Causes of corrosion and fracture of ceramic rollers and preventive measures

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The causes of corrosion and fracture of ceramic rollers and preventive measures were found during production. Ceramic rollers that have been used as insulation materials for a period of time are highly brittle and easy to break during replacement, maintenance, and cleaning. The fractures are light yellow and the texture is obviously different from new ones. This is caused by corrosion of the rollers. ? 1. Corrosion of roller rods The corrosion of roller rods is related to the vapors of metal oxides such as lead and alkali in specific areas of the kiln. The results of a study by the Italian ICRA laboratory show that: Preheating and firing zones have different contamination conditions. The composition of rollers that have been used for a long time will change greatly due to the selective accumulation of lead and alkali oxide vapor (the lead and alkali metal oxidation insulation materials brought into the kiln by the product volatilize at a certain temperature, and these vapors will flow toward the kiln head with the flue gas. Affected by changes in the temperature, pressure, and flow rate of the flue gas in the kiln, the steam will condense on the ceramic rollers in specific areas, which is called selective accumulation of corrosive elements) and permeate. Its composition will change greatly. Chemical analysis of contaminated rollers in the temperature range of 730 to 880°C showed that the PbO content was as high as 6% to 14%. ?The basic factors causing chemical corrosion of roller rods are: The glass phase produced by the material during use and the open pores of the material itself allow corrosive elements to invade the roller. ? 2 Breakage of the roller rod Chemical corrosion of the roller rod destroys various properties of the roller rod, such as the elastic coefficient, rigidity, strength, etc. of the insulation material, thus affecting the performance of the roller rod and the operating quality of the product. In addition, the serious consequence of chemical corrosion is the quenching crack of the roller rod. The roller rod was extracted from the kiln and placed in the air to cool naturally. When it reached a certain temperature, a large area of ​​natural fracture occurred. The quenching crack of the roller rod causes the consumption of the roller rod to increase sharply. ?Research shows: The glass body produced in the ceramic roller produces new crystal phases due to subsequent crystallization, such as: Anorthite, albite, garnet, spinel. The changes caused by vitrification and crystallization lead to changes in the physical and mechanical properties of the material, resulting in quenching cracks in the roller after being used for a period of time. ?In summary, the corrosion and fracture process of the roller rod can be summarized as: ?1) Inhalation of corrosive elements from the outside (through contact or gas phase exchange) ； ?2) Decomposition of existing phases (except ZrO2) ； ?3) The formation of the glass phase becomes a carrier for corrosive elements to invade the insulation material roller rod ； ?4) Crystallization of glass body ； ?5) Increase in pores at the contact surface between the corrosion layer and the ceramic material body ； ?6) The increase and expansion of micro-cracks and the different thermomechanical properties of crystalline insulation materials lead to quenching cracks during cooling. ? 3 Preventive measures Therefore, preventing the corrosion and fracture of the roller rod must start from the manufacturing and use of the roller rod. The main measures include the following: ?1) Alkaline oxides such as CaO, Na2O, K2O, MgO should be introduced into the formula as little as possible ； ?2) Improve the purity of raw materials and reduce the content of impurities such as Fe2O3 and TiO2 ； ? 3) Starting from the formulation and firing aspects, the insulation material should try to reduce the opening porosity of the roller rod. ； ?4) Apply a protective layer of alumina slurry on the surface of the roller, which is mainly composed of zirconium silicate, high-quality corundum sand and kaolin. The protective layer of alumina slurry, a thermal insulation material, protects against chemical corrosion on the surface of the roller and reduces the formation of adhesives on the surface of the roller. ； ? 5) Avoid pollution and corrosion from lead, boron and alkaline oxides ； ? 6) Do a good job in maintaining the rollers, and promptly replace and clean the rollers that are dirty and corroded insulation materials. This post was last edited by yutr on 2009-2-27 16:52 ]