Rare earth magnet, methods for its manufacture and use

Abstract

The invention relates to a rare-earth magnet with the following composition: + 96 to 99 wt% magnetic powder with the composition: - 17-18 wt% neodymium (Nd) - 5-6 wt% praseodymium (Pr) - 1-8 wt% Lanthanum (La) - 0.5-1.5 wt% boron (B) - 1-2 wt% Zircon (Zr) - Remaining amount: Iron (Fe) + 1 to 4 wt% binder + 0.05 to 0.1 wt% additives

Description

[0001] The invention relates to a rare earth magnet, a method for its production and its use.

[0002] Rare-earth magnets, particularly neodymium magnets, are often used for permanent-magnet spindle motors. These are permanent magnets made from an alloy of neodymium, iron, and boron, forming a tetragonal crystal structure Nd2Fe14B. Neodymium magnets are used in many applications in modern products that require strong permanent magnets, such as electric motors, hard disk drives, and magnetic fasteners.

[0003] Compared to conventional ferrite magnets or other rare-earth magnet materials, such as samarium cobalt magnets (SmCo), neodymium magnet material has a very high remanence (Br), coercive field strength (Hci), and magnetic energy density (BHmax). Remanence describes the strength of the magnetic field, coercive field strength describes the material's resistance to demagnetization, and energy density describes the power that can be extracted from the material. Neodymium magnets are manufactured using sintering processes from traditional powder metallurgy or the bonded magnet process. During the sintering process, the raw materials are melted in a furnace, poured into a mold, and cooled. The resulting blocks are pulverized and ground; the powder is then sintered into dense blocks. The blocks are heat-treated, cut to shape, surface-treated, and magnetized.In the bonded magnet process, a powder is made from a NdFeB alloy, mixed with a polymer and formed into bonded magnets either by pressure die casting or injection molding.

[0004] Neodymium magnets have a higher remanence, higher coercivity, and higher energy product, but often a lower Curie temperature than other magnet types, such as samarium cobalt (SmCo) magnets. Furthermore, neodymium has a negative coefficient, meaning that the coercivity and magnetic energy density decrease with increasing temperature.

[0005] Neodymium-iron-boron magnets have a high coercivity at room temperature, but from about 90°C, the coercivity decreases noticeably up to the Curie temperature (about 320°C). This drop in coercivity leads to a significant reduction in the magnet's magnetization with increasing temperature. To reduce the temperature-induced decrease in magnetization, it is known to add dysprosium (Dy) or terbium (Tb) to the NdFeB alloy, although this increases the magnet's cost even further.

[0006] The object of the invention is to provide a rare earth magnet suitable for applications in a temperature range from -40°C to +110°C. This object is achieved by a rare earth magnet having the features of patent claim 1.

[0007] A method for its production is specified in claim 6.

[0008] A use of such a magnet is claimed in claims 9 and 10.

[0009] A spindle motor with such a rare earth magnet is the subject of patent claim 11.

[0010] The rare earth magnet according to the invention has the following composition: + 96 to 99 wt% magnetic powder + 1 to 4 wt% binder + 0.05 to 0.1 wt% additives

[0011] The magnetic powder used has the following composition: • 17-18 wt% neodymium (Nd) • 5-6 wt% praseodymium (Pr) • 1-8 wt% lanthanum (La) • 0.5-1.5 wt% boron (B) • 1-2 wt% zirconium (Zr) • Residual amount: Iron (Fe)

[0012] The advantage of the magnetic powder according to the invention is its higher temperature resistance, as at high temperatures above 90°C, the coercive field strength and magnetization decrease significantly more slowly than with conventional neodymium magnets. Therefore, these magnets are particularly suitable for applications with a wide temperature range from -40°C to +110°C.

[0013] In addition, the magnets are cheaper to manufacture than pure NeFeB magnets, as the rare earth elements lanthanum and praseodymium are cheaper to procure than neodymium. The reduced proportion of neodymium in the magnet alloy leads to cost reduction. An epoxy resin is preferably used as a binder. A lubricant / sliding agent may be included as an additional additive.

[0014] After pressing and heat treatment, the finished magnet material is preferably coated with a corrosion-resistant coating with a thickness of 10 to 30 micrometers. An epoxy resin, for example, can be used as a corrosion-resistant coating.

[0015] The inventive method for producing the rare earth magnet comprises the following steps: - Mixing the magnetic powder with a binder - Pressing the mixture into a mold - Heat treatment of the pressed magnet material at 140°C to 190°C for 10-40 minutes and - Magnetizing the pressed magnetic material.

[0016] Preferably, an additive in the form of a lubricant / lubricant can be added to the mixture before pressing.

[0017] After heat treatment, the formed magnet material can be protected by applying a corrosion-resistant coating.

[0018] The magnets produced are particularly intended for use in the permanent magnetic excitation of a spindle motor.

[0019] The invention is explained in more detail below using exemplary embodiments with reference to the drawing figures, wherein further features and advantages of the invention are described and illustrated. Fig. Figure 1 shows a flow chart of a manufacturing process for plastic bonded pressed magnets. Fig. 2 schematically shows a compression molding device for pressing the plastic-bonded magnetic material mixture. Fig. 3 shows a section through a first embodiment of a spindle motor with a magnet according to the invention. Fig. 4 shows a section through a second embodiment of a spindle motor with a magnet according to the invention. Fig. 5 shows a section through a third embodiment of a spindle motor with a magnet according to the invention.

[0020] In Fig. Figure 1 shows a schematic flow diagram of the manufacturing process of the magnets according to the invention.

[0021] In the first process steps 100, 101, and 102, magnetic powder, epoxy resin, and additives, such as lubricants, are provided. The magnetic powder consists of an alloy of 17-18 wt% neodymium (Nd), 5-6 wt% praseodymium (Pr), 1-8 wt% lanthanum (La), 0.5-1.5 wt% boron (B), 1-2 wt% zirconium (Zr), and the remainder iron (Fe). The alloy is formed into ingots, which are ground into magnetic powder.

[0022] In step 103, the provided components 100, 101, 102 are mixed and kneaded.

[0023] In step 104, the magnetic material mixture is pressed into the desired shape in a compression molding device.

[0024] In the next step 105, the pressed magnet material is heat-cured in an oven at a temperature of 140°C to 190°C for a period of 15 to 35 minutes.

[0025] In a next step 106, the pressed and baked compact is cleaned if necessary and its shape is finely machined.

[0026] In a subsequent step 107, the finished compact is provided with an anti-corrosive coating, for example by means of galvanic deposition or by means of a spraying process or in an immersion bath.

[0027] After a test 108 of the coated component, magnetization takes place in step 109, after which the finished plastic-bonded and pressed rare earth magnet is obtained in step 110.

[0028] Fig. 2 schematically shows a compression molding device 200 with a lower part 201 and an upper part 203.

[0029] A mixture 205 of magnetic powder, binder, and additives is introduced into a mold 206 and pressed into a desired shape by means of movable lower and upper punches 202, 204. After compression molding, the compact is heat-treated, which is carried out in the mold equipped with a heater or in a separate furnace.

[0030] The magnetic powder is preferably embedded in a thermosetting plastic matrix. Epoxy resin, for example, is used as the plastic. The magnetic material is pressed axially in the compression molding device 200. Due to the very high filler content, up to 97% magnetic powder (mass percent), significantly higher magnetic values ​​can be achieved compared to sintered magnets. The tools for compression molding are simpler and less expensive than those for injection-molded magnets.

[0031] In contrast to sintered magnets, plastic-bonded, pressed magnets can be manufactured with much more delicate geometries. For example, thin-walled rings with a diameter of 27 × 24 × 30 mm and diameter tolerances of only approximately ±0.05 mm can be produced. Typically, no further machining is required afterward. However, for particularly stringent requirements, the magnets can also be ground to tighter tolerances. Fig. 3 shows a section through a spindle motor with a fluid dynamic bearing system in which the plastic-bonded and pressed rare earth magnet 1 is used.

[0032] The spindle motor comprises a motor base 6 on which the motor components are mounted. A sleeve 8 is held in a cylindrical opening of the motor base 6, into which a bearing bush 4 is pressed and / or glued. A shaft 5 is rotatably mounted in the bearing bush 4, which shaft has an annular pressure plate 7 at one end. The pressure plate 7 is arranged in a space between the bearing bush 4, the sleeve 8, and a cover 9 that tightly seals the sleeve 8, and can rotate freely together with the shaft 5 in the space.

[0033] Between the surface of the shaft 5 and the bearing bush 4 remains a bearing gap 14 a few micrometers wide, which is filled with a bearing fluid and whose upper end is sealed by means of a capillary sealing gap 15.

[0034] The bearing gap 14 filled with bearing fluid continues between the surfaces of the pressure plate 7 and the bearing bush 4, sleeve 8 and cover 9.

[0035] The bearing bush 4 and the shaft 5 form two axially spaced fluid dynamic radial bearings 10, 11, which have bearing groove structures arranged on the bearing bush and / or the shaft 4, which generate a hydrodynamic pressure in the bearing gap 14 when the shaft 5 rotates in the bearing bush 4.

[0036] The two end faces of the pressure plate 7 form, with opposite end faces of the bearing bush 4 and the cover 9, fluid-dynamic axial bearings 12, 13, the bearing surfaces of which also have bearing groove structures which generate a hydrodynamic pressure in the bearing gap 14 when the pressure plate 7 rotates.

[0037] A hub 3, which forms the rotor component of the spindle motor, is attached to the free end of the shaft 5. The rare earth magnet 1 is arranged on an inner circumferential surface of the hub 3. If the hub 3 is made of a non-magnetic material, such as aluminum or plastic, a return plate 16 can be arranged on the magnet 1.

[0038] Radially opposite the magnet 1 there is an electric stator 2 with windings which is attached to the motor base 6.

[0039] The height of the spindle motor is preferably between 19 mm and 25 mm. The diameter of the hub 3 is preferably approximately 30 mm.

[0040] Fig. 4 shows a spindle motor with a fluid dynamic bearing system, with a fixed shaft 5 and a bearing bush 4 rotatably mounted on the shaft 5. The components and the functionality correspond to the spindle motor of Fig. 3.

[0041] The shaft 5 with the pressure plate 7 is non-rotatably mounted in the motor base 6. The bearing bush 4 rotates around the shaft 5 together with the hub 3 attached to it and is stabilized by two fluid-dynamic radial bearings 10, 11 and two fluid-dynamic axial bearings 12, 13. The neodymium magnet 1 according to the invention is attached directly to the hub 3, which in this embodiment is made of steel, so a separate magnetic return path is not necessary.

[0042] Fig. 5 shows a spindle motor with a similar structure as in Fig. 4, with the difference that here two rolling bearings 40 are used as the bearing system, which absorb the radial and axial forces. The hub 3 is rotatably mounted directly on the shaft 5 by means of the two rolling bearings 40. No bearing bushing or thrust plate is required, as is the case with a fluid-dynamic bearing system.

[0043] A special feature of the spindle motors in the Fig. 4 and Fig. 5 is the low height Lm of the magnet system, consisting of stator 2 and magnet 1, compared to the height Lh of hub 3. The height Lm of the magnet system is preferably less than 50% of the height Lh of hub 3. The height Lh of hub 3 and its diameter are preferably 25 mm or less. For larger spindle motors, the height Lh of hub 3 and its diameter can also be up to 40 mm. List of reference symbols 1 magnet 2 stator with windings 3 Hub 4 bearing bush 5 Wave 6 Motor base 7 printing plate 8 sleeve 9 Cover 10 fluid dynamic radial bearing 11 fluid dynamic radial bearing 12 fluid dynamic thrust bearing13 fluid dynamic thrust bearing 14 Bearing gap 15 Sealing gap 16 return plate 40 rolling bearings 100 - 110 process steps 200 compression molding device 201 lower part 202 lower stamp 203 Top 204 upper stamp 205 Magnetic powder mixture 206 press mold Lh Hub height Lm height of the magnet system

Claims

[1] Rare earth magnet with the following composition + 96 to 99 wt% magnetic powder with the composition: - 17-18 wt% neodymium (Nd) - 5-6 wt% praseodymium (Pr) - 1-8 wt% lanthanum (La) - 0.5-1.5 wt% boron (B) - 1-2 wt% zirconium (Zr) - Residual quantity: Iron (Fe) + 1 to 4 wt% binder, + 0.05 to 0.1 wt% additives. [2] Rare earth magnet according to claim 1, characterized by that the binder comprises an epoxy resin. [3] Rare earth magnet according to claim 1 or 2, characterized by that the additive includes a lubricant. [4] Rare earth magnet according to one of claims 1 to 3, characterized by that it has a corrosion-resistant coating with a coating thickness of 10 to 30 micrometers. [5] Rare earth magnet according to claim 4, characterized by that the corrosion-resistant coating comprises an epoxy resin. [6] A method for producing the rare earth magnet (110) according to any one of claims 1 to 5, characterized by following steps: - Mixing (103) the magnetic powder (100) with a binder (101) - Pressing (104) the mixture in a mold (206) - Heat treatment (105) of the pressed magnet material at 140°C to 190°C for 10-40 minutes - Magnetizing (109) the pressed magnetic material. [7] Method according to claim 6, characterized by that an additive (102) in the form of a lubricant is added to the mixture before pressing. [8] Method according to claim 6 or 7, characterized by that after the heat treatment (105) a corrosion-resistant coating (107) is applied to the pressed material. [9] Use of the rare earth magnet according to one of claims 1 to 5 for the permanent magnetic excitation of a spindle motor. [10] Use of the rare earth magnet (1, 110) produced by the method according to one of claims 6 to 8 for the permanent magnetic excitation of a spindle motor. [11] Spindle motor with a rare earth magnet (1, 110) for permanent magnetic excitation of the spindle motor, characterized by that the height (Lm) of the magnet system is preferably less than 50% of the height (Lh) of the hub (3). [12] Spindle motor according to claim 11, characterized by that the height (Lh) of the hub (3) and the diameter of the hub (3) are each 25 mm or less. [13] Spindle motor according to one of claims 10 or 11, characterized by that the spindle motor has a rotor component and a stator (2), wherein the rotor component of the spindle motor is mounted relative to the stator (2) of the spindle motor by at least one fluid-dynamic radial bearing (10, 11) and by at least one fluid-dynamic axial bearing (12, 13).

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