Metallurgy Interview Question:

We make aluminum moulds by press casting, can u suggest any thing so that the moulds should shine after casting?

Submitted by: Administrator

Shininess of castings depends on the surface quality of cast parts. Casting surface finish is always a function of mold surface and characteristics. The selection of mold materials and the accuracy of mold finish maintained in premium casting operations ensure that specified requirements are met. Sometimes there is the possibility of increasing surface finish of castings by increasing their surface tension. This is done for aluminum alloys by allowing formation of oxide inclusions, the most important of which is Al2O3, in the molten metal. The increase in surface tension prevents molten metal from penetrating into the mold depressions since as you know surface finish improves when the melt solidifies in contact with air. However, such a resolution is accompanied by decrease in mechanical properties of castings, as oxides will act as stress concentration sites.

By the way, I have not heard about usage of grain refiners as shine promoters for aluminum castings, though their application in such cases may rely on the same mechanism.
Submitted by: Administrator