JP3905097B2 - Manufacturing method of rare earth sintered magnet - Google Patents

Description

  The present invention relates to a method for producing a rare earth sintered magnet.

A rare earth sintered magnet obtained by press-molding fine powder for a rare earth sintered magnet in a magnetic field and sintering the obtained compact is generally ground using a diamond or CBN grindstone. The reason why grinding processing with low processing capability is performed is that the sintered rare earth magnet is a hard and brittle hard-to-work material and it is difficult to apply processing other than grinding.
One of the methods for improving the processing capability is so-called green processing in which the green body before sintering is processed into a desired size and shape, followed by sintering, but the green body for rare earth sintered magnets contains oxygen in the atmosphere. Reacts to cause deterioration of magnetic properties. Similarly, chips generated during processing react with oxygen, and in the worst case, heat generation and ignition occur.
As a countermeasure, as disclosed in Patent Document 1, a method of performing processing in an inert gas atmosphere such as nitrogen gas is disclosed.
JP-A-53-899

However, the above-described method for performing processing while preventing the molded body from being oxidized in an inert gas atmosphere such as nitrogen gas has the following problems.
First, in order to maintain an inert gas atmosphere, it is necessary to store all of the molded object to be processed, the holding mechanism of the molded object, and the processing tool in a sealed container, and the apparatus becomes larger and complicated. Furthermore, it is mentioned that a gas replacement operation is required to maintain an inert gas atmosphere each time the molded body is carried into the sealed container and taken out after processing.
In addition, since it is a dry process that does not use a machining fluid, clogging of the tool due to chips occurs and the machining capability is reduced. Moreover, since it is difficult to discharge chips, it is necessary to frequently interrupt the processing and perform the above-described gas replacement operation.
Therefore, the problem to be solved by the present invention is to provide a method for producing a rare earth sintered magnet capable of improving the processing capability while preventing the deterioration of magnetic properties due to the reaction between the compact and oxygen.

The method for producing a rare earth sintered magnet according to the present invention comprises: R-Fe-B-based (R is one or more of Y-containing rare earth elements) sintered magnet powder and kinematic viscosity at room temperature. Is formed of a mineral oil or a synthetic oil having a fractional distillation point of 400 ° C. or less, and the mixture is molded, and the resulting molded body is immersed in the oil and processed. The processed compact is taken out from the oil, deoiled and sintered .

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the rare earth sintered magnet which can improve a processing capability, preventing the fall of the magnetic characteristic by reaction with a molded object and oxygen.

  The superior point of the production method of the present invention is that the apparatus is remarkably different from the apparatus that performs the processing in the inert gas atmosphere described above while preventing the deterioration of the magnetic properties due to the reaction between the molded body and oxygen. Simplification is possible, and a gas replacement operation in an inert gas atmosphere that is performed each time the molded body is carried in and carried out after processing is unnecessary.

An embodiment of the present invention will be described with reference to FIG.

(Example)
First, a method for producing a molded body in this example is as follows. Nd having a composition of Nd 27.5% by weight, Pr 2.5%, Dy 1.0%, B 1.0%, Nb 0.6%, Co 4.0%, Al 0.2%, Ga 0.1% and the balance Fe. -Fe-B based coarse magnet powder is finely pulverized in a nitrogen stream, and a mineral oil having a fractional distillation point of 200 to 300 ° C. and a kinematic viscosity at room temperature of 2.0 cSt at the fine powder discharge port of the fine pulverizer A container filled with [Product name: MC Oil P02, manufactured by Idemitsu Kosan Co., Ltd.] was installed, and the fine powder discharged in a nitrogen gas atmosphere was directly collected in the above mineral oil to obtain a raw material mixture. The fine powder weight ratio of this raw material mixture was 70%. The average particle size of this fine powder was 4.0 μm.
A magnetic field of 8 kOe was applied and held in the mold cavity, and the raw material mixture was pressurized and filled into the cavity at a pressure of 10 kgf / cm ² , and then compacted at a molding pressure of 1 ton / cm ² to obtain a molded body 3.

The processing tank 1 houses a moving table 6 on which a molded body 3 is mounted, a processing blade 4 and one end of a main shaft 5. The moving table 6 is held by a slide shaft 7 fixed to the processing tank 1 and has a structure capable of linear movement in the rotational direction of the processing blade 4 by a drive shaft 8.
A piping 11 is provided at the bottom of the processing tank 1 to guide the machining fluid 2 containing chips to the chip collection device 12 by a circulation pump 10. A spacer 9 for adjusting the positional relationship between the machining blade 4 and the molded body 3 is provided between the molded body 3 and the moving table 6.
The processing tank 1 was filled with the mineral oil [made by Idemitsu Kosan Co., Ltd., trade name: MC oil P02] as the processing liquid 2 until the processing blades 4 were all immersed in the processing liquid 2.
In the present embodiment, since cutting was performed, a metal saw having a diameter of 200 mm and a blade thickness of 0.8 mm with a cut at the outer peripheral portion was adopted as the processing blade 4. Since the rotation speed of the main shaft 5 is adjusted in the range of 200 to 500 rpm, the peripheral speed of the machining blade is 125 to 315 m / min.

The machining operation by the above configuration is as follows. Prior to processing, the moving table 6 was pulled up above the surface of the processing liquid 2 by the drive shaft 8. The molded body 3 was fixed to the spacer 9 at this position and assembled to the moving table 6. After the processing blade 4 reaches a predetermined rotation, the movable table 6 is pushed down by the drive shaft 8 so that the molded body 3 comes into contact with the processing blade 4 and is cut. The spacer 9 is provided with a relief groove so that the machining blade 4 and the spacer 9 are not in contact with each other. The chips generated by cutting settle at the bottom of the processing tank 1 but are transferred to the chip collection device 12 together with the processing liquid 2 by the circulation pump 10 through the pipe 11. The machining fluid 2 from which the chips have been removed is returned to the machining tank 1 again. In this embodiment, in order to prevent chips from accumulating on the molded body 3, the molded body 3 is considered to move in the vertical direction.
When the cutting was completed, the moving table 6 was again pulled up on the liquid surface of the machining liquid 2 and the molded body 3 after the machining was removed.

  Usually, the same cutting process of the sintered body is also performed using a diamond grindstone. In this case, the processing speed is about 2 to 5 mm / min. It was possible.

Mineral oil or synthetic oil remains in the molded body after processing, so if normal sintering is performed as it is, the remaining oil will evaporate during heating and contaminate the inside of the sintering furnace, and partly Decomposes and remains in the sintered body. For this reason, the residual carbon amount of the sintered body increases, the sintered body density decreases, and the residual magnetic flux density and the maximum energy product decrease. In order to prevent this, it is necessary to sinter the molded body after processing after deoiling.
The molded body after processing was subjected to deoiling treatment at 200 ° C. for 2 hours under a pressure of 5 × 10 ⁻² Torr, and then heated up to 1070 ° C. at the same pressure at a heating rate of 15 ° C./min. Sintered by holding for 3 hours. The sintered body was heat-treated at 900 ° C. × 1 hour and 620 ° C. × 1 hour once in an Ar atmosphere.

  When the magnetic properties, oxygen content, carbon content and density of this sample were measured, the magnetic properties were a residual magnetic flux density of 13.1 kG, a coercive force of 13.9 kOe, a maximum energy product of 41.0 MGOe, an oxygen content of 1800 ppm, and a carbon content of 0.1. It was 05% by weight and the density was 7.57 g / cc, and no deterioration in magnetic properties was observed.

(Reference example)
Nd-Fe-B system having a composition of Nd 27.5%, Pr 2.5%, Dy 1.0%, B 1.0%, Nb 1.0%, Co 2.0%, Al 0.2%, balance Fe in weight percentage The coarse powder for a sintered magnet was finely pulverized in a nitrogen stream to obtain a fine powder having an average particle size of 3.9 μm.
This fine powder was put into a mold cavity, and pressure-molded under conditions of an orientation magnetic field strength of 10 kOe and a molding pressure of 1.0 ton / cm ² to obtain a molded body. This molded body was immersed in mineral oil [trade name: MC oil P02, manufactured by Idemitsu Kosan Co., Ltd.] and then processed under the same apparatus and conditions as in the examples .
The molded body after processing is subjected to a deoiling treatment in which the temperature is increased from room temperature to 500 ° C. at a temperature increase rate of 5 ° C. under a pressure of 5 × 10 ⁻² Torr. The temperature was increased at a rate of temperature increase / minute, held for 2 hours, and sintered. The sintered body was heat-treated at 900 ° C. × 1 hour and 600 ° C. × 1 hour once in an Ar atmosphere.

When the magnetic properties, oxygen content, carbon content and density of this sample were measured, the magnetic properties were a residual magnetic flux density of 12.2 kG, a coercive force of 14.5 kOe, a maximum energy product of 34.7 MGOe, an oxygen content of 4750 ppm, and a carbon content of 0.1. It is 06% by weight and the density is 7.55 g / cc, indicating that the magnetic properties are lower and the oxygen content is higher than those of the examples.

The types of mineral oil and synthetic oil used in the present invention are not specified. However, when the kinematic viscosity at room temperature exceeds 10 cSt, the binding force between the fine powders increases due to the increase in viscosity, and during wet forming in a magnetic field. This will adversely affect the fine powder orientation. For this reason, it is preferable that the kinematic viscosity at normal temperature of mineral oil and synthetic oil is 10 cSt or less. Further, if the fractional distillation point of mineral oil or synthetic oil exceeds 400 ° C., deoiling during sintering becomes difficult, and the amount of residual carbon in the sintered body increases, resulting in deterioration of magnetic properties. Therefore, the fractional distillation point of mineral oil and synthetic oil must be 400 ° C. or lower .

  The deoiling treatment is performed by holding the compact in a temperature range of 100 to 500 ° C. for 30 minutes or more under a reduced pressure of 0.1 Torr or less. The holding temperature need not be one point as long as it is in the range of 100 to 500 ° C., and may be two or more points. Deoiling can also be performed by setting the rate of temperature increase from room temperature to 500 ° C. under a reduced pressure of 0.1 Torr or less to 10 ° C./min or less.

The sintered body is subjected to heat treatment under conditions corresponding to its composition to obtain a product, but if necessary, additional processing may be performed after the heat treatment to obtain a product with high dimensional accuracy. Further, additional processing may be performed after heat treatment of the sintered body.

1 is an overall view of a molded body processing apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processing layer 2 Processing liquid 3 Molded body 4 Processing blade 5 Spindle 6 Moving table 7 Slide shaft 8 Drive shaft 9 Spacer 10 Circulation pump 11 Piping 12 Chip collection device

Claims (1)

R-Fe-B system (R is one or more of Y-containing rare earth elements) sintered magnet powder , kinematic viscosity at room temperature is 10 cSt or less, and fractional point is 400 ° C or less After forming a mixture comprising a certain mineral oil or synthetic oil , molding the mixture, and processing the obtained molded body by immersing it in the oil, taking out the processed molded body from the oil A method for producing a rare earth sintered magnet, comprising deoiling and sintering.

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