The Machining Advantage Of The Pump Valve Casting And The Surface Finish Of The Cavity
The pump valve casting mainly uses fusible material to make the meltable model, on which there are a lot of dry layer characteristics of the fireproof coating. After drying and hardening, it forms a monolithic shell. Then，use the steam or hot water to melt the model from the shell. Put the shell in the sand box, filled with dry sand molding, and finally put the mold into the baking furnace after high temperature roasting.
The dimensional accuracy of the pump valve casting is relatively high, generally can reach to CT4-6. Due to the complexity of the product process, the factors influencing the size precision of the casting are many, including the shrinkage of the mold, the deformation of the investment, the dimensional change of the shell in the heating and cooling process, the contraction percentage of the alloy and the deformation of the casting during solidification.
In the process of fusible pattern injection, the pump valve will adopt the profiling with high surface finish of the cavity. Therefore, the surface finish of the investment will be high. In addition, the shell is made of a refractory coating prepared by a special binder and refractory material with high temperature resistance. And the inner surface finish of the cavity which directly contact with the metal is high. Therefore, the surface finish of the product is higher than the general casting parts, generally up to Ra.1.6~3.2μm.
The greatest advantage of the pump valve casting is that the product has a high dimensional accuracy and surface finish. Therefore, in the operation，the machining operation can be reduced, only leaving a little finishing allowance on some parts with higher requirements. Even some castings only need sanding and polishing allowance, without machining operation.
The pump valve casting can cast various alloy castings, especially the complex of high temperature alloy castings can be casting. Such as jet engine blades, its outside profile and cooling streamlined with inner chamber, with the machining process can hardly formation. The investment casting process can not only produce batch production, ensure the consistency of the casting, but also avoid the stress concentration of the residual blade after machining.