Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Consolidation of powder prior to sintering
Reexamination Certificate
2001-09-06
2003-12-02
Jenkins, Daniel J. (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Consolidation of powder prior to sintering
C425S078000
Reexamination Certificate
active
06656416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a powder feeding apparatus, a pressing apparatus using the same, a powder feeding method and a sintered magnet manufacturing method. More specifically, the present invention relates to a powder feeding apparatus for feeding a powder into a cavity formed in a die, a pressing apparatus using the same, a powder feeding method and a sintered magnet manufacturing method.
2. Description of the Related Art
Currently, as sintered rear-earth alloy magnets, two kinds, i.e. a samarium-cobalt magnet and a rare-earth-iron-boron magnet, are used extensively in many fields. Of the two, the rare-earth-iron-boron magnet is appreciated in application to variety of electronic devices and apparatuses. (Hereinafter, the rare-earth-iron-boron magnet will be called “R-T-(M)-B magnet”, where R represents a rare-earth element including yttrium, T represents iron or iron partially substituted by a transition metal element, M represents a doped element, and B represents boron.) A reason for this is that the R-T-(M)-B magnet is the most superior of many kinds of magnets in terms of magnetic energy product and relatively inexpensive in terms of price. The transition metal included as T may be cobalt for example. Boron can be partially substituted by carbon.
In manufacture of such a rare-earth magnet, first, a magnetic alloy powder made by milling a rare-earth alloy is pressed into a compact (green compact) by a pressing apparatus. When making the compact, the magnetic alloy powder is fed into a cavity formed by a die hole (through hole) provided in a die and a lower punch inserted into the die. The magnetic alloy powder fed in the cavity is pressed by an upper punch. The compact thus obtained is then sintered at a temperature of 1000° C. -1100° C. approx., and then finished as the sintered rare-earth magnet.
Conventionally, a variety of methods are proposed for feeding the magnetic alloy powder into the cavity in the pressing apparatus.
For example, Japanese Utility Model Publication (of examined Application for opposition) No. 59-32568 and Japanese Patent Laid-Open No. 61-147802 each discloses a technique of vibrating a container which holds the powder and thereby supplying the power into the cavity in sieving action through a metal net.
According to Japanese Patent Laid-Open No. 61-147802, there is described an apparatus comprising a feeder cup (the powder container) having a bottom portion provided with a metal net. The feeder cup is vibrated relatively rigorously by using a solenoid coil, thereby feeding the granular magnetic powder through the metal net into the cavity in a short time.
However, according to the conventional apparatus disclosed in Japanese Patent Laid-Open No. 61-147802, the vibration is generated by means of attracting force between the solenoid coil and an iron core, and of restoring force provided by a spring, and the vibration is given to the feeder cup itself which holds the powder. The iron core (moving part) is fastened to the feeder cup by a connecting hardware. With this arrangement, the vibrating force transmitted to the powder in the feeder cup is only a reciprocating force, and the transmitted force is still not sufficient to break down a lump of powder. In such an apparatus, in order to supply the granular powder into the cavity while preventing bridge formation, one possibility is to use the metal net having a fine grid (mesh). However, use of such a fine-mesh metal net poses another problem that the powder is not quickly sieved and there is a significant increase in the time for feeding the powder.
Another problem with the above conventional apparatus is that it is difficult to increase the stroke (amplitude) of vibration given to the feeder cup. If the feeder cup is moved only in a short stroke, it is difficult to feed the powder uniformly in the cavity.
There is still another problem. Specifically, corner and/or edge regions of the cavity is more difficult to feed with the powder than a center region of the cavity. According to the conventional apparatus therefore, when the rare-earth alloy powder is supplied through the metal net which is provided at a position relatively high above the die surface, the powder tends to form a high portion in the center region. If the powder is fed in such a non-uniform density in the cavity, the compact formed by the pressing operation has an unacceptably large difference in its pressing density, between the corner and/or edge regions and the center region. This density difference can cause a crack in the compact.
This problem is presumable also in an apparatus disclosed in Japanese Utility Model Publication (of examined Application for opposition) No. 59-32568.
Other techniques for feeding the powder into the cavity are proposed in Japanese Patent Laid-Open No. 11-49101 and Japanese Patent Laid-Open No. 2000-248301.
According to the technique disclosed in Japanese Patent Laid-Open No. 11-49101, a feed is fed into a container by means of pneumatic tapping and via a supplying hopper. An arrangement is made so that the feed is present in both of the supplying hopper and the container after the pneumatic tapping. Then, of this mass of the feed present in both of the supplying hopper and the container, a portion of uniform density formed in the container is separated from the feed remaining in the supplying hopper.
Japanese Patent Laid-Open No. 2000-248301 discloses a supplying apparatus, in which a feeder box having an opening in a bottom is moved to above a cavity formed in a die tooling, allowing a rare-earth alloy powder to be supplied into the cavity from the opening. The supplying apparatus comprises rod members which are moved at the bottom portion horizontally within the feeder box. The rod members are reciprocated when the rare-earth alloy powder in the feeder box is supplied to the cavity.
However, according to the technique disclosed in Japanese Patent Laid-Open No. 11-49101, since the feeding into the container is performed by the pneumatic tapping, the feeding density of the feed in the container becomes higher than by means of natural gravitational fall. For example, a rare-earth alloy powder fed by means of natural gravitational fall has the feeding density of 1.8 g/cm
3
approx., versus the feeding density of 3.4 g/cm
3
approx. by means of pneumatic tapping. The feed packed to such a high density does not allow particles of the powder to move easily, requiring a stronger magnetic field in order to orient the powder, leading to increase in manufacturing cost.
According to the technique disclosed in Japanese Patent Laid-Open No. 2000-248301 on the other hand, as shown in
FIG. 21A
, a feeder box
2
is moved toward a cavity
1
. Then, as shown in
FIG. 21B
, when the feeder box
2
is positioned above the cavity
1
, a powder
3
is supplied into the cavity
1
by the weight of the powder
3
itself. The feeding thus performed is not even, and therefore the powder
3
is not distributed uniformly. Thereafter, as shown in FIG.
21
C and
FIG. 21D
, a shaker
4
is activated to fill the cavity
1
with the powder
3
. The shaker
4
forces the powder
3
in, to the density of 2.3 g/cm
3
approx., thereby uniformalizing the feeding density. As a result, a stronger magnetic field is necessary in order to obtain a desired level of orientation.
FIG. 22
shows state changes in the feeding operation performed by this conventional apparatus.
Further, if the cavity is shallow in a direction of the pressing operation provided by the punches, the feeding density inconsistency in the cavity is not easily corrected by the pressing operation, leading to occasional crack development in the compact.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a powder feeding apparatus, a pressing apparatus using the same and a sintered magnet manufacturing method, capable of feeding the powder uniformly and in a short time into the cavity of the pressing apparatus.
Another object of the present invention is to provide
Iwasaki Tadahiro
Matsugami Shouichi
Nakamura Akira
Takano Yoshiro
Tanaka Atsuo
Armstrong Westerman & Hattori, LLP
Jenkins Daniel J.
Sumitomo Special Metals Co. Ltd.
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