There are many factors affecting the surface quality of sand mold castings. From the aspect of sand mold, the material of sand mold, the particle size of raw sand, the strength of molding sand, the material of binder and so on are considered; The pouring process includes pouring temperature, pouring speed, head height, etc. Due to the complexity of sand casting process, the final surface of sand casting is affected by the interaction of many factors. The improvement effect of a single influencing factor should be verified by the test of sand casting in actual production, so as to provide inspection standards for the final optimization process. In addition, coating on the surface of sand mold and sand core is an important means to improve the surface quality of sand mold castings.
The mold coating layer is in direct contact with liquid metal, and its performance has an important impact on the surface quality of sand castings. Therefore, the feasibility of the improved process was evaluated by wet sand mold sand casting; At the same time, the influence of coating types on the surface quality of cylinder block sand castings was studied to further improve the surface quality of sand castings.
(1) The whole core assembly is poured vertically without coating. It is formed by 50 / 100 scrubbed sand core. The sand sticking and sintering in the lower half of the cylinder block is serious, and the finish of the upper half is relatively good; the influence of pouring form on graphite morphology, type and matrix structure is not very significant, which is within the standard provisions.
(2) Due to the thin wall of EA888 cylinder block, the pouring temperature is high and the flow capacity of liquid metal is stronger. Therefore, the dynamic pressure of sand adhesion of sand castings will increase, which will deepen the pores between molten iron and sand particles. The sand adhesion of EA888 cylinder block is mainly mechanical sand adhesion, while the proportion of chemical sand adhesion and mixed sand adhesion is small.
(3) Graphite, corundum and zirconium powder coatings have the same anti sticking effect; HA zirconium powder spray coating is slightly better than the current production state, but the problem of sand sticking at the ground corner of the cylinder block has not been completely solved; Fosco coating uses coatings with high and low specific gravity, and the sand mold has a layer phenomenon after ignition, but there is no abnormality on the surface of the sand mold casting, and ignition and non ignition There is little difference in surface quality of cylinder block.
(4) The research on the defects of cylinder water jacket shows that the use of fine-grained additives and dip coating 451 anti vein coating followed by spraying a layer of zirconium powder coating is conducive to the solution of sand sticking defects.
(5) Using the optimized process to produce cylinder block sand castings, the surface quality of cylinder block is significantly improved, the sand sticking defects at important parts are reduced or easily removed even in the later stage, and the scrap rate of cylinder block caused by surface quality is reduced to less than 1%.