JP2012253162A - Reclaimed magnetic powder for magnet and production method of magnet body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To utilize resource effectively by increasing the mixing ratio of reclaimed magnetic powder to the virgin magnetic powder.SOLUTION: The unusable part of a magnet body produced by performing hot plastic processing of a material, containing virgin magnetic powder obtained by rapid quenching, is subjected to hydrogen absorption pulverization thus obtaining a reclaimed magnetic powder for magnet production. The reclaimed magnetic powder is mixed with the virgin magnetic powder at a ratio of 40-80 mass% of the total quantity to produce a mixed magnetic powder, which is then subjected to hot plastic processing thus obtaining a magnet body.

Description

  The present invention relates to a regenerated magnetic powder for magnets and a method for manufacturing a magnet body, and more particularly to a manufacturing method suitable for manufacturing an anisotropic magnet body.

  Magnetic powder (virgin magnetic powder) obtained by the ultra-quenching method as a manufacturing method of the anisotropic magnet body, cold press forming for shape forming, hot press forming for increasing the density of the molded product, and magnetic anisotropy There is known a method of performing through hot plastic working for imparting. In this case, when the shape after the hot plastic working is a cylindrical shape, the opening edge portion is unusable due to poor magnetic properties. Further, in the case where the shape after the hot plastic working is a bottomed cylindrical shape, magnetic anisotropy cannot be obtained at the bottom wall portion in addition to the opening edge portion, and this portion becomes an unusable portion. Moreover, the whole molded product may become an unusable part by the dimension defect etc. Conventionally, these unusable parts are collected and remelted, and then re-magnetized by a super rapid cooling method. However, this increases the cost and requires time to reuse the unusable parts.

  Therefore, in Cited Document 1, the unusable part of the Nd-Fe-B magnet body is pulverized into a regenerated magnetic powder, which is mixed with virgin magnetic powder at a certain ratio, and this mixed powder is hot plastic processed. A method for obtaining a new Nd-Fe-B magnet body is shown.

JP2002-1000052

  However, since the above conventional method mechanically grinds the recovered unusable part, the obtained regenerated magnetic powder has a chemical composition such as a virgin magnetic powder such as its particle form and oxygen content are increased. Are very different. For this reason, in order to prevent deterioration of the corrosion resistance, mechanical strength, and magnetic properties of the magnet body, the mixing ratio of the regenerated magnetic powder must be suppressed to 40% by mass or less of the total amount, and the utilization rate of the regenerated magnetic powder is still unsatisfactory. There was a problem that it was enough.

  Therefore, the present invention solves such problems, and can produce a regenerated magnetic powder for magnets and a magnet body that can increase the mixing ratio of regenerated magnetic powder to virgin magnetic powder and can effectively use resources. It aims to provide a method.

  In order to achieve the above object, in the method for producing regenerated magnetic powder according to the first aspect of the present invention, the unusable portion of the magnet body produced by hot plastic processing a raw material containing virgin magnetic powder obtained by the ultra-quenching method. On the other hand, a hydrogen storage and pulverization treatment is performed to obtain a regenerated magnetic powder for producing a magnet. Here, the “unusable part” refers to a part that is unsuitable for use as a product, such as a part having a poor magnetic property or a part having a poor dimension in the magnet body.

  The regenerated magnetic powder obtained in the first aspect of the invention can prevent the deterioration of the corrosion resistance, mechanical strength, and magnetic properties of the magnet body because the generation of fine powder with a small particle size that is easy to oxidize is low and the oxygen concentration of the powder is low. As a result, when the magnet body is manufactured, the mixing ratio of the virgin magnetic powder can be increased as compared with the conventional case to effectively use the resources.

  Moreover, in the manufacturing method of the magnet body of this 2nd invention, the said reproduction | regeneration magnetic powder is mixed in the ratio of 40 mass% or more and 80 mass% or less of the whole quantity with respect to virgin magnetic powder. A magnet body is obtained by plastic working.

  The magnet body obtained by the second invention is capable of keeping the deterioration in corrosion resistance, mechanical strength, and magnetic properties within an allowable range with respect to a magnet body manufactured only from virgin magnetic powder. As a result, the effective use of resources can be achieved.

  As described above, according to the present invention, the mixing ratio of the regenerated magnetic powder to the virgin magnetic powder can be increased, so that the resources can be effectively used.

It is the graph which compared the particle size distribution of reproduction | regeneration magnetic powder and virgin magnetic powder. It is sectional drawing which shows the hot plastic working process of a magnet body. It is the whole longitudinal cross-sectional view of a magnet body. It is a figure which shows the BH characteristic of a magnet body.

  The embodiment described below is merely an example, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

  From a Nd—Fe—Co—B alloy composed of Nd: 30% by mass, Co: 4.0% by mass, Ga: 0.5% by mass, B: 0.9% by mass, Fe: remainder, known ultra rapid cooling A thin virgin magnetic powder was obtained by the method. At this time, the particle size distribution of the virgin magnetic powder is in the range of 53 to 355 μm as shown by the thin solid bar graph in FIG. 1, and there is no fine powder of 53 μm or less.

  Such virgin magnetic powder was cold press-molded, a carbon lubricant was applied to the cold press-molded body, and then hot press-molded at 800 ° C. Then, after the hot press-molded body was cooled to room temperature, a carbon lubricant was applied again, and hot extrusion processing (plastic processing) was performed at 800 ° C. to obtain a magnet body. In the hot extrusion process, as shown in FIG. 2, the hot press-molded body is extruded by the molds 2 and 3 inside the mold 1, and the magnet body 4 obtained by this molding is shown in FIG. It becomes such a bottomed cylindrical body.

  Since the opening edge portion 41 and the bottom wall portion 42 of the magnet body 4 are unusable portions such as inferior in magnetic characteristics or incapable of obtaining magnetic anisotropy as described above, these portions 41 and 42 are The cylindrical magnet body 4 is finally obtained by being cut and separated from the magnet body 4. In the present embodiment, the hydrogen storage and pulverization process is performed on the unusable portions 41 and 42 that have been cut and separated.

  That is, the magnet pieces that are the unusable portions 41 and 42 are inserted into the vacuum chamber and evacuated, and then hydrogen is introduced to raise the temperature to a predetermined temperature (400 ° C. in this embodiment). In this state, the hydrogen is occluded by leaving for a predetermined time (in this embodiment, 3 hours). Thereafter, the hydrogen was exhausted, and the temperature was raised again to a predetermined temperature (720 ° C. in the present embodiment). In this state, hydrogen was deaerated for a predetermined time (1 hour in the present embodiment) to obtain a regenerated magnetic powder.

  The particle size distribution of the regenerated magnetic powder obtained by the hydrogen storage and pulverization treatment is shown by a thick solid line bar graph with hatching in FIG. According to this, although the particle size distribution is widely distributed from 53 μm or less to around 1000 μm, as is apparent from the figure, it is easily oxidized and thus the corrosion resistance, mechanical strength and magnetic properties of the magnet body are reduced to 53 μm or less. The proportion of fine powder is as low as 2%. On the other hand, in the conventional mechanical pulverization such as jet mill pulverization, as shown by the broken line bar graph in FIG. 1, the proportion of fine powder of 53 μm or less reaches about 24%.

  Therefore, when only virgin magnetic powder is used, with respect to regenerated magnetic powder obtained by hydrogen storage and pulverization, when only regenerated magnetic powder is used, the total amount is 20 mass%, 40 mass%, 60 mass%, and 80 mass% with respect to virgin magnetic powder. In the case of using mixed magnetic powders (respectively mixed magnetic powder 20, mixed magnetic powder 40, mixed magnetic powder 60, mixed magnetic powder 80) mixed with the above regenerated magnetic powder, the cold press molding, hot press molding, and heat described above are used. Cylindrical magnets having an outer diameter of 30 mm, an inner diameter of 25 mm, and a length of 30 mm were manufactured by the inter-extrusion process, and the respective BH characteristics were measured. This is shown in FIG. As is clear from FIG. 4, good BH characteristics cannot be obtained with regenerated magnetic powder alone, but when the mixing ratio of regenerated magnetic powder is 40% by mass or less, the BH characteristics are hardly deteriorated, and the mixing ratio of regenerated magnetic powder is 60% by mass. Even if it is 80% by mass, the BH characteristics are slightly deteriorated, but still within the allowable range. Therefore, the mixing amount of the regenerated magnetic powder can be increased from about 40% by mass to about 80% by mass.

  Also, only virgin magnetic powder, mixed magnetic powder (mixed magnetic powder A) in which virgin magnetic powder was mixed with 80% by mass of regenerated magnetic powder by hydrogen storage and pulverization, and regenerated magnetic powder by mechanical pulverization was mixed with 40% by mass of virgin magnetic powder. Using the mixed magnetic powder (mixed magnetic powder B) and the mixed magnetic powder (mixed magnetic powder C) in which virgin magnetic powder is mixed with 80% by mass of regenerated magnetic powder by mechanical pulverization, the same cylindrical magnet body is manufactured in the same process as above. Then, the magnetic properties and mechanical strength of each magnet body were measured. This is shown in Table 1.

  Regarding the magnetic characteristics, the total magnetic flux was measured with a magnet analyzer. As is clear from Table 1, the total magnetic flux of the magnet body using only the virgin magnetic powder is 484 μW, whereas the total magnetic flux of the magnet body using the mixed magnetic powder A is a sufficiently large value of 460 μW. On the other hand, in the magnet body using the mixed magnetic powder B, the total magnetic flux amount is not significantly reduced to 449 μW. However, in the magnet body using the mixed magnetic powder C, the total magnetic flux amount is greatly reduced to 420 μW.

As for mechanical strength, the crushing strength was measured as shown in Table 1. Here, the crushing strength is a value in consideration of the dimensions of the sample with respect to a load (crushing crushing load) applied to the sample from the radial direction and broken by the sample. Specifically, it is determined by the pressure ring load × (outer diameter−wall thickness) / (height × (wall thickness) ² ). The wall thickness is a value of (outer diameter−inner diameter) / 2. According to this, the crushing strength of the magnet body using only the virgin magnetic powder is 181 MPa, whereas the crushing strength of the magnet body using the mixed magnetic powder A is 176.3 MPa. On the other hand, in the magnet body using the mixed magnetic powder B, the crushing strength is greatly reduced to 143 MPa. In the magnet body using the mixed magnetic powder G, the crushing strength is remarkably reduced to 110 MPa.

  From the above, when the regenerated magnetic powder obtained by conventional mechanical pulverization is added to the virgin magnetic powder at a mixing ratio of 80% by mass of the total amount, the magnet body molded using this has both magnetic properties and mechanical strength. It is greatly reduced with respect to a magnet body formed using only virgin magnetic powder. On the other hand, even if the regenerated magnetic powder obtained by hydrogen storage and pulverization is added at a mixing ratio of 80% by mass of the total amount with respect to the virgin magnetic powder, the magnet body formed from this uses only the virgin magnetic powder. The decrease in both magnetic properties and mechanical strength compared to the molded magnet body is maintained within an allowable range. Therefore, it is possible to effectively use the regenerated magnetic powder and to effectively use resources.

  1, 2, 3 ... mold, 4 ... magnet body, 41 ... opening edge part (unusable part), 42 ... bottom wall part (unusable part).

Claims (2)

A magnet body produced by hot plastic processing of a raw material containing virgin magnetic powder obtained by a super-quenching method is subjected to hydrogen occlusion and pulverization treatment to obtain a regenerated magnetic powder for magnet production. A method for producing regenerated magnetic powder. The regenerated magnetic powder obtained by the production method according to claim 1 is mixed at a ratio of 40% by mass to 80% by mass with respect to the total amount of virgin magnetic powder to obtain mixed magnetic powder, and the mixed magnetic powder is subjected to hot plastic working. To obtain a magnet body.

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