The Classification of Lightweight Insulating Bricks Applied in Glass Kilns

2024-01-30

The lightweight insulating bricks used in glass kilns can be classified into six major categories based on their different raw materials. The most widely used are lightweight silica bricks and diatomaceous earth bricks. Lightweight insulating bricks have the advantage of good thermal insulation performance but exhibit poor compressive strength, slag resistance, and thermal shock resistance. Therefore, they cannot come into direct contact with molten glass or flames.

1. Lightweight Silica Bricks: These bricks are primarily made from silica stone with a SiO2 content of no less than 91%. The volume of lightweight silica bricks ranges from 0.9 to 1.1 g/cm3, with a thermal conductivity half that of regular silica bricks. They have good thermal shock resistance, and their softening onset temperature under load can reach 1600°C, significantly higher than clay-based insulating bricks. Thus, silica insulating bricks can be used at temperatures up to 1550°C. They are typically produced using crystalline quartzite as raw material, supplemented with combustible materials such as coke, anthracite, sawdust, or by gas foaming to create a porous structure.

2. Diatomaceous Earth Bricks: Compared to other lightweight insulating bricks, diatomaceous earth bricks have a lower thermal conductivity. Their usage temperature varies with purity, generally staying below 1100°C due to significant shrinkage and deformation at higher temperatures. Using pure diatomaceous earth requires firing at elevated temperatures, transforming silica into flake quartz. Lime can be added as a binder and mineralizer to facilitate the conversion of flake quartz during firing, improving the product's heat resistance and reducing sintering shrinkage at high temperatures.

3. Clay Insulating Bricks: These bricks are made mainly from refractory clay with an Al2O3 content ranging from 30% to 48%. The production process involves burnout addition and foam methods. Lightweight clay insulating bricks have a wide range of applications, primarily used in various industrial kilns as insulating layer refractory materials not in contact with molten substances and without other corrosive effects. The usage temperature is 1200 to 1400°C.

4. Alumina Insulating Bricks: These bricks have a high refractoriness and excellent thermal shock resistance, commonly used as high-temperature insulating layers in kilns. The usage temperature ranges from 1350 to 1500°C, while high-purity products can withstand temperatures up to 1650 to 1800°C. They are mainly produced from electrically fused corundum, sintered alumina, and industrial alumina.

5.Lightweight Mullite Bricks: Made primarily from mullite, these bricks are resistant to high temperatures, have high strength, low thermal conductivity, and can directly contact flames. They are suitable for lining various industrial kilns.

6. Hollow Alumina Bubble Bricks: Mainly used for prolonged use below 1800°C, these bricks exhibit good chemical stability and erosion resistance even at high temperatures. Compared to other lightweight insulating bricks, they have a higher safe operating temperature, greater strength, and lower thermal conductivity. Their volume density is also 50% to 60% lower than that of dense products with the same composition, making them able to withstand the impact of high-temperature flames.