Permanent magnet material resistivity reference sample setting device and preparation method

Abstract

This invention relates to the field of rare earth permanent magnet material metrology technology, and discloses a device and preparation method for determining the resistivity reference sample of permanent magnet materials. The device includes a constant current power supply, a DC ammeter, a commutation switch S, a nanovoltmeter, a sample fixture, and a control computer. The constant current power supply has an output current range of 1A to 5A. The DC ammeter is connected in series between the constant current power supply and the sample fixture. The commutation switch S has two independent commutation channels. The sample fixture is used to fix the reference sample to be determined, and its structural design is adapted to the requirements of the van der Bauer method. The nanovoltmeter has a DC voltage measurement range of 0.05mV to 1mV. The control computer is communicatively connected to the constant current power supply, the DC ammeter, the commutation switch S, and the nanovoltmeter, and is used for test process control and data acquisition and storage. This device can eliminate interference factors such as temperature and clamping stress, significantly improving the accuracy, stability, and testing efficiency of resistivity determination, and meeting the requirements for determining the resistivity reference sample of permanent magnet materials.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet material metrology technology, and in particular to a device and preparation method for setting the resistivity reference sample of permanent magnet material. Background Technology

[0002] Permanent magnet materials are key functional materials for intelligent large-scale DC converter transformers and intelligent reactors. They are used to manufacture permanent magnet bias cores, permanent magnet stabilizing components, and low eddy current loss magnetic structures in reactors, instrument transformers, filter inductors, and rectifiers, directly improving the efficiency, temperature rise control, and operational stability of transformers / reactors / inductors. The resistivity of permanent magnet materials directly determines the magnitude of eddy current losses in the magnet, making it a core performance indicator for the efficient and low-loss design of transformers, reactors, and inductors.

[0003] Rare earth permanent magnet resistivity meters, as specialized testing equipment, are widely used in rare earth permanent magnet material manufacturers, research institutions, and metrology and testing organizations. Their measurement accuracy directly determines the reliability of resistivity data. Regular calibration of the resistivity meter using reference calibration pieces is essential to ensure the validity of measurement data and is a core requirement for standardizing testing procedures and improving product quality in relevant industries.

[0004] There is currently no dedicated device for determining the resistivity of permanent magnet materials using the van der Bauer method. The sample clamping cannot accommodate samples of various specifications and does not meet the electrode arrangement requirements of the van der Bauer method, which affects the safety of the testing process and the accuracy and timeliness of the data. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for determining the resistivity of a permanent magnet material resistivity reference sample, thereby solving the problems mentioned in the background art, such as the inability of the sample clamping to accommodate multiple sample sizes and the failure to meet the electrode arrangement requirements of the van der Bauer method.

[0006] The technical solution adopted in this invention is as follows: a permanent magnet material resistivity reference sample setting device, comprising a constant current power supply, a DC ammeter, a commutation switch S, a nanovoltmeter, a sample fixture under test, and a control computer; the constant current power supply outputs a current range of 1A~5A, the DC ammeter is connected in series between the constant current power supply and the sample fixture under test; the commutation switch S has two independent commutation channels, and the nanovoltmeter has a DC voltage measurement range of 0.05mV~1mV; the control computer is communicatively connected to the constant current power supply, the DC ammeter, the commutation switch S, and the nanovoltmeter, respectively, for automated control of the testing process and data acquisition and storage.

[0007] The ring seat has a through hole at its center, and a cleaning ring is installed inside the through hole. The inner wall of the cleaning ring is a conical slope surface, which is used to clean the side of the permanent magnet material.

[0008] The top surfaces of the first and second clamps are rotatably connected to a third clamp via a first rotating shaft. The third clamp is provided with an L-shaped third limiting groove. A fourth spring is connected between the bottom surface of the third clamp and the top surfaces of the first and second clamps to realize the floating clamping of the permanent magnet material. A contact assembly is installed on the third clamp.

[0009] The vertical section of the third limiting groove is symmetrically provided with two blind holes, and an auxiliary clamping rod is installed in the blind holes. The auxiliary clamping rod includes a cylinder, an end cover, a push rod, a fifth spring, a closing ring, an intermediate body, a sixth spring, and a clamping head. The cylinder is filled with hydraulic oil. The push rod is slidably connected to the end cover. The intermediate body is slidably connected to the cylinder. The end face of the intermediate body has a first oil passage and a second oil passage. The closing ring is used to block the first oil passage. The sixth spring is sleeved between the cylinder and the push rod. The clamping head is connected to the free end of the push rod.

[0010] The clamping head includes a first chuck seat and a first chuck body rotatably connected to the first chuck seat. The first chuck body is made of rubber and has a serrated clamping surface. Alternatively, the clamping head includes a second chuck seat, a first hemispherical head, a second hemispherical head, a ball head cover, and a second chuck body. The second hemispherical head is simultaneously connected to the first hemispherical head and the ball head cover via a ball joint. The second chuck body is fixed to the second hemispherical head.

[0011] The horizontal section of the third limiting groove has a sliding hole, and a sliding rod is slidably connected in the sliding hole. A seventh spring is sleeved on the sliding rod. The bottom surface of the third clamp has a track groove, and a wedge-shaped seat is slidably connected in the track groove. The wedge-shaped seat slides in contact with the bottom surface of the sliding rod. The wedge-shaped seat is driven by the third telescopic rod to adjust the height of the sliding rod.

[0012] The lower end of the bearing is connected to a bidirectional lead screw slide. A second vertical plate is fixed on each of the two movable seats of the bidirectional lead screw slide. A suction head seat is connected to the second vertical plate through a cylinder slide. The bidirectional lead screw slide drives the two suction head seats to open and close synchronously to accommodate permanent magnet materials of different sizes.

[0013] The beneficial effects of this invention are as follows: This device is based on the van der Bauer method to design a permanent magnet material resistivity reference sample setting structure. A switchable constant current power supply, combined with a dual-channel commutator with silver alloy contacts, enables current commutation measurement, effectively eliminating thermoelectric potential interference. High-precision DC ammeters and nanovoltmeters ensure accurate current and voltage acquisition, providing precise basic data for sample setting. The first and second motors drive synchronously moving first and second clamps, adapting to clamping permanent magnet material samples of different sizes, such as circular, square, and elliptical, precisely matching the electrode arrangement requirements of the van der Bauer method. Contact components with elastic rounded corner caps and V-shaped adaptive contact rods ensure tight and stable contact between the sample and electrodes, reducing contact resistance and improving acquisition accuracy. The floating clamping structure eliminates clamping stress and prevents sample deformation. Combined with a height-adjustable structure and adaptive auxiliary clamping rods, it adapts to clamping samples of different shapes and thicknesses, significantly improving the device's versatility. A rotatable top rod with a limiting structure enables automatic sample flipping, allowing for double-sided detection without secondary clamping, thus improving detection efficiency. Simultaneously, it avoids positioning errors caused by repeated clamping, ensuring consistency of test data on both sides. A box with serpentine heat exchange pipes, combined with a finned heat exchanger inside the constant temperature chamber, achieves constant temperature control and sample preheating, eliminating the impact of temperature fluctuations on resistivity testing. The automatically opening and closing double-door design ensures the stability of the constant temperature environment, improving the accuracy of the setpoint results. A feeding mechanism with V-shaped guide grooves and a suction assembly with precisely adjustable pitch angle and 0°-180° rotation enable fully automatic sample loading, unloading, and transfer. A bidirectional screw slide allows for flexible adjustment of the suction head spacing to accommodate the adsorption needs of samples of different sizes, simultaneously enabling testing and sample replacement operations, significantly improving overall testing efficiency. A cleaning ring with a conical ramp at the center of the ring seat automatically cleans the sides of the sample, removing dust and impurities to ensure electrode contact. The control computer enables multi-device collaborative control, fully automated testing process management, and real-time monitoring of equipment operation status. When an equipment malfunction is detected, an alarm is immediately triggered and the test is paused, comprehensively ensuring the safety of the testing process and the timeliness and accuracy of the test data. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the process structure of this application.

[0015] Figure 2 This is a schematic diagram of the three-dimensional structure of the fixture for the sample being tested.

[0016] Figure 3 This is a schematic diagram of the front cross-sectional structure of the sample holder.

[0017] Figure 4 This is a schematic diagram of the three-dimensional structure of the top plate.

[0018] Figure 5 This is a schematic diagram of the three-dimensional structure of the ring seat.

[0019] Figure 6 This is a schematic diagram of the first and second circular rings.

[0020] Figure 7 This is a three-dimensional structural diagram of the first clamp.

[0021] Figure 8 This is a top-view cross-sectional structural diagram of the contact assembly.

[0022] Figure 9 This is a top-view cross-sectional structural diagram of the contact rod.

[0023] Figure 10 This is a side view of the top rod structure.

[0024] Figure 11 This is a side view sectional diagram of the top rod.

[0025] Figure 12 This is a side view sectional diagram of the rotating pipe.

[0026] Figure 13 This is a top view of the box's structure.

[0027] Figure 14 This is a schematic diagram of the front sectional structure of the box.

[0028] Figure 15 This is a schematic diagram of the front cross-sectional structure of the constant temperature environment chamber.

[0029] Figure 16 This is a top view of the finned heat exchanger.

[0030] Figure 17 This is a three-dimensional structural diagram of the first door panel.

[0031] Figure 18 This is a schematic diagram of the three-dimensional structure of the third rack.

[0032] Figure 19 This is a side view sectional diagram of the feeding mechanism.

[0033] Figure 20 This is a three-dimensional structural diagram of the feeding mechanism.

[0034] Figure 21 This is a three-dimensional structural diagram of the first guide groove.

[0035] Figure 22 This is a schematic diagram of the three-dimensional structure of the synchronous belt.

[0036] Figure 23 This is a side view of the component structure.

[0037] Figure 24A schematic diagram of the three-dimensional structure of the component.

[0038] Figure 25 This is a schematic diagram of the front cross-sectional structure of the suction head holder.

[0039] Figure 26 This is a schematic diagram of the front cross-sectional structure of the suction head body.

[0040] Figure 27 This is a schematic diagram of the front cross-sectional structure of the cleaning ring.

[0041] Figure 28 This is a three-dimensional structural diagram of the third clamp.

[0042] Figure 29 This is a three-dimensional structural diagram of the first rotating shaft.

[0043] Figure 30 This is a three-dimensional structural diagram of the fourth spring.

[0044] Figure 31 This is a side view sectional diagram of the cylinder.

[0045] Figure 32 This is a side view sectional diagram of the push rod.

[0046] Figure 33 This is a schematic diagram of the main structure of the intermediate.

[0047] Figure 34 This is a top-view cross-sectional structural diagram of the intermediate body.

[0048] Figure 35 This is a side view sectional diagram of the second chuck seat.

[0049] Figure 36 This is a three-dimensional structural diagram of the ball head cover.

[0050] Figure 37 This is a side view sectional diagram of the slide bar.

[0051] Figure 38 This is a side view sectional structural diagram of the second vertical plate.

[0052] In the diagram: 1. Constant current power supply; 2. DC ammeter; 3. Reversing switch S; 4. Nanovoltmeter; 5. Sample holder; 6. Control computer; 7. Base plate; 8. Ring seat; 9. Circular groove; 10. First ring; 11. Second ring; 12. First gear ring; 13. First gear; 14. Second gear; 15. First motor; 16. Second gear ring; 17. Third gear; 18. Fourth gear; 19. Second motor; 20. Top plate; 21. Outer shell; 22. Storage slot; 23. First guide rail; 24. First slider; 25. First rack; 26. Fifth gear; 27. First clamp; 28. First limiting groove; 29. ​​Second guide rail; 30. Second slider; 31. Second rack; 32. Sixth gear; 33. Second... 34. Clamp; 35. Second limiting groove; 36. First groove; 37. Contact assembly; 38. Contact seat; 39. First spring; 40. Contact cap; 41. First hinge seat; 42. First contact rod; 43. First spring seat; 44. Second spring; 45. Top rod; 46. Third spring; 47. First bearing seat; 48. Rotary tube; 49. Third motor; 50. Motor seat; 51. Limiting strip; 52. Box body; 53. Heat exchange pipe; 54. Foot seat; 55. Constant temperature environment chamber; 56. Finned heat exchanger; 57. Thermostatic valve; 58. Box cover; 59. Material inlet; 60. Double-leaf box door; 61. Temperature sensor; 62. Third guide rail; 63. Third slider; 64. Third rack; 65. Seventh gear; 66. Fourth motor; 67. 6. First door panel; 67. Second door panel; 68. Feeding mechanism; 69. Base plate; 70. Rib plate; 71. Fourth guide rail; 72. First slide table; 73. Bearing seat; 74. Notch; 75. Fifth guide rail; 76. Second slide table; 77. Support arm; 78. Suction assembly; 79. Shaft; 80. Guide wheel; 81. First guide groove; 82. First clamping plate; 83. Second guide groove; 84. Second clamping plate; 85. Fifth motor; 86. First pulley; 87. Second bearing seat; 88. Second pulley; 89. Synchronous belt; 90. First support; 91. Third bearing seat; 92. Second support; 93. First telescopic rod; 94. Third support; 95. Shaft seat; 96. Eighth gear; 97. Positioning seat; 98. Limiting rod 99. Fourth support; 100. Fourth rack; 101. Second telescopic rod; 102. Limiting plate; 103. First vertical plate; 104. Cylinder slide; 105. Suction head seat; 106. Main air passage; 107. Air pipe; 108. Vacuum pump; 109. Air valve; 110. Suction head body; 111. Air chamber; 112. Branch air passage; 113. Through hole; 114. Cleaning ring; 115. First rotating shaft; 116. Third clamp; 117. Third limiting groove; 118. Second groove; 119. Second spring seat; 120. Fourth spring; 121. Third spring seat; 122. Blind hole; 123. Auxiliary clamping rod; 124. Cylinder; 125. End cap; 127. Push rod; 128. Spring groove; 129. Fifth spring;130. Closed ring; 131. Intermediate body; 132. Nut head; 133. First oil passage; 134. Second oil passage; 135. Sixth spring; 136. Clamping head; 137. First chuck seat; 138. First chuck body; 139. Second chuck seat; 140. First semi-spherical head; 141. Second semi-spherical head; 142. Ball head cover; 143. Second chuck body; 144. Sliding hole; 145. Sliding rod; 146. Seventh spring; 147. Track groove; 148. Wedge seat; 149. Third telescopic rod; 150. Bidirectional lead screw slide; 151. Moving seat; 152. Second vertical plate. Detailed Implementation

[0053] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0054] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0055] Furthermore, the terms “first,” “second,” “third,” “fourth,” “fifth,” “sixth,” “seventh,” “eighth,” “ninth,” and “tenth” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0056] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation", "connection", and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0057] This resistivity reference sample setting device is based on the van der Bauer method measurement principle and follows the technical requirements of GB / T31967.3-2025 "Test Methods for Physical Properties of Rare Earth Permanent Magnet Materials Part 3: Test of Resistivity", which can achieve accurate setting of the resistivity of permanent magnet material reference samples.

[0058] like Figure 1 As shown in Embodiment 1, a permanent magnet material resistivity reference sample setting device includes a constant current power supply 1: serving as a test circuit current supply unit, with an output current range of 1A~5A. It can switch functions according to the actual size and thickness of the sample to be tested, and cooperates with subsequent voltage acquisition to eliminate thermoelectric potential interference, which meets the "current reversal measurement" requirement in the van der Bauer method, and provides a stable current for resistivity calculation.

[0059] DC ammeter 2: connected in series between constant current power supply 1 and sample fixture 5, DC current measurement range is not less than 5A, maximum permissible error is ±0.1%, can collect the actual current value of the circuit in real time and transmit it to control computer 6;

[0060] Reversing switch S3: The reversing switch uses silver alloy contacts and has two independent reversing channels, which are used to control the current input direction of electrodes AB and BC respectively; the current direction can be switched by controlling computer 6 to realize the injection of equal and opposite currents when measuring the same set of current terminals;

[0061] Nanovoltmeter 4: This is the core unit for voltage acquisition. The DC voltage measurement range is 0.05mV~1mV, and the maximum permissible error is ±0.2%. It is used to test the voltage at the DC and AD terminals.

[0062] like Figure 2-6As shown, the sample fixture 5 is used to fix a permanent magnet material reference sample with a value to be determined. Its structural design is fully adapted to the testing requirements of the van der Burg method. It includes a base plate 7, with a ring seat 8 mounted at the center of its top surface. The diameter of the ring seat 8 is smaller than the diameter of the base plate 7. The side of the ring seat 8 has a circular groove 9, within which a first ring 10 and a second ring 11 are rotatably connected. The first ring 10 is located above the second ring 11. Two symmetrically arranged first toothed rings 12 are connected to the side of the first ring 10. The first toothed rings 12 are arc-shaped and located on the plane containing the longitudinal axis of the first ring 10. A first gear 13 meshes with the first toothed ring 12, and a second gear 14 meshes with the first gear 13. The second gear 14 is driven by a first motor 15, which is connected to the base plate 7. Two symmetrically arranged first toothed rings 12 are connected to the side of the second ring 11. The second toothed ring 16 is arranged in an arc shape, and the two second toothed rings 16 are located on the plane where the transverse axis of the second ring 11 is located. A third gear 17 meshes on the second toothed ring 16, and a fourth gear 18 meshes on the third gear 17. The fourth gear 18 is driven by a second motor 19, which is connected to the base plate 7. A top plate 20 is connected to the top surface of the ring seat 8. The diameter of the top plate 20 is the same as that of the base plate 7. A shell 21 is connected to the outer side wall of the top plate 20 and the base plate 7. The top surface of the top plate 20 has four equally angled storage slots 22. A first guide rail 23 is installed in two longitudinally opposite storage slots 22. A first slider 24 is slidably connected to the first guide rail 23. The bottom of the first slider 24... The component has a first rack 25, on which two symmetrically arranged fifth gears 26 mesh. One of the fifth gears 26 is coaxial with the first gear 13 and rotates synchronously with the first gear 13. A first clamp 27 is mounted on the top surface of the first slider 24. The cross-sectional shape of the first clamp 27 is T-shaped. The top surface of the wide side of the first clamp 27 has a first limiting groove 28, which is L-shaped. A second guide rail 29 is installed in two laterally opposite storage slots 22. A second slider 30 is slidably connected to the second guide rail 29. The bottom of the second slider 30 has a second rack 31, on which two symmetrically arranged sixth gears 32 mesh. One of the sixth gears 32 is coaxial with the third gear 13. Wheel 17 is coaxial, and the sixth gear 32 rotates synchronously with the third gear 17. The top surface of the second slider 30 is equipped with a second clamp 33, which has a T-shaped cross-section and a second limiting groove 34 on its wide side top surface. The second limiting groove 34 is L-shaped. The first clamp 27 and the second clamp 33 are used to place permanent magnet materials of different sizes. The permanent magnet materials can be circular, square, or elliptical. The first motor 15 drives the two first clamps 27 to move synchronously, and the second motor 19 drives the two second clamps 33 to move synchronously, thus realizing the stable installation of the permanent magnet materials. The two first clamps 27 correspond to the positions of the sample electrodes (B, D), and the two second clamps 33 correspond to the positions of the sample electrodes (A, C).

[0063] Control Computer 6: Possesses core functions for multi-device collaborative control, real-time data reception and storage. It supports establishing a stable data interaction chain with the constant current power supply 1, ammeter, reversing switch, nanovoltmeter 4, and testing software via interfaces. It can receive raw current and voltage data transmitted from each module in real time, ensuring the timeliness of test data. In terms of control functions, it can issue current adjustment commands to the constant current power supply 1 (e.g., adjusting from 1A to 5A in steps) according to instructions from the testing software or preset programs, send reversing signals to the reversing switch S3 (switching the current input direction), and trigger voltage acquisition commands to the nanovoltmeter 4, achieving fully automated control of the testing process. It also has a status monitoring function, which can monitor the operating status of each connected module in real time (e.g., the output stability of the constant current power supply 1, and whether the ammeter data acquisition is normal). If an abnormality is detected, it will immediately trigger an alarm and pause the testing process, ensuring the safety and accuracy of the test. Technical problems solved: Existing devices for resistivity determination of permanent magnet materials lack a dedicated adaptation to the Van der Bauer method; unstable current supply cannot eliminate thermoelectric potential interference; current and voltage acquisition accuracy is insufficient; sample clamping cannot accommodate multiple sample sizes and does not meet the electrode arrangement requirements of the Van der Bauer method; multiple devices cannot be coordinated for control; the testing process cannot be automated; and equipment malfunctions are not monitored, resulting in poor test data accuracy and low safety. Beneficial effects: Meets the current commutation measurement requirements of the Van der Bauer method, eliminates thermoelectric potential interference, ensures current and voltage acquisition accuracy, adapts to the clamping of permanent magnet material samples of different sizes such as circular, square, and elliptical, achieves fully automated testing with multi-device coordination, monitors equipment status in real time, and ensures the safety of the testing process and the accuracy and timeliness of the data.

[0064] like Figure 7 and 8 As shown, as an optimization of Embodiment 1, the vertical sections of the first limiting groove 28 and the second limiting groove 34 are provided with a first groove 35, which is located at the central axis. The first groove 35 also includes a contact assembly 36 disposed within the first groove 35. The contact assembly 36 includes a contact seat 37, which is barrel-shaped. A first spring 38 is installed inside the contact seat 37, and a contact cap 39 is connected to the free end of the first spring 38. The contact cap 39 abuts against the side of the permanent magnet material, and the contact surface of the contact cap 39 has a rounded corner structure. Technical problem solved: Existing fixtures have a hard contact between the contact and the permanent magnet material sample, which easily damages the sample. The contact between the contact and the sample is not tight, leading to errors in voltage acquisition. Beneficial effects: Elastic contact prevents the sample from being scratched or damaged, and the rounded corner structure ensures a tight fit between the contact and the side of the sample, reducing contact resistance and improving the accuracy of voltage acquisition.

[0065] like Figure 9As shown, as an optimization of Embodiment 1, the side wall of the contact seat 37 is connected to two symmetrically arranged first hinge seats 40. A first contact rod 41 is hinged to each first hinge seat 40, with the hinge point located at the waist of the first contact rod 41. One end of the first contact rod 41 is a round bar shape, the round bar end face being used to adaptively contact the side of the permanent magnet material. The other end of the first contact rod 41 is connected to a first spring seat 42, and a second spring 43 is connected between the two first spring seats 42, causing the two first contact rods 41 to form a V-shape. Technical problem solved: When the contact area between a single contact and the sample is small, and the sample side has an irregular shape, the contact stability is poor, and the voltage acquisition signal is prone to fluctuation. Beneficial effect: The V-shaped double contact rod structure can adaptively match different contours of the sample side, increasing the effective contact area, improving contact stability, suppressing voltage acquisition signal fluctuations, and ensuring the stability of test data.

[0066] like Figure 10-12 As shown, as an optimization of Embodiment 1, a push rod 44 is rotatably connected to the center of the contact cap 39 on the first clamp 27. The push rod 44 is used to further clamp the permanent magnet material. The push rod 44 extends to the outside of the first clamp 27 (second clamp 33). The free end of the push rod 44 is connected to a third spring 45. Four first bearing seats 46 arranged at equal angles are installed on the outer shell 21. A rotating tube 47 is rotatably connected to the first bearing seat 46. The rotating tube 47 is driven by a third motor 48. The third motor 48 is located on a motor seat 49, which is connected to the first bearing seat 46. The rotating tube 47 is used to connect the third spring 45. The rotating tube 47 has a limiting strip 50 to prevent the push rod 44 from rotating. The push rod 44 slides along the limiting strip 50. After the front of the permanent magnet material is inspected, the push rod 44 still presses against the side of the permanent magnet material. The third motor 48 drives the push rod 44 to rotate 180°, realizing the flipping of the permanent magnet material. The reverse side of the permanent magnet material can be inspected a second time. Technical Problem Solved: Existing devices cannot automatically flip samples, requiring manual secondary clamping for double-sided testing, resulting in low efficiency and positioning errors that affect the consistency of double-sided test data. Movement Process: The first clamp 27 and second clamp 33 release the permanent magnet material. The push rod 44 is connected to the rotating tube 47 via the third spring 45. The push rod 44 presses against the side of the permanent magnet material. The third motor 48 drives the rotating tube 47 to rotate, and the limiting strip 50 inside the rotating tube 47 drives the push rod 44 to rotate synchronously, thereby rotating the permanent magnet material 180° to complete the flipping. Beneficial Effects: Flipping and double-sided testing of the permanent magnet material can be completed without manual secondary clamping, significantly improving testing efficiency, avoiding positioning errors caused by repeated clamping, and ensuring the consistency of double-sided test data.

[0067] like Figure 13 and 14As shown, as an optimization of Embodiment 1, it also includes a housing 51, which has an inner and outer sandwich structure. A serpentine heat exchange pipe 52 is installed within the sandwich of the housing 51. An equally angled foot 53 is installed within the inner cavity of the housing 51, and the top surface of the foot 53 is used to fix the outer shell 21. Technical problem solved: Existing testing devices lack a dedicated protective installation structure, making it easy for external ambient temperature fluctuations to be conducted to the testing area, affecting the resistivity testing accuracy and resulting in poor device installation stability. Beneficial effects: The housing 51 provides stable installation support and protection for the device, while the serpentine heat exchange pipe 52 within the sandwich provides a structural basis for temperature control, blocking the influence of external ambient temperature fluctuations on the testing area and ensuring testing accuracy.

[0068] like Figure 15 and 16 As shown, as an optimization of Embodiment 1, it also includes a constant temperature environment chamber 54. The constant temperature environment chamber 54 has a trough-shaped structure, and two finned heat exchangers 55 are installed inside the constant temperature environment chamber 54. The water inlet of one finned heat exchanger 55 is connected to a thermostatic valve 56, and the water outlet of the finned heat exchanger 55 is used to connect to the water inlet of the heat exchange pipe 52; the water inlet of the other finned heat exchanger 55 is used to connect to the water outlet of the heat exchange pipe 52; a chamber cover 57 is connected to the top surface of the constant temperature environment chamber 54, and the chamber cover 57 has a material inlet 58. A double-leaf chamber door 59 is installed on the top surface of the chamber cover 57; preferably, a temperature sensor 60 is installed on the side wall of the constant temperature environment chamber 54. The finned heat exchanger 55 can preheat the permanent magnet material. Technical problem solved: The resistivity of permanent magnet materials is significantly affected by temperature. Existing devices lack constant temperature control and sample preheating structures, resulting in large temperature fluctuations during testing, leading to large deviations in the set value results. Movement Process: The thermostatic valve 56 controls the entry of the thermostatic medium into the finned heat exchanger 55. The medium circulates through the heat exchange pipe 52, preheating and maintaining the temperature of the housing 51 and the internal permanent magnet material. The temperature sensor 60 collects the temperature data inside the thermostatic environment chamber 54 in real time. Beneficial Effects: Achieves constant temperature control of the testing environment, allows for preheating of the permanent magnet material, eliminates the influence of temperature changes on resistivity testing, and ensures temperature control accuracy through real-time monitoring by the temperature sensor 60, significantly improving the accuracy of the setpoint results.

[0069] like Figure 17-19As shown, as an optimization of Embodiment 1, the double-leaf door 59 includes two sets of symmetrically arranged driving components. Each driving component includes two third guide rails 61, with third sliders 62 slidably connected to the third guide rails 61. The two third sliders 62 are arranged in an alternating pattern, and third racks 63 are connected to the third sliders 62. The two third racks 63 are driven by a seventh gear 64, which in turn is driven by a fourth motor 65 fixed to the third guide rails 61. One third rack 63 is connected to a first door panel 66, and the other third rack 63 is connected to a second door panel 67. When the first door panel 66 and the second door panel 67 are aligned, they can close the material inlet 58. The technical problem solved: Existing constant temperature chamber doors are manually operated, resulting in low automation, poor sealing, and an inability to maintain a stable constant temperature environment. Movement process: The fourth motor 65 drives the seventh gear 64 to rotate, which in turn drives the two meshing third racks 63 to move in opposite directions, thereby causing the first door panel 66 and the second door panel 67 to open and close synchronously, completing the closing and opening of the material inlet 58. Beneficial effects: It enables fully automatic opening and closing of the cabinet door, improves the automation level of the device, and the split structure ensures the sealing effect after the cabinet door is closed, effectively maintaining the temperature stability inside the constant temperature environment chamber 54.

[0070] like Figure 19-22As shown, as an optimization of Embodiment 1, a feeding mechanism 68 is connected to the outer wall of the box 51. The feeding mechanism 68 includes a base plate 69, and a rib plate 70 is connected at the angle between the base plate 69 and the box 51. Two symmetrically arranged fourth guide rails 71 are connected to the top surface of the base plate 69. A first slide table 72 is slidably connected to the fourth guide rails 71. A support seat 73 is installed on the first slide table 72. A U-shaped notch 74 is opened on the support seat 73. Two symmetrically arranged fifth guide rails 75 are connected to the support seat 73, and a second slide table 76 is slidably connected to the two fifth guide rails 75. The sliding direction of slide 6 is perpendicular to the sliding direction of the first slide 72; a support arm 77 is connected to the second slide 76, and a suction assembly 78 is installed on the support arm 77 for transferring permanent magnet materials; a shaft 79 is installed on the support arm 77, and a guide wheel 80 is rotatably connected to the shaft 79, which moves laterally within the notch 74; two symmetrically arranged first guide grooves 81 are formed on the base plate 69, located outside the fourth guide rail 71, and the first guide grooves 81 are V-shaped. The guide wheel 80 rolls in contact with the first guide grooves 81, thereby adjusting the support arm. The position of the suction component 78 on the support arm 77 is such that when the support seat 73 moves to the front end of the first guide groove 81, the suction component 78 on the support arm 77 begins to lower the permanent magnet material (as a detection position). When the support seat 73 moves to the rear end of the first guide groove 81, the suction component 78 on the support arm 77 begins to replace (as a replacement position). A first clamping plate 82 is connected to the support seat 73. Two symmetrically arranged second guide grooves 83 are opened on the base plate 69. The second guide grooves 83 are located inside the fourth guide rail 71. The first clamping plate 82 passes through the second guide grooves 83. A second clamping plate 84 is connected to plate 82; a fifth motor 85, a servo motor, is mounted on base plate 69, and a first pulley 86 is mounted on the shaft end of the fifth motor 85; a second bearing seat 87 is mounted on base plate 69, and a second pulley 88 is rotatably connected to the second bearing seat 87; a synchronous belt 89 is installed between the second pulley 88 and the first pulley 86, and the first clamping plate 82 and the second clamping plate 84 are mounted on the synchronous belt 89. When one side of the first clamping plate 82 is in the detection position of the first guide groove 81, the other side of the first clamping plate 82 is in the replacement position of the first guide groove 81. The technical problem solved: Existing devices use manual loading and unloading, which is inefficient, has poor loading and positioning accuracy, and cannot achieve synchronous operation of detection and loading, resulting in low overall testing efficiency.Movement Process: The fifth motor 85 drives the synchronous belt 89 through the first pulley 86 and the second pulley 88. The synchronous belt 89 drives the carrier 73 to move along the fourth guide rail 71 through the first clamping plate 82 and the second clamping plate 84. The guide wheel 80 rolls along the V-shaped first guide groove 81, driving the second slide table 76 to move along the fifth guide rail 75, adjusting the position of the suction component 78 on the support arm 77. When the carrier 73 moves to the front end of the first guide groove 81, the suction component 78 lowers the sample to the detection position. When the carrier 73 moves to the rear end of the first guide groove 81, the suction component 78 completes the sample replacement. The two carriers 73 simultaneously realize the alternation of detection and replacement operations. Beneficial Effects: It realizes fully automatic feeding and unloading of permanent magnet material samples. The V-shaped guide groove structure ensures the positioning accuracy of the suction component 78. The detection operation and feeding and replacement operation can be carried out simultaneously, greatly improving the overall testing efficiency and feeding accuracy.

[0071] like Figure 23-26As shown, as an optimization of Embodiment 1, the suction assembly 78 includes a first support 90, a third bearing seat 91 mounted on the first support 90, a second support 92 hinged to the third bearing seat 91, a first telescopic rod 93 hinged to the top surface of the second support 92, and the tail end of the first telescopic rod 93 hinged to the first support 90; a third support 94 is connected to the second support 92, a shaft seat 95 is rotatably connected to the third support 94, an eighth gear 96 is connected to the upper end of the shaft seat 95, a positioning seat 97 is connected to the top of the shaft seat 95, the positioning seat 97 is U-shaped, and limit rods 98 are connected to the two vertical sections of the positioning seat 97; a fourth support 99 is connected to the third support 94, a fourth rack 100 that meshes with the eighth gear 96 is slidably connected to the fourth support 99, the fourth rack 100 is driven by a second telescopic rod 101, and the second telescopic rod 101 is connected to the fourth support 99; the fourth support A limiting plate 102 is connected to the seat 99. When the limiting rod 98 abuts against the limiting plate 102, the limiting rod 98 can control the bearing seat 95 to switch between 0° and 180°. The lower end of the bearing seat 95 is connected to a first vertical plate 103. The two sides of the first vertical plate 103 are connected to a cylinder slide 104. A suction head seat 105 is connected to the cylinder slide 104. The suction head seat 105 has a main air passage 106. The upper end of the main air passage 106 is connected to an air pipe 107. The system includes a vacuum pump 108 and an air valve 109 on the side wall of the air pipe 107. A suction head body 110 is connected to the lower end of the main air channel 106. The suction head body 110 is used to pick up permanent magnet materials. The bottom surface of the suction head body 110 is horizontal, and the top surface of the suction head body 110 has an air cavity 111. Four branch air channels 112 are formed on the air cavity 111, penetrating the bottom surface of the suction head body 110. The four branch air channels 112 are arranged at equal angles. The technical problem solved is that existing sample transfer and suction structures cannot achieve precise angle adjustment and flipping of the sample, resulting in uneven distribution of adsorption force, which easily leads to sample displacement, detachment, or even damage, and poor transfer stability. Movement Process: The first telescopic rod 93 drives the second support 92 to swing around the third bearing seat 91, adjusting the pitch angle of the suction assembly 78. The second telescopic rod 101 drives the fourth rack 100 to slide, causing the eighth gear 96 and the shaft seat 95 to rotate. The limiting rod 98 on the positioning seat 97 cooperates with the limiting plate 102 to control the shaft seat 95 to switch precisely between 0° and 180°. The vacuum pump 108 generates negative pressure through the air pipe 107, main air channel 106, air chamber 111 and branch air channel 112, causing the suction head body 110 to adsorb the permanent magnet material sample. Beneficial Effects: It can realize the pitch angle adjustment and precise 0° and 180° flipping during sample transfer. The four sets of branch air channels 112 arranged at equal angles ensure the uniform distribution of adsorption force, avoid sample displacement, falling off and damage, and improve the stability and accuracy of sample transfer.

[0072] like Figure 27As shown, as an optimization of Embodiment 1, the ring seat 8 has a through hole 113 at its center, and a cleaning ring 114 is installed inside the through hole 113. The inner wall of the cleaning ring 114 is a conical slope. Combined with the liftable suction head body 110 and the rotatable shaft seat 95, the cleaning ring 114 can clean the sides of the permanent magnet material. Technical problem solved: Dust and impurities on the sides of the permanent magnet material sample affect the contact effect between the contactor and the sample, leading to increased contact resistance and reduced testing accuracy. Existing devices lack a matching sample side cleaning structure. Movement process: The suction head body 110 drives the permanent magnet material to rise and fall, and the shaft seat 95 drives the permanent magnet material to rotate, causing the sides of the permanent magnet material to rub against the conical slope of the cleaning ring 114, completing the cleaning of side impurities. Beneficial effects: Achieves fully automatic cleaning of the sides of the permanent magnet material sample, removing dust and impurities, ensuring good contact between the contactor and the sample side, reducing contact resistance, and further improving testing accuracy.

[0073] like Figures 28-30 As shown in Embodiment 2, unlike Embodiment 1, the top surfaces of the first clamp 27 and the second clamp 33 are connected to a first rotating shaft 115. A third clamp 116 is rotatably connected to the first rotating shaft 115. The cross-sectional shape of the third clamp 116 is T-shaped, and the narrow side of the top surface of the third clamp 116 has a third limiting groove 117, which is L-shaped. The bottom surface of the third clamp 116 has two symmetrically arranged second grooves 118, which are V-shaped. A second spring seat 119 is installed in the second groove 118, and a fourth spring 120 is connected to the second spring seat 119. The top surfaces of the first clamp 27 and the second clamp 33 are connected to a third spring seat 121, which is used to connect the fourth spring 120, enabling the floating clamping of the permanent magnet material. A contact assembly 36 is installed on the third clamp 116. The permanent magnet material is clamped on the third clamp 116 and will not be clamped on the first clamp 27 and the second clamp 33. Technical Problem Solved: Existing fixtures are rigid clamping structures, which are prone to clamping stress during clamping, causing deformation of the permanent magnet material sample and affecting the accuracy of resistivity test results. They also cannot adapt to the flexible clamping requirements of samples with different morphologies. Movement Process: The third clamp 116 is rotatably connected to the first clamp 27 and the second clamp 33 via the first rotating shaft 115. The fourth spring 120 is connected between the second spring seat 119 of the third clamp 116 and the third spring seat 121 of the first clamp 27 and the second clamp 33, providing floating support for the third clamp 116. The contact assembly 36 is mounted on the third clamp 116 and contacts the sample. Beneficial Effects: This device achieves floating clamping of the permanent magnet material sample, eliminates stress generated during clamping, avoids sample deformation, ensures the accuracy of resistivity test results, adapts to the clamping requirements of samples with different morphologies, and improves the versatility of the device.

[0074] like Figures 31-34As shown, as an optimization of Embodiment 2, the vertical section of the third limiting groove 117 has two symmetrically arranged blind holes 122, and an auxiliary clamping rod 123 is installed in the blind holes 122; the auxiliary clamping rod 123 includes a cylinder 124, the end of the cylinder 124 is provided with an end cap 125, the cylinder 124 is filled with hydraulic oil, and a push rod 127 is slidably connected to the end cap 125. The end of the push rod 127 located in the cylinder 124 is provided with a spring groove 128, and a fifth spring 129, a closing ring 130, an intermediate body 131, and a nut head 132 are arranged sequentially from left to right on the spring groove 128; the spring groove 128 and the intermediate body 131 The intermediate body 131 is slidably connected to the cylinder 124. The end face of the intermediate body 131 has two first oil passages 133 and two second oil passages 134, and the second oil passages 134 are located outside the first oil passages 133. The first oil passages 133 and the second oil passages 134 are located around the intermediate body 131. A closing ring 130 is used to block the first oil passages 133. The outer diameter of the closing ring 130 is smaller than the area where the projection of the second oil passages 134 is located. A sixth spring 135 is sleeved between the cylinder 124 and the push rod 127. The free end of the push rod 127 is connected to a clamping head 136, which is used to assist in clamping the permanent magnet material. During compression, the closing ring 130 opens, allowing hydraulic oil to flow through the two first oil passages 133 and the two second oil passages 134. During reset, the closing ring 130 closes, and hydraulic oil flows through the two second oil passages 134. Therefore, the push rod 127 is easily compressed but difficult to stretch, facilitating rapid assisted clamping and providing good clamping stability. This also helps absorb the energy of the sixth spring 135 (conventional spring-assisted clamping resets quickly, but continuous extension and retraction can easily damage the permanent magnet material). The technical problem solved: Existing spring-assisted clamping structures have a fast reset speed, but continuous extension and retraction can easily generate impacts, damaging the permanent magnet material sample. They also have poor clamping stability and cannot achieve a balance between rapid clamping and buffered reset. Movement process: When the push rod 127 is compressed, the closing ring 130 opens, allowing hydraulic oil to flow simultaneously through the first oil passage 133 and the second oil passage 134, causing the push rod 127 to quickly retract and complete the clamping. During reset, the closing ring 130 blocks the first oil passage 133, allowing hydraulic oil to flow only through the second oil passage 134, and the push rod 127 slowly extends to reset. Beneficial effects: It enables rapid compression clamping and slow buffering reset of push rod 127, avoids impact damage to the sample caused by spring reset, effectively absorbs the spring rebound energy, and improves the stability and safety of auxiliary clamping.

[0075] like Figure 31As shown, as an optimization of Embodiment 2, the clamping head 136 includes a first chuck seat 137, on which a first chuck body 138 is rotatably connected. The first chuck body 138 is made of rubber, and its clamping surface is serrated. The first chuck body 138 is used to assist in clamping permanent magnet materials. Technical problem solved: Existing auxiliary clamping heads have poor contact with the sample, easily slipping and scratching the sample surface during clamping. Beneficial effects: The serrated structure increases clamping friction, preventing slippage during clamping; the rubber material prevents scratching the sample surface; and the rotatable connection structure improves the contact between the clamping head and the sample side.

[0076] like Figure 35 and 36 As shown, as an optimization of Embodiment 2, the clamping head 136 includes a second clamping seat 139, a first hemispherical ball head 140 connected to the second clamping seat 139, a second hemispherical ball head 141 ball-jointed to the first hemispherical ball head 140, a ball head cover 142 connected to the second clamping seat 139, the ball head cover 142 and the second hemispherical ball head 141 ball-jointed, and a second clamping body 143 connected to the second hemispherical ball head 141. The second clamping body 143 is used for adaptive auxiliary clamping of permanent magnet materials. Technical problem solved: When the side of the sample is a non-planar structure, the existing clamping head cannot adaptively conform to the side of the sample, resulting in uneven clamping force and poor clamping reliability. Beneficial effect: The ball joint structure enables full-angle adaptive adjustment of the clamping head, ensuring uniform clamping force on the sample, improving clamping reliability and adaptability, and adapting to clamping samples with different side morphologies.

[0077] like Figure 37 As shown, as an optimization of Embodiment 2, the horizontal section of the third limiting groove 117 has a sliding hole 144, and a sliding rod 145 is slidably connected in the sliding hole 144. A seventh spring 146 is sleeved on the side wall of the sliding rod 145. A track groove 147 is installed on the bottom surface of the third clamp 116, and a wedge-shaped seat 148 is slidably connected in the track groove 147. The wedge-shaped seat 148 is slidably connected to the bottom surface of the sliding rod 145. The wedge-shaped seat 148 is driven by the third telescopic rod 149. By driving the sliding rod 145, the height of the permanent magnet material can be adjusted, so that permanent magnet materials of different thicknesses can fit the contact assembly 36. The technical problem solved is that permanent magnet material samples of different thicknesses cannot guarantee a tight fit with the contact assembly 36, which easily leads to poor contact, affecting the testing accuracy. The device has poor adaptability to samples of different thicknesses. Movement process: The third telescopic rod 149 drives the wedge seat 148 to slide along the track groove 147. The wedge seat 148 pushes the slide rod 145 up and down along the sliding hole 144, adjusting the height of the permanent magnet material on the slide rod 145. Beneficial effects: It can accommodate permanent magnet material samples of different thicknesses, ensuring tight contact between the sample and the contact assembly 36, avoiding poor contact problems, and improving the versatility and testing accuracy of the device.

[0078] like Figure 38 As shown in Embodiment 3, unlike Embodiment 1, the suction assembly 78 includes a first support 90, on which a third bearing seat 91 is mounted. A second support 92 is hinged to the third bearing seat 91, and a first telescopic rod 93 is hinged to the top surface of the second support 92. The tail end of the first telescopic rod 93 is hinged to the first support 90. A third support 94 is connected to the second support 92, and a shaft seat 95 is rotatably connected to the third support 94. An eighth gear 96 is connected to the upper end of the shaft seat 95, and a positioning seat 97 is connected to the top of the shaft seat 95. The positioning seat 97 is U-shaped, and two vertical sections of the positioning seat 97 are connected to limit rods 98. A fourth support 99 is connected to the third support 94, and a fourth rack 100 that meshes with the eighth gear 96 is slidably connected to the fourth support 99. The fourth rack 100 is driven by a second telescopic rod 101, which is connected to the fourth support 99. A limit plate 10 is connected to the fourth support 99. 2. When the limiting rod 98 abuts against the limiting plate 102, the limiting rod 98 can control the shaft seat 95 to switch between 0° and 180°; the lower end of the shaft seat 95 is connected to a bidirectional lead screw slide 150, the movable seat 151 of the bidirectional lead screw slide 150 is connected to a second vertical plate 152, the side of the second vertical plate 152 is connected to a cylinder slide 104, the cylinder slide 104 is connected to a suction head seat 105, the suction head seat 105 has a main air passage 106, the upper end of the main air passage 106 is open to A vacuum pump 108 is connected to the air pipe 107, and an air valve 109 is located on the side wall of the air pipe 107. A suction head body 110 is connected to the lower end of the main air passage 106. The suction head body 110 is used to pick up permanent magnet materials. The bottom surface of the suction head body 110 is horizontal, and the top surface of the suction head body 110 has an air cavity 111. Four branch air passages 112 are opened on the air cavity 111, penetrating the bottom surface of the suction head body 110. The four branch air passages 112 are arranged at equal angles. The technical problem solved is that the existing suction assembly 78 has a fixed suction head spacing, which cannot adapt to the adsorption of permanent magnet material samples of different sizes, resulting in poor versatility and failing to meet the needs of transporting samples of various specifications. Movement Process: The first telescopic rod 93 drives the second support 92 to swing and adjust the pitch angle. The second telescopic rod 101 drives the fourth rack 100 to slide, causing the shaft seat 95 to precisely rotate between 0° and 180°. The bidirectional screw slide 150 drives the two second vertical plates 152 to open and close synchronously, adjusting the spacing of the suction head body 110. The cylinder slide 104 drives the suction head body 110 to rise and fall. The vacuum pump 108 generates negative pressure through the main air channel 106 and the branch air channel 112, causing the suction head body 110 to adsorb the permanent magnet material sample. Beneficial Effects: The spacing of the suction head body 110 can be flexibly adjusted by the bidirectional screw slide 150, adapting to the adsorption and transport of permanent magnet material samples of different sizes, greatly improving the versatility of the device, while retaining the functions of precise rotation and uniform adsorption, ensuring the stability of sample transport.

[0079] Furthermore, a method for determining the resistivity reference sample is proposed, including the following steps:

[0080] Step 1: Preparation before setting values

[0081] 1.1 Environmental Preparation: Adjust the on-site environment to standard testing conditions, with the temperature controlled at 23℃±3℃ and relative humidity ≤80%. There should be no strong external magnetic field interference, mechanical vibration, or dust. Avoid placing iron, cobalt, nickel magnetic materials, or highly conductive substances in the testing area to prevent interference with the electric field distribution of the resistivity reference sample and the transmission of measurement signals. The rate of change in ambient temperature should be ≤1℃ / h to ensure the sample temperature remains stable during the calibration process and minimize the impact of temperature on resistivity measurements.

[0082] 1.2 Equipment and Measurement Device Preparation: Place the rare earth material resistivity reference sample to be measured on the sample fixture, turn on the instrument power, and preheat for 30 minutes to ensure the measurement device is in a stable working state. Select the reference sample prepared according to this invention. Before measurement, the sample surface needs to be cleaned to remove dust, oil, and magnetic debris. Then, clean the sample with alcohol and let it dry to avoid increasing contact resistance and affecting measurement accuracy. At the same time, check the traceability report of the instrument to confirm that it is within its validity period and that all performance indicators meet the requirements. Before testing, the reference sample should be placed in the test environment for no less than 0.5 hours to ensure that the sample temperature is consistent with the ambient temperature.

[0083] 1.3 Preparation of auxiliary tools: Prepare a length measuring instrument, a lint-free cloth, and anhydrous ethanol as auxiliary tools. The length measuring instrument is used to measure the thickness of the reference sample, and the minimum display scale or resolution is no greater than 1 μm.

[0084] Step 2: Resistivity determination (van der Bauer method measurement)

[0085] 2.1 Using a length measuring instrument, select 6 points evenly around the reference sample and measure the thickness of the sample at different positions. Finally, take the average value of the different measurement results as the average thickness of the sample.

[0086] 2.2 Place the first reference sample into the sample holder, ensuring good contact between the sample and the four contacts, with the contacts symmetrically distributed around the sample. Adjust the sample position using the device's built-in positioning tool, aligning the sample's centerline with the instrument's axis. Connect contacts A and B to the constant current power supply, and contacts C and D to the nanovoltmeter, ensuring the electric field distribution conforms to the van der Burg method measurement principle.

[0087] 2.3 After positioning is completed, the resistivity value of the reference sample is determined and measured using the van der Bauer method. The specific steps are as follows:

[0088] 2.3.1 Determine the current I in segments A and B. AB

[0089] The current value should be selected based on the thickness of the reference sample and the magnitude of the test voltage signal, with a current range of 1A to 5A. During testing, the constant current supply should initially be set to 1A. If the nanovoltmeter test voltage signal is below 0.05mV, the current should be increased to 2A, and so on, but the maximum current should not exceed 5A.

[0090] 2.3.2 Test the voltage U at terminals D and C DC

[0091] Two currents of equal magnitude but opposite direction are injected into the same set of current terminals, and the output current of the current source is set to I. AB After the current stabilizes, read the reading U of the nanovoltmeter. DC1 Then, the current is set to zero, the current input terminals A and B are swapped via the reversing switch S, and the current output value is set to I. AB Read the reading U of the nanovoltmeter. DC2 Voltage values ​​U at terminals D and C DC For (U) DC1 -U DC2 ) / 2.

[0092] 2.3.3 Test the voltage U at terminals A and D AD

[0093] Connect terminals B and C to a constant current power supply, and terminals A and D to a nanovoltmeter. Reset the output current of the current source to I. BC I BC Must be equal to I AB Simultaneously read the reading U of the nanovoltmeter. AD1 Then, the current is set to zero, the current input terminals B and C are swapped via the reversing switch S, and the current output value is set to I. BC Read the reading U of the nanovoltmeter. AD2 Voltage values ​​U at terminals A and D AD For (U) AD1 -U AD2 ) / 2.

[0094] 2.3.4 Calculation of resistivity ρ

[0095] The resistivity ρ is calculated according to formula (1), and the unit is microohmmeter (μΩ·m):

[0096] (1)

[0097] In the formula:

[0098] π—the value of a circle's circumference, here expressed as 3.14;

[0099] h — the thickness of the standard sample, in millimeters (mm).

[0100] UDC — The voltage between contacts D and C, in millivolts (mV);

[0101] U AD —The voltage between contacts A and D, measured in millivolts (mV);

[0102] I AB —Input current between contacts A and B, in amperes (A);

[0103] I BC —Input current between contacts B and C, in amperes (A);

[0104] f is the correction factor, which is set to 1 here.

[0105] The calculation results were rounded according to GB / T8170-2008, accurate to 3 decimal places.

[0106] Step 3: Repeatability and stability testing

[0107] 3.1 Repeatability Test: After completing the fixed-value measurement in Step 2, keep the test environment and test parameters (current magnitude, electrode connection method, sample positioning) unchanged, and perform 10 consecutive parallel fixed-value measurements on the same reference sample. Each measurement strictly follows the operating procedure in Step 2, and the resistivity calculation results for each measurement are recorded. The repeatability error is calculated based on the 10 measurement results. The repeatability error is expressed using relative standard deviation. The relative standard deviation of the reference sample should be ≤2% to be considered as passing the repeatability test.

[0108] 3.2 Stability Test: The reference sample was cleaned and sealed according to the standard procedure and stored in a standard environment. The sample was taken out after 1 month, 3 months, 6 months and 12 months of storage, and the resistivity value was measured according to step 2. Each measurement was performed in parallel for no less than 3 times and the average value was taken to ensure that the annual stability of the reference sample was ≤0.5%.

[0109] Step 4: Determination and post-processing of setpoint results

[0110] 4.1 Determination of Resistivity Value: Combining the resistivity measurement value of the reference sample, repeatability test data, and stability test data, if the repeatability error and stability deviation both meet the above requirements, and all data comply with GB / T31967.3-2025 and relevant industry standards, then the resistivity reference sample of the rare earth permanent magnet material is deemed qualified. The average value of 10 repeatability tests is taken as the final resistivity value of the sample. If any test fails to meet the requirements and cannot be eliminated through adjustment, it is deemed unqualified. The sample must be re-inspected (e.g., surface cleaning, electrode condition detection) and re-measured according to this method. Only after passing the re-measurement can the value be determined.

[0111] 4.2 After the setting is completed, turn off all power to the setting device, remove the reference sample from the sample holder, clean the surface and electrodes again with a lint-free cloth soaked in anhydrous ethanol to remove contact marks, tightly wrap the sample with plastic film to ensure no gaps remain, and then put it into a special storage box for storage to avoid sample oxidation or resistivity shift and extend service life.

[0112] 4.3 Clean the workbench and contact points of the setting device, organize auxiliary tools, compile the setting data into a booklet according to the standard format, and prepare a report. The report must include the following: test device model, serial number, manufacturer, test date, environmental conditions, reference sample information (model, traceability report number, validity period), setting data of the reference sample, measurement uncertainty, and signatures of the tester and verification personnel. The report must be archived.

[0113] 4.4 Re-inspection of reference samples: The reference samples need to be re-inspected once every year of use. The re-inspection items include thickness uniformity and resistivity indication error. The re-inspection method refers to the performance testing method of the calibration device of this invention and the requirements of GB / T31967.3-2025. If the re-inspection is qualified, it can continue to be used; if the re-inspection is unqualified, it needs to be scrapped and replaced with a new reference sample.

[0114] V. Beneficial Effects of the Setting Device and Method

[0115] The resistivity reference sample determination device and corresponding determination method for permanent magnet materials based on the van der Bauer method provided by this invention specifically address the problems of insufficient accuracy, non-standard determination methods, and poor adaptability of existing determination devices compared with the prior art. Combined with the dedicated reference sample prepared by this invention, it achieves accurate and standardized determination of the resistivity reference sample for rare earth permanent magnet materials. Specific beneficial effects are as follows:

[0116] 1. The setting device has a reasonable structure and high precision, providing hardware support for accurate setting. The various modules of the device are designed collaboratively, strictly following the van der Burg method measurement principle and the requirements of GB / T31967.3-2025 standard, ensuring setting accuracy from the hardware level and solving the problem of large measurement errors in existing devices.

[0117] 2. The setting process is highly standardized and automated, reducing human error and improving setting efficiency. The setting method of this invention has clear steps and well-defined parameters. From pre-setting preparation and the core measurement of the van der Burg method to repeatability testing, stability testing, result judgment, and post-processing, each step has clear technical requirements and operating specifications, adapting to setting needs in multiple scenarios.

[0118] 3. Strong adaptability, precisely matching the dedicated reference sample prepared by this invention, achieving accurate value transfer. The setting device and method are designed specifically for the sintered NdFeB reference sample prepared by this invention. The fixture size can be flexibly adjusted to adapt to different sample specifications, and the test parameters can be adaptively adjusted according to the sample characteristics, accurately matching the resistivity range and electrode layout of the sample. Simultaneously, the setting process strictly follows national standards, enabling accurate setting of the reference sample's resistivity, ensuring that the value is traceable to national benchmarks, and solving the problems of poor compatibility and inaccurate value transfer of existing setting methods with general-purpose samples.

[0119] Furthermore, a method for preparing a reference sample is proposed, comprising the following steps: using sintered NdFeB as the core substrate, a uniform alloy ingot is obtained through composition design and rapid solidification; fine powder adapted to the forming requirements is prepared through hydrogen pulverization and air jet milling processes; the density and orientation consistency of the billet are improved through orientation forming and isostatic pressing; the grain boundary structure and resistivity characteristics are optimized by vacuum sintering and two-stage tempering; a preset geometric shape and surface state are obtained through precision machining and composite surface treatment; an electrode structure adapted to the van der Bauer method is prepared by vacuum magnetron sputtering technology; after sealing and encapsulation to enhance stability, the overall encapsulation and performance testing are completed, and the permanent magnet material resistivity reference sample is obtained after passing the test.

[0120] Furthermore, the composition design of the sintered NdFeB substrate is based on the Nd-Fe-B core system, taking into account the synergistic optimization of resistivity and magnetic properties. Elemental Nd, Fe, and B are selected as basic raw materials, with the addition of Ce, La (light rare earth elements), and Al and Cu (modifying elements). Ce and La promote the formation of high-resistivity oxides at grain boundaries, while Al and Cu optimize the wettability and continuity of the grain boundary phase. The raw material ratios are determined through thermodynamic calculations and experimental verification to ensure the formation of Nd2Fe... 14 The microstructure of this type of sintered NdFeB material, with boron as the main phase and rare-earth-rich phases as grain boundary phases, conforms to the requirements of GB / T13560-2017 "Sintered NdFeB Permanent Magnet Materials". The resistivity range of this material closely matches the actual application range of rare-earth permanent magnet products, generating a stable and appropriately strong electrical signal to ensure accurate identification during resistivity measurements. It possesses excellent structural stability, is not easily affected by external environmental interference, and maintains resistivity stability over a long period. Grain boundary control technology can further optimize the internal microstructure of the material, improve resistivity uniformity, and provide structural assurance for calibration accuracy.

[0121] Furthermore, smelting and rapid solidification are carried out in a high-vacuum electric arc melting furnace. The proportioned raw materials are placed in a crucible, and after vacuuming, high-purity argon gas with a purity of 99.999% is introduced as a protective gas. Arc melting is then initiated by electric current, with each furnace melting 3-4 times to ensure uniform composition and obtain a uniform alloy ingot. The alloy ingot is then fed into a rapid solidification device, where a copper roller rapid solidification method is used to prepare rapidly solidified thin strips, ensuring the formation of fine and uniform microcrystalline structures and avoiding resistivity unevenness caused by coarse grains. This process conforms to the industry-standard technical specifications for the preparation of sintered NdFeB materials. The powdering process consists of two steps: hydrogen embrittlement and air jet milling. During hydrogen embrittlement, the rapidly solidified thin strip is placed in a hydrogen embrittlement furnace, and high-purity hydrogen gas with a purity of 99.999% is introduced at room temperature and held for 2-3 hours. The powder is broken into coarse powder using the hydrogen embrittlement effect, followed by dehydrogenation at elevated temperature for 1-2 hours. After dehydrogenation, the hydrogen content of the powder is ≤50ppm. The air jet mill uses a supersonic air jet mill and high-purity nitrogen gas with a purity of 99.999% as the grinding medium to obtain fine powder with a particle size of 4μm~10μm. The entire powder making process is carried out under the protection of inert gas to avoid powder oxidation.

[0122] Furthermore, the orientation forming process employs a magnetic field orientation press. Fine powder from the air jet mill is loaded into a mold, and forming pressure is applied at room temperature while simultaneously applying a strong axial magnetic field of ≥1.5T. This causes the powder particles to align along the easily magnetized axis, resulting in a preform density ≥60%. Subsequently, the preform undergoes cold isostatic pressing. After being placed in an elastic sleeve and vacuum-sealed, the preform is placed in a cold isostatic press with hydraulic oil as the pressure transmission medium, applying a pressure of 200MPa~250MPa. This increases the preform density and eliminates internal pores and cracks.

[0123] Furthermore, sintering and tempering are integrated using a vacuum sintering furnace. The cold isostatically pressed green body is placed in a graphite crucible and then evacuated. The heating rate is controlled at 5℃ / min~8℃ / min, followed by low-temperature degassing at 300℃~400℃, medium-temperature pre-firing at 600℃~800℃, and finally heated to 1050℃~1100℃ to achieve densification sintering of the green body, with a density ≥98% after sintering. The tempering process adopts a two-stage treatment: a high-temperature tempering stage and a low-temperature tempering stage, followed by cooling to room temperature at a rate of 5℃ / min. This two-stage tempering process enables the grain boundary phase to form a continuous and uniform thin-layer structure, which improves resistivity uniformity and enhances the corrosion resistance and thermal stability of the sample.

[0124] Furthermore, machining is performed using precision machining equipment. A diamond wire saw precisely cuts the sintered block into circular or rectangular thin-film structures. The diameter or side length of the sample should be between 20mm and 100mm, and the thickness controlled between 1mm and 5mm, with a thickness deviation not exceeding 0.1mm. Waterless cooling is used during the cutting process to avoid secondary powder contamination and performance damage, and the parallelism of the cut surfaces is ≤0.01mm. Surface treatment employs a composite cleaning process, sequentially ultrasonically cleaning with acetone and anhydrous ethanol for 30 minutes each to remove surface oil and machining debris. Then, plasma cleaning is used to remove the surface oxide layer, ensuring a surface roughness Ra ≤0.05μm for the sample.

[0125] Furthermore, the stability treatment includes heat aging and sealing encapsulation. Heat aging involves placing the standard sample in an aging chamber and aging it at 150℃~200℃ for >100 hours to simulate environmental stress during long-term use, accelerating the stabilization of the sample's internal microstructure and reducing long-term resistivity drift. After aging, the sample is naturally cooled to room temperature, and its resistivity is then measured using a rare-earth permanent magnet resistivity calibrator to verify whether the long-term resistivity decay rate meets preset requirements, ensuring that the sample maintains its quantitative stability after aging. Sealing encapsulation uses a plastic sealing film process to completely encapsulate the cooled reference sample. The insulating properties of the plastic film prevent oxidation, moisture absorption, or dust and impurities on the sample surface, avoiding resistivity shifts due to environmental factors. The sample can be removed directly by tearing off the plastic film. After use, the sample is tightly wrapped again with the plastic film to ensure no gaps remain, and then stored in a dedicated storage box to further isolate it from external environmental influences and extend its lifespan.

[0126] Compared with the prior art, the present invention has the following beneficial effects:

[0127] 1. This invention addresses the technical challenge of poor compatibility with existing universal reference samples, achieving precise compatibility with rare-earth permanent magnet resistivity calibrating devices based on the van der Bauer method. Using sintered NdFeB as the core substrate, its resistivity range closely matches the practical application range of rare-earth permanent magnet materials. Furthermore, through compositional control and grain boundary optimization, it simulates the true microstructure and electrical properties of rare-earth permanent magnet materials, effectively avoiding measurement errors caused by insufficient compatibility compared to existing universal metal reference resistors. Simultaneously, the electrode layout strictly adheres to the geometric requirements of the van der Bauer method, precisely matching the electrode design of the measurement device, further enhancing test compatibility.

[0128] 2. Precise resistivity measurements with excellent uniformity ensure reliable value transfer. This invention optimizes the process through rapid melting and solidification, vacuum sintering, and two-stage tempering, effectively improving the uniformity of the sample's internal structure. Combined with precision machining and composite surface treatment, it ensures uniform sample thickness, a smooth surface, and good resistivity uniformity. The electrode contact resistance is low and uniform, avoiding interference from uneven contact resistance on measurement results and ensuring accurate resistivity values. This enables precise value transfer from national standards to industrial measurements, solving the problem of broken traceability chains in existing general-purpose sample measurements.

[0129] 3. Outstanding stability, extended sample lifespan, and reduced testing costs. This invention effectively prevents sample oxidation and moisture absorption through plastic sealing and dedicated storage protection, ensuring short-term and long-term sample stability. The annual stability rate meets the requirements for reference sample use. Compared with existing general-purpose samples that are easily oxidized and drifted, the lifespan is significantly extended, and the samples can be repeatedly used in daily work, reducing enterprise testing costs.

[0130] 4. The preparation process is standardized and highly operable, suitable for industrial mass production. The preparation process of this invention refers to the national standards GB / T13560-2017 and GB / T31967.3-2025. Each process parameter is clear and controllable. From raw material ratio and powder forming to electrode preparation and stability treatment, each step has clear technical requirements and testing standards. No complicated special equipment is required, which can realize industrial mass production. This solves the problem of the chaotic process and inability to mass produce existing special sample preparation processes, and meets the needs of large-scale use in the industry.

[0131] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A permanent magnetic material resistivity reference sample setter, characterized by, The test setup includes a constant current power supply (1), a DC ammeter (2), a commutation switch S (3), a nanovoltmeter (4), a sample holder (5), and a control computer (6). The constant current power supply (1) has an output current range of 1A to 5A. The DC ammeter (2) is connected in series between the constant current power supply (1) and the sample holder (5). The commutation switch S (3) has two independent commutation channels. The nanovoltmeter (4) has a DC voltage measurement range of 0.05mV to 1mV. The control computer (6) is connected to the constant current power supply (1), the DC ammeter (2), the commutation switch S (3), and the nanovoltmeter (4) for test process control and data acquisition and storage. Storage; The sample holder (5) includes a base plate (7), a ring seat (8), a first ring (10), a second ring (11), a first motor (15), a second motor (19), a top plate (20), two sets of first clamps (27) and two sets of second clamps (33); The ring seat (8) is fixed to the center of the top surface of the base plate (7), and the side of the ring seat (8) is provided with a circular groove (9). The first ring (10) and the second ring (11) are arranged vertically and rotatably connected in the circular groove (9); The side of the first ring (10) is provided with a symmetrical first toothed ring (12), and the first toothed ring (12) meshes with the first gear (13) and the second gear (14) in sequence, and the second toothed ring (12) meshes with the first gear (13) and the second gear (14) in sequence. The wheel (14) is connected to the first motor (15) for transmission; the second ring (11) has a symmetrical second toothed ring (16) on its side, the second toothed ring (16) meshes with the third gear (17) and the fourth gear (18) in sequence, the fourth gear (18) is connected to the second motor (19) for transmission; the top plate (20) is fixed to the top surface of the ring seat (8), the top plate (20) has four equally distributed storage slots (22), the longitudinally opposite storage slots (22) are provided with a first guide rail (23), the first slider (24) is slidably connected on the first guide rail (23), the first rack (25) at the bottom of the first slider (24) meshes with a fifth gear (26), the fifth gear ( 26) The first clamp (27) is fixed to the top surface of the first slider (24) and coaxially connected to the first gear (13); the second guide rail (29) is provided in the horizontally opposite storage groove (22), the second slider (30) is slidably connected to the second guide rail (29), the second rack (31) at the bottom of the second slider (30) is engaged with the sixth gear (32), the sixth gear (32) is fixed to the third gear (17) and coaxially connected, the second clamp (33) is fixed to the top surface of the second slider (30); the first motor (15) drives the two sets of first clamps (27) to move synchronously towards or away from each other, and the second motor (19) drives the two sets of second clamps (33) to move synchronously towards or away from each other.

2. The permanent magnet material resistivity reference coupon setting device of claim 1, wherein, The first clamp (27) and the second clamp (33) are both provided with L-shaped limiting grooves. A first groove (35) is provided at the center axis of the vertical section of the limiting groove. A contact assembly (36) is provided in the first groove (35). The contact assembly (36) includes a barrel-shaped contact seat (37), a first spring (38) and a contact cap (39). The first spring (38) is installed in the contact seat (37). The free end of the first spring (38) is connected to the contact cap (39). The contact surface of the contact cap (39) is a rounded corner structure and is used to abut against the side of the permanent magnet material.

3. The permanent magnet material resistivity reference sample setting device according to claim 2, characterized in that, The side wall of the contact seat (37) is symmetrically provided with two first hinge seats (40), and a first contact rod (41) is hinged on the first hinge seat (40). The hinge point is located at the waist of the first contact rod (41). A second spring (43) is connected between the opposite ends of the two first contact rods (41) so that the two first contact rods (41) are V-shaped. The free end of the first contact rod (41) is used to make adaptive contact with the side of the permanent magnet material.

4. The permanent magnet material resistivity reference sample setting device according to claim 2, characterized in that, The center of the contact cap (39) is rotatably connected to a top rod (44). The free end of the top rod (44) is connected to a rotating tube (47) via a third spring (45). The rotating tube (47) is driven to rotate by a third motor (48). The rotating tube (47) is provided with a limiting strip (50) that restricts the circumferential rotation of the top rod (44). The top rod (44) can slide along the axial direction of the limiting strip (50). The rotating tube (47) drives the top rod (44) and the permanent magnet material to rotate 180° to achieve flipping detection.

5. The permanent magnet material resistivity reference coupon setting device of claim 1, wherein, It also includes a box body (51) with an inner and outer sandwich structure, a serpentine heat exchange pipe (52) is provided in the sandwich of the box body (51), and a foot (53) for fixing the sample fixture (5) is provided in the inner cavity of the box body (51).

6. The permanent magnet material resistivity reference coupon setting device of claim 5, wherein, It also includes a constant temperature environment chamber (54), which is equipped with two finned heat exchangers (55). One of the finned heat exchangers (55) is connected to a constant temperature valve (56) at its inlet end. The two finned heat exchangers (55) are connected to the inlet and outlet of the heat exchange pipe (52) respectively. A temperature sensor (60) is provided on the side wall of the constant temperature environment chamber (54).

7. The permanent magnet material resistivity reference coupon setting device of claim 6, wherein, The top surface of the constant temperature environment chamber (54) is provided with a box cover (57) with a material inlet (58), and the top surface of the box cover (57) is provided with a double-opening box door (59); the double-opening box door (59) includes two sets of symmetrical driving components, the driving components include two third guide rails (61), two third racks (63), a seventh gear (64) and a fourth motor (65), the two third racks (63) are slidably connected to the third guide rails (61) through the third slider (62), the seventh gear (64) meshes with the two third racks (63) at the same time, the fourth motor (65) drives the seventh gear (64) to rotate, and the two third racks (63) are respectively connected to the first door plate (66) and the second door plate (67) for closing or opening the material inlet (58).

8. The permanent magnet material resistivity reference coupon setting device of claim 5, wherein, The outer wall of the box (51) is connected to a feeding mechanism (68), which includes a base plate (69), a fourth guide rail (71), a first slide (72), a support seat (73), a fifth guide rail (75), a second slide (76), a support arm (77), a suction assembly (78), and a fifth motor (85). The fourth guide rail (71) is fixed to the top surface of the base plate (69), the first slide (72) is slidably connected to the fourth guide rail (71), the support seat (73) is fixed to the first slide (72), and the fifth guide rail (75) is fixed to the support seat (73). The second slide (76) is slidably connected to the fifth guide rail (75), the support arm (77) is fixed to the second slide (76), and the suction assembly (78) is installed on the support arm (77); the support arm (77) is rotatably connected to the guide wheel (80) through the shaft (79), and the base plate (69) is provided with a V-shaped first guide groove (81). The guide wheel (80) rolls in contact with the first guide groove (81) to adjust the position of the suction assembly (78); the fifth motor (85) drives the carrier (73) to reciprocate along the fourth guide rail (71) through the synchronous belt (89) transmission mechanism.

9. The permanent magnet material resistivity reference coupon setting device of claim 8, wherein, The suction assembly (78) includes a first support (90), a second support (92), a first telescopic rod (93), a third support (94), a bearing seat (95), an eighth gear (96), a fourth rack (100), a second telescopic rod (101), a suction head seat (105), and a suction head body (110). The second support (92) is hinged to the first support (90) via a third bearing seat (91), and the two ends of the first telescopic rod (93) are respectively hinged to the first support (90) and the second support (92). The bearing seat (95) is rotatably connected to the third support (94), the eighth gear (96) is fixed to the upper end of the bearing seat (95), and the fourth rack (100) meshes with the eighth gear (96). Driven by the second telescopic rod (101), a U-shaped positioning seat (97) is fixed on the top of the bearing seat (95). The positioning seat (97) is provided with a limiting rod (98). The third support (94) is provided with a limiting plate (102) that cooperates with the limiting rod (98) to limit the bearing seat (95) to rotate between 0° and 180°. The suction head seat (105) is fixed to the lower end of the bearing seat (95). The suction head seat (105) is provided with a main air passage (106). The upper end of the main air passage (106) is connected to a vacuum pump (108) through an air pipe (107). The lower end of the main air passage (106) is connected to the suction head body (110). The suction head body (110) is provided with an air chamber (111) and four branch air passages (112) distributed at equal angles.

10. A method for preparing a resistivity reference sample of a permanent magnet material, characterized in that, Includes the following steps: (1) Composition design and rapid solidification: Using sintered Nd-Fe-B core system as the core substrate, Nd, Fe, and B elements are selected as basic raw materials, and Ce, La light rare earth elements and Al and Cu modification elements are added. The raw materials are placed in a high vacuum electric arc melting furnace, and after vacuuming, 99.999% high-purity argon gas is introduced for protection. The alloy ingot with uniform composition is obtained by electric arc melting 3-4 times. Then, rapid solidification thin strips are prepared by copper roller rapid solidification method; (2) Powdering treatment: The rapid solidification thin strips are placed in a hydrogen crushing furnace, and 99.999% high-purity hydrogen gas is introduced at room temperature for 2-3 hours. The hydrogen embrittlement effect is used to crush it into coarse powder. Then, the temperature is raised to dehydrogenate for 1-2 hours. The hydrogen content of the powder after dehydrogenation is controlled to be ≤50ppm. Then, the powder is processed. Using a supersonic air jet mill with 99.999% high-purity nitrogen as the grinding medium, fine powder with a particle size of 4μm~10μm was prepared. The entire powder preparation process was carried out under inert gas protection. (3) Orientation forming and isostatic pressing: The fine powder was loaded into a mold and a magnetic field orientation press was used to apply forming pressure at room temperature. At the same time, an axial strong magnetic field of ≥1.5T was applied to orient the powder particles along the easy magnetization axis to obtain a shaped green body with a density of ≥60%. The green body was then vacuum sealed in an elastic sleeve and placed in a cold isostatic press with hydraulic oil as the pressure transmission medium. A pressure of 200MPa~250MPa was applied to complete the cold isostatic pressing treatment. (4) Vacuum sintering and tempering: The green body after cold isostatic pressing was placed in the graphite crucible of a vacuum sintering furnace. Vacuum was drawn in the crucible, and the temperature was raised at a rate of 5℃ / min to 8℃ / min. The crucible was then subjected to low-temperature degassing at 300℃ to 400℃, medium-temperature pre-firing at 600℃ to 800℃, and finally heated to 1050℃ to 1100℃ for vacuum sintering to obtain a sintered block with a density ≥98%. The block was then subjected to a two-stage tempering process and finally cooled to room temperature at a rate of 5℃ / min. (5) Precision machining and composite surface treatment: Precision machining equipment was used to precisely cut the sintered block into thin slices with a diameter or side length of 20mm to 100mm and a thickness of 1mm to 5mm using a diamond wire saw. The thickness deviation was controlled to be no more than 0.1mm and the parallelism of the cut surface was ≤0.01mm. The cutting was carried out using a waterless cooling method. (6) Electrode preparation: Vacuum magnetron sputtering technology was used to prepare an electrode structure suitable for the van der Burg method test on the sample substrate; (7) Stability treatment and performance testing: The sample after electrode preparation was placed in an aging chamber and kept at 150℃~200℃ for >100h for heating aging treatment. After aging, it was naturally cooled to room temperature. The resistivity was detected by a permanent magnet material resistivity determination device to verify the long-term attenuation rate of resistivity. Then, the qualified sample was sealed by a plastic sealing film encapsulation process. After the encapsulation was completed, the permanent magnet material resistivity reference sample was obtained.

Images