My New Pressure Chamber

THIS IS "NOT" A SUGGESTED METHOD. IT IS ONLY A NARRATIVE OF SOMETHING I MADE. ALL RISK IS MINE.

I cast pen barrels on occasion and have always done the onesy towsy thing but I wanted the ability to cast multiple barrels on a 10 inch length of tubing in one shot so I made a long round mold out of 5/8ID PVC tubing. However the overall length of the mold did not allow use of my 2gal paint pot I normally use as a pressure pot for my castings. Needed something longer then the paint pot turned on its side. Three inch PVC to the rescue.

The mold. Its about 13 to 14 inches long, in any case much longer then the depth of the paint pot. More on it in another post.
Attachment 350793

A comparison of the new one to the paint pot.
Attachment 350789

How it is mounted, the pressure end and the access end with the mold inside.
Attachment 350786Attachment 350787Attachment 350788

I used a 3" clean-out adapter for the access end but could not get it to seal. Had two of the threaded plugs so used a section off the bottom of one and glued into the bottom of the thread female section to act as a seat for a gasket. The first pic shows the plug with the psa foam I used as a gasket. The second pic shows the trimmed down plug being used with PSA sand paper to sand the seat smooth.
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Installation of the seat. I took a saw kerf section out of the seat section so that it would collapse a little and go far enough down into the female fitting to allow the plug to use all of it's threads when screwed in. Glued the saw kerf together and filled the back side of the seat with PVC glue to seal it and keep it in place.
Attachment 350796

The only negative to the assemble is that the clean-out is the only part that is not schedule 40 and is not intended for pressure use. However, it does have almost 1/8" deep threads and is nearly 1/4" thick through it's cross section. Although schedule 40 is rated at around 160psi I am running at most 70psi. I tested it to 80psi and noted no creaks or groans so I am not worried about it not holding up. It still leaks a little, drops from 60psi to 40 in about 30 minutes but with a compressor attached overnight that is not a problem.

Appreciate all comments.

I think it all looks interesting, but I don't know what a pen "barrel" is or why it needs pressure.

If it's schedule 40 pipe (about 3/16" wall thickness for 3" pipe), the rated burst pressure is over 500psi, so you've got a lot of margin. You might blow the ends off well before that though, depending on the quality of your weld, so I'd stand to the side, not the front. ;-)

Be aware that OSHA does not allow pvc for compressed air. when it fails it explodes and shrapnel flies everywhere. The old acid type fire extinguisher make good pressure vessels but I do not now how much pressure they can take.
Bill D.

Missed seeing Dave's and Steve posts until Bill's bumped it to the head of the line again.

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Originally Posted by David Freed

I think it all looks interesting, but I don't know what a pen "barrel" is or why it needs pressure.

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Dave, sorry about the late post back. By way of explanation for "pen barrel", many wood workers/turners also make ink pens. We refer to the upper and lower round sections as barrels. Pens can be made(turned) from wood but some of us also cast the "barrels" from acrylic resin, a liquid plastic that can be hardened by mixing it with a designated hardener. The pressure chamber prevents the appearance of air bubbles in the casting while it hardens. Some resin examples are polyester resins like Casting Craft and Simar41. Polyurethane resins like Alumilite are also used. You won't find a lot of turned pens here on SMC but there are a few. Here is an example by Ben Gastfriend from 2009, it shows a two barrel pen made from Cocobolo. Most folks that turn pens are also members of the IAP, International Association of Pen Turners over on penturners dot org. If you are interested in seeing more on casting with pressure chambers that's the place to go, especially check out their library. BTW here is a pic of a casting for a pen I made recently. The upper barrel is a clear casting over a label that pictures a peacock feather.
Attachment 358512
Appreciate you looking and your comments.

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Originally Posted by Steve Demuth

If it's schedule 40 pipe (about 3/16" wall thickness for 3" pipe), the rated burst pressure is over 500psi, so you've got a lot of margin. You might blow the ends off well before that though, depending on the quality of your weld, so I'd stand to the side, not the front. ;-)

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Steve, same as with David, sorry I missed your post. What you are saying is pretty much the way I looked at the PVC. I had looked up the specs and found similar ratings and even higher burst ratings so I feel pretty safe at only using ~60psi. Appreciate you looking and your comments.

Quote:

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Originally Posted by Bill Dufour

Be aware that OSHA does not allow pvc for compressed air. when it fails it explodes and shrapnel flies everywhere. The old acid type fire extinguisher make good pressure vessels but I do not now how much pressure they can take.
Bill D.

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Bill Thanks for bucking this back to the top of the line, had forgotten about it, always try to acknowledge folks posts i my threads. Yes I am ware of the OSHA regs on air and PVC but a that pressure I am using I am not concerned. Had a similar comment on another forum that I posted the same thread on. Really appreciate the thoughts though and thanks for looking and commenting.

500 PSi burst pressure. sounds like plenty of safety margin. I think the pvc failures are from pipe at least 10-20 years old with many daily pressure cycles on it.
Bill D.