Funkerman23
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effects of Vac work on Boroglass?
Had to shorten the title but I have a question for the more seasoned lab folk here. How much stress does vacuum distillation put on our jointed lab
glass? Right now the majority of my glass is Laboy and for the most part it has held up well, But I haven't done any vacuum distillations with it. I
know Chinese glass isn't the same quality as US stuff but brands aside does vacuum work significantly reduce working life? And although I may look
dumb what is considered a "hard" but tolerable vacuum for chem lab work? I thank you and wish you the best.
" the Modern Chemist is inundated with literature"-Unknown
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GammaFunction
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Any reasonable vacuum is as 'hard' as a total vacuum from a mechanical perspective, because it is 1 bar, give or take ten percent. Glass will either
crack or be unaffected. I don't think it is like an aluminum airplane skin that becomes fatigued with repeated flexing.
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Dr.Bob
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In 30 years I have never seen glassware bothered in the least by vacuum work. If you heat it to red hot, maybe, otherwise it will be fine. That
holds for any brand of glassware, as long as it is not cracked. Even minor chips won't weaken glass in most cases, as long as they are not right as
a stress point.
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zed
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Of course, to a certain extent, the stress involved depends on how large your vessel is, and its shape.
Round is good, round is strong, like an arch. Flat surfaces are weaker. Smallish, round vessels can take a lot. A large vessel with a flat
surface, is much more vulnerable.
When you create a hard vacuum, you remove the 15LBs per square inch of pressure that is normal to the inside of your vessel. The 15LBs per square
inch pressure, on the outside of your vessel, continues. The larger the vessel the more total LBs of pressure.
12inchesx12inches=144 Sq. inches 144x15LBs=2160 LBs of pressure.
Personally, I've never had a vessel fail under vacuum. As long as your vessels aren't too large, and they are not flawed or cracked, thing usually
go OK. Still, failures are a possibility.
[Edited on 28-3-2013 by zed]
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Funkerman23
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spooky point but well made. the largest flask I own is a thickwalled chemglass 3 liter rbf but wrong joint size. 2 liters is my usual max size
though. Quote: Originally posted by zed  | Of course, to a certain extent, the stress involved depends on how large your vessel is, and its shape.
Round is good, round is strong, like an arch. Flat surfaces are weaker. Smallish, round vessels can take a lot. A large vessel with a flat
surface, is much more vulnerable.
When you create a hard vacuum, you remove the 15LBs per square inch of pressure that is normal to the inside of your vessel. The 15LBs per square
inch pressure, on the outside of your vessel, continues. The larger the vessel the more total LBs of pressure.
12inchesx12inches=144 Sq. inches 144x15LBs=2160 LBs of pressure.
Personally, I've never had a vessel fail under vacuum. As long as your vessels aren't too large, and they are not flawed or cracked, thing usually
go OK. Still, failures are a possibility.
[Edited on 28-3-2013 by zed] |
" the Modern Chemist is inundated with literature"-Unknown
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