Production method of rare earth sintered magnet and production device used in the production method

Abstract

There is provided a production method and a production device for producing each of the rare earth sintered magnet sintered bodies without carrying a mold in a sintering furnace. The method includes feeding an alloy powder into a mold having side walls divided into two or more sections; filling the alloy powder into the mold to prepare a filled molded-body; orienting the alloy powder in the filled molded-body by applying a magnetic field to the filled molded-body to prepare an oriented filled-molded-body; detaching the side walls of the mold from the oriented filled-molded-body and retrieving the oriented filled-molded-body from the mold; and sintering the retrieved oriented filled-molded-body. The filling step and the orienting step are performed at different locations. A pulsed magnetic field can be applied in the orienting step and inside of the mold can be partitioned into a plurality of cavities by partitions.

Claims

1. A method for producing a magnetic anisotropic rare earth sintered magnet comprising: a powder feeding step of feeding an alloy powder into a mold having side walls divided into two or more sections; a filling step of filling the alloy powder into the mold to prepare a filled molded-body; an orienting step of orienting the alloy powder in the filled molded-body by applying a magnetic field to the filled molded-body to prepare an oriented filled-molded-body; a retrieving step of detaching the side walls of the mold from the oriented filled-molded-body and retrieving the oriented filled-molded-body from the mold; and a sintering step of sintering the retrieved oriented filled-molded-body, wherein the filling step and the orienting step are performed at different locations, and wherein the mold is not carried in the sintering step.

2. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein one or plural removable partitions is built in the inside of the mold and the inside of the mold is partitioned into a plurality of cavities by the partitions.

3. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 2, wherein a partition built-in step is provided prior to the powder feeding step.

4. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein a powder feeding spacer is placed on the mold and a predetermined amount of an alloy powder is charged into a space defined by the mold and the powder feeding spacer in the powder feeding step.

5. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 4, wherein one powder feeding spacer capable of feeding the alloy powder to one or plural cavities of the mold is disposed.

6. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 5, wherein in the filling step, a push-in punch member for housing all of the predetermined amount of the alloy powder charged into a space defined by the mold and the powder feeding spacer within the mold, is placed above the mold, and in this state, the mold is dropped repeatedly from a certain height, and thereby all of the alloy powder is housed within the mold and a density of the alloy powder is increased.

7. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 2, wherein the oriented filled-molded-body is retrieved together with the partitions in one united body in the retrieving step.

8. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein the powder feeding step and the filling step of the respective steps are performed at the same location, and the powder feeding step/the filling step, the orienting step, the retrieving step, and the sintering step are respectively performed at different locations.

9. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein the powder feeding step, the filling step, the orienting step and the retrieving step are performed in a single chamber or plural chambers communicated with one another, and inside of the single or plural chamber is filled with an inert gas.

10. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 9, wherein the partition built-in step is performed prior to the powder feeding step, and the partition built-in step and the powder feeding step are performed in the same chamber.

11. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein the mold is composed of side walls consisting of two side plates and two end plates, and one bottom plate.

12. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein magnetic poles are provided at both internal ends of the mold.

13. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 12, wherein the oriented filled-molded-body is retrieved together with the partitions and the magnetic poles in the retrieving step.

14. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 7, wherein the oriented filled-molded-body is sintered together with the partitions in the sintering step.

15. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 13, wherein the oriented filled-molded-body is sintered together with the magnetic poles in the sintering step.

16. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 12, wherein the oriented filled-molded-bodies are taken off from the partitions/the magnetic poles and discretely sintered.

17. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 8, wherein in the retrieving step, the mold from which the oriented filled-molded-body has been retrieved is conveyed to the partition built-in step or the powder feeding step and reused.

18. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein a magnetic field applied in the orienting step is a pulsed magnetic field.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view showing an assembling process of an example of a mold whose side wall is divided into four sections.

(2) FIG. 2 is a perspective view at the time of inserting magnetic poles and partitions into the mold whose side wall is divided into four sections.

(3) FIG. 3 is a sectional view of the mold immediately after charging an alloy powder in the powder feeding step.

(4) FIG. 4 is a sectional view of a mold at the time of pressing an alloy powder with a flat punch in the filling step.

(5) FIG. 5 is a sectional view of a mold at the time of pressing an alloy powder with a punch with grooves in the filling step.

(6) FIG. 6 is a sectional view of a mold placed in a magnetic field in the orienting step.

(7) FIG. 7 is a view showing a procedure of retrieving an oriented filled-molded-body from the mold in the retrieving step.

(8) FIG. 8 is a photograph showing a state of a post-sintering sintered body on a pedestal in the sintering step.

(9) FIG. 9 is a photograph showing a state of a stacked block placed on a pedestal with a bottom plate in Example 3.

(10) FIG. 10 is a photograph showing a state of a filled molded-body placed on a pedestal in Example 4.

(11) FIG. 11 is a view showing a state at the time of filling a powder in a mold for an arc segment plate-like sintered magnet in Example 5.

(12) FIG. 12 is a view showing a state at the time of filling a powder in a mold for a sectorial flat plate-like sintered magnet in Example 6.

(13) FIG. 13 is a view showing an assembled mold having 30 cavities in Example 7.

(14) FIG. 14 is a view showing a cross-section structure in a connecting portion of the mold of FIG. 13.

(15) FIG. 15 is a view showing an example of a production device of a rare earth sintered magnet.

(16) FIG. 16 is a view showing an example of a production device of a rare earth sintered magnet of the present invention different in configuration from the device of FIG. 15.

MODE FOR CARRYING OUT THE INVENTION

(17) Examples of the present invention will be described below, but the present invention is not limited to these examples. Examples of the rare earth sintered magnet include a NdFeB sintered magnet and a SmCo-based sintered magnet. In the following examples, the result of the NdFeB sintered magnet is technically applicable to the SmCo-based sintered magnet.

(18) (Preparation of Alloy Powder)

(19) Hydrogen disintegration was performed by allowing a strip cast alloy whose composition (weight %) is 23.5% of Nd, 5.5% of Pr, 2.5% of Dy, 0.89% of Co, 0.99% of B, 0.1% of Cu, 0.25% of Al, and rest of Fe to occlude hydrogen, and thereby an alloy crude powder for a NdFeB sintered magnet was obtained. The crude powder was milled by a jet mill using a nitrogen gas to prepare an alloy powder for a NdFeB sintered magnet. A particle size of the powder was measured by laser diffraction-scattering method, and consequently an average particle diameter D.sub.50 was 4.2 m. To the powder, zinc stearate was added in an amount of 0.1 wt %, and the resulting mixture was stirred and mixed by a mixer. A sintered magnet was prepared using this alloy powder in each of the following examples.

EXAMPLES

Example 1

Assembling of Mold Whose Side Wall is Divided into Four Sections

(20) The side wall of the mold prototyped was divided into four sections, and a perspective view of the mold is shown in FIG. 1. The mold is composed of side walls consisting of a pair of side plates 11 and a pair of end plates 12, and a bottom plate 13. Grooves for inserting the partitions 14 and the magnetic poles 15 are provided in the side plate 11. This mold whose side wall is divided into four sections can be exactly assembled using screws and positioning pins not shown. As the mold of the present example, a mold made of non-magnetic stainless steel (SUS 304) and a mold made of carbon were prototyped. Both molds functioned well.

(21) In addition, the side wall may be divided into two sections, and one side plate and one end plate may be integrated into one; however, the case of dividing into four sections was easier to use.

(22) 6 partitions with a thickness of 0.5 mm made of carbon and 2 poles with a thickness of 5.9 mm made of permalloy were inserted into grooved of the side plates 11 to dispose 5 cavities in the assembled mold. A perspective view of this is shown in FIG. 2. A depth of each cavity was 20.0 mm, A length of a side in the longitudinal direction of a cavity opening was 40.0 mm, and a length of a side in the shorter direction (a direction perpendicular to a partition) of the cavity opening was 4.6 mm. The magnetic pole was disposed so that the magnetic field is exactly perpendicular to the partition in the orienting step and particularly so that bending of the magnetic field at the cavities of both ends is prevented. In addition, the partition is also disposed on the surface of the magnetic pole so that the magnetic pole is not brought into contact with the alloy powder to cause welding during sintering.

(23) (Powder Feeding Step)

(24) The powder feeding spacer 21 was put on the upper portion of the mold. Since a density at the feeding of the alloy powder 20 of the present example is 1.8 kg/cm.sup.3 and the packing density at the completion of filling is 3.6 g/cm.sup.3, a height of the powder feeding spacer 21 to be used is determined by calculation. Since the required amount of the alloy powder can be calculated to be 66.2 g from the Internal volume and the packing density of the mold, this amount of the alloy powder was charged into a space defined by the mold and the spacer. A sectional view of the mold immediately after charging the alloy powder 20 is shown in FIG. 3.

(25) (Filling Step)

(26) Flat bottom push-in punch member (flat bottom punch) 22 with flat bottom face was inserted into an opening of the powder feeding spacer 21, and this was dropped on the pedestal not shown with the powder feeding spacer 21 set on the mold having the powder filled 5 times from a height of 5 an to bump the mold bottom plate 13 against the pedestal, and the powder was packed until a bottom face of the flat bottom punch reached about 2 mm above the mold. This state is shown in FIG. 4.

(27) Next, using a push-in punch member with grooves (punch with grooves) which is provided with grooved 23 at the positions corresponding to a top end of the partition, the mold was dropped 5 times from a height of 5 cm as with the above, and filling was completed when all of the alloy powder is housed in the mold. The bulk density of the alloy powder at this time was 3.6 g/cm.sup.3, and a section view of the mold at this time is shown in FIG. 5.

(28) The weight of the punch member at this time was 240 g and a filled area was 10 cm.sup.2. The filled molded-body was thus prepared. In addition, the above-mentioned pressing force was estimated by comparison between the case of pressing by a punch and the case of pressing by an air cylinder, a pressure and a sectional area of the air cylinder.

(29) (Orienting Step)

(30) The powder feeding spacer and the punch were removed and a lid plate 16 is attached to a top surface of the mold using a screws. The mold housing the filled molded-body was moved to the inside of a coil for magnetic orientation. A pulsed magnetic field of 4 tesla was applied in a direction perpendicular to the partition. A sectional view of the mold at this time is shown in FIG. 6. An arrow at the bottom of FIG. 6 indicates a direction of a magnetic field. A magnet alloy powder in the filled molded-body was oriented to form a oriented filled-molded-body.

(31) (Retrieving Step)

(32) The side walls constituting the mold are detached from the oriented filled-molded-body of the magnet alloy powder, and a stacked block of the oriented filled-molded-body with a magnet and the partitions is retrieved from the mold. First, a lid plate of the mold was removed and then side plates 11 were retrieved. FIG. 7 upper drawing is a view of the mold in this situation viewed from above. Subsequently end plates 12 were retrieved. FIG. 7 lower drawing is a view of the mold in this situation viewed from above. In these drawings, a rectangular plate visible under the side walls is a bottom plate arranged at the underside of the mold side-walls. When the side plates and the end plates are removed, the stacked block of the oriented filled-molded-body with a magnet and the partitions becomes a state of being placed on the bottom plate.

(33) (Sintering Step)

(34) The stacked block was shifted from on the bottom plate to on the pedestal and moved to the inside of the sintering furnace. The pedestal made of carbon was used. When the shift from on the bottom plate to on the pedestal is carried out carefully, the stacked block is not collapsed.

(35) After the exhaust of the entire sintering furnace was carried out by a turbo-molecular pump, a temperature of the furnace was raised at a temperature raising rate of 1 C./min to 500 C. Thereafter, the temperature was raised at a temperature raising rate of 2 C./min to 1040 C. After the stacked block was maintained at this temperature for 4 hours, heating was stopped, and the stacked block was cooled to room temperature in the furnace. The Stacked block in which the oriented filled-molded-body has became a sintered body is gently pedestal with the bottom plate from the sintering furnace. Five sintered body on one pedestal were placed at regular intervals in proper alignment without falling down on the pedestal. Dimensions and weights of five sintered bodies were extremely close to one another. A photograph of the stacked block on the pedestal is shown in FIG. 8(a), and a photograph of a state in which the magnetic poles and the partitions were removed from the stacked block is shown in FIG. 8(b). Further, comparisons of weights, densities and dimensions of the five sintered bodies in this example are shown in Table 1. In this Table, the range (%) refers to a value obtained by multiplying (MaxMin)/Max by 100, and the thickness refers to a thickness including warpage, if warpage occurs. Dimensions were measured with a vernier caliper.

(36) In Table 2, measurements of magnetic characteristics (coercive force, maximum energy product, remanent flux characteristic) of sintered bodies of cavities No. 2 and No. 3 are shown. These characteristics are almost equal to those of a magnet of maximum quality obtained by a transverse-field pressing method.

(37) TABLE-US-00001 TABLE 1 Weight and Dimension of Sintered Body Dimension Cavity Weight Density Longer side Shorter side Thickness No. (g) (g/cm3) (mm) (mm) (mm) 1 13.08 7.59 34.11 16.99 3.05 2 13.29 7.59 34.14 17.05 3.09 3 13.37 7.60 34.18 17.06 3.05 4 13.15 7.59 34.16 17.05 3.08 5 13.04 7.57 34.09 17.01 3.05 Range 2.4 0.4 0.3 0.4 1.3 %

(38) TABLE-US-00002 TABLE 2 Magnetic Characteristics Remanent Cavity Coercive force Maximum Energy Product Flux Density No. [kOe] BHmax [MGOe] Br [kG] 2 20.2 43.8 13.5 3 20.4 43.5 13.3
[Rationalization of Production Process]

(39) It is important in actuality to save wasteful expenditure and rationalize a production process.

(40) An example of contriving how the bottom plate is used for several purposes will be described. In the present invention, the plate arranged at the underside of the mold side-walls is not required in all steps and is required in only the powder feeding step, the filling step and the orienting step. When moving the filled molded-body from the filling step to the orienting step, the filled molded-body can be conveyed even though the plate is not present. Therefore, the plate arranged at the underside of the mold side-walls in the powder feeding step and the filling step may be different from the plate arranged in the orienting step. That is, the bottom plate does not need to be conveyed when a bottom plate is always placed at a location of the powder feeding step and the filling step, and placed at a location of the orienting step. When doing in this way, the number of parts constituting the mold throughout all steps can be reduced resulting in a rationalization of steps.

(41) Similarly, since the step in which the lid plate is absolutely required is only the orienting step, one bottom plate may be always kept at the orienting step and used for several purposes.

(42) Such a rationalization measures is not essential, and specifically there are various rationalization measures.

Example 2

(43) Using a resin plate having the same size in place of the magnetic poles of Example 1, the effect of the magnetic pole was examined. When the magnetic pole is not used, the magnetic field at the orienting step is slightly deviated from a uniform magnetic field and the orientation of the oriented filled-molded-bodies at both ends is disturbed. The effect of the disturbance was examined.

(44) The respective steps were performed in the same manner as in Example 1 except that using a resin plate, powder feeding/filling/orienting steps were performed and the resin plate was removed before the sintering step. Further, comparisons of weights, densities and dimensions of the five sintered bodies after sintering are shown in Table 3. In this Table, as with Example 1, the range (%) refers to a value obtained by multiplying (MaxMin)/Max by 100, and the thickness refers to a thickness including warpage, if warpage occurs.

(45) TABLE-US-00003 TABLE 3 Weight, Dimension and Variation without Magnetic poles Dimension Cavity Weight Density Longer side Shorter side Thickness No. [g] [g/cm3] [mm] [mm] [mm] 1 13.17 7.55 34.05 17.07 3.13 2 13.04 7.59 34.25 17.06 3.18 3 13.26 7.60 34.29 17.13 3.17 4 13.07 7.60 34.16 17.06 3.12 5 13.25 7.59 34.07 17.06 3.16 Range % 1.7 0.7 0.7 0.4 1.9

(46) Comparing Table 1 with Table 3, it is found that thicknesses of the sintered bodies at both ends are significantly large in Table 3. This thickness includes warpage, and it is visually found that the sintered bodies at both ends are warped. That is, it is found that when the magnetic pole is not used, the magnetic field does not become uniform in the orienting step, the sintered body is warped by the amount. However, it is found that in accordance with the present invention, a thin-shaped magnet having high magnetic characteristics and dimensional variation is small can be produced even though the magnetic pole is not used. When the magnetic pole is used, the dimensional variation is reduced a little.

Example 3

(47) The stacked block 27 is placed with the bottom plate 13 on the pedestal 25, and other operations were carried out in the same manner as in Example 1. The result substantially agrees with that of Example 2. This state is shown in FIG. 9.

(48) When the bottom plate is made of a material which is not damaged in the sintering step and does not react with the alloy powder, the stacked block may be sintered with the bottom plate. This way is more safe particularly when strength of the oriented filled-molded-body is not adequate since the stacked block of the oriented filled-molded-body of the alloy powder does not need to move from the bottom plate to the pedestal.

Example 4

(49) After the orienting step, the stacked block was dissected out, partitions and the magnetic poles were removed, and only the filled molded-body of the alloy powder was sintered. Other steps were performed in the same manner as in Example 1. This method can be applied to only the case in which the filled molded-body is firmly solidified after orientation and a shape of the oriented filled-molded-body is not collapsed even when removing the partitions. Only the filled molded-body 26 was placed on the pedestal 25 and sent to the sintering step. The drawing of this is shown in FIG. 10. By sintering the molded body of FIG. 10, the same results as in Example 1 were obtained.

Example 5

(50) Example 2 was an example of production of a flat plate-shaped rectangular sintered body. In the present example, an arc segment plate-like sintered body was produced in the same manner as in Example 2. A magnetic pole was not used. A view of the post-filling step mold viewed from above is shown in FIG. 11. In this case, the partition needs to be formed into an arc segment plate-shape as with a product. A silicon steel plate of 0.5 mm in thickness was heated at 500 C. for 1 hour, and then punched out by pressing to prepare partitions. Five arc segment-shaped sintered bodies could be prepared with the same high dimensional precision as in Example 2 by sintering the oriented filled-molded-body of the alloy powder in the same manner as in Example 2.

Example 6

(51) Example 2 was an example of production of a flat plate-shaped rectangular sintered body. In the present example, a sectorial flat plate-like sintered body was produced in the same manner as in Example 2. A magnetic pole was not used. A view of the post-filling step mold is shown in FIG. 12. A view on a left side is a view of the mold viewed from above, and a view on a right side is a sectional side view of the mold.

(52) Also in this case, the same results as in Example 1 were obtained by sintering the oriented filled-molded-body of the alloy powder in the same manner as in Example 2.

Example 7

(53) An assembled mold having 30 cavities was prototyped. A sectional view of the prototyped mold into which 20 g of an alloy powder was filled is shown in FIG. 13.

(54) A size of a cavity was set to 26 mm22 mm4.6 mm, a thickness of the partition was set to 0.5 mm, and a whole length of the mold was about 240 mm including end plats and magnetic poles.

(55) FIG. 14 shows a cross-section structure of a connecting portion positioned at both ends of the mold of FIG. 13, and two tensile springs with a tensile force of about 2 kg which are provided at both ends of the mold, is connected between the end plate and the end plate. Four taper pins are provided in the end plate, and 2 side pates are exactly connected to 2 end plates by fitting in a pin hole provided at a corresponding position in the side plate to compose a side wall of the mold (Refer to an upper drawing of FIG. 14).

(56) A lower drawing of FIG. 14 is a view showing a state at the time of opening the mold. The mold is lifted by picking up four corners at both end of the mold by a retrieving movable member having clicks, disposed in the conveying device, conveyed (the bottom plate is not conveyed), and transferred to a stripping position and placed on a base plate. If the clicks of the conveying device are opened in a direction in which the side plate moves away from the end plate, the stacked block within the mold is separated from the side plate. If the clicks are further opened to a taper portion of the taper pin, the end plates can also moves away from the stacked block by the compression spring.

(57) When the mold is moved upward in this state, the stacked block is left on the base plate and can be retrieved from the mold.

(58) It was verified that 30 sintered bodies can be simultaneously obtained by one mold by preparing a stacked block of the oriented filled-molded-body of the magnet alloy powder based on this mold, and sintering the stacked block in the same manner as in Example 1. In this time, the dimensional accuracy and the magnetic characteristics were also good as with Example 1.

Example 8

(59) An example of the production device 30 is shown in FIG. 15. In this drawing, a mold assembling device 31 is also placed in one chamber filled with an inert gas as with other devices. It is illustrated that in this example, mold parts to be assembled in the mold assembling device are supplied from the outside of the device through a supplying portion 36; however, it is favorable to use the conveying device within the production device since this does not need the closing and opening of the chamber.

(60) In this example, the sintering furnace 35 is disposed in another chamber, and these chambers are connected to each other with an airtight passage smaller in a diameter than these chambers. If an openable and closable door is provided in the airtight passage, the stacked block of the oriented filled-molded-body and the partitions can be conveyed from a left side to a right side of FIG. 15 through the door, and the sintering step can be performed in a vacuum by closing the door.

Example 9

(61) Example of Specific Structure of Production Device of Magnetic Anisotropic Rare Earth Sintered Magnet of the Present Invention

(62) FIG. 16 shows an example of a structure in a preferred example of the production device of the present invention.

(63) The production device is composed of a partition built-in device (mold assembling device), a powder feeding/filling device, a conveying device 1 and a conveying device 2, and operated in a nitrogen atmosphere within a globe box covering the whole device, all steps were performed in a nitrogen atmosphere, and a size of the glove box accommodating the partition built-in device, and the powder feeding/filling device was, for example, 2.5 m1 m1 m.

(64) The orienting device is placed at a position distance from the partition built-in device and the powder feeding/filling device in order to reduce the magnetic field leakage, but it is placed in a chamber communicated with a chamber which houses these devices, and in a nitrogen atmosphere as with these devices.

(65) The number of the molds is 4 in total (1 for in the partition built-in (mold assembling) device, 1 for in the powder feeding/filling device, 1 for in the orienting device, and 1 for a waiting position prior to the partition built-in device). In addition, in FIG. 16, a function of retrieving the filled molded-body of the alloy powder from the mold and a function of cleaning (gas blowing) the powder adhered to the mold are incorporated into the conveying device 2.

(66) In this device, many partitions loaded in a magazine are supplied from the partition supply port, and build in the mold one by one in the partition built-in device, and a raw material powder loaded in a powder container (not shown) is supplied from a connection portion at the upper portion of the powder feeding/filling device.

(67) The mold used has dimensions described in FIG. 13, and the number of the cavities is set to 30.

(68) Then, a block (referred to as a magazine) composed of 31 stainless steel partitions having a thickness of 0.5 mm overlaid is continuously supplied from partition supply port.

(69) In the partition built-in device, the partition is directly drawn from the magazine one by one and inserted into the mold formed of the side plates and the end plates to complete arrangement of 30 partitions within one minute.

(70) Next, a process of the present device illustrated in FIG. 16 will be described.

(71) In the partition built-in device, the partition is inserted in the mold side wall.

(72) The mold having the partitions attached to the side wall is conveyed to the powder feeding/filling device by the conveying device 1. The conveying device 1 is provided with an underlay in order to avoid falling of the partition during conveying. The bottom plate arranged at the underside of the mold side-walls is prepared in the powder feeding device.

(73) A spacer is disposed in the powder feeding/filling device, and to a bottom face of the spacer, the mold is joined to feed the alloy powder, and subsequently filling is performed.

(74) After the powder feeding/filling, the mold housing the filled molded-body is conveyed to a relay point of the orienting device by the conveying 1 and conveying 2 (a bottom plate of the mold is not conveyed). A lower plate is provided on a conveyor of the orienting device, and the mold housing the filled molded-body is placed thereon and conveyed to a center of a coil by the conveyor.

(75) An upper plate is provided above the orienting coil in order to prevent scattering of the alloy powder in orientation, and a pulsed magnetic field magnetic field of 4 tesla was applied with the upper plate pressed against the mold to align directions of particles of the alloy powder in the mold to improve magnetic characteristics.

(76) After completion of the orientation, the mold housing the stacked block is returned to the relay point by the conveyor, and carried out from the orienting device by the conveying device 2.

(77) The stacked block is stripped off the mold by a function incorporated into the conveying device 2.

(78) The stripped stacked block is conveyed out of the glove box through a sintering furnace connection port by a round trip mechanism and conveyed to the inside of the sintering furnace.

(79) The mold after stripping is returned to the waiting position prior to the partition built-in device by conveying 1 after cleaning fine powder adhering to the mold by air blowing by a function incorporated into conveying 2. In addition, when the partition is not built in the mold, the stripped mold is conveyed to the powder feeding device and reused.

(80) In the present device, four molds were used.

(81) A processing ability of the present device was 58 seconds per mold.

(82) Using the alloy powder for a NdFeB sintered magnet (composition of the alloy is described in the paragraph [0076]) obtained by the production method described in the paragraph [0051], 30 sintered bodies were prepared by following the same steps as in Example 1 by the production device of the present invention shown in FIG. 16. Weights, densities and dimensions of the 30 sintered bodies thus prepared are shown in Table 4 and the magnetic characteristics of the sintered bodies of the cavities No. 16 to 25 are shown in the following Table 5.

(83) TABLE-US-00004 TABLE 4 Weight and Dimension of Sintered Body Cavity Weight Density Longer side Shorter side Thickness No. (g) (g/cm3) (mm) (mm) (mm) 1 9.00 7.53 22.12 18.64 2.84 2 8.98 7.54 22.20 18.44 2.85 3 8.94 7.54 22.18 18.63 2.86 4 8.91 7.54 22.14 18.56 2.84 5 8.95 7.54 22.16 18.61 2.86 6 8.97 7.54 22.19 18.61 2.85 7 8.97 7.54 22.21 18.65 2.85 8 8.96 7.54 22.21 18.59 2.84 9 8.93 7.54 22.24 18.62 2.86 10 8.85 7.54 22.28 18.55 2.86 11 8.89 7.54 22.27 18.62 2.85 12 8.99 7.54 22.29 18.62 2.86 13 8.99 7.54 22.26 18.56 2.85 14 8.99 7.54 22.28 18.56 2.85 15 8.84 7.54 22.23 18.50 2.83 16 8.84 7.53 22.21 18.43 2.81 17 8.87 7.53 22.20 18.39 2.81 18 8.87 7.54 22.18 18.48 2.82 19 8.74 7.54 22.26 18.40 2.82 20 8.88 7.53 22.26 18.47 2.82 21 8.88 7.54 22.21 18.41 2.82 22 8.86 7.54 22.21 18.45 2.84 23 8.83 7.53 22.17 18.44 2.81 24 8.84 7.54 22.23 18.49 2.85 25 8.87 7.54 22.16 18.52 2.83 26 8.86 7.54 22.18 18.53 2.84 27 8.84 7.54 22.20 18.53 2.85 28 8.84 7.54 22.16 18.49 2.82 29 8.85 7.54 22.10 18.51 2.82 30 8.95 7.53 22.07 18.64 2.82 Range % 2.8 0.1 1.0 1.4 1.8

(84) TABLE-US-00005 TABLE 5 Magnetic Characteristics Maximum Cavity Coercive force Energy Product Remanent Flux Density No. [kOe] BHmax [MGOe] Br [kG] 16 12.1 50.1 14.3 17 12.3 48.5 14.2 18 12.2 48.6 14.1 19 12.4 48.3 14.0 20 12.2 49.2 14.1 21 12.2 49.6 14.1 22 12.1 50.0 14.3 23 12.2 49.3 14.1 24 12.0 51.0 14.4 25 12.4 49.8 14.0

(85) In the example, a powder having an average particle size of 4.1 m was prepared from an alloy whose weight ratio is 27.0% of Nd, 4.8% of Pr, 0.95% of Co, 0.99% of B, 0.25% of Al, 0.08% of Cu, and rest of Fe, and used for experiments. Values of the magnetic characteristics described in Table 5 can be determined to be high similar to those of an alloy powder according to a transverse-field molding method among NdFeB sintered magnets which are obtained by preparing an oriented molded-body from composition of the alloy and a particle size of the alloy powder used in the present example using a conventional press method and sintering/heat treating the oriented molded-body. It is impossible to prepare the thin-shaped sintered body of 3 mm in thick like the present example by the transverse-field pressing method. It was verified that according to the production method of the present invention, 30 thin-shaped NdFeB sintered magnets which have high characteristics equal to those of NdFeB sintered magnet prepared by the transverse-field pressing method, are simultaneously prepared, and that thin-shaped NdFeB sintered magnet has high magnetic characteristics and small variation. Thereby, it was verified that the production method of the present invention is useful as a technology of directly producing, without a cutting step and with high productivity, the thin-shaped NdFeB sintered magnet which has high magnetic characteristics equal to the transverse-field pressing method, and variation of the and dimensional variation are small.

DESCRIPTION OF REFERENCE SIGNS

(86) 10 Assembled mold 11 Side plate 12 End plate 13 Bottom plate 14 Partition 15 Magnetic pole 16 Lid plate 20 Alloy powder 21 Powder feeding spacer 22 Flat bottom push-in punch member (flat bottom punch) 23 Push-in punch member with grooves (punch with grooves) 25 Sintering pedestal 26 Oriented filled-molded-body 27 Stacked block 30 Production device of a rare earth sintered magnet 31 Mold assembling device (partition built-in device) 32 powder feeding/filling device 33 Orienting device 34 Retrieving part of an oriented filled-molded-body 35 Sintering furnace 36 Supplying part of mold parts or partitions 37 Supplying part of an alloy powder