US3191106A - Rubber-like permanent magnet article and manufacture of same - Google Patents

Description

June 22, 1965 M. BAERMANN RUBBER-LIKE PERMANENT MAGNET ARTICLE AND MANUFACTURE OF SAME 3 Sheets-Sheet 1 Filed Oct. 6, 1960 INVENTOR. MAX BAER MA NN ATTORNEY June 22, 1965 A R 3,191,106

RUBBER-LIKE PERMANENT MAGNET ARTICLE AND MANUFACTURE OF SAME Filed 001:. 6. 1960 3 Sheets-Sheet 2 FIG. 4 FIG. 4a

INVENTOR. MAX BAERMANN ATTORNEY June 22, 1965 aERMA'NN 3,191,106

RUBBER-LIKE PERMANENT MAGNET ARTICLE AND MANUFACTURE OF SAME Filed 001. 6. 1960 FIG. 7

3 Sheets-Sheet 3 FIG. 9

AT TOR N EY United States Patent 0 knit 3,191,106 RUBBER-LIKE PERMANENT MAGNET ARTICLE AND MANUFACTURE OF SAME Max Baennann, Cologne (Rhine), Germany (Bensberg Wulfshof, Bezirlr Cologne, Germany) Filed et. 6, 1969, Ser. No. 60,951 Claims priority, application Germany, Dec. 24, 1959,

56,033 17 Claims. (Cl. 317-401) This invention relates to the art of permanent magnets and more particularly to a flexible and/or resilient permanent magnet particularly adapted to closures.

In recent years, flexible magnets have found widespread acceptance as a locking, sealing or holding material for door gaskets, particularly on refrigerators. For such applications the magnet is in the form of an elongated strip of a flexible and resilient material with particles of permanent magnet material dispersed throughout. In some respects, it may be said that the particles of magnetic material are held in close spaced relationship by a flexible binder material. The permanent magnet particles are magnetized to provide a plurality of spaced apart, opposite polarity permanent magnet poles at a holding face on the strip. These magnet poles produce a substantial magnetic holding force against a magnetically attractable member. For example, the strip may be mounted on the inside of a refrigerator door and the doorway of the refrigerator cabinet, if of steel, may constitute the magnetically attractable member. an arrangement, the magnetic strip provides sufficient holding force to establish a firm seal between the refrigerator door and the refrigerator cabinet.

The basic composition of such a flexible magnetic strip preferably may be as disclosed and claimed in my copending United States patent application Serial No. 693,- 603, filed October 31, 1957, now United States Letters Patent No. 2,959,832. i

One of the objections to such flexible magnet strips is that the known permanent magnet materials are dark in color and impart a dark color to the flexible binder even if the binder per se is colorless or a light color. This dark color is objectionable from an esthetic standpoint.

From viewpoint ofcustomeracceptance, it is highly desirable that the sealing gasket on the door be attractive in appearance and compatible with the over-all color scheme of the refrigerator. In the past, in order to satisfy this requirement, it was necessary to enclose the magnet strip in a sleeve or tube having the desired color, polyvinylchloride being a commonly used material for such sleeve or tube. In practice, such a sleeve or tube had a thickness of about 0.3 mm. which was interposed between the holding face of the magnet strip and the surface of the doorway on the refrigerator cabinet. The interposition of this thickness of non-magnetic material between the holding face of thernagnet strip and the magnetically attractable member to which it provides a seal reduces appreciably the magnetic attractive force of the magnetic strip. Furthermore, the profile of such a sleeve or tube is somewhat complex and its manufacture added to the over-all cost of the door seal.

The present invention is directed to a novel article of manufacture in which the desired color is provided essentially integral with the magnet strip itself, so that 1t is not necessary to provide a separate enclosing sleeve or tube in order to achieve the desired appearance. The provision of the color integral with the magnet strip itself in the present invention reduces the magnetic attractive force of the strip to only a slight extent and much less than the reduction which occurs in the case of a strip enclosed in a non-magnetic sleeve or tube.

The desired color may be provided in various embodi- With such 3,191,106 Patented June 22, 1965 ments of the invention, either by mixing a dry material having a high masking ability into the flexible and resilient binder along with the permanent magnet materials or the coloring can be imparted by forming a thin, flexible layer on the mixture of the flexible and resilient binder and permanent magnetic particles, either as the mixture is being molded or immediately thereafter.

The present invention is further directedto novel apparatus and method for simultaneously applying a thin coating of coloring material to the mixture of permanent magnet materialand flexible binder as such mixture is formed into its ultimate shape, for example, by extruding. Thus the mixture is forced through the passage of an extrusion nozzle while simultaneously introducing the coloring material into such passage midway between its ends.

In one aspect of the invention, a powdered anisotropic permanent magnetic material is employed and the particles thereof, while mixed with the flexible binder, are subjected to an aligning magnetic force while the binder is heated to the plastic state .as the mixture either is being formed into or is actually formed into the ultimate shape.

In accordance With this aspect of the invention, there is provided a method of manufacturing an elongated, flexible permanent magnet. This method comprises the steps of heating a mixture of a flexible thermoplastic material and particles of a permanent magnet material having anisotropic characteristics with preferred axes of magnetization, forcing the mixture through the passage of an extrusion nozzle, which passage has at least one surface defining the holding surface of the magnet, and, simultaneously,subjecting the mixtureto a unidirectional magnetic field having an axis of magnetization perpendicular to the surface whereby the preferred axes of the particles. are parallel to the unidirectional field. The mixture is then cooled. The resultant article is finally magnetized by a field having an axis parallel to the axes of the particles.

The principal object of the invention is the provision of a new and improved flexible or resilient permanent holding magnet which has an attractive color.

Still another object of the invention is the provision of a new and improved colored flexible or resilient permanent flexible magnet which does not require the use of a mounting sleeve or tube to obscure its dark color.

Another object of the invention is the provision of a new and improved flexible permanent holding magnet having embedded therein sufficient coloring matter that the magnet may be used directly without the need for auxiliary coloring.

Still another object of the invention is the provision of a new and improved method for manufacturing flexible permanent magnets which enables a coating to be formed integrally with the magnet at the time of manufacture.

Another object of the invention is the provision of a new and improved method for manufacturing flexible permanent magnets by an extrusion process wherein the full benefits of anisotropic magnetic materials may be obtained.

Still another object of the invention is the provision of a new and improved apparatus for manufacturing flexible permanent magnets wherein anisotropic permanent magnetic material can be magnetized while the flexible binder therefore is still in a semi-plastic state.

The invention may take physical form in certain parts and arrangements of parts and certain steps and combinations of steps preferred embodiments of which will be' described in detail in this specification and illustrated in the accompanying drawings which are a part hereof and wherein:

FIGURE 1 is a fragmentary perspective view of a flexible permanent holding magnet illustrating a preferred embodiment of the invention, and in particular having coloring matter dispersed throughout the flexible binder;

FIGURE 2 is a similar view but showing an alternative embodiment wherein the coloring is applied as an external layer on the magnet body;

FIGURE 3 is a schematic cross-sectional view showing method and apparatus for extruding continuous lengths of flexible permanent magnetic materials with a layer of colored material on its holding face, such apparatus being particularly desirable for isotropic permanent magnetic materials; 7

FIGURE 4 is a cross-sectional view of the magnet formed by the apparatus of FIGURE 3 taken on line FIGURE4a is .a cross section of FIGURE 4 taken on line 4a4a;

FIGURE 5 is a view similar to FIGURE 3 but showing apparatus and method particularly adapted for use with anisotropic permanent magnetic materials;

FIGURE 6 is a perspective view of the magnetizing magnet of FIGURE 5;

FIGURE 7 is a cross-sectional view of FIGURE 5 taken approximately in the line 7-7 .thereof; and,

FIGURES 8 and 9 are views somewhat similar to FIG- URE 7 but showing alternative embodiments.

Referring now to the drawings wherein the showings are for the purposes of illustrating preferred embodiments of the invention and not for the purposes of limiting same, FIGURE 1 shows a flexible permanent holding magnet in the form of a relatively thin elongated strip l0, such strip being comprised of a flexible or resilient base material or binder having dispersed therein particles of permanent magnetic material in combination with means for imparting a color other than the black or dark brown of the permanent magnetic materials. The flexible or resilient base material may be any of the known non-magnetic unity permeability materials which will be flexible and resilient at the temperature of use, e.g., room temperature. Preferably the base material is polyvinylchloride which is able to maintain its flexibility and strength while having mixed therewith large amounts of dry powdered materials.

Preferably, the permanent magnet particles are of permanent magnet material having the highest possible coercive force and the lowest possible permeability. High coercivity materials suitable for this purpose include the following: barium ferrite (iron-barium-oxide) naonre o bismuth manganese (MnBi); lead ferrite (PbO.6Fe O cobalt ferrite (CoO.Fe O cobalt platinum (CoPt); a material composed of 5 to 40% barium oxide, 1 to-l% manganese oxide and the remainder iron oxide, as described in German Patent No. 927,259); a material composed of to 40% barium oxide, 4 to 8% chromium oxide and the balance iron oxide (as described also in said German patent); and a material composed of 65 to 88 mol percent iron oxide, to 15 mol percent lead oxide and 0.8-8 mol percent silicium oxide, in which up to half of the lead oxide content may be replaced by barium oxide or strontium oxide (as described in German Patent No. 1,010,440). The just -mentioned permanent magnet materials all have the characteristics of extremely high coercivity and low permeability which are extremely desirable for the present invention.

It is to be under-stood, also, that other high coercivitylow permeability permanent magnet materials may be used if desired.

Thus, the coercivity of the materials in 100% concentrations should be in'excess of 1500 oersteds and preferably 2000 oersteds while the permeability should be less than 2 and preferably unity.

The permanent magnet materials are preferably ground to a grain size less than 0.30 millimeter and are mixed with the flexible binder in a ratio of 40 to 60% by volume. Actually and desirably the maximum amount of permanent magnet material which a given flexible binder is able to have dispersed therein while still retaining its flexible characteristics is desirable.

The polyvinylchloride binder may be either made soft or mixed with softeners and then mixed in a powdered state with the permanent magnet powder. These materials are then plasticized by heat in a suitable machine and the plasticized mass is then extruded through a nozzle which is shaped to give the desired cross section to the finished magnet.

In accordance with the preferred embodiment of the present invention to impart the desired color to the magnet material fine aluminum powder is dispersed along with the particles of permanent magnet material throughout the base material. The ratio of fine aluminum powder to permanent magnet powder may be from 1 to 25 by weight of the magnet material and 10% being quite satisfactory. it has been found that even with the smaller percentage of aluminum powder, the finished magnetic strip It? has a definitely silvery appearance of all of its surfaces. At the same time it ha been found that this small percentage of aluminum powder in the finished product does not appreciably reduce the over-all magnetic attractive force of the strip and particularly decrease it far less than the sleeves or tubes used heretofore.

As shown in FIGURE 1, the strip 10 has a flat holding face'lll and the permanent magnet particles are magnetized to provide spaced apart, opposite polarity permanent magnet poles at this holding face, designated by the letters N and S in FIGURE 1. In the embodiment shown in FIGURE 1, the respective N and S poles extend continuously along the holdingface ll lengthwise of the strip and are spaced apart from one another transversely across the holding face. However, it is to be understood that the respective N and S poles could be arranged to extend continuously transversely or at an angle across the width of the holding face and to be spaced apart in succession lengthwise along the strip or the poles can alternate in both transverse and lengthwise directions.

If desired, the aluminum powder may be colored blue, yellow or red or any other suitable color as is known to get the desired shade of color in the finished strip. In any case, the color of the relatively small amount of aluminum powder determines the overall color of the finished strip without, however, reducing appreciably the over-all mag netic attractive force of the strip.

The strip itself is quite flexible and is somewhat resilient due to the rubber-like nature of the base material therein.

FIGURE 2 shows an alternative embodiment in which the coloring is imparted by means of a flexible layer of the desired color essentially integral with the base material. In one form the holding magnet article is in the form of a strip 29 of flexible material having permanent magnet powder dispersed therein as already described. The integral coloring is in the form of a metal layer 21 having'the desired color deposited by means of vacuum deposition on the external surfaces of the strip 20 by known processes. The layer may have a thickness on the'order of .001 inch and flexes readily as the strip is flexed. Then a suitable thin coating 22 of transparent material 22 such as a lacquer is provided on the vacuum deposited'metal layer 211. With this arrangement, the extremely thin vacuum deposited metal layer 21 and the transparent protective coating 22. do not appreciably detract from the magnetic attractive force of the strip while at the same time not adversely affecting the flexibility of the strip. At the same time the external surface of'the strip presents the desired color which is suitable for the intended use of the strip.

In another form the flexible layer may be in the form of a thin flexible plastic material of the desired color preferably formed integral with the strip by extruding the strip and colored plastic material through the same extrusion die in such a manner that the colored plastic adheres to and is integral with one ormore surfaces of the base stri F IGURE 3 shows a novel arrangement in accordance with the present invention for providing a colored plastic layer on a base magnetic strip as the strip is being extruded. A thermo-plastic base material containing permanent magnet particles therein is fed in finely divided form from a hopper 31 through an extrusion nozzle 32 having a passage 32a which forms it into the desired cross-sectional shape of the finished strip 43. Heating coils 33 and 34 are provided for heating the thermoplastic base material to a plastic semi-liquid condition. The permanent magnet particles, which are unmagnetized initially, float dispersed in this plastic or liquid mass of base material.

In accordance with the present invention, suitable colored material 35, which preferably is also thermoplastic and flexible when cold, is fed from a hopper 36 in finely divided form through an extrusion nozzle 37 into the passage 32a in the extrusion nozzle 32 for the strip. The nozzle 37 is shown perpendicular to the direction of flow of the material through the passage 32a, although it could be at other angles. The colored material is heated to a plastic state by means of a heating coil 33, so that when the colored material contacts the mixture of base and magnetic materialin the passage 32a, both the base and colored materials are in a heated, plastic state. As a result, the color material immediately Welds or bonds itself to the lower surface of the base material as a layer 42. The thickness of this layer can be regulated n by appropriately controlling the speeds of the respective extruders. In FIGURES 3 and 4 this thickness is exaggerated. In actual practice the colored coating is only a very thin film. The film provides the desired coloring While the base strip provides mechanical strength thereto.

After the base material 30 and 1ayer 42 are bonded, the combined strip is cooled. This may be done by cooling the exit end of the extrusion nozzle, for example, by means of a cooling jacket 44 surrounding the nozzle.

After the cooled composite strip emerges from the extrusion nozzle 32, it must be magnetized. This may be done in a number of ways but preferably its lower face is engaged tangentially by a Wheel 40 which carries a plurality of permanent magnets 41, the outermost poles of which are of successively opposite polarities as is shown inmy co-pending application Serial No. 693,604, now UnitedStates Letters Patent No. 3,051,988. Accordingly, the permanent magnet powder is permanently magnetized by the magnets 41 to produce alternate ,poles of opposite polarity in the strip. The layer or film 42 of colored material extends across the face of the strip at which these magnet poles are located. The finished strip emerging from the extrusion nozzle 32 may have any desired cross-sectional shape, e.g., that shown in FIGURE 4.

The FIGURE 5 shows apparatus embodying and for carrying out another aspect of the present invention. The apparatus shown in FIGURE 5 is particularly intended forutilizingtlieimproved magnetic characteristics of the anisotropic permanent magnet materials. paratus shown in FIGURE 5 is substantially identical to the apparatus of FIGURE 3 with the single exception that the mixture of flexible binder and particles of permanent magnet material in the extrusion passage 32a in advance of the cooling jacket 44, that is to say, at a point where the binder material is at a temperature such as to be in a semi-liquid state, is subjected to a transverse unidirectional magnetic field. This may be accomplished, in a number of diiterent ways, but in the embodiment shown in FIGURE 5, the outer surface of the extrusion nozzle 32 is necked down to provide a relatively thin wall surroundingthe passage 32a at a point close to the heating coil 34. The magnetizing means might take a number of different forms, but in the embodiment shown is comprised of a U-shaped magnet yoke 45 supporting a pair Thus, the apof electro magnets 50, 51 having pole shoes 52, 53 arranged in close spaced relationship to the outer surfaces of the necked in portion of the extrusion nozzle 32. These electro magnets are electrically energized through wires 46 from a suitable source of direct current not shown, so as to provide a unidirectional magnetic field for example, with a north pole on the bottom and a south pole on the top, with the axis of magnetization perpendicular to the surface of the strip 43 which will have the north and south magnetic poles formed thereon by a subsequent magnetizing process.

The magnetic field passes through the walls of the extrusion nozzle 32 and through the mixture of the semiliquid binder and the permanent magnet particles within the passage 32a at this point. If the permanent magnet particles are of the anisotropic type, they will tend to orient themselves in the magnetic field with the preferred axis of magnetization parallel to the axis of the magnetizing field. Thus, if an anisotropic particle enters the passage 32:; with its preferred axis of magnetization parallel to the length of such passage, as the particle enters the magnetic field, it will be physically rotated within such field because it is in essence floating within the semi-liquid binder so that itspreferred axis of magnetization will be parallel tothe magnetizing field. Thereafter as the mixture moves through the passage 3.2a, the binder is hardened due to the transferral of heat to the extrusion nozzle 32 and thence to the water jacket 44, such that the permanent magnet particles will always be retained with their preferred axis of magnetization perpendicular to the surface of the body 35 to be ultimately magnetized. Thus, any subsequent magnetizing forces will not disturb the orientation of the magnetic particles within the binder.

It is important that the magnetic particles be subjected to a strong magnetic field. That is, having a strength of at least 8,000 and preferably 10,000 to 15,000 gauss. If the extrusion nozzle 32 is formed of magnetically permeable material, then the magnetizing means must produce a suflicient magnetic strength to saturate the metal of the nozzle. Such saturation is considerably facilitated if the metal of the extrusion nozzle on each edge of the strip is made relatively thin generally as is shown in FIG- URE 7. h

Alternatively, the extrusion nozzle .32 at this point may be formed of both magnetically permeable and magnetically non-permeable material. FIGURE 8 shows'such a construction. In this embodiment of the invention, the upper and lower sides of the passage 32a are formed of magnetically permeable members 57a and 57b respectively, which are held in spaced relationship by magnetically non-permeable members 58b, which also form the edges of thepassage 320.

FIGURE 9 shows a still further embodiment of the invention where the extrusion nozzle 32, at least where the magnetizing means are placed,'is formed entirely of a magnetically non-permeable material, e.g., plastic, copper aluminum or the like. i In FIGURES 7, Sand 9 the arrows show the course of the magnetic flux through the extrusion nozzle and the mlxture within the nozzle. With the arrangement shown in FIGURE 3, and using isotropic barium ferrite, it has been found possible to obtaln magnetic adhesions of up to 225 grams per square inch Using the arrangement of FIGURE 5 and anisotropic barium ferrite it has been possible to obtain magnetic adhesion up to 325 grams per square inch. In bothinstances, the magnet had a thickness of 3 mm. and an air gap of 0.3 mm. from soft iron.

From the foregoing description, it will be apparent that each of the illustrated embodiments is Well-suited for the accomplishment of the stated purposes of this invention. However, while there have been described herein and illustrated in the accompanying drawing, certain exemplary embodiments of the invention, it is to be understood that various modifications, omissions, and refinements which depart from the disclosed embodiments may be adapted without departing from the spirit and scope of this invention. For example, in each embodiment the rubber-like magnet body may be formed by any suitable technique other than extrusion, such as injection molding, for example. Also, where the magnet body is provided with only a thin colored coating, such coating may be provided by applying a thin foil of colored plastic in strip form to one face of the magnet body while the latter is being extruded. Alternatively, the colored plastic strip may be applied to the rubber-like magnet body by suitable heat treatment following the extrusion of the magnet body.

Having thus described my invention, I claim:

1. A holding magnet for exerting a holding action against a magnetically attractable member, said holding magnet comprising a body of a flexible resilient plastic material having a holding face, said body having dispersed therein particles of permanent magnet material which are magnetized to provide spaced apart opposite polarity permanent magnet poles at said holding face of the body, said magnetic poles developing a magnetic field extending from said holding face and adapted to hold said magnet against said magnetically attractable member, said body having coloring material integral therewith.

2. The holding magnet of claim 1 wherein said coloring material comprises aluminum particles embedded in said body.

3. The holding magnet of claim 2 wherein the ratio of aluminum particles to the permanent magnet particles in the body is of the order of magnitude of 1 to 25 by weight.

4. The holding magnet of claim 1 wherein said coloring material is a vacuum-deposited metal layer on said body, and including a transparent protective coating over said vacuum-deposited metal layer.

5. The holding magnet of claim 1 wherein said coloring material is a coating of colored thermoplastic material bonded to said holding face of the body.

6. A method of making a holding magnet which method comprises the steps of: mixing permanently magnetizable particles with a flexible binder material, and a coloring material, and then forming said mixture into an elongated body with said coloring material forming an integral bond with said particles and said binder and said coloring material being uniformly dispersed in said binder.

7. The method as defined in claim 6 wherein said coloring material is aluminum particles dispersed in said binder.

3. A method of making a holding magnet which method comprises the steps of: mixing permanently magnetizable particles with a flexible binder material, forming said mixture into an elongated body with said particles being uniformly dispersed throughout and embedded within said binder and, then, vacuum-depositing a thin metal layer of a color different from said mixture on said elongated body.

9. A method of making a holding magnet which method comprises the steps of: mixing particles of permanently magnetizable particles with a flexible binder material, extruding said mixture into an elongated body with said particles being uniformly dispersed throughout and embedded within said binder and bonding a thin layer of coloring material onto at least one surface of said elongated body.

iii. A method of making a holding magnet which method comprises the steps of: mixing permanently magnetizable particles with a flexible binder material, extruding said mixture into an elongated body with said particles being uniformly dispersed throughout and embedded within said binder and, simultaneously, extruding a thin layer of plastic coloring material onto at least one surface of said elongated body.

11. A method of making a holding magnet which comprises the steps of heating to a plastic condition a mass of flexible resilient material containing dispersed particles of permanent magnet material and extruding said plastic mass through a nozzle, heating to a plastic condition a colored thermoplastic material, and forcing said colored thermoplastic material against said resilient material transverse to the latters flow so that the colored thermoplastic material becomes bonded to said resilient material to form a colored coating thereon.

12. A holding magnet comprising a body of flexible and resilient material having therein particles of high coercivity permanent magnet material, said permanent magnet particles being magnetized to provide spaced apart opposite polarity permanent magnet poles at the surface of the body which produce a magnetic holding force of at least several grams per square centimeter against a magnetically attractable member when said body is placed thereagainst, said body having coloring material integral therewith of a color different from that of said flexible and resilient material.

13. A holding magnet comprising an elongated flexible strip of flexible and resilient material having a holding face, said strip having therein particles of permanent magnet material with a coercive force at least substantially as high as that of barium ferrite, said permanent magnet particles being magnetized to provide spaced apart opposite polarity permanent magnet poles at said holding face which produce a magnetic holding force of at least several grams per square centimeter against a magnetically attract able member when said holding face is placed thereagainst, said strip being colored at said holding face, at least, to present thereat a color diflerent from that of said flexible and resilient material.

14. The holding magnet of claim 13 wherein there are provided aluminum particles in said strip which provide said different color.

15. The method of manufacturing an elongated flexible and resilient permanent magnet comprising the steps of heating a mixture of a flexible and resilient thermoplastic material and particles of a permanent magnet material having anisotropic characteristics with preferred axes of magnetization, forcing said mixture through the passage of an extrusion nozzle, said passage having at least one surface defining the holding surface of said magnet when completed and simultaneously subjecting said mixture as it passes through said passage to a unidirectional magnetic field having an axis of magnetization perpendicular to said surface whereby said preferred axes of said particles are parallel to said unidirectional field, cooling said mixture to fix the position of said particles in said resilient material and, thereafter, subjecting the resultant article to a final magnetizing field having an axis parallel to the axes of said particles.

16. Apparatus for the manufacture of continuous lengths of permanent magnets comprising in combination means for heating a' mixture of a flexible and resilient thermoplastic binder and particles of permanent magnet material having anisotropic characteristics with preferred axes of magnetization, an extrusion nozzle having a longitudinally extending passage therethrough with one surface for forming the surface of the holding face of said permanent magnet, means for forcing said mixture through said passage, means adjacent the entrant end of said passage for heating saidmixture to allow said particles to float in said binder, and means adjacent the exit of said passage for cooling said mixture to fix the position of said particles in said binder, and means between said heating and cooling means for subjecting said material in said passage to a unidirectional magnetic field having an axis perpendicular to said surface to orient said preferred axes of said particles in a parallel relationship with said unidirectional field.

17. The apparatus of claim 16 wherein means are provided between said heating and cooling means for ex- 9 truding into said passage at least thl'ough said surface a flexible thermoplastic layer on said holding face of said magnet whereby said mixture and said last-mentioned layer may be bonded and extruded simultaneously.

References Cited by the Examiner UNITED STATES PATENTS 2,076,711 4/37 Eagleson 1859 Murray 18-13 Foley 317201 Charles et a1. 317--201 Westmijze 317-201 Baermann 317-203 Hahn 317-159 JOHN F. BURNS, Primary Examlzner.

10/51 Orsini 18---48 10 SAMUEL BERNSTEIN, Examiner.

Claims (1)

1. A HOLDING MAGNET FOR EXERTING A HOLDING ACTION AGAINST A MAGNETICALLY ATTRACTABLE MEMBER, SAID HOLDING MAGNET COMPRISING A BODY OF A FLEXIBLE RESILIENT PLASTIC MATERIAL HAVING A HOLDING FACE, SAID BODY HAVING DISPERSED THEREIN PARTICLES OF PERMANENT MAGNET MATERIAL WHICH ARE MAGNETIZED TO PROVIDE SPACED APART OPPOSITE POLARITY PERMANENT MAGNET POLES AT SAID HOLDING FACE OF

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