Re: Pressure tank wanted

From: Andrew Miller (
Date: Fri Apr 18 2003 - 02:12:04 EEST

> I have had better luck with the reverse approach. Instead of forcing the
> material into the mold suck the air out of the mold and the pour material
> will fill the empty space. First, you put your pour material into an
> oversize container and place it in a vacuum chamber.Then you place
> your RTV mold in the chamber, pour in the cleaned pour material and draw a
> vacuum on it.

This approach works fine if you are using low viscosity LONG pot life
materials.....I like the idea of using an old fridge though...clever..

Pressure casting is the only way to make high quality pieces from an RTV
mould in a short timeline...

We do a huge amount of urethane casting and have found that it is just not
economically feasible to vacuum cast parts if you can only do 2 parts a day
because you are either waiting for the machine to mix and degas or you're
waiting 6-8 hours for demold..

Our average mould cycle here is a little over an hour

One cycle equals Prepared mould --> shoot Material-->
Pressurize -->Depressurize -->Open and demould --> clean and prep mould -->
Prepared mould ready to shoot again.

We have some moulds/resins we can turn around in 35 Min.

10-12 parts from a mould per day is not unusual for us

We've worked with more than 30 different resins and 10 different silicones
We can now consistently produce 80-100 pcs per mould with minimal flash and
excellent dimension retention.

Big trick is not to entrain any air into the material as you mix it....
which means static mixers and cartridge or meter/mix equip (I can point you
to all the cheapest places for that stuff too if you need it)
trust me $2-$3 in disposables for each part will save a TON in time and

anyway...if anybody wants to know the ins and outs of pressure
me...we have been through the learning curve three ways to Sunday and
back....I can save you some grief...

Andrew Miller

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