Author Topic: Needed: "slow" stir plate  (Read 1649 times)

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Marcilla

  • Guest
Needed: "slow" stir plate
« on: December 17, 2003, 11:03:00 AM »

Osmium

  • Guest
A variable hot plate stirrer.
« Reply #1 on: December 17, 2003, 12:03:00 PM »
A variable hot plate stirrer. Every type I have used so far was able to stir slowly. Unless there were lots of solids in it, then you need an overhead stirrer.


bio

  • Guest
no external heat
« Reply #2 on: December 17, 2003, 06:56:00 PM »
There are cheap plastic water powered stirrers intended for submersible application. Water flow determines speed. They will go very slowly and can go right in the cooling bath. The one I had was kind of flimsy for about $20.

Marcilla

  • Guest
WTF?!?!?
« Reply #3 on: December 25, 2003, 03:13:00 AM »
I U'dTFSE. I U'dTFSE!!! There is nothing under "slow stir plate". I'm not sure what you think I should have used(???)

Anyway, yes, my hot plate stirrers have had variable speeds. But even the slowest speed is several revolutions per second probably.

And I don't understand a "water-powered" stirrer? How could it bee water-powered unless you are sticking this in a running river or something. Sorry if I'm too dumb to catch on. My ex-was the PhD. I just cooked the hunny the way my hunny taught me.

XXOO (and Merry X-mass),

Marcilla


lugh

  • Guest
Merry Xmas
« Reply #4 on: December 25, 2003, 04:07:00 AM »
Apparently, Rhodium's page eluded you, see

https://www.thevespiary.org/rhodium/Rhodium/chemistry/equipment/magstirrer.html



A magnetic stirrer consists of a pair of magnets turned by a motor, here's construction instructions and a drawing of an air-powered stirrer:

Using a circular Alnico magnet and equipment found in most laboratories, it is easy to construct an air-driven magnetic stirrer. This stirrer is powered with a compressed air jet and may be used with inflammable liquids without the danger of sparking associated with an electric motor.
A 5" cubical box is constructed of 1/2" plywood and provided with a thin removable cover of aluminum, glass or other nonmagtietic material. An inverted 4" watchglass is placed in the bottom of the box. Two strips of plywood, each about 2" wide, are nailed horizontaliy inside the box, one above the other and about 2 1/2" apart, the lower strip being an inch above the bottom of the box. A 3/8" hole is drilled in each strip to hold vertically in the center of the box a 3 1/2" length of 9 mm glass tubing, which serves as a bearing and rests on the watchglass.
A 1 1/2" circular Alnico magnet is centered on top of a cylindrical cork, about 2" in diameter and 1" high, into the rim of which are cut serrations or notches about 1/4" apart. The magnet is held in place on the cork by inserting four pins or small nails. The cork is fastened on the upper end of a 6 mm glass rod which sits inside the 9 mm glass tubing, the length of the rod being such that the magnet is as close to the alumintun cover as possible. The lower end of the rod, rounded by fire-polishing, rests on the inverted watchglass. This contact between rod and watchglass offers littie friction when the rod is rotating.
The jet of compressed air, which strikes the serrations of the cork and rotates the magnet, enters through a piece of 9 mm glass tubing running into the ride of the box at the same height as the cork and near the edge thereof. This tubing may be held firmly in place by drilling in the plywood a hole for a No. 4 one-hole rubber stopper through which the tubing passes. The end of the tubing is fashioned to form a vertical "wing-tip," which provides for a more effective flow of air against the cork.
The "stirring rod" is made by sealing iron filings or a nail in a piece of small glass tubing. The completed rod should not be over an inch long, since long rods rotate with difficulty and short ones easily stir the contents of large beakers. For stirring liquids which will not react with iron, a nail or piece of iron wire about one inch long may he used without being encased in glass.
The beaker containing the liquid to be stirred is placed on the aluminum cover and a "stirring rod" is dropped into the beaker. The rotating magnet turns this rod and the speed of stirring is controlled by the amount of air striking the cork. If the magnet rotates too rapidly, it gets "out of phase" with the stirring rod and stirring ceases or becomes very erratic.




The water powered stirrers work the same as the air powered one, using a molded plastic circular arrangement of paddles, instead of notches, and having an outlet to allow the water to drain. They attach to a water source such as a faucet, forget about silly ideas such as a river, unless you happen to own a dam  ;D  They really are as inexpensive as mentioned above, and buying one from a lab supplier would probably be your best bet, unless you're crafty enough to build one for less  ;)


biotechdude

  • Guest
An Observation
« Reply #5 on: December 29, 2003, 11:18:00 AM »
Swix has a magnetic stirrer/hotplate combo (and it rocks!).  Anyway, sometimes when the volume of solution is low, the spinner is too fast (on the lowest setting).

SO, Swix observed that when you crank the spin speed UP in speed, the magnet looses its 'grip' on the spinner bar.  This results in the spin bar agitating (which is good) and making about 1 revolution per 5 secs or so.  Other agitation/spin combos can bee achieved as well (OK, I WAS BORED!!)

So in conclusion, don't assume the lowest speed setting is the slowest.  Experiment with different spin bars, solution volumes and spin speeds.  Also, putting the spin bar off axis with the magnet can create some nice 'swirl' actions.  All these motions can bee maintained for hours unless disturbed.