INBDE (Integrated National Board Dental Examination) Practice Exam

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What causes shrinkage porosity of metal?

  1. Too slow cooling

  2. Too fast cooling

  3. Insufficient pressure

  4. Too thin sprue preventing molten metal from flowing effectively into the mold

The correct answer is: Too thin sprue preventing molten metal from flowing effectively into the mold

Shrinkage porosity of metal occurs when there is a lack of sufficient molten metal able to flow effectively into the mold cavity during the casting process. This can happen if the sprue (the channel through which molten metal enters the mold) is too thin, hindering the proper flow and resulting in voids or porosity in the final metal product. Therefore, option D is the correct answer. Options A and B, involving cooling rates, are not the main factors leading to shrinkage porosity. The speed of cooling can affect the overall structure of the metal but is not directly related to shrinkage porosity. Option C, insufficient pressure, is not the primary cause of shrinkage porosity. While pressure can influence the casting process, the primary issue leading to shrinkage porosity is the inadequate flow of molten metal into the mold due to a thin sprue.

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