Top 9 Refractory Bricks for Glass Kilns – Types & Working Principles Explained

Glass kilns are the core equipment in glass production, and refractory bricks serve as one of their most critical components. These bricks endure extreme temperatures and chemical corrosion, playing a vital role in ensuring continuous production and product quality. This article provides a detailed introduction to 9 common types of refractory bricks used in glass kilns, along with their working principles.

1. Silica Brick

Silica bricks, as acidic refractory materials, play a crucial role in the glass industry. Their primary component, tridymite, grants them exceptional high-temperature resistance, making them ideal for constructing high-temperature zones in glass kilns. Their load deformation temperature ranges between 1640°C and 1680°C, close to the melting points of tridymite and cristobalite (1670°C and 1713°C, respectively), ensuring structural stability under extreme heat.

High-quality silica bricks exhibit outstanding physical and chemical properties:

• High purity and dense structure enable resistance to extreme temperatures without significant deformation.
• High load softening temperature, low reheat shrinkage, and excellent high-temperature creep resistance ensure structural integrity during glass melting.
• Strong room-temperature compressive strength, optimal mineral composition, low true density, and precise dimensions enhance their suitability for glass kilns.

However, as glass kilns grow larger and melting temperatures increase, silica bricks face challenges due to their relatively low refractoriness (1690°C–1730°C) and poor thermal shock resistance (only 1–4 water-quench cycles). These limitations make them unsuitable for high-temperature areas like the crown of the melting zone. Nevertheless, they remain the preferred refractory material for the upper structures of cooling sections.

In summary, silica bricks are indispensable in glass kilns, offering unmatched performance in high-temperature applications despite certain limitations.

2. Fireclay Brick

Fireclay bricks, slightly acidic refractory materials, hold significant importance in the ceramic and glass industries. Their unique chemical composition and physical properties make them ideal for specific applications.

Key characteristics:

• Refractoriness up to 1700°C, but load softening temperature around 1300°C, limiting their use in high-load, high-temperature environments.
• Low thermal expansion, fine crystalline structure, and uniformly distributed small pores grant excellent thermal shock resistance, making them stable under rapid temperature changes.
• Effective thermal insulation due to reduced thermal conductivity with increasing Al₂O₃ content.

Fireclay bricks are commonly used in secondary kiln sections, such as flues, where they provide durable insulation and stress buffering.

3. High-Alumina Brick

High-alumina refractories contain over 48% Al₂O₃ and are classified into three grades:

• Grade I: Al₂O₃ > 75%
• Grade II: Al₂O₃ 60–75%
• Grade III: Al₂O₃ 48–60%

Performance Highlights:

• Higher refractoriness and load softening temperature than fireclay bricks, ensuring stability in extreme heat.
• Enhanced thermal conductivity, reducing heat stress accumulation.
• Thermal shock resistance between fireclay and silica bricks, making them ideal for glass kiln crown insulation layers and edge bricks.

The Al₂O₃ content directly influences microstructure and performance:

• Below 71.8% Al₂O₃: More mullite crystals form, improving strength.
• Above 71.8% Al₂O₃: Corundum (α-Al₂O₃) increases, enhancing hardness and erosion resistance.

4. Sillimanite Brick

Sillimanite and mullite bricks are preferred in glass kilns due to their:

• Higher load softening point than fireclay bricks, ensuring stability under extreme heat.
• Dense, fine-grained structure, minimizing bubble formation when in contact with molten glass.
• Ideal for critical zones like glass discharge outlets, ensuring smooth glass flow.

5. Mullite Brick

Mullite bricks, with mullite (3Al₂O₃·2SiO₂) as the primary crystal phase, offer:

• Refractoriness up to 1850°C.
• High load softening temperature and low high-temperature creep.
• Superior thermal shock and acid slag resistance.
  Commonly used in vertical flues and horizontal flue linings in glass factories.

6. Fused Mullite Brick

Produced from high-purity bauxite, fused mullite bricks contain:

• 72% Al₂O₃ + 28% SiO₂, forming mullite and corundum crystals.
• 7–8.5% ZrO₂ addition refines crystals, reduces cracks, and enhances glass corrosion resistance.
• Used in flue structures due to low thermal expansion and excellent thermal shock resistance.

7. Fused Zirconia Corundum Brick (AZS Brick)

AZS bricks (Al₂O₃-ZrO₂-SiO₂ system) are classified by ZrO₂ content (33%, 36%, 41%).

Advantages:

• Superior glass corrosion resistance due to corundum + zirconia crystal phases.
• ZrO₂-rich glass phase forms a high-viscosity protective layer, slowing erosion.
• Used in severe erosion zones (e.g., tank walls, kiln crowns).

8. Fused Corundum Brick

Made from high-purity Al₂O₃, fused corundum bricks feature:

• 45–55% α-Al₂O₃ + 45–60% β-Al₂O₃, forming an interlocking crystal structure.
• Exceptional erosion resistance, second only to pure α-Al₂O₃.
• Ideal for glass tank walls and melting zone crowns.

9. Zirconia-Containing Refractories

These materials (containing ZrO₂ or ZrSiO₄) offer:

• Melting points up to 2677°C, usable at 2500°C.
• Low thermal conductivity and high mechanical strength (up to 1500°C).
• Excellent resistance to molten glass, making them ideal for glass furnace linings.

10. Conclusion

The 9 refractory bricks used in glass kilns each have unique compositions and properties, ensuring optimal performance in different zones. Selecting the right brick is crucial for production efficiency and product quality. By understanding their working principles, glass kiln designs can be optimized for higher durability and performance.