Method for producing radially anisotropic multipolar solid magnet adapted to different waveform widths

Abstract

A method and device for producing a radially anisotropic multipolar solid magnet adapted to different waveform widths are provided. A mold core is removed from a mold for molding the magnet, and outer oriented poles, the number of which is the same as that of poles of the radially anisotropic multipolar solid cylindrical magnet, are arranged outside the mold. The width of a front end of a single outer oriented pole is determined according to the desired width of a single waveform of the radially anisotropic multipolar solid cylindrical magnet after being magnetized. The sum L of widths or arc lengths of front ends of all the outer oriented poles is less than 0.9πD, particularly less than 0.7πD, where D is the outer diameter of a mold sleeve. Magnetic particles in a mold cavity are rotated with the mold only during magnetization.

Claims

1. A method for molding a radially anisotropic multipolar solid cylindrical magnet adapted to waveforms of different widths, comprising following steps of: (1) preparing magnetic particles; (2) melting the magnetic particles and casting the magnetic particles in a vacuum furnace to obtain an ingot or a rapidly quenched ribbon; (3) crushing the ingot or treating the ribbon with a pulverizing method to obtain micron-sized magnetic particles; (4) preparing a cylindrical mold with a mold cavity; (5) mounting the mold in a magnetic field generation device and arranging, outside the prepared mold, outer oriented poles, the number of which is the same as that of poles of the radially anisotropic multipolar solid cylindrical magnet, wherein the width of a front end of a single outer oriented pole is determined according to the desired width of a single waveform of the radially anisotropic multipolar solid cylindrical magnet after being magnetized, the radial anisotropy is adjusted by adjusting the sum of widths or arc lengths of front ends of outer oriented poles arranged outside the mold, wherein the sum L of widths or arc lengths of front ends of all the outer oriented poles is less than 0.9πD, where D is an outer diameter of a mold sleeve; (6) filling the micron-sized magnetic particles in the mold cavity; (7) applying a first magnetic field and continuously rotating the mold and the magnetic particles in the mold cavity; (8) stopping the rotation of the mold and the micron-sized magnetic particles, applying a second magnetic field, wherein an intensity of the second magnetic field is lower than an intensity of the first magnetic field, the intensity of the first magnetic field being 1.5 to 3 times the intensity of the second magnetic field, applying an increased stress to the micron-sized magnetic particles in the mold cavity by an upper ram and a lower ram, and maintaining this stress for a certain period of time to obtain a blank; or, by keeping the lower ram unmoved, moving the upper ram down to apply an increased stress to the micron-sized magnetic particles in the mold cavity and maintaining this stress for a certain period of time; or, by keeping the upper ram unmoved, moving the lower ram up to apply an increased stress to the micron-sized magnetic particles in the mold cavity and maintaining this stress for a certain period of time; (9) when the micron-sized magnetic particles in the mold cavity cannot recover to an out-of-order state before orientation after leaving the oriented magnetic field, applying a third magnetic field wherein an intensity of the third magnetic field is 1 to 0.1 times the intensity of the second magnetic field, and continuously applying a stress by the rams until the blank has a desired density; (10) applying a fourth magnetic field to demagnetize the blank, wherein an intensity of the fourth magnetic field is 0.5 to 0.01 times the intensity of the second magnetic field; (11) stopping the application of stress, and demolding to obtain the blank; and (12) sintering and aging the blank to obtain the magnet.

2. The method according to claim 1, wherein the sum L of widths or arc lengths of front ends of all the outer oriented poles is less than 0.7πD, where D is the outer diameter of a mold sleeve.

3. The method according to claim 1, wherein the stress in the step (8) is 20 MPa to 200 MPa.

4. The method according to claim 3, wherein the stress in the step (8) is 50 MPa to 150 MPa.

5. The method according to claim 1, wherein, in the step (10), an alternating magnetic field is applied to demagnetize the blank in the mold cavity, wherein the alternating magnetic field alternates between a forward magnetic field and a reverse magnetic field.

6. The application in permanent magnetic motor rotors according to claim 1, wherein the magnet is configured to be used as a rotor of a high-precision micro-motor wherein the rotor has an inner diameter less than 3 mm.

7. The application in permanent magnetic motor rotors according to claim 1, wherein the magnet is configured to be used as a rotor of a high-precision micro-motor wherein the rotor has a diameter less than 3 mm.

8. The application in permanent magnetic motor rotors according to claim 1, wherein the magnet is mounted, as a component for providing a permanent magnetic field, on a motor shaft by forming a hole with a desired inner diameter in the center of the magnet.

9. A molding device using the method according to claim 1, comprising a mold, a magnetic field generation device, a rotating mechanism and a stress applying device by rams; the mold comprises a mold sleeve, a mold cavity, an upper ram and a lower ram; the magnetic field generation device comprises outer oriented poles, the number of which is the same as that of poles of a radially anisotropic multipolar solid cylindrical magnet and which are arranged outside the mold, wherein the width or arc length of the front end of a single outer oriented pole is determined according to the desired width of a single waveform of the radially anisotropic multipolar solid cylindrical magnet after being magnetized; the radial anisotropy is adjusted by adjusting the sum of widths or arc lengths of front ends of outer oriented poles arranged outside the mold, wherein the sum L of widths or arc lengths of front ends of all the outer oriented poles is less than 0.9πD, where D is an outer diameter of a mold sleeve, and the outer orientated poles are symmetrically arranged at equal intervals around the magnet within 360′; and the rotating mechanism enables anisotropic magnetic particles in the mold cavity to continuously rotate with the mold only during magnetization.

10. The molding device according to claim 9, wherein the sum L of widths or arc lengths of front ends of all the outer oriented poles is less than 0.7πD.

11. The method according to claim 1, wherein the magnetic particles comprise, by weight percentage: 29% to 31% of rare-earth Praseodymium+Neodymium (Pr+Nd), 0.5% to 5.0% of one or more of Dysprosium (Dy), Terbium (Tb), Holmium (Ho), 0.5% to 3% of Cobalt (Co), 0.95% to 1.15% of Boron (B), 0.5% to 2% of Niobium+Zirconium (Nb+Zr), 1.0% or less of Copper (Cu), 1.0% or less of Aluminum (Al), and the remaining of Iron (Fe) and impurities.

12. The method according to claim 11, wherein the step (12) comprises: (i) vacuumizing, in advance, a sintering furnace to below 10.sup.−2 Pa; (ii) heating the molded blank, while vacuumizing, to a sintering temperature of 1000° C. to 1120° C.; (iii) sintering the molded blank in a vacuum and maintaining the sintering temperature for between 30 minutes to 3 hours; (iv) feeding an inert gas and cooling; and (v) aging the molded blank at 400° C. to 600° C. for between 0.5 hours to 2 hours, or aging at 840° C. to 950° C. for between 0.5 hours to 1 hour and then aging at 400° C. to 600° C. for 0.5 hours to 1 hour to obtain the magnet.

13. The method according to claim 12, wherein in the step (8), four outer oriented poles are arranged outside of the prepared mold and the number of poles of the radially anisotropic multipolar solid cylindrical magnet is four.

14. The method according to claim 13, wherein the intensity of the first magnetic field is 3 KGs to 15 KGs, the intensity of the second magnetic field is 2 KGs to 10 KGs, the intensity of the third magnetic field is 1 KG to 5 KGs, and the intensity of the fourth magnetic field is 5 KGs to 0.01 KGs.

15. The method according to claim 14, wherein the intensity of the fourth magnetic field is 1 KG to 0.01 KGs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings illustrate one or more embodiments of the present disclosure and, together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment.

(2) FIG. 1 is a schematic view of preparation of a radially anisotropic solid cylindrical four-polar magnet according to the present disclosure (L<0.7πD);

(3) FIG. 2 is a schematic view of preparation of a radially anisotropic multipolar solid polyhedral magnet according to the present disclosure;

(4) FIG. 3 is a sectional view of preparation of a radially anisotropic multipolar solid cylindrical magnet according to the present disclosure; and

(5) FIG. 4 shows a magnetization waveform of the radially anisotropic solid cylindrical four-polar magnet prepared by a method according to the present disclosure (L<0.7πD);

(6) in which: 1: mold sleeve; 2: mold cavity; 3, 4, 7 and 8: magnetic poles; 5: upper ram; and, 6: lower ram.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

(7) The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.

(8) The present disclosure will be further described below in detail by specific implementations, and the protection scope of the present disclosure is not limited thereto.

Embodiment 1

(9) A method for manufacturing a radially anisotropic solid cylindrical four-polar sintered magnet adapted to different waveform widths is provided, including the following steps. (1) RFeB typed magnetic particles to be molded are prepared. The magnetic particles include the following specific components (wt %): 29% to 31% of rare-earth Pr+Nd, 0.5% to 5.0% of one or more of Dy, Tb, Ho and Tb, 0.5% to 3% of Co, 0.95% to 1.15% of B, 0.5% to 2% of Nb+Zr, 1.0% or less of Cu, 1.0% or less of Al, and the remaining of Fe and inevitable impurities. (2) The magnetic particles are melted and cast in a vacuum furnace to obtain an ingot or a rapidly-quenched ribbon. (3) The ingot is crushed or the rapidly-quenched ribbon is treated by conventional pulverizing methods such as coarse crushing and jet milling to obtain micron-sized magnetic particles. Preferably, the magnetic particles have an average particle size of less than 5.5 μm, preferably about 3.5 μm. (4) According to the desired shape and size of the magnet to be molded, a corresponding solid cylindrical magnet mold is designed and prepared (as shown in FIG. 1). The mold is made from a non-ferromagnetic material, ensuring that the magnetic field can go through the mold cavity from one side to the other side. The mold includes a mold sleeve 1, a mold cavity 2, an upper ram 5 and a lower ram 6, without a mold core. (5) The prepared molding mold is mounted in the magnetic field generation device. Poles 3, 4, 7 and 8 of the radially anisotropic multipolar solid cylindrical magnet are arranged around the mold at equal intervals. The sum L of widths or arc lengths of front ends of all the outer oriented poles is less than 0.9πD, preferably less than or equal to 0.7πD, where D is the outer diameter of the mold sleeve. (6) The magnetic particles prepared in the step (3) are filled in the mold cavity, and the upper ram 5 of the mold is moved to a position in the mold cavity at the same height as upper edge of the poles for the oriented magnetic field or a position slightly lower than the upper edge of the poles for the oriented magnetic field. Accordingly, it is ensured that the magnetic particles will not flow out of the mold cavity during the rotation of the mold and/or the magnetization by the magnetic field, and it is also ensured that the magnetic particles in the mold cavity have enough space to continuously rotate in the magnetic field, so that non-uniform magnetic performance resulted from the non-uniformity of the oriented magnetic field can be solved by the continuous rotation of the magnetic particles. (7) The magnetic field generation device is activated to generate an oriented magnetic field having an intensity of 3 KGs to 15 KGs, to fully magnetize the magnetic particles in the mold cavity. During magnetization, the mold is continuously rotated with the magnetic particles in the mold cavity. (8) The rotation of the mold and the magnetic particles is stopped, and a second magnetic field is applied. The intensity of this magnetic field is lower than that of the first magnetic field used during magnetization, and is 2 KGs to 10 KGs. A gradually increased stress is applied to the magnetic particles in the mold cavity by both the upper and lower rams 5, 6 until the stress reaches 20 MPa to 200 MPa, preferably 50 MPa to 120 MPa, and this stress is maintained for a certain period of time. The stress maintaining duration is determined according to the desired density of the blank, and is preferably 2 min to 2 h. Or, the lower ram is kept unmoved and the upper ram is moved down to apply an increased stress to the magnetic particles in the mold cavity, and this stress is maintained for a certain period of time. When the stress is increased to a level at which the stress is to be maintained, the frictional force f.sub.resistance between the anisotropic magnetic particles in the mold cavity is greater than the recovery force f.sub.recovery required for the recovery of the easy directions of magnetization of the magnetic particles from an in-order state to an out-of-order state but less than the orientation force f.sub.orientation to the anisotropic magnetic particles by the approximately two-dimensional magnetic field. At this time, 100% (by volume) of the magnetic particles in the mold cavity are radially anisotropic. When the magnetic particles cannot recover to the out-of-order state before orientation after leaving the oriented magnetic field, a third magnetic field having an intensity of 1 KGs to 5 KGs is applied. In this stage, the anisotropic magnetic particles in the mold cavity have been radially aligned along the oriented magnetic field. (9) A stress is continuously applied by the rams until the blank in the mold has a desired density, and a fourth magnetic field having an intensity of 5 KGs to 0.01 KGs (preferably 1 KGs to 0.01 KGs) is applied to demagnetize the molded blank. The fourth magnetic field is a reverse magnetic field or a forward/reverse alternating magnetic field. (10) The application of the stress is stopped, and demolding is performed to obtain a molded solid cylindrical blank. (11) The molded magnet blank is sintered and aged, specifically including steps of: (i) vacuumizing, in advance, a sintering furnace to below 10.sup.−2 Pa; (ii) heating, while vacuumizing, to a sintering temperature of 1000° C. to 1120° C.; (iii) sintering in vacuum and maintaining the temperature for 30 min to 3 h; (iv) feeding an inert gas (e.g., nitrogen) and cooling; and (v) aging at 400° C. to 600° C. for 0.5 h to 2 h, or aging at about 850° C. to 950° C. for 0.5 h to 1 h and then aging at 400° C. to 600° C. for 0.5 h to 1 h, to obtain a radially anisotropic solid cylindrical four-polar magnet.

(10) The VSM test shows that the magnetic energy product of the magnet prepared in this embodiment is generally increased by 3 MGOe to 8 MGOe in comparison to the magnet prepared by using the same steps and parameters but not rotating the magnetic particles during magnetization.

(11) FIG. 4 shows a magnetization waveform of four poles of the radially anisotropic solid cylindrical magnet produced in this embodiment. The surface magnetic flux of the magnetized poles is generally increased by 5% to 10%, or even above 15% for magnets with a certain diameter, with excellent magnetic performance.

Embodiment 2

(12) A radially anisotropic solid tetrahedral sintered magnet is manufactured by a process the same as that in Embodiment 1. This embodiment differs from Embodiment 1 in that a corresponding tetrahedral mold, without a mold core, is designed and prepared according to the desired size of the solid tetrahedral magnet to be molded in the step (4) (as shown in FIG. 2). By the steps (1) to (11), a radially anisotropic solid tetrahedral sintered magnet with excellent magnetic performance is obtained, with the surface magnetic flux of the magnetized poles being increased by above 8%.

Embodiment 3

(13) A radially anisotropic solid cylindrical bonded magnet is manufactured by a process the same as that in Embodiment 1. This embodiment differs from Embodiment 1 in that an adhesive is added in advance to the magnetic particles obtained in the step (6), and conventional heat treatment is performed in the step (11) to solidify the adhesive in the bonded magnet. In this way, a radially anisotropic solid cylindrical bonded magnet with excellent magnetic performance is obtained, with the surface magnetic flux of the magnetized poles being increased by above 6%.

(14) It is to be particularly noted that the present disclosure can also produce radially anisotropic oriented cylindrical or polyhedral magnets such as samarium cobalt, ferrite and bonded neodymium iron boron by changing the type of anisotropic magnetic particles in the mold cavity.

(15) The forgoing embodiments merely show preferred implementations of the present disclosure, and should not be interpreted as limiting the protection scope of the present disclosure. It is to be noted that various alterations, replacements and improvements may be made by a person of ordinary skill in the art without departing from the concept of the present disclosure, and these alterations, replacements and improvements shall fall into the protection scope of the present disclosure.