Wednesday, July 18, 2007

Outcast degassing instructions for casting

Palladium is a strange element that present certain unique problems to the jewelry caster. Unlike gold, silver, copper, and platinum, palladium can absorb hydrogen for later release as porosity or other major casting flaws. Outcast does not contain volatile elements.

As a result, Outcast (or pure Pd) can be degassed by placing in a casting machine that has a vacuum pump. Pull full vacuum, then heat the metal to full flow temperature (usually indicated on a SEIT optical pyro at about 1380C). After the palladium is at full molten temperatures, shut off the heat and allow the palladium to freeze. Repeat once. This will also allow you to see how your pyrometer reads Outcast. Use your safety lens protected eyes to establish how your pyrometer reads Outcast. Each pyrometer is set for a different emissivity. So, palladium readings are only consistent on a given machine. After this process you may cast.

To cast-Flood the casting chamber with your neutral gas, (argon may be best) place the crucible, close up the machine, reheat to full flow temperature, and cast. We suggest full torque. We suggest substantial sprues. Experience in Los Angeles suggests a very good results after three casts without fresh metal. One caster says the second or third time around is the best. This might indicate the degassing process works.

A phenomenon we see is that the gases tend to move to the last part to freeze. So, sprueing is critical. Whatever is the last part to freeze happens to be, voids and shrinkage will often be found. It is not uncommon for large voids to show up in the button.

Questions? Call daniel


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