Agitating – Stirrer within stationary mixing chamber – Magnetic stirrer
Patent
1995-03-09
1996-12-24
Jenkins, Robert W.
Agitating
Stirrer within stationary mixing chamber
Magnetic stirrer
B01F 1308
Patent
active
055868231
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to a magnetic stirring system and in particular to a magnetic stirrer and a method of magnetically stirring a liquid within a closed culture bottle.
BACKGROUND TO THE INVENTION
Magnetic stirring of liquids within a closed bottle is a well known technique. A stirrer bar in the liquid to be stirred is moved with a stirring action by a magnetic field producing means outside the bottle. The magnetic field producing means outside the bottle may be motor driven magnets or solid state switched coils. The stirrer bar normally used hitherto in such systems is of relatively high quality, being strongly magnetised and costly to manufacture. Accordingly, it is normal to recover the stirrer bar after use and wash it for further use.
Known from German Specification No. 1 757 099 is a magnetic stirring means for a bank of test tubes. Stirrer bars of unquantified magnetisation are driven in unspecified motion by an external permanent magnetic means driven in rotation. Also known from U.S. Pat. No. 4,090,263 is a magnetic stirrer system in which a magnetisable stirrer bar is coupled to an external drive magnet. It is well understood, however, that in a closed culture bottle an essential aim of any stirrer system is to promote gas exchange with the bottle headspace by disturbing the liquid surface. It is not apparent that the known stirrer systems are able to achieve this aim.
However, there are applications for magnetic stirrers, such as the stirring of cultures in microbiology, where the fluid is often extremely hazardous and recovery of stirrer bars would require protected sterilisation. In such circumstances, removal of the stirrer bar from the culture bottle would be a very undesirable process. Furthermore, culture bottles are themselves a disposable product, and must be of cheap manufacture. The incorporation of expensive stirrer bars in such bottles has therefore not been considered a practicable procedure, so that magnetic stirring has not been considered possible in this field of application.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a magnetic stirrer comprising a bottle unit constituted by a bottle having a base and a stirrer bar of relatively low power magnetisation lying on the bottle base within the bottle, and a permanent magnet means of relatively high power located beneath the bottle base in close proximity thereto, and driving means for continuously rotating the external permanent magnet means about an axis substantially normal to the bottle base so that its rotating strong magnetic field entrains the stirrer bar in continuous rotation in a plane parallel to and above the bottle base within the liquid in the container.
According to another aspect of the invention, there is provided a method of magnetically stirring a liquid within a bottle, wherein a stirrer bar of relatively low power magnetisation is inserted into the bottle to lie on the bottle base, a permanent magnet means of relatively high power is continuously driven in rotation beneath the bottle base in close proximity thereto and about an axis substantially normal to the bottle base, causing its rotating strong magnetic field to entrain the stirrer bar in continuous rotation in a plane parallel to and above the bottle base within the liquid in the container.
The invention is based on the realisation that an infallible magnetic coupling between an internal stirrer bar and an external magnetic driver can be achieved, with a low cost stirrer bar of low magnetisation, provided that the necessary coupling can be ensured by use of a high power magnetic drive.
In the field of blood culture bottles especially, a reliable magnetic coupling between the stirrer bar and its magnetic driving means is an essential requirement, because the bottle containing the sample is effectively opaque, so that visible checking of the operation of the stirrer bar is virtually impossible.
Because the stirrer bar is of relatively low power, it can be sufficiently cheaply
REFERENCES:
patent: 2350534 (1944-06-01), Rosinger
patent: 2951689 (1960-09-01), Asp et al.
patent: 3384353 (1968-05-01), Worth
patent: 5120135 (1992-06-01), Ullman
Jenkins Robert W.
Unipath Limited
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