Back pressure porosity can be avoided by________________?
Correct answer: B. Placing the sprue at least one quarter inch away form the end of casting ring
- A. Using asbestos linear
- B. Placing the sprue at least one quarter inch away form the end of casting ring
- C. Preventing rapid heating the investment in burnout oven
- D. Using a short and wide sprue
Explanation
Back-pressure porosity results when air or gases cannot escape from the mold as molten alloy enters it. Keeping the sprue at least about 6 mm, or one-quarter inch, from the ring end leaves investment around the pattern for better gas escape and mold support.
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