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Troubleshooting Air Bubbles in Wax Patterns
Air bubbles trapped in wax patterns used for jewelry investment casting can cause surface defects in cast precious metal jewelry. The defect will be a recessed cavity on the surface of the jewelry casting that can vary in size and shape. Air bubbles inside wax patterns will break during the final vacuum cycle of the investing procedure. When the air bubbles in the wax pattern break, investment plaster will fill the hole in the wax pattern creating a hole in the metal casting. The most common causes and corrections of air bubbles in wax patterns are as follows;
AIR PRESSURE TOO HIGH ON WAX POT. - Check the air pressure settings on wax pot
WAX TEMPERATURE TOO HOT OR COLD - Check temperature settings on wax pot.
WAX POT LOW ON WAX - Try to keep the wax pot about half full.
RUBBER MOLD HELD AT WRONG ANGLE TO NOZZLE - Hold mold on same plane as nozzle.
LACK OF VENT LINES IN RUBBER MOLD - Cut vent lines to release trapped air in mold.
MOISTURE IN WAX ADDED TO WAX POT - Store wax in covered container in cool, dry place.
MOISTURE IN COMPRESSOR OR AIR LINES - Drain compressor daily - use moisture traps on pots.
TRAPPED AIR BUBBLES IN WAX POT - Adjust temperature and stir wax to release air bubbles.
To check wax patterns for air bubbles, a simple and effective method is to place wax patterns in a box, place the box under the vacuum system in the investing area and seal the unit holding full vacuum for 2 to 3 minutes. The vacuum will pop the air bubbles in the waxes making the defect visible on inspection. If multiple wax pots are used, place the waxes to be popped in separate numbered boxes to determine which wax pot is causing the problem. Another method is to check the waxes over a strong light source to look for light spots in the waxes.
A method for removing air bubbles from injection waxes is to turn up the temperature on the wax pot to a temperature where the wax is very liquid. Pour the wax into a stainless steel cooking pot that will fit into the vacuum unit in the investing area. Place the pot with the wax on a hot plate or stove to keep the wax very liquid, fresh wax can be added at this time. Place the pot of heated wax on a heat resistant pad in the vacuum unit in the investing area. Seal the vacuum unit and hold full vacuum for 2 to 3 minutes. Release the vacuum, open the unit and give one shot of silicone mold release spray to the top of the molten wax to break the air bubbles on the surface of the wax. The wax can now be returned to the wax pot. Set the temperature on the wax pot and allow the wax to return to normal operation temperature. If mixed waxes are used, weigh the exact amount of each wax, place in the stainless steel pot, heat the mixed wax until very liquid, stir the wax mix and follow the previously mentioned procedure. If a supply of wax for several wax pots is being prepared, the de-bubbled wax can be poured or ladled into cupcake or muffin pans making wax muffins that can be kept as a stock for refilling the wax pots.
The wax can be de-bubbled in non-automated wax pots by turning up the temperature on the pot, shut off air supply and disconnect it. Open the wax pot and fill with wax, when wax is very fluid close the wax pot and attach a vacuum line to the air inlet port. Turn on the vacuum pump and hold the vacuum for 3 minutes. Shut off the vacuum pump, disconnect the vacuum line and open the wax pot. Give one shot of silicone mold release to the top of the molten wax to break the air bubbles. Turn down the temperature on the wax pot to normal operation temperature and re-connect the air line. Allow the wax temperature to return to normal before injecting the wax patterns.
No Guarantees are made for the aforementioned methods that are provided as information to United customers.