The way to Cast Bronze and Other Metals with Plastic Molds

Your very first thought when you find this is that the plastic mold would melt or catch fire! You are right! The way it’s done is as follows…

This is going to be a story about a foundry that cast propellers for boats. That’s exactly where I figured out how plastic molds are used to cast metal.

I once rented space in a foundry that cast props. It was a dark and dusty place. Also extremely hot some days! Like when the furnace was heating metal. It was a little noisy then to. There are huge fans running to feed air into the furnace.

Here is how they will use the plastic molds.

First they will cast in plaster, using the clear plastic mold. Next the plaster casting will be used to make a whole new mold using sand. This mold is referred to a “pattern” and will be used to help make the sand mold for the metal to be poured into. This’s done in a Sand box!! I am certain you’d already guessed that? The plaster pattern is placed in the box and sand is packed around it. This is special sand that can’t be reused. It’s mixed in a huge machine with waterglass just before it is to be used. This is packed into CO2 and place it blown over it to harden it.

When this is ready the metal is heated in the furnace and then poured into the mold. It’s allowed to cool twelve hrs or even so (this is dependent upon the size of the casting – bigger equals longer). Once it’s cooled the sand is broken away and discarded. The casting is cooled for another twelve or even so hours after which you can ground and polished.

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