Re: Aluminum shrinkage?


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Posted by bpfink on April 12, 19100 at 21:52:17:

In Reply to: Re: Aluminum shrinkage? posted by Jack Fisher on April 12, 19100 at 21:17:59:

One of the methods I use when trying to make multiples that could tax my patience may work for you also.

Make one (positive) model of what you need (with the 1.6% increase in size... as per another posted calculation suggestion) and this can be in wood or fiberglas or wax or anything that works for you.

Make a urethane rubber mold (negative) of that and then seal that with a good separator before casting several more (one at a time of course) urethane rubber (positive) models. The addition of some other coloring added to the rubber will make it so you can see the separation better.

Using these positives make up a rubber match plate with the rubber forms in a pattern of say 6 or 8 per plate. Add sprues and vents and a good pouring feed cup as part of it.

Next cast investment on each side of it so when set up you can simply remove the rubber model with the 6 or 8 unit impression. Close the mold again, make 25 of them, and burn out the water at a much lower temperature.

The rubber models flex enough that even good undercuts will not be a problem and you can have a much lower temperature and shorter period needed to burn it out. (Like 600F to 700F even)

This means you might only have to cast 25 molds instead of 200 (or whatever).

I use plaster based investments for this since it is already here and sets up fast enough that I can make about 10 poured investments a day with lots of other free time between pours. There are many other molds that would also work for this... like bonded sand or etc. and then the burnout can be totally eliminated also.

Keep us posted and if you get another woman instead let us know how far the tank took you first.


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