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Slush Casting


Slush casting is a variation of permanent mold casting that is used to produce hollow parts. In this method neither the strength of the part nor its internal geometry can be controlled accurately. This metal casting process is used primarily to manufacture toys and parts that are ornamental in nature, such as lamp bases and statues.

The Process

When producing a cast part using the slush casting method, a permanent mold is employed and set up. See basic permanent mold casting . The mold is clamped together and prepared for pouring.


Mold For 
Slush Casting Ready To Be Poured

After pouring the mold will set, as solidification begins to take place.


Mold For 
Slush Casting Immediately After Pouring

The main principle of this casting process relies on the fact that when a metal casting hardens in a mold, it will solidify from the mold wall towards the inside of the casting. In other words a metal skin forms first, (as the external geometry of the part). This skin thickens as more of the metal casting's material converts to a solid state.


Section Of 
Casting Near Mold Wall A Short Time After Pouring


Section Of Casting Near Mold Wall A Longer Time After Pouring


Sectional View Of Inside Of Casting A Certain Time T1 After Pouring


Sectional View Of Inside Of Casting A Longer Time T2 After Pouring


Same View 
Of Casting At Longest Time Interval T3 After Pouring

In slush mold casting, during the solidification of the material, when the solid-liquid boundary has reached a certain point, the mold is turned over and the remaining liquid metal from the casting is poured out.


Liquid Metal 
Poured From Slush Casting

This will leave only the solidified skin with the exterior geometry of the metal cast part and a hollow interior. The longer the metal casting was allowed to solidify before pouring out the excess metal, the greater the casting's wall thickness will be.


Metal In 
Solidified Outer Shell Remaining In Mold

The cast part is then removed from the die and allowed to cool.


Part Removed From Mold

Properties And Considerations Of Manufacturing By Slush Casting

  • Slush casting is a type of permanent mold casting, therefore many of the basic principles of a permanent mold process will apply.

  • Slush casting is mainly suited to lower melting point materials, zinc, tin, or aluminum alloys are commonly slush cast in manufacturing industry.

  • With this process you need to have a mechanical means of turning over the mold in order to pour out the molten metal from the cast part.

  • When manufacturing by slush casting it is difficult to accurately control the metal casting's strength and other mechanical properties.

  • The casting's internal geometry cannot be effectively controlled with this process.

  • The hollow metal castings manufactured by this process are lighter than solid parts and save on material.

  • Good surface finish and accurate exterior geometry are possible with the slush casting manufacturing process.