U.S. patent application number 13/904504 was filed with the patent office on 2013-09-26 for sintered bearing and preparation method thereof.
The applicant listed for this patent is Hyundai Steel Company, Orient Precision Industries Inc. Invention is credited to Tae-Young Choi, Gyo-Jin Chu, Hae-Sik Kim, Hyun-Tae Kim, Soon-Jae Tae, Tae-Il Yoon.
Application Number | 20130251586 13/904504 |
Document ID | / |
Family ID | 44957708 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130251586 |
Kind Code |
A1 |
Tae; Soon-Jae ; et
al. |
September 26, 2013 |
SINTERED BEARING AND PREPARATION METHOD THEREOF
Abstract
The present invention relates to a sintered bearing and a
preparation method thereof, wherein the method comprises: a step
for forming a mixed powder by mixing metal powder, kish graphite,
and lubricant; forming a molded body by applying pressure to the
mixed powder; forming a sintered body by sintering the molded body;
and impregnating the sintered body in oil. The invention is
prepared by adding 0.01-10 parts by weight of kish graphite to
metal powder and thus provides excellent abrasion resistance,
strength, and self lubricity.
Inventors: |
Tae; Soon-Jae; (Dangjin,
KR) ; Yoon; Tae-Il; (Pyeongtaek, KR) ; Kim;
Hae-Sik; (Sungnam, KR) ; Kim; Hyun-Tae;
(Sungnam, KR) ; Choi; Tae-Young; (Sungnam, KR)
; Chu; Gyo-Jin; (Sungnam, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Orient Precision Industries Inc
Hyundai Steel Company |
Sungnam
Incheon |
|
KR
KR |
|
|
Family ID: |
44957708 |
Appl. No.: |
13/904504 |
Filed: |
May 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/KR2011/009164 |
Nov 29, 2011 |
|
|
|
13904504 |
|
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Current U.S.
Class: |
419/11 ;
75/243 |
Current CPC
Class: |
F16C 33/1095 20130101;
C22C 9/02 20130101; B22F 3/26 20130101; C22C 38/00 20130101; B22F
3/16 20130101; F16C 33/145 20130101; B22F 5/106 20130101; B22F
1/0059 20130101; F16C 2202/52 20130101; B22F 1/007 20130101; F16C
33/128 20130101; B22F 5/00 20130101 |
Class at
Publication: |
419/11 ;
75/243 |
International
Class: |
B22F 1/00 20060101
B22F001/00; B22F 5/00 20060101 B22F005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 29, 2010 |
KR |
10-2010-0119557 |
Claims
1. A sintered bearing, comprising metal powder, kish graphite, and
a lubricant.
2. The sintered bearing of claim 1, comprising, based on a total
weight thereof, 0.01.about.10 parts by weight of the kish graphite,
0.01.about.1.0 parts by weight of the lubricant, and a balance of
the metal powder.
3. The sintered bearing of claim 1, wherein the metal powder is one
or more selected from the group consisting of a pure iron system,
an iron-copper system, an iron-carbon system, an iron-carbon-copper
system, a bronze system, and an iron-carbon-copper-nickel
system.
4. The sintered bearing of claim 1, wherein the kish graphite is a
byproduct of iron production.
5. A method of manufacturing a sintered bearing, comprising: mixing
metal powder, kish graphite, and a lubricant, thus forming a powder
mixture; applying pressure to the powder mixture, thus forming a
molded body; sintering the molded body, thus forming a sintered
body; and impregnating the sintered body with oil.
6. The method of claim 5, wherein the powder mixture comprises,
based on a total weight thereof, 0.01.about.10 parts by weight of
the kish graphite, 0.01.about.1.0 parts by weight of the lubricant,
and a balance of the metal powder.
7. The method of claim 5, wherein the metal powder is one or more
selected from the group consisting of a pure iron system, an
iron-copper system, an iron-carbon system, an iron-carbon-copper
system, a bronze system, and an iron-carbon-copper-nickel
system.
8. The method of claim 5, wherein the kish graphite is in a powder
form having a particle size of 50 mesh or less.
9. The method of claim 5, wherein the kish graphite has a purity of
90.about.100% after refining.
10. The method of claim 5, wherein the lubricant contains zinc
stearate (C.sub.36H.sub.70O.sub.4Zn), Acrawax
(C.sub.38H.sub.76N.sub.2O.sub.2), Kenolube paraffin, or any
combination thereof.
11. The method of claim 5, wherein a pressure of 50.about.350 MPa
is applied to the powder mixture at room temperature.
12. The method of claim 5, wherein the molded body is performed so
that the molded body has a compact density of 5.4.about.7.0
g/cm.sup.3.
13. The method of claim 5, wherein the molded body is sintered at
850.about.1300.degree. C. under atmospheric pressure.
14. The method of claim 5, wherein the molded body is sintered for
1.about.6 hr.
15. The method of claim 5, wherein the sintered body is impregnated
at 50.about.150.degree. C. in a vacuum.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application under 35
U.S.C. .sctn.365(c) of International Application No.
PCT/KR2011/009164, filed Nov. 29, 2011, which claims priority to
Korean Application No. 10-2010-0119557, filed Nov. 29, 2010. The
entire contents of the aforementioned patent applications are
incorporated herein by this reference.
TECHNICAL FIELD
[0002] The present invention relates to a sintered bearing and a
method of manufacturing the same and, more particularly, to a
sintered bearing using kish graphite which is a byproduct of iron
production and to a method of manufacturing the same.
BACKGROUND ART
[0003] Kish graphite is one of many byproducts generated from
integrated iron and steel making processes in iron mills, including
a blast furnace process, an iron making process, a steel making
process, etc.
[0004] Kish graphite is mainly generated in blast furnaces, KR
facilities, TCC plants, slag treatment plants, etc.
SUMMARY OF THE DISCLOSURE
[0005] An object of the present invention is to provide a sintered
bearing and a method of manufacturing the same, in which kish
graphite which is a byproduct of iron production is added to metal
powder, thus manufacturing a sintered bearing which is improved in
durability, lubricity, etc.
[0006] In order to accomplish the above object, the present
invention provides a sintered bearing, comprising metal powder,
kish graphite, and a lubricant.
[0007] The sintered bearing may comprise, based on the total weight
thereof, 0.01.about.10 parts by weight of the kish graphite,
0.01.about.1.0 parts by weight of the lubricant, and a balance of
the metal powder.
[0008] The metal powder may be one or more selected from the group
consisting of a pure iron system, an iron-copper system, an
iron-carbon system, an iron-carbon-copper system, a bronze system,
and an iron-carbon-copper-nickel system.
[0009] The kish graphite may be a byproduct of iron production.
[0010] The present invention provides a method of manufacturing a
sintered bearing, comprising mixing metal powder, kish graphite,
and a lubricant, thus forming a powder mixture; applying pressure
to the powder mixture, thus forming a molded body; sintering the
molded body, thus forming a sintered body; and impregnating the
sintered body with oil.
[0011] The powder mixture may comprise, based on the total weight
thereof, 0.01.about.10 parts by weight of the kish graphite,
0.01.about.1.0 parts by weight of the lubricant, and a balance of
the metal powder.
[0012] The metal powder may be one or more selected from the group
consisting of a pure iron system, an iron-copper system, an
iron-carbon system, an iron-carbon-copper system, a bronze system,
and an iron-carbon-copper-nickel system.
[0013] The kish graphite may be in a powder form having a particle
size of 50 mesh or less.
[0014] The kish graphite may have a purity of 90.about.100% after
refining.
[0015] The lubricant may be any one or a mixture of two or more
selected from the group consisting of zinc stearate
(C.sub.36H.sub.70O.sub.4Zn), Acrawax
(C.sub.38H.sub.76N.sub.2O.sub.2), and Kenolube paraffin.
[0016] The forming the molded body may be performed by subjecting
the powder mixture to pressing at a pressure of 50.about.350 MPa at
room temperature.
[0017] The forming the molded body may be performed so that the
molded body has a compact density of 5.4.about.7.0 g/cm.sup.3.
[0018] The forming the sintered body may be performed at
850.about.1300.degree. C. under atmospheric pressure. The forming
the sintered body may be performed for 1.about.6 hr.
[0019] The impregnating with oil may be performed at
50.about.150.degree. C. in a vacuum.
[0020] According to the present invention, a sintered bearing is
manufactured by adding 0.01.about.10 parts by weight of kish
graphite to metal powder, thus exhibiting superior abrasion
resistance, strength and self-lubricity.
[0021] In particular, kish graphite having excellent slipping
properties enables self-lubricating action of the sintered bearing
upon initial operation, thus reducing the friction between a
bearing shaft and a pin, thereby facilitating the initial operation
and remarkably improving abrasion resistance of the sintered
bearing.
[0022] Also, kish graphite having high thermal conductivity can
rapidly emit the frictional heat of the sintered bearing,
ultimately decreasing abrasion loss.
[0023] Therefore, a high-quality sintered bearing can be supplied
to automobile industries and a variety of equipment industries, and
is favorable in terms of reducing the manufacturing cost and is
eco-friendly, by virtue of the recycling of kish graphite which is
a byproduct of iron production.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a graph illustrating the coefficient of friction
upon initial operation of the sample of Table 1;
[0025] FIG. 2 is a graph illustrating the coefficient of friction
upon initial operation of the sample of Table 2;
[0026] FIG. 3 is a graph illustrating the coefficient of friction
upon initial operation of the sample of Table 3;
[0027] FIG. 4 is a graph illustrating the coefficient of friction
upon initial operation of the sample of Table 4;
[0028] FIG. 5 is a graph illustrating the hardness and abrasion
loss of the samples of Examples 1 to 4 depending on changes in the
amount of added kish graphite and in the density of the sample;
[0029] FIG. 6 is a graph illustrating the hardness of the sintered
sample depending on the amount of added kish graphite;
[0030] FIG. 7 is a graph illustrating the coefficient of friction
upon initial operation of the sample of Table 5;
[0031] FIG. 8 is a graph illustrating the abrasion loss based on a
difference in the weight of the sample before and after an abrasion
test for 1 hr; and
[0032] FIG. 9 is a graph illustrating the hardness of the sintered
sample depending on the amount of added kish graphite.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0033] Hereinafter, a detailed description will be given of the
present invention.
[0034] According to the present invention, a sintered bearing
includes metal powder, kish graphite, and a lubricant.
[0035] The sintered bearing includes, based on the total weight
thereof, 0.01.about.10 parts by weight of kish graphite,
0.01.about.1.0 parts by weight of the lubricant, and a balance of
the metal powder.
[0036] The sintered bearing is a mechanical part used to rotate a
shaft which is fixed at a predetermined position, in automobiles,
electronic products, industrial machinery, construction machinery,
etc., while supporting the weight of the shaft and the load applied
to the shaft. The sintered bearing is manufactured by adding kish
graphite to metal powder so as to improve durability, lubricity,
etc.
[0037] Kish graphite is a byproduct of iron production.
[0038] Kish graphite is dispersed in a metallic bearing upon
sintering, thereby increasing strength of the bearing, and
functions as a solid lubricant so as to enable self-lubricating
action of the sintered bearing upon initial operation at which time
oil is not discharged.
[0039] Artificial graphite and natural graphite, which are not
metal components but are inorganic materials, function to interfere
with and suppress the sintering of a metallic bearing. Because of a
large specific volume, even when only ones of wt % of the above
graphite in a powder form is contained in metal, it is difficult to
perform molding and sintering of a bearing.
[0040] However, kish graphite has higher crystallinity compared to
typical artificial graphite and has a smaller lamellar thickness
compared to natural graphite. As a result of analyzing X-ray
diffraction, the crystalline lattice gap of kish graphite is 3.359
.ANG., which is similar to the theoretical value of graphite, and
the crystallinity calculated by the X-ray diffraction bandwidth of
d.sub.(002) plane is measured to be 178 .ANG..
[0041] Also, kish graphite has high thermal conductivity and thus
rapidly emits fractional heat of the sintered bearing, increases
abrasion resistance of the sintered bearing, and functions as a
solid lubricant upon initial operation, thus exhibiting superior
mechanical properties.
[0042] Kish graphite may include any kish graphite generated in
iron mills, and may contain a variety of impurities such as iron,
iron oxides, non-metal oxides, dust, etc., depending on the
generation site, and thus the trapped and collected kish graphite
is used after refining. Chemical refining treatment includes froth
flotation and pickling.
[0043] Preferably, kish graphite, which may be easily subjected to
trapping, collection and refining and has a purity of 10% or more,
is used. For example, kish graphite generated in KR (mechanical
stirring desulfurization) facilities and TCC (molten iron
treatment) plants is particularly useful. Kish graphite generated
in KR facilities has a density of 2.8 g/cm.sup.3 and a purity of
90.about.98%.
[0044] Kish graphite generated in KR facilities includes large dust
particles and SiO.sub.2 particles, but its purity is as high as 90%
or more, and thus only a mechanical separation process (separation
depending on size) is performed without additional chemical
refining treatment, making it possible to remove large dust
particles and SiO.sub.2 particles.
[0045] Kish graphite generated in TCC plants has a purity of about
60% and includes iron and iron oxides as impurities. Kish graphite
generated in TCC plants is preferably subjected to chemical
refining treatment and sorting, so that the purity thereof is
controlled to about 90% or more. The refined kish graphite is
sorted to a size of 50 mesh (300 .mu.m) or less before use, and the
recovery rate thereof is 90% or more. The large particles separated
via sorting may be reused via additional grinding.
[0046] As such, the purity of kish graphite and the composition of
impurities were analyzed using EPMA (Electron Probe Micro
Analyzer).
[0047] Kish graphite is contained in an amount of 0.01.about.10
parts by weight based on the total weight of the sintered bearing.
If the amount of kish graphite is less than 0.01 parts by weight
based on the total weight of the sintered bearing, improvements in
strength of the sintered bearing and self-lubricating action
thereof are insignificant. In contrast, if the amount thereof
exceeds 10 parts by weight, the strength of the sintered bearing
may increase but sinterability may deteriorate due to an excess of
kish graphite, undesirably lowering abrasion resistance.
[0048] Kish graphite is preferably contained in an amount of
0.5.about.5.0 parts by weight based on the total weight of the
sintered bearing, so as to enhance strength of the sintered bearing
and to improve self-lubricating action and sinterability. The
reason why the amount of kish graphite is limited as described
above is that the use of kish graphite exceeding 5.0 parts by
weight depending on the composition of metal powder may result in
deteriorated sinterability undesirably lowering abrasion
resistance.
[0049] The metal powder is any one or a mixture of two or more
selected from the group consisting of a pure iron system, an
iron-copper system, an iron-carbon system, an iron-carbon-copper
system, a bronze system, and an iron-carbon-copper-nickel system.
The metal powder is a main component of the sintered bearing, and
pure metal or a metal alloy is used in order to ensure mechanical
strength such as abrasion resistance, hardness, etc.
[0050] The lubricant plays a role in lubricating the bearing. The
lubricant is used in an amount of 0.01.about.1.0 parts by weight
based on the total weight of the sintered bearing. When the amount
of the lubricant falls in the above range, strength is not
decreased and lubrication effects may be exhibited.
[0051] The lubricant may be any one or a mixture of two or more
selected from the group consisting of zinc stearate
(C.sub.36H.sub.70O.sub.4Zn), Acrawax
(C.sub.38H.sub.76N.sub.2O.sub.2), and Kenolube paraffin.
[0052] The method of manufacturing the sintered bearing includes
mixing metal powder, kish graphite, and a lubricant, thus forming a
powder mixture, applying pressure to the powder mixture, thus
forming a molded body, sintering the molded body, thus forming a
sintered body, and impregnating the sintered body with oil.
[0053] Upon forming the powder mixture, the metal powder is mixed
with kish graphite and the lubricant, thus obtaining the powder
mixture. Kish graphite is contained in an amount of 0.01.about.10
parts by weight based on the total weight of the powder mixture,
the lubricant is contained in an amount of 0.01.about.1.0 parts by
weight based on the total weight of the powder mixture, and the
balance is metal powder.
[0054] The reason why kish graphite is used is that high-quality
flake graphite having very high crystallinity contained in kish
graphite is recycled, and thus kish graphite is refined so as to
use kish graphite having a purity of 90% or more. If the purity of
kish graphite is less than 90%, improvements in abrasion
resistance, lubricity, and strength of the sintered bearing are
insignificant.
[0055] Kish graphite in a powder form having a particle size of 50
mesh or less is used to facilitate the dispersion of carbon upon
sintering. To this end, refined kish graphite is sorted using a
sieve having an opening size of 50 mesh (300 .mu.m). Mesh is a unit
which indicates the opening of a sieve or the particle size.
[0056] The metal powder is any one or a mixture of two or more
selected from the group consisting of a pure iron system, an
iron-copper system, an iron-carbon system, an iron-carbon-copper
system, a bronze system, and an iron-carbon-copper-nickel
system.
[0057] The lubricant may be any one or a mixture of two or more
selected from the group consisting of zinc stearate
(C.sub.36H.sub.70O.sub.4Zn), Acrawax
(C.sub.38H.sub.76N.sub.2O.sub.2), and Kenolube paraffin.
[0058] Upon forming the powder mixture, a mixing process may be
performed using a super mixer or a high-speed mixer, and the mixing
rate may be set to 50.about.100 rpm and the mixing time may be set
to 1.about.120 min in order to accomplish homogeneous mixing.
[0059] Upon forming the molded body, the pressure applied to the
powder mixture is set to 50.about.350 MPa using a press of
10.about.30 tons, and pressing at room temperature is performed,
thus obtaining the molded body having a compact density of
5.4.about.7.0 g/cm.sup.3 and an internal porosity of 10.about.30
vol % relative to the total volume ratio.
[0060] If the pressure is less than 50 MPa, the molded body is not
formed. In contrast, if the pressure exceeds 350 MPa, the internal
porosity of the resulting sintered body is remarkably decreased,
making it difficult to impregnate the sintered body with oil. Also,
if the compact density is less than 5.4 g/cm.sup.3, the molded body
is not formed. In contrast, if the density exceeds 7.0 g/cm.sup.3,
porosity may decrease, making it impossible to impregnate the
sintered body with oil.
[0061] The molded body may be sintered at 850.about.1300.degree. C.
under atmospheric pressure for 1.about.6 hr. Upon sintering the
molded body, kish graphite is dispersed in the sintered body, so
that the sintered body is strengthened thus enhancing strength.
[0062] The sintering temperature 850.degree. C. corresponds to the
minimum temperature able to form the sintered body, and it is
unnecessary to use a high temperature exceeding 1300.degree. C. If
the sintering time is less than 1 hr, the sintering effect becomes
insignificant. In contrast, if the sintering time exceeds 6 hr, the
internal porosity of the sintered body may decrease due to
excessive sintering.
[0063] The sintered bearing has pores therein due to the sintering,
and oil functions to impregnate the pores of the sintered bearing
therewith, thus increasing the strength of the sintered bearing.
Impregnation with oil is performed in a vacuum at
50.about.150.degree. C.
[0064] Upon impregnation with oil, if the temperature is lower than
50.degree. C., there is no oil fluidity, making it impossible to
perform impregnation. In contrast, if the temperature is higher
than 150.degree. C., deformation of oil components may occur.
[0065] The method of manufacturing the sintered bearing according
to the present invention enables recycling of waste kish graphite
and is thus eco-friendly, and enables the abrasion resistance of
the sintered bearing to be increased and the self-lubricity to be
ensured.
[0066] A better understanding of the present invention may be
obtained via the following examples which are set forth to
illustrate, but are not to be construed as limiting the present
invention.
Example 1
[0067] NC100.24 powder as pure iron powder, kish graphite powder
having a particle size of 300 .mu.m or less, and zinc stearate as a
lubricant were mixed, thus preparing a powder mixture of Table 1
below. For reference, NC100.24 is the trade name of pure iron
powder available from Hoganas.
[0068] Mixing was performed using a high-speed mixer at a rotation
rate of 100 rpm for 10 min. The prepared powder mixture was
subjected to pressing at room temperature using a 20-ton press,
thus obtaining an abrasion resistance test sample having a compact
density of 5.6 g/cm.sup.3 with a disc shape.
[0069] The disc shaped sample was sintered at 1000.degree. C. for 3
hr.
[0070] Table 1 below shows the composition of the sample of Example
1.
TABLE-US-00001 TABLE 1 Kish graphite Zinc stearate Density NC100.24
(wt %) (wt %) (wt %) (g/cm.sup.3) Note 99.2 0 0.8 5.6 98.7 0.5 0.8
5.6 98.2 1.0 0.8 5.6 96.2 3.0 0.8 5.6 94.2 5.0 0.8 5.6 93.2 6.0 0.8
5.6 Deteriorated Sinterability
[0071] FIG. 1 illustrates the coefficient of friction upon initial
operation of the sample of Table 1 (In FIG. 1, KG indicates kish
graphite).
[0072] As is apparent from Table 1 and FIG. 1, when kish graphite
was added in an amount of 3.0 wt %, the maximum initial coefficient
of friction was 0.088, which was lower compared to when the amount
of added kish graphite was 0, 0.5 and 1.0 wt %, thus exhibiting low
abrasion of the sample upon initial operation.
[0073] Although not shown in FIG. 1, when the amount of kish
graphite was 6.0 wt %, abrasion of the sample occurred easily,
undesirably deteriorating the sinterability of the sample.
Example 2
[0074] NC100.24 powder as pure iron powder, kish graphite powder
having a particle size of 300 .mu.m or less, and zinc stearate as a
lubricant were mixed, thus preparing a powder mixture of Table 2
below.
[0075] Mixing was performed using a high-speed mixer at a rotation
rate of 100 rpm for 10 min. The prepared powder mixture was
subjected to pressing at room temperature using a 20-ton press,
thus obtaining an abrasion resistance test sample having a compact
density of 6.0 g/cm.sup.3 with a disc shape.
[0076] The disc shaped sample was sintered at 1000.degree. C. for 3
hr.
[0077] Table 2 below shows the composition of the sample of Example
2.
TABLE-US-00002 TABLE 2 Kish graphite Zinc stearate Density NC100.24
(wt %) (wt %) (wt %) (g/cm.sup.3) Note 99.2 0 0.8 6.0 98.7 0.5 0.8
6.0 98.2 1.0 0.8 6.0 96.2 3.0 0.8 6.0 94.2 5.0 0.8 6.0 93.2 6.0 0.8
6.0 Deteriorated Sinterability
[0078] FIG. 2 illustrates the coefficient of friction upon initial
operation of the sample of Table 2.
[0079] As is apparent from Table 2 and FIG. 2, the coefficient of
friction upon initial operation of the sample was decreased in
proportion to an increase in the amount of added kish graphite.
When the amount of added kish graphite was 3.0 wt %, the maximum
initial coefficient of friction was 0.059, which was lower compared
to when the amount of added kish graphite was 0, 0.5 and 1.0 wt %,
thus exhibiting low abrasion of the sample upon initial
operation.
[0080] Although not shown in FIG. 2, when the amount of kish
graphite was 6.0 wt %, abrasion of the sample occurred easily,
undesirably deteriorating the sinterability of the sample.
Example 3
[0081] NC 100.24 powder as pure iron powder, kish graphite powder
having a particle size of 300 .mu.m or less, and zinc stearate as a
lubricant were mixed, thus preparing a powder mixture of Table 3
below.
[0082] Mixing was performed using a high-speed mixer at a rotation
rate of 100 rpm for 10 min. The prepared powder mixture was
subjected to pressing at room temperature using a 20-ton press,
thus obtaining an abrasion resistance test sample having a compact
density of 6.4 g/cm.sup.3 with a disc shape.
[0083] The disc shaped sample was sintered at 1000.degree. C. for 3
hr.
[0084] Table 3 below shows the composition of the sample of Example
3.
TABLE-US-00003 TABLE 3 Kish graphite Zinc stearate Density NC100.24
(wt %) (wt %) (wt %) (g/cm.sup.3) Note 99.2 0 0.8 6.4 98.7 0.5 0.8
6.4 98.2 1.0 0.8 6.4 96.2 3.0 0.8 6.4 94.2 5.0 0.8 6.4 93.2 6.0 0.8
6.4 Deteriorated Sinterability
[0085] FIG. 3 illustrates the coefficient of friction upon initial
operation of the sample of Table 3.
[0086] As is apparent from Table 3 and FIG. 3, the coefficient of
friction upon initial operation of the sample was decreased in
proportion to an increase in the amount of added kish graphite.
When the amount of added kish graphite was 3.0 wt %, the maximum
initial coefficient of friction was 0.086, which was lower compared
to when the amount of added kish graphite was 0, 0.5 and 1.0 wt %,
thus exhibiting low abrasion of the sample upon initial
operation.
[0087] Although not shown in FIG. 3, when the amount of kish
graphite was 6.0 wt %, abrasion of the sample occurred easily,
undesirably deteriorating the sinterability of the sample.
Example 4
[0088] NC100.24 powder as pure iron powder, kish graphite powder
having a particle size of 300 .mu.m or less, and zinc stearate as a
lubricant were mixed, thus preparing a powder mixture of Table 4
below.
[0089] Mixing was performed using a high-speed mixer at a rotation
rate of 100 rpm for 10 min. The prepared powder mixture was
subjected to pressing at room temperature using a 20-ton press,
thus obtaining an abrasion resistance test sample having a compact
density of 6.8 g/cm.sup.3 with a disc shape.
[0090] The disc shaped sample was sintered at 1000.degree. C. for 3
hr.
[0091] Table 4 below shows the composition of the sample of Example
4.
TABLE-US-00004 TABLE 4 Kish graphite Zinc stearate Density NC100.24
(wt %) (wt %) (wt %) (g/cm.sup.3) Note 99.2 0 0.8 6.8 98.7 0.5 0.8
6.8 98.2 1.0 0.8 6.8 96.2 3.0 0.8 6.8 94.2 5.0 0.8 6.8 93.2 6.0 0.8
6.8 Deteriorated Sinterability
[0092] FIG. 4 illustrates the coefficient of friction upon initial
operation of the sample of Table 4.
[0093] As is apparent from Table 4 and FIG. 4, when the amount of
added kish graphite was 3.0 wt %, the maximum initial coefficient
of friction was 0.094, which was lower compared to when the amount
of added kish graphite was 0, 0.5 and 1.0 wt %, thus exhibiting low
abrasion of the sample upon initial operation.
[0094] Although not shown in FIG. 4, when the amount of kish
graphite was 6.0 wt %, abrasion of the sample occurred easily,
undesirably deteriorating the sinterability of the sample.
[0095] FIG. 5 illustrates the hardness and abrasion loss of the
samples of Examples 1 to 4 depending on changes in the amount of
added kish graphite and in the density of the sample.
[0096] In FIG. 5, the abrasion loss based on the difference in the
weight of the sample before and after an abrasion test for 1 hr is
depicted.
[0097] As illustrated in FIG. 5, the samples containing
0.5.about.3.0 wt % of kish graphite were lower in abrasion loss
compared to the sample without kish graphite. When the amount of
added kish graphite was 3.0 wt %, abrasion loss was
0.049.about.0.067 g, which was evaluated to be the lowest among all
the density conditions.
[0098] FIG. 6 illustrates the hardness of the sintered sample
depending on the amount of added kish graphite.
[0099] As illustrated in FIG. 6, the hardness of the sample was
increased in proportion to an increase in the amount of added kish
graphite. This is because carbon is dispersed in the pure
iron-based master alloy in proportion to an increase in the amount
of kish graphite in the pure iron-based sample, thus enhancing the
strength of the sample.
Example 5
[0100] NC 100.24 powder as pure iron powder, DMH powder comprising
pure iron-25 wt % copper powder, kish graphite powder having a
particle size of 300 .mu.m or less, and zinc stearate as a
lubricant were mixed, thus preparing a powder mixture of Table 5
below.
[0101] Mixing was performed using a high-speed mixer at a rotation
rate of 100 rpm for 10 min. The prepared powder mixture was
subjected to pressing at room temperature using a 20-ton press,
thus obtaining an abrasion resistance test sample having a compact
density of 6.0 g/cm.sup.3 with a disc shape.
[0102] The disc shaped sample was sintered at 1000.degree. C. for 3
hr.
[0103] Table 5 below shows the composition of the sample of Example
5.
TABLE-US-00005 TABLE 5 Kish NC100.24 DMH graphite Zinc stearate
Density (wt %) (wt %) (wt %) (wt %) (g/cm.sup.3) Note 91.2 8.0 0
0.8 6.0 90.2 8.0 1.0 0.8 6.0 89.2 8.0 2.0 0.8 6.0 88.2 8.0 3.0 0.8
6.0 87.2 8.0 4.0 0.8 6.0 81.2 8.0 10.0 0.8 6.0 Deteriorated
Sinterability
[0104] FIG. 7 illustrates the coefficient of friction upon initial
operation of the sample of Table 5.
[0105] As is apparent from Table 5 and FIG. 7, when the amount of
added kish graphite was 2.0 wt %, the maximum initial coefficient
of friction was 0.063, which was lower compared to when the amount
of added kish graphite was 0, 1.0, 3.0 and 4.0 wt %, thus
exhibiting low abrasion of the sample upon initial operation.
[0106] When comparing the amounts of kish graphite in the pure
iron-based samples of Examples 1 to 4 and the iron-copper-based
sample of Example 5, the amount of added kish graphite should be
appropriately adjusted depending on the composition of metal
powder.
[0107] FIG. 8 illustrates the abrasion loss based on the difference
in the weight of the sample before and after an abrasion test for 1
hr.
[0108] As illustrated in FIG. 8, when 2 wt % of kish graphite was
added to the iron-copper-based alloy, abrasion loss was 0.038 g
which was evaluated to be the lowest, and then abrasion loss was
increased in proportion to an increase in the amount of kish
graphite.
[0109] FIG. 9 illustrates the hardness of the sintered sample
depending on the amount of added kish graphite.
[0110] As illustrated in FIG. 9, the hardness of the sample was
increased in proportion to an increase in the amount of kish
graphite in the iron-copper-based alloy. This is because carbon of
kish graphite is dispersed in the iron-copper-based master alloy as
the amount of kish graphite added to the iron-copper-based alloy
increases, thus enhancing the strength of the sample.
[0111] Consequently, in the iron-copper-based sintered bearing,
when kish graphite was contained in an amount of 2.0 wt %, not only
initial lubricity but also effects of enhancing strength and
reducing abrasion loss were superior.
[0112] Thereby, upon manufacturing the sintered bearing, kish
graphite is added in an amount of 0.01.about.10 parts by weight so
that abrasion resistance of the sintered bearing is enhanced and
lubricity is imparted, resulting in a sintered bearing having high
durability.
[0113] The scope of the present invention is not limited to the
above examples but rather is defined as disclosed in the
accompanying claims, and those skilled in the art will appreciate
that various modifications and adaptations are possible, without
departing from the scope described in the claims.
[0114] The present invention can provide a high-quality sintered
bearing for automobile industries and a variety of equipment
industries. Because kish graphite which is a byproduct of iron
production can be recycled upon manufacturing the sintered bearing,
the method of the invention is favorable in terms of reducing the
manufacturing cost and is eco-friendly.
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