So I bout the Pyrex coated stir bar listed in the link below and figured that should keep things plenty insulated from demagnetization. It’s fared well for me for multiple runs, but it sounds like it’s skipping and having a rough time when throttling above 500rpm on the run I have going right now. Mantle temp is at 223c and material temp is at 138c right now. Of course, this is all happening while I’m using a glass thermowell for the first time and I’m terrified of breaking the damn thing mid-run. I’m also confused as to why it would lose stability with speed yet seems very stable around 480-500 rpm. I’m wondering if it could be my Lanphan mantle? The spin speed reading seems to jump all over when I’m around 600rpm. Does anyone else have experience with these spin bars?
Also, this is my first time running with adsorbents in the flask of that makes any difference.
U need a fat center on the bar. The tips are dragging on the glass and the center is not touching at all… change style.
Some of mine will do that until i get above 500. What i do is shut it off and then set it for 700 or so and see if it keeps on track
@Concentrated_humbold s answer is valid yet make sure to spin right ahead after stopping for when the powders start dropping to the botom the bar will have more problems to start spinning again
If the bar is completely flat it’s for a beaker, flat round flask, reactor, etc. Round bottom flask needs a high center bar. I believe the one your using is straight and flat. I use a football shaped bar
Thanks guys! I decided not to risk the bar spinning off and shattering my thermowell, so I just replaced it with a smaller green PTFE coated bar. I didn’t want to use the white egg shaped bar the mantle came with for fear of cooking it mid-run since it’s likely not high temp rated, where supposedly this little green one is. I’m not getting the best vortex going with this little bar, but it’s better than nothing
I’m thinking I need to get one of those $80-$100 egg shaped rare earth bars and quit screwing around with these junk $20-$30 bars.
I’ll definitely be ordering a football bar today. Any suggestions on your personal favorite brand and type @Paragon1?
No real preference. Mine are all ptfe lined. I believe I got them off Amazon. Might be Fischer Scientific… Just go with a good brand. It’s important that its balanced well too.
that can cause some issues with stirring depending if its lumped together or settled to the bottom, it could also be the magnet de gaussing slowly from temp cycles.
I was shopping for stir bars a couple months ago and found some decent manufacturers documentation about selecting the correct stir bar. This doc at this link good example:
https://us.vwr.com/assetsvc/asset/en_US/id/20642381/contents
Anyone ever use the Saturn stir bars?
If there are an appreciable amount of solids in your solution you might consider an egg shaped rare earth stirbar as they tend to be stronger than the ceramic pivot ring magnets in round bottom flasks and fringe benefit, tend to be more heat resistant in Re: losing magnetic strength over time. Different shapes fit different types of glass but also different types of solution.
What is the correct size for a 5L and 10L bf
Try a 63.5 x 19mm for 5L or 76 x 19.1mm if you wanna go big, 76x19.1mm should work for 10L+ as well.
Edit: That’s egg shaped dimensions, this PDF shows actual sizes Bel Art Spinbar Sizing
I have some really cool digital mantles and some specialist rare earth stir bars that will solve the issue of mixing forever.
Sometimes when this happens to me I just turn it off and slowly increase it from 0 by like 10-20 at a time
I’ve also noticed that it can depend on what I’m running and obviously the temperature
Post a pic of your stir bars and your heating setups.
Yeah like so many things, start low and go slow
Other people have largely said this already:
Make sure it’s a properly shaped bar for the flask, it should be the egg type, not the straight bar type, if you’re using it in a round flask. Make sure it is properly sized, as well.
Start the speed low and slowly ramp it up as it stabilizes at each interval.
Take note of your consistency, if you’ve added other new ingredients, such as adsorbents, to the flask it could change the consistency. If it’s thicker, then it would be normal for the stir bar to be thrown off at lower speeds.