Method for producing rare-earth sintered magnet, and molding machine therefor

1. A method for producing a rare earth sintered magnet, comprising the steps of:

1) preparing a slurry including an alloy powder and a dispersion medium, the alloy powder containing a rare earth element;

2) disposing an upper punch and a lower punch in respective through holes provided in a die, thereby preparing a plurality of cavities enclosed by the die, and the upper punch and the lower punch, at least one of the upper punch and the lower punch being movable toward and away from the other one, at least one of the upper punch and the lower punch including an outlet for discharging the dispersion medium of the slurry;

3) applying a magnetic field in each of the cavities by an electromagnet in a direction substantially parallel to a direction in which at least one of the upper punch and the lower punch is movable, and then supplying the slurry into the plurality of cavities via slurry flow paths connected to slurry supply paths extending from an outer peripheral side surface of the die to each of the cavities, wherein at least a part of a portion of the slurry flow path passing through a magnetic field formed by the electromagnet is covered by an external magnetic field shielding material being capable of shielding the magnetic field;

4) producing a molded body of the alloy powder in each of the cavities by press molding in the magnetic field, the upper punch and the lower punch coming closer to each other while applying the magnetic field; and

5) sintering the molded body;

wherein the external magnetic field shielding material allows the magnetic field to pass therethrough preferentially as compared to the slurry in the slurry flow path covered by the external magnetic field shielding material;

wherein the slurry supply path is not branched within the die; and

wherein the slurry supply paths linearly extend from the outer peripheral side surface of the die toward the plurality of cavities.

2. The production method according to claim 1 , wherein the electromagnet comprises:

a first electromagnet having a hollow portion; and

a second electromagnet opposed to and spaced from the first electromagnet and having another hollow portion.

3. The production method according to claim 2 , wherein the slurry is supplied into the cavities via the slurry flow path, at least a part of a portion of the slurry flow path passing through a magnetic field generated in the hollow portion of the first electromagnet, the hollow portion of the second electromagnet, a space for connecting between the hollow portion of the first electromagnet and the hollow portion of the second electromagnet, and an opposed space between the first and second electromagnets is covered by the external magnetic field shielding material being capable of shielding the magnetic field.

4. The production method according to claim 2 , wherein the slurry is supplied into each of the plurality of cavities via the slurry flow path, at least a part of a portion of the slurry flow path passing through a magnetic field generated in the hollow portion of the first electromagnet, the hollow portion of the second electromagnet, and the space for connecting between the hollow portion of the first electromagnet and the hollow portion of the second electromagnet is covered by the external magnetic field shielding material being capable of shielding the magnetic field.

5. The production method according to claim 1 , wherein, in the step 3), the slurry is supplied into each of the cavities at a flow rate of 20 to 600 cm 3 /second.

6. The production method according to claim 1 , wherein a magnetic field strength of the magnetic field is 1.5 T or more.

7. A molding device for a rare earth sintered magnet, comprising:

an upper punch and a lower punch, at least one of the upper punch and the lower punch being movable toward and away from the other one;

a die having at least one through hole, the die comprising at least one cavity, each of the at least one cavity being enclosed by the upper punch and the lower punch disposed in each through hole, and the through hole;

an electromagnet for applying a magnetic field in at least one cavity in a direction substantially parallel to a direction in which at least one of the upper punch and the lower punch is movable;

a slurry supply path extending from an outer peripheral side surface of the die to each cavity, the slurry supply path being capable of supplying a slurry including an alloy powder and a dispersion medium to the cavity; and

a slurry flow path connected to the slurry supply path, wherein at least a part of a portion of the slurry flow path passing through a magnetic field formed by the electromagnet is covered by an external magnetic field shielding material being capable of shielding the magnetic field;

wherein the external magnetic field shielding material allows the magnetic field to pass therethrough preferentially as compared to the slurry in the slurry flow path covered by the external magnetic field shielding material;

wherein the slurry supply path is not branched within the die; and

wherein the slurry supply paths linearly extend from the outer peripheral side surface of the die toward the plurality of cavities.

8. The molding device according to claim 7 , wherein the electromagnet comprises:

a first electromagnet having a hollow portion; and

a second electromagnet opposed to and spaced from the first electromagnet and having another hollow portion.

9. The molding device according to claim 8 , wherein at least a part of a portion of the slurry flow path passing through a magnetic field generated in the hollow portion of the first electromagnet, the hollow portion of the second electromagnet, a space for connecting between the hollow portion of the first electromagnet and the hollow portion of the second electromagnet, and an opposed space between the first and second electromagnets is covered by the external magnetic field shielding material being capable of shielding the magnetic field.

10. The molding device according to claim 8 , wherein at least a part of a portion of the slurry flow path passing through a magnetic field generated in the hollow portion of the first electromagnet, the hollow portion of the second electromagnet, and the space for connecting between the hollow portion of the first electromagnet and the hollow portion of the second electromagnet is covered by the external magnetic field shielding material being capable of shielding the magnetic field.