U.S. patent application number 11/257552 was filed with the patent office on 2006-02-16 for process for making a roller chain.
This patent application is currently assigned to Tsubakimoto Chain Co.. Invention is credited to Isamu Okabe, Takashi Tohara.
Application Number | 20060032207 11/257552 |
Document ID | / |
Family ID | 19195952 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032207 |
Kind Code |
A1 |
Okabe; Isamu ; et
al. |
February 16, 2006 |
Process for making a roller chain
Abstract
In a roller chain having cylindrical pins rotatably fitting into
bushings on which the rollers are disposed, a vanadium carbide
layer formed on the cylindrical pin surfaces avoids abnormal wear
elongation of the chain, and allows smooth articulation of the
chain over a long period of time, even when the lubricating oil is
in an extremely deteriorated condition due to oxidation.
Inventors: |
Okabe; Isamu; (Osaka,
JP) ; Tohara; Takashi; (Osaka, JP) |
Correspondence
Address: |
HOWSON AND HOWSON;ONE SPRING HOUSE CORPORATION CENTER
BOX 457
321 NORRISTOWN ROAD
SPRING HOUSE
PA
19477
US
|
Assignee: |
Tsubakimoto Chain Co.
Osaka
JP
|
Family ID: |
19195952 |
Appl. No.: |
11/257552 |
Filed: |
October 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10444302 |
May 23, 2003 |
|
|
|
11257552 |
Oct 25, 2005 |
|
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Current U.S.
Class: |
59/4 |
Current CPC
Class: |
F16G 13/06 20130101 |
Class at
Publication: |
059/004 |
International
Class: |
B21L 9/02 20060101
B21L009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2002 |
JP |
2002-213944 |
Claims
1. A process for making a roller chain comprising: subjecting a pin
having a cylindrical surface and two ends, and containing 0.1 to
0.4 wt % carbon, along with manganese and silicon, and further
containing chromium, molybdenum, or both chromium and molybdenum,
with the balance being iron and impurities, to sufficient
carburization hardening to form a high-carbon surface layer having
a carbon content of 0.7 to 1.0% on the cylindrical surface of the
pin; thereafter forming a hardened vanadium carbide layer on said
high-carbon surface layer by a powder penetration process in which
vanadium powder or vanadium alloy powder is added to said high
carbon surface layer of the pin, and the vanadium carbide layer is
subjected to heat treatment; and incorporating said pin into a
roller chain comprising a pair of inner plates in side-by-side,
spaced, relationship and having outwardly facing surfaces, a pair
of outer plates disposed adjacent said outwardly facing surfaces of
the respective inner plates, a cylindrical bushing, and a roller
surrounding said bushing, by passing said pin though said bushing,
wherein the pin fits rotatably in said bushing, the ends of the
bushing are fixed to said inner plates, and the ends of the pin are
fixed to said outer plates.
2. The process according to claim 1, in which the heat treatment is
carried out at a temperature in the range from 900.degree. C. to
1100.degree. C., for 5 to 25 hours.
3. The process of making a roller chain power transmission
comprising the steps of: subjecting pins having a cylindrical
surface and two ends, and containing 0.1 to 0.4 wt % carbon, along
with manganese and silicon, and further containing chromium,
molybdenum, or both chromium and molybdenum, with the balance being
iron and impurities, to sufficient carburization hardening to form
a high-carbon surface layer having a carbon content of 0.7 to 1.0%
on the cylindrical surface of the pin; thereafter forming a
hardened vanadium carbide layer on said high-carbon surface layer
by a powder penetration process in which vanadium powder or
vanadium alloy powder is added to said high carbon surface layer of
the pin, and the vanadium carbide layer is subjected to heat
treatment; incorporating said pins into a roller chain the links of
which comprise pairs of inner plates in side-by-side, spaced,
relationship and having outwardly facing surfaces, pairs of outer
plates disposed adjacent said outwardly facing surfaces of the
respective inner plates, cylindrical bushings, and rollers
surrounding said bushings, by passing each of said pins though one
of said bushings, wherein the pins fit rotatably in said bushings,
the ends of the bushings are fixed to inner plates, and the ends of
the pins are fixed to outer plates; and incorporating the roller
chain thus made into a power transmission, wherein the chain is
lubricated by oil subject to deterioration by oxidation.
4. The process according to claim 3, in which the heat treatment is
carried out at a temperature in the range from 900.degree. C. to
1100.degree. C., for 5 to 25 hours.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of application Ser. No. 10/444,302,
filed May 23, 2003, now abandoned. The disclosure of application
Ser. No. 10/444,302 is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a roller chain of the kind used for
power transmission mechanism in an automobile or industrial
machine, and in a conveyor mechanism, and more particularly to a
process for making the roller chain.
BACKGROUND OF THE INVENTION
[0003] Metal roller chains have come into increasing use, instead
of toothed belts, as power transmission media in automobiles
because of the demand for high load capacity, high speed, and
maintenance-free operation.
[0004] In conventional roller chain configuration, both ends of a
cylindrical bushing are fixed to a pair of inner plates of the
chain by fitting into bushing holes in the inner plates. A pin fits
rotatably into, and extends through, the bushing. The ends of the
pin are fixed to a pair of outer plates disposed outside the inner
plates. A roller fits rotatably on the bushing.
[0005] In conventional roller chains, in order to obtain improved
strength and avoidance of wear elongation, the pins have been
subjected to heat treatment such as quench hardening/tempering,
carburization hardening/carburization tempering or the like. In
some roller chains, a chromium carbide layer is formed on the pin
surface.
[0006] In spite of the heat treatment of the pins, and the
formation of a chromium carbide layer on the surfaces of the pins
in chains used as timing chains in automobile engines and the like,
it has been reported that a small number of chains do not exhibit
the expected wear resistance, and abnormal wear elongation occurs.
Therefore, there was an urgent need to eliminate abnormal wear
elongation in order to achieve an improvement in the reliability of
the engine.
[0007] As a result of our continued study of this problem, we have
found that the abnormal wear elongation of the roller chains is
caused by the fact that lubricating oil in the engine becomes
extremely deteriorated, and when the oxidation of the lubricating
oil causes the pH of the oil to be less than 3, the pin surfaces
become corroded by the lubricating oil, and wear of the pin surface
is accelerated through sliding contact with its bushing. It has
also become clear that powder generated by the wear of the pin
surface exists as an inclusion between the pin and the bushing,
causing further acceleration of wear by abrasion of the sliding
contact surfaces of the pin and the bushing. It has also become
clear that, when the pin and the bushing are made of materials
having a high affinity for each other, both materials are liable to
agglomerate, and the agglomeration of these materials causes
further acceleration of wear.
[0008] Accordingly, the principal objects of this invention are to
solve the above-described problems of conventional roller chains,
and to provide a roller chain which does not exhibit abnormal wear
elongation, and which articulates smoothly over a long period of
time, even when lubricated by an extremely deteriorated oil having
a high degree of oxidation.
[0009] In a roller chain in accordance with the invention, a pair
of inner plates, having outwardly facing surfaces, are provided in
side-by-side relationship, and two outer plates are disposed
adjacent the outwardly facing surfaces of the inner plates. A
cylindrical bushing has its ends fixed to bushing holes of the
inner plates, and a pin having a cylindrical pin surface fits
rotatably in the bushing, with its ends fixed to pin holes in the
outer plates. A roller fits rotatably onto the bushing. The chain
is characterized by a vanadium carbide layer formed on the
cylindrical pin surfaces.
[0010] Each connecting pin of the roller chain in accordance with
the invention has a cylindrical surface and two ends, and contains
0.1 to 0.4 wt % carbon, along with manganese and silicon, and
further contains chromium, molybdenum, or both chromium and
molybdenum, with the balance being iron and impurities. The pin is
subjected to sufficient carburization hardening to form a
high-carbon surface layer having a carbon content of 0.7 to 1.0% on
the cylindrical surface of the pin. Thereafter, a hardened vanadium
carbide layer is formed on the high-carbon surface layer by a
powder penetration process in which vanadium powder or vanadium
alloy powder is added to the high carbon surface layer of the pin,
and the vanadium carbide layer is subjected to heat treatment,
preferably carried out at a temperature in the range from
900.degree. C. to 1100.degree. C., for 5 to 25 hours. The pin is
incorporated into a roller chain by passing said pin though a
bushing of the chain.
[0011] The vanadium carbide layer formed on the pin surfaces
improves the corrosion resistance of the pins, allowing the chain
to articulate smoothly over a long period of time without abnormal
wear elongation, even in the low pH environment caused by
deterioration of lubricating oil. Furthermore, since the vanadium
carbide is formed on the pin surface, the affinity between the pin
and the bushing is reduced, and agglomeration of particles
resulting from wear of both the pin and the bushing is
prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an exploded perspective view showing a portion of
a roller chain in accordance with the invention;
[0013] FIG. 2 is a graph showing the results of chain elongation
tests, in oxidized, deteriorated oil, of conventional roller
chains, and a roller chain according to invention;
[0014] FIG. 3 is a graph showing the results of chain elongation
tests, in new oil, of conventional roller chains, and a roller
chain according to invention; and
[0015] FIG. 4 is a graph showing the results of chain elongation
tests, in soot-containing oil, of conventional roller chains, and a
roller chain according to invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] In FIG. 1, the assembled structure of a portion of the
roller chain 10 is shown along with the individual parts of the
chain. Both ends of a cylindrical bushing 12 are fixed to bushing
holes 11a in a pair of inner plates 11. Pins 15 are inserted
through the bushings 12, and rotatable therein. The ends of the
pins are fixed to pin holes 14a in a pair of outer plates 14
disposed adjacent the outer sides of the pair of inner plates 11. A
roller 13 is rotatably fitted onto the bushing 12.
[0017] In the roller chain of the invention, a hardened layer of
vanadium carbide, having a thickness of 6 to 20 .mu.m, is formed on
the cylindrical surface of the pins. The pin is formed by the
following process. First, a pin containing 0.1 to 0.4 wt % carbon,
along with manganese and silicon, and further containing chromium,
molybdenum, or both chromium and molybdenum, with the balance being
iron and impurities, is subjected to carburization hardening to
form a high-carbon surface layer having a carbon content of 0.7 to
1.0% on the surface layer of the material. Then, a hardened
vanadium carbide layer is formed on the pin surface layer by a
powder penetration process in which vanadium powder or vanadium
alloy powder is added to the pin surface layer and subjected to
heat treatment, at a high temperature in the range from 900.degree.
C. to 1100.degree. C., for 5 to 25 hours.
[0018] FIGS. 2 to 4 show the results of chain elongation tests,
which were carried out in order to evaluate the wear resistance of
the roller chain according to the invention, and to compare its
wear resistance with the wear resistance of conventional roller
chains. FIG. 2 shows the results of tests carried out on chains
lubricated in oxidized, deteriorated oil. FIG. 3 shows the results
of tests carried out on chains lubricated in new oil. FIG. 4 shows
the results of tests carried out on chains lubricated by oil
containing abrasive carbon soot as its principal contaminant. In
conventional example 1 a carburized pin was used, and chromium
carbide was formed on the surface of the pin of conventional
example 2.
[0019] As shown in FIG. 3, in new oil, the elongation of the roller
chain of the invention was about 1/3 the elongation of the chain of
conventional example 1, having a carburized pin. However, the
elongation of the roller chain of the invention in new oil was no
better than that of conventional example 2, in which a pin having a
surface layer of chromium carbide was used.
[0020] However, as shown in FIG. 2, in oxidized deteriorated oil,
the elongation of the roller chain of the invention was about 2/3
the elongation of the chain of conventional example 2. Furthermore,
as shown in FIG. 4, the elongation properties of the roller chain
of the invention are superior to those of conventional examples 1
and 2 in soot-containing oil.
[0021] These test results lead to the conclusion that, in the
roller chain of the invention, wear resistance in oxidized
deteriorated oil is significantly improved, since vanadium carbide
has corrosion resistance superior to that of chromium carbide in
the deteriorated oil environment. Furthermore, since the roller
chain pins having a vanadium carbide layer are harder than those
subjected to carburization heat treatment and also harder than
those having a chromium carbide layer, the wear resistance
properties of the roller chain in accordance with the invention are
superior in soot-containing oil.
[0022] Heretofore, surface treatment by the formation of a vanadium
carbide layer was not recognized to be significantly advantageous
as compared with other surface treatments such as carburization
heat treatment and the formation of chromium carbide layer.
However, vanadium carbide has proven to be highly superior as a
coating material for the pins of a roller chain used under severe
conditions such as in oxidized deteriorated oil or in
soot-containing oil.
[0023] The vanadium carbide layer formed on the pin surfaces
improves the corrosion resistance of the pins and dramatically
improves their wear resistance properties in oxidized, deteriorated
oil. As a result, excellent durability and reliability of the
roller chain are achieved, and abnormal elongation of the chain is
avoided over a long period of time. Consequently, noise, tooth
jumping, and impaired performance due to increased wear elongation
of the chain, are avoided.
[0024] Even if a foreign substance such as carbon or the like
enters the lubricating oil, the roller chain articulates smoothly
without abrasion. Furthermore, with the roller chain of the
invention, the time between oil changes is increased, and a
reduction in the cost of operation is made possible. Moreover,
since a vanadium carbide layer can be formed by the same
conventional production process used in forming a chromium carbide
layer, there is no increase in the cost of production of the roller
chain.
[0025] By way of summary, we have found that abnormal wear
elongation of a roller chain is due to the oxidation and
deterioration of the lubricating oil, and taking this observation
into account, we have determined that vanadium carbide is the most
suitable material for coating the surfaces of the pins of the
roller chain. The invention has a high technical significance in
industry, since it allows abnormal wear elongation to be
reproducibly avoided.
* * * * *