Patent Application
20180294095
This invention relates to a method for producing rare earth magnet by coating a sintered magnet body with a rare earth compound-containing powder and heat treating for causing the rare earth element to be absorbed in the sintered magnet body, wherein the rare earth compound powder is efficiently coated and rare earth magnet having excellent magnetic properties is efficiently produced; and a rare earth compound application device suited for use in the rare earth magnet producing method.
Rare earth permanent magnets including Nd—Fe—B base magnets find an ever spreading application owing to their excellent magnetic properties. Methods known in the art for further improving the coercivity of these rare earth magnets include a method for producing a rare earth permanent magnet by coating the surface of a sintered magnet body with a rare earth compound powder, and heat treating the coated body for causing the rare earth element to be absorbed and diffused in the sintered magnet body (Patent Document 1: JP-A 2007-053351, Patent Document 2: WO 2006/043348). This method is successful in increasing coercivity while suppressing any decline of remanence.
In the prior art, for coating the rare earth compound, methods of applying a slurry of a rare earth compound-containing powder dispersed in water or organic solvent to a sintered magnet body by immersing the magnet body in the slurry, or spraying the slurry to the magnet body, to coat the magnet body with the slurry, and then drying are generally employed. In the case of immersion coating, it is common in view of productivity to adopt a net conveyor system wherein a plurality of sintered magnet bodies are continuously conveyed and coated by means of a net conveyor.
That is, the net conveyor system includes a net conveyor c as shown in
However, the net conveyor system tends to give rise to problems that in the coating steps including entry and immersion of sintered magnet bodies 1 in the slurry 2, and withdrawn of sintered magnet bodies 1 from the slurry 2, the sintered magnet bodies 1 move on the conveyor to come in contact with each other, causing coating failures on the contact surfaces, that the slurry tends to deposit or stick to the conveyor system to invite mechanical failures, and that the slurry 2 is carried over outside the coating tank t by the conveyor belt, indicating that noble rare earth compound is consumed in waste. There is also a problem that the system tends to occupy a large footprint because the steps from slurry coating to drying are carried out while the sintered magnet bodies are conveyed horizontally by the net conveyor.
PRIOR ART DOCUMENTS
Patent Document 1: JP-A 2007-053351
Patent Document 2: WO 2006/043348
An object of the invention, which is made under the above circumstances, is to provide a method for producing rare earth magnet comprising the steps of applying a slurry of a powder in a solvent to the surface of a sintered magnet body of R1—Fe—B composition (wherein R1 is one or more elements selected from Y, Sc and rare earth elements), the powder containing one or more compounds selected from an oxide, fluoride, oxyfluoride, hydroxide and hydride of R2 (wherein R2 is one or more elements selected from Y, Sc and rare earth elements), drying the slurry to coat the magnet body with the powder, and heat treating the coated magnet body, the method being capable of applying the slurry uniformly and efficiently to coat the powder uniformly and efficiently, while effectively suppressing the wasting of the rare earth compound, and reducing the area of the system for carrying out the coating steps; and a rare earth compound application device suited for use in the rare earth magnet producing method.
To attain the above object, the invention provides a method for producing rare earth magnet as defined below as [1] to [8].
providing a conveyor drum having a plurality of holding pockets circumferentially arranged in its periphery,
rotating the conveyor drum while a portion of the drum is immersed in the slurry,
placing a sintered magnet body in one holding pocket at a predetermined position of the drum prior to entry into the slurry, so that the sintered magnet body is held in the holding pocket, the sintered magnet body being conveyed along the rotational track of the conveyor drum, immersed in the slurry, then withdrawn from the slurry, and conveyed further whereby the slurry is dried and the sintered magnet body is coated with the powder,
recovering the sintered magnet body from the pocket at a predetermined position after the drying treatment and prior to re-entry into the slurry, and
subjecting the sintered magnet body to the subsequent heat treatment.
To attain the above object, the invention also provides a slurry application device as defined below as [9] to [14].
the device comprising
an applicator tank for containing the slurry,
a conveyor drum which rotates while a portion of the drum is immersed in the slurry,
a plurality of holding pockets circumferentially arranged in the periphery of the conveyor drum, and
drying means for blowing air into the holding pocket for drying the sintered magnet body accommodated in the pocket,
wherein a sintered magnet body is supplied into one holding pocket at a predetermined position of the drum prior to entry into the slurry, the sintered magnet body held in the pocket is conveyed along the rotational track of the conveyor drum, immersed in the slurry, then withdrawn from the slurry, and dried by the drying means, and the sintered magnet body is recovered from the pocket at a predetermined position after the drying treatment and prior to re-entry into the slurry.
That is, according to the producing method and application device of the invention, as a conveyor drum rotates while being partly immersed in a slurry, sintered magnet bodies are conveyed by the conveyor drum while being accommodated in holding pockets arranged in the periphery of the conveyor drum, and in the course of conveyance, the magnet bodies are passed through the slurry, coated therewith, and dried whereby the sintered magnet bodies are surface coated with the powder.
As mentioned above, sintered magnet bodies are conveyed by the conveyor drum while being accommodated in holding pockets of the drum, coated with the slurry and dried. Even when the coating step is carried out continuously on a plurality of sintered magnet bodies, it is avoided that sintered magnet bodies come in contact with each other so that coating failures occur at contact areas. The slurry is uniformly and properly applied, and sintered magnet bodies are uniformly and efficiently coated with the powder. Since the conveyor drum rotates while a portion thereof is immersed in the slurry in the coating tank, the slurry carried over by the conveyor drum is returned to the coating tank as a result of rotation of the drum, so that little of the slurry is carried out of the coating tank. As compared with the net conveyor system, the wasting of rare earth compound is effectively minimized. Furthermore, since the conveyance track of sintered magnet bodies by the conveyor drum is a circular track delineated above the coating tank by rotation of the conveyor drum, the system is made compact to substantially reduce its footprint, as compared with the net conveyor system entailing a horizontal conveyance track.
In addition, according to the producing method and application device of the invention, the sintered magnet bodies are uniformly coated over the entire surface with the rare earth compound powder and the coating step is carried out quite efficiently. Rare earth magnet having improved magnetic properties including a fully increased coercivity can be efficiently produced.
As described above, the method for producing rare earth magnet according to the invention includes the steps of applying a slurry of a powder in a solvent to sintered magnet bodies of R1—Fe—B composition (wherein R1 is one or more elements selected from Y, Sc and rare earth elements), the powder containing one or more compounds selected from an oxide, fluoride, oxyfluoride, hydroxide and hydride of R2 (wherein R2 is one or more elements selected from Y, Sc and rare earth elements), drying the slurry to coat the magnet bodies with the powder, and heat treating the coated magnet bodies for causing R2 to be absorbed in the magnet bodies.
The R1—Fe—B sintered magnet body used herein may be one obtained by any well-known method. For example, a sintered magnet body may be obtained by coarsely milling a mother alloy containing R1, Fe and B, finely pulverizing, compacting and sintering according to the standard method. It is noted that R1 is one or more elements selected from Y, Sc and rare earth elements, specifically Y, Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu.
According to the invention, the R1—Fe—B sintered magnet body is shaped to a predetermined shape as by grinding, if necessary, coated on its surface with a powder containing one or more compounds selected from an oxide, fluoride, oxyfluoride, hydroxide and hydride of R2, and heat treated for causing absorption and diffusion (grain boundary diffusion) of R2 into the sintered magnet body, thereby obtaining the desired rare earth magnet.
It is noted that R2 is one or more elements selected from Y, Sc and rare earth elements, specifically Y, Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu, like R1 mentioned above. It is preferred, though not limited, that R2 contain at least 10 at %, more preferably at least 20 at %, and even more preferably at least 40 at % in total of Dy and/or Tb. It is more preferred in view of the object of the invention that R2 contain at least 10 at % of Dy and/or Tb and the total concentration of Nd and Pr in R2 be lower than the total concentration of Nd and Pr in
According to the invention, the powder is coated by dispersing the powder in a solvent to prepare a slurry, applying the slurry to the surface of the sintered magnet body, and drying. While the particle size of the powder is not particularly limited, a particle size commonly employed as a rare earth compound powder used for absorptive diffusion (grain boundary diffusion) may be selected, and specifically, an average particle size of preferably up to 100 μm, more preferably up to 10 μm. The lower limit of particle size is preferably at least 1 nm, though not limited. The average particle size may be determined as a weight average value D50 (i.e., particle size corresponding to a cumulative weight of 50% or median diameter) using a particle size distribution measuring system based on the laser diffraction method or the like. The solvent in which the powder is dispersed may be water or an organic solvent. Examples of the organic solvent include ethanol, acetone, methanol, and isopropyl alcohol, but are not limited thereto. Inter alia, ethanol is preferably used.
Although the amount of the powder dispersed in the slurry is not particularly limited, a slurry having the powder dispersed in a dispersing amount of preferably at least 1%, more preferably at least 10%, even more preferably at least 20% as mass fraction is used in order to coat the powder effectively and efficiently. Since too much dispersing amounts give rise to inconvenience such as failure to form a uniform dispersion, the upper limit is preferably up to 70%, more preferably up to 60%, even more preferably up to 50% as mass fraction.
According to the invention, as the method of applying the slurry to the sintered magnet body and drying to coat the surface of the magnet body with the powder, a method of using a conveyor drum, conveying the sintered magnet body thereby, passing the magnet body through the slurry, thereby immersing the magnet body in the slurry and coating the magnet body with the slurry, and drying while further conveying the magnet body by the conveyor drum is employed. Specifically, coating of the powder may be carried out using the application device shown in
The conveyor drum 4 is provided with a plurality of (twelve in the figure) holding pockets 42 which are circumferentially arranged in a row and at an equal spacing. As the drum 4 rotates with the sintered magnet bodies 1 accommodated and held in the holding pockets 42, the sintered magnet bodies 1 are conveyed along a circular track. The holding pockets 41 are pockets of circular bore shape axially extending throughout the drum and are open at both side surfaces of the drum.
The size of the holding pocket 42 may be set as appropriate depending on the size and shape of the sintered magnet body 1 to be accommodated therein. Although the size is not particularly limited, the diameter of the holding pocket 42 is preferably equal to the maximum diameter in cross section of the sintered magnet body 1 (maximum diagonal in case of rectangular shape) plus about 1 to 2 mm. This setting ensures that the sintered magnet body 1 is smoothly inserted and removed and the sintered magnet body 1 accommodated in the holding pocket 42 is conveyed in a steady manner without substantial movement within the pocket 42. The depth of the holding pocket 42 may be set as appropriate depending on the size of the sintered magnet body 1 and is generally at least 50%, preferably about 70 to 90% of the length of the sintered magnet body 1. Furthermore, the spacing between holding pockets 42 is preferably at least 10%, more preferably at least 30% of the diameter of the pocket. Since too large a spacing can detract from productivity, the spacing is preferably up to 100% of the pocket diameter.
As the conveyor drum 4 rotates, each holding pocket 42 enters the slurry 2 whereupon the slurry 2 flows into the holding pocket 42 from the openings at both ends, whereby the sintered magnet body 1 accommodated in the holding pocket 42 is immersed in the slurry. At least the main body of the conveyor drum 4 provided with the holding pockets 42 is preferably composed of a frame (not shown) and a mesh metal or punching metal in order that the slurry 2 flow into the pocket 42 and the sintered magnet body 1 accommodated in the pocket 42 be immersed in the slurry.
When the main body of the conveyor drum 4 is formed using a mesh metal or punching metal, the sintered magnet body 1 is effectively immersed in the slurry 2, and the amount of the slurry carried over by rotation of the conveyor drum 4 is reduced. This enables stable slurry coating. The efficiency of drying is increased during the drying step to be described later. The opening of the mesh metal or punching metal is preferably at least 1 mm so that the slurry 2 and drying air effectively flow therethrough. The upper limit is arbitrary as long as the sintered magnet body 1 is held in a stable manner.
As the conveyor drum 4 having the sintered magnet bodies 1 accommodated in the holding pockets 42 rotates clockwise as viewed in the figure, the sintered magnet bodies 1 are conveyed. Although the rotational speed of the conveyor drum 4 is not particularly limited, the rotational speed is set depending on the diameter of the drum, preferably so as to give a circumferential speed of 200 to 2,000 mm/min, more preferably 400 to 1,200 mm/min at the position where the holding pockets 42 are formed. If the circumferential speed, i.e., conveying speed is less than 200 mm/min, it is difficult to attain an industrially acceptable throughput. If the circumferential speed exceeds 2,000 mm/min, there may be inconvenience that short drying often occurs during treatment in a drying zone 3 to be described later, the size of a blower or the number of blowers must be increased in order to ensure drying, and the drying zone 3 must be scaled up. It is noted that although the rotation of the conveyor drum 4 may be continuous or intermittent, intermittent rotation is preferable when the efficiency of replacement operation of sintered magnet bodies 1 to be described later is taken into account.
As shown in
Now, in a first half portion of the drying zone 3, for example, in a range of the conveyor drum 4 corresponding to 9 to 10:30 o'clock on the clock dial, a residual droplet removing means (not shown) of injecting air may be set as a residual droplet removal section. Then the residual droplet removal section acts to inject air to the sintered magnet body 1 to remove any residual slurry on the surface of the sintered magnet body 1 before drying is carried out by blowing hot air as mentioned above. The residual droplet removal section (residual droplet removing means) is not necessarily essential. With the residual droplet removal section omitted, removal of residual droplets may be carries out at the same time as drying by the drying means. If drying is carried out with residual droplets remaining on the surface of sintered magnet body, there is a likelihood of uneven coating of the powder. It is preferred in this sense that residual droplets are fully removed by the residual droplet removal section (residual droplet removing means) before drying is carried out. In some cases, in order to accelerate drying, the air blow injected by the residual droplet removing means may also be hot air blow like that of the drying means.
The drying means and residual droplet removing means may be constructed by arranging a plurality of air injection nozzles (not shown) outside the conveyor drum 4 and along the circumference of the drum. Air or hot air is injected from the air injection nozzles to carry out the drying or residual droplet removal. Herein, the shape, size and angle (injection angle) of each nozzle may be set as appropriate depending on the size and shape of sintered magnet bodies 1, the material (mesh metal or punching metal) of the conveyor drum 4, and the like, and adjusted such that air or hot air may smoothly flow through the holding pockets 42 to effectively carry out drying and residual droplet removal.
It is noted that the flow volume of air or hot air injected from the nozzles in the drying means and residual droplet removing means may be adjusted as appropriate depending on the conveying speed of sintered magnet bodies 1, the length of drying zone 3 (the length of residual droplet removal section), the size and shape of sintered magnet bodies 1, the concentration and coating weight of the slurry 2 and the like. Although the flow volume is not particularly limited, it is typically adjusted in a range of 300 to 2,500 L/min, more preferably 500 to 1,800 L/min.
Though not shown, it is preferred that the drying zone 3 including the residual droplet removal section be provided with dust collecting means for recovering the rare earth compound powder removed from the surface of sintered magnet bodies 1 during the residual droplet removal and drying, by enclosing the dry zone 3 in a suitable chamber and installing a dust collector in the chamber for collecting dust. This enables coating of rare earth compound powder without wasting the rare earth compound containing noble rare earth element. In addition, the provision of the dust collecting means shortens the drying time, prevents hot air blow from diverting to the slurry coating section consisting of the coating tank and slurry agitating means as much as possible, and effectively prevents the slurry solvent from evaporating by the hot air blow. While the dust collector (not shown) may be of wet or dry type, it is preferred to select a dust collector having a greater suction capability than the flow volume of air injected from the nozzles in the residual droplet removing means and drying means.
As shown in
With respect to the replacement of sintered magnet bodies 1, in one procedure, the coated sintered magnet body is taken out of the holding pocket 42 and thereafter the uncoated sintered magnet body is inserted into the holding pocket 42. In another procedure, the uncoated sintered magnet body is inserted into the holding pocket 42 from one side surface of the conveyor drum 4, and the coated sintered magnet body accommodated in the holding pocket 42 is displaced by this uncoated sintered magnet body to the other side surface of the conveyor drum 4 and recovered, whereby supply and recovery of sintered magnet bodies 1 are performed at the same time.
The supply and recovery of sintered magnet bodies 1 may be performed manually or automatically by providing a suitable supply mechanism and recovery mechanism. In either case, a support member (not shown) such as a rail is preferably provided so that the sintered magnet body 1 in a stable attitude may be guided to the holding pocket 42 or the sintered magnet body 1 in a stable attitude be moved out of the holding pocket 42.
Though not shown in
When the sintered magnet body 1 is coated on its surface with a powder (rare earth compound powder) containing one or more compounds selected from an oxide, fluoride, oxyfluoride, hydroxide and hydride of R2 (wherein R2 is one or more elements selected from Y, Sc and rare earth elements) using the application device defined above, first the slurry 2 having the powder dispersed in a solvent is contained in the coating tank (not shown), and the slurry 2 is appropriately stirred by the agitating means (not shown) to maintain the powder in the slurry 2 to be uniformly dispersed in the solvent. In this state, as shown in
As described above, the sintered magnet body 1 which is accommodated in the holding pocket 42 in the load/unload zone 5 is conveyed forward by rotation of the conveyor drum 4 while it is held in the pocket 42, introduced into the slurry 2, where the magnet body is immersed in the slurry 2, passed through the slurry 2 over a predetermined time, and withdrawn from the slurry 2. In this course, the sintered magnet bodies 1 are successively coated with the slurry 2.
As the conveyor drum 4 rotates, the sintered magnet body 1 having the slurry 2 applied thereto is conveyed further and introduced into the drying zone 3 where drying operation is performed to remove the solvent of the slurry 2, the rare earth compound powder is tightly deposited on the surface of the sintered magnet body 10, to form a coating of rare earth compound powder on the surface of the sintered magnet body 10. At this point, if the drying zone 3 is provided with the residual droplet removal section, residual droplets are removed from the sintered magnet body 1 as withdrawn from the slurry 2, before drying treatment is performed on the sintered magnet body.
The sintered magnet body 1 which has been coated with the rare earth compound powder as mentioned above is conveyed further to the load/unload zone 5 again. In the load/unload zone 5, the sintered magnet body 1 coated with the rare earth compound powder is taken out of the holding pocket 42 and recovered, and the holding pocket 42 is charged with a new sintered magnet body 1 in the load/unload zone 5. Upon recovery and supply of sintered magnet bodies 1, a newly supplied uncoated magnet body is inserted into the holding pocket 42 from one side surface of the conveyor drum 4, and the coated magnet body which has been accommodated in the holding pocket 42 is displaced by this uncoated magnet body and recovered, thereby simultaneously performing recovery and supply of sintered magnet bodies 1. By repeating the series of operations continuously, a multiplicity of sintered magnet bodies are successively coated with the rare earth compound.
At this point, the step of coating the rare earth compound using the application device is repeated plural times on one sintered magnet body to coat the magnet body with the rare earth compound powder in an overlay manner, whereby a thicker coating is obtainable and the uniformity of a coating is improved. For repetition of the coating operation, the magnet body may be fed through one device plural passes to repeat the coating operation. The repeat operation may include feeding the sintered magnet body 1 to the conveyor drum 4, rotating the drum plural turns rather than one turn, and thereafter recovering the magnet body. In the case of double coating, for example, the sintered magnet body 1 is fed to the conveyor drum 4, the drum is rotated two turns to repeat the operation from slurry immersion to drying two times, and thereafter, the magnet body is recovered.
When the conveyor drum 4 having an even number of holding pockets 42 as shown in
In another embodiment, a plurality of conveyor drums 4 are juxtaposed with their side surfaces closely opposed. The powder coating process is carried out on each conveyor drum, the sintered magnet body is inserted into the holding pocket in one drum, and at the same time, the sintered magnet body which has been accommodated in the pocket is displaced into the pocket in another drum and accommodated therein, whereby the coating process from slurry immersion to drying is repeated plural times.
In the case of double coating, for example, as shown in
In a further embodiment, the juxtaposition of plural conveyor drums as shown in
In this way, the powder coating process from slurry application to drying is repeated plural times to achieve overlay coating of thin layers until a coating of desired thickness is reached. The overlay coating of thin layers is effective for reducing the drying time whereby the time-basis efficiency is improved.
In the inventive method for coating a sintered magnet body with a rare earth compound powder using the application device as mentioned above, as the sintered magnet body 1 is conveyed by the conveyor drum 4 while it is accommodated in the holding pocket 42 in the drum 4, it is subjected to slurry coating and drying. Even when coating step is continuously performed on a plurality of sintered magnet bodies 1, it is avoided that sintered magnet bodies come in contact with each other so that coating defects form at the contact areas. The slurry 2 can be uniformly and properly applied, and the powder be uniformly and efficiently coated. Since the conveyor drum 1 rotates while a portion thereof is immersed in the slurry 2 in the coating tank, the slurry 2 carried over by the conveyor drum 1 is returned to the coating tank due to rotation of the drum 1, and little of the slurry is carried out of the coating tank. The wasting of rare earth compound is suppressed quite effectively, as compared with the net conveyor system. Further, since the conveyance track of the sintered magnet body 1 by the conveyor drum 4 is a circular track about the horizontal axis extending above the coating tank, the device is made compact and the footprint of the device is substantially reduced, as compared with the net conveyor system entailing a horizontal conveyance track.
Accordingly, the sintered magnet body is coated on its surface with the rare earth compound powder uniformly and efficiently. The sintered magnet body uniformly coated with the powder is heat treated to cause absorptive diffusion of the rare earth element R2 whereby a rare earth magnet having a fully increased coercivity and improved magnetic properties is efficiently produced.
Notably, the heat treatment to cause absorptive diffusion of the rare earth element R2 may be performed by a well-known method. After the heat treatment, any well-known post-treatments including aging treatment under suitable conditions and machining to a practical shape may be performed, if necessary.
Embodiments of the invention are described by referring to Example although the invention is not limited thereto.
A thin plate of alloy was prepared by a so-called strip casting technique, specifically by weighing amounts of Nd, Al, Fe and Cu metals having a purity of at least 99 wt %, Si having a purity of 99.99 wt %, and ferroboron, high-frequency heating in argon atmosphere for melting, and casting the alloy melt on a copper single roll in argon atmosphere. The resulting alloy consisted of 14.5 at % Nd, 0.2 at % Cu, 6.2 at % B, 1.0 at % Al, 1.0 at % Si, and the balance of Fe. The alloy was exposed to 0.11 MPa of hydrogen at room temperature for hydriding, and then heated at 500° C. for partial dehydriding while evacuating to vacuum. It is cooled and sieved, obtaining a coarse powder having a size of up to 50 mesh.
On a jet mill using high-pressure nitrogen gas, the coarse powder was finely pulverized to a weight cumulative median particle size of 5 μm. The resulting fine powder was compacted in a nitrogen atmosphere under a pressure of about 1 ton/cm2 while being oriented in a magnetic field of 15 kOe. The compact was then placed in a sintering furnace in argon atmosphere where it was sintered at 1,060° C. for 2 hours, obtaining a magnet block. Using a diamond cutter, the magnet block was machined on all the surfaces, cleaned with alkaline solution, pure water, nitric acid and pure water in sequence, and dried, obtaining a block-shaped magnet body of 50 mm×20 mm×5 mm (in magnetic anisotropy direction).
Next, dysprosium fluoride powder was mixed with water at a mass fraction of 40% and thoroughly dispersed therein to form a slurry. Using the application device shown in
Coating tank volume: 10 L
Circulating flow rate of slurry: 60 L/min
Conveying speed: 700 mm/min
Flow volume of air for droplet removal and drying: 1,000 L/min
Temperature of hot air for drying: 80° C.
Coating number: single coating
Number of block-shaped magnet bodies: 100
The slurry spilling from the coating tank during treatment of 100 magnet bodies was collected, dried and weighed, which value is reported as the carry-over of slurry from the coating tank. Also the number of block-shaped magnet bodies which were brought in surface contact after coating was counted. The results are shown in Table 1.
The magnet bodies having a thin coating of dysprosium fluoride powder formed on their surface were heat treated at 900° C. for 5 hours in Ar atmosphere for absorptive treatment, age treated at 500° C. for 1 hour, and quenched, obtaining rare earth magnet samples. All magnet samples had satisfactory magnetic properties.
As in Example, there was furnished a block-shaped magnet body of 50 mm×20 mm×5 mm (in magnetic anisotropy direction). Also, dysprosium fluoride powder having an average particle size of 0.2 μm was mixed with water at a mass fraction of 40% and thoroughly dispersed therein to form a slurry, which was contained in a coating tank t of the prior art coating system shown in
Type: conveyor belt
Form: triangular spiral
Spiral pitch: 8.0 mm
Rod pitch: 10.2 mm
Rod gauge: 1.5 mm
Spiral gauge: 1.2 mm
As in Example, the carry-over of the slurry from the coating tank was measured. Also the number of block-shaped magnet bodies which exited the drying zone 3 in mutual surface contact state after coating was counted. The results are shown in Table 1. It is noted that the slurry carry-over is reported as an index provided that the carry-over of Example 1 is 1.
As in Example, the magnet bodies having a thin coating of dysprosium fluoride powder formed on their surface were heat treated at 900° C. for 5 hours in Ar atmosphere for absorptive treatment, age treated at 500° C. for 1 hour, and quenched, obtaining rare earth magnet samples.
As is evident from Table 1, a comparison of slurry carry-over from the coating tank reveals that the carry-over of the application device comprising a rotating drum is about 89% smaller than that of the net conveyor system of serial movement. As is also evident from Table 1, the number of block-shaped magnet bodies which exited in mutual surface contact after coating is nil in the rotary drum pocket system of the invention (Example), demonstrating effective coating of powder.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-092038 | Apr 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/062202 | 4/18/2016 | WO | 00 |
