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Finning

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Finning presents as sharp metal fins that appear perpendicular to the surface of the casting and vary in severity from superficial (about 1 mm high) to heavy (several mm high). This defect indicates that a portion of the shell has cracked during shelling or dewax and metal fills the crack. Superficial finning typically occurs when the primary shell coat has cracked and is especially prevalent on round parts due to hoop stress. Heavy finning typically occurs when the entire ceramic shell has cracked is especially prevalent on edges. 

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The causes of this defect are evident in the wax, shell and other portions of the process. To cure these causes, R&R recommends taking the following actions.