Study On Special Purpose Coating Of Squeeze Casting Of Iron And Steel

ABSTRACT:Die life was a restricted link of popularization and application of squeeze casting of high melting point alloys. Using coating on mold surface in squeeze casting to enhance the mold service life is one measure both economy and effective. At present there is still no special-purpose coating for squeeze casting of high melting point alloys. Therefore, in this paper, a special-purpose coating system and their component design, the performance test method, the physical chemistry and mechanics behavior of special-purpose coating of non-solid state pressure forming of iron and steel materials under the exploitation conditions were systematically studied. Based on these research results, the special-purpose coatings were developed for the high chromium cast iron, the high manganese steel and the plain steel.According to the characteristic of squeeze casting of iron and steel, the defined performance attribute parameters, spurtable index, high temperature adhesion and anti-fusion welding coefficient can respond essential performance of coating. Each test method of attributed parameter had been determined by the research. The experimental examinations and the error analysis indicated that the reliability of each test method is high, and which can meet the practical application needs.Through analysis of the mold working conditions in squeeze casting of iron and steel, the double-decked coating thought is proposed. This double-decked coating system includes thermal insulation layer-first floor coating and the refractory layer-surface layer coating. The first floor coating aggregate is diatomite; According to different alloys the surface layer coating aggregate respectively is ferrochrome powder, forsterite powder and bauxite powder. Sodium-bentonite and CMC are determined as the inorganic-organic compound deflocculant of coating. The research indicated that the spurtable index of the coating which using compound deflocculant was obviously higher than which using one kind of deflocculant alone, moreover in the compound deflocculant the bentonite content has a best value, this compound deflocculant suspension mechanism belongs to the electro-adsorption network bridge joint mechanism. Sodium silicate and sodium hexametaphosphate are determined as the compound cementing agent of the first floor coating, and high temperature adhesive strength of first floor coating presents a tendency which increases first and then reduce with the percentage increase of sodium silicate and sodium hexamedtaphosphate. Aluminum phosphate and the sodium hexametaphosphate are determined as the compound cementing agent of the surface layer coating, and high temperature adhesive strength of the surface floor coating obvious increases with the percentage increase of aluminum phosphate and increases first and then reduce with the percentage increase of sodium hexametaphosphate. The compound cementing agent is complex to the anti-fusion welding coefficient of the surface layer coating. The anti-fusion welding coefficient of the chromite-diatomite coating increases with the increasing of aluminum phosphate and the reducing of sodium hexametaphosphate. The anti-fusion welding coefficient of the ferrochrome-diatomite coating reduces with the increasing of aluminum phosphate and sodium hexametaphosphate; the correlation of aluminum phosphate and sodium hexametaphosphate can increase the anti-fusion welding coefficient. The anti-fusion welding coefficient of the bauxite-diatomite coating reduces with the increasing of aluminum phosphate and increases with increasing of sodium hexametaphosphate.Product problems found under the exploitation conditions, such as the possibility of the complex chemical reaction and phase-change occurring, and the stability of production were studied by using applied thermodynamics. The application temperature of the aggregate and the cementing agent are carried on the control. To avoid the forming of the low melting point ferrospinel, the chromites powder of less Al2O3 content should be chosen as the aggregate of chromites coating. To reduce the production of low melting point protobastite, the forsterite with high scale of MgO/SiO2 should be chosen for the forsterite powder. To produce high point mullite which can display fully fire performance of the aggregate, the bauxite which contains high percentage of Al2O3 should be chosen as aggregate of the coating.From analysis of mechanics, the main reasons which destroy special purpose coating for squeeze casting of iron and steel are the thermal load and the impact stress from liquid flow. The dynamic model of the coating's destroying was built, which indicates that the crack will expand, and the coating will quick break and flaking off when the sum of thermal load and liquid flow impact stress is higher than the critical stress on the coating material. The coating integrity mechanics criterion was obtained from this model. The strength of the coating can meet the requirements by controlling thermal load and liquid flow impact stress. Based on the comparison of the microscopic morphology and chemical composition of the coated and un-coated surface, it is found that the coating expiration mechanism is coating flaking in the micro crack.There are three kinds of special-purpose coating were developed, in the present work. They are chromite-diatomite coating for squeeze casting high chromium cast iron, ferrochrome-diatomite coating for high manganese steel and the bauxite-diatomite coating for plain steel. Compared with other commodity coatings, the special-purpose coatings have the advantages of easy availability, low price and low production cost. Performance test indicates that these coatings have the good nature of spurt spreads, high anti-wearing capability at high temperature, and excellent anti-melt welds capability. The achievements of this work ranked at the advanced level in China.