In order to prevent shrinkage cavity, shrinkage porosity, improve the density of organization, make the casting under pressure and no leakage, so to strengthen the feeding, make strong directional solidification. Increased, however, that the temperature difference of different parts of castings, the formation of thermal stress of castings, so led to the casting hot crack. In order to prevent the crack defects formation of castings, must take the following measures:

1.The use of cold iron castings. At the local small hot cracks easily occur (such as body and the flange used) put cold iron, accelerate the speed of solidification, the sequential solidification strength, implementation of a small scale solidification at the same time, to reduce the hot crack and shrinkage defects. Cold iron has fine grains, increase the role of local high temperature strength, castings used in cast steel three-way valve casting production, will be formed under overall directional solidification principle that local solidification principle at the same time, to prevent the formation of thermal cracking and shrinkage.

2.Achieve rapid pouring. Rapid casting, the filling time is short, less liquid steel cooling, the temperature is uniform, is beneficial to reduce the thermal stress, also easy to buoyancy inclusions, gas, etc.

In the process of production, the following process: (1) using macroporous out for design the cross-sectional area, in every guarantee the whole casting process of large flow, low speed, smooth, clean filling; (2) using ladle pouring flow is low, and make the sprue cup liquid level height and diameter of SPR to maintain a certain proportion, in case of slag and gas in cavity. (3) in order to prevent the gas or liquid steel in the choke when pouring, the box on the firm enough to vent, smooth discharge gas inside the cavity, the vent area should be greater than the SPR cross-sectional area.