Slush Casting

 

You know you are a nerd when you enjoy learning about obscure, obsolete production methods.

Slush Casting

Slush casting is a casting process where molten metal is poured into a cavity, the molten metal is allowed to remain in the cavity or mold long enough for a frozen shell to form and then the core of molten metal is poured out leaving just the shell.

Another version is where a core is inserted into the molten metal and the shell freezes around the core much like wax solidifying around the wick of a hand-dipped candle.

Slush casting offers some advantages over modern methods. For one-thing, the dies or molds are simpler. You only need one side.

There is no need for high-pressure die-casting or plastic injection molding equipment.

Another advantage is that you can use alloys with higher impact strength because you do not need the fluidity to flood long, thin sections. Most of the alloying elements that improve liquidity, silicon in aluminum alloys for instance, make the alloy more brittle.

Of course, if you choose to slush-cast aluminum alloys you need non-reactive crucibles and to float a salt-bath on top to isolate the liquid aluminum from oxygen.

A simple example

Suppose we were in spicy times and the frame for your power drill broke. Suppose all of your other parts were in fine working order but nobody had a spare frame to sell you.

Looking downward into the battery well of a power drill

If you were patient, you could shape a metal form* to dip into molten zinc foundry alloy** or molten aluminum and create a new frame for your power-drill. Obviously, it would not be reinforced polymer like the original and it would lack some of the external detail like stippling.

But if sufficient care was used in making the dipping mold, you could conceivably make fifteen-or-twenty external frames for your model of power-drill. Who knows, they might have "trading value".

*Gray cast iron would be the material of choice. It is easy to shape with simple files and hand-powered, metal cutting tools.

**Zinc foundry alloy is relatively brittle and it would behoove you to radius internal angles to eliminate stress risers.