ceramic kilns and refractories
January 22, 2021
Modern ceramic technology has greatly adjusted the chemical composition of ceramics, the types of raw materials and the structure of kiln.
(1) Characteristics of chemical composition change: enhancing flux action, reducing high temperature viscosity of liquid phase, but not significantly affecting firing temperature range. Taking sanitary ceramics as an example, the total solvent content increased from 5%~6% to 6%~8%, the RO content increased from 1.3% to 3%, the total amount of R₂O increased little, but the increase was mainly the content of Na₂O.
(2) Characteristics of raw materials: the use of good heat conduction, drying shrinkage, firing shrinkage and small linear expansion coefficient of raw materials, reducing quartz content and burning reduction.
The modern ceramic kiln adopts high speed burner, airflow stirring, air cooling; adopts the frame composed of prop-beam-shed plate to support the billet; adopts the kiln material with low heat storage, high strength, high heat conduction and high thermal shock resistance, and adopts super light weight, low heat storage kiln car and high heat preservation kiln body. Because of the significant enhancement of effective heat transfer and the great reduction of ineffective heat transfer, the technical and economic indexes such as output, fuel consumption, cost and life of kiln have been greatly improved.
A Properties of Common Ceramic Refractories
Boron nitride has poor oxidation resistance, quartz glass products have good thermal shock resistance, but there is crystallization tendency above 1100℃. Although the temperature and strength of cordierite materials are not high, they have good thermal shock resistance. Silicon nitride and silicon carbide materials have oxidation problems, but have high strength, thermal conductivity and thermal shock resistance. The use temperature of mullite-corundum material is very high and there is no oxidation problem, but the strength, thermal conductivity and thermal shock resistance are not ideal. Zirconia materials are difficult to sintering, high price and thermal shock resistance.
Silicon carbide, cordierite- mullite and mullite-corundum are selected as main kiln materials in modern ceramic kiln, and ceramic refractory fiber is used as main insulation material. Magnesium-aluminum spinel, zirconia and aluminum titanate materials can be used in special cases. Magnesium-aluminum spinel material is suitable for gaskets and containers for contact with alkaline materials. The introduction of zirconia in mullite products can improve thermal shock resistance. The use temperature of aluminum titanate is high, the thermal shock resistance is good, but the strength is low, the medium temperature is easy to decompose, especially in the reduction atmosphere. After improvement, the material of aluminum titanate reduces the disadvantages, and can be used in high temperature, rapid change of temperature and less long service time, such as making special crucible, filter and flow regulating device.
B Main Refractories in Modern Ceramic Kiln
Cordierite - mullite material is suitable for low temperature, low working stress and high thermal shock resistance. The low temperature fast burning kiln's shed board, the column, the cushion plate and so on often uses the cordierite - mullite material manufacture.
Silicon carbide is suitable for situations where the temperature is not very high and requires high working stress, high heat conduction and high thermal shock resistance. The materials of silicon carbide system are divided into oxide binding, reaction sintering and recrystallization silicon carbide materials and nitride binding. Oxide combined with silicon carbide is a low-grade kiln tool. However, the temperature should not be higher than 1350℃, which is suitable for low temperature fast burning kiln. recrystallized silicon carbide has good dimensional stability and high temperature bearing capacity, which is suitable for occasions where the temperature is higher than 1350℃. The effects of nitrides combined with silicon carbide vary greatly according to purity, mineral composition and microstructure. The mullite-corundum series is suitable for high calcination temperature, such as alumina ceramics and ferrite ceramics.