A method for recycling neodymium (Nd), iron (Fe), and boron (B) (NdFeB) type magnets, an anisotropic powder obtained from the recycling, and a method for manufacturing a permanent magnet from the powder.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- マグ リーソース
- Filing Date
- 2022-05-06
- Publication Date
- 2026-06-05
Smart Images
Figure 0007870789000001 
Figure 0007870789000002 
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Abstract
Description
[Technical Field]
[0001] This invention relates to the field of recycling rare-earth permanent magnets. In particular, this invention relates to powders obtained from the recycling of neodymium magnets (of type NdFeB), and to recycling methods for obtaining said powders. This invention also relates to a method for manufacturing NdFeB permanent magnets from said powders. [Background technology]
[0002] Resources of rare earth metals (especially neodymium (Nd)) for the manufacture of permanent magnets with high residual magnetism and coercivity are limited, and demand for these magnets is expected to increase significantly in the coming years, as they are useful in many electrical and electronic devices, as well as in emerging fields such as hybrid or electric vehicles (motors) and wind turbines (generators).
[0003] NdFeB magnets are the most commonly used rare-earth permanent magnets. They are primarily manufactured by sintering processes (solid magnets), or by injection molding or compression molding processes, the latter involving a polymer binder between NdFeB material particles (bonded magnets). Additive manufacturing techniques are also beginning to be implemented to produce NdFeB magnets that have strong flexibility in the shape of the magnetic object, regardless of whether they are solid or polymer-bonded.
[0004] To address the problem of rare earth resources, particularly neodymium, several methods have been proposed for recycling NdFeB permanent solid magnets at the end of their lifespan. In particular, European Patent No. 2646584 describes a method comprising exposing an assembly containing an NdFeB magnet to a decrepitation process known to disintegrate the magnet, and then separating the resulting NdFeB powder from the rest of the assembly by sieving the assembly through a rotating porous container (where the powder, rather than the heavier parts of the whole, is discharged through the pores).
[0005] Starting from this type of method, it remains important to improve the recycling process to streamline it while maintaining environmental harmony (simplifying the process, limiting the time required, and achieving a robust, reliable, and safe foundation). Furthermore, it is considered necessary to optimize the properties of the powder obtained at the end of the recycling process to facilitate and enhance the performance of new permanent NdFeB magnets from this recycled powder. [Overview of the Initiative] [Problems that the invention aims to solve]
[0006] The present invention addresses the above-mentioned problems. The present invention relates in particular to a method for recycling reliable NdFeB solid magnets, and to an anisotropic and coercive powder obtained from this method, which is particularly suitable for the manufacture of new, powerful NdFeB magnets by additive manufacturing. [Means for solving the problem]
[0007] The present invention relates to a method for manufacturing an NdFeB magnet, comprising the following steps. a) A process for collecting waste containing NdFeB solid magnets to be recycled, wherein the NdFeB magnets are Nd2Fe 14 A process comprising a magnetic main phase and a non-magnetic grain boundary secondary phase. b) A step of preheating waste to a preheating temperature of 300°C to 500°C in an inert atmosphere, wherein the waste is contained in a first chamber that has been heated to the preheating temperature in a first station equipped with a heating means, c) Hydrogen decrepitation applied to the high-temperature waste obtained from step b) under a hydrogen partial pressure or total hydrogen pressure of 0.1 bar to 10 bar, wherein the high-temperature waste is contained in a second chamber located at a second station different from the first station, which is equipped with a hydrogen source and pumping means, and the decrepitation is carried out at a temperature of 200°C to 500°C, and the temperature in the second chamber is maintained within this temperature range due to the exothermic nature of the hydrogenation reaction of the NdFeB magnet, and c) Nd2Fe 14 A step that results in the formation of a first powder having a main phase B and / or grain boundary secondary phases and particles having a size of 5 mm or less.
[0008] According to other advantageous non-limiting features of the present invention, either alone or in any technically feasible combination, the following may be achieved: The first and second chambers are formed by a single chamber, which is moved from the first station to the second station between steps b) and c), and is connectable to the hydrogen source and pumping means of the second station. The waste collected in step a) includes a metal part that is integrated with the NdFeB magnet to be recycled, and the method includes a sieving step d) with a sieve size of 1 cm, which is performed during or after step c) to separate the part from the first powder. This method includes step d) of sieving the first powder during or after step c), This method includes step e) after step c), or during or after the sieving step d), grinding the first powder or a fraction of the first powder to obtain a second powder having particles with a size of 500 microns or less. • Particles consisting of at least one compound rich in rare earth elements are added to the first powder during step e) to enrich the second powder with a grain boundary secondary phase. • In step e), grinding is carried out in a ball mill, or by a ring mill, or by a gas jet mill. • At least one compound of a fresh alloy material of the TRFeB type, particularly NdFeB (TR=Nd, Pr, Dy, Tb) and / or TR2Fe 14 At least one magnetic phase compound of type B, particularly Nd2Fe 14 B is added to the first powder or the second powder during the recycling process. At least one non-magnetic metal compound (excluding rare earth elements) having a low melting point (typically below the melting point of the grain boundary secondary phase) is added to the first or second powder during the recycling process, and the compound is intended to promote bonding between NdFeB particles during the manufacture of a new magnet. This method includes step f) dehydrogenating the first powder or the second powder.
[0009] The present invention further comprises several Nd2Fe phases separated from each other by grain boundary secondary phases. 14 This relates to a powder obtained from the above-mentioned method for recycling NdFeB magnets, comprising particles composed of metal crystal grains with a B magnetic main phase, wherein the metal crystal grains of the same particles have a common crystal orientation that generates magnetic anisotropy.
[0010] Advantageously, powder is, - The first number of occupied particles centered on the first size, - It has a dual particle size distribution, with a second occupied particle number centered on a second size, where the first size is 1.5 to 10 times larger than the second size.
[0011] Advantageously, the powder contains 1% to 50% by volume of grain boundary secondary phase. More preferably, the powder contains 10% to 30% by volume of grain boundary secondary phase.
[0012] Advantageously, the powder contains 1% to 50% by volume of a non-magnetic metal compound (excluding rare earth elements). More preferably, the powder contains 1% to 20% by volume, or 1% to 10% by volume, of a non-magnetic metal compound.
[0013] Finally, the present invention is a method for manufacturing NdFeB permanent magnets, which comprises, from the aforementioned powders, - sintering technology, or - injection technology or compression technology for producing plastic bonded magnets, or - injection molding technology including debinding and sintering, or - a method of implementing additive manufacturing technology.
[0014] According to a preferred embodiment, the manufacturing method is based on additive manufacturing technology including melting of at least one phase of the powder, and the melting is performed at a temperature below the melting temperature of the Nd2Fe 14 B main phase, whereby melting all or part of the grain boundary secondary phase or non-magnetic metal compound不含稀土 when present, rather than the Nd2Fe 14 B main phase.
[0015] In this preferred embodiment, the powder particles containing the main phase are preferably oriented before or during the densification of the NdFeB magnet in the form of a printed object in order to impart magnetic anisotropy to the magnet.
[0016] Other features and advantages of the present invention will become apparent from the following detailed description of the present invention with reference to the accompanying drawings.
Brief Description of the Drawings
[0017] [Figure 1] It is a diagram showing the steps of the recycling method according to the present invention. [Figure 2] It shows an image created by a scanning electron microscope (SEM) of the particles of the first powder, and a graph showing the typical particle size distribution of the particles of the first powder measured by laser diffraction at the end of step c) of the recycling method. [Figure 3a]Images created by scanning electron microscopy (SEM) of the particles of the second powder after step e) of the recycling method according to the present invention are shown for different grinding conditions. Similar to Figures 3a and 3c, graphs showing the particle size distribution of the particles of the second powder obtained for the different grinding conditions are shown, where the particle size is measured by laser diffraction (Figures 3a and 3b) and image analysis (Figure 3c). [Figure 3b] Images created by scanning electron microscopy (SEM) of the particles of the second powder after step e) of the recycling method according to the present invention are shown for different grinding conditions. Similar to Figures 3a and 3c, graphs showing the particle size distribution of the particles of the second powder obtained for the different grinding conditions are shown, where the particle size is measured by laser diffraction (Figures 3a and 3b) and image analysis (Figure 3c). [Figure 3c] Images created by scanning electron microscopy (SEM) of the particles of the second powder after step e) of the recycling method according to the present invention are shown for different grinding conditions. Similar to Figures 3a and 3c, graphs showing the particle size distribution of the particles of the second powder obtained for the different grinding conditions are shown, where the particle size is measured by laser diffraction (Figures 3a and 3b) and image analysis (Figure 3c). [Figure 4] This image shows a scanning electron microscope image of the second powder particles after the addition of particles of a rare earth-rich grain boundary phase compound. [Modes for carrying out the invention]
[0018] The present invention relates to a method for recycling NdFeB type solid magnets. The solid magnet is only metallic, i.e., it does not contain a polymer binder in addition to the NdFeB alloy. Thus, in the present invention, the term "solid magnet" excludes polymer-based composite materials such as, for example, plastic bonded magnets. Further, throughout this specification, NdFeB magnets are described, but this term encompasses any NdFeB magnet, i.e., an NdFeB magnet that can contain various additives and / or other rare earth metals such as neodymium (e.g., dysprosium). By analogy, some types of rare earth metals and additives may be contained, but the magnetic main phase of these magnets is Nd2Fe 14 is referred to as the B phase.
[0019] The first step a) of the method consists of recovering waste containing the NdFeB solid magnet to be recycled. The waste is understood to mean solid NdFeB magnets rejected from production, which also means any type of mechanical or electronic part at the end of its life or aged in the manufacturing process, including NdFeB magnets whose material is recyclable. As an example, the waste may consist of NdFeB magnets of hard disks fixed to steel tabs, NdFeB magnets of electric motors, etc. Due to their magnetization characteristics, these magnets are often very firmly attached to the mechanical (metal) parts related to their previous use, but nevertheless, it is possible to obtain waste consisting only of NdFeB magnets, i.e., separated from the mechanical parts of their previous use.
[0020] Generally, NdFeB magnets from waste may be exposed or typically covered with a protective layer of a metal (e.g., based on nickel or zinc) or a polymer (epoxy).
[0021] The bulk magnet NdFeB to be recycled typically corresponds to 85 volume% (+ / - 10 volume%) of the alloy of Nd2Fe 14It forms an alloy containing a B magnetic main phase. The melting temperature of this main phase is approximately 1180°C. The alloy also contains Nd2Fe 14 The alloy contains a non-magnetic secondary phase, called the grain boundary secondary phase, which is used to magnetically separate (isolate) the main phase metal crystal grains. The secondary phase consists of several rare-earth-rich phases with melting temperatures ranging from 500°C to 800°C, depending on the alloy composition. The grain boundary secondary phase typically accounts for 15 volume percent (+ / -10 volume percent) of the alloy.
[0022] Next, the recycling method includes step b) preheating the waste 100 in a first chamber 10 to a preheating temperature of 300°C to 500°C, preferably 350°C to 450°C, and especially about 400°C (Figure 1(b)). For this purpose, the waste 100 is introduced into a first chamber 10 located in a first station 1 equipped with heating means 11. The first station 1 may consist of, for example, an annealing furnace in which the first chamber 10 filled with waste 100 is located. The first station 1 is advantageously equipped with gas circuits 12, 13 including at least one neutral gas source 12 and a gas discharge 13, which are connected to a first enclosure 10 and can regulate its internal atmosphere. Thus, the atmosphere inside the first chamber 10 is advantageously selected to be inert, for example, based on argon. The first chamber 10 is preferably completely sealed and can withstand a pressure of several bar and a temperature typically up to 600°C.
[0023] This preheating of waste 100 is advantageous in that it promotes the demagnetization of the various materials contained in the waste, and therefore facilitates the physical separation of parts that are potentially fixed by magnetic attraction.
[0024] However, the inventors hereby demonstrate that this preheating step b) has other important advantages with respect to the reliability and efficiency of the recycling method.
[0025] Step c) of the recycling method corresponds to hydrogen decrepitation applied to the high-temperature waste 101 at a temperature of 200°C to 500°C under a hydrogen partial pressure or total hydrogen pressure of 0.1 bar to 10 bar, preferably 1 to 4 bar. The high-temperature waste 101 is located in a second chamber 20, which is situated in a second station 2, separate from the first station 1, and is equipped with a hydrogen source 21 and pumping means 22 (Figure 1(c)).
[0026] According to a preferred embodiment, the first chamber 10 and the second chamber 20 are formed by a single chamber that is moved from the first station 1 to the second station 2 between steps b) and c) and is connectable to the hydrogen source 21 and pumping means 22 of the second station 2. In this case, the enclosure 10 is disconnected from the gas circuits 12, 13 of the first station 1 at the end of step b), and then, when the enclosure 10 is positioned in or on the second station 2, the enclosure 10 is connected to the hydrogen source 21 and pumping means 22.
[0027] According to another possible embodiment, the high-temperature waste 101 is transferred from the first enclosure 10 into the second chamber 20 between step b) and step c). Care is taken to limit the decrease in the temperature of the waste 101 during this transfer so that the temperature of the waste 101 remains above 250°C at the start of step c).
[0028] Regardless of the embodiment, if the waste is in the second chamber 20, air is expelled from the chamber 20 by the pumping means 22 before the chamber 20 is supplied by the hydrogen source 21. The second chamber 20 is completely sealed and can withstand pressures in the range of at least 10 bar and temperatures typically in the range of up to 600°C. It is also advantageous to control the distribution of hydrogen by the hydrogen source so that the hydrogen pressure in the second chamber 20 is maintained above a predetermined threshold, for example, a threshold of 25% or less of the initial pressure, throughout the entire duration of declépitation, since the hydrogen is absorbed by the NdFeB alloy of the waste 100.
[0029] Since the hydrogen decrepitation in step c) is an exothermic reaction, the temperature in the second chamber 20 is self-sustaining without the need for any heating means at the second station 2. The NdFeB magnet contained in the high-temperature waste 101 (i.e., a temperature of 250°C or higher) immediately initiates the hydrogenation reaction and decrepitation phenomenon upon contact with the hydrogen atmosphere. Advantageously, the decrepitation temperature is close to the preheating temperature and can actually be between 200°C and 500°C. Automated control of the amount of hydrogen introduced allows for limiting the temperature rise and maintaining it below 500°C, the temperature at which the NdFeB alloy decomposes.
[0030] Performing steps b) and c) at two separate stations 1 and 2, respectively, significantly simplifies the equipment and basic structure for implementing the recycling method by uncorrelating the heating request (first station 1) from the hydrogen input (second station 2) and ensuring operation.
[0031] Step c) has a typical duration of several minutes to 12 hours. The end of the hydrogenation reaction is detected by a decrease in the temperature of the second chamber 20 (measured via a temperature sensor embedded in the chamber 20) or by measuring the pressure in the second chamber 20, which tends to remain constant because the NdFeB magnet of waste 100 no longer absorbs hydrogen.
[0032] In the temperature range of 200-500°C, more specifically 300-500°C, it is essentially the grain boundary secondary phase of the NdFeB alloy that is hydrogenated. 14 The main phase B is either not hydrogenated at all, or only very slightly hydrogenated, because the associated hydride is not stable above 200°C. In fact, the main phase absorbs hydrogen, producing a stable hydride at lower temperatures, typically room temperature to 150°C.
[0033] The advantage of this hydrogen decrepitation process c), which is carried out at 200°C to 500°C, preferably 300°C to 500°C, or 350°C to 450°C, is that it reduces the amount of hydrogen (H2) required to hydrogenate, because only the grain boundary secondary phase is targeted, which generally accounts for less than a quarter of the alloy's volume. This typically decreases from 4 g of H2 per kg of hydrogenated magnet at room temperature to 1.25 g of H2 per kg of hydrogenated magnet at 400°C. Another advantage stems from the fact that the magnetic main phase metal grains are hardly affected or modified by this process and therefore retain their initial properties and structure (i.e., those they had in the recycled NdFeB magnet). In particular, the overall magnetic orientation of the metal grains is the same within the same powder particles.
[0034] The second station 2 is advantageously equipped with an agitation system 23 that can transmit motion to the second chamber 20 during step c). The agitation system may consist of a vibrating system (typically with a vibration amplitude of 0.5 mm to 3 mm) or a wave vibration system. By agitating the inside of the second chamber 20, the separation of the NdFeB magnet from the other parts and the fragmentation of the NdFeB alloy by hydrogen declépitation are promoted. Thus, the NdFeB magnet of the waste 100 processed in step c) is transformed into a powder (hereinafter referred to as the first powder 110) as this process progresses, and its particles are Nd2Fe 14 It contains the B main phase and / or grain boundary secondary phases, and has a size of 5 mm or less, or 1 mm or less.
[0035] Preferably, the recycling method includes a step d) of sieving the first powder 110, which is performed during or after the decrepitation step c) (Figure 1(d)).
[0036] To perform sieving during step c), it is necessary to incorporate at least one sieve 31 (not shown) into the second chamber 20. As the high-temperature waste 101 is placed on the sieve 31 and the NdFeB alloy is hydrogenated, particles of the alloy smaller than the mesh size of the sieve 31 fall into the enclosure below the screen. The falling of alloy particles from the sieve 31 is facilitated by stirring applied to the second chamber 20 located in the second station 2.
[0037] Alternatively, the first powder of the NdFeB alloy and any other waste residue (if any) obtained at the end of step c) are transferred from the second chamber 20 to the sieving device 30 by a hatch associated with a valve (not shown) located at the bottom of the second chamber 20, for example. The sieving device 30 may comprise one or more sieves 31. It may optionally be located at the second station 2 and, like the second chamber 20, be subject to the movement of the agitation system 23, or it may comprise its own agitation system 33 (Figure 1(d)).
[0038] The mesh size of the screen(s) 31 used in the sieving step d) may be 1 cm, 5 mm, 1 mm, 500 microns, 300 microns, 150 microns, 100 microns, 50 microns, 10 microns, or less. It is possible, if desired, to pre-grind the powder by adding balls larger than the particles of the first powder 110 (for example, 10 times larger) to the sieve 31 to facilitate the sieving of the powder.
[0039] If the waste recovered in step a) includes a metal part integrated with the NdFeB magnet, at least the sieving step d) is performed using a 1 cm mesh to separate the part from the first powder 110. If the metal part or other chips generated during decrepitation (e.g., chips of the NdFeB alloy coating layer) are smaller in size, it is possible to consider sieving with a finer mesh, e.g., 1 mm, 500 microns, 150 microns, 100 microns, or less.
[0040] Optionally, step d) may include sieving the first powder 110 obtained from step c) with a screen size of 800 to 100 microns, thereby separating a batch 112 of fine-grained powder that can be used directly in the subsequent manufacture of new magnets from a batch 111 of coarse-grained powder that is intended to undergo a subsequent grinding step, which may be carried out by the recycling method according to the present invention.
[0041] This separation in batches allows for limiting the process steps for a fraction of the volume of recycled NdFeB magnets. Beyond economic benefits, applying fewer processing steps to the alloy makes it possible to maintain its initial quality as much as possible.
[0042] It should also be noted that the first powder 110 may also be sieved through an ultrafine sieve having a mesh size of typically less than 10 microns, or less than 5 microns, for example, about 1 micron. If the metallic ultrafine particles, which are essentially formed from the grain boundary phase at this stage, have degraded (e.g., due to excessive oxidation) or no longer have a suitable composition, this ultrafine sieving allows them to be separated from the remainder of the first recycled powder. They may be optionally replaced with grain boundary phase particles (recycled or new) of good quality or optimized composition to improve the properties of the new magnets manufactured from the recycled powder.
[0043] The particles of the first powder 110 are mostly angular in shape (Figure 2), and a typical example of the particle size distribution after the sieving process d) at 800 microns is shown in Figure 2. The particle size referred to here is the "Sauter mean diameter." The "Sauter mean diameter" is the diameter of spheres that behave identically during particle size measurement using a defined technique.
[0044] This first powder 110 can be adapted to specific methods for manufacturing new magnets. For example, a fraction of particles smaller than 50 microns is adapted to conventional sintering techniques for manufacturing new magnets. A fraction of particles between 100 and 500 microns is adapted to conventional techniques for manufacturing plastic bonded magnets by injection or compression.
[0045] Finally, for additive manufacturing techniques, NdFeB alloy particles typically have a size of less than 300 microns or less than 100 microns, but their shape is preferably less angular.
[0046] To adjust the particle size distribution of the recycled alloy particles and to soften their shape, the recycling method may include step e) grinding the first powder 110 (or a fraction thereof) after step c) and / or during and / or after step d), thereby obtaining a second powder in which particles having a more rounded shape have a size of 500 microns or less, 300 microns or less, or 100 microns or less, or 50 microns or less.
[0047] Any known grinding method, particularly a ball mill, ring mill, or gas jet mill, may be used in step e). The latter technique is well known and is typically used to grind powders.
[0048] Ring milling is performed by vibrating the ring and core in a circular and horizontal manner on a vibrating plate. The sample is then fragmented into pieces that may be less than 20 microns in size under pressure, impact, and frictional forces.
[0049] The following description relates in particular to a preferred embodiment of the present invention, which is ball mill grinding. The ball mill comprises rotating blades arranged in a rotating drum or a stationary drum, in which all or part of the first powder 110 is placed, either alone or with balls. Thus, the first powder 110 or its thickness that is intended to undergo the grinding process is transferred from a second station 2 to a third grinding station.
[0050] When used, these balls may be selected from stainless steel and, advantageously, have a diameter of 1 mm to 30 mm, preferably 1 mm to 10 mm, for example, including 5 mm. The mass ratio of the first powder to the balls is preferably selected to be 0.5 to 3.
[0051] With or without balls, the grinding in step e) is advantageously carried out by applying a stirring sequence for 10 seconds to 1 hour, e.g., 10 minutes, at a drum rotation speed of 100 rpm to 800 rpm, e.g., 450 rpm, followed by a rest sequence of a few seconds (typically 5 seconds) to 40 seconds, e.g., 20 seconds. The stirring and rest sequences may be repeated 2 to 500 times consecutively until a specified particle size of the second powder is obtained.
[0052] For example, Figures 3a, 3b, and 3c correspond to SEM images of the second powder particles at the end of grinding step e) for different iterations of the aforementioned stirring and resting sequences, 10, 30, and 300 iterations, respectively. In these examples, grinding was performed using balls. In addition to the particle size distribution, changes in their shape can be observed (Figures 3a, 3b, and 3c).
[0053] The recycling method ultimately includes a dehydrogenation step f), which may be applied to the first powder 110 (or a sieved fraction thereof) or a second powder obtained from the grinding step e) in order to extract hydrogen present in the alloy particles. Dehydrogenation is carried out by heating the powder to about 800°C under secondary reduced pressure in a fourth chamber located in a fourth station equipped with heating and pumping means.
[0054] Dehydrogenation is the process of hydrogen being converted into Nd2Fe 14 The process consists of two consecutive steps: release from the main phase B (which may optionally be slightly hydrogenated during step c) to 200°C, and then release from the grain boundary secondary phase to 350-800°C (depending on composition, temperature conditions, and vacuum dynamics).
[0055] As mentioned above, the alloy particles are essentially hydrogenated grain boundary secondary phases during the declépitation step c), and therefore contain a low hydrogen content. Consequently, the dehydrogenation step f) is faster than the declépitation step typically performed in the prior art.
[0056] The alloy powder (first powder or second powder) obtained from the recycling method according to the present invention is Nd2Fe 14 The alloy powder contains particles composed of one or more metal crystal grains of a B magnetic main phase, and if several metal crystal grains are present, they are separated from each other by a rare-earth-rich non-magnetic grain boundary secondary phase. A strong advantage of the alloy powder according to the present invention is that the metal crystal grains contained in the same particle have a common crystal orientation that generates magnetic anisotropy. Therefore, these polymetallic crystal grain particles can be used as anisotropic monometallic crystal grain particles in the manufacture of new NdFeB magnets.
[0057] Anisotropic powders are typically obtained through expensive and complex processes such as HDG (Hydrogenation-Disproportionation-Desorption-Recombination). The recycling method according to the present invention makes it possible to obtain good quality anisotropic powders easily and economically.
[0058] The first powder 110 and the second powder obtained from the recycling method according to the present invention contain 1% to 50% by volume, preferably 10% to 30% by volume, of grain boundary secondary phase. These powders can be used directly in the manufacture of NdFeB permanent magnets.
[0059] According to an advantageous modification of the recycling method, particles consisting of a rare earth-rich compound may be added to the second powder to adjust the grain boundary secondary phase content or change its composition, if necessary.
[0060] This addition may be carried out, for example, with neodymium (Nd), or other rare earth compounds containing elements such as Nd, Dy, Tb, Pr, Co, Fe, Cu, Al, Nb, Zr, and Ti. The following methods may be used in particular to introduce rare earth(s)-rich grain boundary secondary phase compounds. -The compound is hydrogenated, for example, at a temperature of 150°C and a pressure of 8 bar, to form a hydride. - The hydride is ground, for example, according to the grinding step e) of the recycling method, which makes it possible to easily obtain very fine particle sizes of the hydride, i.e., typically 10 microns or less, 2 microns or less, or 1 micron or less. This grinding involves mixing the hydrogenated compound with the first powder 110, -Note that if the hydrogenated compound is not ground during step e), it may be ground during the grinding step e) of the recycling method described above by adding the compound powder to the second powder at a fraction of a volume percent to several volume percent (typically 1% to 10%) during a small co-grinding.
[0061] Dehydrogenation is performed either during step f) of the recycling method or independently for the rare earth compounds and powders mixed at the end of dehydrogenation.
[0062] The SEM image in Figure 4 provides an overview of the mixture obtained after the final addition of grain boundary phase compound particles to the second powder. The finest particles (<1 micron) correspond to the added grain boundary phase, which is rich in rare earth elements. The largest particles are part of the second powder.
[0063] According to another variant, to improve the performance of new magnets formed from recycled powder, compounds with a composition similar to that of the original magnet (fresh TRFeB material) can be added, typically in amounts of 1% to 90%, preferably 1% to 40%, or preferably 2% to 15%. Alternatively, TR2Fe 14 Type B, especially Nd2Fe 14 It is possible to add only compounds consisting of the magnetic phase of B.
[0064] According to yet another modification that can be combined with the aforementioned modification, a non-magnetic metal compound (excluding rare earth elements) having a low melting point (typically below the melting point of the grain boundary phase) may be added, and its particles may have a particle size corresponding, for example, to the particle size of the second powder. Such a compound is intended in particular to promote bonding between NdFeB particles during the creation of new magnets by additive manufacturing.
[0065] In the different variant forms mentioned, the compound to be added is either added to the waste and simultaneously processed according to the recycling method described above, or processed and modified in powder form, and then added to the first or second powder according to the present invention in any step of the method before or after the dehydrogenation step f).
[0066] According to a first aspect, the present invention relates to a method for manufacturing an NdFeB permanent magnet from the first powder 110 (described above) or from the second powder according to the present invention, and is a method for carrying out the following well-known techniques. - Sintering technology, - Injection or compression technology for producing plastic bonded magnets, - Powder injection molding technology including decoupling and sintering, or - Additive manufacturing method including a polymer matrix.
[0067] According to a second aspect, the present invention relates to a method for manufacturing an NdFeB magnet, preferably from a second powder, using a metal additive manufacturing technique.
[0068] Among the well-known techniques in additive manufacturing of metals, we can particularly mention powder bed fusion (Selective Laser Melting, SLM® or "Laser Beam Powder Bed Fusion, BLF"), electron beam additive manufacturing (EBAM), metal binder jetting (MBJ), directed energy deposition (DED), and cold spray additive manufacturing (CSAM). In the first two techniques cited, a light beam (laser or electrons) is directed point by point to weld together free powder particles on the bed to form an object. In the third technique, the particles on the bed are welded together by droplets of a binder. In the last two examples, it is the spraying of powder onto a support, which enables their collective adhesion by supplying energy. These various techniques involve subjecting metal powders to various flows, stresses, and processing measures, and at least the first two cited techniques are based on the melting of alloy powders, followed by the compaction of the alloy in the form of the object to be printed. Unoptimized input powder properties directly lead to inconsistent finished part (NdFeB magnet) properties and the possibility of defects.
[0069] Two crucial properties of powder for printed parts where quality is limited are density (layer density) and fluidity. Sufficiently compacted powder, to give high density, is associated with the production of parts with consistent quality and fewer defects. Fluidity is more closely related to process efficiency for that part. The ability to distribute uniformly on the bed and form a uniform thin layer without reduced pressure is essential for powder bed melting processes, while consistent fluidity as aerated powder flow is required for spraying technology. These requirements become more stringent as the additive manufacturing speed increases.
[0070] Both bulk density and fluidity are directly influenced by the size and shape of powder particles. Generally, smooth particles with a regular shape flow more easily than particles with a rough surface and / or irregular shape. Rougher surfaces result in increased interparticle friction, while particles with an uneven shape are more susceptible to mechanical aggregation. These two effects reduce fluidity. Similarly, spherical particles tend to compact more effectively than irregular ones, giving them a higher apparent density. Sphericity is widely recognized in industry, which explains why most powders commonly used in additive manufacturing are produced by gas atomization.
[0071] In terms of particle size, metal powders are necessarily fine enough to meet the requirements for forming a powder bed, for example, several tens of microns thick. However, because interparticle attractive forces increase with decreasing particle size, finer powders generally do not flow as freely as larger powders. The highest density is achieved with a distribution containing both coarse and fine particles, where finer particles increase density by filling the gaps left by the largest ones.
[0072] Therefore, the second powder according to the present invention can be proven to be particularly suitable when it has a dual distribution in particle size, that is, when it has a first number of occupied particles centered on a first size and a second number of occupied particles centered on a second size, and the first size is 1.5 to 10 times larger than the second size. Typically, the first size may be 15 to 90 microns and the second size may be 1 to 15 microns. In the example shown in Figure 3c, the first size is about 15 microns and the second size is about 9 microns. Such a dual distribution can be obtained, in particular, by applying multiple grinding iterations as described above in the recycling method.
[0073] Furthermore, the presence of particles of non-magnetic metal compounds that do not contain rare earth elements and / or particles of grain boundary phase compounds that are rich in rare earth elements reduces the interaction between magnetic particles, which significantly improves the injectability of the powder. Therefore, this eliminates constraints on particle shape and gives remarkable fluidity even to angular particles.
[0074] Conventionally, the additive manufacturing techniques described above provide a large amount of energy that enables the complete melting of NdFeB alloy powder particles. In the manufacturing method according to the present invention, the melting is Nd2Fe 14 This process is carried out at a temperature below the melting point of the main B phase, thereby melting all or part of the grain boundary secondary phase and / or nonmagnetic metal compound that does not contain rare earth elements (if present), rather than the main phase. This melting temperature is approximately 1180°C, but can vary substantially depending on the composition of the NdFeB alloy.
[0075] Therefore, typically, the melting temperature in the manufacturing process is below 1180°C, preferably below 1000°C, or below 800°C, or below 600°C. Thus, compaction between the powder particles is achieved by partial melting of the NdFeB alloy. This has the advantage of not affecting the metal crystal grains of the magnetic main phase in terms of size, shape, or composition. Therefore, the intrinsic magnetic properties of the second powder alloy can be better preserved.
[0076] For efficient particle compaction to occur, it is important that a sufficient amount of the grain boundary secondary phase is present in the second powder. Therefore, the second powder preferably contains 10% to 30% by volume of this phase.
[0077] In the aforementioned modified form in which a low-melting-point non-magnetic metal compound (without rare earth elements) is added to the second powder, the compound may be formed from one or more elements selected from Al, Zn, Sn, In, Li, Bi, Cd, Pb, alloys thereof, or other alloys without rare earth elements (e.g., Ag-Cu). The compound typically has a melting point of 800°C or less.
[0078] Preferably, the powder contains the non-magnetic metal compound in an amount of 1% to 50% by volume, 1% to 20% by volume, or 1% to 10% by volume.
[0079] Other specific properties of NdFeB magnet powder are necessary for the finished magnetic component to be an efficient solid magnet.
[0080] A magnet is primarily characterized by three main values: coercivity (denoted by Hc and expressed in kA / m), remanent magnetization (or residual magnetization, denoted by Br and expressed in Tesla), and maximum energy product (denoted by BHmax and expressed in MGOe). Coercivity corresponds to the magnet's resistance to demagnetization when exposed to an environment that is either demagnetized or high temperature (above 100°C). Therefore, a stronger coercivity indicates better temperature tolerance during operation. Residual magnetization indicates the magnetization and thus represents the magnetic force that the magnet can provide to a system. The maximum energy product is a characteristic of the total energy that the magnet can provide at its operating point.
[0081] The second powder obtained from the recycling method according to the present invention typically has a coercivity of 500 kA / m to 2400 kA / m and a remanent magnetization of 0.5 T to 1.4 T, and its magnetic properties are very favorable for the fabrication of new permanent magnets.
[0082] In the manufacturing method according to the present invention, the residual magnetism can be optimized during additive manufacturing by the magnetic or mechanical orientation system of the particles before compaction, due to the crystal orientation of the metal crystal grains of the magnetic main phase. The second powder is anisotropic particles (i.e., magnetic phase metal crystal grains Nd2Fe having a common crystal orientation that generates magnetic anisotropy) 14 Because B) is included, magnets or electromagnets (magnetic orientation systems) carefully placed around or near the object being printed allow each particle, including the main phase, to be oriented immediately before compaction.
[0083] Alternatively, the newly printed layer can be subjected to a forging operation in a direction perpendicular to the plane of the layer at a deformation rate of at least 8 / second, thereby mechanically textured each powder particle and / or magnetic phase metal crystal grain, and thus resulting in an anisotropic magnetic orientation of the layer. This mechanical orientation system can optionally be coupled to the aforementioned magnetic orientation system.
[0084] To perform anisotropic magnetic orientation and / or to densify the powder bed (particularly to avoid porous defects or cracks in printed objects), another type of mechanical operation may be replaced, if desired, with a forging operation (e.g., using rolls to simulate rolling or a vibrating system to obtain compaction).
[0085] Coercivity increases overall because, in the printed object, the magnetic main phase metal crystal grains are uniformly surrounded by the grain boundary secondary phase for effective magnetic separation of the metal crystal grains. Coercivity is generated if the quality of the inert atmosphere (oxygen content less than 0.1%) is maintained in the printing chamber during compaction.
[0086] In the manufacturing method according to the present invention, the fact that the temperature is kept lower than the melting temperature of the magnetic main phase means that the recycled initial magnet Nd2Fe 14This method enables the maintenance of magnetic quality (good residual magnetism) of B-phase metal crystal grains and simplifies the process for manufacturing new magnets. Furthermore, the simple melting of the grain boundary secondary phase (and / or, if present, a non-magnetic metal compound without rare earth elements) facilitates the coating of the magnetic main phase metal crystal grains, thus enabling the acquisition of high coercivity in new printed magnets.
[0087] The method for manufacturing permanent NdFeB solid magnets by additive manufacturing according to the present invention can find applications in several areas requiring permanent magnets that are efficient in a wide variety of object shapes that are particularly attainable by 3D printing, such as electronic devices, automobiles, and computers.
[0088] Naturally, the present invention is not limited to the embodiments and examples described, and modified embodiments may be provided without departing from the scope of the invention as defined by the claims.
Claims
1. A method for recycling NdFeB magnets, a) A step of collecting waste (100) containing NdFeB solid magnets to be recycled, wherein the NdFeB magnets are Nd 2 Fe 14 A process comprising having a magnetic main phase and a non-magnetic grain boundary secondary phase, b) A step of preheating the waste (100) to a preheating temperature of 300°C to 500°C in an inert atmosphere, wherein the waste is contained in a first chamber (10) in a first station (1) equipped with a heating means (11) that has been heated to the preheating temperature, c) Hydrogen decrepitation applied to the high-temperature waste (101) obtained from step b) under a hydrogen partial pressure or total hydrogen pressure of 0.1 bar to 10 bar, wherein the high-temperature waste (101) is contained in a second chamber (20) located in a second station (2) different from the first station (1), which is equipped with a hydrogen source (21) and pumping means (22), the decrepitation is carried out at a temperature of 200°C to 500°C, the temperature in the second chamber (20) is maintained within this temperature range due to the exothermic nature of the hydridation reaction of the NdFeB magnet, and step c) is Nd 2 Fe 14 A step of forming a first powder (110) having particles having a size of 5 mm or less, comprising a main phase B and / or a grain boundary secondary phase, Methods that include...
2. The recycling method according to claim 1, wherein the first chamber (10) and the second chamber (20) are formed by a single chamber that is moved from the first station (1) to the second station (2) between step b) and step c), and is connectable to the hydrogen source (21) and the pump means (22) of the second station (2).
3. The recycling method according to claim 1, further comprising step d) of sieving the first powder (110) during or after step c).
4. The recycling method according to claim 1, further comprising step e) after step c), or during or after the sieving step d), grinding the first powder (110) or a fraction of the first powder to obtain a second powder having particles having a size of 500 microns or less.
5. The recycling method according to claim 4, comprising adding particles consisting of at least one rare earth-rich compound to the first powder (110) during step e) to enrich the second powder with grain boundary secondary phases.
6. The recycling method according to claim 4, wherein in step e), the grinding is performed in a ball mill, by a ring mill, or by a gas jet mill.
7. At least one compound of a fresh alloy of type TRFeB (wherein TR is Nd, Pr, Dy and / or Tb), in particular NdFeB and / or TR 2 Fe 14 Type B magnetic phase compounds, especially Nd 2 Fe 14 The recycling method according to claim 4, wherein B is added to the first powder (110) or the second powder during the recycling method.
8. The recycling method according to claim 4, wherein at least one rare earth-free nonmagnetic metal compound having a melting point below the melting point of the grain boundary secondary phase is added to the first powder or the second powder during the recycling method, the compound being intended to promote bonding between NdFeB particles during the manufacture of a new magnet.
9. The second powder is - The first number of occupied particles centered on the first size, - A second number of occupied particles centered on a second size, wherein the first size is 1.5 to 10 times larger than the second size, The recycling method according to claim 4, comprising a double particle size distribution.
10. The recycling method according to claim 4, wherein the second powder comprises 1% to 50% by volume of a grain boundary secondary phase and / or 1% to 50% by volume of a rare earth-free nonmagnetic metal compound.
11. The recycling method according to claim 1, comprising step f) dehydrogenation of the first powder (110).
12. The recycling method according to claim 4, further comprising step f) dehydrogenation of the second powder.
13. A step of carrying out the method for recycling an NdFeB magnet according to claim 11 or 12, The powder obtained after carrying out step f) above, - Sintering technology, or - Injection or compression technology for producing plastic bonded magnets, or - Injection molding techniques including debonding and sintering, or - Additive manufacturing technology A method for manufacturing an NdFeB permanent magnet, which involves the following steps.
14. Based on a layered manufacturing method technology including melting of at least one phase of the powder, the melting is carried out at a temperature lower than the melting temperature of the Nd 2 Fe 14 B primary phase, whereby, instead of the Nd 2 Fe 14 B primary phase, all or part of the grain boundary secondary phase or, if present, a rare earth-free non-magnetic metal compound is melted. The manufacturing method according to claim 13.
15. The manufacturing method according to claim 13, wherein the powder particles containing the main phase are oriented before or during compaction of the NdFeB magnet in the form of a printed object to impart magnetic anisotropy to the magnet.