific operating environment and project requirements.