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RB211
07-15-2011, 01:16 AM
Before I attempt to make a positive mold for a project, I would like to know if anyone has successfully used a silicone mold for a silicone casting? Do I need a release agent like lard?

macona
07-15-2011, 01:51 AM
We use it at work, in fact we buy the silicone by the 55 gal drum. There are specific mold releases for the silicone, use them.

Allan Waterfall
07-15-2011, 02:21 AM
Probably find any info you need here..

http://www.smooth-on.com/

I've used the polyurethane rubbers and you generally need a softer mould than the article you are moulding.

Vaseline as a release agent worked okay for the polyurethane rubber I did. Put it on and wipe it off just leaving a film,however the slightest mark will be reproduced if it matters.

There are various aerosol release agents.

Allan

TexasTurnado
07-15-2011, 02:25 AM
Before I attempt to make a positive mold for a project, I would like to know if anyone has successfully used a silicone mold for a silicone casting? Do I need a release agent like lard?

You gonna make a mold for implants?....:D :D I thought those were filled with liquid silicone for a more natural feel.....:rolleyes:

mc_n_g
07-15-2011, 10:19 AM
Like Allan I have used Vaseline and it works but may end up thicker in some areas when you put it on. I think an aerosol release spray would be an overall better choice if you have never worked with molds before.
You do not want to go too think on the release agent as it can reduce part details.
Out of curiosity why are you going the silicone on silicone route? There is nothing wrong with it but you need to be careful because silicone sticks to silicone.

scmw
07-15-2011, 12:32 PM
Smooth-on is one source. Another is Alumilite in Kalamazoo, MI. Their website is http://www.alumilite.com

We use Polyester Parfilm Ultra 4 from Price-Driscoll (http://www.price-driscoll.com/) for our silicone to silicone release. Just spray on enough to cover the pattern, weigh, mix, vacuum, then pour your RTV.

Drop me a PM if you need help. We have a casting house at our shop.

Hope this helps,

Michael Moore
07-15-2011, 12:52 PM
I've been using the white Vinamold compound to do cylinder head port moldings:

http://www.conservationresources.com/Main/section_38/section38_08.htm

It is a thermoplastic, not a two-part compound. I heat it in a Pyrex cup in a $20 CL microwave (outside, NOT in the kitchen microwave again!) and it doesn't seem to need any release agents. It cools in about 5 minutes in the port so the entire "drag out the oven, heat, pour, demold" process takes about 10 minutes which for me beats accurately mixing the silicone and then waiting hours if not days for it to set up.

Of course, if the item you are molding can't take the temperature this would not be the product you need.

The white is not the softest one but it has been plenty stretchy to make it easy to pull out of the ports. It will shrink some as it cools, but so far that has all taken place in the center of the compound, and the extra space makes it that much easier to squish it around to get it out of the port. If you build a little dam of modeling clay around the mouth of the port you can add extra Vinamold to that riser to feed the shrinkage.

A nice thing is that it is reuseable. Just chop up the no longer needed mold and melt it down for the next one. I bought 2kg, and I suspect that even with keeping some molds for reference I'll never use it all up.

I'll save the two-part silicone/urethane compounds for making small rubber parts (unless I need to mold something at a low temperature).

Here's a photo of a mold. The Vinamold picks up very small details, and if there's any Sharpie writing on the part it picks that up too, just like Silly Putty does.

http://www.eurospares.com/graphics/engine/flowbench/160Mod002.jpg

cheers,
Michael

Paul Alciatore
07-15-2011, 02:03 PM
Thanks to all for the links I didn't already have.