US2999275A

US2999275A - Mechanical orientation of magnetically anisotropic particles

Info

Publication number: US2999275A
Application number: US748705A
Authority: US
Inventors: Scott Jr Blume Walter
Original assignee: Leyman Corp
Current assignee: Leyman Corp
Priority date: 1958-07-15
Filing date: 1958-07-15
Publication date: 1961-09-12
Anticipated expiration: 1978-09-12
Also published as: DE1302093B; DE1302093C2; CH398822A; NL112334C

Description

Sept. 12, 1961 w. s. BLUME, JR

MECHANICAL ORIENTATION OF MAGNETICALLY ANISOTROPIC PARTICLES Filed July 15, 1958 INVENTOR.

J Z: iami ATT02A/EY5.

United States Patent MECHANICAL ORIENTATION OF MAGNETICAL- LY'ANISOTROPIC PARTICLES Walter S.:Blume, Jr, Cincinnati, Ohio, assignor to'Leyman:.Corporation,-Cincinnati, Ohio,.a corporation of.

Ohio

Filed JulyTlS, 1958, Ser. No. 748,705 7 Claims. (Cl. 18-55) This "iIlVEIllIlOIFTBlZt'tCS'Tit) permanent magnets and is directed particularly toimprovements in the manufacture of "permanent magnets from magnetically anisotropic materials.

A principal objective of the invention has been to provide permanent magnets "having excellentmagnetic prop erties but which are readily machinable whereby they may be cut to desired shapes as required by the purposes'which the magnets serve.

Products displaying excellent'or good permanent magnetic properties heretofore have been available from metal alloys such asAlnic'o, but such materials' are-so hard that they'cannot be-cut except by grinding "with abrasive wheels. 'For that reason the con ventional mode' of fabrication has been to cast the molten alloy composition into a mold conforming to theultimate shape desired. Where dimensional accuracy is requisite; the casting is then ground to former size The cost of-this modeoffabrication obviously is appreciablm:

the surface .finishwsof :the-unground casting generallyis poor andthereis considerable variation from piece to piece in all .unground dimensions.

More recently, it has. been experimentally determined that barium .ferrite corresponding to the generalchemical...

formula BaFe O and similar ferrites ofleador strontiumrcanbe madetopossess desirable permanentmag,

netic properties. by compressing particles. thereof .and sintering the compressed particle mass by subjecting ,the compressed mass to .high temperature.

civity and thereby defeats the improvement of magnetic qualities which the sintering is intended to provide. In

addition, the products tend to fracture duringsintering,

Machinable magnets have been produced by the compression or injection molding ofzmixtures of "subdivided magnetic material andplastic, .but.no method of orientation has been known to permit theutilization of thesuperior properties peculiar to ultrafine anisotropic materials in such procedures, and .the' magnets inevitablydisplay low energy products."

Permanentmagnets of the ferrite materials are potentially less expensive than metal alloys such as Alnico because the materials from which the ferrites are made are much more 'abundant'and'readily available; However, because thefe'rritesare of a crystalline refractory natureto'begin with, the pressing and sintering technique This technique for preparing magnets of such non-metallic or ceramic'-.

is not even as Well suited to the production of permanent magnets in a variety'ofshapesas is the -casting method.

The permanent magnets'of the presentinvention embody magnetically anisotropic materials and display-permanent magnetproperties comparable to or exceeding those .of: the ferromagnetic materials previously known, but they alsopossessqualities of 'machinabiiltypworke, ability, 1 or cutability which --make them" amenable to fabrication in simple or intricate shapes, as desired, by-

ice

2 Z the use of ordinary cutting tools or instrumentalities as distinguished from the grinding to which past products have been limited. The products of the invention preferably aremade from particles of barium, strontium, or lead ferrite,"or'mixtnres thereof, but the methods of fabrication which this invention provides also may be used in the preparation of readily machinable permanent mag-' nets made from various elements, compounds, or alloys Such'as manganese-bismuth, finely divided iron, etc. In

substance,-the products of this invention possess the im proved permanent magnet properties of past materials plus the'quality of machinability in which the past materials have beendeficient, and the finished products are limited as to shape only by the nominal costs involved in the production machining, punching, or cutting of bulk solids;

In order adequately to describe the invention, it is convenicnt to refer to certain recent discoveries in the physical nature'of magnetism: For many years, according to theclassical theory ofmagnetism, it was believed that the .individual atoms ormolecules of a magnetic substance were in themselves elemental magnets, and that the substance; was'ffmagnetized when these elemental magnets were" aligned in a certain fashion, for example, in a manner similarto thatin which iron filings align themselves when scatteredon a paper placed over the poles of a common horseshoe-magnet. However, as described in Bozorth s -Ferromagnetism,.D. Van Nostrand Co., Inc,

1951, it isxnow known that all ferromagnetic' materials are. composed of many small magnets or fdomains, each of which consists of many atoms. Within a domain all. of the atoms arealignedin parallel and the domain is. thus saturated, even when no field is applied. The ma-' terial'is therefore said to be spontaneously magnetized. Whenthermagnetization of the materialis changed, the

atoms turn'together in groups (eachatomicmagnet about its own axis), the atoms in each group remaining parallel to eachother so that they are aligned more nearly with the magnetic field appliedto the materiaL. So .far as is I known presently, the exact. size or configuration of a do-v main varies withpthe material; withrespectto. barium ferrite the domain size is of tlreorderrof one micron.

In" the: case-of 'certainfine grain permanentmagnet materials,- particularlythe ferrites of barium, lead, and strontium; these domains are strongly magnetically aniso-., tropic, that is, they aromagnetizedmore easily. (and their'residu'al inductance and 'coercivity are better) if they were aligned in a certain so-called preferred. crystallographic direction with" respect to the magnetizing field: The crystal structure of barium,. strontium, and lead-ferrites is hexagonal with thedirection of easy mag-.

netization being along the 00.1 axis. In the absence of such alignment; the magnetizing force which must-beapplied to saturatethe material, i.e., toeffect its full magnetization,--is greater and the characteristics of the magnetuponremovalof the field are not as good as if the: particles had been properly aligned. Extensively baiLmilled' or attrition milled ferrites of barium, strontium;.or;-.lead 'have been shown by electron microscopy to fracture 'alongthe basalplane into plate-shaped particles having two-substantially parallelsurfaces and an irregularedge perimeter. The diameter of these plates when properlycomminuted is in the range of approximately .5 :micron. Peculiarly," the preferred direction of magnetization of the ferrite plates is normal to the two parallel. surfaces; i.e., the :domain plates are more easily magnetized-if theimagnetic lines. of force of the'applied external field areperpendicular. tot-the plate. Apparently,-

ferred directions of all of the particles are parallel has:

heretofore been done magnetically. The domains, being themselves elementary magnets, are acted upon and tend to be aligned by an externally applied magnetic field.

Where the domains are embedded or embodied in a matrix material, however, the frictional stresses or the formation of interlocking dipoles between adjacent domains and the general immobility of the domains contained in a matrix tends to resist the orienting force of the externally applied field. While that field exerts a torque about the domains when they are not aligned and thereby tends to align them, still, as the domains are very small, so is the torque in relation to the inter-particle forces and may overcome or orient them only to a small degree, if at all. For that reason, alignment accomplished by application of an external field at best is small or only partial, and the method is incapable of enabling the full magnetic potentialities to be realized. v

The essence of the present invention lies in the concept of mechanically orienting or aligning the preferred magnetic axes of the domains with respect to each other, rather than doing it magnetically by means of an external field. It has been found that much better orientation can be achieved in this manner and this method can be practiced with great economy since a magnetic field need not be maintained nor high temperature utilized.

In accordance with this invention, alignment of the particles and the property of machinability are obtained in a permanent magnet of the consolidated powder type by a method wherein particles ground to a suitable state of fineness, preferably domain size, are disposed in an elastomeric or plastic medium, such as rubber, polyethylene, plasticized polyvinyl chloride, or the like.- Dispersed heterogeneously in this medium, the particles are relatively immobile and cannot be made favorably to respond, just as the medium itself is relatively immobile. But I have discovered that the particles or domains can be made to disarrange themselves from a heterogeneous pattern of disorganization into an orderly pattern of orientation and alignment by subjecting the composition to strong mechanical force in the nature of shearing stress such as is exerted internally and externally upon a mass as it passes through one or a series of closely spaced rollers or an extrusion plate. Various preferred methods for achievmg proper orientation are subsequently disclosed in detail,

- but to illustrate one practice of the method, by way of example, the orientation may be conducted by adding domain-sized ferrite powder to a natural rubber base and milling the resulting composition into thin sheets by means of a conventional roller-type rubber mill wherein the composition is subjected to the shearing action of dilferentially speeded rolls between which the material is passed, preferably a number of times. The milling process disperses the magnetic material evenly in and throughout the rubber base, but as an incident thereof also orients the domains, so that the preferred directional axes of the individual particles are parallel to one another.

Apparently what happens is that such an operation rotates the plate-like particles within the composition as it forms the composition into a sheet whereby the plane surfaces of the plates assume positions parallel to the plane surfaces of the sheets with the preferred magnetic axes of the plate normal to the sheet surface. After milling is completed, a plurality of the sheets may be stacked on top of each other until a desired thickness is obtained. The stacked sheets may then be consolidated by the application of pressure and heat to cure the matrix material thereof, after which the products are magnetized. In the alternative, shapes may be punched from the sheets and the shapes may be stacked for consolidation to produce a given form which may then be cured and magnetized as desired. Moreover, the individual sheets themselves when cured may be used individually to furnish thin permanent magnets as desired for specialized purpose or use. Such magnets are durable, easily machinable, and possess ex- 4 cellent magnetic qualities, comparable even with those of the Alnico alloys. They are inexpensive to produce since the raw materials are themselves inexpensive, and the process involves no unusually costly methods.

The immobilizing matrix may be a resinous or plastic composition, or elastomeric semi-solid, or viscous liquid in which the powder can be evenly dispersed and which is capable of hardening, setting, or being cured to a solid state. According to one method, for example, the ferritic or potentially magnetic powder is dispersed in uncured rubber which, upon being milled, is cured to immobilize the particles within it. Application of heat and pressure to the mass after orientation cures or stabilizes the rubber to provide the desired coherence without disdisposed domain particles to move relative to one another in response to the shear forces exerted by milling or extrusion.

While the invention is disclosed in relation to the use of barium, lead, or strontium ferrite by way of illustration on'account of their low cost and abundancy, the method of orientation provided by the present invention is equally applicable to any anisotropic magnetic material having domain-sized particles, which particles are capable of being acted upon by internal shear stresses in a manner achieving orientation. The only limitation on the material, in other words, is that the particles possess a preferred magnetic axis which will lie consistently on a geometrically unique axis such that the mechanical shearing forces or turning moments acting upon the particles during the orienting step will not act in any one of several directions with equal probability.

The desirable orientation, once obtained, is not disturbed by subsequent handling of the composition once it has been cured or set, as the case may be, nor does subsequent cutting or working of magnets formed from laminated sheets of the composition cause the magnets to lose their orientation or magnetic properties. Localized surface shearing forces, such as are set up during machining of the material, may disturb the orientation of particles in a thin layer near the surface, but such effects are negligible where the magnet is other than of very small size, since the portion of the magnet in which orientation is effected is inconsequentially small in comparison with the total volume of the magnet.

Although the individual ceramic particles constituting the magnetic phase of the finished product possess their usual hardness, the application of a cutting tool to the finished product severs the matrix and thereby readily permits the product to be shaped. The product may be tropic particles of permanent magnet material is being formed into 'a sheet;

FIGURE 2 is a perspective view illustrating the magv netization of a laminate formed in accordance with the invention;

FIGURE 3 is a sectional view through a cavity in which a stack of forms cut from a sheet produced in accordance with the invention are integrated under pressure and magnetized between the pole pieces of an electromagnet; and

5:1 FIGUREr l is la .cross-sectionalview through t-an:ex-.-.. trusion :Tassernbly, and illustrates 1 an 1:. alternative: :method i;. ofzaligning':anisotropicrzparticles::of;:permanentpmagnet materialsin a martix.

The. following" examples .:illustrate-i.typical:.practice f the invention:;

Ermnplad To' prepare barium ferrite for use" in .the'process. of the present invention, barium .carbonateis admixedwithi ball .mill'; the preferred practice' is .to ball. millithe barium ferrite in'water for 90"hdurs, then remove the powder from the ball-mill, dry it, and .heat treat it for minutes at .a temperature of approximately ,1000 C; after-which the powder is again subjected to ball milling for. another hours. In the alternative; bariumferritei. may be comminuted in..an attrition millffo'in example, a standard Szegvariattrition mill'usingstainless steel shot for a length of-time sufficientto reduce the particles to domain size.. In. general, the attritionmill is in the, order is preferred. The .heat. treating step. is desirable because thistreatmentincreases the coercivity of the final prod-r uct; in.,thecaseoflead ferritethe 'increasemay be as much as although the effect of the heat treatment is somewhat less incthecasemof. bariumand. strontium ferrite Itwillbe. recognized that the. foregoing method of preparing. barium ferrite: is offered only by way of illustratio nand that. other methods are known in the art which also be recognized that powdered barium ferrite and other ferromagneticmaterials adapted for use in the practice of this invention are available from commercial supply houses.

In general, the-milled particle size should be in the 4 rangeof .5 micron, although magnets having good prop erties have been obtained using particles which in average size .were. somewhat larger. After final milling, the powder is dried, any lumpy agglomerations are reduced, and the powder is thenready for use. The attainment of domain size maybe determined .by vmeans of periodic inspection of the material withan electron microscope or, more easily, though somewhat less accurately,rbycomparing the color of a smear .of powder ofunknown particlesize with that of a smearof powder known to be A of: domain'size, whichin the case of barium ferrite has a -.deep,red color. As the size reduction continues, the color of a barium ferrite powder initiallyfired at a high temperature, for example, 1250'C.,- changes from black. 55

to purple to reddish brown.

A suitable rubber base or matrix to which this ferrite maybe added has a composition as follows:

Percent by weight Those skilled in the art ofcompounding elastomeric compositions'or-'the like readily will understand thata 70 wide variety: of cornpounding agents, 1 plasticizers, vul-' cani-zingagentsyand the like is availableto provide vari-" ations in workability, curability, -'or hardness of the matrix composition-"to adapt it' to special purposes within the purview of thei present inventiorr- 1 fur, of course, istheprimary curingagent in the vulcanizin-gprocess-i The-:remaining organics areaccelerators which enter. into the :vulcanizationas .well as accelerate thezaction of. thesulfur.-- The various substances areadded in'the ordergivem v By volume the bariumferrite.

ferric oxide, for example, inlthe. proportionof mol .mtrnay' be'added tothe extent .of 65%-oftthet0tal.volume of the mixture.

Invthe blending and'milling process,:the uncompounded natural rubber: iszzfirst run-through: a standard two-roll rubber mill: geared; for example; so -that thev speeds. of 1 5 the two rolls bear a 1.1:.1' ratiosto eachother; .Thespeed differential causes 1 a shearingustress toxbe' exerted on the rubb'enasit sheetsbetween th'e two'rolls," one surface of: the 1 rubber. being "accelerated relative" to the: other .isur-y'" face wher'eby a masticating-ieifectisachieved; The milling: thusiserves' to-fwork. the rubberito soften it and? make itsomewhatplastic. Throughoutltherrnixing. and milling, .water-ipreferably is circulated through the mill.

rolls to maintain the rubbermix-at an operating temperatureinthe range'fromabout:120- F; Above the of ..10-'20...times fastenthanthe' balllnrilLand therefore 25: 'latter'temperat'ure'thevrubbgr'mix may tend to'vulcanize prematurely:

The cruderubber is mixed with itself for approximately" 5 rninutes, duringwhich time it forms a smooth band= with an 'even bank between the two rolls.- After this:- period'the other materials are added.'- This blending conveniently may take place roughly over a 20 minute per-' iod; The materials are pouredor sprinkled evenly along the sheet just priorto its repassage between the rolls. As 35 the magnetic material is addedg'it initially tends' to- Y I make-the rubber softer than before. It is not known" maybe usfid m place of the procedurexshown' It W111 whether this change in. the-physical consistency of the rubber'may be-du'e to the increasedheat of friction reness which makes-them 'self sustaining 'evenwhen the 0 sheet: thickness is very low.-

After all of the ingredients have-been added, the rub-" bercomposition is sheeted off the mill,'thesheets'prefcr-' ably being thin, e.g., about'say,'.02 .03-inch. As a rule ofthumb, the thinner the sheet, the-more"easil-y the desired degree of orientation is obtained;

In theaccompanying drawings, FIGUREI illustrates a presently offered explanation of the'processthrough which mechanical'domain orientation is achieved in the practice of this invention. The figure is a vertical section through a conventional rubber mill. Matrix ferrite mixture'is indicated generally at 1, where it collects prior to passing between the respective rolls 2 and -3. Roll 2 is'rotating at a slightly greater rate than roll 3. Barium ferrite plates 4 in the mixture are randomly oriented in-the mixture:

ahead of the rolls, as at 1. At 5, where the mixture passes between the rolls, the shearing forces acting on-the-rubber due to the differential in'the speed of the two rolls, and perhaps additionally the compressional forces acting as the rubber is squeezed between the two, coact so as to .tip over the plates, soto speak, so that the plane surfaces of all'plates are approximately'parallel to thesurface of the rubber sheet.- This result may not be achieved in a single pass but is progressive in repeated-passages of the:

material through the .rolls.

In :the' drawing the relative size of the plates is,yof

course; greatly exaggerated for purposes of illustration..-. However; it will readily be seen'that when one roll is mov-- ing at a greater surface speed-than the other, the materialbetween. therolls is subjected to shearing-forces which presumably are transmitted .across or throughtheentire thickness as the material internally accommodates itself to the speed gradient. It is this effect, apparently, which causes particles no symmetrically disposed in the plane of movement through the rolls to move within the matrix into that attitude wherein they are subjected to the least turning moment or that position wherein the turning moments at the opposite faces of the particles are opposite and equal. At least in passage through the rolls the anisotropic particles become oriented magnetically. This is confirmed by both magnetic and X-ray diffraction analyses.

Although differential speeding of rolls produces a speed gradient within the material as it passes between them, a second aligning effect is believed to be conferred upon the magnetic particles in the material by reason of the reduction in thickness of the material as it passes through the rolls, whether or not they are differentially speeded. In this case, as is exemplified by calender rolls, the mate rial is dragged frictionally from the mass or accumulationexisting at the roll nip, and the reduction in thickness from this mass produces a speed gradient internally of the material which may be greater or less depending upon the amount of reduction in thickness.

As shown in FIGURE 4, similar orientation is efiected wherein the passageway through which the ferrite-matrix compostion is forced is in the form of an extrusion orifice 45 having draft and feed favorably disposed to the plane of the desired alignment rather than in the form of an opening between mill rolls. In this case one explanation for the desirable result may reside in the fact that the composition moving along but in contact with the throat of the extrusion orifice 45 is subjected to more drag or at least is moving at a rate whichis different from the rate at which the composition at the interior of the stream is moving whereby differential forces occur internally of the material to cause those anisotropic particles which are not disposed in the plane of the stream to assume that attitude and thereby become aligned with the others. Again, it must be noted that this explanation is by way of illustration and not limitation and comprises no part of the invention. It is merely theorization about an empirically obtained result which has been found to be particularly useful.

In a typical milling operation, barium ferrite to the extent of 65% by volume of the mix is incorporated into the rubber, although a still greater quantity may be introduced. A theoretical limit on ferrite concentration, i.e., loading factor, is reached when the mix contains such a concentration of ferrite particles that they tend to interloc with each other. When this condition is reached the inter-particle frictional forces then prevent the impinging shear forces from aligning the particles. Experimentally, it has been found possible to obtain loadings as high as 70% by volume. However, the uncured composition is then diificult to process and does not have good strength after curing, there being a tendency to crumble. The greater resiliency of the 65 volume materials makes such materials the more suitable for general purpose'usage.

After the milling and sheeting processes are completed, the thin sheets resulting therefrom may be cured and magnetized as such or stacked up until a laminate of the desired thickness is obtained. Since the ferrite domain particles of each of the sheets are aligned so that their preferred directions are normal to the sheet, when the sheets are stacked in facial juxtaposition, the resulting laminate has a preferred magnetic direction normal to its plane surfaces. This is so, it will be seen, regardless of the number of sheets in the laminate.

While the invention has been disclosed particularly in relation to plate-like particles as exemplified by barium ferrite and the like, orientation is obtained with equal facility where the particles are elongated as in the case preferred axis of the' sheet will be in the" plane of the sheet rather than in a direction normal to the plane.

To bind'or afiix the laminated sheets to each other to form a unitary whole, the laminate is placed under a pressure of about pounds per square inch for example and heated to a temperature of about 300 F. or whatever temperature is required to eifect curing of the particular matrix composition. In this operation the laminated sheets are integrated. Magnets of the desired conifiguration may then be cut from the composite. During these operations the orientation of the particles is not disturbed because they are held immobile in the matrix.

The product thus formed is permanently magnetized by placing it in a magnetic field with respect to which it is located so that the applied field is parallel to the preferred direction of the magnet. FIGURE 2, for example, shows a proper method of magnetizing a small right cylindrical magnet manufactured according to this invention. In the figure, 10 and 11 are the pole pieces of an electromagnet which, upon being energized, magnetizes the ferrite particle magnets in the laminate. The dashed lines 12 indicate the magnetic field between the pole pieces. The laminated magnet 13 is shown in the proper magnetizing position in the field, the arrow 14 indicating the preferred direction of magnetization. The arrow 14, it will observed, is parallel to the lines of force 12 of the external field. Thus, if the pole 10 is the north pole of the electromagnet, the opposing face 15 of the laminated magnet 13 will be the south pole of that magnet, and so on.

Rather than cutting the magnets from the cured laminated sheets, as was above described, the magnet may alternatively be formed by punching forms of the desired cross-section out of a single sheet and then laminating and curing the stacked punched-out forms. method is desirable to eliminate waste since the uncured trim readily may be reworked. FIGURE 3 illustrates this procedure. The punched-out forms 40 from the single sheets are stacked in a cavity 41 within a mold 42 having end pieces 43 which may be moved so as to compress the sheets within the mold. Heat is then applied in any suitable manner so as to cure the sheets.

A suitably magnetized specimen containing 65% barium ferrite by volume made in accordance with the method of this invention had a residual induction of about 2100 gauss, a coercivity of 1200 oersteds, and a maximum energy product of .9 10 gauss-oersteds. The magnet can be handled and worked freely without danger of breakage and may readily be cut with a knife or other edged tool. The same material measured at right angles to the preferred direction of mechanical alignment had a maximum energy product of 28x10 gauss-oersteds, a residual induction of 1200 gauss, and a coercivity of 800 oersteds. In place of magnetizing after curing, a magnetizing field as illustrated by the lines 44 may be applied while the magnet there formed is being cured in the mold by making the end caps 43 of the mold themselves serve as the pole pieces of an electromagnet 45.

Example 2 This example generally follows the preceding example except that lead ferrite is substituted for barium ferrite as the magnetic material. Lead ferrite may be produced as follows: 17.5 parts by weight of lead monoxide (1.5 mol PhD) is intimately mixed with 50 parts by weight of ferric oxide (6.0 mol Fe O This mixture is fired in a surrounding atmosphere of air, starting from 700 C. and increasing the temperature gradually .-to 900 C. over a period of six hours in order to produce crystalline lead ferrite. After quenching in air, the lead ferrite so produced is then milled to domain size (for example, by grinding two hours in the attrition mill,

then heat treated for 15 minutes at 850 C. and reground for one hour), after which it is dried.

This

'Ihie' matrix composition --towhich the lead ferrite is add'e'd may be-the same as that-described -'-above,-- except that the Plead:- ferrite --is added in the *amount of 1 l6.0 parts by weightg- In this amount-the ferrite comprises 57% 'byevolume of-the--composite.- Other matrix ma terials may be-usedin---place of rubber-ias previously *de scribed.

In respect to this and ''other examples concerning the practice .of the -invention it is .toube'unoted that the maximum energy product, coercivity, and other magnetic qualities exhibited by the final material varies as to the nature of the particular ferrite selected, the manner in which it is prepared, the grinding period, and the nature of the matrix material, etc.

Example 3 Strontium ferrite may be the selected ferromagnetic material. To prepare strontium ferrite, the following procedure is satisfactory: 7.7 parts by weight of strontium carbonate (1 mol SrCO is intimately mixed with 50 parts by weight of ferric oxide (6 mol Fe O The mixture thus prepared is fired in an air atmosphere for approximately one hour at a temperature of 1250 C. and then milled and treated as described in Example 1.

Strontium ferrite so produced is incorporated with the rubber in the amount of 123.0 parts by weight, the weights of the other components being as specified previously. In this amount it is 62% by volume of the composite.

Example 4 Those skilled in the art will readily understand that a wide variety of thermo-plastic or thermo-setting materials may be used to form the matrix in place of rubber. For example, the ferromagnetic material may be incorporated into a plastic of the polyvinyl chloride type. In such cases a material is selected which is susceptible of being sheeted between rolls or of being extruded through a narrow orifice into elongated shapes whose surface area is great relative to their volume. The shearing forces set up within the composition during the extrusion or milling process cause local orienting movement of one portion of the composition relative to another portion, and apparently therein lies the reason for the observed orientation which takes place.

It will be understood that the chemical and physical characteristics of the particular matrix material selected will determine the exact nature of the milling or orientation process, but the fundamental conception remains the same in that the milled composition, whatever its nature, enables the potentially permanently magnetic domain particles to be oriented or aligned in a mechanical way which affords excellent utilization of their potential properties.

Having described my invention, I claim:

1. A method of producing permanent magnet material, said method comprising, mixing anisotropic, substantially domain size particles of a permanent magnet material with a workable non-magnetic matrix material, and milling the resulting mixture between rolls into elongated form, whereby the preferred magnetic axes of said particles are aligned substantially perpendicularly to the surface of said elongated form, said permanent magnet material being adapted to be magnetized to form an anisotropic permanent magnet by applying to said material a magnetizing field which is directed perpendicularly to the surface of said material.

2. A method of producing permanent magnet material, said method comprising, mixing substantially domain size particles of a material selected from the class consisting of the ferrites of barium, strontium and lead with a workable non-magnetic matrix material, and milling the resulting mixture between rolls to form an elongated body therefrom, whereby as a result of said milling said elongated body displays a preferred direction of magnetization which is substantially normal to its surface, said 3. 'A method'of producing permanentmagnet material;v

said-method comprising, mixin g substantially domain-size particlesrof a material selected from theclass consistingofirthe fer-rites of barium, strontiumsand lead iwithra workable. non-magnetic matrix materiah and extruding thez-resu-lting mixture throughra narrow-extrus-ion orifice? having a minimum of draft and relief to form an elongated body therefrom, whereby as a result of said extrusion said elongated body displays a preferred direction of magnetization which is substantially normal to its surface, said permanent magnet material being adapted to be magnetized to form an anisotropic permanent magnet by applying to said material a magnetizing field which is directed perpendicularly to the surface of said material.

4. A method of producing permanent magnet material, said method comprising, mixing substantially domain size particles of a material selected from the class consisting of the ferrites of barium, strontium and lead with a workable non-magnetic matrix material selected from the class consisting of rubber, elastomers, and resins, and rolling the resulting mixture between rolls to reduce its thickness and thereby form it into a sheet, whereby the preferred magnetic axes of said particles are aligned substantially normally to the surface of said sheet, said permanent magnet material being adapted to be magnetized to form an anisotropic permanent magnet by applying to said material a magnetizing field which is directed perpendicularly to the surface of said material.

5. The method of claim 4 wherein said mixture is rolled between said rolls a number of times, the thickness of said mixture being reduced each time.

6. The method of making a permanent magnet material which comprises, mixing substantially domain size particles of a material selected from the class consisting of the fer'rites of barium, strontium, and lead with a non-magnetic matrix material having the approximate workability characteristics of uncured rubber, sheeting the resulting mixture between rolls to form a magnetizable sheet having a preferred direction of magnetization which is substantially perpendicular to its surface, and laminating a plurality of such sheets stacked in facial engagement to form a thicker permanent magnet material having a preferred direction of magnetization which is substantially perpendicular to its surface, said permanent magnet material being adapted to be magnetized to form an anisotropic permanent magnet by applying to said material a magnetizing field which is directed perpendicularly to the surface of said material.

7. A method of producing permanent magnet material, said method comprising, disposing anisotropic, substantially domain size particles of a permanent magnet substance in a workable, non-magnetic matrix, and rolling the resulting mixture between rolls to reduce the thickness of said mixture and thereby cause said mixture to become relatively thinner and more elongated, whereby the mechanical forces incidental to said rolling cause said particles to move in said matrix into positions such that the preferred magnetic axes of said particles assume substantially uniform angular relationships with the surface of said material said permanent magnet material being adapted to be magnetized to form a permanent magnet therefrom by applying to said material a magnetizing field in a direction parallel to the direction of the preferred magnetic axes of said particles.

UNITED STATES PATENTS 2,720;453 Altman 001-. 11,1955 1 7 3314 Mcconoughey; June 10 930 2,751,525 Hekelaar V... June 19, 1956 1,991,143 EhIerS Feb. 12; 1935 2,848,748 Cramp 26, 1958 1,994,534 Robinson Mar. 19, 1935 23491312 w Aug; 1958 9 011159 V h Aug 20 1935 6 I fl Cormsh --1---.- -V 1953 2 017 705 spmxton Oct 1935 2,951,246 p a1 1960 2,064,773 Voght Dec. 15, 193 6 2,546,344 Levy Mar. 27, 1951 FOREIGN PATENTS 2,651,105 Neel v Sept, 8, 3 749,969 Great Britain June 6, 1956 2,694,831 Benedict e 51 Nov. 23, 1954

Claims

1. A METHOD OF PRODUCING PERMANENT MAGNET MATERIAL, SAID METHOD COMPRISING, MIXING ANISOTROPIC, SUBSTANTIALLY DOMAIN SIZE PARTICLES OF A PERMANENT MAGNET MATERIAL WITH A WORKABLE NON-MAGNETIC MATRIX MATERIAL, AND MILLING THE RESULTING MIXTURE BETWEEN ROLLS INTO ELONGATED FORM, WHEREBY THE PREFERRED MAGNETIC AXES OF SAID PARTICLES ARE ALIGNED SUBSTANTIALLY PERPENDICULARLY TO THE SURFACE OF SAID ELONGATED FORM, SAID PERMANENT MAGNET MATERIAL BEING ADAPTED TO BE MAGNETIZED TO FORM AN ANISOTROPIC PERMANENT MAGNET BY APPLING TO SAID MATERIAL A MAGNETIZING FIELD WHICH IS DIRECTED PERPENDICULARLY TO THE SURFACE OF SAID MATERIAL.