Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Controlled cooling after sintering
Reexamination Certificate
1998-10-21
2001-07-24
Mai, Ngoclan (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Controlled cooling after sintering
C419S026000, C148S586000
Reexamination Certificate
active
06264886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sintered metallic alloy suitable for an internal gear such as a planetary gear, a method of manufacturing the sintered metallic alloy, and a sintered alloy gear employing the sintered metallic alloy.
2. Description of the Related Art
Regarding such a kind of conventional sintered metallic alloy, a method of manufacturing the sintered metallic alloy, and a sintered alloy gear employing the sintered metallic alloy, a sintered metallic gear manufactured, for example, through manufacturing steps such as those shown in FIG.
12
(
a
) through FIG.
12
(
g
) is known.
That is, metallic materials, such as iron powder, any other metal powder, and a lubricant, for sintered metallic parts such as a sintered internal gear
10
, such as those shown in FIG.
12
(
a
), are blended and mixed at a predetermined ratio by a mixer
11
, as shown in FIG.
12
(
b
). As shown in FIG.
12
(
c
), a predetermined weight of the mixed metallic materials is poured into a metal mold
12
.
Then, an upper punch
12
a
and a lower punch
12
b
of the metal mold
12
are slid to move toward each other along the core rod
13
, and a pressure of 3 to 7 tonf/cm
2
is applied to the mixed metallic materials from directions above and below, whereby compression molding is performed.
Next, as shown in FIG.
12
(
d
), the compression molded compacts
15
are heated in a sintering furnace
14
for a predetermined time at a high temperature less than the melting point, whereby the diffusion bonding of metal particles in the compacts
15
is promoted to solidify them.
In order to further enhance the quality and characteristics and obtain finished products corresponding to various purposes or uses, after-treatment is performed.
Subsequently, as shown in FIG.
12
(
e
), in order to obtain the sintered internal gear
10
, the solidified compact
15
is put into a sizing metal mold
16
. An upper punch
16
a
and a lower punch
16
b
of this sizing metal mold
16
are slid to move toward each other along the core rod
17
, and a pressure is applied to the compact
15
again from directions above and below. By that, sizing is performed.
After sizing, inspection is performed as shown in FIG.
12
(
f
), and a sintered metallic part such as the sintered internal gear
10
is obtained as a finished product (FIG.
12
(
g
)).
An after-treatment technique related to the aforementioned after-treatment is disclosed in Japanese Laid-Open Patent Publication No. SHO 58-19412 (19412/83). The disclosed after-treatment technique is as follows. That is, after sintering in a sintering furnace, quenching is performed at a re-raised temperature of 860° C., and thereafter, tempering is performed at about 180° C., whereby the resistance of the sintered alloy gear to high surface pressure is enhanced.
However, in the sintered alloy gear constructed in the aforementioned manner, the structure in a range of 0.02 to 0.3 mm from the exterior surface toward the inside consists of an austenite layer having conformability, so that due to quenching and subsequent tempering, a thin austenite layer containing austenite entirely different in toughness in high density is formed on the surface of an inner martensite layer containing martensite having high brashiness in high density, and therefore, the inner and outer structures of the sintered alloy gear are separated from each other.
For this reason, the surface of the internal gear including relatively narrow area of contacting surface portion, which high pressure is applied to, is constituted by the aforementioned martensite layer. As a result, toughness is insufficient at microscopic portions and it is difficult to support stress load at a point.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a sintered metallic alloy having toughness capable of supporting stress load at a point by constructing its structure so that each portion having different rigidity is distributed approximately uniformly without separation of layers different in toughness.
Another object of the present invention is to provide a method of manufacturing the aforementioned sintered metallic alloy.
Still another object of the present invention is to provide a sintered alloy gear employing the aforementioned sintered metallic alloy.
To achieve the aforementioned objects of the present invention and in accordance with one aspect of the invention, there is provided a sintered metallic alloy wherein structure portions with high toughness are distributed approximately uniformly from a surface thereof toward the inside thereof.
In the sintered metallic alloy constructed as described above, structure portions with high toughness are distributed approximately uniformly without separation of layers different in rigidity, so that stress load exerted at a point is supported by the entire surface. For this reason, there is no possibility that a portion of the sintered metallic alloy will cave in due to concentration of stress, and the stress between members with a small contacting area can be supported.
In accordance with another aspect of the present invention, there is provided a method of manufacturing a sintered metallic alloy, wherein a sintered metallic alloy, which is cooled to about an ambient atmosphere of a room temperature by being cooled slowly after being sintered in a form of a predetermined shape of metallic materials for sintering in a sintering furnace, is heated up as a toughness stabilizing process so that structure portions with high toughness are distributed approximately uniformly.
In the aforementioned manufacturing method, the metallic materials for sintering, which is formed in a predetermined shape, is cooled to about an ambient atmosphere of a room temperature by being cooled slowly after being sintered in the sintering furnace. Then, the structure portions in the sintered metallic alloy having high toughness are distributed approximately uniformly mainly owe to the changes of the high-rigidity structure portions to structure portions having high toughness with holding rigidity by re-raising of temperature of the sintered metallic alloy to the predetermined temperature. As a result, the structure portions having respective rigidities are distributed approximately uniformly, whereby the toughness is enhanced in the form of a surface.
In accordance with still another aspect of the present invention, there is provided a sintered alloy gear employing a sintered metallic alloy, wherein a generally disk-shaped flange portion provided with a boss portion at its center is formed integrally on one end face of a main body of an internal gear provided with a gear surface arranged almost in a shape of a circle at its interior surface.
In the sintered alloy gear constructed as described above, though the generally disk-shaped flange with a boss portion at the approximate center thereof is formed integrally on one end face of the internal gear main body forming a general ring shape and comprising its gear surface at the interior surface portion, stress due to molding can be reduced and flower blooming after cooling can be suppressed, because structure portions having different values of rigidity are distributed approximately uniformly without separation of layers different in rigidity. For this reason, dimensional accuracy can be enhanced.
In the aforementioned manufacturing method, sizing may be performed before the toughness stabilizing process is performed. In this case, sizing is performed before the toughness stabilizing process is performed, so that the internal stress, produced at the time of execution of the sizing, is released by performing the toughness stabilizing process. For example, the flower blooming of a flanged internal gear is suppressed, and therefore, the dimensional accuracy can be enhanced.
In addition, sizing may be performed after the aforementioned toughness stabilizing process. In this case, sizing is performed after the toughness stabilizing process. Therefore, for instance, compared with the
Mizuta Muneo
Tomihari Yoshihisa
Yabe Yasushi
Jacobson Price Holman & Stern PLLC
Jatco Corporation
Mai Ngoclan
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