74-30 RTV Liquid Urethane Mold Rubber

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Canadian_Kid

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Has anyone tried to use this stuff for making molds? http://www.uscomposites.com/moldmaking.html

From their site: [SIZE=-1]The 74-30 is the softest of our RTV rubbers. These rubbers can be used for making durable, easy releasing molds for casting gypsum plasters, waxes, cement, epoxy resins polyester resins along with urethane and acrylic

Thanks. Don.
[/SIZE]
 
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it works, but you need a release for PR. and if used for urethane without
a release, the mold will be permanently filled :eek:
 
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I've been looking for the answer to this question myself, and after doing much research, it appears the link you provided for US Composites has one of the best prices around...just scroll down to the 70-25 silicone section. $119 for 9 lbs. Most others are selling it for $134 and up.

I'm not sure if this is the exact hardness that is ideal, but it looks like it fits the bill otherwise.
 
[FONT=Arial,Helvetica][SIZE=-1]Well, here is what I found on that topic..[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1][/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1]GI-Series (Tin Catalyzed)[/SIZE][/FONT]
form1.gif
[FONT=Arial,Helvetica][SIZE=-1]Condensation cure two-component silicone rubbers are excellent for most general mold making and prototype applications. The GI rubbers are not sensitive to inhibition, meaning they will cure at room temperature over virtually any surface. They're easy to mix and de-air, and they cure with only a slight degree of shrinkage. The speed at which the rubber hardens can be accelerated with special activators. Finished GI silicone molds are excellent for casting polyester, epoxy, polyurethane, masonry, gypsum and candle wax.[/SIZE][/FONT]

[FONT=Arial,Helvetica][SIZE=-1]P-Series (Platinum Catalyzed)[/SIZE][/FONT]
form2.gif
[FONT=Arial,Helvetica][SIZE=-1]Addition cure two-component silicone rubbers offer superior heat resistance and cure with virtually no shrinkage. Although the P rubbers can be inhibited by tin, sulphur or amines, they can be cured in total confinement, and the cure rate can be dramatically accelerated with heat. Finished P silicone molds are ideal for casting epoxies, low melting-point metals and polyurethanes.[/SIZE][/FONT]

I think maybe platinum cure is overkill?
 
I just finished making a stopper mold with Mold Max 40. As long as you have an accurate scale and some way to apply a vacuum to degas the mixture it is great to work with. The stopper blanks shoot out of the molds if you use a little shot of air down the side. A lot of people answered my questions here - http://www.penturners.org/forum/showthread.php?t=76362.

I bought it from Sculpture Supply Canada in Toronto but if I remember correctly the Smooth-On site listed some retailers closer to you.

If you don't want to degas it then the Oomoo 30 or 40 is supposed to be good also but I haven't used it.

Michael
 
Thanks for the replies. I saw a video on YouTube (cant find it now) about de-airing without vacuum. If you pour from a few feet up the mix gets so thin as it stretches before hitting the mold, it gets all the air out (or most at least (according to the vid). It also said to pour in a corner and let the buildup run over the mold instead of pouring on top of any detail. I would love to find this video again so if anyone has the link please share.

Don.
 
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