Inclusions (Ceramic)

Technical Support

Struggling with a specific casting defect or just need general technical support?

  • Missing areas of metal in the casting; appearing as small, round, irregular or angular craters, depressions or cavities of various sizes; typically superficial with traces of ceramic and refractory material

  • Indicates that something is present in the mold cavity that prevents the casting from fully filling to the shell; typically ceramic shell debris, bits of the pour cup, or the inner mold surface broke off into the molten metal during pouring and were left behind on the casting surface

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

Poor wax assembly – undercuts.


When patterns are attached to the sprue and the connection is not completely filled or contains undercuts, these undercuts fill with slurry. When the shell is dewaxed, this ceramic extends into the shell cavity and can be dislodged when metal is poured resulting in a ceramic inclusion. Wax assemblies should include gates with smooth radii, allowing for easy metal flow.





Shell

Cracks in mold.


See shell cures for finning defect.




Shell formed pour cups, jagged rim.


Use a ceramic pour cup or ensure an even top cut.




Invested pour cup is brittle, jagged and/or fragile.


As a result, the invested pour cup is breaking when the metal is being poured, becoming entrapped as inclusions. Use preformed ceramic cups.




The primary coat layer is spalling.


See options under scabbing/delamination defect.




Inadequately dried shells.


Verify that the shell is dry before applying additional layers. If necessary, add appropriate equipment or cycle time to ensure the shell is dry between coats.




Out of control slurry.


Check binder solids.





Other

Housekeeping.


Cover molds after dewax and use a filter.




Molds are being fired with the cup upright, entrapping dust or ash from residual wax residue.


Fire molds with the cup facing down. This eliminates the potential for foreign material to enter the mold cavity and become a metal inclusion later in the process.




Dust particles are trapped in the shell cavity.


If a double-firing cycle (firing/preheating) is occurring, blow the molds out prior to preheat. Consider covering the molds after firing to prevent foreign material from entering the mold cavity. Cleaning the top of the ladle or furnace prior to pouring metal may also eliminate the opportunity to introduce foreign material into the shell.





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