Making and using a Vacuum Pump/Chamber

[SW1]

Just wondering if anyone has had any actual experience in successfully making a Vacuum Chamber for degassing rubber for mould making?

 

Trying to work out if I'm best off buying one at +£200 or going down the self build route. I know they can be dangerous if they go wrong so only interested in feedback from people who either have successfully made or work with them or really know what they're talking about!

 

Other questions bouncing around in my head are do you need to pull all the air out (perfect vacuum) to de-gas silicon rubber or will getting a partial vacuum work? Also would the type of vacuum pump you'd use for a chamber work also for making a Plastic Sheet Vacuum Form?

 

I'm going to be resurrecting my scenery build threads if I can get this to work. :D

[Grotsmasha]

I suggest hitting Subtle Discord with a PM, he's the only person I recall 100% who's mentioned they use one.

 

Cheers,

Jono

[Red_Shift]

Mangozac from warseer has a site called resin addict where you can ask questions re casting and lots of useful threads/advice.

[White Wolf]

I would buy one, as well as a pressure pot. There is a lot to go wrong with them, and while the pressure pot is far more hazardous in a malfunction, the vacuum chamber can still go really wrong. I've bought both my pot and chamber and am really happy with the professional build quality on both.

 

ATB WW

[SW1]

Cheers for the comments.

 

@Jono - Will send SD a PM! Lol ... Should have though to do that first.

 

@ Red Sift - will have a gander over there thanks for the direction

 

@ WW - which makes of vacuum/pressure chambers did you get?

[Rogue Crusader]

A vacuum chamber is pretty easy to get set up, the most common ones are converted from a 5 gallon cooking pot that has an acrylic lid. It's not under much stress compared to a pressure pot, in absolute worst case scenario if it were to fail it'd implode and suck in it might smash the contents inside but there'd be no explosion to worry about (unlike with pressure pots)

 

Resin Addict is a really good source for info, I helped Mod on there for a while and wrote a bunch of articles for it. (Paulson Games) I've been casting models as my full time business for the last 7 years, so if you need any help feel free to ask. 

 

You don't need to get a perfect vacuum for degassing, but the closer you can get the better. One thing to be aware of is that when it's in a vacuum silicone expands to about 3 times it's normal volume so you will need a container that can hold far more volume than what you are trying to mold otherwise you end up with it running out everywhere and then when you release the vacuum it all shrinks back down to it's regular size.

 

A number of companies (like Smooth-On) make self degassing silicone which eliminates pretty much all the major bubbles and you don't need to degas.

 

I don't degas any of my molds but I do place them under pressure while they cure. This helps eliminate any micro bubbles that might still be in the silicone, the pressure gives them extra hep squeezing their way to the surface. You also want it to cure at the same pressure level you intend to cast at that way you don't end up with micro air bubbles in the mold which resin squeezes into when they are cast under pressure. The pressure will drop over time as the mold cures but that's ok as it only needs to reach full PSI for a couple minutes when it's first poured.

 

If you create the molds at room pressure then cast under 60 PSI you can end up with tiny little balls of resin formed on the surface of your models which look like small BBs. So basically after I pour the molds I pressurize them to 60 PSI which is also the same level I do my casting at and they work perfectly without any degassing required.

For the best results you may still want a vacuum chamber as it really helps remove bubbles from the resin, but you can do very good work with just using pressure by itself. You may need to add a few extra vents but it's certainly viable just using pressure alone. 

 

The pressure pot is not something you want to go cheap on, I've done it but the cheaper converted pots wear out quickly and by the time you replace it you end up paying more money than if you'd just bought a quality pot to start with. The cheaper Harbor Freight pots can also fail and blow up which I've had happen firsthand and it has also happened twice to one of my friends. Fortunately we didn't get injured but it could have been very serious. CA Technologies makes a pressure pot that's already set up for casting and doesn't require you to do any conversion work other than adding some ball valves. It's meant to handle pressure up to 70 PSI where the harbor freight pots can barely handle 40 PSI, the CA Tech pot also lasts an incredibly long time as their clamps are much better designed and won't pop loose while it's under pressure or dig into the lid. I wore out several Harbor Freight lids in less than 6 months while my CA pot has been in use daily for the last 4 years and still going strong. 

http://www.finishsystems.com/resincastingpressurepots.html


You can go cheap on the vacuum chamber and pump, but try not to go cheap on the pressure pot.

 

 

You can use the same vacuum pump for vacuumforming plastic, but you'll need to build a vacuform table. Vacuforming uses a much weaker pull than resin and silicone and most people just use a shop vacuum to create their suction as it's cheaper. Although a stronger pump can help you get much sharper details on the formed plastic sheet.

 

I bought my vacuum pump and chamber off of ebay, basically all you need is a 1/2 or 3/4 inch thick acrylic sheet with a rubber gasket to hold it against the rim of the pot. You'll want at least a 3 CFM pump, I'd highly recommend a 6 CFM as there shouldn't be much of a price difference. The lid from my vacuum chamber happened to fit the CA tech pressure pot perfectly so I just use it for both my vacuum and pressure, all I need to do is load it up once then switch the lids which saves a ton of time. (vacuum first, then pressure)

There's several places that offer services to custom cut acrylic, all you need is a 1/4 inch hole drilled in it for the hose. If you want to go the extra mile you can have a groove milled into it to fit a 10 inch gasket so it's recessed into the lid which will work a bit better than if you have a gasket just glued onto the lid.

This is pretty close to the one I have, if you want to multi purpose your pressure pot you can always contact the seller to see if they will sell just the vacuum lid but you'll want to ask about the gasket size and make sure it covers the lip of the pressure pot. Building your own would cost a little under half the price. 

http://www.ebay.com/itm/3-Gal-Vacuum-Chamber-NEW-/201706291205?hash=item2ef6a1c005:g:cnUAAOSwx2dYHUyq

[White Wolf]

Hi SW1, I don't know the exact make - I was lucky enough to buy it second hand from a professional model maker and it was in "as new" condition, I believe it costs about £2.5k new, so I was really lucky.

You can get ones from HVACstore.co.uk for about £165.00 which will do the job although they are about a quarter of the size of mine. For professional level kit you need to go to vacuum-degassing.com, I have a kit similar to the 76 litre kit.

Hope this helps

ATB WW