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Upsilon
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Constructing a vacuum chamber
Disclaimer: This project is a significant and expensive undertaking. At this point in time this is merely speculation, and this plan is nowhere near
ready for execution.
I am thinking of ways to construct a fairly large vacuum chamber that can also double as an inert gas environment. While the chamber is filled with
inert gas, I would like to be able to interact with its contents whilst still maintaining a sealed environment from the outside. This is typically
done with inverted gloves connected to the chamber. My problem is keeping these gloves from being destroyed while the chamber is in vacuum state.
Essentially I would pull all of the air out of the chamber, and then let the inert gas in. I feel that this is much more efficient and effective than
the usual method of simply flooding the chamber with the inert gas until all air has been displaced. Like I said, however, is keeping the inverted
gloves from being sucked into the chamber while the vacuum is being pulled.
For the chamber itself, I am considering a 1'x1'x1' cube. I realize this is a poor design for a vacuum chamber, but forming steel into a ball or even
a cylinder is too difficult to do in a typical garage. This means that each face of the cube must support over 2000 pounds of pressure, but with 1/4"
thick steel plates reinforced with a frame of 1" square solid steel bars will have no issue with these loads (obviously welded togerher; this design
may even allow me to enlarge my design beyond a cubic foot). It will be inlayed with PTFE sheets to protect the steel from corrosion due to the
presence of certain chemicals inside. Connections would include a connection to the vacuum pump, a connection from a gas cylinder to allow gases in,
and electrical outlets to plug in equipment. I will also obviously need a removable lid that can effectively seal when a vacuum is pulled.
The most challenging aspect, I believe, is going to be integrating the inverted gloves into the design. I'm not even sure if it's plausible. If I were
to design it, though, it would obviously need to be multiple layered gloves. Perhaps some high-strength glove on the outside like a welding glove to
withstand the force pushing it into the chamber. Inside would be a rubber or PVC glove to make it airtight. These would be bolted to the outside of a
hole I would cut in the side of the chamber.
I would not even hope to use these gloves while the chamber is under a vacuum, since they will be so stiffly inflated that I would barely be able to
maneuver them. However it is a practical option when the chamber is repressurized with a different gas.
Like I said, this is just a rough plan, and I won't even consider beginning construction until at least a few months from now. Any suggestions will be
appreciated.
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aga
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Make it small.
Make it Sealed.
Make little robots to do the dirty inside the box.
Edit:
I had an idea to make a small robotic lab, remote controlled, when i first toyed with the notion of doing any EM stuff after joining this site.
Chose to not do any EM at all as i'd have to and physically get the Products by hand.
What the hell. You only live once, and there's no fun in dying intact.
[Edited on 21-9-2015 by aga]
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gdflp
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What kind of vacuum are you hoping to be able to pull with this chamber? 20mm, 1mm, 0.1mm? If you are planning on using 1/4" thick steel for most of
the construction, which is quite thick!, what lid material are you planning to use that will be able to withstand an equivalent amount of pressure?
If you just want an inert atmosphere, pulling a 20mm vacuum then backfilling with inert gas two to three times will essentially remove all air from
the apparatus, drawing a stonger vacuum is unnecessary. I would recommend seeing if you can have a removable panel with glove holes or no glove
holes, similar to the lid, if you are hoping to pull a hefty vacuum as I agree that having gloves present will be a nuisance.
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MrHomeScientist
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You could have a closure system for the glove ports. Let's see if I can describe this well enough. For each glove port, there would be a disk of steel
with tabs around the outside rim and a handle on one face. The tabs could be made by slicing segments out of the edges of a larger disk. The glove
port would have a similar set of tabs. The disk would sit inside the box and you'd insert your hand into the glove, pick it up by the handle, bring it
up to the inner side of the glove port, and turn to lock it in place, sealing the glove essentially outside the box. Sort of like the closure system
used by those containers that 100 packs of CD-R's come in.
Also I assume one side of this box will not be steel, otherwise it would be pretty hard to see what you were doing. This face will also have to
withstand the pressure differentials, of course. Since this is really just a small glove box, I'd look at how those are designed.
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aga
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Nope.
You got to do a Video or at least a Photo these days.
Mere descriptive power no longer works.
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Upsilon
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I'm not particularly aiming for a certain level of vacuum; I'm just going to pull until my vacuum pump can no longer pull. The one I have is old but
fairly powerful, I'd have to go dig it up and bring the specifics back to you all. I'll do that a little later.
As for the suggestion to pull a light vacuum, refill with inert gas, release, and repeat a few times, this would work but like I said in the OP I'd
rather have as little waste as possible. This way I only need to fill the chamber once and would waste less gas.
Also I forgot to mention how I'm planning on including a window. To do that I'm going to cut a small square out of the top side of the chamber. I
would then take a thick piece of Plexiglass larger than the hole and use some sort of epoxy to seal it to the steel panel. I may put a piece of glass
on the inner side of the window to protect the Plexiglass from corrosive material, but this would not bear any loads.
I'm not entirely sure what I want to do for a door yet. Most likely it will be the majority of one side of the chamber with hinges, sealed with, well,
I don't really know what it's called but its that stuff they seal refrigerator doors with. As the vacuum is pulled, the pressure should push it down
to increase the strength of the seal.
MrHomeScientist, I think I understand what you're saying. The tricky part with that will be trying to open the little door with the gloves in the way,
but it shouldn't be too hard to figure out.
If I were to change the size of the box, I would probably just extend its length to 18". I think this is fairly reasonable; I don't see a problem with
it withstanding the extra load.
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j_sum1
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IIRC, danvizine designed, constructed and posted details of a vac chamber. You should look it up.
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aga
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As per the OP, No, you're not.
Not Doing Anything really, just Talking about an idea.
Do Something, even if it's just a plastic bottle with a syringe attached to make a partial vacuum. Suck hard on a bit of pipe if you need to.
Thinking is Good.
Thinking and Doing is how we (as a species) Discover stuff.
It's also much more Entertaining than mere speculation.
I like the bit where the legs fall off best.
Oh ! We have not gotten to that bit yet. Appologies.
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WGTR
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This is what you're talking about. You just don't realize it yet:
https://www.youtube.com/watch?v=HxX0QUjn_Gk&feature=yout...
http://www.mtixtl.com/desktopstainlesssteelvacuumglovebox24x...
They even have dimensioned drawings on their page. Have fun!
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Upsilon
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Wait a second, are they actually using those puny latex gloves in the chamber while it is under vacuum? I don't believe that; the gloves should
inflate like crazy until they explode.
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Upsilon
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Just dug up the old vacuum pump. It's a 5 CFM.
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gdflp
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That has nothing to do with the absolute pressure that the
pump can pull. It simply indicates the airflow of the pump at atmospheric pressure. The pump should indicate the maximum(technically minimum)
pressure that it is capable of achieving, typically the unit will be torr or mmHg, but it may also be psi.
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Upsilon
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That was the only information that the pump had written on it. I guess I'll be looking up the model number.
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Oscilllator
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Upsilon you are way overthinking this. Buy a pressure cooker or similar and follow a tutorial like this one, and you should be able to get one without to much effort. 1/4" steel plates is way overkill, no to mention the potential issues with
making airtight welds.
Making a glovebox will be much more difficult. I would suggest making the above chamber first, then considering this option once you have some
experience and know what you're getting into.
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Fulmen
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Upsilon: If you study those chambers WTGR brought up you'll see that they are equipped with pressure equalizing lids for the gloves. So they aren't
meant for use while evacuated.
One wild idea: If the content/sample isn't fragile, easily disturbed or with sharp edges you could simply use a large inflatable balloon to flush out
the air.
We're not banging rocks together here. We know how to put a man back together.
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Magpie
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If you just want an inert atmosphere in which to work you don't need to pull a vacuum. Your work space can be as simple as an inflatable clear
plastic bag. Craft shops even sell such for this kind of work.
The single most important condition for a successful synthesis is good mixing - Nicodem
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macckone
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The inert atmosphere in industry is usually done by flushing with a large quantity of
inert gas and then recirculating through an oxygen remover (usually micro ground
iron particles and salt). This mix is available as hand warmers in most places. I think
you will spend more on the vacuum chamber than the inert gas and scrubber. Of
course that assumes your reaction is not nitrogen sensitive and what your oxygen
tolerance is. Cylinders of nitrogen are really inexpensive for rental. Argon cost
more for the gas. If CO2 is an acceptable gas then it gets even cheaper
and you don't need a cylinder but you do need a drier tube.
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phlogiston
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I don't know how large your hands are, but a 1 foot cube seems like an awfully small space to work in with both hands. I expect it will be impractical
to do much.
The size of your box is entirely restricted by your requirement of being able to pull it vacuum, but you never intend to work with the gloves in a
vacuum. Therefore, I think it makes more sense to make a largeish glovebox for inert atmosphere work, that you can work in comfortably and a separate,
smaller vacuum chamber with no gloves.
View it from a pragmatic perspective.
While a nice challenge, you should consider the possibility that the money you spend on realising the design you are now planning will buy you a lot
of inert gas, possibly more than you will ever save by having the ability to do the vacuum/gas cycles. And that is not counting your time (You could
spend the time building this delivering pizza's and buy the gas). Especially if you eventually find the cramped space so impractical that you will
eventually hardly ever use the box, it would be a dissappointing waste of your time and money.
That being said, if you decide to pursue this further, why build a square box using lots of steel if you can use a discarded fire extinguisher or
other source of pipe which is a much more optimal shape? You will only need to worry about the end caps then.
For gloves, check out what NASA uses for their spacesuits.
[Edited on 22-9-2015 by phlogiston]
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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Twospoons
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The other starting point for your chamber could be an empty propane or LPG cylinder. They come in many sizes, and are relatively cheap. Just be sure
to flush out any residual gas if using a second hand one - you don't want a spark igniting anything when cutting into the cylinder. The usual method
is to fill the cylinder with sand.
I rather like the pressure cooker idea - its almost ready to go.
Helicopter: "helico" -> spiral, "pter" -> with wings
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Dr.Bob
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Magpie is right, the simple answer is to just use a disposable type glove bag. You can suck a vacuum on one, then inflate it and have a decent
air-free space which is somewhat easy to work in. I have used one before for working with potassium hydride in a humid area, and it worked well. I
have also worked in a real glove box, and those are not easy to work in at all, but do work well.
They are great to use, but even they have issues, if you use more than one chemical at a time, the vapors of them can mix in the inert gas system and
make a mess (think HCl and TEA for example). So while it seems great to be able to uncap butyl lithium and just pour it without care, in reality,
you have to still handle it with a syringe and needle still. But a glove bag can allow you to make air-sensitive metal complexes, handle strong
bases, work with pyrophorics, and use sensitive catalysts with less trouble. But you have to be careful as when you unassemble your glove bag/box,
the remaining compounds have a tendency to still catch fire or still be toxic, so best to work inside a hood or outdoors.
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Upsilon
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The glove bag is an appealing idea, but it seems like it would be difficult to pull a good vacuum over some flask, for example. I feel like the bag
would seal over the mouth of the flask and prevent the air in the flask from being sucked out.
That, and if you accidentally start generating a lot of gas somehow, it'll probably pop. Or, if you're intentionally generating gas with electrolysis.
That's another thing, it doesn't seem like a good idea to use a bag to melt NaOH in.
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Upsilon
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Alright, so after much thinking I have decided against the steel cube design I was considering. It seems like a big headache to me. I have no
experience with steelworking so I doubt I could make a very good box on the first go. Not to mention it's expensive.
So, I am now thinking of a more modest design, made from a 1' length of 6" diameter schedule 40 PVC pipe. This is supposed to have a 5/8" thick wall
so I think it will be perfectly fine holding a vacuum. The problem is, I still want to be able to heat substances inside of the chamber. PVC pipe has
a max temperature of about 140C. While I won't really be melting anything at very high temperatures, I would still like to achieve around 300C if
possible. I think this is doable with insulation - the PVC pipe would be the outer layer, with a healthy layer of insulation inside, and finally an
aluminum foil innermost layer.
The biggest problem I see is the heat transfer from an outside source of heat. I would need to use a steel disk to seal the end of the pipe that I'll
be heating from. Which means I would need insulation between the steel disk and the PVC pipe's circumference. Doing that compromises the airtight
seal. I would need some kind of high-temperature seal to coat on the outside of this insulation ring to keep it airtight.
First, what kind of insulation material would be best for this? And does anyone have an idea for a high-temperature sealant?
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careysub
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Quote: Originally posted by Upsilon  | Alright, so after much thinking I have decided against the steel cube design I was considering. It seems like a big headache to me. I have no
experience with steelworking so I doubt I could make a very good box on the first go. Not to mention it's expensive.
So, I am now thinking of a more modest design, made from a 1' length of 6" diameter schedule 40 PVC pipe. This is supposed to have a 5/8" thick wall
so I think it will be perfectly fine holding a vacuum. The problem is, I still want to be able to heat substances inside of the chamber. PVC pipe has
a max temperature of about 140C. While I won't really be melting anything at very high temperatures, I would still like to achieve around 300C if
possible. I think this is doable with insulation - the PVC pipe would be the outer layer, with a healthy layer of insulation inside, and finally an
aluminum foil innermost layer.
The biggest problem I see is the heat transfer from an outside source of heat. I would need to use a steel disk to seal the end of the pipe that I'll
be heating from. Which means I would need insulation between the steel disk and the PVC pipe's circumference. Doing that compromises the airtight
seal. I would need some kind of high-temperature seal to coat on the outside of this insulation ring to keep it airtight.
First, what kind of insulation material would be best for this? And does anyone have an idea for a high-temperature sealant? |
What advantage does this have over a old pressure cooker?
If you making a PVC chamber you should be looking at doing the heating inside the chamber with some kind of resistive heater. Then a PVC cap, with a
gasket could be used to close.
Fiberglass batts are probably the best insulation.
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Upsilon
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| Quote: Originally posted by careysub |
What advantage does this have over a old pressure cooker?
If you making a PVC chamber you should be looking at doing the heating inside the chamber with some kind of resistive heater. Then a PVC cap, with a
gasket could be used to close.
Fiberglass batts are probably the best insulation. |
Well, a pressure cooker is designed to contain high pressures, not a vacuum, so I don't know how well it would work. They operate at about twice
atmospheric pressure, and the structure is more efficient at containing a high pressure rather than a low one. Pulling a vacuum in it would be putting
it against its normal operating pressure but from the outside instead of inside. That, and I don't have a pressure cooker, and I want to be able to
easily cut a window and other holes, and also because I feel like the aluminum would corrode much faster than PVC against certain substances. Granted,
the aluminum foil in the PVC design will also corrode, but this can be cheaply replaced. The pressure cooker may work perfectly, but I think the PVC
pipe is a more feasible option in my situation.
Also, the heating element inside of the chamber sounds like a good idea, but I wasn't completely sure if I'd be able to fit something in there.
Remember, the pipe only has a 6" inner diameter, and after insulation I may only have 4" of space. Still, it seems like a better idea than trying to
seal a steel plate to the pipe. This will also help the heater to be extremely efficient; no loss by convection, and much of the radiation can be
reflected back by the foil. Hell, I could probably get away without even insulating the PVC since it will absorb very little heat this way. But I also
want this to function as an inert gas chamber so I'll have to insulate it anyway.
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careysub
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Try looking at Goodwill for a pressure cooker, any you find there will be aluminum. I see a new 6 Qt aluminum on eBay for $19 including shipping. You
don't need a premium model for this.
Holes can be put into aluminum with a hole saw, it drill and taps with ease. You would need a good gasket of course (if buying used). Silicone gaskets
should take pretty high temperature.
Pressure cookers do hold vacuum - after you have finished canning or cooking and the cooker has cooled you have to break vacuum before you can open
it. You will be attaching this to a pump so small leakage (if any exists) will be taken out by the pump.
Also consider buying a battle-scarred All American pressure cooker on eBay or Craig's List. These are the Cadillacs of pressure cookers, are large
(for canning) 10-20 qt and use an aluminum metal-to-metal seal (no gaskets). Options exist for under $100.
I wonder if a wide angle peep hole viewer could be installed in a tapped hole for viewing, with a small incandescent bulb installed inside.
[Edited on 1-11-2015 by careysub]
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