Vacuum chamber lid - crazing on underside

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Thread: Vacuum chamber lid - crazing on underside

  1. #1
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    Vacuum chamber lid - crazing on underside

    Hello all,

    Over the weekend Iíve been stabilising a number of blanks however noticed on the 2nd batch that the lid, which is 18mm Acrylic, had I thought cracked but after taking a closer look its only surface crazing on the underside. It seems ok although not sure I want to trust it for ever.

    1) Has anyone had any experience of this or similar?

    2) is it safe to continue using?

    3) How can I stop this getting worse or when replaced happening again?

    Have tried to take a few photos and will attempt to attach or include in the post, although not sure how well itís come out or if itís visible.

    I bought as a set inc. pump off of the ďgreatĒ auction site and the item was shipped from Europe. Iíve had it roughly a year but havenít really had much opportunity to use it a much & this was probably only the 2nd or 3rd time.

    Iím using Cactus Juice and I had filled the pot pretty full and used 3 ice cream containers stacked on each other with top one also being coloured blue with alumilite resin. The lid wasnít touched by the cactus juice nor did any of the containers overflow. Have included a photo takes before the crazing happened.

    Any suggestions or advice greatefully received.

    Many Thanks,

    Myles


     
     
  2. #2
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    I can't help Miles as I know nothing about vacuum chambers but was involved in semi finished plastics as a main distributor for ICI Perspex among other products and to the best of my knowledge ( from memory ) they are stress fractures and I would suggest caused by poor machining of the hole, you will see that the crazing spreads away from that. We did sell very thick sheet for specific engineering products and ICI at the time published clear information on machining Perspex as cutting, drilling and routing causes stress in the material which needs to be relieved as much as possible.
    I would doubt the acrylic will crack at that thickness but imho it's faulty and I would be chasing the supplier for redress.
    Bob

    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better. (Samuel Beckett)

     
     
  3. #3
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    From my side as an aircraft mechanic when younger. Acrylic does not like solvents or ammonia. I causes it to craze. The off gassing of some of the solvent could contribute to that but after a lot of use. I also agree with Bob about the hole not being smooth. Best way is to have the fitting in the side of the chamber instead of the lid but then it reduces the height of stuff in it. PVC is harder to find but is a better product and that is what Curtis (Cactus Juice) makes his vacuum chambers from. If you moved the fittings you could use very thick (20mm to 25mm) tempered glass. If the seller/maker won't replace the lid I would take the fitting off and polish the hole and underside to remove the crazing. Wet and dry used with water, followed by micro mesh can remove the crazing for a while.

    Pete

     
     
  4. #4
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    Hereís a picture of mine a few years ago that had the same issues (the rubber seal was the only thing holding the lid together, for the photo) The company I bought it from replaced the lid & weíve been using it since just for deceasing silicone with no problems, Iíve now use some turtex style vacuum chambers that I made from PVC which are dedicated for stabilising.
    I donít think the cactus juice was the cause of the issue, I think these pots are made for off gassing resins which take a matter of minutes under vacuum, when stabilising you are putting the lid under vacuum for hours & hours, which a Perspex lid with a hole in canít cope with the extended vacuum. If I was to need a larger pot than the 8Ē turntex ones for stabilising, I would buy or make one with the holes in the side of the tank, so that there where no holes in the lid.

    This is the conclusion that I had come to after researching into it at the time, I did also have people mention that it was may be due to the quality on the machining of the hole, like others have suggested.

    After my experience I would recommend not using it, as I was 3 rooms away & I heard a hell of a bang when it went, so I certainly wouldnít like to have been in the same room.

    4C127759-5EC1-4E94-85E5-6C040A3CA230.jpg
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  5. #5
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    Quote Originally Posted by Bucks View Post
    as I was 3 rooms away & I heard a hell of a bang when it went, so I certainly wouldn’t like to have been in the same room.
    I proberly could sit next to it and not hear it.

    COOPER 01/08/1998-31/01/2012

     
     
  6. #6
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    Quote Originally Posted by wm460 View Post
    I proberly could sit next to it and not hear it.
    Only due to the sound of your teeth chattering in snowy Australia.
    Enjoy Life you only get it once and there is no Apprenticeship

     
     
  7. #7
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    Quote Originally Posted by Pierre View Post
    Only due to the sound of your teeth chattering in snowy Australia.
    One snowflake and Australia comes to a stand still
    "The only people who never fail are those that never try"


    DL Woodart

     
     
  8. #8
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    Like you I have had a lid implode ,a definately bum clenching moment, but actually perfectly safe ( once underwear changed anyway ). The resin i used , stickfast , attacked the acrylic and to my surprise dissolved the araldyte resin used to seal the fittings in place.

    I made a new polycarbonate lid after checking it didn’t attack polycarbonate by leaving some scrap bits with multiple scratches on in it for 3 days then hitting it with a hammer , no damage to polycarbonate ie no brittleness so new lid then made. Has worked well so far.

     
     
  9. #9
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    Quote Originally Posted by Dalboy View Post
    One snowflake and Australia comes to a stand still
    WE did receive snow as a result of a number of zero days,rain and sleet,would not flinch saying it was ugly,I have no envy for you turners living in snow country,d,ont mind being called any names but sure looking forward to better conditions,I have outside work to do and at the end of September replacement of three big awnings following the one in a hundred yrs hail storm on January 21 when our suburb was the epicentre for this ghastly experience. Always appreciate your comments mate,all the best Peter.
    Nil Desperandum

     
     
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  11. #10
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    Quote Originally Posted by Pierre View Post
    Only due to the sound of your teeth chattering in snowy Australia.

    Quote Originally Posted by Dalboy View Post
    One snowflake and Australia comes to a stand still


    It hailed here once, we were having smoko at the time by the time we got out side it had melted.

    COOPER 01/08/1998-31/01/2012

     
     
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