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Has anyone used these small plastic vacuum desiccators?

Posted: Mon Apr 24, 2017 1:23 am
by Paul Loatman
I first should say that i have no interest in building fusors, sorry, i just can't find anywhere else to discuss vacuum technology. After a few searches i haven't come up with anything related to what i'm looking for, so i figured i would just ask.

Has anyone used those small plastic desiccator vacuum chambers? LIke these: https://assets.labequipmentdepot.com/pr ... /55214.jpg

They're usually made of polycarbonate, and i'm skeptical of it's ability to hold a vacuum. So if anyone has an experience with these and could confirm or deny whether these actually work as advertised, i would appreciate it.

Or, if anyone has better options for a reasonable cost: I need something that can hold a vacuum for prolonged periods to protect delicate machine and instrument parts from the atmosphere, but i don't want to keep a vacuum pump constantly running to do this. A small container that can be put under vacuum, sealed, and left would be ideal. Any ideas?

Thanks,

-Paul

Re: Has anyone used these small plastic vacuum desiccators?

Posted: Mon Apr 24, 2017 7:01 am
by John Futter
They hold vacuum just fine but not a deep vacuum
polycarbonate sublimes @ high vac.We use the exact same one under backing pump vac to house our sputter targets ie gandolinium Calcium etc to keep oxygem away from them

Re: Has anyone used these small plastic vacuum desiccators?

Posted: Mon Apr 24, 2017 9:34 am
by Dennis P Brown
Do realize that such a chamber can never support any type of plasma (ionized gas.) So, unless your application is just a storage chamber such a vacuum container would not appear very useful.

I made a small sputtering chamber out of a old wine bottle (used a bottle cutter to remove its base - then polished with emery cloth) and a small piece of scrape aluminum (for the grounding base), a O-ring seal from a piece of scrap rubber (hand cut with scissors) and a rubber cork for the upper electric feed thru using some heavy gauge copper wire; far cheaper than a standard desiccator vacuum storage container ... .

Not that is what you want but making a viable vacuum chamber can cost just a few dollars if one is creative.

Re: Has anyone used these small plastic vacuum desiccators?

Posted: Tue Apr 25, 2017 6:44 am
by Richard Hull
My fusor I, (demo), was built in late 1997 and was in a plastic desicator. There are images of all of my fusors in images du jour. FusorI taught me a lot and I studied vacuum and ionized gases for over 6 month with it. The best I could do was about 35 microns when the plasma was on due to the beams outgassing the poly carbonate as noted above. Fusor II was made in a nice bell jar system in early 1998. I got that down to 8 microns and saw the fist star rays.

Poly carb desicators are not a great choice for a demo fusor.

Richard Hull

Re: Has anyone used these small plastic vacuum desiccators?

Posted: Wed Apr 26, 2017 12:10 pm
by ian_krase
If you want to seal stuff in vacuum, you should probably look at either metal tube that can be pinched off or glass tubing that can be melted off. Dismountable seals are not going to be an easy thing to have, and with no pump you will be vastly more vulnerable to leaks, virtual leaks, and outgassing. Depends a lot on how good of a vacuum - also, high vacuum does not necessarily equal cleanliness.

Re: Has anyone used these small plastic vacuum desiccators?

Posted: Thu Apr 27, 2017 2:04 am
by Paul Loatman
I have a vacuum pump for another application that i could use, or i could always get another, i just don't want to leave a vacuum pump running constantly since this is all being done in a residential building. The reason why i want to seal this stuff is mostly to remove them from the atmosphere to prevent corrosion on ferrous metals (by removing the oxygen), not necessarily to keep them clean, although i would keep the internals of the chamber and the parts inside clean. I would only need a vacuum down to 30 inHg, but i want to be able to hold that vacuum for prolonged periods, but not indefinitely. I want access to the parts whenever i need them without having to do much to re-seal them.

I've been thinking about this the last few days and have been reading everything posted in this thread. I'm starting to think that making something myself would be my best option, since my application seems fairly specialized since i can't find anything that would really suit my needs exactly.

I might machine some chambers out of aluminum and test how well they can hold a vacuum with a cover screwed down and an o-ring between. I've seen acrylic chambers that have wall thickness of 1 inch, so i would imagine that 1 inch aluminum would be fine, especially if it's a nearly solid chamber, with the exception of the cover. I also acquired some 1"x4" round sight glasses which will give me a good view of what's inside. The only downside again is the cost of the aluminum, it's very expensive to get enough to make a chamber the size that i want, since it has to be one solid piece to machine out the chamber. The internals will probably be around 5" round x 2.5" deep. Which means a 7" diameter bar of at least 3.5" length, which is a pretty big chunk of metal.

For now, i'm sticking with a desiccant cabinet and Pyrex labware, but i'm more and more becoming interested in miniature vacuum chambers for storage.

Re: Has anyone used these small plastic vacuum desiccators?

Posted: Thu Apr 27, 2017 3:46 am
by Frank Sanns
The glass variant with high vacuum grease on the mating surfaces and the vacuum port on the lid will hold a decent vacuum for a long time as in months. No outgassing there and a very slow leak down rate.

The other technique with these is to put some desiccant in them to keep totally dry if any air gets in or some getter that will suck up any oxygen that might makes its way in. We used to keep some potential nasties in there with no problem for a year at a time.

Re: Has anyone used these small plastic vacuum desiccators?

Posted: Thu Apr 27, 2017 11:02 am
by Dennis P Brown
A very simple solution would be using a "Mason" jar (that has a flat top for an opening; these are used for food "canning" and are rather strong); cut a rubber gasket to fit the opening, get a metal plate that can fit across it and add a pump out line/valve to the plate. One could use the glass top if you wanted to use a glass cutting drill bit (these in the form of "hole" saw blades work very well.) Then use epoxy to seal in a pump out line. Then the Mason jar's standard lid and gasket will work fine to hold a vacuum.

Either of these methods result in a very low cost storage chamber. Once pumped out, should hold a serviceable vacuum for many weeks. And easy to re-pump out as needed. No need to machine a special chamber.