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space Cracking Problem !  

The most common problem associated with silicon alloys is cracking. Cracking may occur from
any of the following conditions:
Please check:

1. Check the quench time on the flasks after casting, quenching too quickly can cause cracking
in the castings. After casting should be waiting at least 15 minute before quenched in water.
2. Check the casting temperature, silicon de-oxidized alloys may crack if cast too cold. The proper casting temperature can read on the instruction sheet of United's alloy.
3. Check the flask temperature, cracking in very thin castings may be caused by too low of
a flask temperature being used.
4. Hydrochloric acid or Muriatic acid should not be used in investment remover solutions as it may cause stress corrosion cracking in lower karat alloys.
5. Inadequate or incorrect placement of sprues on the castings can cause cracking especially at
or near the sprue junction with the casting.
6. Designs with think to thin to thick sections will often crack on the thin sections. This is due to
uneven solidification. Additional sprues or U shaped feeders connecting the heavy sections
may help.
7. Overuse of the metal may cause cracking due to oxide build up in the metal being used for
casting. Contaminated gold or alloy may cause cracking in the castings made with it.
8. Check the vacuum assist unit on a regular basis. If the vacuum release is too slow, the molten metal will not fill the cavity completely. The cracks usually appear on the sides, shoulders and tops.
9. Fine Gold/Fine Silver contamination. Cracking is usually caused by reactions with arsenic,
antimony, bismuth, selenium, tellurium, sulfur, residual chlorides. Iron and traces of other metal.

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