0. Hello Hobart Technical College Tasmania, Australia
A Sealed Stirring Mechanism
The stirring device here described can be used when a leakproof seal is required for enclosed chemical reactions. I t can replace the more elaborate mercury seals for many operations. The stirring paddle D is rotated by pivotting it within a flexible seal, C, which is made from a piece of soft polythene tubing. This tubing is first fitted through a hole bored in the bottom of a hollow plastic stopper, B, from which the top has been removed. The glass rod, D, is pushed through afterwards as shown in the diagram. The top of rod D fits loosely within a hole drilled approximately 0.25 in. off center in the wooden disk, A. By rotating A with a large (0.1 hp) or geared-down laboratory stirrer motor, even viscous solutions can be stirred adequately. The tubing C should fit tightly around the stirrer only where it passes through the plastic stopper. Also the stirring rate should not be above2 or 3 rps, otherwise the tubing will break down quickly. A test was made stirring glycerine eight hours daily for three days. During the stirring an approximate 2-cm Hg vacuum was maintained, and, between stirring, the system was closed off. There was only a small drop in vacuum overnight, and at the end of the test no glycerine, which was put in the hollow stopper to provide some lubrication, showed up on the bottom half of tube C, proving that the seal did not break down during the complete test. The seal could be further improved if the plastic stopper and the bottom half of C were molded in one piece. For higher temperature applications, a Teflon molding could be made with a thin or bellows bottom in which part or the whole of the stirring rod could be incorporated. The power required for stirring could be reduced if a small roller bearing were put within the
eccentric hole in A to reduce the friction with the glass rod. If the rod driving A is long a clamped guide7'should be provided near the disc, so that. the disc will;keep a central relation to the stopper.
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$tirring
Volume 44, Number
I , January 1967
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35
