The shape of sands affect the surface much. Widely use are round, square and triangle sands. Triangle sands are the worst. The gap between sands are big during sands mixing. If it's resin sand casting, it costs lots of resins.
2)Required material of castings
Some materials are not suitable for sand castings, such as some materials with very low manganese. Components cast from such materials are with severe shrinkage and the surface is extremely rough.
3)Pouring system
If the pouring system is not designed reasonably, there will be shrinkage and insufficient cast defects. If the suppress slag system is not reasonable, the slags will flow into the casting cavities, which will cause the sand pore defects. This will affect the roughness.
4)Slagging
If the slags in melt iron waters are not remove enough or not filtrated clearly during pouring process, the slags will be poured into the cast cavity. This will caused the slag inclusion defects. This will affect the roughness.
5)Improper operation
Improper operation can also caused the casting defects and rough surface. Such improper operations include, sand not cleared enough during moulds assembling, sands not compacted during modelling, and wrong matching rate between sands. If the sands or the model is not strong enough, sand holes defects will be caused.
6)Percentage of P & S exceeded
If the P & S elements exceeded during material mixing, there will be cracks on the casting surface. This affect the surface roughness much.
According to experience, adding some high temperature resistances can improve the surface roughness of precoated sand casting. Such high temperature resistances can achieve solid phase sintering, which increase the roughness or smooth level of iron castings.
Edited by Santos Wang from Ningbo Zhiye Mechanical Components Co.,Ltd.
https://www.zhiyecasting.com
santos@zy-casting.com
86-18958238181