Plastic article or earthenware shaping or treating: apparatus – Means for molding powdered metal
Reexamination Certificate
2001-01-25
2004-12-07
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means for molding powdered metal
C425S345000, C425S353000, C029S623100
Reexamination Certificate
active
06827567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a method and an apparatus for compression molding of a mixture of powder materials to manufacture ring-like pellets and to a dry cell, such as an alkaline-manganese dry cell, which contains pellets made of the powder mixture produced by the method and apparatus.
2. Description of Related Art
The market for alkaline-manganese dry cells has sharply been expanded with the spread of portable electronic appliances such as personal computers which consume a large amount of power. Alkaline-manganese dry cells which contain pellets made from a powder mixture are classified into six different types ranging from the standard R20 (D type) to a rectangular 9-Volt cell and are all fabricated in the form of a ring. These pellets are manufactured by compressing a mixture of powder materials in a ring-like mold with a compression molding machine, and hermetically loaded in a cell case.
The molding of such mixture pellets is generally performed with a rotary type compression molding machine as disclosed in Japanese Published Unexamined Patent Application No. 6-23597 or Japanese Published Utility Model Application No. 6-23694. The rotary compression molding machine of such type comprises a rotary disk
53
mounted by a bearing unit
52
to a center shaft
51
and driven by a drive unit
54
for rotation about the center shaft
51
, as shown in FIG.
10
. The rotary disk
53
carries at its circumferential edge a number of molding units
55
arranged at equal intervals. The molding unit
55
consists of a die
56
, a lower plunger
57
, and an upper plunger
58
. After the powder material is supplied into the die
56
as the rotary disk
53
is rotated, it is compressed with the vertical movements of the lower plunger
57
and the upper plunger
58
which are actuated at predetermined locations by a lower pressing roller
59
a
and an upper pressing roller
59
b
, respectively. The formed pellet is pressed out and ejected from the die
56
by the upward movement of the lower plunger
57
which is actuated by a cam
60
.
The conventional rotary compression molding machines disclosed in the above mentioned publications are designed for forming disk-like pellets. For molding a ring-like pellet, the die has to be replaced with an appropriate one equipped with a center pin.
A forming operation in a conventional rotary compression molding machine being constructed as mentioned above is now explained referring to
FIGS. 11 and 12
. As shown in a longitudinal sectional view of the rotary compression molding machine of
FIG. 11
, a rotary disk
31
has a plurality of molding units
32
arranged at equal intervals on a concentric circle about the center of rotation. Each molding unit
32
comprises a die
33
, a center pin
34
, a lower plunger
35
, and an upper plunger
36
. The die
33
is fixed to the rotary disk
31
and the center pin
34
is fitted into an axial bore of the lower plunger
35
for sliding movement in relation to the lower plunger
35
. The lower plunger
35
and the upper plunger
36
are arranged to engage with a lower pressing roller
38
and an upper pressing roller
39
respectively at their corresponding locations as the rotary disk
31
is rotated so as to compress the powder material filled in an annular space between the die
33
and the center pin
34
from upper and lower sides to form a ring-like pellet
40
. The molded ring-like pellet
40
is then pressed upwardly out from the die
33
by the lower plunger
35
which is greatly lifted up by the engagement with a cam
41
.
A procedure of forming the pellet
40
with the rotary compression molding machine described above is explained in more detail referring to FIG.
12
.
FIG. 12A
illustrates an initial state where the die
33
, the lower plunger
35
, and the center pin
34
are flush with each other at the top after the previous pellet
40
is unloaded. When the lower plunger
35
is lowered from its initial position, an annular space for compression molding is formed between the die
33
and the center pin
34
as shown in FIG.
12
B. The annular space is then filled with a powder material
42
. As a feed shoe
43
runs along the top sides of the die
33
and the center pin
34
located flush with each other, an excess of the powder material
42
is removed to measure out a predetermined amount to be molded into one pellet
40
. This is followed by a step where the lower plunger
35
is lifted up and the upper plunger
36
is lowered as shown in
FIG. 12D
, by which the powder material
42
in the annular space is compressed from upper and lower sides, thus forming the pellet
40
. The pellet
40
is then unloaded upwardly from the die
33
by the upward movement of the lower plunger
35
as shown in FIG.
12
E and taken out as a compression molded product.
Such conventional procedure of compression molding has, however, a drawback that the powder material
42
when being supplied into the annular space between the die
33
and the center pin
34
is likely to produce a bridge, particularly when a thin pellet
40
having a small diameter is formed. Because of the bridges frequently formed, it is difficult to constantly supply a given amount of the powder material
42
, thus making the weight of pellet
40
unstable. In order to feed a fixed amount of the powder material
42
into the die
33
, it is of course attempted to destroy the bridge by stirring the heap of the powder material
42
on the die
33
with a plurality of feed shoes
43
provided at an angle to the direction of movement of the die
33
and driven by the rotation of the rotary disk
31
. This attempt at eliminating the bridge is yet insufficient to fully prevent the variation in weight and height of the pellets
40
.
The pellet
40
formed in the compression molding is pressed upward and unloaded from the space defined by the stationary center pin
34
and the die
33
by the ejecting action of the lower plunger
35
. Since the pellet
40
is stuck to the center pin
34
and the die
33
at the inner side and outer side thereof respectively by the pressure given during the compression molding, the lower plunger
35
is required to have a considerable amount of strength to unload the pellet
40
by pushing it up. This causes severe abrasion on the sliding surfaces between the lower plunger
35
at its bottom and the surface of the cam
41
which functions to lift up the lower plunger
35
as the rotary disk
31
rotates.
Further, the pellet
40
is forcibly unloaded by the ejecting action of the lower plunger
35
though it is almost fixedly stuck to the inner side of the die
33
and the outer side of the center pin
34
. For preventing the pellet
40
from being damaged during the removal from the die
33
, the pellet
40
is required to be tapered both on its inner and outer sides at a relatively wide angle. When the pellet
40
of a ring-like shape is tapered both on the inner and outer sides, its overall weight is decreased. This cannot be compensated by setting the height of the pellet
40
vertical to the radial direction to be greater, because the lower part of the pellet
40
becomes too small in thickness due to the tapering.
Since the pellet
40
is small both in height h and weight, three or four pellets
40
are needed for filling a cell case
62
as a positive electrode material to construct an alkaline-manganese dry cell
61
of R20 to R03 types as shown in FIG.
13
. As the number of the pellets
40
to be encased increases, more steps are needed for compression molding and filling process, thus declining the efficiency of production and soaring the overall cost. The gaps made between the inner side of the pellet
40
and a separator
64
and between the outer side of the pellet
40
and the cell case
62
obstruct the smooth flow of the electric current. Also shown in
FIG. 13
are a label cover
63
, a gel negative electrode
65
, a collector
66
, a resin seal
67
, insulators
68
, and a bottom cap
69
.
In general, the ring-like pell
Hattori Shigeharu
Kouda Minoru
Nakatsuka Saburo
Sanukiya Toshio
Takebayashi Hiroshi
Davis Robert
Nguyen Thu Kanh T.
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