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　　 In recent years, many foundry enterprises have a headache about how to prevent shrinkage defects of large castings, because once such problems occur, they will give production. It has a great impact.

　　It is understood that the biggest problem in the production of large castings is the shrinkage defect. In order to solve this problem, many experts have studied it. Now the following points are summarized for solving the shrinkage defect of castings:

　　Firstly, change the position of inner runner of large castings.
　　Second, reasonable process design. The inner runner is located at the relative Pubi of the machine tool castings, which is scattered for many hours. The liquid metal that enters the thick wall first solidifies, and then solidifies at the thin wall, so that the equilibrium solidification is basically achieved everywhere. For machine tool castings with uniform wall thickness, multiple inner runners and vents are adopted. There are many internal runners, which are dispersed and evenly distributed, so that the overall heat is balanced. Exhaust holes are small and many, which means smooth exhaust and heat dissipation.
　　Thirdly, rapid solidification is carried out at the thick and hot spots formed by the structure of machine tool castings, which results in the basic balance of temperature field in all parts of machine tool castings artificially. The internal and external chills are used, and the heat-accumulating zircon sand, chromite ore or special coatings are used locally.