Magnetic stir bar with pivot disk........


#1

Hello everybody, I am needing to purchase a magnetic stir bar destined for a 12L LS Short Path. I believe I’ve been plagued the past run in part, to my choice of spinner. The 2.5 inch octagonal egg shaped spinner would be thrown off tilt over 350rpm. That coupled with a poor performance from the pump (low grade vac oil) led to a very lengthy distillation with fluctuating vacuum. I wanted to throttle the speed with the spinner and just could not…very frustrating. I’ve had good luck in a 2L setup using a stir bar that has a disk which slides, and centers on the stir bar. The spinner pivots on this disk and spins very smoothly and handles very high rpm. I have no idea where the stir bar came from or what they are called. Does anyone here know what they are called or have suggestions on magnetic stir bars? has anyone else tried this type of spinner and liked/or not liked them? Thanks


#2

I like to test new bar shapes in the flask you intend to use them in full of water. The egg shaped ones are specifically for round bottom flasks, the octagonal and barbell shape work well for flat bottom vessels.

was it a spin fin bar? https://www.fishersci.ca/shop/products/bel-art-scienceware-spinfin-magnetic-stirring-bars-6/p-4680813

You can check out the entire catalogue here:
https://www.fishersci.ca/ca/en/products/I9C8L36G/stir-bars.html#nav=30492&page=1&offset=0

call them up and ask for a bar to stir viscous liquids in a 12 liter flask up to 250c


#3

Thanks for the reply. It is not the spin fin that I was thinking of although the shape of that is intriguing. Imagine a rod shaped stir bar with a slight indent in the center of the bar, onto which, a washer slides tightly over the spinner, and sits centered in the middle of the bar. So only this disk and depending on length of spinner possibly the end will make contact with the flask bottom. Ill snap a picture when I get back to Maine. Ill peruse the catalog. And, I will give them a call, thanks for the input. :slight_smile:


#4

https://www.fishersci.ca/shop/products/bel-art-scienceware-spinbar-octagon-rare-earth-magnetic-stir-bar-4/p-4374371
This one sounds like what you described, only the “washer” is built in, and it’s rare earth which I’ve heard are awesome, not sure myself so dont exactly take my word for it…


#5

This is the spinner I was referring to.


#6

Where do you get this


#7

That looks like a teflon washer over the magnetic stir bar. My stir bars have the raised ring in the middle, like most do…I could turn some teflon in the lathe making a washer, and cut an internal groove to locate and seat on the raised ring of the stir bar. Easy peasy. Come Monday I’ll be back around my lathe and a bunch of teflon…I’ll be back with pictures next week.


#8

It would be interesting to see that spin in a flasj


#9

Its a bit unstable. I should have used a longer bar. I’ll reduce the OD of the washer a bit tomorrow…

I can’t get the video to upload. Its quite effective when spinning though.


#10

#11

Nice work man. That didn’t take you long to make. Let me know if you make any more.


#12

I’m a machinist, so I get to play every day. If you’d like one, I’d make you one. Unfortunately it’s a custom fit to the stir bar…its a press fit essentially. The washer comes off as well so you can always go back to the standard bar.

If you sent me a stir bar or two and included a self addressed envelope with postage paid…I’d make you one and send it back to you. No charge. Takes me 5 min to make.


#13

This concept is trick of the trade stuff
If You can make a clear writeup i think Many can benefit from iT
Tread " Tricks of the trade " :+1:


#14

The thing about it is…its literally another trade. I took teflon barstock, put it in a 40k dollar lathe with another 10k in tooling, and made the washer in a few minutes. You don’t need $50k of machines and tooling to do this, and my lathe at home would work just fine and was an investment of a few thousand. Unless your involved with the R&D side of the extraction trade, where your manufacturing components from raw stock, I dont expect many have the access to the machines required to turn bar stock into a precision part. But…there must be some odd ducks out there like me that do a bit of everything…

My hobby is cannabis and its extraction. My day job is more along the lines of precision areo space manufacturing. But…I’m here to help in any capacity I can. Fancy metal stuff is my expertise though.