US3849213A

US3849213A - Method of producing a molded anisotropic permanent magnet

Info

Publication number: US3849213A
Application number: US00312906A
Authority: US
Inventors: M Baermann
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-09-01
Filing date: 1972-12-07
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19

Abstract

There is provided a method of producing a molded anisotropic permanent magnet from particles of permanently magnetizable material, which particles have preferred axes of magnetization. This method includes magnetizing the particles along the preferred axes either before or after they are formed from bulk magnetic material and then molding the particles with a binder under the influence of a low order aligning field.

Description

iJnited States Patent Baermann Nov. 19, 1974 [54] METHOD OF PRODUCING A MOLDED 2,984,871 5/1961 Yenerus 264/24 ANISOTROPIC PERMANENT MAGNET 5,33%; 3/132; glumem, 1 2121182 aermann Inventor: Max Baermann, 506 Bensberg 3,066,355 12/1962 Schloemann et a1. 148/105 Wolfshof, Bezirk, Cologne, 3,266,954 8/1966 Hokkeling et al. 148/3157 Germany 3,422,407 1/1969 Gould et a1, 34/174 NA 3,560,200 2/1971 Nesbitt et al. 148/103 [221 Flled? 7, 1972 3,596,350 8/1971 Steingroever 29/608 N0: 3,677,947 7/1972 Ray et al 148/105 Rehted Application Data FOREIGN PATENTS OR APPLICATIONS C i i f S No 425 g 5 970 882,712 11/1961 Great Britain 264/24 abandoned, which i a continuation in pafl of Sen 955,698 4/1964 Great Br ta n 148/108 No. 2 2 4 Aug 22 9 7 abandoned. 750,537 6/1956 Great Blltam 148/101 [30] Foreign Application Priority Data Primary Examiner-Walter R. Sattrfield Sept. 1, 1966 Germany 1288317 [57] ABSTRACT [52 Cl i There is provided a method of producing a molded an- [511 Int Cl C21 d [04 isotropic permanent magnet from particles of perma- [58] Fieid 31 55 nently magnetizable material, which particles have 'j'5g 22 f preferred axes of magnetization. This method includes 40717 4 magnetizing the particles along the preferred axes either before or after they are formed from bulk mag- [56] References Cited netic material and then molding the particles with a binder under the influence of a low order aligning UNITED STATES PATENTS field.

2,964,793 12/1960 Blume 264/24 2,965,953 12 1960 Baermann 264/24 14 Clalms, N0 Drawmgs METHOD OF PRODUCING A MOLDED ANISOTROPIC PERMANENT MAGNET This is a continuation application of priof application Ser. No. 61,425, filed Aug. 5, 1970, now abandoned, which was a continuation-in-part application of my prior application Ser. No. 662,284, filed Aug. 22, 1967, now abandoned.

This invention pertains to the art of producing permanent magnets and more particularly to a method of producing a molded anisotropic permanent magnet formed from high coercivity alloyed permanent magnet material.

The invention is particularly applicable to the production of an anistropic permanent magnet of the typewhich is to be magnetized with opposite polarity magnetic poles, and it will be described with particular reference thereto; however, it should be appreciated that the invention has much broader applications and may be used for the production of anisotropic permanent magnets of more general use.

in the production of anisotropic permanent magnets, from alloyed material such as those formed primarily from an alloy of aluminum, nickel,-cobalt, titanium and iron, the alloy is cast and then heat treated within a strong magnetic field so that the casting is oriented to produce anisotropic properties. The casting remains in the field until it has been cooled under the Curie Point ofthe alloy. If the permanent magnet material, or alloy, develops a spike or needle-like crystal elongated in the direction of the magnetic field, themo st favorable magnetic values are obtained for the alloy casting. After the heat treatment, the permanent magnet material is demagnetized, so that it may be subsequently machined to obtain the necessary shape. This process is used only to produce solid anisotropic permanent magnets having I simple shapes, and it does not lend itself satisfactorily to producing intricate shapes To produce a permanent magnet having various shapes and various pole arrangements, it has been generally the practice to form the magnets from permanent magnet powders molded together by a binder, such as disclosed in U.S. Pat. Nos. 3,024,392; 2,959,832; 2,965,953; and 3,051,988. If an anisotropic magnet is to be produced, the particles are anisotropic. To obtain the highest degree of orientation ofthe anisotropic particles, so that the anisotropic characteristics of these particles was more effectively used, a high order magnet aligning field was applied to the particles in a given direction. This magnetic aligning field, as mentioned was of a relatively high order." This indicates that the magnetic field had an intensity approaching the intensity to saturate the material forming the anisotropic particles. This aligning field was applied to the particles while the particles were capable of being movable. in this manner, the particles would turn themselves into their preferred direction oforientation so that the preferred axes of magnetization of the various particles tended to be parallel to the direction of the magnetic aligning field being applied. This alignment was best effected while the mixture of particles and binder was falling into the mold. At this time, particles were sufficiently movable so that they could achieve orientation while falling into the mold.

In another instance, the mold was vibrated while the high order aligning magnetic field was applied to the particles within the mold. Still another arrangement for between the various particles. All of these arrange-- ments had certain disadvantagess. It was difficult to apply a strong aligning field to the particles as they were falling,or avibrating device was necessary for the mold, or it was necessary to provide a means for ex tracting the liquid from the particles while they were in the mold. 'All of these arrangements made the production of a bonded anisotropic permanent magnet ct somewhat complex.

One of the primary disadvantages of these prior methods for aligning anisotropic particles within a mold prior to pressing the particles into a permanent magnet was the need for a high magnetic field aplied to the mold or across the mold during the melding of the permanent magnet. This required a complex mold structure which often involved certain elements formed from non-magnetic materials, which had to be highly resistant to pressure and wear. This was difficult; therefore, the molds were expensive and had to be repaired often.

in addition, the prior methods for forming bonded anisotropic permanent magnets was not completely satisfactory for such applications as rotors, wherein a number of opposite polarity, closely spaced magnetic poles were required on the surface of the resulting permanent magnet. Mass production of this type of magnet was relatively complex, and somewhat uneconomical when using the prior known methods ofproducing bonded anisotropic permanent magnets. For these reasons, anisotropic permanent magnets including particles held together by a binder have been used in only limited applications. The anisotropic magnets did provide additional energy content; however, this additional energy content wasnot sufficiently higher than that obtained by isotropic permanent magnets to justify widespread use of pressed anisotropic magnets.

The present invention overcomes the disadvantages of the prior methods of producing anisotropic permanent magnets from individual particles held together by a binder and results in an anisotropic permanent magnet with an extraordinary good alignment and a high energy content. in addition, relatively inexpensive equipment can be used for aligning the particles within the permanent magnet during the production thereof. indeed, a permanent magnet can be used to produce the aligning field.

In accordance with the present invention, there is provided a method of producing an anisotropic permanent magnet,'including the steps'of providing anisotropic particles magnetized to at least approximately saturation in their preferred axes of magnetization; placing the particles and a binder within a mold; and, molding the particles and binder into a unit while the particles are under the influence of an aligning field is dependent upon the coercivity of the particular particles being used. The aligning field is substantially below this saturation level and, preferably, is in the neighborhood of LOGO-4,000 Gauss. This level of magnetic field can-be created by a permanent magnet, without requiring the use of non-magnetic material within the mold itself. it has not been known procedure to premagnetize anisotropic particles before they are placed in an aligning field so that the turning moment on the particles in an inter-action of the magnetic field of the particles itself and the magnetic aligning field. [n the past, the aligning field had to have sufficient magnetic intensity to generate the complete torque'for turning the particles into their desired or oriented positions.

in accordance with a more limited aspect of the present invention, there is provided a method, as defined above, wherein the anisotropic particles are magnetized along their preferred axes, at least to approximately saturation, and are then molded into a magnet, while under the influence of an aligning field having an intensity substantially below the saturation level of the particles.

In accordance with another aspect of the present invention, there is provided a method, of the type described above. wherein the magnetic material from which the particles are to be formed is cast into a blank with a given preferred direction of magnetization. Thereafter, the blank is magnetized along its preferred direction of magnetization and is broken into particles which are small enough to be subsequently formed into an anisotropic permanent magnet. The particles are then molded, with a binder, into a magnet under the influence of an aligning field having an intensity substantially below the saturation level of the particles.

In accordance with the present invention particles of high coercivity magnet material are premagnetized and mixed with a binder, and then the mixture is molded under the influence of a low order aligning field having a configuration matching the desired pole arrangement for the magnet. in this manner, the resulting magnet has the desired magnetization without requiring magnetization after the bonded magnet has been formed.

Since the saturation level of the particles may vary according to the particular material being used in producing the particles, the pre-magnetization of the particles involves a field having an intensity determined by the particles. The aligning field then may be of relatively low order, such as l,000-4,000, Gauss.

The primary object of the present invention is the provision of a method for producing a molded anisotropic permanent magnet formed from particles in a binder, which method is economical, requires inexpensive equipment, and results in high energy anisotropic magnets. 1

Another object of the present invention is the provision of a method for producing a molded anisotropic permanent magnet formed from particles in a binder, which method involves the pre-magnetization of the particles along their preferred axes to reduce the magnitude of the subsequently used aligning field.

These and other objects and advantages will become apparent from the following description used to illustrate the preferred embodiments of the invention and not to limit the same.

The present invention relates to a method or methods of producing anisotropic permanent magnets of the bonded type, which have a high energy level or content, can be manufactured by relatively inexpensive equipment, and require a relatively low level or weak magnetic aligning field. Since a relatively weak aligning field is anticipated for use in the present invention, this term can be defined as a field having an intensity in the neighborhood of LOGO-4,000 Gauss which can be produced by an electromagnet or permanent magnets. In the past, the aligning field for producing bonded anisotropicpermanent magnets was relatively strong and was determined by the particular characteristics of the particles being aligned within the magnet being molded.

In accordance with the present invention, an anisotropic permanent magnet is produced by premagnetizing the permanent magnet material to, or nearly to, saturation in the preferred direction of the material. If bulk or cast material is premagnetized, it is then crushed into small particles for use in the magnet. Otherwise, the anisotropic particles themselves are premagnetized. These pre-magnetized particles are then subjected to a low order aligning field so that they orient themselves according to the preferred direction of each anisotropic particle. The particles are molded together by a binder, either in a pelleting treatment, which forms a blank for subsequent pressing into a magnet, or a final pressing treatment which forms the resulting permanent magnet.

It is appreciated that powdered permanent magnet material in a binder at times has been subjected to a low order magnetic field before molding, not for the purpose of producing an anisotropic permanent magnet, but to avoid disassociation of the mixture while it was being placed into a pressing mold. This concept is completely different than the concept to which the present invention is directed. it has never been realized that pre-magnetization' of individual particles along their preferred axes, before an aligning field was applied, would allow use of an aligning field having a very low strength. It was also not known that an excellent alignment of the permanent magnet particles within the magnet would result by this method. Never before have the particles been pre-magnetized to near saturation before a bonded magnet was formed. The use of this concept has proven successful in producing anisotropic permanent magnets pressed together and bonded by a binder, which magnets have a high energy content and are relatively inexpensive to produce. This is a substantial advance in the art of producing bonded permanent magnets. For the purpose of the present invention, all of those anisotropic permanent magnet materials which have a high coercive force, i.e. greater than 1200 Dersteds, may be used in producing the pre-magnetized particles-from which the permanent magnet is formed. By having a relatively high coercive force, the aligning field does not demagnetize the particles during alignment. To the contrary, the aligning field causes the separate particles to align along their preferred axes, as opposed to along their elongated axes.

In accordance with one embodiment of the present invention, the permanent magnet material is cast in a manner to produce a preferred direction of magnetization within the resulting casting. For this purpose, it is suitable to cast the anisotropic raw material in the form of flat, round or rectangular plates with the preferred direction of magnetization being'perpcndicular to the surface. Consequently, if the plates should break during handling, the preferred direction of magnetization can be easily recognized. Any known process can be employed for producing anisotropic material having a selected preferred direction of magnetization. Thereafter, a strong magnetizing field is imposed on the anisotropic casting so that the casting is magnetized along its preferred direction of magnetization. By selecting the preferred direction of magnetization perpendicular to its surface, it can be readily recognized for subsequent magnetization. The magnetizing field is such that the permanent magnet material is saturated or nearly saturated. Thereafter, the magnetized permanent magnet casting is powdered into relatively small particles. The size of these particles is dependent upon the subsequent processing and may be varied substantially as long as they may be mixed with a binder and molded into a permanent magnet having a generally homogeneous composition. Since the magnetized permanent magnet particles attract each other, the combination of the particles with an appropriate binder is, in accordance with the preferred embodiment of the present invention, effected by dissolving a plastic resin binder in a solvent and placing the magnetized permanent magnet particles within this mixture. Thereafter, the solvent is evaporated leaving the individual particles coated with a plastic resin film. Of course, the particles may be mixed with the resin, or binder, in accordance with other known procedures. The coated permanent magnet particles are now ready for subsequent use in the production of an anisotropic permanent magnet, in a manner to be hereinafter described.

ln order to facilitate powdering or crushing of the permanent magnet material which have been magnetized to saturation and then mixing the same with a binder, the permanent magnet material may be partially demagnetized after it has been saturated. The pre-magnetization to saturation has already established the preferred direction of magnetization of the particles and this cannot be destroyed by partial demagnetization of these particles for ease in subsequent processing.

When the anisotropic permanent magnet material is magnetized before it is crushed into a powder, care must be taken that a certain grain size, depending upon the particular magnet to be produced, is not exceeded during subsequent crushing. In order to achieve this result, the powder material may be passed between rollers spaced from each other a distance which can be adjusted to limit the maximum grain size of the crushed particles. The larger grain sizes are then reduced to the maximum size allowed by the rollers, and subsequent sifting or grading of the individual particles is not necessary.

In accordance with another aspect of the present invention, the anisotropic permanent magnet material can be pre-magnetized after it has been crushed into the desired size. In this process, the crushed particles are first mixed with a binder, and the mixture of permanent magnet particles and binder is weighed into quantities necessary for filling the permanent magnet mold or the pelleting mold. At this time, the particles are subjected to a high intensity magnetic field sufficient to saturate the particles. This can be done even when the particles are introduced into the mold which will be used for forming the permanent magnet or a pellet to be subsequently used in forming the permanent magnet. The end result is that the particles are magnetized in a direction which established their preferred direction of magnetization so that they resemeble the particles produced in accordance with the first-mentioncd embodiment of the invention. I

The permanent magnet particles, having either the resin coated thereon, or mixed with the resin, are then pressed while under the influence of a magnetic aligning field, the strength of which can be substantially lower than the aligning field heretofore used in this type of process. The field of the magnet particles coact with the aligning field to provide an aligning torque which orients the particles in accordance with the preferred axes of magnetization. It is essential that the aligning field is not of a magnitude that will twist the particles to align their long axes parallel to the aligning field. It is possible that the preferred axes of magnetization of the individual particles does not correspond to the elongated axes of the individual particles. The preferred axes, not the long axes, are to be aligned to produce superior magnetic properties.

Heretofore, alignment of anisotropic particles was effected by a magnetic'field having a relatively high field strength or intensity. In contrast to this, the process, in accordance with the present invention, requires only a relatively low level field strength. The field strength contemplated by the present invention must not be so high that the particles are turned due to their shape as mentioned above, but due to their magnetic moment which they receive during the pre-magnetization step. In this manner, particles are aligned in accordance with their preferred directions of magnetization. Also, the strength of the aligning field must not change the direction of magnetization established by the pre-magnetization of the particles. Consequently, the aligning field must be substantially lower than a field which would saturate or demagn'ctize the previously magnetized particles. It has been found that a field strength between LOGO-4,000 Gauss can be used in practice of the present invention. For this reason. it is possible to use a relatively weak elcctromagnet or a permanent magnet to produce the aligning magnetic field. This results in a substantial reduction in the cost of the tools required to align and mold the particles into a finished permanent magnet.

The production of a permanent magnet in accor dance with the invention described above results in a higher degree of alignment of the individual particles within the magnet then heretofore possible with other methods of alignment. The particles are aligned so that they can be later magnetized with a variety of pole arrangements. Since the particles have a relatively high coercive force, several magnetic poles extending in a radial direction or arranged on one side of the perma nent magnet are possible upon subsequent magnetization of the permanent'magnet. The lines of magnetic force extending inside the permanent magnet from one pole to the other form a generally, semi-circular path which results in an external magnetic field which protrudes from the permanent magnet a substantial distance.

It is also possible toutilize the present invention to produce a permanent magnet which is magnetized in a direction parallel to its length, across its thickness or across its diameter, depending upon the particular shape and desired end use of the permanent magnet. Since the aligning field is relatively low, it can be produced by permanent magnets. lndeed, permanent magnets are preferred for use as the source of the low level aligning field. Such permanent magnets must have a low permeability because the field strength existing at the edges of the poles are relatively low in suchmagnets. Also, such magnets allow small distances between the poles whereby the lines of magnetic force leaving the magnet take effect deeply into the mold which con tains the particles to be aligned.

The form of the magnetic field used in aligning the particles within the mold should be that which corresponds to the desired final pole arrangement on the particular permanent magnet being formed. If electromagnets with soft iron cores are used for producing the aligning fields, these cores, especially in the case of closely spaced poles, should not come into direct contact with the material being aligned. If such iron cores are used, the magnetic field through the cores should not approach the saturation level for the core. An electromagnet without an iron core can also be employed for producing the low level aligning field.

In accordance with another aspect of the present invention, the aligning magnetic field may be incorporated with a pelleting mold which is used to produce a blank to be finally pressed into a magnet, or in the final pressing mold itself. According to the present invention, however, it is advantageous to produce pellets and effect alignment during their production because these pellets can be produced at a temperature which is only slightly higher than room temperature. After the magnet particles have been aligned, the final magnet may be'made by a molding operation which includes higher temperature to bond the particles with the binder. It is also advantageous to produce relatively thin pellets which have aligned particles. These thin pellets may be stacked upon each other and. then pressed into a final magnet. This is especially useful when the direction of pressure in forming the final magnet is along a substantial dimension of the magnet. The use of thin, previously aligned pellets overcomes the need for an aligning field in the final molding process. If the final pressing operation requires the use of heat and if plastic binders are used, the lack of an aligning field may be extremely beneficial.

It is preferred, in accordance with the invention, that the magnetic aligning field be imposed upon the previously magnetized particles in a direction vertical to the direction of pressure. In this manner, especially when the longitudinally shaped particles are used, the aligning field will not require a change in the basic position of the pre-magnetized particles. The anisotropic magnets constructed in accordance with the present invention must be marked so that during the final pressing operation the direction of the aligning field is applied in the direction of the pre-magnetization. In some instances, it may be suitable to demagnetize the magnet immediately after it has been finally formed. In this manner, further processing of the magnet can take place without being affected by the magnetization of the permanent magnet. Thereafter, the permanent magnets are magnetized in accordance with known procedures, preferably after or during their assembly into the device in which they are to be used.

By producing a permanent magnet in accordance with the present invention, it is possible to obtain an anisotropic permanent magnet having magnetic values of uniform quality and various magnetization patterns which' were not heretofore obtainable by known processes or producing such anisotropic magnets.

Example I One example of the present invention includes the following procedure.

a. An alloy of Al, Ni, Co, Ti and Fe is melted, alloyed and poured into an appropriate mold in accordance with well known principles used in producing Alnico. In order to make this alloy anisotropic, it is heated beyond its Curie point (870C) and then cooled within a magnetic field to about 780C for a period of l-2 minutes. The alloy is then cooled to 700C within about 5 minutes and to 500C within an additional 10 minutes. The magnetic field is then removed and the alloy is allowed to cool to ambient temperatures.

The mold used to cast the alloy has a shape to produce a generally flat plate-like casting of alloy. The magnetic field is generally perpendicular to the flat surfaces and through the smallest dimension. After the field treatment, the casting has obtained anisotropic permanent magnetic properties. The casting is then demagnetized and cleaned by sandblasting to remove scale from the surfaces.

b. The resulting alloy has a coercive force of about 2000 Oersteds. It is placed between two magnet poles directed toward the fiat surfaces. Then the alloy is magnetized to or nearly to saturation by energizing the poles with a field of approximately 6000 Gauss. The field is in the same direction as the anisotropy of the alloy; therefore, the alloy is premagnetized in the preferred direction.

c. After magnetization, the casting is crushed to a 'relatively coarse grain. Then this coarse grain is ground to small particles the size of which allows them to pass through a -200 mesh screen. As is known, an alternating field may be used-to agitate the particles as they are passed through the screen. It is possible to grind the coarse grains by passing them through crushing rolls so spaced from each other that the maximum particle size is sufficient to pass through a 100-200 mesh screen.

d. The premagnetized particles are mixed with an appropriate binder in dry or liquid condition. A large vari ety of known binders can be used according to the invention. For instance, a thermoplastic material having a relatively low viscosity when in heated condition, such as nylon or polystyrene, can be used. lt is also possible to use a thermosetting binder such as phenol formaldehyde or carbamide resin. Epoxies are also suitable for this method. In accordance with this example the premagnetized particles are mixed with a heated thermoplastic binder of low viscosity; i.e. Nylon, until the particles are evenly distributed in the low viscosity binder.

e. Then the viscous mixture of binder and premagnetized particles are injection molded into a nonmagnetic mold having a low order aligning field or field associated therewith. The aligning field is in the range of 1000-5000 Oersteds. The direction of the aligning field or fields corresponds to the direction of magnetization of the finished magnet. For instance, if a ringshaped or cylindrical magnet having poles of alternating polarity arranged on its circumference, is to be produced, the aligning field in the mold must have the same pole arrangement.

f. The molded mixture is then allowed to cool and a magnetized permanent magnet is produced with the desired pole arrangement. Subsequent magnetization in this pole arrangement may or may not be used.

Example ll A permanent magnet may be produced by modifying the steps in Example I as follows.

a. After step (a) of Example I, the anisotropic alloy is ground into unmagnetized particles of a sufficiently small size to pass through a 100-200 mesh screen.

b. The unmagnetized particles are moved through a funnel-shaped fixture and past two spaced pole faces at the throat of the fixture which are constantly energized with a magnetic field of approximately 6,000 Gauss.

The field rotates the individual particles and magnetizes them in their preferred directions. This produces premagnetized particles magnetized to or about to saturation in their preferred directions. Thereafter, (d), (e) and (f) are performed to produce a permanent magnet with a selected pole arrangement and which may'not require any additional magnetization.

Example Ill The present invention can be used for extremely high coercive force permanent magnet material to produce a magnetized permanent magnet. The material presents extreme difficulties in final magnetizing with close opposite polarity poles. The reason is that magnetization of this material may require a magnetizing field of 60,000l00,000 Gauss which demands high ampereturns. To produce closely spaced poles, the high current flowing in adjacent conductors of the magnetizing fixtures will short between the conductors. The present invention produces a magnetized anisotropic magnet which can have a variety of pole arrangements established by a low order aligning field, i.e., i0005000 Gauss. An example of the use of this invention includes the following steps.

a. Some of'the extremely high coercive force magnet materials are platinum cobalt, manganese aluminum and rare earth magnet materials. The rare earth materials include an alloy of a rare earth, such as Samarium (Sm), Praseodymium (Pr), Neodymium (Nd), Gadolinium (Gd), Terbium (Tb) and Cerium (Ce) with cobalt and, sometimes copper. These permanent magnet materials are based on hexagonal intermetallic compounds and they exhibit a very high coercive force, i.e., over 5000 Oersteds and generally above 10,000 Oersteds and have a crystal anisotropy. For magnetization, high field strength exceeding about 35,000 Gauss must be used.

b. In using the present invention, according to this example, a rare earth permanent magnet material, such.

as Samarium is alloyed with copper and cobalt. The alloy is melted and poured into a metallic mold, which is generally water cooled, to form thin sheets or small flat bars. The thickness of the alloy sheets or bars is in the range of 3-6 mm.

c. The material is removed from the mold and heated to and held at a temperature of approximately 400C for about 4 hours.

d. The sheets or bars are then magnetized through their small dimensions by a magnetic field having a strength of at least 35,000 Gauss.

e. A permanent magnet is then made with this magnetized material by following steps (c)-(f) of Example Example IV In this example, a procedure of steps (a) and (b) of Example lll are followed, then steps (b) of Example ll and then steps (c)-(f) of Example I.

The production of a permanent magnet in accordance with the present invention as outlined above results in substantial savings and permanent magnets having quality and characteristics not hereto obtainable.

A permanent magnet constructed by the method taught herein may be injection molded, pressed or extruded. The particles forming the magnet are not ground to domain size which would make them pyrophoric, especially when rare earth magnetic materials are involved. Consequently, no precautions are needed to prevent burning of the particles during processing. In the formation of a permanent magnet, the particles are not heated to a temperature above their Curie point which can result in demagnetization due to thermal decay. The resulting magnet has a high dimensional accuracy and a high energy product.

By aligning the premagnetized particles in accordance with a preselected pole arrangement, it is possible to produce high coercive force magnets with closely spaced magnetic poles. For extremely high coercive force materials, such as platinum cobalt, manganese aluminum and the rare earth magnetic materials, such closely spaced poles could not be produced in a permanent magnet. A cylindrical permanent magnet can be produced with several poles facing in a radial direction with north and south poles or a flat permanent magnet can be produced with closely spaced opposite polarity magnetic poles. This is especially useful in magnetic materials having a coercive force of over i200 ()crsteds.

When the permanent magnet is removed from the mold in the above examples, the magnet is magnetized and can be used. However, in some instances subsesmall dimension and generally perpendicular to said surfaces;

c. crushing said casting into anisotropic particles each having a preferred magnetic axis and a size which can pass through a mesh screen;

d. mixing said particles with a plastic binder to form a non-magnetically aligned mixture;

e. molding said mixture in a mold under the influence of a magnetic field having an intensity in the range of l,00O-4,000 Gauss and with a configuration generally matching said selected pole arrangement.

2. The method as defined in claim 1 wherein said magnet alloy is an alloy of at least aluminum, nickel, and cobalt.

3. The method as defined in claim 1 wherein said magnet alloy is platinum cobalt.

4. The method as defined in claim 1 wherein said magnet alloy is manganese aluminum.

5. The method as defined in claim 1 wherein said alloy is a rare earth metal selected from the group consisting of Sm, Pr, Hd, Gd, Th and Ce with a metal selected from the group consisting of cobalt and copper.

6. A method of making a plastic bonded magnetized permanent magnet having a selected pole arrangement, said method comprising the following steps:

a. providing a casting of a permanent magnet alloy having a coercive force greater than 1,200 Oersteds and a preferred magnetic direction;

b. crushing said casting into anisotropic particles each having a preferred magnetic direction and a size which can pass through a 100 mesh screen;

c. magnetizing said particles along said directions to at least saturation by a magnetizing field between two poles as said particles pass between said poles;

d. mixing said particles with a binder to form a nonmagnetically aligned mixture;

e. molding said mixture in a'mold under the influence of a magnetic field having an intensity in the range of l,0O-4,000 Gauss and with a configuration generally matching said selected pole arrangement.

7. The method as defined in claim 6 wherein said magnet alloy is an alloy of at least aluminum, nickel, and cobalt.

8. The method as defined in claim 6 wherein said magnet alloy is platinum cobalt.

9. The method as defined in claim 6 wherein said magnet alloy is manganese aluminum.

10. The method as described in claim 6 whereinsaid alloy is a rare earth metal selected from the group consisting of Sm, Pr, Hd, Gd, Th and Ce with a metal selected from the group consisting of cobalt and copper.

11. A method of producing a plastic bonded anisotropic permanent magnet comprising the steps of:

a. melting a permanent magnet alloy;

b. casting the alloy in a mold to form a casting;

0. heat treating said casting in a magnetic field to make said casting anisotropic with a preferred magnetic axis;

d. demagnetizing said casting;

e. magnetizing said casting to at least approximately saturation by a field aligned with said preferred magnetic axis;

f. crushing said casting to relatively coarse grained particles;

g. mixing said particles with a plastic binder;

h. injection molding said mixture into a mold; and,

i. applying an aligning field in the range of LOGO-4.000 Gauss to said mixture in said mold.

12. A method of producing a plastic bonded anistropic permanent magnet from alloyed permanently magnetizable particles, said particles being anisotropic and having a preferred direction of magnetization, and a plastic binder, said method comprising the following steps:

a. magnetizing said particles to approximately saturation in their preferred directions of magnetization to form external magnetic fields corresponding to the preferred directions of said particles;

b. partially demagnetizing said magnetized particles;

c. mixing said magnetized particles and said plastic binder into anon-magnetically oriented mixture; d. placing said mixture of magnetized particles and binder into a mold;

e. subjecting said mixture to the field of a permanent magnet, said field having an intensity substantially below the saturation level of said particles;

f. after said particles are generally aligned in said mold, molding said particles into a bonded permanent magnet.

13. A method of making a bonded aluminum-nickelcobalt anisotropic permanent magnet, said method comprising the following steps:

a. providing a generally flat plate-like casting of anisotropic aluminum-nickel-cobalt alloy having flat surfaces and a preferred axis of magnetization gen erally perpendicular to said surfaces;

b. magnetizing said casting to at least approximately saturation along said preferred axis of magnetization;

c. crushing said casting to anisotropic particles having a size which will pass through a -200 mesh screen;

d. mixing said particles with a heatedthermoplastic binder to form a viscous mixture;

e. injection molding said mixture into a mold having a low order aligning field corresponding to the desired direction of magnetization of the finished magnet; and,

f. allowing said mixture to cool in said mold.

14. A method of making a bonded aluminum-nickeleobalt anisotropic permanent magnet, said method comprising the following steps:

a. providing a generally flat plate-like casting of anisotropic aluminum-nickel-cobalt alloy having flat surfaces and a preferred axis of magnetization generally perpendicular to said surfaces;

b. crushing said casting to anisotropic particles having a size which will pass through a 100-200 mesh screen;

e. magnetizing said particles to at least approximately saturation along the preferred directions of said particles;

d. mixing said particles with a heated thermoplastic binder to form a viscous mixture;

f. allowing said mixture to cool in said mold.

Claims

1. A METHOD OF MAKING MAGNETIZED PLASTIC BONDED PERMANENT MAGNET HAVING A SELECTED POLE ARRANGEMENT, SAID METHOD COMPRISING THE FOLLOWING STEPS; A. PRODUCTING A FLAT CASTING OF PERMANENT MAGNET ALLOY HAVING A COERCIVE FORCE GREATER THAN 1,200 OERSTEDS, SAID CASTING HAVING A SMALLEST DIMENSION LOCATED BETWEEN TWO GENERALLY FLAT SURFACES AND A PREFERRED MAGNET DIRECTION PREPENDICULAR TO SAID TWO FLAT SURFACES; B. MAGNETIZING SAID CASTING TO AT LEAST ABOUT SU.ATURATION BY A MAGNETIZING FIELD PASSING THROUGH SAID SMALL DIMENSION AND GENERALLY PERPENDICULAR TO SAID SURFACES; C. CRUSHING SAID CASTING INTO ANISOTROPIC PARTICLES EACH HAVING A PREFERRED MAGNETIC AXIS AND A SIZE WHICH CAN PASS THROUGH A 100 MESH SCREEN; D. MIXING SAID PARTICLES WITH A PLASTIC BINDER TO FORM A NONMAGNETICALLY ALIGNED MIXTURE; E. MOLDING SAID MIXTURE IN A MOLD UNDER THE INFLUENCE OF A MAGNETIC FIELD HAVING AN INTENSITY IN THE RANGE OF 1,000-4,:.000 GAUSS AND WITH A CONFIGURATION GENERALLY MATCHING SAID SELECTED POLE ARRANGEMENT.

6. A method of making a plastic bonded magnetized permanent magnet having a selected pole arrangement, said method comprising the following steps: a. providing a casting of a permanent magnet alloy having a coercive force greater than 1,200 Oersteds and a preferred magnetic direction; b. crushing said casting into anisotropic particles each having a preferred magnetic direction and a size which can pass through a 100 mesh screen; c. magnetizing said particles along said directions to at least saturation by a magnetizing field between two poles as said particles pass between said poles; d. mixing said particles with a binder to form a non-magnetically aligned mixture; e. molding said mixture in a mold under the influence of a magnetic field having an intensity in the range of 1,000-4,000 Gauss and with a configuration generally matching said selected pole arrangement.

10. The method as described in claim 6 wherein said alloy is a rare earth metal selected from the group consisting of Sm, Pr, Hd, Gd, Th and Ce with a metal selected from the group consisting of cobalt and copper.

11. A method of producing a plastic bonded anisotropic permanent magnet comprising the steps of: a. melting a permanent magnet alloy; b. casting the alloy in a mold to form a casting; c. heat treating said casting in a magnetic field to make said casting anisotropic with a preferred magnetic axis; d. demagnetizing said casting; e. magnetizing said casting to at least approximately saturation by a field aligned with said preferred magnetic axis; f. crushing said casting to relatively coarse grained particles; g. mixing said particles with a plastic binder; h. injection molding said mixture into a mold; and, i. applying an aligning field in the range of 1,000-4,000 Gauss to said mixture in said mold.

12. A method of producing a plastic bonded anistropic permanent magnet from alloyed permanently magnetizable particles, said particles being anisotropic and having a preferred direction of magnetization, and a plastic binder, said method comprising the following steps: a. magnetizing said particles to approximately saturation in their preferred directions of magnetization to form external magnetic fields corresponding to the preferred directions of said particles; b. partially demagnetizing said magnetized particles; c. mixing said magnetized particles and said plastic binder into a non-magnetically oriented mixture; d. placing said mixture of magnetized particles and binder into a mold; e. subjecting said mixture to the field of a permanent magnet, said field having an intensity substantially below the saturation level of said particles; f. after said particles are generally aligned in said mold, molding said particles into a bonded permanent magnet.

13. A method of making a bonded aluminum-nickel-cobalt anisotropic permanent magnet, said method comprising the following steps: a. providing a generally flat plate-like casting of anisotropic aluminum-nickel-cobalt alloy having flat surfaces and a preferred axis of magnetization generally perpendicular to said surfaces; b. magnetizing said casting to at least approximately saturation along said preferred axis of magnetization; c. crushing said casting to anisotropic particles having a size which will pass through a 100-200 mesh screen; d. mixing said particles with a heated thermoplastic binder to form a viscous mixture; e. injection molding said mixture into a mold having a low order aligning field corresponding to the desired directioN of magnetization of the finished magnet; and, f. allowing said mixture to cool in said mold.

14. A method of making a bonded aluminum-nickel-cobalt anisotropic permanent magnet, said method comprising the following steps: a. providing a generally flat plate-like casting of anisotropic aluminum-nickel-cobalt alloy having flat surfaces and a preferred axis of magnetization generally perpendicular to said surfaces; b. crushing said casting to anisotropic particles having a size which will pass through a 100-200 mesh screen; c. magnetizing said particles to at least approximately saturation along the preferred directions of said particles; d. mixing said particles with a heated thermoplastic binder to form a viscous mixture; e. injection molding said mixture into a mold having a low order aligning field corresponding to the desired direction of magnetization of the finished magnet; and, f. allowing said mixture to cool in said mold.