Method of making a magnetic material and fluidized bed mixer for making a magnetic material

Abstract

A fluidized bed mixer for combining a first powder material with a second powder material for manufacturing a magnet and a method of preparing the magnet using the fluidized bed mixer. The first powder material is an alloy powder containing neodymium (Nd), iron (Fe), and boron (B), and the second powder material is an alloy powder containing one or more of dysprosium (Dy) and terbium (Tb) or an elemental metal powder. The fluidized bed mixer includes a fluidized bed section at an upper portion of a mixing chamber, a cascade baffle system below the fluidized bed section, and a combined powder collection zone below the cascade baffle system. The fluidized bed mixer is configured to homogeneously combine the first powder material and the second powder material such that particles of the second powder material adhere to and cover an outer surface of particles of the first powder material.

Description

Technical Field

[0001] This disclosure relates to a method for preparing magnets for electric motors, and more specifically to a method for preparing magnetic materials using a fluidized bed mixer and a fluidized bed mixer for preparing magnetic materials. Background Technology

[0002] In an electric motor, current is transmitted through windings in the stator to generate a moving magnetic field. This moving magnetic field interacts with a rotor placed within the stator to generate torque that causes the rotor to rotate. Synchronous motors are commonly used in the propulsion systems of electric and hybrid vehicles. In a typical synchronous motor, the rotor uses permanent magnets to generate a constant magnetic field (CMF), which interacts with a rotating magnetic field (RMF) generated by the three-phase alternating current (AC) supplied to the field coils of the stator. The permanent magnets used in the rotor are typically formed from magnetic materials made of expensive rare-earth materials so that the permanent magnets have a sufficient magnetic field to maintain engagement with the RMF.

[0003] Therefore, while current methods for preparing permanent magnets have achieved their intended purpose, it is still necessary to ensure a homogeneous mixture of core and rare earth powders when preparing magnetic materials for permanent magnets, and to improve the productivity of such magnetic materials to meet the needs of compact electric motors. Summary of the Invention

[0004] According to several aspects, a method for preparing magnetic materials is disclosed. The method includes: mixing a first powder material and a second powder material in a fluidized bed mixer to form a combined powder material; grinding the combined powder material; and sintering the ground combined powder material into a solid structure. The first powder material includes neodymium (Nd), iron (Fe), and boron (B), and the second powder material includes one or more of dysprosium (Dy) and terbium (Tb). The combined powder material includes particles comprising a core and a surface, the core having Nd, Fe, and B, and the surface coated with one or more of Dy and Tb.

[0005] In an additional aspect of this disclosure, a first powder material is gravity-fed to the top of a fluidized bed mixer and a second powder material is sprayed into the fluidized bed mixer, such that the second powder material collides with and coats the surface of the first powder material.

[0006] In another aspect of this disclosure, the first powder material includes one of a positive charge and a negative charge, and the second powder material includes the other of a positive charge and a negative charge. A solvent can be sprayed onto the first and second powder materials in a fluidized bed mixer. Such solvent may include methanol, ethanol, kerosene, and / or gasoline.

[0007] In another aspect of this disclosure, the method further includes injecting an inert gas stream into a fluidized bed reactor, the inert gas stream being sufficient to keep the first and second powder materials suspended in the fluidized bed, but causing the combined powder material to fall from the fluidized bed. The combined powder material falling from the fluidized bed is homogenized by a cascaded baffle system.

[0008] In another aspect of this disclosure, the method further includes grinding the combined powder material exiting the cascaded baffle system in a rotary drum and ball mill. Solvents such as methanol, ethanol, kerosene, and / or gasoline may be added during the grinding process. The ground combined powder material may then be passed again through a fluidized bed mixer for drying with the assistance of a heated inert gas stream.

[0009] According to several aspects, a fluidized bed mixer for preparing magnetic materials is disclosed. The fluidized bed mixer includes a shell, a fluidized bed section, a cascaded baffle system, and a combined powder material collection area. The shell has an inner surface defining a mixing chamber, the fluidized bed section is located in the upper part of the mixing chamber, the cascaded baffle system is located in the middle part of the mixing chamber below the fluidized bed section, and the combined powder material collection area is located in the lower part of the mixing chamber below the cascaded baffle system.

[0010] In an additional aspect of this disclosure, the fluidized bed mixer further includes: a first powder inlet and at least one injection nozzle. The first powder inlet is configured to gravity feed a first powder material into the fluidized bed portion; the at least one injection nozzle is configured to inject a stream of second powder material into the fluidized bed portion, such that the second powder material collides with the first powder material to form a plurality of particles having a core of the first powder material and a surface coated with the second powder material.

[0011] In an additional aspect of this disclosure, the fluidized bed mixer further includes a gas inlet for conveying an inert gas stream to maintain the first and second powder materials suspended in the fluidized bed, while allowing the combined powder materials to fall out of the fluidized bed. The inert gas stream may be heated before entering the fluidized bed mixer.

[0012] In another aspect of this disclosure, a cascaded baffle system includes a plurality of baffles. Each baffle includes a first end attached to an inner surface of a wall and an opposing second end angled downward across the centerline A of the mixing chamber. The baffles are arranged in a decreasing alternating order such that a plurality of particles flow from the upper baffle to the lower baffle in a cascaded sequence. One or more perforations are made in the baffles.

[0013] In another aspect of this disclosure, the fluidized bed mixer further includes at least one inert gas inlet disposed between a pair of baffles and an inert gas outlet located above the fluidized bed portion.

[0014] According to several aspects, the fluidized bed mixer further includes: a first electrostatic sprayer and a second electrostatic sprayer. The first electrostatic sprayer is configured to impart a positive charge and a negative charge to a first powder material; the second electrostatic sprayer is configured to impart a positive charge and a negative charge to a second powder material.

[0015] Further applications will become apparent from the description provided herein. It should be understood that the specification and specific examples are for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0016] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0017] Figure 1 This is a schematic diagram of a fluidized bed mixer according to an exemplary embodiment;

[0018] Figure 2 This is a schematic diagram of a ball mill according to an exemplary embodiment;

[0019] Figure 3 This is a block diagram of a method for preparing magnetic materials according to an exemplary embodiment;

[0020] Figure 4A This is a schematic diagram of the powder mixture in the steps of the method according to an exemplary embodiment;

[0021] Figure 4B This is a schematic diagram of the powder mixture in another step of the method according to an exemplary embodiment; and

[0022] Figure 4C This is a schematic diagram of the powder mixture in another step of the method according to an exemplary embodiment. Detailed Implementation

[0023] The following description is merely exemplary in nature and is not intended to limit this disclosure, its application, or its use. Reference is made to the accompanying drawings, in which similar reference numerals denote corresponding parts in several figures. The drawings are not necessarily to scale, and certain features may be enlarged or minimized to show detail of particular features. The specific structural and functional details disclosed are not intended to be construed as limiting, but rather as a representative basis for teaching those skilled in the art how to practice the disclosed concepts.

[0024] Permanent magnets made from rare-earth materials possess higher energy density than most other magnets, thus enabling more compact and powerful electric motors. These rare-earth permanent magnets are also used in other automotive applications such as starters, small motors, alternators, sensors, instruments, and other applications requiring rotational torque. The manufacture of the magnetic material used in these permanent magnets involves combining a core powder material containing neodymium (Nd), iron (Fe), and boron (B) with a rare-earth powder material containing one or more of dysprosium (Dy) and terbium (Tb) in predetermined proportions to form a combined powder mixture. It is desired that the combined powder mixture results in a uniform distribution of rare-earth-containing powder material particles on the surface of the core powder material particles. The combined powder mixture is then mechanically ground and sintered to form the magnetic material.

[0025] Figure 1 A schematic diagram of a fluidized bed mixer 100 for combining a first powder material 101 and a second powder material 103 to manufacture a magnetic material suitable for use in permanent magnets of electric motors is shown. The fluidized bed mixer 100 is configured to homogeneously combine the first powder material 101 and the second powder material 103 such that particles of the second powder material 103 uniformly adhere to and cover the outer surface of the particles of the first powder material 101. The first powder material 101 is an alloy powder containing neodymium (Nd), iron (Fe), and boron (B), and the second powder material 103 is an alloy powder or elemental metal powder containing one or more of dysprosium (Dy) and terbium (Tb).

[0026] The fluidized bed mixer 100 includes a housing 102 having an inner surface 104 defining a mixing chamber 106 extending along a central axis A (also referred to as a centerline). The housing 102 includes a top wall 108, a bottom wall 110 spaced apart from the top wall 108, and side walls 112 connecting the top wall 108 to the bottom wall 110. The mixing chamber 106 includes a fluidized bed portion 114 located proximal to the top wall 108 in the upper portion 116 of the mixing chamber 106, a cascaded baffle system 118 located below the fluidized bed portion 114 in the middle portion 120 of the mixing chamber, and a combined powder material collection area located proximal to the bottom wall 110 in the lower portion 124 of the mixing chamber below the cascaded baffle system 118.

[0027] The fluidized bed mixer 100 further includes a first powder inlet 126 configured to gravity feed a first powder material 101 into a fluidized bed section 114 and at least one injection nozzle 128 configured to inject a second powder material 103 stream into the fluidized bed section 114. The first powder inlet 126 is located near the top wall 108. The at least one injection nozzle 128 is configured to inject the second powder material 103 stream using a compressed inert gas (e.g., nitrogen or argon). The second powder material 103 stream is injected into the fluidized bed section 114 such that the second powder material 103 stream collides with the first powder material 101 as it is gravity fed through the inlet 126. In the illustrated embodiment, a pair of injectors 128 inject the second powder material 103 stream such that the second powder material 103 intersects the path of the first powder material 101 at an angle of approximately 90 degrees.

[0028] Located below the fluidized bed section 114 relative to the direction of gravity is a cascaded baffle system 118 with multiple perforated plates 132. Each perforated plate includes a first end 134 extending from the inner surface 104 of the wall and an opposing second end 136 angled downward across the centerline A. The perforated plates are arranged such that the combined powder material 125 falling from the fluidized bed section 114 flows from the upper plate to the lower plate in a cascaded sequence. The combined powder material 125 flows through each plate in a cascaded sequence until the combined powder material settles on the bottom wall 110.

[0029] The fluidized bed mixer 100 further includes at least one inert gas inlet 140 and an inert gas outlet 142 located above the at least one inert gas inlet. The inert gas inlet 140 is configured to inject a compressed inert gas stream upward toward the fluidized bed portion 114 to hold the first powder material 101 and the second powder material 103 in the fluidized bed. In the illustrated embodiment, the inert gas inlet 140 is positioned between a pair of perforated plates. The compressed inert gas stream facilitates further mixing of the combined powder material 125 as it cascades down from the baffle system 118. The compressed inert gas stream may be preheated to aid in drying the combined powder material 125.

[0030] The compressed gas flow travels upward through alternating channels defined by alternating plates and through perforations 144 in the plates to the fluidized bed. The volume and velocity of the inert gas entering the mixing chamber through the inert gas inlet 140 are sufficient to fluidize the powder material above the baffle system 118 before it leaves the inert gas outlet 142.

[0031] Figure 2A schematic diagram of a ball mill 200 for manufacturing magnetic materials is shown. The magnetic materials can be used to prepare permanent magnets. The ball mill includes a rotating horizontal drum 202 partially filled with small steel balls 204. The drum 202 can be made of stainless steel. The balls 204 can be made of stainless steel and coated with alumina, silicon carbide, silicon nitride, or ceramic. As the drum 202 rotates, the balls 204 fall onto and grind the combined powder 206 extracted from a fluidized bed mixer 100, causing a second powder material 103 to uniformly coat the outer surface of the first powder material 101.

[0032] Figure 3 It is through the use of Figure 1 A block diagram of a method for preparing magnetic materials using a fluidized bed mixer 100. Method 300 begins at block 302.

[0033] Move from box 302 to box 304. In box 304, a first powder material 101 containing an alloy including neodymium (Nd), iron (Fe), and boron (B) is provided. A second powder material 103 containing an alloy or elemental metal including dysprosium (Dy) and terbium (Tb) is provided. Dy or Tb, or both, can be used as needed. When needed, the Dy to Tb ratio can be up to about 10. The first powder material 101 and the second powder material 103 each independently have a diameter ranging from about 1 micrometer (μm) to about 200 micrometers.

[0034] Moving from frame 304 to frame 306, the first powder material 101 is gravity-fed into the fluidized bed section 114 through the first powder material inlet 126. The second powder material 103 is sprayed into the fluidized bed section 114, causing it to intersect and collide with the first powder material 101 to form a composite powder material 125 having a core comprising the first powder material 101, the outer surface of which is coated with the second powder material 103. The first powder material 101 can be positively charged and the second powder material 103 negatively charged. Alternatively, the first powder material 101 can be negatively charged and the second powder material 103 positively charged. Compressed inert gas is injected upwards into the mixing chamber through the injection nozzle 128 to keep the first powder material 101 and the second powder material 103 suspended in the fluidized bed.

[0035] While the first powder material 101 and the second powder material 103 are held in the fluidized bed, the second powder material 103 collides with the first powder material 101, causing the second powder material 103 to coat the outer surface of the first powder material 101. The opposite charges of the first powder material 101 and the second powder material 103 facilitate the adhesion of the second powder material 103 to the outer surface of the first powder material 101. The volume, pressure, and velocity of the compressed inert gas flow are sufficient to keep the first powder material 101 and the second powder material 103 suspended in the fluidized bed, but cause the heavier combined powder material 125 to fall off the fluidized bed.

[0036] Figure 4A This is a schematic diagram of the powder mixture in step 306 of the method. Once the outer surface of the first powder material 101 is coated with the second powder material 103, the combined powder material 125 becomes heavy enough that it falls from the fluidized bed section 114 and flows downward through the baffle system 118 to the combined powder material collection area. Coating the surface of the first powder material 101 with the second powder material 103 by the fluidized bed mixer 100 provides a uniform distribution of the Dy or Tb coating on the Nd-Fe-B core powder material. The second powder material 103 forms a layer with a thickness of about 1 micrometer to about 100 micrometers.

[0037] Moving from frame 306 to frame 308, the combined powder material 125 is loaded into the ball mill along with steel balls. The powder mixture is then ground for the desired duration. The mill drum is operated at a speed of approximately 50 rpm to approximately 400 rpm (typically approximately 250 rpm). The grinding time is approximately 0.5 hours to approximately 12 hours. The type, particle size, and particle size distribution of the grinding balls to powder weight ratio are approximately 1:10 to approximately 20:1, with a typical ratio of approximately 5:1. Solvents can be used during the grinding process. Organic solvents such as methanol, ethanol, kerosene, and gasoline can be added during grinding. The combined powder material 125 is ground by being treated with a heated inert gas stream in a fluidized bed mixer, and the solvent is removed by heating after grinding. Figure 4B This is a diagram of the powder mixture in step 308 of the method after the grinding process.

[0038] Moving from frame 308 to frame 310, hot isostatic pressing (HIP) can be applied to the milled and dried composite powder material 125 to form a magnetic material. HIP involves simultaneously applying high temperature and pressure to metals and other materials for a specified time period to obtain solid parts for improving the mechanical properties of the metals and other materials. During the HIP process, a high-temperature furnace is enclosed in a pressure vessel. Temperature, pressure, and processing time are precisely controlled. These parts are heated in an inert gas (typically argon) that applies uniform isostatic pressure in all directions. Figure 4CThis is a schematic illustration of the powder mixture in block 310 of the method according to an exemplary embodiment. In an alternative embodiment, instead of HIP, the material can be hot-pressed in a mold.

[0039] The magnet moves from frame 310 to frame 312, where a permanent magnet is created from the magnetic material formed in frame 310.

[0040] Fluidized beds suspending alloy particles via an inert gas flow exhibit fluid-like properties. The benefits of using fluidized bed reactors include: 1) extremely high surface area contact between gas and solid per unit bed volume; 2) high relative velocity between the gas and the dispersed solid phase; 3) high degree of miscibility of the particle phases; and 4) frequent particle-particle and particle-wall collisions. All of these promote highly homogeneous mixing of two or more powders with different compositions, such as Nb-Fe-B based powders with Dy and Tb alloy powders.

[0041] Objects with a density higher than the buoyancy of a fluidized bed will sink, while objects with a density lower than the buoyancy of a fluidized bed will float. Therefore, a fluidized bed can be considered to exhibit the fluid behavior predicted by Archimedes' principle. A fluidized bed can be modified by changing the inert gas component, and powder materials with densities different from those in a fluidized bed can be made to sink or float by changing the fluid or solid components. In a fluidized bed, the contact between solid particles and the fluidizing medium (inert gas) is greatly enhanced.

[0042] The description in this disclosure is exemplary in nature only, and changes that do not depart from the general meaning of this disclosure are intended to fall within its scope. Such changes should not be considered as departing from the spirit and scope of this disclosure.

Claims

1. A method for preparing magnetic materials, comprising: A first powder material is gravity-fed to the top of a fluidized bed mixer, and a second powder material is sprayed into the fluidized bed mixer, such that the second powder material collides with the first powder material to form a combined powder material. The fluidized bed mixer includes a shell defining a mixing chamber, a fluidized bed portion located above the mixing chamber, and a cascaded baffle system located below the fluidized bed portion. The first powder material includes neodymium (Nd), iron (Fe), and boron (B), and the second powder material includes one or more of dysprosium (Dy) and terbium (Tb). An inert gas stream is injected into the fluidized bed mixer, the inert gas stream being sufficient to keep the first and second powder materials suspended in the fluidized bed, but causing the heavier combined powder material to fall from the fluidized bed into the cascaded baffle system, wherein the cascaded baffle system includes a plurality of baffles, each of the plurality of baffles including a first end attached to an inner surface of a sidewall of the housing and a opposing second end angled downward across the centerline of the mixing chamber, the plurality of baffles being arranged in a decreasing alternating order such that the combined powder material flows from the upper baffle to the lower baffle in a cascaded sequence to homogenize the combined powder material; The method of injecting an inert gas stream into the fluidized bed mixer further includes: injecting a compressed inert gas stream upward toward the fluidized bed portion from an inert gas inlet disposed between at least one pair of the plurality of baffles to further mix the combined powder material falling in cascades along the plurality of baffles; Grinding the combined powder material; and The ground composite powder materials are sintered into a solid structure.

2. The method according to claim 1, wherein the combined powder material comprises alloy particles, the alloy particles comprising a particle core and a particle surface, the particle core having Nd, Fe and B, and the particle surface being coated with one or more of Dy and Tb.

3. The method according to claim 1, wherein the first powder material comprises one of a positive charge and a negative charge, and the second powder material comprises the other of the positive charge and the negative charge.

4. The method of claim 3, further comprising spraying a solvent onto the first powder material and the second powder material in the fluidized bed mixer; the solvent comprising at least one of methanol, ethanol, kerosene and gasoline.

5. The method of claim 1, further comprising: The combined powder material leaving the cascaded baffle system is ground in a rotary drum and ball mill; and a solvent is sprayed onto the combined powder material during grinding.

6. The method of claim 5, further comprising a combined powder material that has been dried and ground in the fluidized bed mixer prior to sintering.

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