Stainless steel pipe chamber

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Rich Feldman
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Re: Stainless steel pipe chamber

Post by Rich Feldman » Thu Jun 29, 2017 7:09 pm

You can clean up sawed pipe ends with an angle grinder. If the pipe is cut to length at a metals store, they might do it with a bandsaw that could make a pretty straight cut.

It doesn't take much wall thickness to make a strong enough cylinder. The ends are another matter, if you are talking about flat material and pipe diameter over 6 inches.

Look up a fusor thread by David Kunkle (?) a couple of years ago, as he was planning an 18 or 20 inch cylindrical chamber, and talking about strength of materials.
After running the numbers for flat disk thickness requirement, he went with ready-to-weld convex "tank heads", same wall thickness as the cylinder.
For somewhat smaller cylinders, have you considered hemispherical heads?
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ian_krase
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Re: Stainless steel pipe chamber

Post by ian_krase » Thu Jun 29, 2017 11:09 pm

Yeah depending on circumstances a sphere with nonstructural "ends" might be easier.

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Rich Feldman
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Re: Stainless steel pipe chamber

Post by Rich Feldman » Fri Jun 30, 2017 11:43 pm

Oops, just saw that the early posts talk about a flat (cyclotron-like) chamber. If the cylindrical section's length is to be much less than it radius, and dished or hemispherical heads are out...

1. For end plate thickness requirements, try searching for "plate deflection calculator" or "plate deflection formula". Here's one: http://www.roymech.co.uk/Useful_Tables/ ... lates.html which has, right at the top, "circular plate, uniform load, edges simply supported" and "edges clamped". Note the factors of t cubed and r to the fourth.
plate2.PNG
plate2.PNG (18.86 KiB) Viewed 1229 times
2. How about making the cylindrical section out of a flat strip (aka thin rectangular bar), bent into a circle, instead of starting with a tube? Then the surfaces where it joins the end plates would be nice to begin with. You would have more choices of material and thickness, and infinite flexibility on the diameter. Cutting would be minimal if cylinder length matches the width of a stock product.
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Rich Feldman
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Re: Stainless steel pipe chamber

Post by Rich Feldman » Sat Jul 01, 2017 4:13 am

Just saw the flat strip idea posted by Ian, within the first few replies to OP. For some reason I can't edit my post from a couple hours ago, to add that acknowledgement.

As for end plate thickness:
I bet Chris will find that the minimum for strength (not bursting under load; optionally springing back to original flatness when load is removed)
is less than the minimum for stiffness (i.e. not deflecting so much that it looks alarming, or interferes with other workings).
Same applies to the design of floor joists in buildings, when the span between supports is large.

Chris, in OP you mention grooves for Viton gaskets. Parker Hannifin's O-Ring Handbook has a wealth of information about design of glands for elastomeric seals. Here's a bit about face seals. https://promo.parker.com/promotionsite/ ... Type-Seals
One non-expert reader, me, notes that the O-ring compression is predictably determined by metal to metal contact. O-ring's job is to seal, not to bear the axial clamping force. Unlike, say, engine head gaskets, or classical bell jars.
Last edited by Rich Feldman on Sat Jul 01, 2017 4:46 am, edited 1 time in total.
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Re: Stainless steel pipe chamber

Post by ian_krase » Sat Jul 01, 2017 4:36 am

Yeah, ignoring that rule ends badly. Of course rather than grooves you can use shims (like kf centering rings) or chamfers (like O Ring Boss hydraulic fittings).

Chris Mullins
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Re: Stainless steel pipe chamber

Post by Chris Mullins » Sat Apr 07, 2018 8:56 pm

Thought I'd give an update/answer to my question. We were able to make a decent vacuum chamber out of schedule 80 stainless steel pipe. We bought a 2 foot length of 10" diameter pipe, and 3/16" 304 steel plate for the lids. My son created mechanical drawings for the chamber and lids, including the 1" section of pipe, o-ring glands, KF-16 port holes and threaded screw holes, and we had a local shop do the machining. They re-faced the 1" section of pipe and the inside of the lids, but no extra polishing was performed. The results look great, and performed pretty well. It wasn't much extra cost to have them cut and finish a couple more chambers, so we got two with 10 KF-16 ports (for the cyclotron), and one with just a single KF-16 port (for vacuum testing).

Our "no-chamber" best vacuum (diffusion pump blanked off with just vacuum gauges and a length of SS tubing) is around 1.8E-6 torr. Best vacuum with the single-port chamber was 2.8E-6 torr, and best with the 10-port chamber was 3.4E-6 torr (9 of the 10 ports blanked off).

So, using stainless steel pipe as the raw material for a chamber worked pretty well!

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Re: Stainless steel pipe chamber

Post by Richard Hull » Sun Apr 08, 2018 7:22 am

Stainless is always the choice of the pro's assembling a system. However they tend to buy the stuff flanged and ready to bolt together like a matching part erectors set. Of course, they tend to have the big bucks or use someone else's deep pockets. You obviously did it the hard way and yet, as many do here, succeeded nicely while saving a bit of money.

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Re: Stainless steel pipe chamber

Post by Chris Mullins » Sun Apr 08, 2018 10:55 am

Well, we did wimp out when it came to the KF16 flanges. I had visions of learning to TIG weld, and then welding the 10 KF16 flanges to the chamber. That was just too much to take on while going through the learning curve of vacuum pumps and leak troubleshooting, magnet construction, etc. Instead, we used Hysol to epoxy the weld flanges in place. The chamber wall is about 0.47" thick, and the port hole diameter was only a few mils larger than the weld flanges. We coated the flanges in a thin film of Hysol, inserted them into the chamber port holes, cleaned up any excess epoxy, and cured them under heat (hair dryer). Seems very strong, and getting us in the low 10E-6 torr, so it's working out. The spare chamber was to be used if the Hysol version failed - that one would have the KF16 flanges TIG welded by a professional.

PS - in case anyone is interested, here are some pics from the build:

chalkboard design:
chalk.jpg
raw pipe - 2' of schedule 80S 10" diameter pipe, nominal thickness 0.500", around $240 purchased online:
raw_pipe.jpg
chamber and lid (with 273 o-ring installed) after machining:
chamber.jpg
lid.jpg
curing epoxied KF16 flanges with hair dryer (3 hours at around 150F), one at time:
curing.jpg
Assembled chamber:
assembled.jpg
Chamber with cyclotron attachments. Our best vacuum with all attachments is about 6E-6 torr, although more typical is closer to 8E-6 to 1E-5 torr. The weak link for vacuum seems to be the hydrogen feed, which uses Swagelok connections and a needle valve.
built_out.png

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Rich Feldman
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Re: Stainless steel pipe chamber

Post by Rich Feldman » Sun Apr 08, 2018 4:56 pm

Looks beautiful, Chris. Thanks for sharing.

Under vacuum, does the lid deflection match your expectation? As mentioned before, it could have plenty of strength margin & still move visibly with respect to a straight edge (and cyclotron dees). I'm personally curious as to where the answer falls between Simply Supported Edge and Clamped Edge. I like your choice to go easy on the tapped holes in SS, instead of screwing the heck out of it.

If the screw holes are countersunk or counterbored, here's a possibly fun way to visualize the deflection pattern. Might see if outer edge tilts up between the screws. With chamber flat on the bench, cover lid with a flat clear plate of glass or plastic. Fill the air gap with a bit of liquid that can provide optical contrast between contact places and 10-mil-gap places. Colored water? oil? milk? fluorescent dye? Of course the vacuum need not be "high", and the clear plate need not be super flat.

[edit] In case you didn't already think of it, here's one way to reduce the deflection without tapping more holes in the chamber wall. Maybe even allow thinner lids for shorter magnet gap. Extend the lids beyond the OD of the cylinder. Drill them for lots and lots of screws, that go into 1" long threaded standoffs shared with screws from the other lid. If the standoffs are a smidge shorter than the chamber, and not as close as they could be, you might even be able to dial in a preload that makes the lids convex outward when not under vacuum.
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Re: Stainless steel pipe chamber

Post by Michael Bretti » Sun Apr 08, 2018 7:22 pm

Very cool project, it's really awesome to see a cyclotron build! If it weren't for the size and cost of the magnet I'd consider pursuing one myself. Is this a personal project, group project, etc? Certainly not an easy endeavor!

Based on the diameter and the size of the dees, the pole piece and subsequent magnet are going to need to be very large and exceptionally heavy, since the pole piece needs to ideally be the same size as the dee to allow for a uniform accelerating field. Buying one will be very expensive, and building one yourself no trivial task, it will be a huge endeavor on its own to properly design and construct. What is the final energy are you looking to achieve for the particles in your system?

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