Self-fixed permanent magnet, preparation method therefor, and application thereof

Abstract

Disclosed in the present invention are a self-fixed permanent magnet, a preparation method therefor, and the application thereof. The permanent magnet of the present invention comprises a partition slot, wherein the partition slot is provided on the permanent magnet; and only a slot of the partition slot is filled with an expandable material, and the expandable material is not provided on the surface of the permanent magnet. The self-fixing of the permanent magnet prepared in the present invention in a magnetic steel slot can be realized; and because an organic coating and a glue injection or injection molding space are saved on, a gap between the permanent magnet and the magnetic steel slot on an iron core can be reduced as much as possible, thereby making up for magnetic flux loss caused by the partition slot, and improving the effective utilization rate of the magnetic flux of the permanent magnet.

Description

A self-fixing permanent magnet and its preparation method and application

[0001] This application claims priority to a prior application filed with the State Intellectual Property Office of China on November 27, 2023, with patent application number 202311593719.6, entitled “A Self-Fixing Permanent Magnet, Its Preparation Method, and Application.” The entire text of the prior application is incorporated herein by reference. Technical Field

[0002] The present invention relates to a high-resistivity self-fixing permanent magnet, a preparation method and application thereof, and in particular to a high-magnetic flux utilization, high-resistivity self-fixing permanent magnet, a preparation method and application thereof. Background Art

[0003] With the rapid development of the new energy vehicle industry, demand for rare earth permanent magnets is growing. Furthermore, with the recent upgrades in new energy vehicles, the speed of drive motors has been increasing both domestically and internationally. This increasing speed also leads to higher eddy current losses in permanent magnets. Therefore, reducing eddy current losses and lowering the temperature rise of rare earth permanent magnets remains an important research topic in this field.

[0004] From the perspective of permanent magnets, there are two main ways to reduce eddy current loss in permanent magnets: (1) using bonded magnets, which form magnetic assemblies by bonding small pieces of magnets together with glue to increase the resistivity of the magnets. However, this method is relatively complex and has high processing costs. (2) Increasing the resistivity of the permanent magnets themselves can be achieved by setting up multiple separation slots, but this method will reduce the effective magnetic flux of the magnets. In addition, both of the above products require the magnets to be fixed in the iron core by methods such as glue filling or injection molding, which is a complex process. In addition, the gap between the permanent magnet base and the iron core magnetic steel slot is large, which further reduces the effective utilization rate of magnetic properties.

[0005] Patent publication number CN104454852A discloses a method for insulating and bonding permanent NdFeB magnets, using specialized extrusion tooling to ensure insulation between the bonded magnets. However, the production process is complex, and securing the magnets within the core requires methods such as glue potting or injection molding.

[0006] Patent publication number CN209134150U discloses a permanent magnet with multiple separating slots. This permanent magnet features a simple manufacturing process, high resistivity, and effective reduction in magnetic losses. However, the separating slots reduce the magnet's effective magnetic flux, and securing the magnet in the core still requires methods such as glue potting or injection molding, further reducing the magnet's effective magnetic flux.

[0007] In summary, current methods for reducing magnetic loss by modifying the magnet's macrostructure are relatively complex and fail to effectively improve magnetic performance utilization, resulting in a certain degree of magnetic performance loss. Therefore, it is necessary to develop a NdFeB permanent magnet with high resistivity, high magnetic performance utilization, and a simple preparation process.

[0008] Summary of the Invention

[0009] In order to improve the above problems, the present invention provides the following technical solutions:

[0010] A permanent magnet includes a dividing groove provided on the permanent magnet; an expandable material is filled only within the groove of the dividing groove, while the expandable material is not applied to the surface of the permanent magnet. By filling the expandable material only within the dividing groove and not coating the surface of the permanent magnet with the expandable material, the present invention reduces the gap between the permanent magnet and the core magnetic steel slot, thereby improving the effective utilization rate of the permanent magnet's magnetic flux.

[0011] According to an embodiment of the present invention, the permanent magnet may be a permanent magnet known in the art, such as a neodymium iron boron permanent magnet.

[0012] According to an embodiment of the present invention, the dividing groove passes through the permanent magnet in a first extension direction of the dividing groove and does not pass through the permanent magnet in a second extension direction of the dividing groove, wherein the first extension direction of the dividing groove is parallel to the magnetization direction of the permanent magnet, or the first extension direction of the dividing groove and the magnetization direction of the permanent magnet have an angle. Preferably, the second extension direction is parallel to the width direction or the length direction of the permanent magnet, or the second extension direction of the dividing groove and the width direction or the length direction of the permanent magnet have an angle. Preferably, the angle is 0 to 90 degrees, for example, 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees or 80 degrees.

[0013] In one embodiment, the first extension direction is perpendicular to the second extension direction.

[0014] According to an embodiment of the present invention, in the second extension direction, the length of the separation groove is more than 50% of the length of the permanent magnet, preferably 70%-90%.

[0015] According to an embodiment of the present invention, the width of the separation groove is 0.5-1.5 mm, preferably 0.8-1.2 mm, and the width refers to the distance between two side walls in the separation groove.

[0016] According to an embodiment of the present invention, the distance between two adjacent separation grooves is 4-8 mm, preferably 5-7 mm.

[0017] According to an embodiment of the present invention, in a direction perpendicular to the magnetization direction of the permanent magnet, the projected area of ​​the separation groove accounts for 6-10%, preferably 7.5-9% of the projected area of ​​the permanent magnet.

[0018] According to an embodiment of the present invention, the separation grooves are distributed on the permanent magnet in a single-sided or double-sided manner, preferably double-sided. In the present invention, single-sided grooves refer to at least one separation groove being provided on at least one surface of the permanent magnet substrate; double-sided grooves refer to at least one separation groove being provided on two opposing surfaces of the permanent magnet substrate.

[0019] According to an embodiment of the present invention, the expansion ratio of the expandable material under free expansion conditions is 3-4, preferably 3.5-3.8. The expansion ratio is defined as the ratio of the volume of the expandable material after expansion to the volume of the expandable material before expansion.

[0020] According to an embodiment of the present invention, the expandable material comprises the following raw materials: resin, foaming agent, curing agent, inorganic filler, leveling agent, pigment, brightening agent and anti-settling agent, or is prepared from the above raw materials.

[0021] According to an embodiment of the present invention, the weight percentage of the resin in the expandable material is 45-65 wt %, for example, 50-60 wt %.

[0022] According to an embodiment of the present invention, the resin is selected from one or more of epoxy resin, acrylic resin and polyester resin, preferably mainly epoxy resin.

[0023] According to an embodiment of the present invention, the weight percentage of the foaming agent in the expandable material is 10-30 wt %, for example, 15-25 wt %.

[0024] According to an embodiment of the present invention, the foaming agent is selected from thermoplastic expanded microspheres, and the diameter of the expanded microspheres is 5-30 μm, preferably 5-20 μm, and exemplified by 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm or 30 μm.

[0025] Preferably, the average diameter of the expanded microspheres is 10-15 μm, exemplified by 10 μm, 12 μm or 15 μm.

[0026] Preferably, the expansion temperature of the expanded microspheres is 110-210°C, exemplified by 110°C, 120°C, 150°C, 160°C, 170°C, 180°C or 200°C.

[0027] Preferably, the maximum heat-resistant temperature of the expanded microspheres is 145-235°C, exemplified by 145°C, 160°C, 180°C, 200°C, 215°C or 235°C.

[0028] According to an embodiment of the present invention, the curing agent is selected from one or more of dicyandiamide, modified or accelerated dicyandiamide, and dimethylimidazole.

[0029] Preferably, in the expandable material, the weight percentage of the curing agent is 3-10 wt%, for example, 7 wt%.

[0030] According to an embodiment of the present invention, the inorganic filler is selected from one or more of calcium carbonate, mica powder and barium sulfate.

[0031] Preferably, in the expandable material, the weight percentage of the inorganic filler is 5-15 wt%, for example, 8 wt%.

[0032] According to an embodiment of the present invention, the leveling agent is selected from at least one of acrylate and organosiloxane.

[0033] Preferably, in the expandable material, the weight percentage of the leveling agent is 0.1-1 wt%, for example, 0.8 wt%.

[0034] According to an embodiment of the present invention, the pigment is at least one selected from carbon black, zinc oxide, and the like.

[0035] Preferably, in the expandable material, the weight percentage of the pigment is 1-5 wt%, for example 3.5 wt%.

[0036] According to an embodiment of the present invention, the brightener is selected from acrylate copolymers.

[0037] Preferably, in the expandable material, the weight percentage of the brightener is 0.5-1.5 wt%, for example, 1 wt%.

[0038] According to an embodiment of the present invention, the anti-settling agent is selected from at least one of silicon dioxide and montmorillonite.

[0039] Preferably, in the expandable material, the weight percentage of the anti-settling agent is 0.1-0.7 wt%, for example 0.7 wt%.

[0040] According to an embodiment of the present invention, the expandable material in the permanent magnet expands, enabling the permanent magnet to self-fix during assembly. In the present invention, when the permanent magnet is inserted into the core magnetic steel slot for assembly, the gap between the permanent magnet and the magnetic steel slot is small, compensating for the magnetic performance loss caused by the separation slot. When the entire core is heated, the expandable material in the permanent magnet's separation slot expands due to the heat, causing the expandable material in the separation slot to overflow from the separation slot and fill the gap between the permanent magnet and the core magnetic steel slot, thereby fixing the permanent magnet in the core magnetic steel slot.

[0041] According to an embodiment of the present invention, the gap between the permanent magnet and the core magnetic steel slot is 0.05-0.15 mm, preferably 0.08-0.12 mm, for example 0.1 mm.

[0042] According to an embodiment of the present invention, the expandable material fills at least part of the surface of the permanent magnet after expansion, for example, fills 80-100%, for example, 80%, 85%, 90% or 95% of the surface area of ​​the permanent magnet.

[0043] The present invention also provides a method for preparing the above-mentioned permanent magnet, which comprises preparing a permanent magnet with a separation groove, filling the separation groove with an expandable material, and then pre-curing to obtain the permanent magnet, wherein the expandable material has the meaning as described above.

[0044] According to an embodiment of the present invention, the permanent magnet with separation grooves can be prepared by a method known in the art.

[0045] According to an embodiment of the present invention, the permanent magnet with separation grooves may also undergo a pre-treatment process, which may be at least one of phosphating, passivating, ceramicizing, silanizing, chelating and blackening treatments.

[0046] According to an embodiment of the present invention, after the pre-treatment process, the permanent magnet with the separation grooves is filled with expandable material in the separation grooves.

[0047] According to an embodiment of the present invention, the step of filling the expandable material includes: filling the dividing groove with the expandable material for the first time, compacting it, and then repeatedly filling it, preferably repeating it 3-5 times. Preferably, the filling method can be spraying or paving.

[0048] According to an embodiment of the present invention, the pre-curing conditions include: a pre-curing temperature of 90-130° C., preferably 100-110° C.; and a pre-curing time range of 15-40 min, preferably 20-30 min.

[0049] According to an embodiment of the present invention, after pre-curing, the density of the expandable material in the separation groove is 1.1-1.4 g / cm 3, preferably 1.2-1.3g / cm 3 .

[0050] The present invention also provides an application of the permanent magnet, such as application in a motor rotor.

[0051] According to an embodiment of the present invention, the process of fixing the permanent magnet in the motor rotor includes: inserting the permanent magnet into the magnetic steel slot of the motor rotor, and fixing the permanent magnet in the motor rotor after heating and curing.

[0052] According to an embodiment of the present invention, the conditions for heat curing include: a curing temperature of 170-230° C., preferably 190-210° C.; and a curing time of 2-5 min, preferably 3-5 min.

[0053] In the present invention, the separation groove may also be selected from the separation groove in the Chinese patent publication number CN110890798A.

[0054] The beneficial effects of the present invention are:

[0055] 1. The permanent magnet with a separator groove of the present invention is filled only with expandable material, initially without an expandable coating on the surface. When heated, the expandable material melts and expands, overflowing the separator groove to fill the gap between the magnet and the steel slot. After cooling, the magnet is secured to the core. The expandable material overflowing from the separator groove replaces traditional glue or injection molding agents, simplifying the process and being environmentally friendly.

[0056] 2. In the permanent magnet provided by the present invention, the expandable material filled in the separation groove is an insulating material, which can increase the resistivity of the permanent magnet and reduce the eddy current effect of the permanent magnet.

[0057] 3. The permanent magnet provided by the present invention can realize self-fixation of the permanent magnet in the magnetic steel slot, and since the space for organic coating and glue injection or injection molding is saved, the gap between the permanent magnet and the iron core magnetic steel slot can be reduced as much as possible, which can compensate for the magnetic flux loss caused by the separation slot and improve the effective utilization rate of the magnetic flux of the permanent magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG1 is a schematic diagram of a permanent magnet with a separation slot filled with expandable material (slotted on one side) in a core magnetic steel slot (before expansion);

[0059] FIG2 is a schematic diagram of a permanent magnet with a separation groove filled with expandable material (slotted on both sides) in a core magnetic steel groove (before expansion);

[0060] Reference numerals: 1-expandable material / separation groove, 2-permanent magnet with separation groove, 3-separation groove spacing, 4-iron core magnetic steel groove.

[0061] FIG3 is a schematic diagram of a permanent magnet with a partition slot filled with expandable material in a core magnetic steel slot (after expansion);

[0062] Reference numerals: 5 - overflowing expanded material. DETAILED DESCRIPTION

[0063] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0064] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0065] Example 1

[0066] A NdFeB permanent magnet with dividing grooves, wherein the base of the NdFeB permanent magnet is a 40mm×20mm×6mm square NdFeB. The length of the dividing grooves in the second extension direction is 70% of the length of the permanent magnet in the same extension direction. The dividing grooves are distributed in a double-sided groove pattern, as shown in FIG2 . The width of the dividing grooves in this embodiment is 1mm, and the spacing between the dividing grooves is 6mm. In the magnetization direction perpendicular to the permanent magnet, the projected area of ​​the dividing grooves accounts for 8.75% of the projected area of ​​the permanent magnet.

[0067] The gap between the permanent magnet matrix and the iron core magnetic steel slot is 0.1 mm.

[0068] The permanent magnet separation groove is filled with expandable material, which includes: 50wt% epoxy resin, 12wt% acrylic resin, 15wt% expandable microspheres, 7wt% dicyandiamide, 10wt% calcium carbonate, 0.8wt% polyacrylate, 3.5wt% carbon black, 1wt% brightener C701 (Hubei Laisi Chemical), and 0.7wt% silicon dioxide.

[0069] The pre-curing conditions of the expandable material are a temperature of 100° C. and a time of 20 minutes. After pre-curing, a NdFeB permanent magnet with a separation groove filled with the expandable material is obtained.

[0070] The NdFeB permanent magnet with a partition groove filled with expandable material is inserted into the magnetic steel slot and heated by electromagnetic induction. Within 3 minutes, the temperature of the permanent magnet is heated from room temperature to 200°C. The expandable material in the partition groove expands due to the heat and spreads from the partition groove to the magnet surface of the permanent magnet. It is then cooled at room temperature to complete the fixation of the NdFeB permanent magnet in the magnetic steel slot.

[0071] Example 2

[0072] A NdFeB permanent magnet with dividing grooves, wherein the base of the NdFeB permanent magnet is a 40mm×20mm×6mm square NdFeB. The length of the dividing grooves in the second extension direction is 70% of the length of the permanent magnet in the same extension direction. The dividing grooves are distributed in a double-sided groove pattern, as shown in FIG2 . The width of the dividing grooves in this embodiment is 1mm, and the spacing between the dividing grooves is 8mm. In the magnetization direction perpendicular to the permanent magnet, the projected area of ​​the dividing grooves accounts for 7% of the projected area of ​​the permanent magnet.

[0073] The gap between the permanent magnet matrix and the iron core magnetic steel slot is 0.1 mm.

[0074] The permanent magnet separation groove is filled with expandable material, which includes: 50wt% epoxy resin, 12wt% acrylic resin, 15wt% expandable microspheres, 7wt% dicyandiamide, 10wt% calcium carbonate, 0.8wt% polyacrylate, 3.5wt% carbon black, 1wt% brightener C701 (Hubei Laisi Chemical), and 0.7wt% silicon dioxide.

[0075] The pre-curing conditions of the expandable material are a temperature of 100° C. and a time of 20 minutes. After pre-curing, a NdFeB permanent magnet with a separation groove filled with the expandable material is obtained.

[0076] The NdFeB permanent magnet with a partition groove filled with expandable material is inserted into the magnetic steel slot and heated by electromagnetic induction. Within 3 minutes, the temperature of the permanent magnet is heated from room temperature to 200°C. The expandable material in the partition groove expands due to the heat and spreads from the partition groove to the magnet surface of the permanent magnet. It is then cooled at room temperature, completing the fixation of the NdFeB permanent magnet in the magnetic steel slot.

[0077] Example 3

[0078] A NdFeB permanent magnet with dividing grooves, wherein the base of the NdFeB permanent magnet is a 40mm×20mm×6mm square NdFeB. The length of the dividing grooves in the second extension direction is 70% of the length of the permanent magnet in the same extension direction. The dividing grooves are distributed in a single-sided slotting manner, and the slotting method is shown in FIG1. ​​The width of the dividing grooves in this embodiment is 1mm, and the spacing between the dividing grooves is 8mm. In the magnetization direction perpendicular to the permanent magnet, the projected area of ​​the dividing grooves accounts for 7% of the projected area of ​​the permanent magnet.

[0079] The gap between the permanent magnet matrix and the iron core magnetic steel slot is 0.1 mm.

[0080] The permanent magnet separation groove is filled with expandable material, which includes: 50wt% epoxy resin, 12wt% acrylic resin, 15wt% expandable microspheres, 7wt% dicyandiamide, 10wt% calcium carbonate, 0.8wt% polyacrylate, 3.5wt% carbon black, 1wt% brightener C701 (Hubei Laisi Chemical), and 0.7wt% silicon dioxide.

[0081] The pre-curing conditions of the expandable material are a temperature of 100° C. and a time of 20 minutes. After pre-curing, a NdFeB permanent magnet with a separation groove filled with the expandable material is obtained.

[0082] The NdFeB permanent magnet with a partition groove filled with expandable material is inserted into the magnetic steel slot and heated by electromagnetic induction. Within 3 minutes, the temperature of the permanent magnet is heated from room temperature to 200°C. The expandable material in the partition groove expands due to the heat and spreads from the partition groove to the magnet surface of the permanent magnet. It is then cooled at room temperature to complete the fixation of the NdFeB permanent magnet in the magnetic steel slot.

[0083] Example 4

[0084] A NdFeB permanent magnet with a separation groove and filled with an expandable material was prepared with reference to Example 1. The difference from Example 1 is as follows:

[0085] The permanent magnet separation groove is filled with expandable material, which includes: 52wt% epoxy resin, 8wt% acrylic resin, 18wt% expandable microspheres, 8wt% dicyandiamide, 8wt% calcium carbonate, 0.7wt% polyacrylate, 3.7wt% carbon black, 1.1wt% brightener C701 (Hubei Laisi Chemical), and 0.5wt% silicon dioxide.

[0086] Example 5

[0087] A NdFeB permanent magnet with a separation groove and filled with an expandable material was prepared with reference to Example 1. The difference from Example 1 is as follows:

[0088] A NdFeB permanent magnet with dividing grooves. The base of the NdFeB permanent magnet is a 40mm×20mm×6mm square NdFeB. The length of the dividing grooves in a second extension direction is 70% of the length of the permanent magnet in this extension direction. The second extension direction of the dividing grooves is 60° to the length direction of the permanent magnet. The dividing grooves are distributed in a double-sided groove pattern. The width of the dividing grooves is 1mm, and the spacing between the dividing grooves is 6mm. In the magnetization direction perpendicular to the permanent magnet, the projected area of ​​the dividing grooves accounts for 8.93% of the projected area of ​​the permanent magnet.

[0089] Comparative Example 1

[0090] The invention discloses a NdFeB permanent magnet without a separation groove. The base of the NdFeB permanent magnet is a square NdFeB with a size of 40mm×20mm×5.65mm.

[0091] The gap between the permanent magnet matrix and the iron core magnetic steel slot is 0.45 mm.

[0092] The expandable material is coated on two large surfaces of the NdFeB permanent magnet, with a single-side coating thickness of 0.15 mm. After coating, the size of the NdFeB permanent magnet is 40 mm×20 mm×5.95 mm.

[0093] The expandable material includes: 50wt% epoxy resin, 12wt% acrylic resin, 15wt% expandable microspheres, 7wt% dicyandiamide, 10wt% calcium carbonate, 0.8wt% polyacrylate, 3.5wt% carbon black, 1wt% brightener C701 (Hubei Laisi Chemical), and 0.7wt% silicon dioxide.

[0094] The pre-curing conditions of the expandable material are a temperature of 100° C. and a time of 20 minutes. After pre-curing, a neodymium iron boron permanent magnet filled with the expandable material is obtained.

[0095] The NdFeB permanent magnet filled with expandable material is inserted into the magnetic steel slot and heated by electromagnetic induction. Within 3 minutes, the temperature of the permanent magnet is heated from room temperature to 200°C, and then cooled at room temperature to complete the fixation of the NdFeB permanent magnet filled with expandable material in the magnetic steel slot.

[0096] Comparative Example 2

[0097] A NdFeB permanent magnet with dividing grooves. The base of the NdFeB permanent magnet is a 40mm×20mm×6mm square NdFeB. The length of the dividing grooves in a second extension direction is 70% of the length of the permanent magnet in this extension direction. The dividing grooves are distributed in a double-sided groove pattern. The width of the dividing grooves is 1mm, and the spacing between the dividing grooves is 3.5mm. In a magnetization direction perpendicular to the permanent magnet, the projected area of ​​the dividing grooves accounts for 14% of the projected area of ​​the permanent magnet.

[0098] The gap between the permanent magnet matrix and the iron core magnetic steel slot is 0.1 mm.

[0099] The permanent magnet separation groove is filled with expandable material, which includes: 50wt% epoxy resin, 12wt% acrylic resin, 15wt% expandable microspheres, 7wt% dicyandiamide, 10wt% calcium carbonate, 0.8wt% polyacrylate, 3.5wt% carbon black, 1wt% brightener C701 (Hubei Laisi Chemical), and 0.7wt% silicon dioxide.

[0100] The pre-curing conditions of the expandable material are a temperature of 100° C. and a time of 20 minutes. After pre-curing, a NdFeB permanent magnet with a separation groove filled with the expandable material is obtained.

[0101] The NdFeB permanent magnet with a partition groove filled with expandable material is inserted into the magnetic steel slot and heated by electromagnetic induction. Within 3 minutes, the temperature of the permanent magnet is heated from room temperature to 200°C. The expandable material in the partition groove expands due to the heat and spreads from the partition groove to the magnet surface of the permanent magnet (as shown in Figure 3). It is then cooled at room temperature to complete the fixation of the NdFeB permanent magnet in the magnetic steel slot.

[0102] Comparative Example 3

[0103] A NdFeB permanent magnet with dividing grooves. The base of the NdFeB permanent magnet is a 40mm×20mm×6mm square NdFeB. The length of the dividing grooves in a second extension direction is 40% of the length of the permanent magnet in the same extension direction. The dividing grooves are distributed in a double-sided groove pattern. The width of the dividing grooves is 1mm, and the spacing between the dividing grooves is 6mm. In a magnetization direction perpendicular to the permanent magnet, the projected area of ​​the dividing grooves accounts for 5% of the projected area of ​​the permanent magnet.

[0104] The gap between the permanent magnet matrix and the iron core magnetic steel slot is 0.1 mm.

[0105] The permanent magnet separation groove is filled with expandable material, which includes: 50wt% epoxy resin, 12wt% acrylic resin, 15wt% expandable microspheres, 7wt% dicyandiamide, 10wt% calcium carbonate, 0.8wt% polyacrylate, 3.5wt% carbon black, 1wt% brightener C701 (Hubei Laisi Chemical), and 0.7wt% silicon dioxide.

[0106] The pre-curing conditions of the expandable material are a temperature of 100° C. and a time of 20 minutes. After pre-curing, a NdFeB permanent magnet with a separation groove filled with the expandable material is obtained.

[0107] The NdFeB permanent magnet with a partition groove filled with expandable material is inserted into the magnetic steel slot and heated by electromagnetic induction. Within 3 minutes, the magnet temperature is heated from room temperature to 200°C. The expandable material in the partition groove expands due to the heat and spreads from the partition groove to the magnet surface of the permanent magnet. It is then cooled at room temperature to complete the fixation of the permanent magnet in the magnetic steel slot.

[0108] Comparative Example 4

[0109] A NdFeB permanent magnet with a separation groove and filled with an expandable material was prepared with reference to Example 1. The difference from Example 1 is as follows:

[0110] The permanent magnet separation groove is filled with expandable material, which includes: 60wt% epoxy resin, 10wt% acrylic resin, 8wt% expandable microspheres, 9wt% dicyandiamide, 8wt% calcium carbonate, 0.7wt% polyacrylate, 3.5wt% carbon black, 0.4wt% brightener C701 (Hubei Laisi Chemical), and 0.4wt% silicon dioxide.

[0111] Comparative Example 5

[0112] Referring to Example 1, a neodymium iron boron permanent magnet with a separation groove filled with expandable material was prepared. The difference from Example 1 is that the expandable material was filled in the permanent magnet separation groove, and the expandable material included: 35wt% epoxy resin, 5wt% acrylic resin, 35wt% expandable microspheres, 3wt% dicyandiamide, 18wt% calcium carbonate, 0.3wt% polyacrylate, 3.3wt% carbon black, 0.2wt% brightener C701 (Hubei Laisi Chemical), and 0.2wt% silica.

[0113] Test Case

[0114] The NdFeB magnets prepared in the above examples and comparative examples were tested for resistivity and magnetic flux. The NdFeB magnets that were expanded and fixed in the magnetic steel slots were tested for 150°C push-out force and expansion coating coverage area. The specific test methods are as follows:

[0115] 1) Resistivity: The resistance R of the magnet is measured using a resistance meter. The resistivity ρ of the magnet is then calculated using the formula: ρ = RS / L, where S is the cross-sectional area of ​​the magnet and L is the distance between the voltage detection terminals.

[0116] 2) Magnetic flux: After the magnet is saturated and magnetized, a fluxmeter is used to measure the magnetic flux of the magnet.

[0117] 3) 150℃ push-out force: Tested at an ambient temperature of 150℃ with reference to GB / T 7124-2008.

[0118] 4) Expansion coating filling ratio test: After pushing the NdFeB magnet out of the magnet slot, measure the coverage area of ​​the expansion coating on the NdFeB magnet / magnet area.

[0119] The test results are recorded in Table 1.

[0120] Table 1

[0121] From the results in Table 1 we can see that:

[0122] Comparison of Example 1 and Comparative Example 1 shows that when the spacing between the dividing slots is 6 mm and the length of the dividing slots in the second extension direction is 70% of the length of the permanent magnet in that direction, the projected area of ​​the dividing slots accounts for 8.75% of the projected area of ​​the permanent magnet. The resistivity of the permanent magnet is significantly higher than that of a permanent magnet without dividing slots, eddy current losses are reduced, and magnetic properties are improved. The magnetic flux is essentially the same as that of a permanent magnet without dividing slots, and the smaller gap between the magnet and the steel slots results in higher magnetic flux utilization. The push-out force is essentially the same at 150°C.

[0123] The comparison results of Example 1 and Comparative Example 2 show that when the separation groove spacing is small and the separation groove projection area ratio is high, although the resistivity is high and the 150°C push-out force is equivalent, the magnetic flux loss of the magnet is large.

[0124] The comparison results between Example 1 and Comparative Example 3 show that: when the length of the separation groove in the second extension direction is shorter and the proportion of the separation groove projected area is lower, the magnetic flux is basically the same, but the resistivity will be significantly reduced. In addition, due to the smaller slot volume and the lower filling ratio of the expansion coating, the 150°C push-out force will also be significantly reduced.

[0125] The comparison results of Example 1 and Example 2 show that when the separation groove spacing and the ratio of the projected area of ​​the separation groove are not within the preferred range, the magnetic flux will be slightly increased, the resistivity will be slightly decreased, the filling ratio of the expansion coating will be slightly decreased, and the 150°C push-out force will be slightly decreased.

[0126] The comparison results of Example 2 and Example 3 show that when other conditions are the same and the only difference is that the separation groove is grooved on both sides or grooved on one side, the resistivity of Example 3 with grooves on both sides is slightly higher, the filling ratio of the expansion coating with grooves on both sides is slightly higher, and the push-out force at 150°C is slightly higher.

[0127] Comparison results between Example 1 and Example 4 show that different expandable material formulations can also achieve a significant increase in resistivity, and the magnetic flux and push-out force at 150° C. are substantially equivalent to those of a permanent magnet without a separation groove.

[0128] Comparison results between Example 1 and Example 5 show that when the first extension direction of the separation groove forms an angle with the length direction of the permanent magnet, a magnet with high resistivity, high magnetic flux and high ejection force can be obtained by adopting the solution of the present invention.

[0129] The comparison results of Example 1 and Comparative Example 4 show that when the formula of the expandable material changes, resulting in a lower self-expansion rate, the filling ratio of the expandable coating will decrease and the push-out force at 150°C will become smaller.

[0130] The comparison results of Example 1 and Comparative Example 5 show that when the formula of the expandable material changes, resulting in a higher self-expansion rate, the expansion coating filled between the permanent magnet and the magnetic steel slot will become loose and the 150°C push-out force will become smaller.

[0131] The above describes exemplary embodiments of the present invention. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A permanent magnet, characterized in that: The permanent magnet comprises a dividing groove, and the dividing groove is arranged on the permanent magnet; the expandable material is only filled in the groove of the dividing groove, and the expandable material is not arranged on the surface of the permanent magnet.

2. The permanent magnet according to claim 1, characterized in that: The separation groove passes through the permanent magnet in a first extension direction of the separation groove, and does not pass through the permanent magnet in a second extension direction of the separation groove, wherein the first extension direction of the separation groove is parallel to the magnetization direction of the permanent magnet, or the first extension direction of the separation groove has an angle with the magnetization direction of the permanent magnet. Preferably, the second extension direction is parallel to the width direction or the length direction of the permanent magnet, or the second extension direction of the separation groove forms an angle with the width direction or the length direction of the permanent magnet.

3. The permanent magnet according to claim 1 or 2, characterized in that: In the second extending direction, the length of the separation groove is greater than 50% of the length of the permanent magnet. Preferably, the width of the separation groove is 0.5-1.5 mm. Preferably, the distance between two adjacent separation grooves is 4-8 mm. Preferably, in a direction perpendicular to the magnetization direction of the permanent magnet, the projection area of ​​the separation groove accounts for 6-10% of the projection area of ​​the permanent magnet. Preferably, the separation grooves are distributed on the permanent magnet in a single-sided groove or a double-sided groove. Preferably, the expansion ratio of the expandable material under free expansion conditions is 3-4.

4. The permanent magnet according to any one of claims 1 to 3, characterized in that: The expandable material comprises the following raw materials: resin, foaming agent, curing agent, inorganic filler, leveling agent, pigment, brightening agent, anti-settling agent, or is prepared from the above raw materials.

5. The permanent magnet according to any one of claims 1 to 4, characterized in that: The weight percentage of the resin in the expandable material is 45-65wt%. Preferably, the resin is selected from one or more of epoxy resin, acrylic resin and polyester resin. Preferably, the weight percentage of the foaming agent in the expandable material is 10-30wt%. Preferably, the foaming agent is selected from thermoplastic expanded microspheres, and the diameter of the expanded microspheres is 5-30 μm. Preferably, the average diameter of the expanded microspheres is 10-15 μm. Preferably, the expansion temperature of the expanded microspheres is 110-210°C. Preferably, the maximum heat-resistant temperature of the expanded microspheres is 145-235°C. Preferably, the curing agent is selected from one or more of dicyandiamide, modified or accelerated dicyandiamide, and dimethylimidazole. Preferably, in the expandable material, the weight percentage of the curing agent is 3-10wt%.

6. The permanent magnet according to any one of claims 1 to 5, characterized in that: The inorganic filler is selected from one or more of calcium carbonate, mica powder and barium sulfate. Preferably, in the expandable material, the weight percentage of the inorganic filler is 5-15wt%. Preferably, the leveling agent is selected from at least one of acrylate and organosiloxane. Preferably, in the expandable material, the weight percentage of the leveling agent is 0.1-1wt%. Preferably, the pigment is selected from at least one of carbon black and zinc oxide. Preferably, in the expandable material, the weight percentage of the pigment is 1-5wt%. Preferably, the brightener is selected from acrylate copolymers. Preferably, in the expandable material, the weight percentage of the brightener is 0.5-1.5wt%. Preferably, the anti-settling agent is selected from at least one of silicon dioxide and montmorillonite. Preferably, in the expandable material, the weight percentage of the anti-settling agent is 0.1-0.7wt%.

7. The permanent magnet according to any one of claims 1 to 6, characterized in that: The gap between the permanent magnet and the iron core magnetic steel slot is 0.05-0.15mm. Preferably, the expandable material fills at least a portion of the surface of the permanent magnet after expansion. Preferably, the expandable material fills 80-100% of the surface area of ​​the permanent magnet after expansion.

8. The method for preparing a permanent magnet according to any one of claims 1 to 7, characterized in that: The preparation method comprises preparing a permanent magnet with a separation groove, filling the separation groove with expandable material, and then pre-curing to obtain the permanent magnet.

9. The preparation method according to claim 8, characterized in that: After the pre-treatment process, the permanent magnet with the separation groove is filled with expandable material in the separation groove. Preferably, the step of filling the expandable material comprises: filling the expandable material into the dividing groove for the first time, compacting it and then repeatedly filling it. Preferably, the pre-curing conditions include: a pre-curing temperature of 90-130° C.; and a pre-curing time range of 15-40 min. Preferably, after pre-curing, the density of the expandable material in the separation groove is 1.1-1.4 g / cm 3 .

10. Use of the permanent magnet according to any one of claims 1 to 7 in a motor rotor. Preferably, the process of fixing the permanent magnet in the motor rotor includes: The permanent magnet is inserted into the magnetic steel slot of the motor rotor, and after heating and curing, the permanent magnet is fixed in the motor rotor. Preferably, the conditions for heating and curing include: curing temperature of 170-230° C.; curing time of 2-5 min.

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