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Thread: Vacuum pressure tolerence of 3.3 boro glass

  1. #1
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    Vacuum pressure tolerence of 3.3 boro glass

    I have looked everywhere... Duran catalgoe, MIT youtube demonstrations ect however i cannot find for the life of me acceptable vacuum pressure tolerance for glassware. What is the hghest reasonable vacuum i can pull and reasonably safely and slowly heat up ???....!!!!!!!!

    It doesnt say anywhere, and the glassblowers themselves are always apprahensive on giving advice about how to use equipment because of the liability it could place on them if things go wrong..

    What pressures and temperatures have you guys comfortably worked with?
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  2. #2
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    Why don't you start low and if necessary go high pressure?
    For example I would heat the glass and subsequently close it when warm. Boro should stand this procedure.

    If you are afraid from being hit by the breaking glass (unlikely but possible) wear safety goggles and/or encapsule the glass with plastic/"tin" foil or clay.

    You could also try doing the procedure with a vessel made out of a metal (copper would fit imo ;-)).

    PS. Sour cucumbers or marmelades seem to be unsuited as magnets ;-)

  3. #3
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    Unfortunatly this must be glass. And this is the thing. By trial and error i run a very large risk of breaking the glassware and that is just stupid and a waste of the devils currencies.
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    For what it's worth, I'll offer these two token bits with no assumption of liability, just as a thought.

    In theory, the max strain on any vacuum should be around 14.5 psi. That's "empty" inside and atmospheric pressure squeezing from the outside. This doesn't seem right though for obvious reasons when you actually hook something to a pump, so I'm probably overlooking something important.

    Second, smaller vessels stand up better to pressure differentials than larger ones. A 10,000 gallon cement tank can burst at 10psi while a soda bottle can hold dozens of pounds. PSI times surface area gives you the total amount of force stressing the vessel. So definitely use the smallest bottle you can reasonably get the results you need.

    I don't see temp being an issue here, unless you start closing on the annealing point.

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  6. #6
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    Ive decided on a safe -400mbar relative pressure. The brochure says that the glass can handle almost 10 psi which is almost pure vaccume but i highly fuckin doubt that and will no be creeping into those zones.
    Join me; on a voyage of stupidity, and self discovery: https://www.youtube.com/watch?time_c...&v=vccZSHroTG4

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