white_fly
white_fly HalfDork
4/19/21 10:01 p.m.

I've recently set out to make a vacuum chamber that is both larger and cheaper than what I have found available commercially. I've found a suitable vessel, made fittings, and even found a decent gasket. But so far the lid has confounded me. 

I need the lid to be clear so I can see when the contents of the vacuum chamber have stopped bubbling. Inch thick acrylic is expensive and doesn't react well with the chemicals I'll be using. I've thought about sealing it with a protective film, but I like the idea of using glass better as I have a source for free or nearly free cutoffs from a glass company.

The trouble is the glass I have access to isn't nearly thick enough. So I purchased some glass lamination film and started experimenting. The glass was most certainly laminated, but there are lots of little air bubbles. I'm looking for a way to eliminate the air bubbles with something that is going to be safe at the 225* necessary to melt the laminating film. I think the professional way to do it is using a vacuum bag and autoclave, but I don't currently have access to all the equipment necessary to do that. 

Do I need to acquire it and keep experimenting? Is there another way? Am I completely off my rocker?

Mr_Asa
Mr_Asa UberDork
4/19/21 10:39 p.m.

Sheet of tempered glass in the required dimensions, max of 3/16" thick, then layer thin acrylic on top till you get to the required thickness?  Between the layers pour B-72?

Many layers of thin stuff eventually will approximate one layer of thick stuff.

white_fly
white_fly HalfDork
4/19/21 11:09 p.m.

In reply to Mr_Asa :

So, I tried something similar to this with a thick piece of acrylic and UV curing adhesive. The glass ended up cracking under the pressure of the clamping even as I struggled to get enough clamping pressure to eliminate bubbles and get everything to line up. I did not use tempered glass as it cannot be cut and wasn't available for free.
 

Also, I should probably add that the lid needs to be about 18" in diameter. I also think I could get rid of most of the bubbles with adequate clamping, even in the absence of vacuum.

Lee
Lee UberDork
4/20/21 10:14 a.m.

Is there a reason the whole thing needs to be transparent?

Make a lid out of metal or something with a smaller more affordable acrylic portal in it?

white_fly
white_fly HalfDork
4/21/21 12:05 p.m.

The whole thing doesn't have to be transparent, but it's ideal and I want to make a few of these, so I think it's worth coming up with a good solution.

Kendall_Jones
Kendall_Jones HalfDork
4/21/21 12:17 p.m.

Vacuum is like PSI but in reverse - 18" diameter?  that is a ton of square inches, like 250 or so.    We're at 14.7 psia and if you pull 10 psia out of that your at 2500 pounds on that 18" window.  Thats like a miata.

make it out of steel and put a small window port in it - or use trial and error and a timer.

 

white_fly
white_fly HalfDork
10/23/22 12:50 a.m.

This is a necrothread, but I think it needed closure. I did end up using the lamination film with a vacuum bag in a regular home oven. The bag worked well and the film was fully melted, but the line I was using for vacuum also collapsed with the heat. I ended up with a lid that was more than usable, but had a bunch of little bubbles in it. I need to try making another lid with a vacuum line that can stand up to the heat. Another option would be to use the (expensive) UV curing glue and slowly ramp up the vacuum pressure to avoid cracking the glass again.

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