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Vacuum chamber question?


Mig Eater

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I want to start casting my own parts & I'm looking into getting a vacuum chamber to help with degassing the rubber for the moulds &/or the resin. However I'm unsure about when would be best time to use the vacuum chamber, should I degas the rubber/resin in the mixing cup & then pour it into the part/mould, or is it better to degas the whole part/mould etc? The size of the vacuum chamber that I need will depend on which method I use & could mean spending £200 or £800.

An extra side question; Nearly all 2 part resins that I can find for sale are clear, to get the typical beige/white colour is it just a mater of adding a dye to the resin?

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I dont have the budget to get both a vacuum & pressure chamber, especially if they need to be big enough to put the whole mould into both of them. That would cost thousands of pounds for all the necessary equipment 😕 

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What sort of size and complexity are the parts you hope to mould?  I have been making resin castings for many years without a vacuum to degass or pressure to keep bubbles down, mainly relying on a gravity pour which is led down underneath the main mould area and then displaces the air out via vents as the resin rises through the mould.

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I'm planning to scratch build/3D print several 1/35 tanks & I want to cast copies of them, which would include everything from individual tracks to large hull plates. The hull of the largest tank will be around 28cm long so I'd need chambers 35cm+ in height/width to hold the mould, which can be very expensive. I was hoping I could just vacuum the resin in the mixing cup which wouldn't need as large a chamber.

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I looked into modifying a pressure cooker but I couldn't find one big enough, the largest one I could find was 17 litre but I'd need something about 40-50l though.

 

Anyway to my main question, it's best to put the whole mould in the vacuum chamber then?

Edited by Mig Eater
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  • 11 months later...

I haven't used a vacuum chamber yet. It seems a necessity for finer parts. I have a paint pressure pot that painters use to pressurize paint for spraying in houses. It's about the size of a 5 gal pail, bit shorter. It just needs a bit of valving, air line quick connects and a pressure guage. I'm not exactly sure on the parts. I have a picture of one set up. It's cast aluminum with locks on the lid. For vacuum I was going to try a refridgerator pump, but never did more than find the pump. I also just got some semi clear Smooth-on mold rubber called "sorta clear" I saw a video on it and you can see through it which will be very helpful. I also used Alumiltie slow set resin. I found it has a much better shelf life than Smooth-on which has a short life once opened even with the air displacing spray. The lids I guess don't seal to good no matter what. I do a little casting, just small stuff. Don't have anyone to instruct me on doing bigger stuff and I'm limited to space for a proper set up, have to keep it movable.

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  • 4 months later...

This post is a bit old now but I'll chip in case anyone is interested. 

 

In answer to the original questions regarding degassing in the mold or the pot, it's fine to degass in the pot and you can do it in several stages when working with silicone rubbers if your chamber isn't big enough. So you don't have to mix it all in one go. Typically most rubbers will be left overnight and there should be enough pot life so you don't have to panic when mixing and degassing, however if you haven't done it before I'd recommend selecting one with a fairly generous pot life as the thorough mixing can take a while. Speaking to one of the Notcutt reps might be useful in terms of recommendations but perhaps Silastic RTV 3481. You might be aware there are two main types of silicone rubber, tin cured (condensation) and platinum cured (addition), as the names suggest the platinum one is more expensive however you'll get many more 'pulls' from it although it's a bit more pernickety to work with.  As regards degassing the resin, you might find you don't need to, if your cast has lots of undercuts or areas where bubbles might get trapped you could try a sort of slush casting approach, where you mix up a small amount of resin and swill it around in the mould in order to coat the surfaces first - wait for that to cure and pour the remainder of the resin. Most PU resin's tend to be a creamy or amber colour when mixed unpigmented, there are a few that cure white and a few that cure clear. If you're going to be painting these things you'll need to think about what resin takes paint better (maybe SG2000) and obviously you wouldn't need a clear version. That's probably too much info but perhaps useful to someone.

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