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Feeding Permanent Mold Castings


Quality permanent mold castings begin with good gating practices. Shannon Wetzel, Senior Editor


“[The Alcoa system] restricts the fl ow of the metal and


keeps the turbulence down,” Reamer said. “For short castings, I never saw a better gating system than that.” Bob Pischel, applications manager at Foseco, Cleve-


land, similarly recommends a runner system with a width larger than its height. If the runner is opposite, meaning tall and narrow, as the metal fi rst enters the system, it runs to the bottom of the system fi rst and fi lls from there, according to Pischel. This causes a back fl ow of metal at the top of the system running counter to the initial fl ow of metal and producing excessive turbulence and oxides (Fig. 1). The runner system won’t stabilize until fi ve or six seconds after the pour, Pischel said. “If you have a short, wide


runner system, you eliminate the possibility of the metal fl owing in two directions at the same time while the system is trying to stabilize itself,” he said. The tilt-pour permanent


mold process lends itself to a smoother mold fi ll than static pour, but Pischel warns that the gating system should still be properly confi gured. In many cases with permanent mold, the gating is inherited


MODERN CASTING / June 2010


from another process, such as sand casting, which can be detrimental to the goals of a permanent mold gating system. The effects can be more adverse when trying to apply a static pour sand casting gating system to tilt-pour permanent mold, Pischel said. Certain process parameters also can affect the tranquility


of the pour in tilt-pour permanent mold. For example, the pour cup size should match the amount of metal needed to make the part. Randy Oehrlein, vice president of engineer- ing at Carley Foundry, Blaine, Minn., said to imagine you are pouring a glass of water fi lled to the top into another glass. As you tip the glass, water will begin to pour out almost immediately. Now imagine a glass that is only half full. You have to tilt the glass much further before any water comes out, and the more it is tilted, the higher the velocity of the water and the more it splashes into the empty glass. “You want to get the pour


cup size matched to your part, so as soon as you start tilting, metal comes out,” Oehrlein said. If the pour cup is too small,


Fig. 1. Tall, narrow runners (bottom) can result in backfl ow of metal, re- sulting in turbulence and oxides. Short, wide runners (top) are preferred.


as the ladle fi lls the cup, the excess metal will spill into the part while the mold is still hori- zontal and begin to solidify.


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