Abstract:

Many different alloys are being cast using the investment casting process. Some alloys require the use of ceramic materials with extreme inertness and chemical stability in the face coat of the mould, while other alloys have far less stringent requirements. The ceramic system for the face coat must be selected in accordance with the reactivity of the alloy. While aluminium parts can be produced using an alumino silicate-based face coat, titanium and other reactive alloys require much more “high-tech” materials (like zirconia or yttria) in the face coat.

The requirements for backup coats are quite uniform. Sufficient mechanical strength, good dimensional stability throughout the IC process, and easy knock-out are needed, regardless of the alloy. Therefore, backup systems for various alloys can also be quite specific, from a technical point of view.

Synthetic minerals are certainly used in the IC process to provide necessary refractoriness and resistance against molten alloy attack. But, they can also be used to build shells with exceptional hot dimensional stability. Synthetic minerals are used to build shells designed to withstand high temperatures for an extended period of time, in SX and DS castings, and can also be adapted to ensure the tightest possible dimensional control during the production of turbo charger wheels. In this paper we will review mould systems particularly suitable for steel and stainless steel, for equiaxed casting of Ni-based alloys, and for Ti and TiAl alloys. We will discuss the selection of appropriate materials for the face coat for each alloy type, speak about ways to increase the build-up speed of the backup, and present application examples and case studies.