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​What is the surface finish of an investment casting?

Investment casting is a large concept,we could also call it precision casting.In fact,investment casting consists of three castings processes(water glass casting,lost foam casting,silica sol casting).And each process have its own surface finish.

Water glass casting:Water glass casting is the most used process in investment casting.People always think it as lost wax casting.Lost wax casting is a process using wax as the casting process,so silica sol casting also belongs to this process.We could adopt water glass castings to make cast steel castings,like alloy steel investment castings,carbon steel investment castings from 0.5kg-100kg.Standard surface finish of water glass casting is 12.5 rms.

Lost foam casting:Lost foam casting is also an investment casting process.But it is produced for cast iron castings,like gray iron investment castings,ductile iron castings.But it is more suitable for small iron castings.For large iron parts,we can choose sand casting process,which surface finish will be worse.The surface finish of lost foam casting could be 12.5-15.0 rms,near to water glass casting.

Silica sol casting:The surface finish is silica sol casting is much better than other two investment casting processes.It could reach 6.3rms.So even with tight tolerances,we may not need to do machining.But the wax of silica sol casting is much better than that of water glass casting,so the production cost is much higher.Silica sol casting is more likely to make stainless steel investment castings.But for small alloy steel and carbon steel castings,if the budget is enough,this process is also feasible.