UnintentionalChaos
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Overhead Stirrers
I am looking to purchase an overhead stirrer (the motor). I already have a bearing and 10mm stir shaft with teflon paddles. I will probably not be
stirring anything more than a 1liter flask, maybe 2 to 3 liters in the long run. However, I expect some chunky reaction mixtures, which is my prime
reason for choosing this over my existing magnetic stirring.
What I seem to find is that the minimum RPM for many stirrers is quite high. I was looking at a Wheaton #903475 and the only place I can find any sort
of data is their amazon page (their site has almost no information) which states 300-5000rpm. This is way too fast. I was hoping for 50-60rpm as the
lower end. Will it stir slower under a load, or does that depend on the particular model?
I know many members here have overhead stirring setups. What brands/models are good choices?
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Magpie
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I have a Wheaton 903475 which I picked off eBay for a very reasonable price. I did have to buy an adapter from McMaster-Carr and a chuck from my
local hardware store as it came without these.
I somehow aquired an owner's manual...probably ordered it through Wheaton. It says that this stirrer is primarily designed for tissue cutting. RPM
range is 1000-10,000.
I have used mine several times for stirring in RBFs using the teflon folding propeller and bearing. It does the job although as you say it runs too
fast. It doesn't turn steadily until a setting of about 3 on the 0-10 speed scale. It turns pretty fast at this setting...probably 100-300 rpm.
I have seen other stirrers for sale that seem more tailored for stirring for chemical reactions. I don't know the brand/model but it seems like
benzylchloride1 has one as shown in his lab tour, or maybe it was in his latest batch of pictures. You should also be able to find it in the VWR or
Fisher catalogs.
The single most important condition for a successful synthesis is good mixing - Nicodem
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watson.fawkes
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Quote: Originally posted by UnintentionalChaos  | What I seem to find is that the minimum RPM for many stirrers is quite high. I was looking at a Wheaton #903475 and the only place I can find any sort
of data is their amazon page (their site has almost no information) which states 300-5000rpm. This is way too fast. I was hoping for 50-60rpm as the
lower end. Will it stir slower under a load, or does that depend on the particular model?
I know many members here have overhead stirring setups. What brands/models are good choices? |
The Wheaton
model you reference has a Jacobs chuck for clamping on to the shaft of the stirrer. I don't know how much space you have in your lab or your tolerance
for improvisation, but that stirrer looks a lot like a drill press to me, just without the quill (vertical motion). For reference, there's a Harbor Freight 12-speed bench model that's on sale right now for only $130 (regular $170). Its lowest speed is 250 rpm.
As for the question of low end torque, the best way is to gear the motor down rather than to use electronic speed control. Pretty much every
electronic version works, in the end, by reducing power transferred to the motor. This will obviously slow it down, but it will also reduce torque.
It's still useful to have some speed control like that and to uprate the motor accordingly.
Nevertheless, for low speeds and standard fractional horsepower motors, it's better to step down the motor mechanically. The decreases the speed and
multiplies the torque accordingly. Which brings us back to the drill press. The model I referenced uses a belt drive system to step down the motor.
The electric motor it has stated at 1/2 HP, even if that's probably the "inrush-current HP", so really more like 1/4 - 1/3 HP, after mechanical step
down, it still has lots of torque to spare. Anybody who's ever been sloppy clamping at the drill press will attest to the torque available. So a unit
like that and a cheap speed controller should do you just fine.
As for silly practicalities, the quill arms just unscrew, so you can remove them after initial setup and not worry about jostling the stirrer height.
There's a quill lock, so you get some height adjustment in the stirring head for free. The table acts like an inconvenient "lab jack" platform, if you
want it, or can be removed entirely with a little wrenching.
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fledarmus
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There are things like this:
Caframo Ultra-torque
I don't remember the manufacturer anymore, but about ten years ago I had a nice old overhead stirrer that had two output shafts at 90 degrees to each
other - one came out of the bottom and one came out the side. There was about a 4:1 or 6:1 reducing gear inside to give a low speed and high speed
output. That was very useful for large paddles or particularly chunky reactions.
Edited - ah, found some examples searching "double shaft overhead stirrer". Here's one...
Talboy
[Edited on 16-1-2012 by fledarmus]
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Magpie
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Here's a link to the Talboys site:
http://www.troemner.com/equip_talboys_heavyduty.php
showing their most beefy mixers, up to 1/4hp.
[Edited on 16-1-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Panache
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I've driven two ika's very hard for many years, both to their well deserved graves. One was a simple a two gear system that used internal gearing to
switch between high and low, the speed was adjusted through a mechanical mechanism that slide the motor forward nd backwrds. Lo speef was 10-60 rpm or
something, high speed ws 100-2000. Torque at the low speeds was enough to easily break glass shafts less good on high speeds which is what is needed.
I recomend this stirrer it is great and quiet.
I also don't suggest gtting a drill press. This is one piece of seemingly simple kit where there is no easy second. If you were doing just the one
thing it myine but fine by for flexibility it immediatly become useles.
Also remember drill presses have no flame proof or sparkfree moto.
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