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debequem
10-04-2003, 09:03 AM
I need to make or buy a pressure vessel to the following specifications:

max operating pressure = 60 psi.

Cavity size = apprx 8" by 6" by 4"

Door must be able to be rapidly opened/closed

maintain pressurized state for 1 to 3 hours

The purpose is to pressurize plastic cast materials as they cure. Since the pot life of the plastic once it is mixed is very low (a few minutes), the door must operate quickly and the vessel pressurized before the cure stage reaches maturity.

Any ideas?

Marv

BC21OSH
10-04-2003, 10:15 AM
Marv,

Would the tanks used for industrial paint application would work for your application? They have a gasketed top that is secured with swing away clamps with large knobs that can be quickly tightened.

The other option is to build one. We use a shop made unit that is a heavy square steel plate with a heavy steel cylinder welded to it. The top is a turned steel plate that is recessed to fit into the cylinder. The cylinder then has two heavy steel ears welded to it that project up above the top of the cylinder a couple inches at 180 degrees. The ears have a hole bored in each. There is a shaft with a "T" handle about 1 1/4-1 1/2" diameter that slides across the top of the lid through the holes in the ears. The shaft is turned down offset in two spots that line up with the holes to provide a cam action. When the shaft is turned in the holes, the cam action forces the fatter section of the shaft against the top of the lid securing it. The center of the turned lid has a raised portion in the center so that the shaft will have a bearing surface to clamp against rather than relying on resting against the entire top surface of the lid. The lid is about 3/4" thick material.

My brother-in-law used to be a denturist and he used a pressure cooker for curing resin for dental work, however I don't know what pressures he was working at. I know the pressure cookers are not normally rated that high.

Hope this long winded reply helps. If I was at work today, I would take a digital photo and post it for you.

Bernard

debequem
10-04-2003, 12:13 PM
Thanks. Some good ideas. I will look into the paint tank idea. Should be easy to see what pressure they are rated at.

Your idea sounds similar to what I was thinking. I was considering 1/2" plate aluminum, but the door could swing inward. On the contact surface between the door and wall I would line with a rubber gasket. I was thinking that the compressed air would keep the door sealed since it would press the door into the seal at pressure.

Instead of welding I was considering bolts so I could assemble the container with the door in place.

I am not sure that this would be mechanically sound or not. The last thing I would want is the box to burst! If it doesn't cause bodily harm, it sure would cause a mess upon rapid decompression!!!

Marv

Evan
10-04-2003, 12:46 PM
Marv,

If you build such a chamber I suggest you design a pressure actuated safety interlock that will not permit the door to be opened while the vessel is under pressure.

[This message has been edited by Evan (edited 10-04-2003).]

bikewrench
10-04-2003, 01:49 PM
Try a local SCUBA dive shop for a condemned 80 cu.ft aluminum cylinder they are 8 1/4 in. dia. and 3/4" wall.The dive shop or fire exstinguisher test places dispose of them when they crack at the neck or fail hydro test at 3000 P.S.I.! The remaining tank is great for adaptation to small pressure vessel.We sawed one off at 10" high and made a quick close door out of 4 pieces of laminated polycarbonate to pressurize dive computers to 100 p.s.i. to test for leaks. A single tank will yield all the material for the parts except for the flat plate/window for the top.And the best part is they will give them to you FREE or scrap price.Being designed for 3000 p.s.i. they will easily hold 100-200 psi for pressure vessels.I have a pressurized coolant tank for my mill made from one holds about three gallons and fills with air from shop compressor.Check your phone book for dive shops and go visit,They will usually be greatful to get rid of the "junk" tanks as long as you don't try to fix or fill them.

Bruce Griffing
10-04-2003, 02:11 PM
Don't know if they are good to your design pressure, but what came to my mind is a kitchen pressure cooker.

winchman
10-04-2003, 02:14 PM
If the vessel were round, how big would the inside diameter have to be, and how deep would it have to be?

Allmetal
10-04-2003, 02:19 PM
I use an old pressure cooker that has 6 thumb screws on the top and an air conditioner gauge set up for both vacuumming out any air bulbs and then switch over to high pressure to stop any gassing of the material for final cure. I pretested the cooker to over 75 lbs. outside and covered with a tarp to maintain it could handle the regulated 60 lbs pressure used. The arrangement is set up so the vacuum pump is on the low side of the A/C gauge and regulated 60lbs pressure is on the high side and the center hose goes to the cooker. I start out by placing the item in the cooker and at the same time start the vacuum pump which helps to seal the top as I draw down the thumb screws, as soon as I get to about 28 inches of vacuum I shut off the vacuum valve and open the pressure valve. These steps take only seconds to go from one to the other. I have also used a 2 gallon painting vessel but it can't take the bigger pieces I was doing.

Cass
10-04-2003, 02:53 PM
I just checked my storage room and I have a pressure tank made by EFB company. It is about 6.5" ID x 7.5" deep. It has 4 swing toggles that hold an O ring sealed lid. It has a pressure pop off valve and a pressure regulator with pressure gauge. It has removable plastic liner. It made of cast aluminum is rated for 100psi. It appears to be in new unused condition. Send me some email if you want it for $100 plus shipping.

debequem
10-04-2003, 03:20 PM
The pressure cooker sounds like a possibility. I have one I use for vacuum, but I wasn't sure if it would handle that much pressure. It has a screw type lid and is made by Ultrex.

I don't know what max pressure they are designed for. A clue might be what pressure the relief valve goes at. Might look around on the internet.

Marv

winchman
10-04-2003, 06:59 PM
From what I could find, it looks like pressure cookers are used up to 15 psi. Even with a generous safety margin in the design, using one at 60 psi seems a bit risky.

Alistair Hosie
10-04-2003, 07:08 PM
I used a pressure cooker pot all the time in dentistry to stop porosity when curing plastic. Buy a standard pressure cooking pot take of the valve that goes with it put on a pressure gauge, then a standard tyre valve fitting preferably a metal one with screw fitting as opposed to the pull through type, then a standard washing machine water valve to release the pressure this can all be done quite safely. Just drill or elongate the holes already there and fit the new parts it should work fine, releases in an instant Alistair

Alistair Hosie
10-04-2003, 07:09 PM
I forgot to add put some warm (not hot) water in the pot even immersing the plastic this should help speed up the cure time .Alistair

firbikrhd1
10-04-2003, 07:18 PM
A friend of mine recently took a bunch of aluminum cylinders for Self Contained Breathing Apparatus to the recycler. He got them at an auction where Fire Department equipment was being sold, they went for $1 each, he being the only bidder. They normally hold 2216 PSI working pressure and had a flat bottom that could be modified to install a door. There was a valve on the other end that the high pressure hose is connected to for the breathing apparatus that could be used to pressurize and later bleed off pressure.
You might keep an eye out at city/county auctions for similar cylinders.

laddy
10-04-2003, 08:19 PM
Hey,
Dentists used to vulcanize dentures , when the denture bases were made of rubber. They used vessels about a foot tall and 6-8 inches in diameter. These were filled with water and the dentures were placed inside and then the top was put in. The top had a guage attached and the pressure was applied. Pressure pots are used daily in the dental field to cure the acrylics used to make denture, partial denture, temporaries and the like.

Alistair Hosie
10-04-2003, 09:23 PM
these old vulcanisers are not so easy to come buy the material war a rubber vulcanite .Good grief your going back to well before the war any way that's too heavy a deal for what you want.A simple device called in dentistry a hydro flask will be fine for the dimensions you need no heat required such as with a vulcaniser,simple and cheap ( unless you buy from a dental supplier then the price is tenfold).Alistair

docsteve66
10-05-2003, 01:02 AM
an old propane tank? they take much more than 60 PSI. just keep away from square corners and huge openings. If they are too big, stuff them with scrap or Maybe even plaster of paris (depending on temps needed).

Evan
10-05-2003, 01:09 AM
Before you try cutting or welding on an old propane tank leave it open for a year or two. The propane soaks into the steel and will be released by the heat of a torch. I have a number aging as we speak, including a 100 pounder. (HA, Steve, how many do you have?) I even have a 30lb jug of freon 502B. Worth big bucks now.

darryl
10-05-2003, 02:54 AM
Pressure cookers are designed for 15-30 lbs. I have two, tested both to 75 lbs, and both distorted the bottom past the elastic limit. I wouldn't feel safe using either one over 40 lbs. One I now use only for de-airing resins and molding rubber. I made a pressure/vacuum vessel from two brake drums, put lexan windows in the openings, glued with shoo goo. Also a metal backup ring to hold against the vacuum. The drums have a groove where the gasket fits. Not having a suitable gasket, I made a hoop out of heavy duty surgical tubing, crazy glued the ends together. Holds pressure and vacuum, no problem. A simple hinge holds them in alignment, and for opening. No clamping is needed for vacuum, and for pressure, I made a band, in two pieces, from channel, rolled them to suit the curvature of the outside of the drums. When the band is cinched around the edges of the two drums, it covers the lips on the drums, preventing them from separating. Each is hinged, so it's quick to undo the clamp, swing the bands to the side, and lift the top drum to open the vessel. The clamp is a heavier duty version of the tool-box type wire loop hook thingy. It doesn't take any pressure, just prevents the band from opening. This thing I tested to 150 psi, no problem. You can see the lexan flexing, but not much. I used 3/8 thick. I don't recall exactly, but there's about 15,000 lbs trying to blow the drums apart, at a pressure of 100 psi. I don't like the hinge that holds the drums together when it's open, I had to make it sloppy so the drums could come together when under vacuum, compressing the gasket. If my lathe was bigger, I would have turned the lips and groove area to be more suitable for the gasket, that would have been easy with a larger machine. I had to build up part of the groove with silicone to take up some space so the gasket could get a seal.
There's a lot more to the story, including a second pressure vessel made from heavy pvc pipe, 8 in diameter, and about a foot long. That one had major sealing problems, still does.
I found when in use, relaxing the pressure steamed up the interior of the chambers for a short time. One mold I totally blew by not de-airing the clay form, then vacuumed the thing with molding rubber in it. Now I just de-air the rubber prior to putting it in the form.

ibewgypsie
10-05-2003, 08:35 AM
I used to use a large pressure cooker, a vacuum pump from a oldsmobile diesel car to evacuate bubbles from the investment for castings. 30 psi if I remember..

It worked great.

Pressure was about the same, don't over pressurize it thou. (pushing the other way)

David.

[This message has been edited by ibewgypsie (edited 10-05-2003).]

debequem
10-05-2003, 10:44 AM
All the data I found was that pressure cookers operate at 15 psi. Given a safety factor of at least 2X that puts it at 30 psi which is 1/2 of my goal. I am not comfortable with that stretch.

Pressure paint pots are rated to 80 to 100 psi and come ready to use. Cost is $80 to $100 new. Sears sells one and I am sure other manufactures do, too.

This may be the best rout since any more than two hours of effort to build something robs me of two hours I could charge someone else on a job, which pays for a new paint pot.

Of course, I would have never come to this delusion without the help of the list! Great to get such a broad spectrum of ideas to spark the imagination.

Thanks,

Marv

Thrud
10-05-2003, 04:48 PM
Have a "B" pressure certified welder weld an end on a piece of drill stem and then make a cap for it - you will have no problem with a few hundred PSI. The cap can be clamped or screwed on.

Steve Steven
10-06-2003, 01:55 PM
I have a friend who makes such pressure vessels for plastic modelers, If you are interested I can get his email address. He makes them from steel pipe, welded bottoms with hinged plate doors, rubber gaskets, pressure/vaccum ports with gages. Most of them are somewhat bigger than your quoted size, however he will make to order. Price (I think) is quite reasonable.
Steve

<font face="Verdana, Arial" size="2">Originally posted by debequem:
I need to make or buy a pressure vessel to the following specifications:

max operating pressure = 60 psi.

Cavity size = apprx 8" by 6" by 4"

Door must be able to be rapidly opened/closed

maintain pressurized state for 1 to 3 hours

The purpose is to pressurize plastic cast materials as they cure. Since the pot life of the plastic once it is mixed is very low (a few minutes), the door must operate quickly and the vessel pressurized before the cure stage reaches maturity.

Any ideas?

Marv </font>

debequem
10-06-2003, 05:55 PM
Steve,

Yes! I am interested. Please get a quote.

Thanks,

Marv

[This message has been edited by debequem (edited 10-06-2003).]

wierdscience
10-06-2003, 08:58 PM
Two words-steam autoclave,you can find these at surplus auctions,hospital supply companies and there are probibly more than a few on ebay,they are rated for something like 600 psi,are corrosion resistant,and have a hatch like the end of a torpedo tube,in addition they have steam coils around the chamber so if you wanted to heat or cool the assembly it would be easy.

SJorgensen
10-06-2003, 11:06 PM
I had two thoughts. One was to use a large diameter pipe and caps. The other was to use a small water heater with reinforcing. These are built to stand higher pressures and have a relief valve, but I thought against it after concideration. If a pressure vessel containing water exceeds the maximum pressure and it ruptures it would rip and spray water everywhere. However a compressed gas would have a completely different failure mode and have a very loud noise and probably fragment the container. That being said, I don't think 60psi is too difficult to design for. I think the problems do increase depending on the volume of the space. You should consider some kind of device like a water bladder that could take up some of the extra space. This would make it quicker to pump up and easier to release the pressure because of the reduced volume of compressed gas. Good luck and be sure to let us see what you come up with.

Thanks,

Spence

BC21OSH
10-23-2003, 09:25 PM
Some pictures of the pressure tank we used at work as described in my lengthy post.

http://photobucket.com/albums/0903/BC21OSH/0271b57e.jpg
http://photobucket.com/albums/0903/BC21OSH/96e1bc0f.jpg
http://photobucket.com/albums/0903/BC21OSH/18815df3.jpg
http://photobucket.com/albums/0903/BC21OSH/10da84cd.jpg
http://photobucket.com/albums/0903/BC21OSH/0c90007b.jpg

Bernard

SJorgensen
10-23-2003, 11:37 PM
If you powder coated that, I'd swear that you'd bought it! Looks good. Have you tried to hydrostatically test it? I wonder how much pressure it could hold and what would break first. Looks plenty tough.

Spence

darryl
10-24-2003, 02:28 AM
Looks good. It looks like the tabs that rise from each side of the container are 1/4 in flat bar. The metal remaining to the sides of the holes looks to be about 1/4 in square. So in total, you have about 1/4 x 1 in of metal being tensioned when the container is under pressure. If that can is 8 in across (looks to be), there's about 5000 lbs tension total on those weak links, assuming pressure of 100 psi, for easy calculations. That's a tension of 20,000 psi for the metal. You're probably in the safe continuous operation range up to about 200 psi. It's possible the pin would bend, relieving the pressure, before the tabs would let go, I didn't do the math for that (cause I don't know how to). Sorry for the analysis, it's just something I went through recently when I made my vessel.
What I didn't look at is the strength of the welds holding the tabs on. I'm assuming there's considerable sq area of metal there. Each tab would have to be able to withstand a 2500 lb pull, at operating pressure of 100 psi. If the diameter of the vessel is 6 inches, all the figures are cut almost in half, safe to 400 psi operating pressure, in my estimation.

[This message has been edited by darryl (edited 10-24-2003).]

BC21OSH
10-24-2003, 05:54 AM
darryl,

It is about 8 inches across. It has a relief valve on it set at 50 psi so I don't know what it is really capable of, we have never had it tested.

Bernard