DIY Stirrer Mantle

MargaretThatcher · Thu Mar 31, 2005 2:37 am

I though this was pretty good:

http://www.geocities.com/brainfevert/heatstir.html

No attention to safety standards and element should be better embedded but good none the less.

IndoleAmine · Dreamreader Deluxe

The idea/theory behind it is awesome, I think if we consider their apparatus as early prototype, this could become the best, most OTC and cheap, cheap, cheap homemade heating/stirring method one can think of.....

i_a

MargaretThatcher · Thu Mar 31, 2005 6:12 am

The hardest part is getting the right motor. Something reliable and controllable from 300-1300 rpm. Harder than it sounds. I've played around with PC fans and pulse width modulation: it works, but not reliable enough for me to trust to a several hour experiment. Larger rare earth magnets are ideal though. Very powerful.

Played around with DIY stirbars too. Very difficult to seal a magnet within a glass tube and balance properly. When unbalanced, stirbar unstable at high speed.

ApprenticeCook · DILLIGAF

thats pretty cool, i have heard of the cement home made ones but never seen pictures... i was quite sceptical but it actually looks quite impressive!
I would rather make one of the fabric type mantles instead of something clunky and heavy such as a cement moulded version.
Some kind of pre-treatment to normal fibreglass would burn away any coatings... say acid etch or use a blow torch and heat it? were only talking about a small amount so any treatments wouldnt be labour intensive.
And the heating wire could be stiched into the fibre glass with a few threads of fibre glass. Easy!

The electrics could be improved, as you said, use this as a model to develop the synthetical(R) brand stirring heating mantle.... used by clandestine chemists worldwide... hahaha

-AC

IndoleAmine · Dreamreader Deluxe

MargaretThatcher · Mon Apr 04, 2005 4:40 am

I was thinking of the same thing. PTFE is shaped under pressure at high temperature (I think it starts breaking down before becoming liquid). It looks pretty difficult to do yourself.

The RC motor controllors use Pulse Width Modulation to regulate speed - they are good if you don't want to build a circuit yourself. Google yields loads of circuits if you want to DIY.

RC motors are powerful enough but tend to be fast - 10 000 rpm and I had trouble finding a reliable reduction gear of the correct ratio.

You find stirrers in unexpected places. I've seen them at retailers that sell process control equipment and also at a home-dyeing outlet. The only stable stirbar I was able to make was by epoxying a small alnico bar magnet into a glass tube. That worked pretty well, but the epoxy was exposed at the ends. Samarium-Cobalt magnets are stronger than alnico - both are resistant to high temperature.

ApprenticeCook · DILLIGAF

small cylindrical magnets like those used in stir bars can be found where you normally buy magnets, as for the coating, theres places specialising in plastic coatings, ring up, ask for teflon coatings and see how much it costs...
At a place ive looked into teflon is spray applied (in its monomer form with a polymerisation agent?) to any object you want to any thickness you want....
Same with any other plastic coating, these same people had a massive list of plastics they could coat with.

I think spray coating with teflon like these people did is probably the only way to get an even coating without seams.

-AC

bio · Working Bee

Have tried melting PTFE and had some half ass sucess coating some stir rods but it is very difficult. Teflon does not decompose at the glass transition temp (Mp) but if it is contaminated at all or heated too quickly or unevenly it turns into a real mess. Forget exactly but the heating rate must be very slow and even. Even a regular oven doesn't cut it and you can forget a torch although limited sucess can be had with a test tube over a soldering iron that has a triac type dimmer for small pieces.

Yet there is hope for us DIYers. It's been out for a couple years now and is a Teflon coating which can be painted on then baked at normal oven temps. I've never seen it available in real small containerst The industrial suppliers have it or can order it but is waaaay expensive but probably worth it. Novolac epoxy is pretty good too for most chems below 150 deg or so. The ceramic filled version is great.

Now where would you go to find out all about it? Why; at http://www.teflon.com/ of course.

Rock wool is better than fiberglass for soft mantles as the glass even binder free still burns pretty damn easy, I used two 100watt heating cords embedded in the wool with the bottom element shaped into a thin aluminum disk formed to the bottom of the flask. The housing is asbestos sheet about 2mm thick that was cured and formed into shape with a coffee can when heated in the can with some NiCr wire. Takes a few hours too burn all the crap off but turns out real nice. Hard almost like ceramic unlike the flexible starting board.

primathon · modified

I think it was Osmium over at the Hive who suggested wrapping a suitable magnet with a bunch of PTFE tape and letting it spin away in an oil bath at some nice high temperature for an hour or so, cool it off and take it out. He made it sound like the PTFE fused together into a solid mass surrounding it. I dunno, just remembering what I heard.

Guest · Mon Jun 13, 2005 10:19 am

God dang that is a great post,

This is what really makes all of us, have a moment of silence and thank such industrious members.

Simply a beautiful way to make, an often prohibitively priced item affordable for the hobbyist chemist.

thankyou
s

p.s.
What about finding a suitable solvent that solvates teflon, then one could drop it in, then let it dry.
Maybee another way around this would be to not use teflon, how about borosilicate glass, or even soda glass to seal it.
ie. by purchasing very thin walled small diameter tubing, that lets the magnet snuggly fit inside, then apply heat from a propane/air heater to seal it closed.
How about even placing the magnet between two pieces of thin lab glass, and heat till it melts and makes a seal.

This might be a great viable way of making it work.

bio · Working Bee

........What about finding a suitable solvent that solvates teflon, then one could drop it in, then let it dry. ................

Unfortunately teflon has no solvent or adhesive. It has been etched with HF or Na and sort of glued together.

Fortunately the new teflon coating (paint) developed a few years back is suitable for DIYers provided you have an oven large enough to cure the parts. Home oven temps are enough .

See http://www.dupont.com/teflon/coatings/p_m_guide.html#teflons

Will have to try the oil bath magnet coating technique/ Have had limited success by wrapping the magnet with PTFE (white virgin) placing on the ceramic hotplate and slowly heating to 240-260deg while rolling gently until the tape fuses. It's easy to scorch and doesn't really melt fully.

Guest · Tue Jun 14, 2005 2:06 pm

Could somebody explain to me to theory behind the polarity of the stirrer, and the actuall maget need to rotate the stirrer, as want to give this a go,

My understanding is that you need a NS bar for the stirrer, and then you have two neo(scary) magnets placed a few centimetres apart, one facing N-UP, and the other Facing N-down.

Is that right?

For me, sealing with glass would probably be the easiest, as I have a fair bit of glassblowing exp.
You know how back in the pre 60's they used to encapsulat needles with glass, I am thinking along the same lines

syn

MargaretThatcher · Tue Jun 14, 2005 10:22 pm

bio · Working Bee

..........For me, sealing with glass would probably be the easiest, as I have a fair bit of glassblowing exp. You know how back in the pre 60's they used to encapsulat needles with glass, I am thinking along the same lines .......................

Never used the glass encapsulated magnets but seems they would be needed for only
very high temps or with the very few things that attack teflon.

My question is that it seems that a glass magnet would destroy the boiling flask in short order! Is this correct?

Maybe this is accepted when using them because they are readily available.

MargaretThatcher · Wed Jun 15, 2005 5:12 am

I tried making a glass stirbar and it took me quite a few goes. Very difficult to get the thing balanced and smooth for a novice glass worker. I first tried fixing the magnet in the centre of the glass tube with a blob of epoxy. Of course, as soon as I tried to close the last end of the tube, the epoxy heated up, outgassed and blew out the tube end.

I can't see that a commercial model would destoy a flask. The stirbar would be very smooth and also lubricated by whatever it was stiring.