– Kiln and furnace engineering
Glass production and engineering processes are primarily high-temperature processes that demand from the equipment components used high load resistance in the prevailing operating conditions, especially where molten glass is involved.
For measurement and control purposes or for specific gas supply in glass melting furnaces, equipment and tank components made of Al2O3 and ZrO2 ceramics are frequently used.
Material purity higher than 99.5 % enables the cost-efficient operation of machine and plant components in oxidizing and reducing conditions even at temperatures well above 1500 °C. The small amount of foreign substance present is found predominantly at the grain boundaries of the microstructure. Its influence on the stability of the ceramics in operating conditions is low compared with that of less pure material types.
With the selective adjustment of the chemical composition of the grain boundary phase, the corrosion resistance of the ceramics and therefore their behaviour on contact with the molten glass and constituents of the furnace atmosphere can be favourably influenced.
Optimum design of the crystallite and pore size distribution in the microstructure enables products with a low tendency towards high-temperature creep and therefore with high long-term shape stability.
The main requirements to be met by the ceramic components used in glass melting equipment can be generally summarized as follows:
- Thermal strength
- Thermal shock resistance
- Corrosion resistance
- Creep resistance and dimensional stability
- Abrasion resistance
- Electrical insulation or electrical conductivity, depending on the measurement requirements
Some or all of the above-mentioned properties are generally required depending on the requirements of the type of molten glass. Generally, such requirements are reliably met by products made of high-grade oxide ceramic materials.
Oxide ceramic materials are also used on the finished glass products as components in machine tools. One material that has proven effective for such purposes for many decades is, for example, selectively doped Al2O3 ceramic, which achieves a significant increase in its hardness and therefore its abrasion resistance as a result of the incorporation of Cr3+ ions in the Al2O3 structure.