Allow a 2 hour set up time after investing the flasks before putting into a preheated steam de-waxer. The steam de-wax cycle should be limited to 1 hour maximum followed by immediate transfer to a preheated burn out oven set at 275 to 300 degrees F. Leaving flasks in a steam de-waxer longer than 1 hour can result in water marks on the castings or investment breakdown. Do not allow flasks to cool down once the de-wax cycle has started.
BURN OUT OVENS NEED ACCURATE CALIBRATION for gemstone in place casting. Incorrect temperature read outs can cause burning or discoloration of gemstones if overheating occurs. Be aware of any hot spots in the burn out oven that may cause uneven heating of the flasks.
BURN OUT OVENS USED IN THIS PROCESS, require adequate air inlet and exhaust. The bottom plate in the burn out oven should have grooves in it to allow proper air flow into the flasks. If the oven does not have grooves in the bottom plate some ceramic supports should be used to slightly elevate the flasks to allow better air flow into the main sprue area.
BURN OUT PROCEDURES FOR GEMSTONE IN WAX CASTING. There are 2 methods commonly used for gemstone in place casting, a low temperature method using regular investment and a higher temperature method using special investments or investment additives. Most manufacturers now use the higher temperature method with the special stone casting investments to protect the gemstones from heat.
BURN OUT CYCLE FOR THE LOW TEMPERATURE METHOD using regular investment mixes that do not contain additives to protect the stones:
STEAM DE-WAX - 1 HOUR
300 deg. F - 2 HOURS
500 deg. F - 2 HOURS
750 to 800 deg. F - 10 HOURS
DON’T EXCEED 850 deg. F