Castings

Casting "PureGold" is easily accomplished and anyone familiar with platinum casting will have no difficulties. The microalloy freezes very quickly and care must be taken to ensure there is an adequate supply of molten metal to the solidifying piece. Therefore, gating is critical as is the design of the piece. Casting should be carried out in an inert atmosphere since one of the elements added to increase the hardness and cold work strengthening of the microalloy is reactive to oxygen when molten. Moreover, since alloy melts at 1073.9°C, it is best to use an induction heated melting device. A casting temperature of 1175°C is a recommended starting point for most patterns and a flask temperature of 600°C. These can be fine tuned depending on the models being cast and their degree of fine versus heavy metal sections. This casting temperature also indicates that the investment should be phosphate bonded as the temperature where gypsum bonded investment begins to decompose. A gypsum bonded investment can be used of the wax patterns are first coated with a ceramic emulsion before investment. The ceramic shell prevents contact of the molten metal with the gypsum. It also provides a very fine surface to the cast pieces.
The narrow freezing range indicates that gating is critical for successful casting. There should be no transitions from thin to thick metal sections without a supply of molten metal to the thick section being filled by the gate.
Following casting and cool down period (at least thirty minutes is recommended), investment can easily be removed with a high pressure water stream. Any oxidation on the castings that might result from residual oxygen in the flask can be easily removed with a quick rinse in pickle. Following removal of the gates, and before final finishing, the age hardening step is completed. First, the castings are brought to a uniform state by heating to 800°C for 30 minutes followed by quenching. Then casting can be age hardened at 250°C for three hours. They are then allowed to air cool. Both of these steps can be carried out in air. air.