US3384353A - Magnetic stirrer - Google Patents

Description

May 21, 1968 L. R. WORTH MAGNETIC STIRRER Filed May 31, 1967 INVENTOR.

FIG. 3.

LOW HIGH 7 MED.

FIG.

United States Patent 3,384,353 MAGNETIC STIRRER Lewis R. Worth, Deerfield, Ill., assignor to Cole-Farmer Instrument & Equipment Company, Chicago, 111., a corporation of Illinois Filed May 31, 1967, Ser. No. 643,317 7 Claims. (Cl. 259-108) ABSTRACT OF THE DISCLOSURE A magnetic stirrer is described in which a compound magnet comprised of two magnet structures is utilized. Means are provided for supporting a liquid container having a stirring element formed of magnetic material therein within the field established by at least one of the magnet structures of the compound magnet. The rotation of the compound magnet causes a concurrent rotation of the stirring element within the liquid in the container.

This invention relates to magnetic stirrers and, more particularly, to an improved magnetic stirrer which is capable of utilization in connection with [a wide range of sizes of stirring elements or bars at their maximum efliciency without sliding, drifting or jumping.

Magnetic stirrers are used to agitate fluid in a container or vessel in a manner which facilitates access to and visibility of the fluid in the container. No agitator shafts or other devices extend into the container when used with a magnetic stirrer, thereby presenting minimal obstruction at the open top of the container. The particular instances in which a magnetic stirrer may be found to be of advantage are numerous and include, for example, laboratory type procedures, such as titration, involving the mixing of various chemicals wherein it is important to control the amount of chemical being added, observe the process, and maintain a uniform distribution of the chemicals within the container.

A magnetic stirrer is generally used in connection with a magnetic stirring element disposed within the vessel containing the fluid to be stirred. The magnetic stirrer incorporates a magnet structure providing a magnetic field, and the fluid containing vessel is supported such that the stirring element therein is within the magnetic field. The magnet structure is then rotated or otherwise moved to cause a corresponding movement of the stirring element and consequent agitation of the fluid. The magnetic stirrer may incorporate a hot plate for maintaining the fluid at a desired temperature, a light or lights for providing illumination of the fluid in the vessel, and means for varying the speed of the magnet structure to provide for different degrees of fluid agitation.

Magnetic stirrers of heretofore known construction have sometimes been subject to certain limitations. O e major limitation frequently encountered in prior art devices has been their inability to accommodate a wide range of magnetic stirring element sizes. Thus, a given size magnetic stirrer of prior known construction may only be usable for a limited range of vessel sizes. Previous attempts at designing magnetic stirrers to accommodate a wide range of stirring element sizes have been generally unsatisfactory in that, for many sizes, when the stirring elements are moved in a manner for peak efficiency, the elements may slide, drift, or jump out of position in the vessel due to inadequate holding ability of the magnetic field produced by the magnet structure within the stirrer.

It is, accordingly, an object of this invention to provide an improved magnetic stirrer.

Another object of the invention is to provide a mag- 3,384,353 Patented May 21, 1968 "ice netic stirrer capable of utilization in connection with a relatively wide range of stirring element sizes.

A further object of the invention is to provide a magnetic stirrer capable of utilization in connection with a wide variety of stirrer element sizes at their maximum efliciency without sliding, drifting or jumping.

It is another object of the invention to provide 1311 improved magnetic stirrer generally of the type described, which is low in cost and of simple reliable construction.

Other objects of the invention will become apparent to those skilled in the art from the following description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a perspective view of a magnetic stirrer constructed in accordance with the invention, and having the top broken away to illustrate internal elements, and

illustrating a beaker broken away to show a stirring element therein;

FIGURE 2 is a top view of a portion of an alternative embodiment of the invention; and

FIGURE 3 is a side view of the elements illustrated in FIGURE 2.

Very generally, the magnetic stirring device 11 of the invention comprises a firstpermanent magnet structure 12 formed of a material such as Alnico and having a pair offirst pole portions 13 of opposite polarity, and a second permanent magnet structure 14 also formed of a material such as Alnico and having a pair of second pole portions 16 of opposite polarity spaced from the first pole portions. The second pole portions are disposed between the first pole portions on a line extending between the first pole portions. The first and second magnet structures are positioned with the respective first and second pole portions of like polarity closest to each other. Means 17 are provided for supporting afluid containing vessel 18 with a stirringelement 19 therein within the magnetic field established by the first and second magnet structures. Means are provided for moving the first and second pole portions in a manner to stir the fluid in the vessel.

Referring now in greater detail to the invention, the magnetic stirrer 11 is illustrated in FIGURE 1 for use in stirring thefluid 21 in thevessel 18. The vessel illustrated is a conventionally shaped beaker; however, vessels of other shapes and sizes may also be utilized in connection with the invention.

The stirringelement 19 disposed within thevessel 18 may be of any shape suitable for achieving the desired stirring eflect. The particular shape of the stirring element 11 will depend upon the shape of the vessel and the materials of which the vessel and the stirring element are comprised. Thus, if the vessel has a curved bottom, a stirring element of a generally egg shaped form, rather than the elongated rod form illustrated, may be preferable. Moreover, although the stirring element is comprised of magnetic material, it may be coated with a protective substance such as glass or Teflon, depending upon the nature of the fluid being stirred. If desired, the stirring element may include a raised portion (not shown) intermediate its ends so that the element may more easily spin in the vessel.

The magnetic stirrer 11 includes ahousing 23 having the beaker supporting means or table 17 and acontrol panel 24. The control panel is provided with aspeed control 26, aload mode control 27, and a power-onlight 28.

viscosity of the fluid being stirred. The speed control is for providing the desired degree of agitation in the fluid.

Themotor 29 is for rotating the pair ofmagnet structures 12 and 14, described in detail below, and has a drive shaft, not visible. The drive shaft is drivingly connected to afan 31 for providing a circulation of cooling air, and to acylindrical mount 32, the latter also constituting part of the means for moving the pole pieces.

Thecylindrical mount 32 is drivingly secured to the end of the motor drive shaft and supports the twomagnet structures 12 and 14. Themagnet structure 12 includes anelongated bar 33 supporting thepole portions 13 at each end thereof. Each of thepole portions 13 comprises a generally elongated pole piece and the two pole pieces are disposed parallel to each other. The pole pieces are tapered toward the tips thereof, and the tips of the pole pieces lie in the same plane, a plane which extends generally parallel with the plane of the supporting table 17 and just underneath it. Theelongated bar 33 is comprised of a suitable magnetized material so that thepole pieces 13 are of opposite polarity as indicated in the drawing.

The second magnet structure 14 is provided with the second pole portions 16 thereon. The magnet structure 14 comprises a generally U-shaped magnet with the pole portions 16 disposed at each tip. The magnet structure 14 is supported on theelongated bar 33, and a non-magnetic (e.g., aluminum) shim orspacer 34 separates the U-shaped magnet structure 14 from the elongated bar. Theelongated bar 33 rests in a diametrical channel or slot provided in thecylindrical mount 32, projecting from each end thereof. The assembly of the two magnet structures may be held together by any suitable means, but it is preferable that the bond be accomplished by means of baked and cured epoxy, not illustrated.

The smaller U-shaped magnet structure 14 is oriented so that its pole portions 16 and thepole portions 13 of themagnet structure 12 are all in general alignment. In addition, the two magnet structures are positioned with their respective pole portions of like polarity closest to each other, as indicated in the drawing.

The result of the foregoing described construction is the production of two magnetic fields. The larger field, produced by themagnet structure 12, is highly concentrated at thepole portions 13 due to the tapering shape of the pole portions or pieces, and due to the effect of the smaller magnetic field established by the magnet structure 14. This smaller magnetic field forces the flux lines of the larger magnetic field outwardly toward the opposite ends of themagnet structure 12.

The gap between thepole portions 13 and the pole portions 16 is selected to be sufiicient to prevent thelarger magnet structure 12 from excessively degrading the effect of the small magnet structure 14. The precise positioning of thepole portions 13 and the pole portions 16 may be arrived at empirically, depending upon the range of stirring element sizes it is desired to accommodate. Thus, for example, where themagnet structure 12 is 3 inches in the horizontal direction from the outside surfaces of therespective pole portions 13, and where the second magnet structure 14 is centered on theelongated bar 33, being about of an inch between outside surfaces and having a centered inch wide gap about of an inch deep, the device is capable of accommodating bar type stirring elements in the length range from about of an inch to slightly over 3 inches. Naturally, this geometry can be changed, if necessary to accommodate other ranges of stirring element sizes. It is preferred that the tops of all pole faces or portions be even or coplanar.

In operation, smaller size stirring elements are centered and held by the smaller magnetic field established by the magnet structure 14. Larger stirring elements may be centered on and are held securely by the highly concentrated field established at thepole portions 13 of thelarger magnet structure 12. This particular arrangement insures that a variety of stirring element sizes may be securely locked in and held by the rotating magnet structures.

In assembling the magnetic stirrer illustrated in FIG- URE 1, it is preferable that a keeper or magnetic shunt (not shown) be placed on the smaller structure 14 to reduce the effect of its magnetic field and to enable the magnet structures to be positioned more readily with respect to each other. It is preferable that the magnet structures be oriented properly (i.e., north to north) before bringing them together, and that the smaller magnet structure 14 be brought down perpendicularly to thebar 33 and that relative rotation be avoided.

Referring now to FIGURES 2 and 3, an alternative construction for part of the magnetic stirrer of the invention is illustrated. In the alternative structure, a bushing 41 and adrive shaft 40 are used to support and drivingly secure the two magnet structures described below to a drive shaft of the motor. Afan 42 is secured to the bushing 41, as is the large-r magnet structure 43. Thelarger magnet structure 43 consists of an elongated magnet having itsends 44 and 46 turned to extend transversely of itsmiddle portion 47 and parallel with each other. The ends 44 and 46 are tapered and comprise pole portions or pieces of themagnet structure 43. The polarities are indicated in the drawing.

Thesmaller magnet structure 48 consists of a cylindrical or button type magnet having aslot 49 extending between the opposite poles orpole portions 51 and 52. A shim or spacer 53 is positioned between themagnet structure 48 and themiddle portion 47 of themagnet structure 43. The shim or spacer 53 is of non-magnetic material. The entire assembly of the two magnet structures may be held together as before, that is, by a suitable epoxy, not illustrated.

The construction illustrated in FIGURES 2 and 3 provides a similar arrangement of two magnetic fields as is established by the device illustrated in FIGURE 1.

It may therefore be seen that the invention provides an improved magnetic stirrer of simple, sturdy and economical construction. The magnetic stirrer of the invention is capable of accommodating a range of sizes of stirring elements without being subject to sliding, drifting or jumping thereof. The stir-ring elements are securely locked in irrespective of their size, within the size range for which the magnetic stirrer is designed.

Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modificaions are intended to fall within the scope of the appended claims.

What is claimed is:

1. A magnetic stirring device comprising, a first magnet structure having a pair of first pole portions of opposite polarity, a second magnet structure having a pair of second pole portions of opposite polarity spaced from said first pole portions, said second pole portions being disposed between said first pole portions on a line extending between said first pole portions, said first and second magnet structures being positioned with the respective first and second pole portions of like polarity closest to each other, means for supporting a fluid containing vessel with a stirring element therein within the magnetic field established by said first and second magnet structures, and means for moving said first and second pole portions in a manner to move the stirring element.

2. A device according to claim 1 wherein said moving means include a rotary support mechanically coupled to said first and second magnet structures for rotating same.

3. A device according to claim 2 wherein the axis of rotation of said rotary support is perpendicular to a line extending through said pole portions and is aligned with a space between said second pole portions.

4. A device according to claim 1 wherein said pole portions comprise generally elongated mutually parallel pole pieces having their tips lying generally in the same plane.

5. A device according to claim 4 wherein said first pole pieces of said first magnet structure are tapered toward their tips to concentrate magnetic flux thereat.

6. A device according to claim 1 wherein said first magnet structure includes an elongated bar and a pair of elongated pole pieces extending perpendicularly thereto, one at each end, wherein said second magnet structure includes a generally U-shaped magnet supported on said elongated bar, and wherein a non-magnetic spacer is disposed between said bar and said U-shaped magnet.

7. A device according to claim 1 wherein said first magnet structure includes an elongated magnet having its ends turned to extend transversely of its middle portion and parallel with each other, wherein said second magnet structure includes a button magnet supported on the middle portion of said elongated magnet and having a. slot therein between opposite poles, and wherein a nonmagnetic spacer is disposed between the middle portion of said elongated magnet and said button magnet.

References Cited UNITED STATES PATENTS 2,655.011 10/1953 Ihle 259-108 X 3,138,370 6/1964 Anderson 259108 3,211,433 10/1965 Ohrostowski 259108 3,245,665 4/1966 Steel 259108 X ROBERT W. JENKINS, Primary Examiner.

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