Producing method of R-T-B-based sintered magnet

1. A producing method of an R-T-B-based sintered magnet, comprising:

a coarsely pulverizing step of obtaining coarsely pulverized powder of raw-material alloy for R-T-B-based sintered magnets;

a mixing step of adding a pulverization aid to the coarsely pulverized powder and mixing the coarsely pulverized powder and the pulverization aid, wherein the pulverization aid is a hydrocarbon-based lubricant dissolved in oil in a range of 0.01 to 0.20 wt % with respect to the coarsely pulverized powder or the pulverization aid is a fatty acid or derivative of fatty acid in a range of 0.01 to 0.10 wt % with respect to the coarsely pulverized powder;

a fine pulverizing step of supplying, to a jet mill device, the coarsely pulverized powder in which the pulverization aid is mixed in the mixing step, of finely pulverizing the coarsely pulverized powder in inert gas, of recovering the fine pulverized fine pulverized powder in a solvent composed of one kind of mineral oil, synthetic oil and vegetable oil, and of obtaining slurry fine pulverized powder;

a forming step of wet forming the fine pulverized powder in a magnetic field to obtain a compact for R-T-B-based sintered magnets; and

a sintering step of removing the solvent in the compact for the R-T-B-based sintered magnets, and sintering the same to obtain an R-T-B-based sintered magnet, wherein

the coarsely pulverizing step includes:

a hydrogen storing step of storing hydrogen into the raw-material alloy for the R-T-B-based sintered magnet accommodated in a processing container;

a heating step of heating the coarsely pulverized powder which is pulverized by storing the hydrogen and dehydrogenating the coarsely pulverized powder;

a cooling step of cooling the heated coarsely pulverized powder; and

a recovery step of recovering the cooled coarsely pulverized powder into a recovery container,

the recovery step is carried out in a recovery chamber which is adjacently connected to a processing chamber where at least the cooling step is carried out,

the recovery container includes

inert gas introducing device 42 which introduces inert gas,

evacuating device 43 which discharges gas in the recovery chamber,

a carry-in port through which the processing container is carried into the recovery chamber from the processing chamber,

a discharge port disposed in a lower portion of the recovery chamber, and

the recovery container connected to the discharge port,

the recovery step includes

a carrying-in step of carrying the processing container from the processing chamber into the recovery chamber through the carry-in port after inert gas was introduced into the recovery chamber by the inert gas introducing device 42 ,

a discharging step of discharging the coarsely pulverized powder in the processing container into the recovery chamber after a pressure in the recovery chamber was reduced by the evacuating device 43 ,

a gas introducing step of introducing inert gas into the recovery chamber by the inert gas introducing device 42 after the coarsely pulverized powder was discharged into the recovery chamber, and

an alloy accommodating step of recovering the coarsely pulverized powder into the recovery container through the discharge port after a pressure in the recovery chamber is brought into a pressure by inert gas, and

addition of the pulverization aid in the mixing step is carried out in the alloy accommodating step in the recovery step after the cooling step.

2. The producing method of the R-T-B-based sintered magnet according to claim 1 , wherein the coarsely pulverized powder and the pulverization aid are mixed in the mixing step by rotating the recovery container.

3. The producing method of the R-T-B-based sintered magnet according to claim 2 , wherein the coarsely pulverized powder is supplied to the jet mill device by connecting the recovery container rotated in the mixing step to a raw material tank of the jet mill device.

4. The producing method of the R-T-B-based sintered magnet according to claim 3 , wherein inert gas is introduced into a connecting portion between an on/off valve of the recovery container and an on/off valve of the raw material tank and oxygen concentration in the connecting portion is set to 20 ppm or less and then, the on/off valve of the recovery container and the on/off valve of the raw material tank are opened, and the coarsely pulverized powder in the recovery container is supplied to the raw material tank.

5. The producing method of the R-T-B-based sintered magnet according to claim 1 , wherein the jet mill device finely pulverizes the coarsely pulverized powder in inert gas in which oxygen concentration is 20 ppm or less.

6. The producing method of the R-T-B-based sintered magnet according to claim 1 , wherein an oxygen-containing amount of the R-T-B-based sintered magnet obtained in the sintering step is set to 600 ppm or less.

7. The producing method of the R-T-B-based sintered magnet according to claim 1 , wherein one kind of mineral oil, synthetic oil and vegetable oil is sprayed to or dropped onto the compact for the R-T-B-based sintered magnet obtained in the forming step.

8. The producing method of the R-T-B-based sintered magnet according to claim 1 , wherein

the recovery chamber includes turn-over device 44 for turning over the processing container upside down,

the processing container is provided at its upper surface with an opening, and

the raw-material alloy for the R-T-B-based sintered magnet in the processing container is discharged by an upside down turning over operation carried out by the turn-over device 44 .

9. The producing method of the R-T-B-based sintered magnet according to claim 8 , wherein after the upside down turning over operation was carried out by the turn-over device 44 , the turn-over device 44 carries out a swinging operation in a state where the opening is directed downward.

10. The producing method of the R-T-B-based sintered magnet according to claim 8 , wherein

the processing container is provided with a lid which covers the opening thereof,

the opening is covered with the lid when the evacuating device 43 carries out a decompressing operation, and

the lid is detached from the opening after the pressure in the recovery chamber was reduced by the evacuating device 43 and before the upside down turning over operation is carried out by the turn-over device 44 .

11. The producing method of the R-T-B-based sintered magnet according to claim 10 , wherein the hydrogen storing step, the heating step and the cooling step are carried out in a state where the opening of the processing container is covered with the lid.

12. The producing method of the R-T-B-based sintered magnet according to claim 1 , wherein the raw-material alloy for the R-T-B-based sintered magnet is discharged from the processing container under a reduced pressure of 1000 Pa to 1 Pa in the recovery chamber.

13. The producing method of the R-T-B-based sintered magnet according to claim 1 , wherein inert gas is previously substituted for air in the recovery container such that oxygen concentration becomes 20 ppm or less, and the pressure in the recovery chamber is set to the same as the pressure in the recovery container.