Gasket for vacuum chamber?

Discussion in 'General foundry chat' started by Zapins, Feb 11, 2019.

  1. Zapins

    Zapins Silver

    I'm sorting out a vacuum chamber for my friend, we got a piece of 1/2" plexiglass cut into a circle 18" in diameter. I'll be hunting for a huge pot soon. But we need a seal of some kind. Any idea what or where we can get a gasket for the lid to pot?

    I read Viton is the material of choice for vacuum chambers? But I'm open to anything that works and doesn't cost a few fingers/toes.
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    You would be surprised at what you can do with a tube of silicone...
     
  3. Zapins

    Zapins Silver

  4. DavidF

    DavidF Administrator Staff Member Banner Member

    Probably too porous, plus you said 18" in dia..
     
  5. DavidF

    DavidF Administrator Staff Member Banner Member

  6. DavidF

    DavidF Administrator Staff Member Banner Member

  7. Is this for outgassing resins and coatings?. A friend made one with a square window for a ten inch diameter chamber: the unequal stresses caused his plastic window to shatter, blow into the chamber and hit the bottom before bouncing back out the hole and cutting the brim off the front of his felt hat with the shrapnel. I'm not sure of the strength of 1/2" thick plexiglass but it's going to have to withstand 3.141592 * 9^2 * 14.7 PSI = 3740 lbs force from atmospheric pressure. If it's a thin stainless pot it will be crumpled by air pressure too: my brother did that while proudly demonstrating his vacuum chamber to me for the first time.
     
    Last edited: Feb 12, 2019
  8. Zapins

    Zapins Silver

    Wow no kidding.

    What to use for a vacuum chamber then?

    I think my personal chamber has a half inch thick lid of plexiglas so I think that part is ok. But the chamber itself. A steel stock pot isn't going to work??
     
  9. Jason

    Jason Silver Banner Member

  10. Have you got any information about the strength of your particular plexiglass?, even scaling down to 12" diameter will reduce the force to 1660 odd lbs or 45% of an 18" window. A pressure cooker might be a more suitable chamber for vacuum service and if it were me I'd get the thickest plastic I could get, as age and scratches are going to introduce failure points. A smaller CIRCULAR (look up the DeHavilland Comet) window say 4-5 inches will have a lot less force (288 lbs) and could be siliconed over the outside of a hole cut in some 1/2" aluminium plate.
     
  11. Mach

    Mach Copper Banner Member

    I use a 15" paint pressure pot that's crazy heavy with a 1" thick piece of acrylic. My plan is to use RTV silicone to pour a new gasket. If you needed a bigger chamber like 18", you might consider heavy wall pipe welded to steel plate.
     
  12. Zapins

    Zapins Silver

    That might be the way to go. I found a perfect size pressure pot at walmart for 79 bucks but that seems a bit pricey. I hope the 1/2" works...
     
  13. Zapins

    Zapins Silver

    David does that https://www.riogrande.com/product/Gum-Rubber-Pad-Center-Cut-18L-x-18W/705039 have an adhesive backing to it or is it just a sheet of rubber?

    I got the go ahead for the pressure pot from wally world. It is 15" in diameter. so thats 2596 lbs of force. Also in a stroke of luck, for some reason the 1/2" plexiglass purchase didn't go through on ebay. So I put in a question with another seller on a piece of 1"x16"x16" section. Hopefully not more than 30-50 bucks.

    How does acrylic thread? Drills ok I assume?
     
  14. DavidF

    DavidF Administrator Staff Member Banner Member

    Its just a sheet of gum rubber.
    Acrylic likes to crack sometimes, not sure if I would thread it for what your doing.
    Might put some serious stresses at the threaded area when you pull a vacuum on it. Better off just letting the vacuum pull it down.
    Polycarbonate would be nice, but really expensive...
     
  15. DavidF

    DavidF Administrator Staff Member Banner Member

    Why not just buy one of the vacuum chambers off e bay???
     
  16. Zapins

    Zapins Silver

    Because they are a bit small. Would be nice to have a larger chamber. Also how is the quality of those chambers? They look like a cheap metal pot no?
     
  17. DavidF

    DavidF Administrator Staff Member Banner Member

    I'd say they are tough to beat for the money.
    They do have larger ones.
    What are you sucking on exactly that wont fit in a 3 gallon can?? :rolleyes:
     
  18. Jason

    Jason Silver Banner Member

  19. DavidF

    DavidF Administrator Staff Member Banner Member

  20. Jason

    Jason Silver Banner Member

    lol.. Sorry, I'm taking about domes.. those are cheap crackpots. Large domes get pricey. I've only seen them at science companies. I didnt look on ali, but I bet you can get them there. Anyone that sells dildos by the gross is bound to have whatever you can imagine!
     

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