frequent in castings made with greater pouring height, which points to air entrained in the pour as the source of the gas. As the pouring height increases, the velocity of flow increases and more air is entrained in the molten metal. Consequently, more defects would be expected in those castings done with a greater pouring height. This is consistent with the results obtained. Determining whether venting
was adequate is more difficult. The diameter of the vent passage increased with the diameter of the core. As the core diameter decreased, it became more diffi- cult to remove the unbound sand from the vent passage. It was im- possible to remove the unbound sand in the smallest cores. While gases could likely flow through spaces between sand grains, the area available for flow would be drastically reduced. T e area of fl ow decreases
Fig. 5. The tubes were checked to fi nd evidence of core defl ection.
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Fig. 6. Non-fi ll was apparent on the longer 0.25-in. tubes.
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Nov/Dec 2015 | METAL CASTING DESIGN & PURCHASING | 31
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