Shell Investment Casting

FIGURE 12.37 Modem shell investment casting pattern production. 

It is interesting to note that 12-14 nm sols were the first products to become commercially available and at that time only 30% product was available. This product was used as delivered for most of the early shell investment casting work. The smaller particle size sols were not available then and the ability to produce the 12-14 nm sols at 40%, which we take for granted now, had not been developed. Thus, fortuitously, the first product available was produced at the optimum concentration for use as an investment casting binder. 

Steps in the production of a ceramic shell investment casting (from Ref. 

This process is used to produce intricate, thin-section parts with great dimensional accuracy, fine detail, and very smooth surfaces. All ferrous and nonferrous alloys can be cast in investment molds. Investment casting begins with expendable wax patterns that are assembled into clusters, then coated with a series of successively coarser ceramic slurries. The assembly is then fired in a furnace to dry and harden the ceramic shell and to melt out the wax, leaving a cavity into which molten metal is poured to form the casting. 

Roberts, W.O. Factors Affecting Shell Strength Investment Casting Institute Proceedings 25th Aimual Meeting. 

INVESTMENT CASTING, LOST FOAM CASTING AND SHELL MOULDING... 

Investment casting, lost foam casting and shell moulding... 

Briefly describe the shell moulding process. What tolerance can be expected on relatively small investment cast products ... 

A combination of colloidal silica with an organic polymer binder for making precision investment casting shell molds is patented by Emblem, Mountford, and Morely(516). 

Investment Casting. A process for the casting of small metal components to a close tolerance. In the usual process a wax replica of the part to be cast is coated ( invested ) with refractory powder, suitably bonded, and the whole is then warmed (150°C) to melt out the wax - hence the alternative name Lost-wax Process the refractory mould is then bred at 1000-1100 C. The refractory used may be powdered sillimanite or alumina, or specially prepared cristobalite the latter is particularly used in the application of the process in dentistry. B.S 1902 Pt 10 specibes methods for the determination of resistance to deformation at elevated temperatures permeability and standard air bow capacity at elevated temperatures thermal proble determination, for refractories for investment casting shell mould systems prefabricated brickwork, in which reinforcement is provided by steel rods running horizontally across perforations in the blocks. 

Figure 8.10 shows a ceramic shell ready for casting and typical products produced by investment casting are shown in Fig. 8.11. 

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