Finning
Technical Support
Struggling with a specific casting defect or just need general technical support?
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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)
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Indicates that a portion of the shell has cracked during shelling or dewax and metal fills the crack
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Superficial finning typically occurs when the primary shell coat has cracked and is especially prevalent on round parts due to hoop stress
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Heavy finning typically occurs when the entire ceramic shell has cracked is especially prevalent on edges
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Causes of this defect are evident in the wax, shell and other portions of the process; to cure, R&R recommends taking the following actions:
Wax
Parting line was not removed and serves as stress point for a shell crack.
High melting point/viscous wax.
Runner wax out of control (runner wax melt point > part wax).
Wax pattern not clean.
Shell
Weakness of ceramic shell.
Too brittle of shell.
Low green permeability.
Poor shell buildup.
Primary layer(s) crack in shell building process due to temperature variation during drying.
Finished shell temperature not controlled.
Other
Slow loading of dewax.
Insufficient heat capability in dewax process (improper dewax operation).