A cast iron, T-type fitting is being produced for the oil drilling industry, using an air-set or no-bake sand for both the mold and the core. A silica sand has been used in combination with a catalyzed alkyd-oil/urethane binder. Figure CS-13 shows a cross section of the mold with the core in place (part a), and a cross section of the finished casting (part b).The final casting contains several significant defects. Gas bubbles are observed in the bottom section of the horizontal tee. A penetration defect is observed near the bottom of the inside diameter, and there is an enlargement of the casting at location C.
1. What is the most likely source of the gas bubbles? Why are they present only at the location noted? What might you recommend as a solution?
2. What factors may have caused the penetration defect? Why is the defect present on the inside of the casting, but not on the outside? Why is the defect near the bottom of the casting, but not near the top? What factors led to the enlargement of the casting at point CI 3. What would you recommend to correct this problem?
4. Another producer has noted penetration defects on all surfaces of his castings, both interior and exterior. What would be some possible causes? What could you recommend as possible cures?
5. Could these molds and cores be reclaimed (i.e., recycled) after breakout? Discuss.

Mold Penetration Core Gas Mold cavity (enlargement) b) tal FIGURE CS-13