Factors affect surface roughness of investment castings

The surface of investment castings would be oxidized for high temperature during metal liquid pouring and solidification process.As the oxide layer is uneven and metal oxide on the casting surface would have effect on oxide in shell.Prompting uneven falling from of investment casting surface,which will obviously add the surface roughness of investment castings.

Casting cooling under protective atmosphere is one of the most important aspects of the high quality surface.For example,investment castings after pouring,cooling under the condition of inert gas or reducing atmosphere,combine preventing oxidation with preventing surface decarbonization until casting surface could not reach oxidation temperature.After shelling,the surface of investment castings with good surface protection is silver,silver white or oxidation color.Cleaning surface also have great infulence on surface roughness of investment castings.As roughness of cast surface is low,so we should choose sand blasting,or water sand cleaning way to clean the surface.Sand blasting method is twice better than shot blasting which often damages casting surface.To stainless steel investment castings,we could also adopt shot blasting method to improve efficiency.But the shot blasting diameter should be less than 0.3mm.

In a word,surface quality is a very important factor on investment castings.Surface quality include surface roughness and surface defects.Surface roughness refers to the even mircoscopic roughness of casting surface.Therefore,there are many factors that affect surface roughness,we need to preform a set of strict measures from raw material,molding to clearance to reduce casting surface roughness.