Talk-Polywell.org

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http://bluco.com/index.php

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They are having problems with their isp so you have to use IE to read the page for the next week or so.

Go down to the bottom of the page and have a look at the guy welding the large sphere.

I saw the ad for them in the April Issue of Modern Applications News page 31:

http://www.modernapplicationsnews.com/

I recall having the "large" chamber built. When we visited the plant, and saw our 12-ft long 6-ft diameter chamber out on the floor, I realised the hemispherical end cap of another chamber they were building could be placed over ours with room for several more like it! They can supposedly build them up to about 36 ft diameter.

Evidently, they usually set up facilities like this near shipbuilding facilities. There is a rolling process used to make curved plates for ships that is also good for vacuum chamber parts, especially domed ends. Plus, how else would you move a big chamber?

My experience with large tanks was we had them built in place from sheet stock with rolled stiffeners.
Worked fine for 20' & 35' dia mild steel tanks.
It is standard technology you can get lots of competitive bids.
I can see no reason why the fabricators could not do the same thing with stainless steel sheets.
Just a little tweaking of the welding parameters.
They may well already do it for the chemical industry.
We don't have to transport 36' dia chambers.
Also, think boiler makers.

Vacuum chambers require some special tricks that need to be remembered. Basically they all revolve around virtual leaks and avoidance of same.

Yes and real pinhole leaks.
Usually where the welder starts and stops.
I have seen a semi automated welding rig go 2 times around a 30' diameter tank without stopping.
The crew does this day in and day out. They are good.
Virtual leaks are a different issue they usually involve cavities inside or in between structures placed inside the vacuum.
And yes they can be a real bear to track down because they don't respond to a helium leak checker.
I would be surprised if anyone could get a 36' diameter chamber leak checked in less than 2 months. (that’s for just the chamber)

Tombo,

I've used both a helium leak checker and a residual gas analyzer. I conclude helium leak checkers are a waste of time. The RGA will do that job perfectly well, but it will also distinguish between a real leak and various types of outgassing.

Once the actual leaks are sealed up (the RGA will show prominent nitrogen and oxygen peaks, and will easily show helium or argon test gas, usually with an audio indication of peak height just like a leak checker), the real utility shows up. The dominant peaks will initially be a water triplet, telling you it is time to stop wrenching and start bakeout.

A lot of newer systems use UV lights instead of heat, which blasts water off faster and far more efficiently. One key to all of this is to have a really smooth interior finish. Some grades of stainless already have a good start on this finish, and I had the big chamber at EMC2 electropolished. You want minimal surface area, hopefully no porosity, and nothing hidden from the UV light.

Wire brushing is one of the worst things you can do. It smears metal over depressions, making pockets that are very difficult to clean out.

Running a plasma will clean things up fast.

Once the water is gone, the primary background gasses will be hydrocarbons and hydrogen. Meticulous cleaning before assembly helps minimize the hydrocarbons.

It should not take all that long to leak check the system, but it can take a very long time to understand why the pressure won't go down if you don't have an RGA, and can't tell what the source of the gas is. Once you identify the source, you know what you have to do.

When we got the big chamber at EMC2, in which WB4 and WB6 were run, I had it under vacuum in a few hours. Pumping it down, I found one 2 3/4" conflat fitting was not tightened, thanks to the RGA. That took an hour or two to find. The chamber then pulled down to the "high eights" overnight on one of its six 1000 l/s turbopumps, on a Roots blower and a large forepump. I was delighted by how fast it pulled down and how quickly it dried.

I might want to add never ever make a pressure vessel or vacuum chamber from welded Aluminum. Trust me, if you do, you will regret it.

It depends on what you mean by "vacuum". For the food industry, it's not a problem.

For science, you are correct!!

Speaking of food industry vacuum.

I worked at an Armor plant when I was a kid ('63) and we had a huge vacuum chamber to dehydrate top quality ground beef for the military. Maybe 100 or 200 sq ft of floor space about 8 ft high. I got to roll in tall racks of frozen meat rectangles for vacuuming. It took about 12 hrs to get all the water out.

One of our favorite tricks was to snag a few meat patties before the racks were rolled in and cook them by dipping them in vats of hot oil used to render pork rinds. About 2 or 3 minutes would do the trick. Yum.

Dr Mike
When I worked for the DOE Accelerator lab I delegated to design a Ultra High Voltage conduit from the Ultra High Voltage power supply to the Electron Beam Injector. This conduit required a 90 deg elbow, The EE in charge of the high voltage system insisted the elbow be made from Aluminum, specifically from the quarters of a large spun corona ring. The idea was to make the elbow light weight so it could be moved easily. I wanted it to be made from a standard stainless steel pipe elbow that could have been fairly easily modified to the requirements and would be easy to weld. He was the boss, so I drew up the elbow using ribs to counteract the Hoop stresses, another no no as I knew the elbow was going to flex. We finally got this monster welded up and hydrotested it. Every single weld cracked. It leaked like a sieve. By that time we had to use it and I think that it cost $6000 to fix the welds. Never again will I ever let an EE second guess me on pressure vessel construction.

What will the requirements for the IEC vacuum chamber be that are different than those that are used by NASA and/or the satellite industry to test satellites prior to launch? This is an established technology for large chambers and a good springboard for defining additional requirements for an IEC vessel. Am I off base?

Thanks JEB

I think you are right on - NASA has lots of huge chambers that pull down to 10^-8 or better. At some point the outer wall doesn't matter, it's the inner coil size that matters. If a tank has the shape of a cylinder it should be fine. Easier to maintain too.

JC - yikes! I guess some people have to learn things the hard way.

I would always go the machine shop and ask for the best way to build things. Once the guys understood what I was trying to do, they always came up with great ways to make it. I think just understanding the tools in the machine shop are a really important factor in designing anything.

This might be more of use with small fusor design if any, but could there be any advantage to putting the vacuum chamber and pump inside of an outer vacuum chamber. Use the pump to evacuate the outer chamber half way down, seal it, then pump out the inner chamber into the outer chamber the other half way, and seal that. The chamber walls and pump wouldn't require the same high strength and tolerance as the single chamber design. Possibly then construction material could be chosen more for heat resistance.

Unfortunately you need feedthroughs, which will be harder to arrange and cost more because you have twice as many. The obvious solution is to do it in space but the cost of lifting things to near-earth-orbit is still pretty staggering.

Regards,
Tony Barry

choff wrote:This might be more of use with small fusor design if any, but could there be any advantage to putting the vacuum chamber and pump inside of an outer vacuum chamber. Use the pump to evacuate the outer chamber half way down, seal it, then pump out the inner chamber into the outer chamber the other half way, and seal that. The chamber walls and pump wouldn't require the same high strength and tolerance as the single chamber design. Possibly then construction material could be chosen more for heat resistance.

Choff,

You are only talking 15 PSI which is nothing for a metal walled chamber. For a glass bell jar that is a little more of a problem, but thicker walls are cheaper than a double chamber.