ฝังพลอยที่เทียน( wax set) กับ คุณสันต์ ภาณุสฤษฏิ์ -2

DEWAX AND BURNOUT CYCLES SRS do not recommend steam dewaxing for stone in wax casting of diamonds or precious stones where a special investment or additive has been used. There is a danger that the steam will wash away the additive protecting the diamonds. If you do steam dewax take great care that the steam is not too aggressive.There are however good reasons for using steam dewaxing.Wax carbons must be removed as much as possible at the beginning of the cycle end since the burnout temperatures are lower in the stone in wax processResidual carbon left in the mould can result in metal casting defects and effect the quality of the metal in the final product.Load flasks into a pre-heated steam de-waxing unit and de-wax for one hour then transfer the flasks immediately into a pre-heated oven set at 150° C (302° F)Do not allow the flasks to cool down below the boiling point of water, (220° F). This will help reduce the chance of any rapid heat changes that can stress some stones set in wax, facilitating and speeding up the wax elimination process.BURNOUT CYCLE FOR STONECAST INVESTMENT (DIAMONDS & PRECIOUS STONES)BURNOUT CYCLE FOR NON PRECIOUS STONES CZ ETCGENERAL COMMENTS ON BURNOUTCYCLEMaintaining 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.OVERLOADEDGOOD STACK ALLOY SELECTION A wide variety of silver and gold alloys work well for stone in wax casting, some casters prefer alloys that contain de-oxidizing agents and alloys with low shrinkage rates which are most suitable for this process.Do not over heat the alloy as this will add to the total system temperature applied to the mould and stones and can cause burningit is generally acceptable to slightly super heat an alloy by 100-150° C over the liquidus range of the alloy.Always consider that the stone in the mould is experiencing a total system temperature, which is the combination of the flask, and the metal temperatures and this combined temperature effects the ambient temperature experience within the core of the mould. * The flask should be cast at the lowest possible temperature to still fill the patterns with out burning the embedded stones.Sterling, yellow gold’s of various karats, white gold including Palladium white gold, have all been cast successfully using the stone in wax process.Flask cooling and investment removal:It is important that the cast stone in flask be allowed to properly cool prior to performing any devesting processes. Quenching a hot flask of stone in patterns can shock the stones and result in extensive damage to the patterns. An appropriately cooled flask should be cool enough to be held in the hand and depending upon the size of the flask, will take two hours or longer. Waiting this long for a flask makes the investment more difficult to remove and will make the metal very soft however this waiting period will prevent the gemstones from experiencing thermal shock and cracking.Never quench the stone-in flask in water while it is still hot as the thermal shock will certainly break the stones!A simple dry process is as follows:Wait 45 minutes after castingDo not quench in water but tap bottom of tree and sides of flask with small hammer.At this point the casting normally falls out of flask. The powder falls off the stones easily but is caked onto the metal.Wait for the tree to be hand hot i.e. so that you can pick it up without gloves.Holding the tree gently in your hand tap the bottom of the tree so that it vibrates gently.Most of the powder will fall off.To clean finally use water jet under pressure.Thoroughly check the tree for any loose or missing stones and account for these before continuing with any further finishing processes.FINISHING PROCESSClip the stone in cast patterns from the tree and carefully quality inspect them for any defects.Hand polishing is always a method of finishing for stone in castings however if careful quality control was performed on the front end of the process most castings should be suitable for mass finishing using mechanical tumbling or magnetic pin finishing.It is important to choose polishing media that is non aggressive and do not attach the stone facets and surfaces.Certain types of ceramic and steel shots are considered dangerous for softer stones while materials like plastic medias and organic wood based medias are more appropriate.Steel shot can also work harden your pieces so it is best to watch the times closely if this process is used. Diamonds are not damaged by steel medias and suitable finishing options are by magnetic finisher.SRS recommend OTEC, Germany as a suitable supplier of mass finishing machinery for stone in wax cast pieces.Consult your supplier for recommended medias for finishing stone in castings.SOLDERING ON STONE IN CASTINGSMost gemstones that can withstand the heat of a torch can be soldered on after stone in wax casting.Stones like CZ will likely stress and break from the concentrated heat of soldering so castings with CZ should not be worked on with a torch after casting.Some stone in wax casters have begun to use laser welding units to repair minor issues in stone in castingsPoorly cast or damaged stone in castings should be scrapped and lessons learned for future preparation of master models and wax patterns.Direct technical helpIf you need any direct technical help please feel free to contact the following SRS personnel:Stone in wax setting enquiries:Mr Peter Croton, peterc@srs-ltd.co.ukMr Martin Cookson martinc@srs-ltd.co.ukGeneral casting enquiries:Mr Peter Croton, peterc@srs-ltd.co.ukMr Martin Cookson, martinc@srs-ltd.co.uk