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Making a high pressure vacuum chamber

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No_Shorty:

--- Quote from: james_s on March 09, 2023, 06:31:26 pm ---There are small labs such as universities using "Instant Pot" pressure cookers as low cost autoclave machines, perhaps that would work? Conventional pressure cookers that you put on a stove sometimes turn up in thrift stores.

--- End quote ---

Yea I had started to look in to this as a pressure cooker is a common thing to use in a 'DIY' vacuum chamber for degassing epoxy and the like. They are typically rated for only 15psi however, so believing I needed something that could do 100psi I abandoned the idea (and then subsequently learned the 100psi was for a pressure chamber, not a vacuum chamber). However, 15psi may be plenty to suck the bubbles out from under a screen using the LOCA glue, as it is fully liquid.


--- Quote ---The most common application for an autoclave machine is sterilizing medical devices such as surgical instruments. They are just a fancy pressure cooker, using superheated steam in a sealed pressure vessel to sterilize the tools.
--- End quote ---

Yes, this was confusing when I first started looking up 'autoclaves' - as the ones for electronics obviously do not use steam. They are more commonly referred to as "bubble remover machine" when referring to mobile phone repair or assembly. Although "autoclave" is sometimes used. They do not use steam to create the pressure but a pump.


--- Quote from: HighVoltage on March 09, 2023, 07:03:44 pm ---There are plenty of spezilized companies that make special glass for pressure chambers to be safe.

I have built a pressure chamber once for up to 200 bar and it required a 32mm thick glass at about 120mm diameter. It was tested for up to 400 bar, so I was on the safe side.

DO NOT play with acrylic and pressure chambers!!!

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It was only as acrylic is used for a lot of DIY chamber 'guides' you find online that I had been considering it (and of course the ability to see whats going on inside) - do you think there is no safe level of vacuum in which acrylic can be used?

I would have thought glass - if you get it wrong - would be even more dangerous, and I would guess specialised glass that is specced for such things is gonna be pretty expensive to 'experiment' with?

At this stage I have pretty much abandoned the idea of a high vacuum chamber. As it seems unachievable and the tools for removing bubbles use pressure chambers not vacuum chambers in any case.

I a considering the kind of vacuums that seem to be common for 'pressure cooker' builds - so around 15psi (in lieu of knowing how to trqnslate that from pressure to vacuum unit, if that is erroneous) - this is why I was still considering acrylic, as it is common in these builds and would allow me to make something the right size. As opposed to having to buy a heouge pressure cooker.

dmills:
Acrylic is horrible for this, it just loves to propagate cracks if you even look at it funny, and that is not a good thing.

Were I trying this I would be taking a leaf from the model engineering communities boiler making practises, and obviously doing some fairly hard core hydrostatic tests before even thinking of pressurising with air.


 

Ian.M:
+1
Acrylic plastics are notorious for poor impact resistance, micro-cracking, and sudden catastrophic failure under tensile or bending stress.

Polycarbonates are a lot better (tougher) as long as you respect their chemical compatibility limitations.  Using the wrong sealant or plasticizer migration from the wrong choice of gasket material or exposure to solvent vapours can trigger catastrophic failure by removing its toughness, making the Polycarbonate plastic extremely brittle with little or no visible signs of the incipient failure.  With this known issue, I would personally not be comfortable with a Polycarbonate viewport design unless it was protected against chemical contamination, and was constrained by a strong metal mesh and supporting grid on the outside to contain any catastrophic failure under pressure.

If you *NEED* visibility inside your vacuum/pressure chamber and cant afford a commercially available, new pressure rated viewport, consider a video camera inside the chamber.

No_Shorty:
Ok, noted. Given the acrylic would need to host a metal valve as well I can see that being a source of fractures. As I said I had only really leant toward it as it was a common material in DIY projects, but I know those are often done without any knowledge of the materials.

The visibility was more for inspection of bubbles, not really achievable with a camera I don't think. I would have also allowed me to pull the vacuum as well as cure the LOCA whilst under vacuum. to ensure no bubbles creep back in - but this was a 'nice to have' idea, not an essential.

I could afford to consider something up to about £1.5k if it was the 'right' solution (like one of the bubble remover machines linked above) but I certainly can't be experimenting with how well a vacuum chamber works for LOCA for that kinda money. I probably can afford to drop a couple of hundred on a pressure cooker style vacuum/degassing chamber from Amazon, so may go down that route for testing.

If I was to DIY a solution then I would probably go for 3 pieces of thick steel or alu, with a hole cut out of the center piece - so same as my original idea but no visibility.

Ian.M:
Vacuum bagging would be worth a try.  Its pretty easy to DIY, easy to inspect the lamination process, and doesn't require a pressure vessel.  However it only gives a maximum of 1 bar pressure, and in practice significantly less, because its generally desirable to reduce the vacuum to reduce the size of residual bubbles after pulling a higher vacuum to de-gas the adhesive.   You *MIGHT* be able to reach higher pressures without a pressure vessel using a press, and an elastomer pressure pad on top of the vacuum bag, but that would only be practical for thermal or chemical cure adhesives as it would block access for the light source for UV curing.

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