What is the preparation principle of wear-resistant and refractory castables?

The preparation principle of wear-resistant and refractory castables is based on the comprehensive application of materials science and high-temperature engineering. By optimizing the raw material ratio, microstructure design, and process control, the synergistic improvement of high wear resistance, high temperature resistance, and mechanical strength is achieved. The following is a detailed analysis of its core principles:

1、 Raw material selection and proportioning design

High hardness aggregate dominates wear resistance

High melting point (>2000 ℃) and high hardness (Mohs hardness ≥ 9) materials such as fused alumina (white corundum, brown corundum), silicon carbide, zirconium corundum, etc. are used as aggregates, accounting for 60%~70%. Through multi-level particle grading (3-4 levels), tight packing is achieved to reduce porosity.

Functional aggregate supplementation: such as silicon carbide (SiC) to enhance thermal shock resistance, and zircon micro powder (ZrSiO ₄) to enhance corrosion resistance.

Synergistic strengthening of powder and binder

Ultra fine powder filling: Silica micro powder (particle size ≤ 0.1 μ m) is used to fill the gaps between aggregates, reducing water demand and increasing density.

Adhesive selection:

Hydraulic combination: Calcium aluminate cement (low calcium type) or ρ - Al ₂ O3 forms high-temperature stable aluminate crystals through hydration reaction.

Chemical bonding: Phosphate or silica sol forms a network structure through thermal hardening, with a temperature resistance of up to 1600 ℃.

Functional regulation of additives

Reinforced fibers: stainless steel fibers (resistant to mechanical impact), polypropylene fibers (anti explosion).

Dispersant: Polycarboxylate water reducer optimizes flowability and reduces water addition to 5%~6.5%.

2、 Principles of microstructure optimization

Tight packing theory

By combining coarse (5-20mm), medium (0.15-5mm), and fine (≤ 0.088mm) particles, the powder further fills the micropores and forms a dense structure.

Application of nanotechnology: Introducing nano alumina or zirconia to refine grain size and enhance interfacial bonding strength.

High temperature phase transition control

The binder generates high melting point phases (such as mullite and corundum) during the sintering process, avoiding the formation of low melting points (such as plagioclase) and ensuring high temperature stability.

Expansion compensation: Add bluestone powder (converted to mullite and expanded at 1200-1400 ℃) to counteract high-temperature shrinkage.

3、 Key steps of preparation process

Mixed process

Dry mixing: Dry mix aggregates, powders, binders, etc. for 2-3 minutes until uniform.

Wet mixing: Control the amount of water added (5.5%~6.5%), wet mix for 3-5 minutes to avoid fiber aggregation.

Forming and maintenance

Vibration compaction: After pouring, vibrate to remove bubbles and ensure that the density is greater than 2.8 g/cm ³.

Maintenance system:

Curing with mold for 24-48 hours (above 20 ℃).

Wet curing for 5-7 days after demolding (covered with wet burlap bags).

Baking and sintering

Three stage baking:

Eliminate free water at 110-115 ℃ (24-48 hours);

Remove crystallization water at 350 ℃ (24-48 hours);

After being uniformly heated at 600 ℃, it rises to the working temperature.

High temperature sintering: Some prefabricated parts need to be baked at 1500 ℃ to form a stable crystal structure.

4、 Performance control mechanism

Improved wear resistance

High hardness aggregates (such as SiC) directly resist wear, tightly packed to reduce peeling.

The normal temperature wear amount is ≤ 10 cm ³ (ASTM704C standard).

Thermal shock resistance design

Low thermal expansion aggregates (such as zirconia alumina) combined with microcrack toughening (fibers or nano additives) can withstand water cooling cycles of 1000 ℃ for at least 30 times.

Chemical resistance

High purity raw materials (Fe ₂ O3<0.05%) reduce slag infiltration, while chromium oxide micro powder (Cr ₂ O3) inhibits alkali corrosion.

5、 Application scenario adaptation

Cement industry: C4/C5 feeding pipes are made of silicon carbide castables to resist skinning.

Power industry: The lining of circulating fluidized bed boilers is mainly made of corundum silicon carbide system.

Metallurgical industry: The lining of the steel trough needs to be prefabricated and baked at high temperature.

Through the comprehensive application of the above principles, wear-resistant and refractory castables have achieved long-term stable service in high temperature and high wear environments. The specific formula and process need to be dynamically adjusted according to the working conditions (temperature, medium, mechanical stress, etc.).