JP4407834B2 - Molding method of magnetic powder - Google Patents

Description

  The present invention relates to a molding method in which magnetic powder is pressure-molded by an upper punch, a lower punch, and a die, and more specifically, a technique for improving the orientation in the lower part of a molded body in which the orientation tends to be reduced due to the weight of the powder. It is about.

Molding in a magnetic field is performed as one step in the process of manufacturing an anisotropic sintered magnet, for example. R-Fe-B sintered magnets (R is a rare earth element including Y), which is a typical anisotropic sintered magnet, includes main phase crystal grains made of R ₂ Fe ₁₄ B ₁ compound and R-rich grain boundary phase. In order to increase the residual magnetic flux density (Br), it is necessary to increase the degree of orientation of the main phase crystal grains in the direction of the easy axis in magnetic field molding.

  Conventionally, when performing molding in a magnetic field, in order to supply magnetic powder into the cavity (molding space) of the molding apparatus, the feeder box (or feeder cup) is slid onto the cavity and the powder's own weight in the feeder box is used. Had fallen into the cavity. According to such a supply method using a conventional feeder box, the powder can be reliably supplied into the cavity, and the volume of the supplied powder can be controlled to be almost constant by “slicing”.

  However, as disclosed in Patent Document 1, the closer to the bottom of the cavity, the stronger the pressure due to the weight of the powder, the lower the fluidity of the powder, so that it is difficult to orient in a magnetic field. As a result, the orientation degree of the portion near the bottom of the cavity in the supplied powder is lower than the orientation degree of other portions, and the magnetic properties of the finally obtained R-Fe-B sintered magnet vary depending on the portion. Will occur. This problem becomes prominent particularly when a long R—Fe—B sintered magnet is manufactured. This is because the self-weight pressure received at a position near the bottom of the cavity increases as the length increases. Moreover, since the specific gravity of the R-Fe-B magnetic powder is larger than that of the ferrite magnetic powder, when the R-Fe-B magnetic powder is supplied into the cavity, the bottom of the cavity is higher than that of the ferrite magnetic powder. A greater self-weight pressure is generated at a position close to.

  Patent Document 1 discloses a method for eliminating such an orientation failure due to its own weight pressure at the bottom of the cavity, a step of arranging magnetic powder outside the cavity, a step of forming a magnetic field in a space including the cavity, and the magnetic field is magnetic powder. The magnetic powder is moved into the cavity while orienting the magnetic powder in the direction of the magnetic field by the force exerted on the magnetic field, and it is proposed to move the magnetic powder into the cavity after starting the application of the magnetic field. is doing. The proposal of Patent Document 1 is intended to supply magnetic powder while applying a magnetic field, and is intended to eliminate orientation obstacles due to its own pressure by terminating the orientation of the magnetic powder when the supply is completed.

  Further, in Patent Document 2, in order to reduce the variation in magnetic characteristics, one of the pair of upper and lower punches is displaced with respect to the die in the pressurizing process for forming in a magnetic field. It has been proposed to comprise a first step of pressing and a second step of displacing the other of the pair of upper and lower punches with respect to the die, thereby pressing the raw material powder. Furthermore, in Patent Document 3, in order to reduce the variation in magnetic characteristics, after reaching the predetermined value at which the apparent density of the rare earth alloy powder in the cavity is 47% or more of the true density within the period of the pressurization process. It is proposed to apply a pulse magnetic field substantially perpendicular to the pressurizing direction only. However, the variation in magnetic characteristics in Patent Document 2 and Patent Document 3 has a problem of variation in magnetic characteristics exclusively in the direction parallel to the pressurizing direction, and does not assume that the alignment obstacle at the bottom of the cavity is eliminated.

JP 2001-226701 A Japanese Patent Laid-Open No. 2003-272942 JP 2004-2998 A

The proposal described in Patent Document 1 can eliminate the orientation failure due to the self-weight pressure at the bottom of the cavity, but a special powder feeding device for applying a magnetic field to the magnet powder above the cavity is necessary. In addition, it is necessary to newly provide a magnetic circuit for applying a sufficient magnetic field above the cavity.
The present invention has been made on the basis of such a technical problem, and an object thereof is to improve the magnetic field orientation of a molded body without providing a new mechanism in a conventional magnetic field molding machine.

  When the area of the cavity bottom is constant, the self-weight pressure at the cavity bottom increases as the supply amount of magnetic powder increases. In other words, in order to reduce the self-weight pressure at the bottom of the cavity, the supply amount of the magnetic powder may be reduced. Focusing on this, when a magnetic field was applied each time a part of the magnetic powder was supplied to the cavity, it was confirmed that the magnetic field orientation was easy at the bottom of the cavity. As a result, as shown in the examples described later, the magnetic properties, particularly the residual magnetic flux density (Br), of the sintered magnet obtained by sintering the obtained molded body were improved.

In the magnetic powder molding method of the present invention based on the above knowledge, the step (a) of supplying a part of the magnetic powder into the cavity formed by the lower punch and the die, and the step of supplying the step (a) (B) applying a magnetic field to the magnetic powder existing in a non-pressurized state, and after the step (a) and the step (b) are performed a plurality of times, the lower powder and the die are used to remove the magnetic powder into the cavity. The magnetic powder present in a pressurized state is pressure-molded to obtain a molded body. The number of times the step (a) and the step (b) are performed can be appropriately set according to the dimensions of the molded body, and can be set to 2 to 8 times, for example. Although the step (a) and the step (b) can be performed alternately, the step (a) and the step (b) may not necessarily be performed alternately. After the step (a) is performed a plurality of times, the step (B) may be implemented. For example, you may implement each process in order of a process (a), a process (a), a process (b), a process (a), a process (a), and a process (b). In addition, when performing a process (a) again after implementing a process (b), prior to implementation of a process (a), a magnetic field application is once stopped. Before stopping the magnetic field application, a magnetic field may be applied in the direction opposite to the previously applied magnetic field.
Further, the non-pressurized state in the present invention means a state where the magnetic powder is not pressed by the upper punch, the lower punch and the die. When magnetic powder is further supplied onto the magnetic powder supplied into the cavity, pressure is applied to the magnetic powder already contained in the cavity. Even if such pressure is applied, the upper punch If the magnetic powder is not pressed by the lower punch and the die, it is referred to as a non-pressurized state.

  In the step (b) of applying a magnetic field, it is preferable to apply a magnetic field (transverse magnetic field) in a direction substantially perpendicular to the pressing direction of the magnetic powder. This is because application of a transverse magnetic field can provide higher magnetic characteristics than a mode in which a magnetic field (longitudinal magnetic field) in a direction substantially parallel to the pressing direction of the magnetic powder is applied. By applying the molding method of the present invention to such transverse magnetic field molding, the orientation in the lower part of the molded body is improved, and the residual magnetic flux density (Br) is improved in the case of a sintered magnet.

The supply of the magnetic powder is preferably performed by a suction filling method which is a kind of fraying filling method. The contents of the suction filling method will be described in detail in the examples to be described later. The outline of the suction filling method is that the magnetic powder is supplied into the cavity while lowering the lower punch relatively and increasing the cavity depth intermittently or continuously. That's it. There are at least two ways to lower the lower punch relatively. One is a method of lowering the lower punch relatively by lowering the lower punch itself, and the other is a method of lowering the lower punch relatively by raising the die. The magnetic powder may be supplied by a drop filling method which is a kind of scraping filling method. In the drop filling method, the magnetic powder is supplied into the cavity after the cavity depth is made constant by lowering the lower punch relatively. The wear-off filling method has advantages such as easy and low-priced improvement in magnetic properties, easy application to a large number of pieces, and short molding time.
It is of course possible to supply the magnetic powder by a quantitative filling method. Since the filling weight can be accurately controlled in the quantitative filling method, when applied to the production method of the present invention, the effect of reducing variations in product weight and magnetic properties is great.

Further, the present invention has a great effect of improving the magnetic properties when the magnetic powder is a granule. In the present specification, those having a bulk density / true density (%) of 25% or more are referred to as granules. The upper limit of the bulk density / true density (%) is not particularly limited, but is, for example, about 40%.
The method further includes a step of firing the molded body obtained by the present invention, and finally a sintered body such as a giant magnetostrictive material composed of a sintered magnet and a sintered body can be produced.

  According to the present invention, it is possible to eliminate an alignment failure due to the self-weight pressure at the bottom of the cavity without providing a new mechanism in the conventional magnetic field molding machine. Thereby, the orientation in the lower part of a molded object is improved, and if it is a sintered magnet, a residual magnetic flux density (Br) will improve.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 is a cross-sectional view showing a configuration of a magnetic field forming apparatus 20 in the present embodiment.
The magnetic field molding apparatus 20 is for forming a cylindrical molded body. After supplying a part of the magnetic powder into the cavity 100 formed by the mold and applying the magnetic field, the magnetic powder is further supplied. A magnetic field is applied, and after the supply amount of the magnetic powder reaches a predetermined amount, the magnetic powder existing in a non-pressurized state in the cavity 100 is pressurized to perform molding in the magnetic field to form a compact. .

The magnetic field forming apparatus 20 includes a support plate 21 that supports the die 40, a lower punch base 22 that supports the lower punch 50, and an upper punch base 23 that supports the upper punch 60.
The support plate 21 is supported by a lower ram 24 that can be driven up and down by a drive mechanism such as a hydraulic cylinder, a ball screw, and a cam with respect to a base (not shown) of the molding apparatus 20 in a magnetic field. Yes.
The lower punch base 22 is fixedly supported by a base (not shown) of the molding apparatus 20 in a magnetic field via a support column 26.
The upper punch base 23 is provided to face the upper side of the lower punch base 22, and can be driven up and down by a drive mechanism such as a hydraulic cylinder, a ball screw, and a cam on the base (not shown) of the magnetic field forming apparatus 20. The upper ram 27 can be moved up and down.

  As shown in FIG. 1, the mold is composed of a die 40, a lower punch 50, and an upper punch 60, and a bolt or the like is used with respect to the support plate 21, the lower punch base 22, and the upper punch base 23 of the magnetic field molding apparatus 20. The attachment member is detachably attached.

The die 40 is provided such that its center coincides with the center of the magnetic field generated by the coils 72a and 72b.
A die hole 41 which is a through hole having a shape corresponding to the shape of the molded body to be molded is formed in the die 40 made of a nonmagnetic material. In this embodiment, in order to produce a cylindrical shaped body, the die hole 41 has a perfect circular opening. Further, the center of the die hole 41 coincides with the center of the die 40.
A feeder 10 for supplying magnetic powder into the cavity 100 is provided on the upper surface of the die 40. The feeder 10 includes a storage unit 10a that stores magnetic powder and has an opening (not shown) on the lower surface, and a drive unit (not shown) that reciprocates the storage unit 10a in a predetermined direction. When the feeder 10 passes over the die hole 41, the magnetic powder in the accommodating portion 10a is supplied into the cavity 100 through an opening (not shown).
The lower surface of the die 40 is connected to the support plate 21 via a pair of lower guide posts 25 penetrating the lower punch base 22. The support plate 21 is connected to a hydraulic cylinder (not shown) via the lower ram 24. Therefore, the die 40 can be moved in the vertical direction by this hydraulic cylinder.

  Around the die 40, a magnetic field generator 70 for orienting the magnetic powder in the cavity 100 is provided. The magnetic field generator 70 has a pair of yokes 71 a and 71 b that are objectively arranged so as to be sandwiched from both sides of the die 40. The yokes 71a and 71b are made of a soft magnetic material having a high magnetic permeability. Coils 72a and 72b are wound around the yokes 71a and 71b, respectively, and when energized, a magnetic field in a direction (dotted arrow) perpendicular to the pressing direction is generated by the lower punch 50 and the upper punch 60, and the cavity 100 Orient the magnetic powder inside.

  The lower punch 50 is attached to the lower punch base 22 in the magnetic field forming apparatus 20 by a lower punch holder 51. The lower punch 50 is disposed at a position corresponding to the die hole 41 of the die 40. The lower punch 50 held by the lower punch holder 51 has its upper end inserted into the die hole 41 of the die 40.

  An upper punch base 23 is disposed above the die 40, and an upper punch 60 is provided on the lower surface of the upper punch base 23 at a position where it can be inserted into the cavity 100. An upper ram 27 is provided on the upper surface of the upper punch base 23. A hydraulic cylinder (not shown) is connected to the upper ram 27. A pair of upper guide posts 28 provided in the vertical direction are inserted in the vicinity of both ends of the upper punch base 23, and the lower end portion of the upper guide post 28 is fixed to the upper surface of the die 40. The upper punch base 23 can be moved in the vertical direction by the hydraulic cylinder while being guided by the upper guide post 28, and the upper punch 60 can be moved in the vertical direction accordingly, and is inserted into the cavity 100.

  Now, the forming apparatus 20 in a magnetic field is provided with the controller 80 which controls the operation | movement. The controller 80 controls the vertical movement of the die 40 and the upper punch 60 by operating a hydraulic cylinder (not shown). Further, the controller 80 is energized with the drive unit of the feeder 10 and controls the reciprocating motion of the feeder 10. The controller 80 applies a magnetic field to the cavity 100 at a predetermined timing by controlling energization to the coils 72a and 72b from a power source (not shown). This control will be described with reference to FIGS. 2 and 3 are diagrams showing the steps of the molding method in a magnetic field, and FIG. 4 is a diagram showing a control flow of the controller 80. As the feeder 10, either a method of supplying a fixed amount of magnetic powder P or a method of scraping and filling the cavity 100 using a feeder box, etc. may be adopted. Will be explained.

  When starting the molding in the magnetic field, the die composed of the die 40, the lower punch 50, and the upper punch 60 is set to an initial state (FIG. 2 (a), FIG. 4 S101). In the initial state of the mold, the lower punch 50 is disposed at a predetermined position with respect to the die 40, whereby the cavity 100 is formed by the lower punch 50 and the die 40. At this time, the upper punch 60 is retracted above the die 40. This is to form a space sufficient to supply the magnetic powder to the cavity 100 by the feeder 10. When starting molding in a magnetic field, the controller 80 sets in advance the amount of magnetic powder P supplied by the feeder 10 at one time and the total weight of the magnetic powder P used in one molded body.

  In the initial state of the mold, the magnetic powder P is supplied to the cavity 100 formed by the lower punch 50 and the die 40 using the feeder 10 (FIG. 2B, FIG. 4 S103).

After supplying the magnetic powder P to the cavity 100, the controller 80 applies a magnetic field to the magnetic powder P supplied to the cavity 100 by energizing the coils 72a and 72b from a power source (not shown) (FIG. 2 (c), FIG. 4 S105). Although the applied magnetic field is indicated by a white arrow, in the present embodiment, so-called transverse magnetic field shaping that is orthogonal to the pressing direction by the lower punch 50 and the upper punch 60 is applied. By applying this magnetic field, the magnetic powder P has its easy axis oriented in the direction in which the magnetic field is applied. The magnetic field intensity in the magnetic field application step (S105 in FIG. 4) may be 1.0 to 2.5T, preferably 1.0 to 2.0T. The application time of the magnetic field may be 0.05 to 30 seconds, preferably 0.1 to 5 seconds.
When the magnetic powder P is a granular powder, most of the granules are collapsed by applying a magnetic field in S105. That is, the coupling between the primary particles constituting the granules is released by applying a magnetic field.

Subsequently, the controller 80 determines whether or not a predetermined amount of supply has been completed (S107 in FIG. 4). Here, it is assumed that the amount of the magnetic powder P supplied by the feeder 10 at one time is 10 g, and the total weight of the molding material is preset to the controller 80 to be 30 g. In this case, if the supply frequency of the magnetic powder P is once or twice, the controller 80 determines that the supply of the predetermined amount is not completed, and supplies the magnetic powder described above until the supply of the predetermined amount is completed (see FIG. 4 S103) and magnetic field application (FIG. 4, S105) are repeated.
If NO is determined in S107 in FIG. 4 and the process returns to the magnetic powder supply (S103 in FIG. 4), the magnetic field application is stopped in advance so that the magnetic powder P in the feeder 10 is not magnetized. Before stopping the magnetic field application, a magnetic field may be applied in the direction opposite to the previously applied magnetic field (hereinafter referred to as “reverse magnetic field application”). When a reverse magnetic field is applied, the magnetic powder P in the cavity 100 is not magnetized, so that there is an advantage that the supply of the magnetic powder P is stabilized.

  On the other hand, when the supply of 3 times of 10 g is completed, that is, when the steps of FIGS. 2A to 2G are performed, it is determined in S107 that the supply of a predetermined amount is completed, and the controller 80 lowers the upper punch 60. (FIG. 3 (h), FIG. 4 S109). The upper punch 60 is inserted into the through hole of the die 40, and the lowering position of the upper punch 60 is preferably from the upper end of the magnetic powder P to a position having a predetermined gap. Although the upper punch 60 may be brought into contact with the upper end of the magnetic powder P, the orientation of the magnetic powder P by applying a magnetic field can be sufficiently ensured by forming a predetermined gap.

  Subsequently, the controller 80 controls the magnetic powder P existing in the non-pressurized state in the cavity 100 by pressurizing by applying a magnetic field and narrowing the interval between the lower punch 50 and the upper punch 60. (FIG. 3 (i), FIG. 4 S111). The operation of the die 40, the lower punch 50, and the upper punch 60 is not limited as long as the pressure molding can be performed. In the present embodiment, since the lower punch 50 is fixed, pressure molding is performed by lowering the upper punch 60. If the lower punch 50 is a magnetic field molding apparatus 20 that can move up and down, the lower punch 50 can be raised and pressure-molded. At this time, the upper punch 60 can be lowered. Further, the die 40 can be moved up and down.

When the pressure molding is completed, the controller 80 controls the power supply to demagnetize the coil 72a, 72b by applying a magnetic field in the opposite direction to the molded body (magnetic powder P) (FIG. 3). (J), FIG. 4 S113).
After demagnetizing for a predetermined time, the magnetic field application is stopped (FIG. 3 (k), FIG. 4 S115).
After the magnetic field application is stopped, the die 40 is lowered and the upper punch 60 is further raised to discharge the compact C from the cavity 100 (FIG. 3 (l), FIG. 4 S117).

  Thus, one cycle of the molding in the magnetic field is completed. When the process of one cycle is completed, the controller 80 sets the mold to the initial state in order to perform the molding in the magnetic field of the next cycle (FIG. 2 (a), FIG. 4 S101). Thereafter, the controller 80 controls the operations of the die 40 and the upper punch 60, and controls the powder supply by the feeder 10 and the magnetic field application by the coils 72a and 72b so that the subsequent steps are executed.

  As described above in detail, by supplying a part of the magnetic powder P to the cavity 100 and applying a magnetic field after each supply, the self-weight at the bottom of the cavity is not provided in a conventional magnetic field molding machine. An alignment failure due to pressure can be eliminated. In the method for forming in a magnetic field of the present invention, the number of times of powder supply and magnetic field application is plural, but pressure forming is not performed every time powder is supplied as in the so-called multistage forming, but one press forming (FIG. 4). S111). In multi-stage molding, since temporary molding is performed multiple times, even if the main molding is performed by pressing each molded body integrally after that, it is easy to form a molded body in which cracks are generated at the temporary molding location. It tends to cause deterioration of characteristics. On the other hand, in the molding method in a magnetic field of the present invention, temporary molding is not necessary, and the magnetic powder P existing in the cavity 100 is pressed at a time in a non-pressurized state. Are less prone to cracks and have good magnetic properties as shown in the examples described later.

In the above description, the case where the amount of the magnetic powder P supplied by the feeder 10 at one time is described as an example. However, the amount of the magnetic powder P is not necessarily constant and may be varied. In the case of variation, it is preferable that the initial powder supply amount is smaller than the second and subsequent powder supply amounts. It is the powder disposed at the bottom of the cavity that is particularly problematic in orientation failure, but the orientation of these powders can be improved by reducing the initial supply amount of the powder.
The intensity of the applied magnetic field is not necessarily constant, and may be varied as appropriate. For example, the first magnetic field application may be performed with a stronger magnetic field than the second and subsequent times while the amount of the magnetic powder P supplied at a time is constant. Further, the magnetic field strength may be varied according to the powder supply amount.

Next, using FIG. 5, while showing the positional relationship of the feeder 10 and the cavity 100, the other form of a magnetic powder supply process (FIG. 4 S103) is shown. In the embodiment shown here, the lower punch 50 can be raised and lowered, and the raising and lowering movement is controlled by the controller 80.
5 and 6 are diagrams schematically showing a method of supplying the magnetic powder P to the cavity 100 by a suction filling method of fraying and filling.
As shown in FIG. 5 (a), a die composed of a die 40, a lower punch 50, and an upper punch 60 is set to an initial state. At this time, the upper punch 60 is retracted above the die 40 so as not to hinder the operation of the feeder 10.
As shown in FIG. 5B, when the lower punch 50 is lowered, the cavity 100 is formed by the lower punch 50 and the die 40. Lowering of the lower punch 50 may be continuous or intermittent.
As the lower punch 50 moves down, the feeder 10 approaches the cavity 100. As shown in FIGS. 5B, 5 </ b> C, and 6 </ b> D, when the feeder 10 passes through the cavity 100, a predetermined amount of magnetic powder P is supplied to the cavity 100. Even while the feeder 10 reciprocates on the cavity 100 with a predetermined stroke L, the lower punch 50 descends continuously or intermittently to form a new cavity 100. In this application, the method of supplying the magnetic powder P to the cavity 100 formed over time is called a suction filling method. According to the suction filling method, it is easier to supply the magnetic powder P into the cavity 100 than in the form shown in FIG.

  After the feeder 10 has reciprocated once over the cavity 100 as shown in FIG. 5 (b), FIG. 5 (c), and FIG. 6 (d), for example, as shown in FIG. Retreat to a predetermined position outside the range. This is to prevent the magnetic powder P housed in the feeder 10 from being magnetized. When the magnetic powder P is magnetized in the feeder 10, the magnetic powder P is magnetically agglomerated and it is very difficult to supply the magnetic powder P into the cavity 100. The retracted position of the feeder 10 needs to be appropriately determined according to the magnetic field strength applied in the magnetic field applying step (S105 in FIG. 4). From the viewpoint of preventing the magnetic powder P from being magnetized, When the maximum magnetic field strength is 100%, the feeder 10 is retracted to a position where the magnetic field is at least 50% or less (including 0), preferably 15% or less, more preferably 5% or less of the reference magnetic field. Is preferred. However, as the retracted position of the feeder 10 is closer to the cavity 100, the moving time of the feeder 10 can be shortened, which leads to a reduction in molding time and a reduction in molding cost. ) Is preferably set to a position where the magnetic field is 5 to 50%, more preferably 5 to 20% of the reference magnetic field.

  As described above, there is a drop filling method in addition to the suction filling method as the scraping filling method, and the magnetic powder P can be supplied into the cavity 100 by the drop filling method. In the case of adopting the drop filling method, for example, as shown in FIG. 2A, the lower punch 50 is relatively lowered to control the magnetic powder P by the feeder 10 while keeping the depth of the cavity 100 constant. Is supplied into the cavity 100.

When the controller 80 detects that the feeder 10 has been retracted to a predetermined position, a magnetic field is applied to the magnetic powder P supplied to the cavity 100 by energizing the coils 72a and 72b from a power source (not shown) (FIG. 4, S105, FIG. 4). 6 (f)).
Even when the suction filling method is employed, the steps after S107 in FIG. 4 are performed as described above.
The controller 80 can make the determination of S107 shown in FIG. 4 based on the lowering amount of the lower punch 50 and / or the number of reciprocations of the feeder 10. In addition, during pressure molding (S111 in FIG. 4), the feeder 10 is retracted to the same position as in the magnetic field application step (FIG. 6 (f)).

  The molding method of the present invention can be applied to sintered magnets and giant magnetostrictive materials, for example. Basically, these sintered bodies are prepared by producing a raw material alloy, grinding it to a predetermined particle size, producing a compacted body by a method in a magnetic field, and then sintering the ground alloy powder (magnetic powder). It is common in that it is manufactured through a typical process.

In the present invention, the sintered magnet can be applied particularly to an R—Fe—B based sintered magnet. This R—Fe—B based sintered magnet contains 25 to 37 wt% of rare earth element (R). Here, R has a concept including Y. Therefore, one or two of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Selected from more than species. If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the R—Fe—B based sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%.

Moreover, this R—Fe—B based sintered magnet contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of B is set to 4.5 wt%. A preferable amount of B is 0.5 to 1.5 wt%, and a more preferable amount of B is 0.8 to 1.2 wt%.
This R—Fe—B based sintered magnet contains Co of 2.0 wt% or less (excluding 0), preferably 0.1 to 1.0 wt%, and more preferably 0.3 to 0.7 wt%. can do. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

  Moreover, this R—Fe—B based sintered magnet allows the inclusion of other elements. For example, elements such as Al, Cu, Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is preferable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is preferably 5000 ppm or less, more preferably 3000 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.

The present invention is not limited to the R—Fe—B based sintered magnet as described above, but can be applied to other rare earth sintered magnets. For example, the present invention can be applied to an R—Co based sintered magnet.
The R—Co based sintered magnet contains R, one or more elements selected from Fe, Ni, Mn, and Cr, and Co. In this case, it preferably further contains at least one element selected from Cu or Nb, Zr, Ta, Hf, Ti and V, and particularly preferably from Cu and Nb, Zr, Ta, Hf, Ti and V. Containing one or more selected elements. Among these, especially, an intermetallic compound of Sm and Co, preferably a main phase _Sm 2 _{Co 17} intermetallic compounds, the grain boundary exists by-phase mainly composed of SmCo ₅ system. The specific composition may be appropriately selected according to the production method, required magnetic characteristics, and the like. For example, R: 20 to 30 wt%, particularly about 22 to 28 wt%, Fe, Ni, Mn, and Cr Above: about 1 to 35 wt%, one or more of Nb, Zr, Ta, Hf, Ti and V: 0 to 6 wt%, especially about 0.5 to 4 wt%, Cu: 0 to 10 wt%, especially 1 to 10 wt% To the extent, the composition of Co: remainder is preferred.
The R-Fe-B sintered magnet and the R-Co sintered magnet have been mentioned above, but the present invention does not prevent application to other rare earth sintered magnets.

The rare earth sintered magnet can be manufactured through the following steps.
The raw material alloy can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably an argon atmosphere.
When an R—Fe—B based sintered magnet is obtained, a so-called alloy using a R ₂ Fe ₁₄ B crystal grain (low R alloy) and an alloy containing more R than a low R alloy (high R alloy) is used. A mixing method can also be applied.

First, the raw material alloy is subjected to a grinding process. In the case of the mixing method, the low R alloy and the high R alloy are pulverized separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process.
In the coarse pulverization step, the raw material alloy is coarsely pulverized to a particle size of about several hundred μm to obtain a coarsely pulverized powder. This coarsely pulverized powder corresponds to the raw material alloy powder in the present invention. The coarse pulverization is preferably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Prior to coarse pulverization, it is effective to perform pulverization by allowing hydrogen to be stored in the raw material alloy and then releasing it. The hydrogen storage process and the hydrogen release process are not essential processes. This hydrogen pulverization can be regarded as coarse pulverization, and mechanical coarse pulverization can be omitted.

  After the coarse pulverization process, the process proceeds to the fine pulverization process. An airflow pulverizer is mainly used for fine pulverization, and finely pulverized coarsely pulverized powder to obtain finely pulverized powder (ground powder) having an average particle size of 2.5 to 6 μm, preferably 3 to 5 μm. The airflow type pulverizer generates a high-speed gas flow by opening a high-pressure inert gas through a narrow nozzle, accelerates the coarsely pulverized powder by this high-speed gas flow, and collides between coarsely pulverized powders, targets or container walls. This is a method of pulverizing by causing a collision.

  In the case of the mixing method, the timing of mixing the two kinds of alloys is not limited. However, when the low R alloy and the high R alloy are separately pulverized in the pulverization step, the pulverized low R alloy powder is used. And high R alloy powder in a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. The mixing ratio when the low R alloy and the high R alloy are pulverized together is the same.

  The finely pulverized powder obtained as described above is subjected to molding in a magnetic field by the method described above. The molded body obtained by molding in a magnetic field is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a difference of an average particle diameter, and a particle size distribution, what is necessary is just to sinter at 1000-1200 degreeC for about 1 to 10 hours in a vacuum.

  Now, after sintering, the obtained sintered body can be subjected to an aging treatment. This process is an important process for controlling the coercive force. When the aging treatment is performed in two stages, holding for a predetermined time at 750 to 1000 ° C. and 500 to 700 ° C. is effective. When the heat treatment at 750 to 1000 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by heat treatment at 500 to 700 ° C., the aging treatment at 500 to 700 ° C. is preferably performed when the aging treatment is performed in one stage.

The present invention also relates to a sintered body having a composition represented by RT _y (wherein R represents one or more rare earth metals, T represents one or more transition metals, and y represents 1 <y <4). The present invention can also be applied to the giant magnetostrictive material.
Here, R represents one or more selected from lanthanoid series and actinoid series rare earth metals including Y. Among these, R is particularly preferably a rare earth metal such as Nd, Pr, Sm, Tb, Dy, and Ho, more preferably Tb and Dy, and these can be used in combination. T represents one or more transition metals. Among these, as T, transition metals such as Fe, Co, Ni, Mn, Cr, and Mo are particularly desirable, Fe, Co, and Ni are more desirable, and these can be used in combination.

In the composition formula RT _y , the RT ₂ Laves type intermetallic compound formed by R and T when y = 2 is most suitable as a magnetostrictive element because it has a high Curie temperature and a large magnetostriction value. Here, when y is 1 or less, the RT phase is precipitated by the heat treatment after sintering, and the magnetostriction value is lowered. When y is 4 or more, the RT ₃ phase or the RT ₅ phase increases, and the magnetostriction value decreases. Therefore, in order to increase the RT ₂ phase, the range of 1 <y <4 is desirable. A plurality of types of rare earth metals may be used as R, and it is particularly desirable to use Tb and Dy.

  In the present embodiment, the magnetostrictive element as described above is a mixture of three kinds of raw material powders having different compositions (hereinafter referred to as raw materials A, B, and C as appropriate) as disclosed in JP-A No. 2002-129274. It is preferable to make them. Moreover, it is preferable that a part of the alloy powder serving as the raw material powder contains a raw material to be subjected to hydrogen storage treatment. By storing hydrogen in the alloy powder, distortion occurs and cracks occur due to the internal stress. For this reason, the alloy powder to be mixed is subjected to pressure when forming a compact, and is pulverized inside the mixed state to become fine, and when it is sintered, a dense high-density sintered body can be obtained. Because.

As the raw material A, a material represented by the formula (1): (Tb _x Dy _1-x ) T _y is used. Here, T of the raw material A is at least one metal selected from the group of Fe, Co, and Ni. In particular, T may be Fe alone. In the formula (1), x and y are in the range of 0.35 <x ≦ 0.5 and 1.7 ≦ y ≦ 2.0.
The raw material B is represented by the formula (2): Dy _t T _1-t (Dy may contain either or both of Tb and Ho, and t is in the range of 0.37 ≦ t ≦ 1.0). A material having a composition to be used is used.
Further, a raw material C containing T is used. As described above, T is at least one metal selected from the group consisting of Fe, Co, and Ni, and among these, Fe is most preferable.

  The raw material A, the raw material B, and the raw material C are weighed and mixed so as to finally have a desired composition, and then pulverized. In the pulverization treatment, a pulverizer such as a wet ball mill, an attritor, or an atomizer can be appropriately selected. In particular, an atomizer is preferable. This is because impact and shear can be applied at the same time, preventing aggregation of the powder and high productivity.

The mixed raw material A, raw material B, and raw material C are formed into a desired shape before sintering. This forming is performed by the above-described forming method in a magnetic field. By this molding in a magnetic field, the raw material A is mainly aligned in a certain direction, and the sintered magnetostrictive material is oriented in the [111] axial direction.
The molded body obtained by molding in a magnetic field is sintered. Sintering conditions are 1100 degreeC or more, Preferably it is 1150-1250 degreeC and it is good to carry out for 1 to 10 hours. The sintering atmosphere is preferably a non-oxidizing atmosphere, and is preferably an inert gas such as Ar gas or in a vacuum.

  As mentioned above, although the example of the material to which this invention is applied was demonstrated, this invention can be widely applied to the magnetic material to which shaping | molding in a magnetic field is applied irrespective of the kind of material.

Hereinafter, the present invention will be described based on specific examples.
A raw material alloy having a composition of 26.5 wt% Nd-5.9 wt% Dy-0.25 wt% Al-0.5 wt% Co-0.07 wt% Cu-1 wt% B-Fe was produced by strip casting.
Next, after hydrogen was occluded in the raw material alloy at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere.
The alloy that has been subjected to the hydrogen pulverization treatment was mixed with 0.05 to 0.1% of a lubricant that contributes to improvement in pulverization and orientation during molding. The lubricant may be mixed for about 5 to 30 minutes using, for example, a Nauter mixer. Thereafter, a finely pulverized powder having an average particle size of 5.0 μm was obtained using a jet mill.

The above finely pulverized powder was put into a chamber of a granulator, and the inside of the chamber was filled with nitrogen to prevent oxidation. As the granulator, a high-speed flow type Spartan Luzer (manufactured by Dalton) having a chamber volume of 4 liters was used. Granulation was performed by adding octanol to produce granules (granule A) having an average particle size of 350 μm and a residual amount of turpineol of 0.5 wt%. The bulk density of the granules A was 2.79 g / cm ³ .

The above granules A were molded in a magnetic field under the following conditions. In each of Experiments 1 to 4, the applied magnetic field was 1.46 T, and the molding pressure was 1.39 ton / cm ² . The application direction of the magnetic field was the transverse magnetic field direction. The sizes of the obtained molded bodies were 20 mm (L) × 18 mm (W) × 13 (H) mm in Experiments 1 and 2, and 20 mm (L) × 18 mm (W) × 26 (H) mm in Experiments 3 and 4. Met.
<Experiment 1>
After supplying the whole amount (20 g) of magnetic powder used for one molded body to the cavity 100 by a quantitative filling method, the upper punch 60 is lowered and the upper punch 60 is inserted into the die 40 by a small amount. The magnetic powder was pressed by applying a magnetic field and lowering the upper punch 60, and then demagnetized to produce a compact.
<Experiment 2>
Of the total amount (20 g) of magnetic powder used in one molded body, 10 g was first supplied to the cavity 100 by a quantitative filling method and then magnetic field orientation was performed. Subsequently, after applying the reverse magnetic field, the remaining 10 g is supplied to the cavity 100, and after applying the magnetic field orientation and reverse magnetic field, the upper punch 60 is lowered, and the upper punch 60 is inserted into the die in a small amount. 60 was stopped, a magnetic field was applied, and the upper punch 60 was lowered to pressurize the magnetic powder, and then demagnetized to produce a compact.
<Experiment 3>
A compact was produced in the same manner as in Experiment 1 except that the total amount of magnetic powder used in one compact was 40 g.
<Experiment 4>
A compact was prepared in the same manner as in Experiment 2 except that the total amount of magnetic powder used in one compact was 40 g and the cycle of powder supply, magnetic field orientation, and reverse magnetic field application was repeated four times.

  The compacts obtained in Experiments 1 to 4 were each fired in vacuum at 1070 ° C. for 4 hours. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 560 ° C. × 1 hour (both in an Ar atmosphere).

The magnetic properties of the obtained sintered magnet were measured. However, the measurement of the magnetic characteristics was performed for each of the divided sintered magnets by dividing the sintered magnets obtained in Experiments 3 and 4 into two parts, upper and lower, in the state during molding in a magnetic field. The sintered body samples obtained in Experiments 1 and 2 were polished as they were without being divided, and the magnetic properties were measured.
The results are shown in Tables 1 and 2.

From Table 1 and Table 2, it can be seen that the residual magnetic flux density (Br) is different if the method of supplying the magnetic powder is different, even if the shape of the compact is the same. Compared to Experiment 1 in which the entire amount of magnetic powder was supplied at once, Experiment 2 in which the magnetic powder was supplied in multiple times showed a higher residual magnetic flux density (Br) of 100 G or more.
In the case of Experiment 3, the residual magnetic flux density (Br) of the sintered magnet positioned on the lower side during molding in the magnetic field is lower than that of the sintered magnet positioned on the upper side. It is noted that the residual magnetic flux density (Br) of the sintered magnet positioned on the lower side during the middle molding is higher than that of the sintered magnet positioned on the upper side. This means that the orientation of the magnet powder located on the lower punch side can be improved during molding in the magnetic field by applying the molding method in the magnetic field of the present invention.

Using the finely pulverized powder prepared in Example 1, granules B and granules C having different bulk densities were prepared by changing the granulation conditions. Table 3 shows the bulk density of the finely pulverized powder, granule B, and granule C.
The above finely pulverized powder, granule B, and granule C were molded in a magnetic field under the following conditions. In any of Experiments 5 to 14, the applied magnetic field and molding pressure were the same as in Example 1, and the size of the obtained molded body was the same as in Experiments 3 and 4.

<Experiments 5, 8, and 11>
A compact was produced in the same manner as in Experiment 1.
<Experiment 6, 9, 12>
A compact was produced in the same manner as in Experiment 2.
<Experiment 13>
A compact was produced in the same manner as in Experiment 2, except that the amount of powder supplied was 5 g and the cycle of powder supply, magnetic field orientation, and reverse magnetic field application was repeated four times.
<Experiment 7, 10, 14>
Of the total amount (20 g) of magnetic powder used in one molded body, 10 g was first supplied to the cavity 100 and then a magnetic field was applied. Subsequently, the remaining 10 g was supplied to the cavity 100, the magnetic field application was stopped after applying the magnetic field for a predetermined time, and the upper punch 60 was lowered. When a small amount of the upper punch 60 was inserted into the die, the upper punch 60 was stopped, a magnetic field was applied, the magnetic powder was pressurized by lowering the upper punch 60, and then demagnetized, and then the molded body was taken out. That is, in Experiments 7, 10, and 14, a reversed magnetic field was not applied after the magnetic field orientation, and a molded body was produced.

  The compacts obtained in Experiments 5 to 14 were subjected to firing treatment and aging treatment under the same conditions as in Example 1, and the magnetic properties of the obtained sintered magnets were measured. The method for measuring the magnetic properties is the same as that for the sintered body samples obtained in Experiments 1 and 2. The results are shown in Table 3.

Comparison of Experiments 5 and 6 shows that magnetic powder can be easily aligned by supplying the magnetic powder to the cavity in multiple batches and applying a magnetic field after each supply to powders other than granules. It could be confirmed.
In addition, as the bulk density of the magnetic powder increases, the residual magnetic flux density (Br) decreases significantly when the entire amount of the magnetic powder is supplied at one time. However, by comparing Experiments 5, 6, 8, 9, 11, and 12, It was confirmed that the larger the bulk density of the powder, the greater the effect of improving the magnetic properties when the present invention is applied.
According to comparison between Experiment 6 and Experiment 7, comparison between Experiment 9 and Experiment 10, and comparison between Experiment 12 and Experiment 14, the residual magnetic flux density (Br) is higher when no reverse magnetic field is applied after powder supply and magnetic field orientation. It turns out that it is obtained.
From the comparison between Experiment 12 and Experiment 13, it can be said that increasing the number of times of supplying the powder and applying the magnetic field is advantageous in obtaining high magnetic properties. However, in consideration of productivity, it can be said that the desirable number of times of powder supply and magnetic field application is 2 to 8 times, more preferably about 2 to 4 times.

In addition, after supplying the whole amount (20 g) of the magnetic powder used for one molded body to the cavity 100 for the granule D produced under a certain condition, the upper punch 60 is lowered and the upper punch 60 is finely applied to the die 40. When a small amount is inserted, the upper punch 60 is stopped, a magnetic field is applied once, four times, or eight times, the magnetic powder is pressurized by lowering the upper punch 60, and then demagnetized to produce a compact. Then, firing treatment and aging treatment were performed under the same conditions as in Example 1, and the magnetic properties of the obtained sintered magnet were measured. The relationship between the residual magnetic flux density of the obtained sintered magnet and the number of applied magnetic fields is shown below, but no improvement in magnetic properties was observed even when a plurality of magnetic fields were applied.
Number of applied magnetic fields Residual magnetic flux density (Br)
Once 12867G
4 times 12860G
8 times 12874G
From the above results, the magnetic properties are not improved by applying the magnetic field a plurality of times, but the magnetic powder is supplied to the cavity 100 in a plurality of times, and the magnetic field is applied by applying the magnetic field after each supply. Can be said to be easier.

  Example 3 shows the result of a comparative study between the case where the magnetic powder is supplied by the scraping filling method and the case where the magnetic powder is supplied by the fixed filling method.

Granule B was molded in a magnetic field under the following conditions. In all of Experiments 15 to 19, the total amount of magnetic powder used in one molded body was 20 g. The applied magnetic field and molding pressure are the same as in Example 1, and the size of the obtained molded body is the same as in Experiments 1 and 2.
<Experiment 15>
Of the total amount (20 g) of magnetic powder used in one molded body, 10 g was first supplied to the cavity 100 by a quantitative filling method and then magnetic field orientation was performed. Subsequently, after applying the reverse magnetic field, the remaining 10 g is supplied to the cavity 100, and after applying the magnetic field orientation and reverse magnetic field, the upper punch 60 is lowered, and the upper punch 60 is inserted into the die in a small amount. 60 was stopped, a magnetic field was applied, and the upper punch 60 was lowered to pressurize the magnetic powder, and then demagnetized to produce a compact.
<Experiment 16>
A molded body was produced in the same manner as in Experiment 15 except that the granule B was supplied in one batch by the suction filling method.
<Experiment 17>
A molded body was produced in the same manner as in Experiment 16 except that Granule B was supplied twice by the suction filling method.
<Experiment 18>
A molded body was produced in the same manner as in Experiment 15 except that the granule B was dropped and supplied in a single batch.
<Experiment 19>
A molded body was produced in the same manner as in Experiment 18 except that the granule B was dropped and supplied twice by the filling method.

  The compacts obtained in Experiments 15 to 19 were subjected to firing treatment and aging treatment under the same conditions as in Example 1, and the residual magnetic flux density (Br) of the obtained sintered magnet was measured. The method for measuring the magnetic properties is the same as that for the sintered body sample obtained in Experiment 1. The results are shown in Table 4. Table 4 also shows the molding time and filling variation in Experiments 15-19. The molding time is the time required until the pressure molding step (S111) is completed in the flowchart of FIG. The filling variation was calculated as follows. That is, 30 molded bodies of each of Examples 15 to 19 were prepared, and the weight was measured, and the standard deviation σ of weight was divided by the average weight σ / ave. Was determined as filling variation.

As shown in Table 4, even when the present invention was applied to the suction filling method and the drop filling method, variations in magnetic properties could be reduced compared to the case where the entire amount of magnetic powder was supplied at once. It has been confirmed that the quantitative filling method is preferable in that the filling variation is small and the magnetic characteristics are stable, and that the fraying filling method is preferable in that the molding time is short.
In drop filling and suction filling, drop filling has a shorter molding time, but suction filling is superior in terms of filling variation and magnetic properties. This is because it is difficult to supply magnetic powder to the bottom when the cavity is deep in drop filling, whereas the cavity depth is deep because the cavity depth changes continuously or intermittently in suction filling. This is because it is easy to supply the magnetic powder to the bottom.

In Example 4, the relationship between the feeder box position and filling variation in the magnetic field application step (S105) of FIG. 4 was confirmed.
Granule B produced in Example 2 was supplied into cavity 100 by suction filling in the manner shown in FIG. 6, and filling variation was measured in the same manner as in Example 3.
The position of the feeder box is indicated by the magnetic field at the feeder box position when the magnetic field is applied. Specifically, the maximum magnetic field strength in the cavity 100 is set to 100%, and a value compared with this reference magnetic field is shown. Table 5 shows the relationship between the feeder box position and filling variation.

From Table 5, it can be seen that the larger the magnetic field, that is, the closer the position of the feeder box to the cavity 100 when the magnetic field is applied, the larger the filling variation. When the magnetic field at the feeder box position exceeds 50%, the filling variation rapidly increases. Therefore, the magnetic field at the feeder box position is preferably 50% or less, more preferably 30% or less of the reference magnetic field. However, the fact that the magnetic field at the feeder box position is small means that the feeder box is located some distance away from the cavity 100. As the feeder box is further away from the cavity 100, magnetic aggregation does not occur and the filling variation is reduced. However, the closer the feeder box is, the less time it takes to move the feeder box and the molding time can be shortened. Cost can be reduced.
From the above results, the feeder box position in the magnetic field application step (S105) of FIG. 4 is preferably adjusted to be 5 to 50%, more preferably 5 to 20% of the reference magnetic field.

It is sectional drawing which shows the structure of the shaping | molding apparatus in a magnetic field in this Embodiment. It is a figure which shows the process of the shaping | molding method in a magnetic field in this Embodiment. It is a figure which shows the process of the shaping | molding method in a magnetic field in this Embodiment. It is a figure which shows the control flow of a controller in this Embodiment. It is a figure which shows typically the method of supplying magnetic powder to a cavity by the suction filling method. It is a figure which shows typically the method of supplying magnetic powder to a cavity by the suction filling method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Feeder, 20 ... Molding apparatus in magnetic field, 21 ... Support plate, 22 ... Lower punch base, 23 ... Upper punch base, 24 ... Lower ram, 25 ... Lower guide post, 26 ... Post, 27 ... Upper ram, 28 ... Upper guide post, 40 ... die, 50 ... lower punch, 60 ... upper punch, 70 ... magnetic field generator, 71a, 71b ... yoke, 72a, 72b ... coil, 80 ... controller, 100 ... cavity, P ... magnetic powder

Claims (6)

In a molding method for pressure-molding magnetic powder with an upper punch, a lower punch and a die,
Supplying a part of the magnetic powder into a cavity formed by the lower punch and the die (a);
And (b) applying a magnetic field to the magnetic powder supplied in the step (a) and existing in the cavity in a non-pressurized state,
After performing the step (a) and the step (b) a plurality of times, the magnetic powder existing in a non-pressurized state in the cavity is pressure-molded by the upper punch, the lower punch and the die, A method for forming a magnetic powder, comprising obtaining a formed body.   The method for molding magnetic powder according to claim 1, wherein the magnetic powder is supplied into the cavity by a suction filling method.   The method for molding magnetic powder according to claim 1, wherein the magnetic powder is supplied into the cavity by a quantitative filling method.   The magnetic powder molding method according to claim 1, wherein a magnetic field is applied in a direction substantially orthogonal to a pressing direction of the magnetic powder in the step (b).   The method for forming a magnetic powder according to claim 1, wherein the magnetic powder is a granule.   The method for molding a magnetic powder according to claim 1, further comprising a step of firing the molded body.

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