Generally speaking, casting usually use the gravity casting sand. Certainly it also could take low pressure casting or centrifugal casting process if there is special requirement. Sand casting could be adopted by small, large, simple piece, complex parts, single and large quantities. The molds that made by sand casting are wood and they are also called wood mold. But the wood mold is easy to be broken or deformed. Casting has higher refractoriness than metal types mold.
However the sand casting also have many disadvantages. Every sand mold could be pured for only one time. The casting is easy to be damage and must be processed again. So the production efficiency of sand casting is usually low. The casting dimension with rough surface is in low precision because of the overall properties of sand soft is soft and with many porous.
Some water pump castings is fed with riser. Then resection riser and return remelting. This will increase the casting cost, and lost a part of metal. The riser size has direct relationship with section thickness and shape. The structure which can reduce shrinkage hole and shrinkage porosity is helpful to reduce riser and even eliminate. Sometimes it cause directional solidification by increasing the wall thickness of casting. Water pump casting weight increased, but it can reduce the consumption of riser metal greatly. In contrast it still reduce the metal consumption.
