US3333829A

US3333829A - Magnetic stirrer and temperature regulation device

Info

Publication number: US3333829A
Application number: US544201A
Authority: US
Inventors: Darrlle D Moore; Vais Edward L Ver
Original assignee: THERMOLYNE CORP
Current assignee: THERMOLYNE CORP
Priority date: 1966-04-21
Filing date: 1966-04-21
Publication date: 1967-08-01
Anticipated expiration: 1984-08-01

Description

Aug. 1, 1967 MQORE ET AL 3,333,829

MAGNETIC STIRRER AND TEMPERATURE REGULATION DEVICE Filed April 21, 1966 T Q22 HHHII will;

DAPRLLE 0. MOORE EDWARD L VER V4/S United States Patent M 3,333 829 MAGNETIC STIRRER AND TEMPERATURE REGULATION DEVICE Darrlle D. Moore and Edward L. Ver Vais, Dubuque,

ABSTRACT OF THE DISCLOSURE A temperature regulation device, utilized in combination with a magnetic stirrer in laboratory and similar applications. A thin, flat, rigid, non-magnetic chamber is positioned on the surface of the magnetic stirrer base, between the stirrer base and a vessel containing a stirring magnet; cooling fluid is circulated through the chamber to regulate the temperature of the vessel contents.

Background of the invention Magnetic stirrers have found increasing use in a variety of applications, particularly in laboratories for use in titrations, culturing, extractions, and other processes. A magnetic stirrer usually includes a base having an appropriate cover or top surface for supporting a beaker or other vessel. A magnetic drive element, usually a permanent magnet, is positioned within the base immediately below the cover. The vessel containing the material to be stirred is supported on the cover of the stirrer and a small permanent magnet or other appropriate magnetic stirring element is placed within the vessel, over the magnetic drive element in the base. Stirring is accomplished by rotating the magnetic drive element, the magnetic field linkage between the drive element and the stirring element causing .corresponding rotation of the stirring element and achieving the desired agitation of the vessel contents.

Some magnetic stirrers of this general kind are provided with opaque covers; the cover may be of nonmagnetic sheet metal or may be made of plastic or other suitable materials. One particularly advantageous commercial form of magnetic stirrer is that described and illustrated in United States Letters Patent No. 3,138,370 issued June 23, 1964 to Cleophas B. Anderson and Germain B. Pins. The magnetic stirrer of the patent is provided with a transparent cover and with one or more electrical lamps mounted within the base. This makes it possible to illuminate the contents of the vessel from be low, through the transparent cover plate, a highly desirable arrangement for many laboratory and other applications.

For many laboratory procedures where magnetic stirrers are employed, it is critically important to prevent heating of the vessel contents during the stirring operation. With virtually all magnetic stirring devices, however, at least some heat is generated and transmitted to the vessel containing the material being stirred. Basically, this heat has three sources. The primary source of the undesired heat is the drive motor for the magnetic drive element. Unless an elaborate fan and ventilation system is adopted, which is usually economically impractical, a substantial amount of the heat developed by the stirrer motor is frequently transmitted to the Vessel in which the stirring operation takes place.

Another principal source of heat is eddy currents in duced in the usual metal housing for the magnetic stirrer base. The rotating magnetic field between the magnetic drive and stirring elements can produce appreciable heat due to eddy currents developed in a metal cover plate on the base. Even where a plastic or other insulator cover is used, the eddy currents developed in the re- 3,333,829 Patented Aug. 1, 1967 mainder of the metal housing for the stirrer base, by the fringe portions of the magnetic field, can be noticeable.

A third source of heat that may be of some importance is present in a self-illuminated magnetic stirrer of the kind described in the Anderson et a1. Patent No. 3,138,- 370. A substantial portion of the heat developed by the lamps used for base illumination may be absorbed by the vessel.

Summary of the invention It is a primary object of the present invention, therefore, to provide a simple, practical and inexpensive temperature regulation device for a magnetic stirrer of the kind described hereinabove.

A further object of the invention is to afford an effective temperature regulation device for a magnetic stirrer that nevertheless permits illumination of a vessel containing the material being stirred directly from below by means of light sources located in the magnetic stirrer base.

Another object of the invention is to aiford a temperature regulation device for a magnetic stirrer that does not inherently add any heat to that already produced by the stirrer.

A further object of the invention is to afford a simple temperature regulation device for a magnetic stirrer that permits moderate but effective cooling or, alternatively, moderate but effecting heating of the material being stirred.

An additional object of the invention is to provide a temperature regulation device for a self-illuminated magnetic stirrer that is eliective as a light filter, in addition to its temperature regulation functions.

Accordingly, the present invention relates to a temperature regulation device for a magnetic stirrer of the kind comprising a base having a cover, a magnetic drive element positioned within the base below the cover, and a magnetic stirring element positioned within a vessel that is supported on the cover. The magnetic stirrer further includes means for rotating the magnetic drive element to stir the contents of the vessel by rotating the magnetic stirring element through the magnetic field linkage between the magnetic elements. The temperature regulation device of the invention comprises a thin, flat housing of non-magnetic material that is also preferably electrically non-conductive; this housing defines a fluidtight chamber having an effective surface area approximating the surface area of the cover of the magnetic stirrer. This housing is positioned on the cover of the magnetic stirrer intermediate the cover and the vessel containing the material being sitrred. The temperature regulation device further includes means, comprising inlet and outlet conduits connected to the chamber, for circulating fluid through the chamber to regulate the contents of the vessel containing the material to be stirred. Usually, the circulating fluid is ordinary tap water.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be made as desired by those skilled in the art without departing from the present invention.

Description of the drawing FIG. 1 is a prespective view of a magnetic stirrer and a temperature regulation device for the stirrer constructed in accordance with the present invention;

FIG. 2 is a plan view of the temperature regulation device mounted in position of use on the magnetic stirrer;

FIG. 3 is an elevation view, partly in cross section, taken approximately along line 33' in FIG. 2;

FIG. 4 is a transverse sectional view of the temperature regulation device taken approximately as indicated by line 4-4 in FIG. 2; and

FIG. 5 is a detail sectional view, drawn to an enlarged scale, taken approximately as indicated by line 5-5 in FIG. 2.

Description of preferred embodiment FIGS. 1, 2'and 3 illustrate a temperature regulation device constructed in accordance with preferred embodiment of the present invention, mounted in position of use upon a magnetic stirrer 11. The magnetic stirrer 11 corresponds in construction to that disclosed in Patent No. 3,138,370. It comprises a sheet metal base 12 having a cover 13. The central portion of the cover 13 constitutes a transparent plastic cover plate 14.

A magnetic drive element is positioned within the base 11 below the coverplate 14 and located centrally with respect to the cover plate. Magnetic drive element 15 constitutes a small permanent magnet. The magnetic drive element 15 is mounted in a diametrical groove in a coupling member 16, being held in place by an appropriate clamp 17. The coupling member 16 is connected, by a hub 18, to the drive shaft of a small electrical motor (not shown), the coupling thus affording a means for rotating the magnetic drive element 15 about the axis of the coupling.

In conventional use of the magnetic stirrer 11, a vessel containing the material to be stirred would be supported directly upon the cover plate 14 of the stirrer base. In accordance with the present invention, however, this practice is not followed. Instead, the temperature regulation device 10 is disposed upon the cover plate 14 of the magnetic stirrer and a vessel 21 containing the material 22 to be stirred is in turn supported upon the temperature regulation device (see FIGS. 1 and 3). A magnetic stirring element 23 that is used with and constitutes a part of magnetic stirrer 10 is positioned in vessel 21; this magnetic stirring element preferably comprises a small permanent magnet and may be provided with an inert coating to permit use of the stirrer in solutions and other materials that would otherwise attack the permanent magnet. In use, magnetic stirring element 23 rotates in response to rotation of the magnetic drive element 15, due to the magnetic field linkage between these elements, and thus stirs the material 22 within vessel 21.

Temperature regulation device 10 comprises a thin .flat housing constructed in the form of two quite shallow dish-

like housing members

26 and 27. The two

housing halves

26 and 27 are sealed to each other around their rims; the rims of the two housing members may be ccmented to each other or a heat fusion bond may be employed if desired, assuming an appropriate material is used in fabricating the housing. Similarly, the central portions of the two housing members are sealed together. In this instance, an eyelet 28 is employed to provide a strong mechanical joint (see FIG. 4). In addition, or by way of substitution, a cement bond or fusion bond can also be used. Other appropriate means for securing the two housing halves together can be utilized, or other manufacturing techniques may be employed to produce a thin-wall housing, as desired, so long as the housing defines a fluid-tight chamber 29 within the housing.

The

housing

26, 27 should be fabricated from a nonmagnetic material. If a magnetic material is employed, it detracts materially from the magnetic coupling between

members

15 and 23 and thus interferes with the desired stirring action. Furthermore, it is preferred that the housing of the temperature regulation device 10 be made of electrically non-conductive material to avoid the generation of eddy currents in the housing. If the housing comprises an electrical conductor, the rotating electrical field extending between the magnetic members 15 and 24 produces eddy currents in the housing and this may lead to undesirable heating. In the preferred form of the invention, as illustrated, the

housing members

26 and 27 are constructed from a transparent plastic. 7

The fluid-tight chamber 29 within the temperature regulator housing has an effective surface area that is generally similar to the useful surface area of the cover of the magnetic stirrer. In the embodiment of the invention as illustrated, the temperature regulating device is somewhat smaller than the cover and this is quite permissible, but the device should be of the same order of magnitude, with respect to surface area, as the stirrer cover in order to afford uniform temperature regulation as described hereinafter.

Temperature regulation device 10 is provided with an inlet conduit or nipple 31 that connects with the interior of chamber 29. A similar outlet conduit 32 is'also provided. Actually,

conduits

31 and 32 are interchangeable and either may be used as the inlet or outlet conduit at different times. These conduits afford a means for circulating fluid through chamber 29.

In the construction illustrated in the drawings, a barrier 33 is located within the

housing

26, 27. Barrier 33, as shown in FIGS. 2 and 4, extends from a point immediately between the inlet-

outlet conduits

31 and 32 to the center of the chamber 29. The use of a barrier such as member 33 is not essential to operation of the device and may be omitted in some instances.

In use, a hose or other similar conduit extension 35 is connected to the inlet conduit 31. In the usual application, the other end of hose 35 (not shown) is connected to a water tap or other suitable source of fluid at a desired temperature. Similarly, a hose or like conduit extension 36 is connected to the outlet conduit 32. Hose 36 may lead to a drain or to a re-circulating pump. Where substantial temperature reduction is required, the

hoses

35 and 36 can be connected to a refrigerating apparatus to reduce the temperature of the fluid used in device 10 well below ambient temperature.

In operation, ordinary cold tap water may be circulated through device 10, introduced into the annular chamber 29 through inlet conduit 31. The fluid is continuously exhausted from the chamber, once the chamber is filled, through outlet conduit 32 and hose 36. In most processes, only a limited cooling effect is desired so that tap water provides sufficient cooling. If water from the cold tap is too cold and reduces the temperature of the material 22 below the desired level, it is a simple matter to connect hose 35 to a conventional mixing faucet and to mix some warm water with cold water to achieve the desired effect. By the same token, if a moderate increased heating effect is desired, warm or hot water alone may be circulated through the temperature regulation device 10 for this purpose.

As noted above,

housing members

26 and 27 are preferably fabricated from a transparent plastic material. Accordingly, where cover plate 14 (FIG. 3') is transparent and where the stirrer 11 includes a light source in the base, as disclosed in Patent No. 3,138,370, the use of a substantially transparent cooling liquid makes it possible to illuminate the bottom portion of vessel 21 with little or no reduction in efficiency. Thus, the temperature regulation device does not interfere with the self-illuminated magnetic stirrer operation.

In some laboratory applications, it is desirable to illuminate vessel 21 with light of a particular color; more expressly, it may be desirable to filter out a predetermined portion of light transmitted from the base of the magnetic stirrer to the vessel containing the material being stirred. This can be accomplished in one of two ways. It is readily possible to add a dye to the fluid circulating through device 10 that will effectively filter the light reaching the vessel 21 from the base of the magnetic stirrer. On the other hand, the

plastic housing

26, 27 may be tinted in manufacture to afford a filter capable of obtaining the desired results.

Hence, While preferred embodiments of the invention have been described and illustrated, it is to be understood that they are capable of variation and modification.

We claim:

1. In combination with a magnetic stirrer of the kind comprising a base having a cover, a magnetic drive element positioned within said base below said cover, a magnetic stirring element positionable within a vessel supported on said cover, and means for rotating said magnetic drive element to stir the contents of said vessel by rotating said magnetic stirring element through magnetic field linkage between said magnetic elements, a temperature regulation device comprising a thin, flat housing of non-magnetic material, defining a fluid-tight chamber having an eifective surface area approximating the surface area of said cover, positionable on said cover intermediate said cover and said vessel, and means, including inlet and outlet conduits connected to said chamber, for circulating fluid through said chamber to regulate the temperature of the contents of said vessel.

2. A temperature regulation device in combination with a magnetic stirrer, according to claim 1, in which said housing is of electrically non-conductive material to prevent development of substantial eddy currents therein.

3. A temperature regulation device in combination with a magnetic stirrer, according to claim 1, in which said chamber is of annular configuration, with said inlet and outlet conduits located closely adjacent each other, and having a barrier extending from a point between said conduits to the center of said chamber to assure flow of said fluid completely around said chamber.

4. A temperature regulation device in combination with a magnetic stirrer, according to claim 1, in which said housing is of transparent plastic material to allow passage of light from said base through said housing to said vessel.

5. A temperature regulation device in combination with a magnetic stirrer, according to claim 4, in which said transparent housing is tinted to filter out predetermined portions of light transmitted from said .base through said device to said vessel.

References Cited UNITED STATES PATENTS 2,518,758 8/1950 Cook 259108 3,138,370 6/1964 Anderson 259-108 3,233,662 2/1966 Chuen l46 WALTER A. SCHEEL, Primary Examiner.

ROBERT W. JENKINS, Examiner.

Claims

1. IN COMBINATION WITH A MAGNETIC STIRRER OF THE KIND COMPRISING A BASE HAVING A COVER, A MAGNETIC DRIVE ELEMENT POSITIONED WITHIN SAID BASE BELOW SAID COVER, A MAGNETIC STIRRING ELEMENT POSITIONABLE WITHIN A VESSEL SUPPORTED ON SAID COVER, AND MEANS FOR ROTATING SAID MAGNETIC DRIVE ELEMENT TO STIR THE CONTENTS OF SAID VESSEL BY ROTATING SAID MAGNETIC STIRRING ELEMENTS, A TEMPERAFIELD LINKAGE BETWEEN SAID MAGNETIC ELEMENTS, A TEMPERATURE REGULATION DEVICE COMPRISING A THIN, FLAT HOUSING OF NON-MAGNETIC MATERIAL, DEFINING A FLUID-TIGHT CHAMBER HAVING AN EFFECTIVE SURFACE AREA APPROXIMATING THE SURFACE AREA OF SAID COVER, POSITIONABLE ON SAID COVER INTERMEDIATE SAID COVER AND SAID VESSEL, AND MEANS, INCLUDING INLET AND OUTLET CONDUITS CONNECTED TO SAID CHAMBER, FOR CIRCULATING FLUID THROUGH SAID CHAMBER TO REGULATE THE TEMPERATURE OF THE CONTENTS OF SAID VESSEL.