localbroadcast
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Overhead stir bar adapter question
Hello. I would like to run a reaction in a 2 neck round bottom flask. 1 neck is for a reflux column, the other neck is for an overhead stirrer. I
ordered a "magnetic stirrer bearing adapter" from laboy for this. Here's a picture of it:
I don't see how this adapter will allow the reaction to stay sealed in the flask and allow the stir bar to turn smoothly when I attach my low RPM
motor. The so called "stir bar adapter" is pretty much the same design as a thermometer adapter, but a bit more robust.
This stir bar adapter allows you to loosen off the top half of the adapter and insert the stir bar. Then you tighten the top half back down, and
since there is a little rubber washer inside the adapter, as you tighten it, the rubber washer gets squished and forms a seal with the stir bar and
the adapter.
The problem I have with this adapter is that if I tighten the stir bar in there to the point where I feel confident there won't be any leaks, then
it's very hard to rotate the stir bar! I thought there would be actual bearings inside the adapter that would allow the rotation to take effect.
Am I missing something? Are most stir bar adapters designed this way? Do I need to buy more parts? Do I need to put bearings in somewhere here??
What's the standard adapter used for people wanting to use an overhead stirbar and want to keep there reaction sealed from the outside world.
Any help is greatly appreciated!
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Magpie
lab constructor
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Mood: Chemistry: the subtle science.
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Magnetic stir bars don't have shafts. I don't know why Laboy would label these shaft bearing/seals as magnetic.
I use these ptfe bearings with my overhead stirrer. And you are right about the fact that getting the seal tight enough to eliminate leakage will
stop the shaft. I tolerate a little leakage as I have a good fume hood.
In the old days this seal was provided by a piece of glassware that contained a pool of mercury. I imagine that some of the better equipped labs
still use them.
See Vogel's 3rd ed, p. 66
[Edited on 4-1-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Dr.Bob
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I have lots of traditional stir shaft bearings, which are typically oiled, but I have some longer Teflon lined type ones which are similar but some
are 3" long or so. The best thing with Teflon ones is to pressurize the reaction enough to keep the reaction under inert atmosphere even with
stirring. For oil, only a slight pressure will work, unless you know what you are doing better than I. I also recently found a box of paddles,
bearings, shafts, and more, so I know have a much larger assortment of paddles now for sale.
[Edited on 5-1-2015 by Dr.Bob]
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localbroadcast
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Yes, I figured it was a mistake for them to put that it is a magnetic stir bar adapter.. I didn't expect it to be magnetic when I got it, but I
thought that it would work better than it does! I have looked on google and there are magnetic stir bar adapters that do work magnetically.. I think
this is probably the only way to have an overhead stir bar work while maintaining a leakproof semi-pressurizable reaction vessel. They are pretty
expensive though and out of my price range.
So there are traditional stirbar shaft bearings and teflon lined shaft bearings available out there.. Can you point me in the direction of any good
quality providers?
[Edited on 5-1-2015 by localbroadcast]
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chemrox
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Bob could you send a pic with something for scale? I think you have my email. If not I'll p2p it.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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