expand as it hardens - reverse shrink epoxy

[jminahan]

I'm doing some sand cast pattern making and I'm looking for something that I could pour over an existing part so that when it hardens it would expand instead of shink.
The reason is that when you cast aluminum it shrinks, about 1.3% therefore your patterns need to be that much bigger.
It follows that I'd need (ideally) something that would expand about that much.

Anything you guys can think of?

Jason
Automotive Engineer

 

[MintJulep]

You'll loose definition of surface features.

 

[Compositepro]

I'm unclear on precisely how you intend to use this expanding material to your benefit. I suspect that you may also be unclear in your thinking and therefore your idea won't work. I'm not saying this to be negative but your question does not contain enough information to elicit useful answers without a lot of assumptions. People have been making molds and patterns for hundreds of years. This suggests that there are reasons that expanding materials are not generally useful.

 

[unclesyd]

Here are a couple of products to take a look at from Dynamold. The have all three types of replication materials and an epoxy shim.

http://www.dynamold.com/dmr.htm

http://www.dynamold.com/shim.htm

 

[unclesyd]

You may also want to look at the Cerro Alloys especially Cerrotru.

http://www.hitechalloys.com/hitechalloys_002.htm