US3639182A

US3639182A - Method for improving the effectiveness of a magnetic field for magnetizing permanent magnets

Info

Publication number: US3639182A
Application number: US818465*A
Authority: US
Inventors: Joseph J Becker
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1969-03-27
Filing date: 1969-03-27
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

A method for increasing the coercive force of a permanent magnet produced by a given magnetizing field. The magnet is subjected to the magnetizing field with the initial position of the magnet being no greater than an angle theta of + OR - 45* formed between a predetermined direction of magnetization of the magnet and the direction of the applied magnetizing field. The magnet and/or magnetizing field are moved in at least a single plane through the angle theta which can range up to + OR - 45*. Such movement is terminated with the magnet in a position in which its predetermined direction of magnetization is substantially parallel to the direction of the magnetizing field.

Description

United States Patent Becker 1 Feb. 1, 1972 [54] METHOD FOR IMPROVING THE EFFECTIVENESS OF A MAGNETIC FIELD FOR MAGNETIZING PERMANENT MAGNETS [52] US. Cl ..l48/103, 148/108, 252/6251, 252/6263 [51] Int. Cl. .1101! 13/00, 1-l01f1/10, 1101f 1/04 [58] Field of Search ..148/100,101,103,108,102; 252/6251, 62.63

[56] References Cited UNITED STATES PATENTS 2,482,364 9/1949 Pfleger ..l48/l08 X 3,036,008 5/1962 Berge ..252/62.63 X 3,066,355 12/1962 Schloemann et a1. ..l48/103 X 3,067,140 12/1962 Davis, Jr. .148/108 UX 3,113,927 12/1963 Cochardt ..252/62.5

Wootten ..l48/108 X Jesmont et a1... ....l48/103 X 3,279,959 10/1966 Oshima et al. ....148/103 3,424,578 l/1969 Strnat et a1. ..75/213 3,428,498 2/1969 Heimke ..148/103 X Primary Examinerl-lyland Bizot Assistant Examiner-G. K. White Attorney-Charles '1. Watts, Paul A. Frank, James M. Binkowski, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman [5 7] ABSTRACT A method for increasing the coercive force of a permanent magnet produced by a given magnetizing field. The magnet is subjected to the magnetizing field with the initial position of the magnet being no greater than an angle 0 of 145 formed between a predetermined direction of magnetization of the magnet and the direction of the applied magnetizing field. The magnet and/or magnetizing field are moved in at least a single plane through the angle 0 which can range up to 245. Such movement is terminated with the magnet in a position in which its predetermined direction of magnetization is substantially parallel to the direction of the magnetizing field.

10 Claims, 1 Drawing Figure PAI'ENIEDFEB 1m? 3;639;l82

DIRECTION OF MAGNETIZING FIELD I-zfi x PREDETERIVIINED DIRECTION OF I MAGNETIIZATION OF MAGNET I, 1 1

\ DIRECTION OF MAGNETIZIING FIELD JOSEPH BECKER H/S ATTORNEY METHOD FOR IMPROVING THE EFFECTIVENESS OF A MAGNETIC FIELD FOR MAGNETIZING PERMANENT MAGNETS The present invention relates generally to the art of making permanent magnets and is more particularly concerned with a novel method for improving the effectiveness of a magnetic field for magnetizing such magnets.

It is generally recognized that the magnetic properties of permanent magnet materials can be enhanced by reducing them to powders. Ordinarily, magnets of such powders are prepared by subjecting them to a magnetic field to orient the particles, compressing the powder and sintering the resulting compacts. The magnetic powder can also be bonded in rubber or plastic to produce flexible permanent magnets having special utility in permanent magnet motors, as magnetic latches, and in many other applications. In some instances, the enhancement of the properties by particle size reduction is offset to a substantial degree by the accompanying decrease in magnetic coercive force. Due to the numerous potential applications of permanent magnets, substantially increasing their coercive force has long been recognized as a desirable objective by those skilled in the art.

I have found that the value of the magnetic coercive force Pi of permanent magnets, especially magnets of cobalt rareearth compounds, shows a pronounced dependence on the magnetizing field H Specifically, magnets formed from permanent magnet material powders, especially powders of cobalt rare-earth compounds, exhibit an unusually large dependence of coercive force on the previously applied magnetizing field. This dependence appears even when the coercive forces have the low values associated with magnets formed from a large particle size material. To develop their best magnetic properties, therefore, the permanent magnets need to be magnetized in as strong a field as possible. The stronger the magnetizing field, however, the greater are the energy requirements for furnishing such a field. In addition, the rate of rise of the coercive force l-l with the magnetizing field H,,,, in some instances, suggests that sufficiently strong magnetic fields are not presently available to any significant extent to impart the highest coercive force.

I have further discovered that the effectiveness of a given magnetic field used for magnetizing a permanent magnet to increase its coercive force can be very substantially enhanced by causing relative motion between the magnetic field and the body being magnetized, such motion being critical in both extent and kind.

According to the present invention, the relative motion between the magnetizing field and the permanent magnet can be carried out in a number of ways. For example, it can be carried out by selective movement of the magnet in the magnetizing field, by selective movement of the magnetizing field along or by selective movement of the magnet and its magnetizing field. Since the magnetizing field is usually supplied by a large magnet secured in place, the preferred embodiment of the present invention is the selective movement of the magnet in the magnetizing field.

' Briefly stated, the preferred embodiment of the present invention comprises subjecting the permanent magnet to a magnetizing field. The initial position of the magnet in the mag netizing field can vary but it should be no greater than at an angle of i45, the angle 6 being formed between a predetermined direction of magnetization of the magnet and the direction of the applied magnetizing field. For convenience, the magnet can be positioned initially with the angle 0 having a value of 0, at which position, the predetermined direction of magnetization of the magnet and the direction of the magnetizing field are substantially parallel. The permanent magnet is then moved in the magnetizing field in at least a single plane through the angle 0 with such angle ranging up to about :45". The movement of the magnet in the magnetizing field is terminated with the predetermined direction of magnetization of the magnet substantially parallel to the direction of the magnetizing field.

The process of the present invention is operable with permanent magnets. Such magnets may be anisotropic or isotropic. If the magnet is anisotropic, it has a magnetically preferred spacial direction, i.e., an easy axis of magnetization, and its predetermined direction of magnetization as used herein is generally such magnetically preferred direction. If the magnet is isotropic, its magnetic properties are the same in all spacial directions, and its predetermined direction of magnetization as used herein can be any desired direction.

The accompanying figure illustrates one method of carrying out the present invention wherein the magnet was positioned initially with the angle 0 having a value of 0, i.e., the predetermined direction of magnetization of the magnet was parallel to the direction of the magnetizing field. As shown by the figure, the magnet was moved in a single plane through an angle of +0, then 0, and then such movement was terminated with the angle 0 having a value of 0.

In carrying out the process of the present invention, the magnet should not be moved through an angle 0 greater than :45 because such movement would tend to cause reversal of the magnetization of those particles whose magnetic axis initially made an angle of more than 45 with the predetermined direction of magnetization of the sample. Although the angle 6 can have a value less than 1-45", an angle 6 having a maximum value of i45 is preferred since it results in most instances in the highest increase in coercive force.

In the instant process, the coercive force can be further improved by movement of the magnet through the angle 0 in a plurality of planes. For example, movement of the magnet through an angle 6 of up to :45" through two perpendicular planes successively further increases the coercive force signifi cantly. Since the angle 0, in circumscription, defines a cone, the maximum coercive force is obtained by successively moving the magnet through a number of different planes with the angle 6 equal to :45 so that all orientations of the magnets particles around the cone are covered.

In the process of the present invention, movement of the magnet in the magnetizing field can be carried out manually or mechanically by a number of conventional techniques. The

rate of movement of the magnet can vary widely since it is not critical. When the desired movement of the magnet is completed, such movement is terminated with the predetermined direction of magnetization of the magnet substantially parallel to the direction of the magnetizing field. After such magnetization, the coercive force of the magnet is measured.

The particular form of the magnet used in the present process can vary widely and is not critical. The greatest improvcment in properties is usually produced with magnets formed from powders of permanent magnet materials. The present process, however, is also operable with permanent magnet materials in bulk form, i.e., thos-e magnets which have never been reduced to particulate form.

Representative of the permanent magnet materials useful in the present invention are cobalt-base permanent magnet materials such as CosY, Co Sm and Co M wherein M is cerium-rich misch metal. Additional representative materials are the magnetically hard ferrite powders. Typical of these powders are bariumferrite (BaO'6 Fe 0 strontium ferrite (SrO'6FeO and lead ferrite (PbO'Fe O Alternatively, the present process can be carried out by moving the permanent magnet in the magnetizing field so that the angle 6 is increased by increments. Specifically, starting with the angle 0 having a value of substantially O, the magnet is moved through an angle 6 having a value greater than 0 but less than 45, through successively different planes so that its predetermined direction of magnetization describes a cone around the direction of the magnetizing field H',,,. With each additional movement of the magnet so that a cone is defined, the angle 6 is increased until it equals i45.

In another embodiment of the present process, movement of the magnet in a series of successive planes displaced from each other by a suitable angular increment can be accomplished by rotating the magnet through a suitable angle around the predetermined axis of magnetization at the completion of each movement in a single plane through the angle 0.

The present invention is further illustrated by the following examples.

EXAMPLE 1 A cylindrical magnet, about five-sixteenths inch in diameter and three-eighths inch long, was prepared from C0,,Sm

' powder which had a particle size of about 325 mesh. The

powder was pressed while in hexane so that excess fluid leaked out of the die during compression. It was compressed lightly in a magnetic field of 8,000 oersteds to orient the particles along their easy axis of magnetization. The resulting compact was then further compressed outside the magnetic field under a Coercive Force Run Magnetizing Procedure (oersteds) 1 With its easy axis of magnetization aligned with the direction of the magnetic field, i.e., the position of the angle 6, the test magnet was magnetized in a magnetic field of 23,600 oersteds to establish a reference state. lt was then magnetized in the opposite directionin a magnetizing field of 15,000 oersteds.

2 The, test magnet was returned to its reference state by magnetizing it in a magnetic field of 23,600 oersteds as in run 1. It was then magnetized in the opposite direction in a magnetizing field of 15,000 oersteds by moving it in the same plane from its 0 position through an angle 6 of 45 then back through the same plane, through the 0 position, through an angle 8 of -45 and back to 0 position as illustrated in the accompanying figure.

3 The test magnet was magnetized as in run 1.

4 The entire procedure of run 2 was repeated except that magnetization of the test magnet in the field of 15,000 oersteds was made by moving it through the angle 0 of :45 in two perpendicular planes successively. The test magnet was magnetized as in run 1.

6 The entire EHOEEKJ rifriwas repea except that magnetization of the test magnet in the field of 15,000 oersteds was made by moving the magnet i45 in four planes at 45 to each other.

7 The procedure of run 1 was used except that a magnetizing field of 20,000 oersteds was used instead of 15,000 oersteds.

8 The procedure of run 2 was used except that a magnetizing field of 20,000 oersteds was used instead of 15.000 oersteds.

9 The procedure of run 4 was used except that a magnetizing field of 20,000 oersteds was used instead of 15,000 oersteds.

The procedure of run 6 was used except that a magnetizing field of 20,000 oersteds was used instead of 15,000 oersteds.

The procedure of run 1 was used except that a magnetizing field of 29,000 oersteds was used instead of 15,000 oersteds.

The procedure of run 6 was used except that a magnetizing field of 29,000 oersteds was used instead of 15,000 oersteds,

The above table illustrates the significant increase in coercive force which can be produced in a cobalt rare-earth permanent magnet material by the method of the present invention. Specifically, runs 2, 4, 6, 9 and 10 illustrate the process of the present invention. Run 2 illustrates movement of the test magnet in one plane with the angle 0 being :45" and shows a significantly higher coercive force than that produced in control runs 1 and 3 where the strength of the magnetizing field was the same but the test magnet was stationary. Runs 4 and 6 show an even higher coercive force than run 2 due to movement of the test magnet in a greater number of planes. Runs 1 1 and 12 illustrate that when the magnetizing field applied is high enough, the coercive force of the test magnet remains unchanged by relative motion between the magnet and the magnetizing field.

The present process is operable, therefore, with any per manent magnet material in the range in which the coercive force depends on the magnetizing field, in which range the effectiveness of a given magnetizing field can be enchanced. As a result, permanent magnets with high coercive forces are available for much wider use than has been heretofore practicable since the high energy requirements of large magnetizing fields are eliminated.

EXAMPLE 2 In this example, a commercial oriented strontium ferrite cylindrical magnet about one-half inch in diameter and about five-sixteenths inch long was used. The magnet had been oriented along its easy axis of magnetization.

After stationary magnetization in a field of 10,000 oersteds, with its easy axis of magnetization substantially parallel, i.e., aligned with the direction of the magnetizing field, i.e., with the angle 0 having a value of 0, the magnet had a coercive force of 3,430 oersteds. It was then magnetized in the same field by moving it from its position of alignment with the direction of the field, i.e., the 0 position of 0, through an angle 0 of :45 in four planes, with each plane at 45 to each other, and terminating such movement with the easy axis of magnetization substantially parallel with the direction of the magnetizing field. After such magnetization, its coercive force was unchanged indicating that the magnetizing field was so high that coercive force no longer varied with relative motion.

In its position of alignment with the field, i.e., with its easy axis of magnetization parallel with the direction of the field, the strontium ferrite magnet was then magnetized in the opposite direction in a magnetic field of 5,000 oersteds. After such magnetization, its coercive force was determined to be 3,000 oersteds. It was then magnetized in the same field by moving it from its position of alignment, through an angle 0 of EXAMPLE 3 The procedure of this example was the same as that set forth in example 2 except that a commercial oriented barium ferrite magnet was used. The magnet had been oriented along its easy axis of magnetization.

After stationary magnetization in a field of 10,000 oersteds with its easy axis of magnetization substantially parallel, i.e., aligned, with the direction of the magnetizing field, i.e., with the angle 0 having a value of 0, the magnet had a coercive force of 2,400 oersteds. It was then magnetized in the same fi'eld by moving it from its position of alignment with the direction of the field through an angle 0 of about :45 in four planes, with each plane at 45 to each other and terminating such movement with the easy axis of magnetization substantially parallel with the direction of the magnetizing field. After such magnetization, its coercive force was unchanged, indicating that the magnetizing field was so high that coercive force no longer varied with relative motion.

In its position of alignment with the magnetizing field, i.e., with its easy axis of magnetization parallel with the direction of the field, the barium ferrite magnet was then magnetized in the opposite direction in a magnetizing field of 5,000 oersteds. After such magnetization, its coercive force was determined to be 2,130 oersteds. It was then magnetized in the same field by moving it from its position of alignment through an angle 6 of about i45 in four planes, with each plane being 45 to each other, and terminating such movement with the easy axis of magnetization substantially parallel with the direction of the magnetizing field. After such magnetization, the coercive force was determined to be 2,380 oersteds.

What is claimed is:

1. A method for increasing the coercive force of a permanent magnet in a given magnetizing field which comprises subjecting the magnet to the magnetizing field, the initial position of said magnet in said magnetizing field being no greater than an angle 6 of i45, the angle 6 being formed between a predetermined direction of magnetization of the magnet and the direction of the applied magnetizing field, causing relative motion between the magnet and the magnetizing field in at least a single plane through the angle 6 with said angle 0 rang-- ing up to i45, and ending such movement with the predetermined direction of magnetization of the magnet substantially parallel to the direction of the magnetizing field.

2. A method for increasing the coercive force of a permanent magnet in a given magnetizing field which comprises subjecting the magnet to the magnetizing field, the initial position of said magnet in said magnetizing fieldbeing no greater than an angle 6 of 1-45, the angle 0 being formed between a predetermined direction of magnetization of the magnet and the direction of the applied magnetizing field, moving the permanent magnet in the magnetizing field in at least a single plane through the angle 6 with said angle 6 ranging up to about 1-45", and ending such movement of the magnet in the magnetizing field with the predetermined direction of magnetization of the magnet substantially parallel to the direction of the magnetizing field.

3. A method according to claim 1 wherein said predetermined direction of magnetization is the magnetically preferred direction of magnetization.

d. A method according to claim 2 wherein the initial position of said magnet in said magnetizing field is at an angle 0 of substantially 0.

5. A method for increasing the coercive force of a permanent magnet in a given magnetizing field which comprises subjecting the magnet to the magnetizing field, the initial position of said'magnet in said magnetizing field being no greater than an angle 6 of the angle 6 being formed between a predetermined direction of the magnet and the direction of the applied magnetizing field, moving the permanent magnet in the magnetizing field in a plurality of planes through the angle 6 with said angle 0 ranging up to about :45, and ending such movement of the magnet in the magnetizing field with the predetermined direction direction of magnetization of the magnet substantially parallel to the direction of the magnetizing field.

6. A method according to claim ll wherein said permanent magnet material is a cobalt rare-earth compound.

7. A method according to claim 6 wherein said cobalt rareearth compound is a member of the group consisting of Co Y, C0,,Sm and Co M wherein M is cerium-rich misch metal.

8. A method according to claim ll wherein said permanent magnet material is a magnetically hard ferrite.

9. A method according to claim 8 wherein said magnetically hard ferrite is selected from thegroup consisting of barium ferrite, strontium ferrite and lead ferrite.

10. A method for increasing the coercive force of a permanent magnet in a given magnetizingfield which comprises subjecting the magnet to the magnetizing field, and causing relative angular motion between the magnet and the magnetizing field within an angle 6 of t45 between a predetermined direction of magnetization and the direction of the applied magnetizing field.

Claims

2. A method for increasing the coercive force of a permanent magnet in a given magnetizing field which comprises subjecting the magnet to the magnetizing field, the initial position of said magnet in said magnetizing field being no greater than an angle theta of + or - 45*, the angle theta being formed between a predetermined direction of magnetization of the magnet and the direction of the applied magnetizing field, moving the permanent magnet in the magnetizing field in at least a single plane through the angle theta with said angle theta ranging up to about + or - 45*, and ending such movement of the magnet in the magnetizing field with the predetermined direction of magnetization of the magnet substantially parallel to the direction of the magnetizing field.
3. A method according to claim 1 wherein said predetermined direction of magnetization is the magnetically preferred direction of magnetization.
4. A method according to claim 2 wherein the initial position of said magnet in said magnetizing field is at an angle theta of substantially 0*.
5. A method for increasing the coercive force of a permanent magnet in a given magnetizing field which comprises subjecting the magnet to the magnetizing field, the initial position of said magnet in said magnetizing field being no greater than an angle theta of + or - 45*, the angle theta being formed between a predetermined direction of the magnet and the direction of the applied magnetizing field, moving the permanent magnet in the magnetizing field in a plurality of planes through the angle theta with said angle theta ranging up to about + or - 45*, and ending such movement of the magnet in the magnetizing field with the predetermined direction direction of magnetization of the magnet substantially parallel to the direction of the magnetizing field.
6. A method according to claim 1 wherein said permanent magnet material is a cobalt rare-earth compound.
7. A method according to claim 6 wherein said cobalt rare-earth compound is a member of the group consisting of Co5Y, Co5Sm and Co5M wherein M is cerium-rich misch metal.
8. A method according to claim 1 wherein said permanent magnet material is a magnetically hard ferrite.
9. A method according to claim 8 wherein said magnetically hard ferrite is selected from the group consisting of barium ferrite, strontium ferrite and lead ferrite.
10. A method for increasing the coercive force of a permanent magnet in a given magnetizing field which comprises subjecting the magnet to the magnetizing field, and causing relative angular motion between the magnet and the magnetizing field within an angle theta of + or - 45* between a predetermined direction of magnetization and the direction of the applied magnetizing field.