Research on Factors Affecting Surface Roughness of Investment Castings

During the process of casting and metal liquid solidification, the surface of the casting will oxidize due to the high temperature, and the oxide layer will be uneven. The metal oxide on the surface of the casting may interact with the oxide in the shell to promote the uneven surface of the casting, which is remarkable. Increase the roughness of the surface of the casting.

Cooling of the casting under a protective atmosphere is an important part of obtaining a high quality surface. After the casting is cast, it is cooled under an inert gas or a reducing protective atmosphere to prevent oxidation and prevent surface decarburization, and to protect the surface of the casting from the oxidation temperature. The surface of the casting with good surface protection is silver grey, silver white or colored oxidized color after shelling. Cleaning has a great influence on the surface roughness of investment castings. The as-cast surface roughness of investment castings is originally low, and blast cleaning or water sand cleaning should be used to clean the surface. The blasting method is better than the surface roughness of the shot peening casting by 2 or more. Peeling often destroys the as-cast surface.

For stainless steel investment castings with high hardness, shot peening can also be used to improve efficiency, but the diameter of shot peening should be less than 0.3mm.

In short, the surface quality of castings is an important quality index for investment castings. The surface quality includes two related and not identical concepts of surface roughness and surface defects. Surface roughness refers to the uniform microscopic unevenness of the surface of the casting. Castings with low surface roughness can be produced only by preventing serious defects on the surface of the casting, and the surface roughness of the casting is low to achieve high dimensional accuracy.

There are many factors affecting the surface roughness of investment castings. It is necessary to carry out a set of strict technological measures from raw materials, molding to cleaning to reduce the surface roughness of castings.