SPRUING AND GATING STONE IN WAX PATTERNS
It is recommended that larger than a normal feed sprue or gate be used for stone in place wax models since they will typically be cast at a lower than usual flask temperature and the additional sprue diameter will aide in the metal filling process.
It is advisable to sprue to the side of the patterns near to where stones are set, multiple sprues may be needed for feeding hot metal into some channel set styles of stone in wax patterns. * Be aware that metal hitting the stones directly could and can move and dislodge the stones from the investment holding themMake sure that there is a good full contact where the sprue meets the pattern; do not restrict the connection and use the full diameter of the sprue to make good contact with the surface of the wax model, restricted flow contact between the sprue and the pattern will prohibit the flow of metal to fill the pattern properly and cause time and labour to be lost.Stone in wax pattern trees can be made in any size/height to match flask capacities.Keep in mind that sometimes on trees larger than 6” tall, the metal force at the top of the tree may cause some flashing around the stone in place patterns. One way to avoid this problem is to tree standard patterns that are non stone in place on the first two levels of the tree then start your stone in pattern treeing on the third row.Conversely, try not to tree down too far on the bottom of the tree close to the button as the pressure for metal fill is lesser here and no fills are most likely to be experienced on the last row closest to the button, try to leave 10-20mm from the top of the button to the first row of wax patterns when treeing.Angle wax patterns outward at about a 45-degree angle as done for most other standard treeing procedures in order to assist in the smooth transition of metal entering the mould areas.When using a hot wax tool for sprueing be careful not to touch the wax patterns or to flood any wax over the stone in wax settings as this will result in metal being cast over the stone in the end product.Quality control all aspects of this process for the optimum quality results.Make sure that any pre-setting holes are open and not closed with wax.Remove any surface tension on the wax patterns by using an anti-static bath or spray on the whole tree.Make certain the tree is completely dry prior to investing.It may be necessary for some multi-stone type settings to position the set stones downward so that bubbles will not form under the stone in wax patterns when investing the tree.
INVESTING AND INVESTMENTS PRECIOUS STONES
For Precious stones you will need a special investment powder (SRS STONECAST) designed for stone in place casting or to make a chemical addition to protect the stones. In addition you will need to adjust your burnout cycle to a lower temperature and to a longer dwell at top temperature.
SRS recommends SRS STONECAST™ [link to SRS web site here] which is a pre-blended investment powder already containing the special additive to protect the stones.
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