Re: ATM Concrete moulds could be DANGEROUS

["Thomas Janstrom" <tomjan@ozemail.com.au>]

The correct amount of cement powder is 10% and the correct amount of water
is 5%. These are all by weight with the remainder being 80 mesh sand.

A mold made from this mix should be allowed to dry for 72 hrs prior to
pouring the metal.

***I don't use this method in my foundry, and I DON'T recommend that it be
used as it has a high potential for the formation of a steam bomb, than
regular sand molding.***

Clear skies, Thomas
http://www.geocities.com/t_janstrom/

----- Original Message -----
From: Peter John Smith <pjifl@bigpond.com>
To: Dominic-Luc Webb molmed <Dominic.Luc-Webb@molmed.ki.se>
Cc: <atm@shore.net>
Sent: Thursday, October 05, 2000 7:50 PM
Subject: ATM Concrete moulds could be DANGEROUS


>
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> From: Dominic-Luc Webb wrote :-
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> >>>
> also find that concrete works in a lot
> more applications than just a mount or counterweights. You
> could for instance use concrete to make molds and pour
> aluminum, etc.
> >>>
>
> Pouring molten Al in a concrete mould can be VERY DANGEROUS.
>
> If the concrete is of normal mix the mould has a very high chance of
> exploding violently showering you with molten Al.
>
> On the other hand, if a coarse sand is mixed with a very small amount of
> cement powder and the cured product dried well it can work quite well.
This
> is probably what is intended.
>
> The critical factor is that the final product must be porous, permeable to
> gases, and able to be well dried.
>
> I think somewhere between 1 % to 5 % cement powder in coarse sand is about
> right but it may be even less.  Do more research on this before trying it.
> You want enough cement to just stop the mould from crumbling when it is
> carefully handled.
>
> Of course some other material like a small amount of clay can be added in
> place of the cement which is what I have used.
>
> Peter Smith.
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