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Steel pipe and the formation of shrinkage and prevention

by:BoQiao Machinery     2020-12-13
1. Shrinkage cavity, shrinkage porosity in the process of cooling solidification, the basic concept of casting due to the liquid contraction of alloy and solidification shrinkage, often appear in the last place the casting solidification holes. Large volume and relatively concentrated hole called shrinkage cavity; Small and scattered holes called shrinkage cavity. The irregular shape of shrinkage cavity, the surface is rough, you can see developed dentrite endings, it can clearly distinguish from the pores. If there is a shrinkage cavity, shrinkage porosity in the casting, on the one hand can make the effective bearing area of the casting is reduced, on the other hand caused by stress concentration, and the mechanical properties of castings to be significantly reduced. At the same time also reduce the air tightness and physical and chemical properties of casting. Especially for the pressure parts, prone to leakage and make the casting scrap. 。 2. The basic reasons for the formation of shrinkage cavity formation of shrinkage and shrinkage cavity, mainly due to the crystallization temperature range wide, alloy dendrites developed, liquid alloy solidification, almost at the same time liquid formation and solidification shrinkage of small, scattered holes without external metal caused by the supplement. Formed in the casting shrinkage and shrinkage tendency between alloy elements and has certain regularity. Directional solidification of alloys tend to produce concentrated shrinkage cavity; Paste solidification of alloys tend to produce shrinkage, the shrinkage cavity and the amount of shrinkage can be mutual conversion, but their total volume basic remain unchanged. 3. Factors affecting the size of shrinkage cavity, shrinkage porosity and prevention measures of casting alloy liquid contraction is larger, the greater the tendency of shrinkage cavity formation; The more alloy crystallization temperature range wide, the greater the solidification shrinkage, the shrinkage tendency to form. Whoever can cause decreased alloy liquid and solidification shrinkage process measures ( Such as adjusting the chemical composition, reduce the pouring temperature and slow pouring speed, increase the casting chilling ability, increase the feeding capacity, in the process of casting solidification during solidification for gray casting can promote the graphitization, etc. ) , is beneficial to reduce the formation of shrinkage cavity and shrinkage. According to the contraction of alloy and solidification characteristics make correct casting process, make the casting during solidification feeding conditions, establish good as much as possible to make the shrinkage into shrinkage cavity, in the final position of solidification and shrinkage cavity. The casting solidification process to make a good feeding conditions, mainly by controlling the casting solidification methods ( Set the riser and chill, is employed to) To meet & other Directional solidification principle & throughout; Or & other At the same time solidification principle & throughout; 。
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