Sprue refers to the supplementary part attached to the top or side of the casting in order to avoid defects. In the casting, the cavity of the sprue is a container for storing liquid metal, and its functions are manifold. Different functions of the riser, its form, size and opening position are not the same, so the design of the gate should consider the nature of the casting alloy and the characteristics of the casting. The role of the sprue is:
1. For alloys with small volume shrinkage during solidification (such as gray cast iron), or alloys that do not produce concentrated shrinkage holes (such as tin bronze), the role of the pouring gate is mainly to discharge the gas in the cavity and collect the liquid metal mixed with inclusions or oxide films at the front of the flow to reduce the defects on the casting.
2. For castings requiring control of microstructure, the pouring riser can collect the cooled metal liquid at the front of the flow to avoid supercooled microstructure on the casting.
3, for the large volume shrinkage during solidification and tend to form concentrated shrinkage of the alloy (such as cast steel, manganese brass and aluminum bronze, etc.), the main role of the pouring gate is to compensate the liquid shrinkage of the metal liquid in the cavity and the shrinkage of the casting during the solidification process, in order to obtain a dense casting without shrinkage.