Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Consolidation of powder prior to sintering
Reexamination Certificate
2000-12-08
2002-08-13
Mai, Ngoclan (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Consolidation of powder prior to sintering
C419S066000, C425S258000, C222S251000
Reexamination Certificate
active
06432354
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method and apparatus for feeding magnetic powder (hereinafter sometimes referred to as “powder feeding”) into a pressing apparatus, a method for forming a magnetic powder compact, and a method for manufacturing a magnet using the magnetic powder feeding method and the powder feeding apparatus.
BACKGROUND OF THE INVENTION
An R-Fe-B type rare earth alloy magnet as a representative high-performance permanent magnet (where R denotes an element or combination of elements selected from the group consisting of rare earth elements and yttrium (Y)), Fe denotes iron, and B denotes boron) has a structure including a major phase of ternary system tetragonal crystal compound (R
2
Fe
14
B phase) and an R-rich grain boundary phase, and exhibits excellent magnetic properties. The R—Fe—B type magnet is now used in wide fields from various electric appliances for domestic use to peripheral devices for a mainframe computer. There are strong demands towards miniaturization, weight reduction, and advanced performance, so that an R—Fe—B type permanent magnet with much higher performance is desired.
In order to increase the residual magnetic flux density (B
r
) of an R—Fe—B type sintered magnet, the following are required: (1) to increase a total volume fraction of ferro-magnetic R
2
Fe
14
B phases, (2) to make a density of sintered compact closer to a theoretical density of the major phase, and (3) to align an axis of easy magnetization of the major phase crystal grains.
When magnetic powder is to be fed into a cavity (a powder compacting space) of a pressing apparatus, conventionally, a feeder box (or a feeder shoe) is slid onto the cavity, and the powder is gravity-fed from the feeder box into the cavity.
FIGS. 1A
to
1
C schematically show a conventional powder feeding method by means of a feeder box. According to the conventional method, as shown in
FIGS. 1A
to
1
C, when a feeder box
13
slides in a transverse direction over a cavity
12
constituted by a die
10
and a lower punch
11
of a powder pressing apparatus, magnetic powder
14
in the feeder box
13
is filled in the cavity
12
. In this method, an upper portion of the filling powder is pressurized downwards (in a direction indicated by an arrow A) by pressurizing means such as a leveling rod (not shown) disposed in the feeder box
13
for the purpose of suppressing feeding inconsistency.
According to such a conventional filling method using a feeder box, the powder can be surely filled in the cavity. In addition, the volume of the filling powder can be controlled to be substantially constant by means of the “leveling” done by the trailing edge of the feeder box.
Even in the case where the volume of the filling powder is constant, however, when a pressure applying to the powder by a leveling bar or the like is varied, the filling density is also varied. This eventually results in increased feeding inconsistency.
Moreover, according to the conventional method, the flowability of the powder becomes lower by a strong pressure due to the self-weight of the powder in a position closer to a bottom portion of the cavity, which leads to poor alignment of the powder in a magnetic field. As a result, as for the filling powder, the degree of alignment in a position closer to the bottom portion of the cavity is lower than the degrees of alignment in other portions. There arises a problem in that the magnetic properties are varied depending on positions.
This problem arises especially in the case where an R—Fe—B type rare earth magnet is to be manufactured. R—Fe—B type magnetic powder has a larger specific gravity as compared with ferrite magnetic powder. For this reason, in the case where the R—Fe—B type magnetic powder is filled in the cavity, a larger self-weight pressure is generated in a position closer to the cavity bottom portion, as compared with the case of the ferrite magnetic powder. Accordingly, in the case where the R—Fe—B type magnetic powder is used, the deterioration in powder alignment cannot be sufficiently suppressed even if the friction coefficient of powder particles is lowered by adding a lubricant to powder, or even if the intensity of the applied aligning magnetic field is increased. Thus, the magnetic properties of the final magnet product are likely to be degraded.
SUMMARY OF THE INVENTION
The invention provides a magnetic powder feeding method that can reduce a variation in degrees of alignment depending on the positions in the cavity.
The invention also provides a method for forming a compact with a uniform and high degree of alignment by using the magnetic powder feeding method, and a method for manufacturing a magnet with excellent magnetic properties.
The invention also provides a magnetic powder feeding apparatus that is suitably used in conjunction with the magnetic powder feeding method.
A magnetic powder feeding method of the present invention for feeding magnetic powder into a cavity of a pressing apparatus includes the steps of: placing the magnetic powder outside the cavity; forming a magnetic field in a space including the cavity; and moving the magnetic powder into the cavity using a force exerted on the magnetic powder by the magnetic field, while the magnetic powder is oriented in a direction of the magnetic field, wherein the step of moving of the magnetic powder into the inside of the cavity is performed after the start of the application of the magnetic field.
A magnetic powder feeding method of the present invention for feeding magnetic powder into a cavity of a pressing apparatus, includes the steps of: placing the magnetic powder outside the cavity; forming a magnetic field in a space including the cavity; and dropping the magnetic powder into the inside of the cavity by using an electromechanical mechanism that operates in an interlocking manner with the formation of the magnetic field.
In a preferred embodiment, a magnetic powder is moved into the cavity at a timing when an intensity of the magnetic field reaches a predetermined value.
In a preferred embodiment, the direction of the magnetic field includes a direction perpendicular to a pressing direction in the inside of the cavity.
In a preferred embodiment, the magnetic field is directed substantially in a horizontal direction in the inside of the cavity.
In a preferred embodiment, a member for preventing the magnetic powder from moving until the magnetic field is formed is inserted between the magnetic powder and the cavity, and after the magnetic field is formed, the member is driven, thereby enabling the magnetic powder to move.
A magnetic powder feeding method of the present invention for feeding magnetic powder into a cavity of a pressing apparatus includes the steps of: placing the magnetic powder above the cavity; forming an aligning magnetic field in a space including the cavity; and dropping the magnetic powder into the cavity while the magnetic powder is oriented in a direction of the magnetic field by using a force by which the aligning magnetic field attracts the magnetic powder.
In a preferred embodiment, the force exerted on the magnetic powder by the aligning magnetic field is in the same direction as the force of gravity on the magnetic powder.
In a preferred embodiment, the magnetic powder of an amount to be filled in the cavity is first placed above the cavity.
In a preferred embodiment, a direction of the aligning magnetic field includes a direction perpendicular to a pressing direction of the pressing apparatus in the inside of the cavity.
In a preferred embodiment, the aligning magnetic field is directed in a horizontal direction in the inside of the cavity.
In a preferred embodiment, a member for preventing the magnetic powder from dropping until the aligning magnetic field is formed is inserted between the magnetic powder and the cavity, and after the aligning magnetic field is formed, the member is driven, thereby enabling the magnetic powder to drop.
In a preferred embodiment, the step of placing the magnetic powder above the cavity is performed b
Ogawa Atsushi
Tamura Toshiaki
Costellia Jeffrey L.
Mai Ngoclan
Nixon & Peabody LLP
Sumitomo Special Metals Co. Ltd.
LandOfFree
Method and apparatus for feeding magnetic powder and method... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for feeding magnetic powder and method..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for feeding magnetic powder and method... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2891653