Key refractory materials in high temperature industry - high alumina castable | Technology Frontier
2025-07-02 15:23:04
I. Overview of high alumina castable
High alumina castable is a refractory castable material made of high alumina bauxite as the main raw material and a variety of additives. It belongs to an important category of amorphous refractory materials. Compared with traditional refractory bricks, high alumina castable has the characteristics of simple construction, good integrity, and excellent thermal shock resistance, and plays an irreplaceable role in modern high temperature industry.
This material is mainly composed of three parts: high alumina aggregate (usually Al2O3 content between 55%-80%), fine powder matrix and bonding system. Its performance advantages are mainly reflected in high temperature strength, slag corrosion resistance and thermal stability, making it an ideal lining material for high temperature equipment in metallurgy, building materials, chemical industry and other industries.
II. Main characteristics of high alumina castable
(I) Physical and chemical properties
The most notable feature of high alumina castable is its high alumina content (usually ≥55%), which directly determines its excellent high temperature performance. Its main technical indicators include:
- Refractoriness: usually ≥1750℃
- Bulk density: 2.3-2.8g/cm³
- Flexural strength at room temperature: 5-15MPa
- Flexural strength at high temperature (1400℃): 3-10MPa
- Linear change rate (1600℃): ±0.5%
(II) Thermal properties
High-aluminum castables exhibit excellent thermal stability:
- Thermal expansion coefficient: 5.0-7.0×10??/℃ (20-1000℃)
- Thermal conductivity: 1.5-2.5W/(m·K) (1000℃)
- Specific heat capacity: 1.0-1.2kJ/(kg·K)
(III) Mechanical properties
After proper heat treatment, high-aluminum castables can form a strong ceramic bond, showing:
- Room temperature compressive strength: 30-80MPa
- Low high temperature creep rate (1400℃, 0.2MPa, 50h): <1.0%
- Excellent thermal shock resistance (1100℃ water cooling): >30 times
III. Production process and technical points
(I) Raw material selection
The quality of high-alumina castables depends first on the selection of raw materials:
- Main raw materials: high-alumina bauxite clinker (Al2O3≥75%), sintered corundum, fused corundum, etc.
- Binder: pure calcium aluminate cement, silica powder, alumina powder, etc.
- Additives: dispersant (such as sodium tripolyphosphate), water reducer, explosion-proof fiber, etc.
(II) Ratio design
Typical high-alumina castable formula includes:
- Aggregate (5-3mm): 35-45%
- Intermediate particles (3-1mm): 15-20%
- Fine powder (<1mm): 35-40%
- Binder: 4-8%
- Additive: 0.1-1.5%
(III) Production process
The production of high-aluminum castables mainly includes the following steps:
1. Raw material pretreatment (crushing, screening)
2. Accurate batching (weighing according to the designed formula)
3. Even mixing (forced mixer)
4. Packaging (moisture-proof treatment)
5. Quality inspection (sampling and testing various properties)
IV. Application areas and construction points
(I) Main application areas
High-aluminum castables are widely used in:
- Iron and steel industry: ladle, tundish, heating furnace, iron outlet, etc.
- Cement industry: rotary kiln mouth, preheater, tertiary air duct, etc.
- Petrochemical industry: catalytic cracking unit, gasification furnace, etc.
- Nonferrous metallurgy: aluminum electrolytic cell, copper smelting furnace, etc.
- Waste incineration: incinerator lining, flue, etc.
(II) Key construction technologies
To ensure that high-aluminum castables can achieve optimal performance, attention should be paid during construction:
- Formwork production: ensure accurate dimensions, sufficient strength and rigidity
- Mixing process: strictly control the amount of water added (usually 5-8%), and the mixing time is 3-5 minutes
- Casting construction: layered vibration, each layer thickness does not exceed 300mm
- Curing system: wet curing at 20-35℃ for 24-48 hours
- Baking curve: formulated according to material properties, usually 5-7 days to gradually increase the temperature to 800℃
V. Technology development trend
With the continuous improvement of high-temperature industry's requirements for material performance, high-aluminum castables are developing in the following directions:
(I) Low cement/ultra-low cement technology
By optimizing the micro-powder system and dispersant, the cement content is reduced to less than 3% to improve high-temperature performance.
(II) Application of nanotechnology
Introduce nanomaterials such as nano-alumina to improve the sintering performance and mechanical properties of materials.
(III) Self-leveling technology
Develop high-aluminum castables with self-leveling properties to simplify the construction process and improve the uniformity of the lining.
(IV) Environmentally friendly materials
Develop high-aluminum castables that do not contain harmful elements such as chromium to meet environmental protection requirements.
(V) Functional design
Develop special castables with special functions (such as resistance to alkali corrosion, resistance to CO corrosion, etc.) for specific working conditions.
VI. Conclusion
As an indispensable key material in modern high-temperature industry, the technological progress of high-aluminum castables is directly related to the production efficiency and energy consumption of related industries. With the continuous development of materials science, the performance of high-aluminum castables will be further improved, and the application field will continue to expand. In the future, intelligent production, precise construction and full life cycle management will become important directions for the development of high-aluminum castable technology, providing stronger support for the sustainable development of high-temperature industry.