The following are excerpts from a training manual for Gemini Platinum, a jewelry manufacturing company. This manual was designed to be a straightforward step-by-step procedural documentation for employees already familiar with the terms and processes involved.
Sprueing
Sprueing is one of the most important steps in the casting process. If the gates (the areas joining the sprue with the shank of the ring) are shaped incorrectly, the molten platinum will not fill the mold properly. We use a slightly larger gate system than average in order to ensure proper mold fill. The excess metal that will be on the finished casting from the gates can be filed away during finishing.
- Using a 5mm round red sprue tube, cut the sides down so that you are left with an approx. 2.5mm X 5mm rectangle. (Fig 1)
- Join the sprue tube to the shank of the wax mold using Lo-Melt sprue wax (gold chunks located at sprueing station).
- Using the fine wire tip wax pen, smooth the edges of the joint where the sprue tube meets the shank so that there are no sharp edges (Fig. 2). There should be enough excess Lo-Melt wax from Step 2 so that you can smooth the edges of the joint without having to add more wax.
- Set the assembled sprue/wax mold aside for 5 minutes to cool. (Usually, during production times, this time is spent sprueing the next wax).
- After it is cooled to room temperature, clean the gates further using a knife to eliminate any remaining angles or edges. The resulting sprue should have soft, rounded edges leading to the shank of the wax mold. (Fig 3)
- Cut the sprue down to the proper length using the Sprue Length Chart to determine the correct ring type/sprue size.
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Vacuuming Molds
After investment of filigreed or detailed pieces, vacuuming may be necessary to ensure that the investment fills around the mold appropriately. This step is generally not necessary for plain pieces (bands, flat earrings, etc.).
- Cut a 6 inch section of absorbent paper from the roll located next to the vacuum table.
- Tape the lower edge of the paper around the upper edge of the invested flask to create a seal. (Fig 14)
- Place the flask in center of vacuum table and turn the vacuum on.
- Place the bell-top over the flask and press down on the table with force until suction is achieved.
- Turn the vacuum lever to “full”.
- Let flask vacuum for full noted time (90 seconds for “B” flasks, 2 minutes for “C” flasks). If proper suction has been achieved, the investment should rise to within ½ inch of the edge of paper ring. If the investment fails to rise, check bell-top for suction seal. If the bell-top does not have adequate suction, repeat Steps 4 and 5. Do not leave flasks unattended on vacuum table! Vacuuming flasks for longer than these times may result in spillage and improperly filled molds.
- After time is up, reset the vacuum lever to “standby” to release pressure.
- Remove bell-top from vacuum table and turn vacuum off.
- Remove tape and absorbent paper from top of flask.
- Send flask to casting station.
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Quenching/Breakout
- After casting is complete, the flasks should rest for a set amount of time (5 minutes for “B” flasks, 8 minutes for “C” flasks. After this resting time, they may be placed into quenching sink. Gently place flasks into quenching sink! Rough treatment may result in fissured mold and rough skins on finished castings.
- After 5-10 minutes, the flasks should be cool enough to handle. Taking each flask gently in one hand, tap outer edge lightly with a rawhide mallet. Rotate flask as you are tapping to remove excess investment. (Fig 19-20)
- After the bulk of the investment is removed, turn casting tree upside down and gently tap the button with the mallet to remove excess investment between pieces and loosen remaining investment.
- Repeat with all flasks from this casting batch in the quench sink.
- Using the rotary hammer flex-shaft attachment (fine tip – set on high) carefully remove as much excess investment from the casting tree as possible. Be cautious not to touch the hammer tip to the castings, as the resulting marks will be deep and difficult to repair!
- After you have removed as much excess investment as possible, place casting tree into devest solution and let rest for approximately 1 hour. Gloves and eye protection must ALWAYS be worn when handling devest solution (see Chapter1 for safety procedures).
