Investment Casting Tolerance

As a precision casting process, the products produced by investment casting have high dimensional accuracy and low surface roughness values. Investment casting is a near net shape casting. Especially when silica sol is used as the raw material for making shell molds, the surface accuracy of investment castings can be better guaranteed. Therefore, the silica sol investment casting process is adopted by more and more metal foundries.

Silica sol is a typical water-based binder with a silicic acid colloid structure. It is a polymer colloidal solution in which highly dispersed silica particles are soluble in water. The colloidal particles are spherical and have a diameter of 6-100nm. The process of investment casting to make the shell is the process of gelling. There are many factors influencing gelation, mainly electrolyte, pH, sol concentration and temperature. There are many types of commercial silica sols, and the most used is alkaline silica sol with a silica content of 30%. In order to overcome the shortcomings of the long shell-making cycle of the silica sol shell, a quick-drying silica sol has been developed in recent years. The process of making silica sol shell is relatively simple. Each process has three processes: coating, sanding, and drying. Each process is repeated many times to obtain a multilayer shell of the required thickness.

The dimensional tolerance level of investment castings can reach CT4 ~ CT7. Among them, the dimensional tolerance grades of cast steel investment castings, cast iron investment castings, nickel-based alloy investment castings and cobalt-based alloy investment castings are generally CT5 ~ CT7. The dimensional tolerance level of light metal and copper alloy investment castings can reach CT4 ~ CT6.