Abstract
A continuous method of manufacturing permanent magnets and the permanent magnets created thereby. A fine powder is created from a combination of magnetic metals. The powder (a metal alloy) is placed in a non-magnetic container of any desired shape which could be, for example, a tube. The metal alloy and tube are swaged while a magnetic field is applied. Once swaging is complete, the metal alloy and tube are sintered and then cooled. Instead of sintering, a bonding agent can mixed into the powder. Following cooling, the metal alloy is magnetized by placing it between poles of powerful electromagnets with the desired field direction. The process of the invention enables mass-produced, cost-effective PM products, which are more robust, easily assembled into products, enables new “wire like” shapes with arbitrary magnetization direction. The process enables mass production of permanent magnets of any desired cross section, produces permanent magnets continuously that may be cut to any length, and may, in an embodiment, result in directional magnets.
Claims
1. A method of continuously manufacturing a permanent powder-in-tube magnet, comprising: heating a plurality of magnetic metals to their melting point under vacuum to create a metal alloy; allowing the metal alloy to cool and solidify; grinding the metal alloy into a powder; placing the metal alloy powder into a tube; applying a magnetic field to the metal alloy while continuously compressing the metal alloy powder and the tube as the metal alloy powder and tube are being translated, such that no magnet mold is required to form the powder-in-tube magnet; sintering the metal alloy and the tube; cooling the metal alloy and the tube; and magnetizing the metal alloy within the tube, forming a permanent magnet having a surrounding tube, that does not require annealing, machining or surface coating.
2. The method of claim 1, wherein the plurality of magnetic metals are further defined to be neodymium, iron and boron.
3. The method of claim 1, wherein compressing the metal alloy comprises swaging the metal alloy and the tube.
4. The method of claim 1, wherein the tube comprises a non-magnetic metal.
5. The method of claim 1, wherein magnetizing the metal alloy comprises: placing the metal alloy between poles of an electromagnet; and energizing the electromagnet.
6. The method of claim 1, further comprising the step of aligning the field direction of the electromagnet such that it produces a desired magnetization direction of the permanent magnet.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating the preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings:
(2) FIG. 1 is a flowchart of a conventional method of manufacturing a permanent magnet.
(3) FIG. 2 is a flowchart of a method of manufacturing a permanent magnet according to an embodiment of the present invention.
(4) FIGS. 3A and 3B are a cross-sectional view (3A) and a perspective view (3B) of a cylindrical tube for use with embodiments of the present invention.
(5) FIGS. 4A and 4B are a cross-sectional view (4A) and a perspective view (4B) of a rectangular prism-shaped tube for use with embodiments of the present invention.
(6) FIGS. 5A and 5B are a cross-sectional view (5A) and a perspective view (5B) of a square prism-shaped tube for use with embodiments of the present invention.
(7) FIGS. 6A and 6B depict perspective views traditional of a permanent magnet (6A) and a traditional permanent magnet array (6B), for the purpose of demonstrating the disadvantage thereof.
(8) FIG. 6C depicts a perspective view of an exemplary pie-shaped cross section permanent magnet wire (PM Wire) produced by the process of the invention as might be used to construct a Halbach array.
(9) FIG. 7 depicts a perspective view of a dual rotor machine using Halbach arrays constructed from PM Wire produced by the process of the invention.
(10) FIG. 8 depicts a pictorial diagram of the steps for manufacturing PM Wire of the invention.
(11) In the figures, like item callouts refer to like elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(12) A detailed description of the embodiments for a method of manufacturing permanent magnets will now be presented with reference to FIGS. 2 through 8. One of skill in the art will recognize that these embodiments are not intended to be limitations on the scope, and that modifications are possible without departing from the spirit thereof. In certain instances, well-known methods, procedures and components have not been described in detail.
(13) As used herein, “tube” includes within its definition any desired shape enclosing an interior volume.
(14) As used herein, “PM Wire” is used to refer to any permanent magnet shape or configuration produced by the inventive method, and is therefore not limited only to “wire” constructs or shapes.
(15) Embodiments of the manufacturing process disclosed herein overcome some of the inherent issues with the conventional manufacturing method and, in particular, enable cost effective manufacturing of complex magnetic arrays, such as Halbach arrays. Embodiments of the manufacturing process enable mass production of permanent magnets that are more mechanically robust than conventional permanent magnets and more easily assembled into complex arrays. In some cases, permanent magnets created can be bent into arcs.
(16) An exemplary embodiment of the inventive process for manufacturing a permanent magnet is shown and described with reference to FIG. 2. An exemplary list of magnetic metals that may be used in the apparatus and method are neodymium, iron, cobalt, boron, gadolinium, dysprosium and alloys such as steel that contain ferromagnetic metals, alone in any combination. These identified magnetic metals listed of should not be taken as limiting. Any magnetic material can be used in the process of the invention to produce permanent magnets of a desired magnetic material or combination of materials. In particular, various novel magnetic materials, currently under development, which are not based on rare-earth materials, can be used.
(17) Referring now to FIG. 2, in a first, step 100, powdered metals are created. To do this, the appropriate amounts of magnetic materials such as, for example and not by way of limitation, neodymium, iron and boron are combined and heated to their melting point under vacuum. The vacuum prevents any chemical reaction between air and the melting materials that might contaminate the final metal alloy. Once the metal alloy has cooled and solidified, it is broken up and crushed into small pieces, which are ground into a fine powder creating a powdered metal alloy.
(18) Still referring to FIG. 2, in a second step 101, pressure is applied to the powdered metal alloy. In this process, the powder is inserted into a tube or other-shaped container of a non-magnetic metal depicted as 001 in FIG. 6C. The non-magnetic metal tube or other-shaped container may be, for example, stainless steel or titanium. The material has to be non-magnetic to allow unhampered penetration of magnetic flux through the tube or other shaped container wall. While the powder is being exposed to a magnetic field to align crystals, swaging is used to compress the powder. The resulting shape can vary depending on the swaging process. Exemplary resulting tube shapes include cylindrical, rectangular prism, square prism, and pie-shaped. Cross-sectional and perspective views of a cylindrical tube are shown in FIGS. 3A and 3B, respectively. Cross-sectional and perspective views of a rectangular prism-shaped tube are shown in FIGS. 4A and 4B, respectively. Cross-sectional and perspective views of a square prism-shaped tube are shown in FIGS. 5A and 5B, respectively. The outer dimensions of the original tube or other-shaped container can vary depending on the desired diameter of the resulting tubes after swaging. The length of the tube can also vary and can be significant. For example, a resulting tube may be one meter long and have a diameter or cross-sectional length of two centimeters or more. Even tubes with very small diameter that can be described as wires are producible by the process of the invention. While the enclosed volume is described herein as a tube for convenience, the container of the invention may take any desired shape as long as it has an interior volume able to contain the powdered metal alloy as described herein.
(19) Still referring to FIG. 2, in a third step 102, once compressed, the powdered metal alloy is heated. The powdered metal alloy, still in its tube, is sintered with the appropriate temperature profile. The alloy is then slowly cooled down.
(20) As an alternative to the sintering process of steps 102 and 202, a bonding agent, such as a chemical bonding agent, epoxy, or the like may be mixed with the powdered metal alloy. The bonding agent is then cured, producing a permanent magnet of a desired shape that is ready for final finishing.
(21) Still referring to FIG. 2, after cool-down, the alloy, still in its tube or other-shaped container (FIG. 2), is magnetized 103. For most applications the magnetization direction will be chosen to be perpendicular to the tube axis. For shorter tube sections, the magnetization direction may also be along the tube axis.
(22) With this powder-in-tube process depicted in FIG. 2, no annealing and machining of the sintered alloy is needed, and no further surface coating, as required for conventional permanent magnets, is required. This is but one of many reasons the inventive method and product produced by the method is an improvement in the state of the art of permanent method manufacture. It can be seen that the inventive method of producing permanent magnets of FIG. 2 comprises fewer steps and is therefore more efficient than the conventional method of producing permanent magnets depicted in FIG. 1.
(23) Using the resulting tubes of permanent magnets, complex assemblies such as, for example, Halbach arrays can be produced. The surrounding support tube, or other-shaped container, provides mechanical strength, which aids in the handling of the permanent magnets created using the powder-in-tube process. Included within the scope of the invention are Halbach arrays comprising permanent magnets produced by the processes and methods described herein.
(24) For powder-in-tube magnets with large aspect ratios of tube length to diameter, for example a length of 500 mm and an outer tube diameter of 5 mm, or wires, a slight bending of the final magnet is possible, creating an arc.
(25) Referring now to FIGS. 6A, 6B, 6C, and 7, an application of the inventive method for producing a permanent magnet which results in a permanent magnet wire (PM-Wire) of pie-shaped cross section is depicted. It is to be understood that the example PM Wire cross section depicted in these figures is one of many cross sections of the PM Wire that may be produced by the process of the invention and that numerous other cross sectional shapes are within the scope of the invention. Further, the exemplary dual Halbach array application depicted in FIG. 7 is but one of many applications of the process and permanent magnet(s) that may be produced by the process. The exemplary application depicted in FIG. 7 is a dual-Halbach array electric motor that may be used in electric engines for aircraft propulsion. One advantage of the pie-shaped PM Wire produced by the process of the invention, as depicted in FIGS. 6C and 7, is the enablement of smaller diameter electric engines producing magnetic field strengths of up to 2.0 tesla, or greater. This is especially true when stator 006 is a double-helix or direct double helix conductor configuration as described in U.S. Pat. Nos. 7,889,042, 7,990,247, or 8,424,193, each of which are incorporated herein by reference in their entirety. To demonstrate the advantage over the prior art, a permanent magnet A produced by traditional means is shown for reference in FIG. 6A, and an array of permanent pie-shaped traditional magnets A such as may be used to form a segment of a Halbach array is shown for reference in FIG. 6B. In contrast to these traditional permanent magnets, a pie-shaped cross section PM Wire produced by the continuous process may be defined as having an inner radius R2′ and outer radius R1′ of the invention is depicted in FIG. 6C. The outer radius R1′ of the PM Wire may be, for example much less than the outer diameter R1 of the traditional permanent magnet, allowing for a smaller diameter engine. Also, the length L′ of the PM Wire produced by the process of the invention may much longer than the length L of a traditional permanent magnet A because the process of the invention is continuous, allowing less expensive and much easier construction of a longer engine comprising, for example, dual coaxial Halbach arrays (or a single Halbach array, if desired) because the for assembling together a plurality of pie-shaped permanent magnets along the axial direction, as would be required to construct a motor of length L′ using traditional pie-shaped permanent magnets as shown in FIG. 6B, is eliminated. This is yet a further distinct advantage of the process of the invention—the elimination of the need to assemble a plurality of traditional permanent magnets in the longitudinal direction in order to construct a Halbach array of desired length L′ as shown in FIG. 6B. Assembly of such a plurality of traditional magnets A into an array forming a long pie-shaped magnet is difficult, expensive, and requires special tooling because of the magnetic forces acting on the individual magnets A. In contrast, by using pie-shaped PM Wire produced by the process of the invention, the need for this assembly tooling is eliminated because the pie-shaped PM Wire may be produced and cut to the desired length, and the individual pie-shaped PM Wire segments of desired length are easily assembled together and the tubes may be affixed by any mechanical means known in the art. For example, the pie-shaped PM Wire segments may be assembled into place and welded together using known fabrication techniques such as electron beam welding. If the Curie temperature can be exceeded in the welding process the PM Wires must be glued together. The result is lower cost and higher speed fabrication and assembly. The sintered, magnetized powdered metal alloy 002 is contained with the pie-shaped tube 001 as shown in FIG. 6C.
(26) In FIG. 7, an outer Halbach array comprises a plurality of PM Wire segments 003, and an inner Halbach array comprises a plurality of pie shaped PM Wire segments 004. The two Halbach arrays, the outer shell, stator 006 and engine shaft 005 are coaxial with the longitudinal axis of the engine.
(27) Referring now to FIG. 8, the steps of an exemplary embodiment of the process for producing PM Wire are pictorially depicted. In the embodiment shown, step 101 comprises placing the powdered metal alloy, such as, for example, NdFeB powder 300, into a tube of any desired cross sectional shape or length 301. The tube with powdered metal alloy inside is then drawn through a die 302 and subsequently swaged 303 and pre-magnetized 304. Then, in step 102, the powder-in-tube is sintered 102 and magnetized with powerful electromagnets 103, producing a permanent magnet of a desired cross sectional shape and desired magnetization.
(28) Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.
(29) Within the scope of the invention are both the processes and methods described herein and the products produced thereby.
