The Cast Oil-Field FittingA 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. The figure shows a cross section of the mold with the core in place
(a) and a cross section of the finished casting
(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?