As the technological capabilities of the Precision Investment Casting process continue to evolve, the requirements placed on the ceramic shell are ever more demanding. Process parameters, such as temperature and materials selection, influence the ceramic shell’s properties and its ability to yield the desired cast piece with the proper specifications and attributes. One such casting application that lays great demands on the shell system is the aerospace casting industry and especially the blade and vane segment.

Both directional solidification (DS) and single crystal (SC) casting processes expose the shells to a high temperature (~ 1500 C) for a long period of time (~ 2 hours) under the load of metal melt. The rigorous processes require the shells to possess adequate high temperature strength and creep resistance at levels that are much more stringent than those normally required in commercial foundries. The requirements can only be achieved by choosing the right combination of refractory and binder for the backup slurry.

A specially designed colloidal silica binder was developed to meet the high temperature demands of the process as well as to successfully create shells for the specific geometric complexity of the trailing edge of a blade casting. This paper will compare the specialty colloidal silica binder to traditional colloidal silica sol. Laboratory test data will be presented to highlight the above properties.

Rolls-Royce plc implemented this specialty binder in production at their Derby operations. Information on the process of converting to this new binder will be presented. This information will highlight the benefits of this binder to the existing process and will also present some of the hurdles that needed to be cleared in order to completely implement the binder into production.