building a (small) vacuum chamber-type device

Hi everybody,
I want to build a device similar in some ways to a vacuum chamber. It should be able to be filled with various gases, a various pressures. In
the chamber, there will be some electrical device. As the device runs, I want to mesure different things: how the heat produced is eliminated depending on the type of gas, its pressure, how is EM radiation released inside, etc.
So basically I need a gas tight enclosure, probably stainless steel or some other non-reactive metal, with some gas ports on it to fill and empty it (no problem), a door to swap the device inside (no problem), some ports for electrical connections (problem).
I do not know how to make an electrically insulated, vacuum and heat resistant electrical port. The material of the port needs to be as inert and heat resistant as possible, it can not release gases or any contaminant under vacuum (thus drilling a hole in the chamber, putting a rod through and sealing it with epoxy or any resin won't work). I thought of using glass, but I can not fuse the glass to the metal because of the different thermal expansion rate of glass and metal.
Any ideas ?
bruno
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
says...

You need to define what pressure you need to achieve.
10e-3 torr?
10e-6 torr?
10e-12 torr?
Once you define a desired pressure range, that will deterrmine the kinds of vacuum feedthroughs you will pick.
Jim
--
==================================================
please reply to:
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bschwand wrote:

As Jim R. said, you have to specify the pressures and voltages you want to work at. That said, if I were building such a thing for a company, I'd call up Deutsch, tell them what I wanted to do, then send them a big check:
http://www.deutschecd.com /
They've been solving this sort of problem for many years.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bschwand wrote:

Depends on what you mean by heat resistant. Torr-seal works to 120 deg C and 10-9 torr.
http://shop.store.yahoo.com/vacuumshopper/toseeqb9.html
I've heard of people using spark plugs as feedthroughs. I doubt they'd be any good at high vacuum though.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Pretty standard chamber, electrical feedthroughs included. I worked in labs where we ran 12-20 lines of coax from various plasma experiments in similar chambers.

feedthroughs are standard parts in the vacuum biz. They have special glass, metal and/or ceramics to deal with the expansion issue. I think the shop a few miles away is ceramaseal (one of many locations for that brand), there are many others. On the crude DIY front, try a sparkplug...
--
Cats, coffee, chocolate...vices to live by

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thank you for setting me in the right direction. It would not be high vacuum, probably at most 0.1 atmosphere. The spark plug idea is brilliant, I'll try that and see if it works. I'll do some googling about vacuum and feedthroughs.
bruno
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I found something that will perfectly fit the bill here:
<http://www2.ceramtec.com/CatalogNew/View_PG_Desc2.cfm?SectionID5&SubsectionID#3&PartDesc1=One%20Conductor&PartDesc2=%2E050%20%5B1%2E3%5D%20Dia%2E%20Conductor
for only $20, so I am not going to mess with spark plugs...
Thanks again. I can find anything once I know the correct keywords :-)
bruno
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That isn't even low vacuum in most labs. Plain old epoxy, or mechanical seals with teflon (or the spark plugs) should be fine for your application - when people are concerned about outgassing, it's generally at pressures a million, billion, or trillon times lower than where you are working...
Where I mostly worked, "low vacuum" was in the 1-300 milliTorr range. 1 atmosphere is about 760 Torr. Most of what that lab considered high vacuum was in the 10e-6 10e-7 Torr range; there are places which consider that pretty high, and commonly work in the 10e-12 or -13 range. Those people have outgassing concerns.
At 76 Torr, outgassing is not likely to be a significant issue.
--
Cats, coffee, chocolate...vices to live by

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Almost anything including duct tape will work at 0.1 atmosphere. No sarcasm here, it really will. Epoxy works fine at considerably below that level. So do O-rings.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
says...

That's about 80 torr. You can use anything for a feedthrough at those pressures.
Jim
--
==================================================
please reply to:
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
For 0.1 atmosphere, RTV around a wire is more than sufficient. The vacuum side is only 14.7PSI and that really isn't much pressure trying to get in. The reason for the glass seals and so forth is that when you are down at nano torr values, the inflow is sufficient to drop that vacuum level real fast. At 0.1 of air pressure, the inflow is so small that it will take years to do significant damage to the vacuum. Remember that a steel (not even a polished steel but just run of the mill steel surface) to rubber interface holds air in a tire for many years in an automobile tire.
-- Why do penguins walk so far to get to their nesting grounds?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Buy hermetic connectors. The 10e-7 torr thermal vacuum chambers I once tested space stuff in (for Gemini and Apollo) used Deutsch connectors.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bschwand writes:

Consider a standard bell jar and baseplate. Lot easier than trying to build something yourself, and easy to see what's going on.
E.g. http://www.fishersci.com /
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I built a vacuum chamber for aluminizing telescope mirrors. Mild steel chamber, plate glass electrical pass thrus, held in place with two part epoxy. 2x10e-5 torr consistently, with a few trips to 9x10e-6 torr.
Oh, and spark plugs work just fine at this range, but, all in all, make terrible electrical pass thrus.
http://lerch.no-ip.com/atm (item 18)
The new and improved chamber: http://lerch.no-ip.com/atm/Projects/Chamber/First_Coating /
Take Care, James Lerch http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site) http://lerch.no-ip.com/ChangFa_Gen (My 15Kw generator project) Press on: nothing in the world can take the place of perseverance. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. Calvin Coolidge
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@no.spam.tampabay.rr.com (James Lerch) wrote:

Use Non-resistor spark plugs ;)
--
Free men own guns, slaves don't
www.geocities.com/CapitolHill/5357/
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

There are many ways to seal glass to metal. Kovar can be directly sealed to Pyrex, vacuum tight!
Randy Hansen SC Glass Tech Scam Diego, Comi-fornia

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

So use a vacuum chamber. The scrap trade for lab scrap is a bit obscure, but it is out there. S/H vacuum systems are there to be found and I've always bought them for no more than scrap steel price. Pumps OTOH are expensive, because there's a good market for those. The _convenience_ of well-designed well-made vacuum plumbing is worth the effort of searching for it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Try this guy.. murphyjunk.bizland.com Mikes a good guy and he has a huge warehouse full of stuff like this He ships everyday and prices are very fair Ihave no stake in this at all
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bschwand wrote:

Check out the Chemistry Dept. of your local University. Look at their "glove boxes" I've worked in several Chem depts. and I think they are exactly what you want. ...lew...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bschwand wrote:
Before you get too far, you might want to think about the effects of your "gases" on your mechanical pump and its oil. On the other hand, at .1 atmosphere, it might be best to just use old refrigerator compressors and throw them away when you are done.' While I think of it, at .1 atmosphere, you still have a lot of air in there. That may well affect the accuracy of your experiments.
Pete Stanaitis -----------------

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.