APMM Community Forum : Casting
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 Subject : Re:Re:Surface Finish on Smooth-On Flex-Foam-iT 6.. 08/10/2020 02:10:27 PM 
Posts: 208
Location: Overland Park, KS
The silicone mold is in a 1/2" plywood box with minimal silicone around. So far distortion hasn't been an issue, but if I find I actually do need to start working crazy high pressure, that's definitely a possibility.
 Subject : Re:Surface Finish on Smooth-On Flex-Foam-iT 6.. 08/10/2020 11:32:36 AM 
Posts: 264
Location: Saint Paul, MN
Can you machine or 3D print the mold? You might need so much pressure the silicone would distort. As long as you're waiting around for new products to arrive anyways.
 Subject : Re:Surface Finish on Smooth-On Flex-Foam-iT 6.. 08/10/2020 09:59:01 AM 
Posts: 208
Location: Overland Park, KS
Robert and Tanya, thank you for that information! Made some adjustments to my mold based on your suggestions and got somewhat better results, but still nowhere near what I need in terms of surface finish. Thinking this may be the wrong product for the purpose, even if I'm doing everything right in terms of the mold and setup.

I also got a few private messages from our fellow members, giving me some further suggestions. The majority of these also pointed to plugging the mold vents/pour spout and creating internal pressure. One comment recommended calculating the proper amount of material to expand into the cavity, then adding 20% to help ramp up that internal pressure.

Other suggestions included using the specific mold release indicated by Smooth-On for this product. Using NO mold release (my mold is silicone so probably no need for it) was also suggested.

Speaking with Smooth-On, and based on suggestions from one of the private comments I received, I've decided to try a few of the denser products in the range (the Flex-Foam-iT! X and 15).

If these products fail, I'm going to try an option I received in a private message over the weekend. The commentor suggested I try a foam from Isotec International, commonly used in the shoe industry, their 103 line. This individual said they used it when working in the shoe industry, and that it has a 55 Shore A density. While I cannot pin down a specific product on the Isotec International website with the 103 moniker, several of their expanding foam lines are described as self-skinning, and I'm sure if I speak with their reps, we can isolate the specific one that is popular with the shoe crowd.
 Subject : Re:Re:Surface Finish on Smooth-On Flex-Foam-iT 6.. 08/08/2020 12:24:57 AM 
Posts: 8
What Robert said. Also, I have used that Smooth On line for a few parts. There are some urethanes that are 'self skinning' and this is not one. I'm not sure if Smooth On has one. Another option depending on your mold and part is to paint a thin surface coat with a compatible urethane that is non expanding and when it gels but is still fresh, back it with the expanding foam.
 Subject : Re:Surface Finish on Smooth-On Flex-Foam-iT 6.. 08/07/2020 10:44:50 AM 
Posts: 16
To get the correct density and consistent bubble size, you may need to add more mixed resin until the pressure equalizes the bubble size. Your mold will need to strong enough to withstand the pressure, which can be enough to pull latches and screws out. Add some band clamps as a safety measure too. Sneak up on the resin size carefully until you get the parts you want or the mold lets go. Wear goggles, gloves and keep people clear. Also, talk to Smooth-On for more info
 Subject : Surface Finish on Smooth-On Flex-Foam-iT 6.. 08/07/2020 10:25:55 AM 
Posts: 208
Location: Overland Park, KS
Does anyone have experience working with the Smooth-On Flex-Foam-iT line of expanding flexible urethanes? We're attempting to create a cushiony foam part for an appearance model, but we want the surface geometry to be accurate and I'm having difficulty getting this stuff to create a consistent surface "skin" that conforms to the mold cavity. Getting a lot of porosity.

First time we've had to work with a flexible foam casting resin so no frame of reference with this material. Any advice would surely be appreciated.
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