Finning

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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)

  • 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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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.

Remove all part line indications.



High melting point/viscous wax.

Change wax or increase green permeability of the shell.



Runner wax out of control (runner wax melt point > part wax).

Evaluate melt points and adjust as warranted (drop melting point of runner wax).



Wax pattern not clean.

Check on pattern cleaning.



Shell

Weakness of ceramic shell.

Increase strength – add polymer and fiber (check on backup slurry specification and control).



Too brittle of shell.

Reduce refractory loading – add polymer.



Low green permeability.

Increase green permeability.



Poor shell buildup.

Evaluate evenness of shell buildup, draining times and positions, stucco picking up.



Primary layer(s) crack in shell building process due to temperature variation during drying.

Evaluate and correct drying conditions.



Finished shell temperature not controlled.

Keep finished shell in controlled environment.



Other

Slow loading of dewax.

Load dewax unit quickly to reduce exposure to heat.



Insufficient heat capability in dewax process (improper dewax operation).

Pressurize to 80 psi in less than 10 seconds. Depressurize from maximum pressure to atmospheric gradually over about 2 minutes (evaluate autoclave operating parameters).