GENERAL COMMENTS ON BURNOUTCYCLE
Maintaining a sustained time period at the top of the burnout schedule will aide in the removal of much of the residual carbon in the mouldIt will not however eliminate all of the carbon from standard investments at this lower casting range.For investments that do not have any additives this may result in some slight gas porosity from the residual carbon which will combine with the free oxygen that can be liberated from the decomposition of the gypsum bonded investment forming CO2 gasAdditives in the investment help to protect the stones and also aide in eliminating carbon in the mould.Reused metal for stone in wax trees will eventually experience some degree of contamination from the low burnout temperatures resulting in SO2 gas exposure, which leads to gas porosity in the metal.Most metal used in the stone in wax process will require complete replacement more frequently than the more standard casting processes, where the metal being used can be refreshed with a percentage of new and continue to be used to a high quality of performance.
CASTING MACHINERY
Casting of a stone in wax jewellery can be done with either vacuum or centrifugal casting methods, however vacuum assist is generally preferred.
Remember to keep the metal temperature as low as possible to avoid heat shocks.Excessive metal pressure sometimes can lead to flashing of metal around the stones; this flash can usually be removed with a metal brush or wheel.The best choice of casting equipment is the machine that will offer the most accurate control of the metal temperature allowing for consistency and assisting in a quality end result in casting.
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