Hybrid magnet for axial flux motor, method for manufacturing the same, and axial flux motor comprising the same

Abstract

The present invention relates to a hybrid magnet for an axial flux motor having excellent magnetic properties and formability, a method for manufacturing the same, and an axial flux motor including the same.

Description

Technology Field

[0001] The present invention relates to a hybrid magnet for an axial flux motor having excellent magnetic properties and formability, a method for manufacturing the same, and an axial flux motor including the same. Background Technology

[0002] Radial flux motors (RFMs), in which magnetic flux flows radially, have been the predominant drive motors for hybrid electric vehicles (HEVs) and electric vehicles (EVs). Radial flux motors have been widely used because their design and manufacturing are relatively simple and they are a technically proven method over a long period. However, they are revealing their limitations as demands for improved space utilization and performance increase. Accordingly, axial flux motors (AFMs), in which magnetic flux flows axially compared to radial flux motors, have recently been attracting attention. As they can provide high torque density and output, there is a trend of active development and application in some industrial sectors.

[0003] Due to their structural characteristics, axial flux motors have a configuration in which permanent magnets are exposed on the surface of the air gap. This leads to a problem where permanent magnets become highly susceptible to eddy current losses. Eddy current loss refers to the current flowing within a conductive magnetic material due to electromagnetic induction within an alternating magnetic field, which can cause heat generation and energy loss in the magnet. To prevent this, when applying conventional sintered NdFeB magnets to axial flux motors, eddy current losses are minimized by using multiple segmented magnetic materials. Generally, a segmented structure with at least 20 segments is used, but even in this case, several limitations exist.

[0004] First, processing sintered magnets into multiple segmented forms generates a large amount of processing scrap, making resource loss inevitable. Additionally, manufacturing costs increase due to the complexity of the process. Second, high-performance magnets resistant to heat are required to reduce eddy current losses, but this has the disadvantage of requiring the use of expensive heavy rare earth elements (such as Dy and Tb). Heavy rare earth elements have limited supply chains and high prices, and securing a stable supply of these resources is also difficult.

[0005] As an alternative to overcome these limitations, a method of applying high resistivity anisotropic bonded injection magnets to axial flux motors has recently been devised. Bonded magnets can be manufactured by mixing magnetic powder and resin and using an injection molding method. Therefore, compared to sintered magnets, it is easier to produce magnets with complex and precise shapes. In particular, applying an insulating coating to the surface of the powder significantly increases resistivity, which can effectively reduce eddy current losses. This method is an important technical alternative that can simultaneously achieve high moldability and the effect of reducing eddy current losses.

[0006] However, such bonded magnets have the disadvantage of having a lower residual magnetic flux density (Br) compared to conventional sintered magnets. In other words, a larger amount of magnet is required to achieve the same magnetic performance, which inevitably leads to a limitation where the motor size must increase. This acts as a significant disadvantage in systems with large space constraints, such as electric vehicles.

[0007] Therefore, to maximize the performance of axial flux motors, development of new magnetic materials and processes capable of improving both magnetic properties and formability is continuing. The problem to be solved

[0008] The present invention was created to solve the various problems of the prior art as described above, and aims to provide a hybrid magnet for an axial flux motor having excellent magnetic properties and formability by including both anisotropic bonded magnets and sintered magnets, a method for manufacturing the same, and an axial flux motor including the same. means of solving the problem

[0009] To achieve the above objectives, a hybrid magnet for an axial flux motor according to one embodiment of the present invention may include an anisotropic bonded magnet and a sintered magnet inside the anisotropic bonded magnet.

[0010] A method for manufacturing a hybrid magnet for an axial flux motor according to one embodiment of the present invention may include the steps of manufacturing an NdFeB-based sintered magnet, injecting an NdFeB-SmFeN-based anisotropic bonded magnet, and placing the NdFeB-based sintered magnet inside the NdFeB-SmFeN-based anisotropic bonded magnet.

[0011] An axial flux motor according to one embodiment of the present invention may include a hybrid magnet for an axial flux motor according to various embodiments of the present invention. Effects of the invention

[0012] The hybrid magnet for an axial flux motor according to the present invention may include not only anisotropic bonded magnets but also sintered magnets.

[0013] Therefore, by placing a bonded magnet on a surface where eddy current loss occurs, eddy current loss is reduced and the heat resistance demagnetization rate is improved, which can improve magnetic properties.

[0014] In addition, the heat resistance performance can be improved by compensating for the lack of heat resistance of the anisotropic bonded magnet with a high-heat-resistant sintered magnet.

[0015] The hybrid magnet for an axial flux motor according to the present invention is manufactured by an injection magnetic field molding method, so that it can be manufactured into a complex shape and dimensional stability can be ensured.

[0016] In addition, various shape deformations and complex forming are possible, allowing for control of magnetic flux density distribution without processing loss.

[0017] In addition, by utilizing the high magnetic properties of sintered magnets, process costs associated with bonding and processing can be reduced. Brief explanation of the drawing

[0018] FIG. 1 is a schematic diagram briefly illustrating a method for manufacturing a hybrid magnet for an axial flux motor according to one embodiment of the present invention. FIG. 2 is a schematic diagram briefly illustrating a method for manufacturing a hybrid magnet for an axial flux motor according to another embodiment of the present invention. Specific details for implementing the invention

[0019] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0020] In this application, terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component.

[0021] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0023] The hybrid magnet for an axial flux motor of the present invention may include an anisotropic bonded magnet and a sintered magnet inside the anisotropic bonded magnet.

[0025] According to one embodiment of the present invention, the anisotropic bonded magnet may include an NdFeB-based magnet and an SmFeN-based magnet.

[0026] An anisotropic magnet refers to a magnet that generates a magnetic force in a specific direction when magnetized in that direction. Therefore, it can possess stronger magnetic properties compared to an isotropic magnet. The anisotropic bonded magnet of the present invention may possess anisotropy by including NdFeB-based magnets and SmFeN-based magnets.

[0027] A bonded magnet refers to a magnet manufactured by mixing magnetic powder and resin using an injection molding method. That is, the above NdFeB-based magnet and SmFeN-based magnet may refer to an NdFeB-based injection-molded magnet and an SmFeN-based injection-molded magnet, respectively.

[0028] Bonded magnets can be manufactured into complex and precise shapes compared to sintered magnets using an injection molding method. That is, the anisotropic bonded magnet of the present invention is manufactured by injection molding, allowing for excellent shape freedom.

[0030] The above NdFeB-based magnet may contain 28 to 29 weight% of Nd, 0.95 to 1.1 weight% of B, and the remainder being Fe and other unavoidable impurities. The above other unavoidable impurities may include elements such as Co, Ga, and Nb. The above other unavoidable impurities may be included in an amount of 0.5 to 0.8 weight%.

[0031] The above SmFeN-based magnet can be manufactured by mixing Sm2O324 to 28 wt%, Fe powder 54 to 60 wt%, and Ca 12 to 22 wt%, followed by reduction diffusion treatment, nitriding treatment, and pickling processes.

[0032] The method for manufacturing SmFeN-based magnets will be explained in detail together with the method for manufacturing hybrid magnets for axial flux motors described later.

[0033] According to one embodiment of the present invention, the NdFeB-based magnet and the SmFeN-based magnet may be included in a weight ratio of 70:30 to 85:15.

[0035] According to one embodiment of the present invention, the sintered magnet may include an NdFeB-based magnet. A sintered magnet refers to a magnet manufactured by sintering at high temperature. The sintered magnet of the present invention may include an NdFeB-based sintered magnet, thereby having anisotropy and excellent magnetic properties.

[0036] The above NdFeB-based magnet may contain 25 to 30 wt% NdPr, 0.91 to 1 wt% B, 1 to 3 wt% Dy and Tb, and the remainder being Fe and other unavoidable impurities. The above other unavoidable impurities may include elements such as Co, Al, Cu, Nb, Ga, Zr, etc. The above other unavoidable impurities may be included in an amount of 1.5 to 3.0 wt%.

[0038] Meanwhile, in the present invention, the sintered magnet may be included in the form of a plurality of magnet segments. When the sintered magnet is included in the form of a plurality of magnet segments, the area of ​​the magnetic field that changes over time is reduced compared to when it is included in the form of a single block, thereby reducing the induced electromotive force and the amount of eddy current. Accordingly, eddy current loss can be minimized.

[0040] Hereinafter, the hybrid magnet for an axial flux motor and the method for manufacturing the hybrid magnet for an axial flux motor according to the present invention will be described in more detail.

[0042] The method for manufacturing a hybrid magnet for an axial flux motor according to the present invention may include the steps of manufacturing an NdFeB-based sintered magnet, injecting an NdFeB-SmFeN-based anisotropic bonded magnet, and placing the NdFeB-based sintered magnet inside the NdFeB-SmFeN-based anisotropic bonded magnet.

[0044] The steps for manufacturing the NdFeB-based sintered magnet of the present invention may further include the steps of preparing raw materials, manufacturing an alloy containing raw materials, pulverizing the alloy, magnetically forming the pulverized alloy, and sintering and heat-treating the molded body.

[0045] Meanwhile, in the step of manufacturing the NdFeB-based sintered magnet of the present invention, the NdFeB-based sintered magnet may be a sintered magnet included in the hybrid magnet for an axial flux motor according to the present invention described above.

[0046] That is, in the step of preparing the raw materials to manufacture such NdFeB-based sintered magnets, the composition may include 25 to 30 wt% of NdPr, 0.91 to 1 wt% of B, 1 to 3 wt% of Dy and Tb, and the remainder being Fe and other unavoidable impurities. The other unavoidable impurities may include elements such as Co, Al, Cu, Nb, Ga, and Zr. The other unavoidable impurities may be included in an amount of 1.5 to 3.0 wt%.

[0047] In the step of manufacturing an alloy containing the above raw material, the raw material may be melted at 1480 to 1500°C in an argon (Ar) atmosphere after removing oxygen in a furnace. Afterward, the molten raw material may be rapidly cooled by rotating it over a copper (Cu) cooling roller to produce a thin strip alloy with an average thickness of 0.1 to 0.5 mm.

[0048] In the step of pulverizing the above alloy, the manufactured alloy can be hydrogen crushed in a hydrogen atmosphere in an oxygen-removed furnace, and then hydrogen removed in a vacuum atmosphere of 500 to 600°C to obtain coarse powder.

[0049] In the step of magnetically forming the above-mentioned powdered alloy, the obtained powder is formed at a rate of 4 to 4.3 g / cm² under a magnetic field of 1.8 T. 3 It can be molded into a rectangular cuboid shape having a density.

[0050] In the step of sintering and heat-treating the above-mentioned molded body, sintering treatment can be performed at 1065 to 1085°C for 4 to 10 hours under vacuum and an Ar atmosphere. After that, a sintered body, i.e., an NdFeB-based sintered magnet, can be manufactured by performing a first heat treatment at 800 to 850°C for 3 to 5 hours and a second heat treatment at 500 to 550°C for 3 to 5 hours.

[0051] In the present invention, the NdFeB-based sintered magnet manufactured as described above may have grades H, SH, UH, or EH depending on the heat resistance of the magnet. Grade H may have a maximum heat resistance temperature of 120°C. Grade SH may have a maximum heat resistance temperature of 150°C. Grade UH may have a maximum heat resistance temperature of 180°C. Grade EH may have a maximum heat resistance temperature of 200°C.

[0052] The H-grade NdFeB-based sintered magnet of the present invention may have a residual magnetic flux density of 12 to 14 kG. In addition, the coercivity (iHc) may be 18 to 20 kOe. In addition, the maximum energy product ((BH)max) may be 40 to 43 MGOe.

[0053] The SH grade NdFeB-based sintered magnet of the present invention may have a residual magnetic flux density of 12 to 14 kG. In addition, the coercivity (iHc) may be 22 to 24 kOe. In addition, the maximum energy product ((BH)max) may be 40 to 43 MGOe.

[0054] The UH grade NdFeB-based sintered magnet of the present invention may have a residual magnetic flux density of 12 to 14 kG. In addition, the coercivity (iHc) may be 24 to 27 kOe. In addition, the maximum energy product ((BH)max) may be 40 to 43 MGOe.

[0055] The EH grade NdFeB-based sintered magnet of the present invention may have a residual magnetic flux density of 12 to 14 kG. In addition, the coercivity (iHc) may be 28 to 32 kOe. In addition, the maximum energy product ((BH)max) may be 40 to 43 MGOe.

[0057] According to one embodiment of the present invention, the NdFeB-based sintered magnet manufactured as described above may consist of a plurality of magnetic segments. Accordingly, as the area of ​​the magnetic field changing over time decreases, the induced electromotive force decreases and the amount of eddy current can be reduced. Accordingly, eddy current loss can be minimized.

[0059] The step of injecting the NdFeB-SmFeN-based anisotropic bonded magnet of the present invention may include the step of manufacturing NdFeB powder, the step of manufacturing SmFeN powder, the step of mixing NdFeB powder and SmFeN powder, and the step of injecting a molded body.

[0060] Meanwhile, in the step of injecting the NdFeB-SmFeN-based anisotropic bonded magnet of the present invention, the NdFeB-SmFeN-based anisotropic bonded magnet may be the NdFeB-based magnet and SmFeN-based magnet described above.

[0062] The step of manufacturing the above NdFeB powder may further include the steps of preparing raw materials, manufacturing an alloy containing raw materials, pulverizing the alloy, grinding the pulverized alloy, heat treating, and surface treating.

[0063] In the step of preparing the above raw material, it may contain 28 to 29 weight% of Nd, 0.95 to 1.1 weight% of B, and the remainder being Fe and other unavoidable impurities. The other unavoidable impurities may include elements such as Co, Ga, and Nb. The other unavoidable impurities may be included in an amount of 0.5 to 0.8 weight%.

[0064] In the step of manufacturing an alloy containing the above raw materials, the alloy can be melted at 1450 to 1550°C under an oxygen-removed Ar atmosphere. Afterwards, an alloy with a thickness of 0.2 to 1.5 mm can be manufactured through a strip casting process that rapidly cools the molten alloy.

[0065] In the step of pulverizing the above alloy, the alloy can be pulverized by controlling the hydrogen partial pressure at 750 to 830°C and going through the steps of hydrogen crushing, phase decomposition, recrystallization, and recombination.

[0066] In the step of grinding the powdered alloy, the powdered alloy can be ground and classified to an average particle size of 50 to 100 μm using a jet stream grinder in a nitrogen atmosphere.

[0067] In the above heat treatment step, the crushed alloy can be heat-treated in a vacuum atmosphere of 700 to 850°C. This allows for the removal of internal stress and the optimization of magnetic properties.

[0068] In the above surface treatment step, the surface can be treated with a silane coupling agent. This prevents oxidation and moisture absorption of the finally manufactured NdFeB powder.

[0069] Meanwhile, the NdFeB powder prepared as described above in the present invention may have a residual magnetic flux density of 12 to 14 kG. In addition, the coercivity (iHc) may be 14 to 16 kOe. In addition, the maximum energy product ((BH)max) may be 33 to 37 MGOe.

[0071] The steps for manufacturing the above SmFeN powder may further include the steps of mixing raw materials, reducing and diffusing the raw materials, nitriding, pulverizing the generated nitride, washing the powder, drying the powder, and surface treating.

[0072] In the step of mixing the above raw materials, 24 to 28 weight% of Sm2O3, 54 to 60 weight% of Fe powder, and 12 to 22 weight% of Ca may be mixed. At this time, Sm2O3 + 17Fe + 3Ca → Sm2Fe 17 The reaction of + 3CaO can occur.

[0073] In the step of reducing and diffusing the above raw material, the above raw material can be reduced and diffusing at 1050°C in an argon (Ar) atmosphere, and finally Sm2Fe 17 + A CaO mixture can be obtained.

[0074] In the step of the above nitriding treatment, the mixture can be nitrided at 400 to 500°C by controlling the partial pressure of ammonia, nitrogen, and hydrogen gases to produce a nitride.

[0075] In the step of pulverizing the nitride produced above, the nitride can be placed in zirconia balls, deionized water, and distilled water and ball-milled. Through this, fine powder with an average particle size of 2.5 to 4 μm can be obtained.

[0076] In the step of washing the powder, the nitride can first be immersed in deionized water and distilled water to remove CaO. Next, the surface of the nitride can be acid-washed to remove residual CaO and other surface impurities. Next, the nitride can be washed with isopropyl alcohol or ethanol to remove residual substances.

[0077] In the step of drying the powder, the washed powder is 10 -4 It can be dried at 100 to 150°C under a vacuum of less than or equal to torr.

[0078] In the above surface treatment step, the surface can be treated with a silane coupling agent. This prevents oxidation and moisture absorption of the finally manufactured SmFeN powder.

[0079] Meanwhile, the SmFeN powder prepared as described above in the present invention may have a residual magnetic flux density of 12 to 14 kG. In addition, the coercivity (iHc) may be 10 to 12 kOe. In addition, the maximum energy product ((BH)max) may be 33 to 37 MGOe.

[0081] The step of mixing the NdFeB powder and SmFeN powder may further include the step of mixing the powder with nylon, the step of cooling after heat treatment, and the step of obtaining injection-molded pellets.

[0082] In the step of mixing the above powder with nylon, the NdFeB powder and SmFeN powder can first be mixed using a 3D mixer. At this time, the NdFeB powder and SmFeN powder can be mixed in a weight ratio of 70:30 to 85:15. Then, a nylon polymer can be mixed in an amount of 5.5 to 8 weight percent relative to the mixed powder.

[0083] In the cooling step after the heat treatment above, the mixture can be high-temperature melted at 200 to 300°C, extruded to 3 to 5 φ, and then cooled.

[0084] In the step of obtaining the above injection pellets, the cooled mixture can be cut into 1 to 5 mm pieces to obtain the pellets.

[0085] The pellets manufactured as described above in the present invention may have a residual magnetic flux density of 8 to 10 kG. In addition, the coercivity (iHc) may be 12 to 14 kOe. In addition, the maximum energy product ((BH)max) may be 17 to 20 MGOe.

[0087] In the step of injecting the above-mentioned molded body, the obtained pellets can be heat-treated at 100 to 120°C to remove residual moisture. After that, the pellets can be mixed with binder resin and placed in a mold. Next, the molded body can be injected under a magnetic field of 1 to 1.4 T with the mold temperature set to 40 to 150°C and the injection machine cylinder temperature set to 210 to 300°C.

[0089] According to one embodiment of the present invention, the NdFeB-based sintered magnet and the NdFeB-SmFeN-based anisotropic bonded magnet are prepared individually and can be assembled by joining them with an adhesive.

[0090] That is, in the step of placing the NdFeB-based sintered magnet inside the NdFeB-SmFeN-based anisotropic bonded magnet, the injection-molded NdFeB-SmFeN-based anisotropic bonded magnet and the manufactured NdFeB-based sintered magnet can be bonded. In one example, the NdFeB-based sintered magnet and the NdFeB-SmFeN-based anisotropic bonded magnet can be bonded using a heat-resistant epoxy adhesive.

[0091] FIG. 1 briefly illustrates a method for manufacturing a hybrid magnet for an axial flux motor according to one embodiment of the above.

[0092] Referring to FIG. 1, the step of placing the NdFeB-based sintered magnet inside the NdFeB-SmFeN-based anisotropic bonded magnet can be achieved by applying the adhesive to one side and the other side of the manufactured NdFeB-based sintered magnet and bonding the injection-molded NdFeB-SmFeN-based anisotropic bonded magnet to both sides.

[0093] Meanwhile, referring to FIG. 1, the NdFeB-SmFeN-based anisotropic bonded magnet may include a groove. Accordingly, by applying the adhesive to the groove, a plurality of NdFeB-based sintered magnet segments can be placed in the groove.

[0095] According to another embodiment of the present invention, the NdFeB-based sintered magnet and the NdFeB-SmFeN-based anisotropic bonded magnet can be joined through insert injection.

[0096] That is, the step of injecting the above NdFeB-SmFeN-based anisotropic bonded magnet can be carried out by placing the manufactured NdFeB-based sintered magnet in a mold and performing insert injection.

[0097] In the case of insert injection, after placing NdFeB-based sintered magnets in the mold, the pellets are mixed with binder resin as in the step of injecting NdFeB-SmFeN-based anisotropic bonded magnets described above, and then the process can be carried out by setting the mold temperature to 40 to 150°C and the injection machine cylinder temperature to 210 to 300°C under a magnetic field of 1 to 1.4 T.

[0098] FIG. 2 briefly illustrates a method for manufacturing a hybrid magnet for an axial flux motor according to one embodiment of the above.

[0099] Referring to FIG. 2, the step of injecting the NdFeB-SmFeN-based anisotropic bonded magnet can be carried out by sequentially inserting to cover one side and the other side of the manufactured NdFeB-based sintered magnet.

[0100] That is, in one embodiment of the present invention, an NdFeB-SmFeN anisotropic bonded magnet can be bonded to one side of an NdFeB-based sintered magnet primarily through insert injection, and an NdFeB-SmFeN anisotropic bonded magnet can be bonded to the other side of the NdFeB-based sintered magnet secondarily through insert injection. Through this, the NdFeB-based sintered magnet can be placed inside the NdFeB-SmFeN anisotropic bonded magnet.

[0102] Meanwhile, the NdFeB-SmFeN-based anisotropic bonded magnet manufactured (injection) according to the various embodiments above may have a residual magnetic flux density of 8 to 10 kG. In addition, the coercivity (iHc) may be 9 to 13 kOe. In addition, the maximum energy product ((BH)max) may be 14 to 18 MGOe.

[0104] The axial flux motor of the present invention may include hybrid magnets for axial flux motors of the various embodiments described above. The axial flux motor of the present invention may include not only anisotropic bonded magnets but also sintered magnets, thereby facilitating shape control as well as magnetic properties.

[0106] The present invention will be explained in more detail below through examples. However, the following examples and experimental examples are intended only to explain the present invention more specifically, and the scope of the present invention is not limited by the following examples and experimental examples.

[0108] Example 1

[0109] To manufacture a bonded hybrid magnet, an NdFeB-based sintered magnet was first manufactured.

[0110] To this end, a raw material was prepared comprising 21.5 wt% NdPr (16.13 wt% Nd, 5.37 wt% Pr), 0.97 wt% B, 0.88 wt% Dy, 1.20 wt% Co, 0.15 wt% Cu, 0.20 wt% Al, 0.30 wt% Nb, 0.18 wt% Ga, and the remainder being Fe. After removing oxygen from the raw material in a furnace, it was melted at approximately 1490°C in an argon (Ar) atmosphere. Subsequently, the molten raw material was rapidly cooled by rotating it over a copper (Cu) cooling roller to produce a thin strip alloy with an average thickness of 0.1 to 0.5 mm. The alloy produced was hydrogen crushed in a hydrogen atmosphere in an oxygen-removed furnace, and then hydrogen was removed in a vacuum atmosphere at approximately 550°C to obtain a coarse powder. The powder obtained in this way is subjected to 4 to 4.3 g / cm² under a magnetic field of 1.8 T. 3 It was molded into a rectangular hexahedral shape having a density. The obtained molded body was sintered at approximately 1075°C for approximately 7 hours under vacuum and an Ar atmosphere, subjected to a first heat treatment at approximately 825°C for approximately 4 hours, and a second heat treatment at approximately 520°C for approximately 4 hours to produce an NdFeB-based sintered magnet. Finally, the produced NdFeB-based sintered magnet was prepared into multiple segments to minimize eddy current losses.

[0111] Meanwhile, the NdFeB-based sintered magnet at this time was of grade H, with a residual magnetic flux density of 12.92 kG, a coercivity (iHc) of 19.53 kOe, and a maximum energy product ((BH)max) of 41.79 MGOe.

[0113] Next, an NdFeB-SmFeN-based anisotropic bonded magnet was manufactured.

[0114] To this end, NdFeB powder was first prepared. A raw material was prepared containing 28.10 wt% Nd, 1.08 wt% B, 0.3 wt% Ga, 0.3 wt% Nb, and the remainder being Fe. The raw material was melted at approximately 1500°C under an oxygen-removed Ar atmosphere and an alloy with a thickness of 0.2 to 1.5 mm was produced through a strip casting process involving rapid cooling. The alloy thus produced was powdered at approximately 790°C by controlling the hydrogen partial pressure and undergoing hydrogen crushing, phase decomposition, recrystallization, and recombination steps. Subsequently, the powdered alloy was ground and classified to an average particle size of 50 to 100 μm using a jet stream grinder under a nitrogen atmosphere. The ground alloy was heat-treated in a vacuum atmosphere at approximately 775°C and surface-treated with a silane coupling agent to produce NdFeB powder.

[0115] Next, to manufacture SmFeN, a raw material was prepared by mixing 26.35 wt% Sm2O3, 55.29 wt% Fe powder, and 18.36% Ca. The above raw material was subjected to a reduction diffusion process at approximately 1050°C under an argon (Ar) atmosphere to produce Sm2Fe 17A mixture of CaO and ammonia was obtained. This mixture was nitrided at approximately 450°C with partial pressure control of ammonia, nitrogen, and hydrogen gases to produce a nitride, and the nitride was ball-milled by placing it in zirconia balls, deionized water, and distilled water. The powder obtained through ball milling was immersed in deionized water and distilled water to remove CaO, and residual CaO and other surface impurities were removed through acid washing. Next, residual substances were removed by washing with isopropyl alcohol or ethanol. Finally, the powder was dried under vacuum at approximately 120°C and then surface-treated with a silane coupling agent to produce SmFeN powder.

[0116] The NdFeB powder and SmFeN powder prepared as described above were weighed at 75.20 wt% and 18.80 wt%, respectively, and mixed using a 3D mixer. Additionally, 6 wt% of polyamide-nylon 12 was added relative to the mixed powder. The mixture was high-temperature melted at approximately 250°C, extruded into a 4 phi (φ), and then cooled to obtain NdFeB-SmFeN pellets with a size of 1 to 5 mm.

[0117] The pellets prepared in this way were heat-treated at approximately 110°C to remove residual moisture, mixed with PA12 binder resin, and placed in a mold. Subsequently, NdFeB-SmFeN-based anisotropic bonded magnets were injected under a magnetic field of 1 to 1.4T, with the mold temperature set to 40 to 150°C and the injection machine cylinder temperature set to approximately 260°C. Meanwhile, grooves were formed in the NdFeB-SmFeN-based anisotropic bonded magnets, and a total of two NdFeB-SmFeN-based anisotropic bonded magnets were injected.

[0118] The anisotropic bonded magnet produced in this way had a residual magnetic flux density of 8.59 kG, a coercivity (iHc) of 10.16 kOe, and a maximum energy product ((BH)max) of 16 MGOe.

[0120] Finally, a heat-resistant epoxy adhesive was applied to the groove formed on a single manufactured NdFeB-SmFeN anisotropic bonded magnet, and the previously prepared multiple NdFeB-based sintered magnet (Grade H) split bodies were bonded. Subsequently, the remaining NdFeB-SmFeN anisotropic bonded magnet was bonded onto the NdFeB-based sintered magnet (Grade H) split bodies to manufacture a hybrid magnet.

[0122] Example 2

[0123] To manufacture a bonded hybrid magnet, an NdFeB-based sintered magnet was first manufactured.

[0124] To this end, a raw material was prepared comprising 23.5 wt% NdPr (17.63 wt% Nd, 5.87 wt% Pr), 0.97 wt% B, 0.96 wt% Dy, 1.20 wt% Co, 0.15 wt% Cu, 0.20 wt% Al, 0.30 wt% Nb, 0.18 wt% Ga and the remainder Fe.

[0125] After removing oxygen from the above raw material in a furnace, it was melted at approximately 1490°C in an argon (Ar) atmosphere. Subsequently, the molten raw material was rapidly cooled by rotating it over copper (Cu) cooling rollers to produce a thin strip alloy with an average thickness of 0.1 to 0.5 mm. The produced alloy was hydrogen-crushed in a hydrogen atmosphere in an oxygen-removed furnace, and then hydrogen was removed in a vacuum atmosphere at approximately 550°C to obtain coarse powder. The powder thus obtained was subjected to a magnetic field of 1.8 T at a concentration of 4 to 4.3 g / cm² 3It was molded into a rectangular hexahedral shape having a density. The obtained molded body was sintered at approximately 1075°C for approximately 7 hours under vacuum and an Ar atmosphere, subjected to a first heat treatment at approximately 825°C for approximately 4 hours, and a second heat treatment at approximately 520°C for approximately 4 hours to produce an NdFeB-based sintered magnet. Finally, the produced NdFeB-based sintered magnet was prepared into multiple segments to minimize eddy current losses.

[0126] Meanwhile, the NdFeB-based sintered magnet at this time was of SH grade, with a residual magnetic flux density of 12.80 kG, a coercivity (iHc) of 23.38 kOe, and a maximum energy product ((BH)max) of 41.11 MGOe.

[0128] Next, two NdFeB-SmFeN-based anisotropic bonded magnets were manufactured in the same manner as in Example 1, and a hybrid magnet was manufactured by bonding the NdFeB-based sintered magnet (SH grade) between them.

[0130] Example 3

[0131] To manufacture an insert injection-type hybrid magnet, an NdFeB-based sintered magnet was first manufactured.

[0132] To this end, a raw material was prepared comprising 28 wt% NdPr (21 wt% Nd, 7 wt% Pr), 0.97 wt% B, 0.15 wt% Dy, 0.45 wt% Tb, 1.20 wt% Co, 0.15 wt% Cu, 0.20 wt% Al, 0.30 wt% Nb, 0.18 wt% Ga and the remainder Fe.

[0133] After removing oxygen from the above raw material in a furnace, it was melted at approximately 1490°C in an argon (Ar) atmosphere. Subsequently, the molten raw material was rapidly cooled by rotating it over copper (Cu) cooling rollers to produce a thin strip alloy with an average thickness of 0.1 to 0.5 mm. The produced alloy was hydrogen-crushed in a hydrogen atmosphere in an oxygen-removed furnace, and then hydrogen was removed in a vacuum atmosphere at approximately 550°C to obtain coarse powder. The powder thus obtained was subjected to a magnetic field of 1.8 T at a concentration of 4 to 4.3 g / cm² 3 It was molded into a rectangular hexahedral shape having a density. The obtained molded body was sintered at approximately 1075°C for approximately 7 hours under vacuum and an Ar atmosphere, subjected to a first heat treatment at approximately 825°C for approximately 4 hours, and a second heat treatment at approximately 520°C for approximately 4 hours to produce an NdFeB-based sintered magnet. Finally, the produced NdFeB-based sintered magnet was prepared into multiple segments to minimize eddy current losses.

[0134] Meanwhile, the NdFeB-based sintered magnet at this time was of the UH grade, with a residual magnetic flux density of 12.86 kG, a coercivity (iHc) of 25.36 kOe, and a maximum energy product ((BH)max) of 41.65 MGOe.

[0136] After placing the manufactured NdFeB-based sintered magnet in a mold, NdFeB-SmFeN-based pellets obtained by the same method as in Example 1 were mixed with PA12 binder resin and placed together in the mold. Then, under a magnetic field of 1 to 1.4 T, the mold temperature was set to 40 to 150°C and the injection molding machine cylinder temperature to approximately 260°C, and an NdFeB-SmFeN-based anisotropic bonded magnet was insert-molded onto one side of the NdFeB-based sintered magnet. Finally, the NdFeB-based sintered magnet was flipped over and placed back in the mold, and an NdFeB-SmFeN-based anisotropic bonded magnet was insert-molded onto the other side of the NdFeB-based sintered magnet under the same conditions as above. In this way, a hybrid magnet was manufactured in which an NdFeB-based sintered magnet (UH grade) is placed inside an NdFeB-SmFeN-based anisotropic bonded magnet.

[0138] Example 4

[0139] To manufacture an insert injection-type hybrid magnet, an NdFeB-based sintered magnet was first manufactured.

[0140] To this end, a raw material was prepared comprising 26.7 wt% NdPr (20 wt% Nd, 6.7 wt% Pr), 0.97 wt% B, 2 wt% Dy, 0.65 wt% Tb, 1.20 wt% Co, 0.15 wt% Cu, 0.20 wt% Al, 0.30 wt% Nb, 0.18 wt% Ga and the remainder Fe.

[0141] After removing oxygen from the above raw material in a furnace, it was melted at approximately 1490°C in an argon (Ar) atmosphere. Subsequently, the molten raw material was rapidly cooled by rotating it over copper (Cu) cooling rollers to produce a thin strip alloy with an average thickness of 0.1 to 0.5 mm. The produced alloy was hydrogen-crushed in a hydrogen atmosphere in an oxygen-removed furnace, and then hydrogen was removed in a vacuum atmosphere at approximately 550°C to obtain coarse powder. The powder thus obtained was subjected to a magnetic field of 1.8 T at a concentration of 4 to 4.3 g / cm²3 It was molded into a rectangular hexahedral shape having a density. The obtained molded body was sintered at approximately 1075°C for approximately 7 hours under vacuum and an Ar atmosphere, subjected to a first heat treatment at approximately 825°C for approximately 4 hours, and a second heat treatment at approximately 520°C for approximately 4 hours to produce an NdFeB-based sintered magnet. Finally, the produced NdFeB-based sintered magnet was prepared into multiple segments to minimize eddy current losses.

[0142] Meanwhile, the NdFeB-based sintered magnet at this time was of EH grade, with a residual magnetic flux density of 12.93 kG, a coercivity (iHc) of 30 kOe, and a maximum energy product ((BH)max) of 42.15 MGOe.

[0144] Next, a hybrid magnet was manufactured in which an NdFeB-based sintered magnet (EH grade) was placed inside an NdFeB-SmFeN-based anisotropic bonded magnet through insert injection in the same manner as in Example 3.

[0146] Comparative Example 1

[0147] A UH grade split-bonded NdFeB-based sintered magnet having a maximum energy product of 52 MGOe was manufactured.

[0149] Comparative Example 2

[0150] An NdFeB-SmFeN-based anisotropic bonded magnet was prepared using the same method as in Example 1.

[0152] Experimental Example 1

[0153] In this experiment, the magnetic flux of the magnets of Examples 1 to 4 and Comparative Examples 1 to 2 was measured. To do this, a fluxmeter and a Helmholtz coil were connected and fixed. After weighing the magnet to be measured using an electronic balance, a pulse magnetic field of 4T at room temperature was applied to fully magnetize the magnet. The magnet to be measured was placed in the middle of the Helmholtz coil, and the magnetic flux was measured in an environment with a temperature of 20 to 25°C and a humidity of 40±30%RH.

[0154] As a result, the hybrid magnets of Examples 1 to 4 had magnetic flux values ​​of 152.82, 150.56, 146.43, and 139.82 mWb, respectively. On the other hand, the magnets of Comparative Examples 1 and 2 had magnetic flux values ​​of 138.65 and 121.41 mWb, respectively.

[0155] In the case of the hybrid magnets of the examples, the sintered magnets included in each magnet are grade H in Example 1, grade SH in Example 2, grade UH in Example 3, and grade EH in Example 4, and heat resistance and coercivity increase as they go from grade H to grade EH. However, it can be seen that the magnetic flux value decreases slightly as additional elements such as Dy are introduced to maintain magnetic properties at high temperatures. Nevertheless, it can be seen that the hybrid magnets of Examples 1 to 4 have very high magnetic flux values ​​compared to Comparative Example 1, which used only sintered magnets, or Comparative Example 2, which used only anisotropic bonded magnets. Through this, it was confirmed that the hybrid magnets of the examples not only have excellent heat resistance at high temperatures but can also generate a stronger magnetic field than the magnets of the comparative examples.

[0157] The present invention has been described above with reference to its preferred embodiments. Those skilled in the art will understand that the present invention may be embodied in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the invention is defined by the claims, not by the foregoing description, and all variations within the scope of the claims should be interpreted as being included in the invention.

Claims

Claim 1 Anisotropic bonded magnet; and a hybrid magnet for an axial flux motor comprising a sintered magnet inside the anisotropic bonded magnet. Claim 2 A hybrid magnet for an axial flux motor according to claim 1, characterized in that the anisotropic bonded magnet comprises an NdFeB-based magnet and a SmFeN-based magnet. Claim 3 A hybrid magnet for an axial flux motor according to claim 2, characterized in that the NdFeB-based magnet comprises 28 to 29 weight% Nd, 0.95 to 1.1 weight% B, and the remainder being Fe and other unavoidable impurities. Claim 4 A hybrid magnet for an axial flux motor according to claim 2, characterized in that the NdFeB-based magnet and the SmFeN-based magnet are included in a weight ratio of 70:30 to 85:

15. Claim 5 A hybrid magnet for an axial flux motor according to claim 1, characterized in that the sintered magnet comprises an NdFeB-based magnet. Claim 6 A hybrid magnet for an axial flux motor according to claim 5, characterized in that the NdFeB-based magnet comprises 25 to 30 wt% NdPr, 0.91 to 1 wt% B, 1 to 3 wt% Dy and Tb, and the remainder being Fe and other unavoidable impurities. Claim 7 A hybrid magnet for an axial flux motor according to claim 1, characterized in that the sintered magnet is a plurality of magnet segments. Claim 8 A method for manufacturing a hybrid magnet for an axial flux motor, comprising the steps of: manufacturing an NdFeB-based sintered magnet; injecting an NdFeB-SmFeN-based anisotropic bonded magnet; and placing the NdFeB-based sintered magnet inside the NdFeB-SmFeN-based anisotropic bonded magnet. Claim 9 A method for manufacturing a hybrid magnet for an axial flux motor according to claim 8, wherein the step of placing the NdFeB-based sintered magnet inside the NdFeB-SmFeN-based anisotropic bonded magnet is characterized by bonding the injection-molded NdFeB-SmFeN-based anisotropic bonded magnet and the manufactured NdFeB-based sintered magnet with a heat-resistant epoxy adhesive. Claim 10 A method for manufacturing a hybrid magnet for an axial flux motor according to claim 9, wherein the step of placing the NdFeB-based sintered magnet inside the NdFeB-SmFeN-based anisotropic bonded magnet comprises applying the adhesive to one side and the other side of the manufactured NdFeB-based sintered magnet and bonding the injection-molded NdFeB-SmFeN-based anisotropic bonded magnet to both sides. Claim 11 A method for manufacturing a hybrid magnet for an axial flux motor according to claim 8, wherein the step of injecting an NdFeB-SmFeN-based anisotropic bonded magnet is performed by placing the manufactured NdFeB-based sintered magnet in a mold and performing insert injection. Claim 12 A method for manufacturing a hybrid magnet for an axial flux motor according to claim 11, wherein the step of injecting an NdFeB-SmFeN-based anisotropic bonded magnet is carried out by sequentially inserting to cover one side and the other side of the manufactured NdFeB-based sintered magnet. Claim 13 An axial flux motor comprising a hybrid magnet for an axial flux motor according to any one of claims 1 to 7.

Images