Study On The Process Of Eliminate Shrinkage Cavity And Porosity By Using Chills

With the development of science and technology, the casting requirements are increasing. But in the process of casting thin-walled ductile flanges, rejection rate remains high because of the generation of shrinkage cavity and porosity. For enterprises how to improve casting quality, solve the issue of shrinkage cavity and porosity conveniently and effectively is imperative.This paper researched the shrinkage porosity defects in the production of thin-walled ductile flanges. On the basis of understanding the formation mechanism of shrinkage cavity and porosity and the previous experience in the production, designed several production processes to prevent the emergence of shrinkage porosity, the principle is accelerate local cooling speed, improve cast temperature filed, balance the different thickness of the wall by adding cold iron.The chemical composition of molten iron is C3.6%-3.9%、Si2.5%-2.7%、 Mn≤0.3%、P≤0.03%、S≤0.03%、Mg0.04-0.06%、Re0.03-0.05%, clay sand molding, the gating system complied with the large orifice discharge theory. Used the ProCAST software to simulate the observation of the temperature field and solidification rate of the casting, Added chills in the hot spots of castings, the procession is using different thickness of directly outside of chills, different thickness of indirectly outside of chills and different sand layer of indirectly outside of chills.Through the method of visual test, ultrasonic examination combined with metallographic observation to detect the shrinkage of castings after machining the castings, through the method of microstructure and brinell hardness test to compared the performance of the castings, with the aim of getting the optimal scheme to produce thin-walled ductile flanges by using chills not only solve shrinkage cavity and porosity but also get good mechanical properties.The results showed that:when the direct external chills were used in the hot section of castings, the shrinkage cavities and porosities were eliminated when the thickness of chills were7mm, through the method of microstructure founded that the size of graphite ball decreased, while the number increased with the increase of chill thickness, but the cementite which is bad to the mechanical properties of the castings was also observed. In the process of using the indirect external chills, with the increase of chill thickness, the shrinkage cavity and porosity reduced, the diameter of graphite ball decreased, while the number increased, and the pearlite content in matrix sturcture increased, hardness increased. When the thickness of sand layer between casting and chill was decreased, the shrinkage cavity and porosity reduced, the diameter of graphite ball decreased, while the number increased, and the pearlite content in matrix sturcture increased, hardness increased. Used the moduli calculation method to verify the casting found that when the modulus of the hot section reduced to90%of the adjacent parts, the casting can be obtained without shrinkage cavity and porosity.