US-12620525-B2 - Manufacturing method for permanent magnet

US12620525B2US 12620525 B2US12620525 B2US 12620525B2US-12620525-B2

Abstract

A manufacturing method for a permanent magnet includes a magnetization step of magnetizing a to-be-magnetized object by a magnetizer including a field magnet unit having a plurality of permanent magnets for magnetization configured to generate a magnetic field on the to-be-magnetized object arranged at equal intervals and a heating unit having a heating surface opposing the to-be-magnetized object in an axial direction of the to-be-magnetized object and configured to heat the to-be-magnetized object. In the magnetization step, the to-be-magnetized object is disposed on the field magnet unit, the to-be-magnetized object is heated by the heating unit to a temperature equal to or higher than a Curie point of the to-be-magnetized object and lower than the Curie point of the permanent magnets for magnetization, and then the temperature is lowered to a temperature lower than the Curie point of the to-be-magnetized object, and a magnetization magnetic field is applied to the to-be-magnetized object by the permanent magnets for magnetization.

Inventors

Yu OKAWARA
Haruhiro Komura

Assignees

MINEBEA MITSUMI INC.

Dates

Publication Date: 20260505
Application Date: 20220516
Priority Date: 20210531

Claims (2)

1 . A manufacturing method for a permanent magnet, comprising a magnetization step of magnetizing a to-be-magnetized object by a magnetizer including a field magnet unit with a plurality of permanent magnets for magnetization configured to generate a magnetic field on the to-be-magnetized object arranged at equal intervals and a heating unit having a heating surface opposing the to-be-magnetized object in an axial direction of the to-be-magnetized object and configured to heat the to-be-magnetized object, wherein in the magnetization step, the to-be-magnetized object is disposed on the field magnet unit, the to-be-magnetized object is heated by the heating unit to increase a temperature equal to or higher than a Curie point of the to-be-magnetized object and lower than the Curie point of the permanent magnets for magnetization and then lower the temperature to a temperature lower than the Curie point of the to-be-magnetized object, and a magnetization magnetic field is applied to the to-be-magnetized object by the permanent magnets for magnetization, the to-be-magnetized object is an anisotropic rare earth iron-based magnet having an average crystal grain size of 0.02 μm or more and 3.59 μm or less, and in the field magnet unit, the permanent magnets for magnetization are arranged having a pole pitch in the to-be-magnetized object after the magnetization step of 0.3 mm or more and 2.6 mm or less.
2 . A manufacturing method for a permanent magnet comprising a magnetization step of magnetizing a to-be-magnetized object by a magnetizer including a field magnet unit with a plurality of permanent magnets for magnetization configured to generate a magnetic field on the to-be-magnetized object arranged at equal intervals and a heating unit having a heating surface opposing the to-be-magnetized object in an axial direction of the to-be-magnetized object and configured to heat the to-be-magnetized object, wherein in the magnetization step, the to-be-magnetized object is disposed on the field magnet unit, the to-be-magnetized object is heated by the heating unit to a temperature equal to or higher than a Curie point of the to-be-magnetized object and lower than the Curie point of the permanent magnets for magnetization, and then the temperature is lowered to a temperature lower than the Curie point of the to-be-magnetized object, and a magnetization magnetic field is applied to the to-be-magnetized object by the permanent magnets for magnetization, the to-be-magnetized object is an anisotropic rare earth iron-based magnet obtained by hot working, and in the field magnet unit, the permanent magnets for magnetization are arranged having a pole pitch in the to-be-magnetized object after the magnetization step of 0.3 mm or more and 3.1 mm or less.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a national stage entry of International Application No. PCT/JP 2022/020303 filed on May 16, 2022, which claims benefit of priority from Japanese application no. 2021-090739, filed on May 31, 2021. The entire contents of the above-identified applications are hereby incorporated by reference. TECHNICAL FIELD The disclosure relates to a manufacturing method for a permanent magnet. BACKGROUND Among rare earth iron-based magnets, in particular, Nd—Fe—B-based sintered magnets have high magnetic characteristics and thus are used in various devices, apparatuses, and motors. However, when the Nd—Fe—B-based sintered magnets are used in a high-temperature environment, a coercive force is decreased due to demagnetization. For this reason, to be used in the high-temperature environment, heat resistance of the Nd—Fe—B based sintered magnets has been awaited. It is typically known that heat resistance is improved by increasing a coercive force of a magnet and that the coercive force is increased by refining the crystal grains of the magnet. A hot-worked magnet capable of making the crystal grain size smaller than a crystal grain size of a sintered magnet is known as an effective means for improving the coercive force by refining the crystal grains of the magnet (see, for example, Toshiyuki Morita, “Effect of Methods to Improve Coercivity on Temperature Dependence in Nd—Fe—B Magnets”, Daido Steel Co., Ltd. Technical Report, Electric Steel Manufacturing, 2011, Vol. 82, No. 1, p. 5-10). The crystal grain size of the hot-worked magnet ranges from 1/10 to 1/100 of the crystal grain size of the sintered magnet, allowing for refinement. Magnetizing the hot-worked magnet is necessary, and a means for pulse-magnetizing a magnet produced by hot working is known (see, for example, JP 01-297807 A). In the manufacturing method for a permanent magnet of JP 01-297807 A, a ribbon-shaped thin strip produced by a quenching method is pulverized into a powder, then a temporary compact is obtained by hot pressing, and the temporary compact is subjected to backward extrusion at a temperature of 700° C. to be plastically deformed, obtaining a magnet material. JP 01-297807 A describes multipolar magnetization of the magnet material with eight poles at a temperature of 50° C. or more and less than the Curie point by using a magnetizer with a coil having a magnetization yoke connected to a pulse power source. According to a manufacturing method of the permanent magnet, the permanent magnet described in JP 01-297807 A is a hot-work magnet described in Toshiyuki Morita, “Effect of Methods to Improve Coercivity on Temperature Dependence in Nd—Fe—B Magnets”, Daido Steel Co., Ltd. Technical Report, Electric Steel Manufacturing, 2011, Vol. 82, No. 1, p. 5-10, and the magnetizer is a so-called pulse type magnetizer. JP 01-297807 A describes the fact that when the magnetic characteristics of the permanent magnet magnetized at room temperature were measured, the maximum energy product was 30 MG·Oe and that the coercive force was 12100 (Oe). SUMMARY However, the maximum energy product (MG·Oe) of the hot-worked magnet has recently increased, and the coercive force of the hot-worked magnet has been higher than 12100 (Oe). For this reason, the magnetizing method described in JP 01-297807 A, that is, the means of “magnetizing a magnet material at a temperature of 50° C. or more and less than the Curie point by using a magnetizer connected to a pulse power source” may not be able to obtain high magnetization characteristics for a hot-worked magnet having a high coercive force. In recent years, to reduce a cogging torque of a motor when used in the motor and to improve resolution of a sensor when used as the sensor, multipolar magnetization of the magnet material has been awaited. For winding a coil around a magnetization yoke and applying a pulse current as in JP 01-297807 A, so-called pulse magnetization, narrowing the magnetization pitch causes the number of turns of the coil wound around the magnetization yoke and the diameter of the coil to be limited, failing to increase the magnetization magnetic field and reduce the magnetization pitch. In view of the above-described problems, an object of the disclosure is to provide a manufacturing method for a permanent magnet to allow for obtaining high magnetization characteristics even by multipolar magnetization on a rare earth iron-based magnet having magnetic anisotropy. To solve the above-described problems and achieve the above-described object, a manufacturing method for a permanent magnet according to an aspect of the disclosure includes a magnetization step of magnetizing a to-be-magnetized object by a magnetizer including a field magnet unit with a plurality of permanent magnets for magnetization configured to generate a magnetic field on the to-be-magnetized object arranged at equal intervals and a heating unit having a heating surface opposing th