Patent Grant
11515086
This application is a U.S. National stage application of International Application No. PCT/JP2013/0647499 filed, Jun. 26, 2013, which claims priority to Japanese Patent Application No. 2012-156982 filed in Japan on Jul. 12, 2012, the contents of each of which are hereby incorporated herein by reference.
The present invention relates to a method for manufacturing sintered magnets used in high-performance motors and the like.
Nd—Fe—B based sintered magnets are widely employed as permanent magnets used in motors of hybrid automobiles and the like, and due to their exceptional magnetic characteristics, demand is expected to increase in the future as well.
The conventional manufacturing method for Nd—Fe—B based sintered magnets involves melting starting materials, such as Nd, Fe, B, and the like, in a vacuum or in an argon gas atmosphere, and then using a jaw crusher and a jet mill or the like to coarsely pulverize and finely pulverize the melted starting material. The pulverized starting material is then molded to a predetermined shape within a magnetic field, sintered and heat treated, subjected to a slicing process or grinding process using a slicer or grinding machine, and after carrying out surface treatment and inspection, is magnetized.
According to Japanese Patent Publication 4329318, in order to minimize precipitation of ferromagnetic compounds, which tends to occur in cases in which transition metals such as Co or the like are added to an Nd—Fe—B based sintered magnet, and to improve the retention force, which is one of the characteristics of a magnet, a powder of a rapidly quenched alloy is sintered at a temperature of 1,000° C. to 1,110° C., forming a sinter. The sinter is then cooled to bring the temperature to below 400° C., and is then reheated to increase it to a temperature of 400° C.-900° C., cooled at a predetermined rate, subjected to heat treatment, and after reaching room temperature, is subjected to a grinding process or the like.
According to Japanese Patent Publication 4329318, by carrying out heating and cooling steps in the aforedescribed manner, the constitution of the grain boundary phase of the sinter is transformed to a structure in which a non-magnetic crystal part is present in an area surrounded by an amorphous layer section, and the retention force of the magnet can be improved. However, when cooling to 400° C. or below is followed by reheating to about 900° C., energy is consumed unnecessarily, as compared with the case of no reheating, and there is a commensurate increase in cost.
Moreover, drastically changing the temperature of the sinter imposes a high thermal load on structures of the apparatus used for heating and cooling, which shortens the lifetime of the apparatus, and leads to increased capital equipment spending. Further, with methods such as that in Japanese Patent Publication 4329318, in which a grinding process is conducted on a material after having passed through a sintering step, metals, including rare earths such as Nd and Dy, contained in the sintered magnet are partially ground away and are not used in the final product, leading to the problem of a poor yield ratio of material.
The present invention is intended to solve the problem mentioned above, and has as an object to provide a method for manufacturing a sintered magnet, with which energy may be used more efficiently from the time of the sintering step to the aging heat treatment step, and with which the yield ratio of material is improved.
According to the method for manufacturing a sintered magnet of the present invention by which the aforedescribed object is achieved, first, a magnet powder for forming an R—Fe—B based sintered magnet having Nd as the principal component and containing a rare earth element R is press-molded, and a green compact formed by compacting the magnet powder is molded. Next, the green compact is sintered in a heated atmosphere heated to sintering temperature, and a sintered magnet is formed. Then, under conditions of heating to a temperature not exceeding the sintering temperature, the dimensions of the sintered magnet are corrected through pressure molding, while utilizing the heated atmosphere produced during dimension correction to carry out aging heat treatment to adjust the texture of the sintered magnet.
Referring now to the attached drawings which form a part of this original disclosure.
The embodiments of the present invention are described below, while making reference to the appended drawings. The technical scope disclosed in the claims, and the definitions of terms, are not limited to the disclosure hereinbelow. In some cases, the proportions of dimensions in the drawings differ from actual proportions, having been exaggerated for convenience in description.
Fabrication of the starting material alloy is carried out in a vacuum or an inert gas atmosphere, by a strip casting method or other molten process (step S1). The sintered magnet according to the present embodiment has a main phase of Nd2Fe14B, into which Dy, Tb, Pr or the like have been added, as appropriate, to the Nd. By adding the aforementioned rare earth metals to the Nd main component, the retention force of the sintered magnet can be improved.
A jaw crusher, Braun mill, or the like is employed to coarsely pulverize the fabricated starting material alloy to a particle size on the order of several hundred μm (step S2). The coarsely pulverized alloy is finely pulverized to a particle size of about 3-5 μm by a jet mill or the like (step S3). High coercive force can be obtained in particular, by bringing the particle size to 3-4 μm in the fine pulverization step, and it is therefore preferable to do so.
Next, the finely pulverized magnetic material is molded in a magnetic field, and a green compact is obtained (step S4). The green compact can be made employing various methods such as a parallel magnetic field molding process, a perpendicular magnetic field molding process, or the like. In the present embodiment, the steps from fabrication of the starting material alloy to molding in a magnetic field are designated collectively as green compact molding.
The green compact molded in the magnetic field is sintered in a vacuum or in a non-oxidizing state, and an R—Fe—B based sintered magnet is obtained (step S5). The sintering temperature will vary somewhat depending on the material composition, the pulverization method, and the particle size of the green compact, but is on the order of 900° C.-1,100° C.
In the dimension correction step, in a generally non-oxidizing state, press-molding of a workpiece W is carried out with an upper mold 213 and a lower mold 214 which constitute a dimension correction section 200 shown in
After dimension correction, aging heat treatment is carried out in a non-oxidizing state, and the coercive force of the sintered magnet is adjusted (step S7). In some cases, dimension correction of the sintered magnet is conducted at a higher temperature than aging heat treatment, and therefore dimension correction of the sintered magnet is conducted prior to aging heat treatment. The reason is that there is a risk that the temperature at which heat treatment is carried out will change the texture of the magnet, with the possibility of affecting the magnet characteristics.
After the aging heat treatment, a surface treatment involving Ni plating or the like is carried out in order to prevent rust and corrosion (step S8). Once the surface treatment has been completed, an inspection of magnetic characteristics, appearance, dimensions, and the like is carried out (step S9), and finally the material is magnetized through application of a pulsed magnetic field or static magnetic field, to manufacture a sintered magnet (step S10).
Next, the apparatus for embodying the sintering step, the dimension correction step, and the aging heat treatment step in the sintered magnet manufacturing method according to the present embodiment will be discussed in detail.
As shown in
The sintering furnace 100 further has an introduction duct 103 for introducing into the sintering furnace 100 a heated atmosphere generated by the heater, an exhaust duct 104 for discharging gases produced during sintering from the sintering furnace interior, and a cooling chamber 107 for cooling the magnet after sintering.
The divider wall 101 is formed by a material having ample heat resistance, such as ceramic, making it possible to heat the sintering furnace interior up to about 1,100° C. As examples of the heater there may be cited a metal heater, which is advantageous from the point of carrying out uniform heating, or a molybdenum heater, which is advantageous from standpoint of being able to withstand high temperatures of 1,000° C. or above; however, there is no limitation to these.
The introduction duct 103 introduces into the sintering furnace interior the heated atmosphere generated by the heater, thereby adjusting the sintering furnace interior to predetermined temperature. The size, shape, placement, and so on of the introduction duct 103 will be determined by the temperature adjustment range of the sintering furnace interior. The exhaust duct 104 is connected to a negative pressure-generating means such as a compressor, and is installed for the purpose of discharging from the sintering furnace interior gases and the like produced from the sintered magnet during sintering, and for bringing the chamber interior to a non-oxidizing state. Due to the installation of the exhaust duct, gases produced during sintering are discharged, maintaining the chamber interior in a non-oxidizing state, and preventing a decline in magnet characteristics.
The shutter mechanism 102 has a shutter 105 that moves in a vertical direction at the entry/exit port of the sintering furnace 100, and a guide rail 106 for guiding the shutter 105 during vertical motion, by a drive mechanism, not illustrated. The shutter 105 opens and shuts the entry/exit port of the sintering furnace 100 by moving along the guide rail 106.
The cooling chamber 107 has, e.g., a water-cooled jacket, to cool the heated sintered magnet down to about room temperature.
The dimension correction section 200, which carries out dimension correction of the sintered magnet, has an upper slide 201 and a bolster 202 capable of moving relatively closer and apart, and a die set 201 capable of being attached to and detached from the dimension correction section 200. The die set 201 has an upper die 211, a lower die 212 positioned in opposition to the upper die 211, and an adjustment mechanism 240 for aligning the positions of the upper die 211 and the lower die 212. The die set 210 also has a containment vessel 220 placed on the lower die 211, and furnished with a correction mold for correcting the dimensions of the workpiece W (the sintered magnet targeted for dimension correction).
The containment vessel 220 has a heater 221 for heating the sintered magnet, a pipeline duct 223 for forming a non-oxidizing state in the interior of the containment vessel 220, a cooling plate 224 for cooling the sintered magnet subsequent to dimension correction, and a cooling pipe 225 for circulating cooling water or the like to the cooling plate 224.
In
The correction mold is formed by an upper mold 213, a lower mold 214 and an outside peripheral mold 215. The knockout bar 203 and the lower mold 214 form a knockout mechanism for extracting the workpiece W. Symbol 204 in
The die set 210 is secured in the dimension correction section 200 by securing the upper die 211 to the upper slide 201 with the linking pin 217, and securing the lower die 212 to the bolster 202 with the linking pin 217. The upper die 211 has interlocking operation with the upper slide 201.
The adjustment mechanism 240 has a guiding rod 241 furnished to the lower die 212, and a guiding cylinder 242 furnished to the upper die 211, for slidably retaining the guiding rod 241. Position alignment of the upper die 211 and the lower die 212 is carried out through sliding motion of the guiding rod 241 within the guiding cylinder 242. In the present embodiment, even when the upper die 211 has been positioned furthest away from the lower die 212, the guiding rod 241 does not detach from the guiding cylinder 242, and accuracy of position is ensured thereby.
The upper die 211 and the lower die 212 are secured to the upper slide 201 and the bolster 202 by the linking pins 217. For this reason, the die set 210 can be readily attached to and detached from the dimension correction section 200, simply by detaching the linking pins 217.
The containment vessel 220 is placed on the lower die 212, so that machining of the sintered magnet targeted for machining may take place in a non-oxidizing state. The pipeline duct 223 is connected to a vacuum pump (not illustrated) for forming a non-oxidizing state within the chamber. A valve (not illustrated) is furnished midway along the pipeline path, and by switching the path with the valve after placing the containment vessel interior in a vacuum, the containment vessel interior can be filled with an inert gas such as nitrogen gas or the like. When metals such as Dy, Tb, Pr, or the like have been added to Nd at a level of 10 ppm or less in an Nd—Fe—B sintered magnet, the oxygen concentration within the chamber is preferably brought to 1 ppm or less. The reason is that Dy, Tb, and Pr are more prone to oxidation than Nd.
With the containment vessel interior maintained in a vacuum state, the correction mold to which the upper die 211 and the lower die 212 have been attached is inserted into the containment vessel interior from the vertical direction in
The containment vessel 220 is furnished with a magnet introduction/removal mechanism for placing on the lower mold the sintered magnet conveyed by the sintering furnace 100, and for replacing the sintered magnet with the next one, after dimension correction.
The magnet introduction/removal mechanism in the present embodiment is formed by a robot arm, not illustrated, for carrying out rapid introduction and removal of sintered magnets extracted from the sintering furnace 100.
The heater 221 is furnished in proximity to the upper mold 213, the lower mold 214, and the outside peripheral mold 215, and is formed to hollow shape to allow sliding motion of the upper mold 213. While there are no particular limitations as the constitution of the heater 221, an electrical heater, a high-frequency induction heater, or the like can be cited.
As shown in
Next, the sintering step, the dimension correction step, and the aging heat treatment step in the sintered magnet manufacturing method according to the first embodiment will be described. First, the shutter 105 of the sintering furnace 100 is raised, and the workpiece W, i.e., the green compact, is conveyed inside. Then, in synchronization with movement of the conveyance path on which the workpiece W has been placed, sintering of the workpiece W is brought about in a non-oxidizing state while heating it to 900° C.-1,100° C. with the heater as shown in
Once cooled to room temperature, the workpiece W is conveyed into the containment vessel interior in the dimension correction section 200, and placed on the mold 214 by the robot arm. The outside peripheral mold 215 then installed, maintaining the position of the workpiece W in the horizontal direction. In consideration of possible deformation of the sintered magnet, the outside peripheral mold 215 does not apply pressure to the sintered magnet; however, in cases of carrying out dimension correction of a side surface, a constitution by which pressure is applied would be acceptable.
Next, employing the heater 221, atmospheric heating or high-frequency heating is carried out to bring the molds 213, 214, 215 and the workpiece W to about 620° C.-1,000° C. Within the 620° C.-1,000° C. range, it is preferable to conduct the operation at 800° C. or below, with a view to preventing thermal deformation of the sintered magnet itself, and accelerated oxidation. Once the workpiece W temperature has reached a set temperature, the upper slide 201 is lowered while maintaining the temperature, whereupon the upper mold 213 is lowered in association with lowering of the upper slide 201, and the workpiece W is press-molded in the space inside the correction mold, as shown in
In preferred practice, the aforedescribed press-molding is carried out for about 0.1-30 minutes with the upper mold 213 maintained at bottom dead center, so that correction can be carried out with good dimensional accuracy. In cases in which the containment vessel interior has been filled with inert gas, holding the system at the set temperature may be carried out by circulating the gas through the containment vessel interior. The pressure applied during press machining should be such that pressure is applied at a pressure level below yield stress, while taking into consideration the fact that the yield stress of the magnet declines due to heating of the sintered magnet.
By carrying out press-molding in the aforedescribed heated atmosphere, strain produced in the sintered magnet during sintering is corrected, and the shape of the magnet can be corrected to within a predetermined dimensional tolerance range.
After dimension correction, with the upper mold 213 still maintained at bottom dead center, an aging heat treatment of predetermined duration is carried out, using the heater 211 to adjust the temperature of the workpiece W to about 500° C.-950° C. lower than during dimension correction. The aforedescribed step improves the relative density of the texture of the sintered magnet, improving the residual magnetic flux density, mechanical strength, and the like.
Once the aging heat treatment is completed, the workpiece W is released from the mold as shown in
In the conventional manufacturing steps for sintered magnets, steps in which the green compact is heated, cooled, and then reheated, are conducted from the sintering step to the aging heat treatment step, for the purpose of adjusting magnet characteristics such as the coercive force. After cooling the magnet to room temperature subsequent to aging heat treatment, grinding machining is carried out by way of dimension correction. Methods in which reheating is conducted subsequent to heating and cooling during the sintering step to the aging heat treatment step have poor energy efficiency, and therefore lead to increased cost of products. Additionally, rare earths used in sintered magnets have high scarcity values, and when a grinding step is carried out, some rare earth that is not used in the product is produced, and the yield ratio of material is poor.
In contrast to this, with the sintered magnet manufacturing method according to the present embodiment, by press-molding the sintered magnet in a heated atmosphere to carry out dimension correction subsequent to the sintering step, the phenomenon whereby a portion of the material is ground away and can no longer be used, such as is the case with grinding machining, is eliminated. Therefore, the yield ratio of material can be improved.
Additionally, because the heated atmosphere generated during dimension correction is utilized in the aging heat treatment, the energy needing to be generated by the heater and the like for the purpose of aging heat treatment can be reduced, and better energy efficiency achieved. Additionally, because dimension correction is carried out under a heated atmosphere, and the heat generated during dimension correction is utilized thereafter when carrying out the aging heat treatment step, the change in temperature to reach that needed for aging heat treatment is smaller, and the change in temperature of structures forming the apparatus can be minimized commensurately.
Further, whereas grinding machining employed in conventional dimension correction was carried out after having cooled the magnet to room temperature subsequent to heat treatment, in the present embodiment, dimension correction is carried out under a heated atmosphere, whereby the time to cool the magnet can be reduced, and the time required for the step can be shortened.
With the sintered magnet manufacturing method according to the first embodiment, as described above, the dimensions of the sintered magnet are corrected through press-molding in a heated atmosphere after the sintering step, and thereafter aging heat treatment is carried out in the containment vessel 220 interior. Therefore, removal of a portion of the material, as occurs with mechanical machining processes, is eliminated, and the yield ratio of material can be further improved.
Additionally, because the aging heat treatment is carried out utilizing the heated atmosphere generated during dimension correction, the amount of heat needing to be generated during heat treatment can be reduced, and more efficient utilization of energy achieved. Additionally, because the aging heat treatment is carried out utilizing the heated atmosphere generated during dimension correction, the change in temperature to reach that needed for aging heat treatment is smaller, and the change in temperature of structures within the apparatus can be minimized. Further, because the dimension correction step is carried out under a heated atmosphere, there is no need to cool the magnet to room temperature as in conventional practice, and the required time for the steps can be shortened.
Additionally, because the sintering step, dimension correction step, and aging heat treatment step are carried out in a non-oxidizing state, oxidation of the sintered magnet can be prevented, and decline in the magnet characteristics prevented.
Additionally, due to a constitution whereby the sintered magnet is heated to 800° C. or below and press-molding is carried out during dimension correction, not only can the yield of material be improved, but thermal deformation of the sintered magnet itself, and accelerated oxidation, can be prevented as well.
In the first embodiment, aging heat treatment is carried out in the containment vessel interior of the dimension correction section 200, and the sintered magnet is cooled; however, the aging heat treatment step and the cooling step may be conducted in the following manner.
In the second embodiment, a heat treatment chamber 300 and a cooling chamber 400 are furnished, in addition to the sintering furnace 100 and a dimension correction section 200a. For convenience in illustration, the sintering furnace 100 is depicted with reduced distance on the conveyance path.
The heat treatment chamber 300 is furnished separately from a dimension correction section 200a, and is designed to contain the sintered magnet having passed through the sintering step and the dimension correction step, and to carry out an aging heat treatment for a predetermined temperature and time. In the second embodiment, the heat treatment chamber 300 connects to the pipeline duct 223 of the dimension correction section 200a, and a heated atmosphere generated in the dimension correction section interior is suctioned in through the duct 223, and directed into the heat treatment chamber 300 through a duct 301.
Additionally, a heater, not illustrated, is installed in the heat treatment chamber 300, and is utilized, together with heated gases fed from the dimension correction section 200a, to increase or maintain the internal temperature of the heat treatment chamber 300 at a predetermined value. In cases in which the treatment time and treatment temperature differ depending on the magnet, by forming the dimension correction section and the heat treatment chamber separately as in the second embodiment, the treatment time and treatment temperature can be readily adjusted.
The cooling chamber 400 is formed similarly to the cooling chamber 107 of the first embodiment, and description thereof is therefore omitted.
Next, the sintering step, the dimension correction step, and the aging heat treatment step in the sintered magnet manufacturing method according to the second embodiment will be described. As in the first embodiment, upon completion of molding in a magnetic field, the green compact undergoes a sintering step carried out at 900° C.-1,100° C. in the sintering furnace 100 as shown in
The workpiece W is then placed on the lower mold 214, positioned by the outside peripheral mold 215, and dimension correction of the outer shape is carried out through press-molding at 620° C.-1,000° C., as shown in
In the sintered magnet manufacturing method according to the first embodiment, the dimension correction step and the aging heat treatment step are carried out in the dimension correction section interior. The dimension correction step is carried out at 620° C.-1,000° C., and the aging heat treatment step at 500° C.-950° C.; with the sintered magnet manufacturing method according to the second embodiment, however, the aging heat treatment step and the cooling step are carried out in separate spaces. For this reason, the need to adjust the chamber interior in the dimension correction section 200a to one suitable for heat treatment subsequent to dimension correction is obviated, and the product cycle time can be shortened commensurately.
Even in cases in which, due to limitations imposed by the layout within the factory, a cooling plate and a cooling pipe cannot be installed in the dimension correction section, by separately installing the heat treatment chamber 300 and the cooling chamber 400 as in the second embodiment, the layout within the factory can be accommodated in a flexible manner. Further, by separately furnishing the dimension correction section 200a on the one hand, and the heat treatment chamber 300 and the cooling chamber 400 on the other, the constitution of each can be maintained on an individual basis, whereby the ease of maintenance can be improved.
With the sintered magnet manufacturing method according to the second embodiment as described above, the aging heat treatment step and the cooling step are carried out in different apparatus from dimension correction step, and therefore the labor entailed for temperature adjustment in the dimension correction section 200a can be eliminated, and the product cycle time shortened commensurately. Moreover, by furnishing the heat treatment chamber 300 and the cooling chamber 400 separately from the dimension correction section 200a, the layout within the factory can be accommodated in a flexible manner. Further, by separately furnishing the dimension correction section 200a on the one hand, and the heat treatment chamber 300 and the cooling chamber 400 on the other, the constitution of each can be maintained on an individual basis, whereby the ease of maintenance can be improved.
In the third embodiment, the containment vessel interior of the dimension correction section is furnished with a conveyance space for the workpiece W, and the sintering step can be conducted in the containment vessel interior.
Functions assigned to the sintering furnace have been consolidated into the containment vessel 220, which is formed such that temperature management of the chamber interior can be accomplished by a heater (not illustrated) in the containment vessel interior. A convey-in port 221 for conveying in the workpiece W is installed in the containment vessel 220.
Next, the sintering step, the dimension correction step, and the aging heat treatment step in the sintered magnet manufacturing method according to the third embodiment will be described. Firstly, the workpiece W, i.e., a green compact, is conveyed in through the convey-in port 221, and a sintering step is carried out at 900° C.-1,100° C. by a heater, until the compact has been conveyed as far as the constitution serving as the dimension correction section, as shown in
Next, the sintered magnet, while placed on the lower mold 214 by the robot arm and positioned by the outside peripheral mold 215, is press-molded in a heated atmosphere at 620° C.-1,000° C., by lowering the upper mold 213, and dimension correction of the outer shape is carried out.
After dimension correction, an aging heat treatment is carried out for a predetermined time on the sintered magnet in the containment vessel interior, with the temperature adjusted to 500° C.-900° C. After the aging heat treatment, the sintered magnet is released from the mold, transported to the cooling plate 224, and cooled to room temperature by a gas from the cooling pipe 225, then conveyed outside the apparatus. With the sintered magnet manufacturing apparatus according to the third embodiment, not only can the heated atmosphere produced during hot pressing be utilized during the aging heat treatment step, but the heated atmosphere produced during the sintering step can be utilized in the dimension correction step as well, whereby energy can be utilized even more efficiently.
Additionally, by utilizing the heated atmosphere produced during the sintering step, the heating time needed to raise the temperature to that necessary for dimension correction can be shortened. Further, because dimension correction and aging heat treatment are carried out while utilizing heat produced during the sintering step, and because the sintering step, the dimension correction step, and the aging heat treatment step are conducted at progressively higher temperatures, deformation due to temperature changes of structures within the apparatus can be minimized, as in the preceding embodiments. Further, because the sintering step, the dimension correction step, the aging heat treatment step, and the cooling step are carried out within a single apparatus, the constitution of the apparatus can be simpler.
With the sintered magnet manufacturing apparatus according to the third embodiment as described above, a conveyance space is installed in the containment vessel interior formed to a non-oxidizing state, and the sintering step, the dimension correction step, the aging heat treatment step, and the cooling step are carried out within the apparatus. Therefore, the heated atmosphere produced in the sintering step can be utilized in the dimension correction step, and greater energy efficiency can be achieved.
Additionally, because the heated atmosphere of the sintering step can be utilized, the heating time to reach the temperature needed for dimension correction can be shortened. Additionally, the sintering step, the dimension correction step, and the aging heat treatment step are conducted at progressively higher temperatures, and deformation due to temperature changes of structures within the apparatus can be minimized. Further, because the sintering step, the dimension correction step, the aging heat treatment step, and the cooling step are carried out within a single apparatus, the constitution of the apparatus can be simpler.
In the fourth embodiment, as in the third embodiment, the containment vessel 220 interior is furnished with a conveyance space for conducting the sintering step, and temperature adjustments can be carried out during the sintering step and the dimension correction step in the containment vessel 220 by a heater, not illustrated. Additionally, in the fourth embodiment, as in the second embodiment, a heat treatment chamber 300 for carrying out aging heat treatment, and a cooling chamber 400 for carrying out a cooling step, are installed separately in addition to a dimension correction section 200c.
Next, the process from the sintering step to the aging heat treatment step in manufacture of sintered magnets according to the fourth embodiment will be described. Firstly, in the same manner as in the third embodiment, the workpiece W, i.e., a green compact, is conveyed in through the convey-in port 221 of the containment vessel 220, and, in synchronization with movement of the conveyance path on which the workpiece W has been placed, the workpiece W is sintered at 900° C.-1,100° C. as shown in
While maintaining the non-oxidizing state, the dimension-corrected sintered magnet is released from the mold, extracted from the apparatus, and undergoes aging heat treatment carried out at 500° C.-950° C. in the heat treatment chamber 300, to adjust the magnet texture. The magnet is then transported to the cooling chamber 400, and after being cooled to room temperature, is conveyed out to the outside, which has not been adjusted to a non-oxidizing state.
With the manufacturing apparatus according to the fourth embodiment, the heated atmosphere produced in the sintering step can be utilized during dimension correction, and the heated atmosphere in the containment vessel interior subsequent to dimension correction can be utilized for aging heat treatment, whereby greater energy efficiency can be achieved. Additionally, by furnishing the heat treatment chamber 300 and the cooling chamber 400 separately from the apparatus for carrying out the sintering step and the dimension correction step, the need to adjust the containment vessel interior subsequent to dimension correction to the temperature necessary for heat treatment is obviated, and the product cycle time can be shortened commensurately.
Additionally, by installing the heat treatment chamber 300 and the cooling chamber 400 separately from the dimension correction section 200c, a factory layout in which a large-scale apparatus cannot be installed can be accommodated in a flexible manner. Additionally, separating the constitution for carrying out the sintering step and the dimension correction step from the heat treatment chamber 300 and the cooling chamber 400 permits shutdown of only the necessary portion of the entire manufacturing apparatus during maintenance, and ease of maintenance can be improved.
Additionally, due to the ability to utilize the heated atmosphere during the sintering step, the heating time to bring the temperature to that necessary for dimension correction can be shortened. Further, because the sintering step, the dimension correction step, and the aging heat treatment step are conducted at progressively higher temperatures, deformation due to temperature changes of the structures forming the apparatus can be minimized.
In the fifth embodiment, in addition to the sintering step, the dimension correction step, and the aging heat treatment step, a grain boundary diffusion step to improve the magnet characteristics is carried out by equipment such as the dimension correction section 200b shown in
Heat is sometimes employed when bringing about diffusion of heavy rare earth elements such as Dy, Tb, and the like, and by carrying out the grain boundary diffusion step, the decline of magnet characteristics such as retention force and the like of the dimension-corrected sintered magnet can be prevented. Additionally, by carrying out the dimension correction step as in the third embodiment, dimension correction of the sintered magnet can be accomplished at a good yield ratio of material; and by carrying out subsequent steps in the same space as that in which preceding steps were carried out, thermal energy losses and production lead times may be reduced, and deformation of structures forming the manufacturing apparatus canis less likely to occur, due to the smaller changes in temperature. In the present embodiment, provided that two or more successive steps, from among steps preferably carried out in the same equipment, can be carried out in the same equipment, the equipment may take the form of separate units, as with the sintering furnace 100 and the dimension correction section 200 of the first embodiment shown in
As in the third embodiment, the sintering step, the dimension correction step, the grain boundary diffusion step, and the aging heat treatment step are carried out in a space in a non-oxidizing state. When the grain boundary diffusion step is carried out, the surface of the magnet, which is rare earth-rich, is in a state of being prone to oxidation, but by carrying out the grain boundary diffusion step in a non-oxidizing state, oxidation of the magnet and decline in the magnetic characteristics due can be prevented.
The present invention is not limited only to the embodiments shown above, and various modifications are possible within the scope set forth in the claims.
Next, tests relating to molding temperature during press machining carried out at the time of the dimension correction process in the sintered magnet manufacturing method according to the present embodiment are described.
For the test, as sintered magnet test pieces (3.8 mm in thickness, cross sectional length of 6 mm×6 mm), magnet test pieces were secured by employing the upper slide, bolster, and outside peripheral mold in the same manner as in
From Table 1 and
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2012-156982 | Jul 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/067499 | 6/26/2013 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2014/010418 | 1/16/2014 | WO | A |
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|---|---|---|---|
| 3892598 | Martin | Jul 1975 | A |
| 4695333 | Inoue | Sep 1987 | A |
| 20060006210 | Nonomura | Jan 2006 | A1 |
| 20060144477 | Cox | Jul 2006 | A1 |
| Number | Date | Country |
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| 102576589 | Jul 2012 | CN |
| S55122823 | Sep 1980 | JP |
| 60-77961 | May 1985 | JP |
| 62-30846 | Feb 1987 | JP |
| S62030846 | Feb 1987 | JP |
| 62-262405 | Nov 1987 | JP |
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| 2005-294558 | Oct 2005 | JP |
| 2007-88206 | Apr 2007 | JP |
| 2007-258377 | Oct 2007 | JP |
| 2008-300853 | Nov 2008 | JP |
| 4329318 | Jun 2009 | JP |
| 2010-74084 | Apr 2010 | JP |
| 2012-23197 | Feb 2012 | JP |
| 2013-98485 | May 2013 | JP |
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| Hirota, K. et al. “Coercivity enhancement by the grain boundary diffusion process to Nd—Fe—B sintered magnets.” 2006. Transaction on magnetics. 42. p. 2909-2911. (Year: 2006). |
| Number | Date | Country | |
|---|---|---|---|
| 20150206654 A1 | Jul 2015 | US |
