Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF_HE INVENTION
1. Field of the Invention
The present invention relates to a sliding part ana a method
for producing the same, said sliding part consisting of a shaft
and a bearing, the former fitting into the latter, such as a com-
bination of a journal and a ~ournal bearing and a combination of
a spline shaft (internal spline) and a hub (external spline).
More particularly, the present invention relates to a sliding
part in which a resin lining is formed on the bearing surface of
the hearing by monomer casting, and it also relates to a method
for producing the sliding part.
2. Description of the Prior ~rt
Sliding parts with a resin lining have been in general use
in automobiles and many other machines. ~he conventional sliding
parts fall under two broad categories: (A) There are sliding
parts constructed of a shaft, a bearing and a bushing interposed
between them, said bushing being formed by coating a flat, metal
plate ~ith a resin, cutting the coated plate to proper size,
curling the cut plate, and fitting the curled plate into the
bearing surface of the bearing, as in the case of a Teflon CT~
resin-coated bushing. (B) There are sliding parts constructed
of a bearing with the bearing surface thereof directly coated
with a resin and a shaft machined to fit into the bearing.
The sliding parts belonging to category (A) have the follow-
ing disadvantages: (1) Both the lining and the shaft should
have a considerably high dimensional accuracy, which sometimes
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needs the selective fitting of accurately matching parts. (~)
Depending on the shape of the bearing surface, it may be diffi-
cult to fit the lining (3) The production cost of the lining
is high. On the other hand, the sliding parts belonging to cate-
gory (B) have the following disadvantages. (1) The machining of
the shaft is indispensable, which adds to the cost of the sliding
part. (2) The machining of the shaft should be performed with
high accuracy and selective fitting may be necessary in some in-
stances.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
sliding part having a highly accurate clearance at sliding
interfaces and outstanding sliding performance.
It is another object of the present invention to provide a
method for producing with ease and certainty a sliding part of
high accuracy and high performance regardless of the dimensional
accuracy of the shaft and bearing.
The present invention is based on the so-called monomer
casting in which a molded item is produced by castiny a monomer,
followed by polymerization and curing, as employed in the case of
nylon monomer casting.
The sliding part of this invention comprises a bearing, a
shaft which is rotably or reciprocatably supported by and fitting
into the bearing, and a lining of resin formed on the bearing
surface of the bearing. The resin lining is formed by pouring a
low-viscosity monomer or prepolymer into a clearance between the
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bearing surface and the shaft and permitting the monomer or
prepolvmer to polymeriæe or cure in situ. The shaft slides on
the resin lining.
The shaft may constit~te an internal spline and the bearing
an external spline. Either the external spline or the internal
spline may be provided with a groove constituting a well for
receiving resin poured into the clearance between the external
and internal splines. The resin lining may be a thin film of
polyamide resin, urethane resin, epoxy resin or polyester resin
The method of this invention for producing the sliding part
by monomer casting is accomplished by pouring a low-viscosity
monomer or prepolymer into a clearance between a shaft and the
bearing surface of a bearing. ~he shaft is fitted into the
bearing and is rotatably or reciprocatably supported by the
bearing and specifically the bearing surface. After polymeriza-
tion and curing, the monomer forms a resin lining on the bearing
surface of the bearing, and the shaft slides on the resin lining.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing the relation between the thickness
and the compression strength of the resin lining of the present
invention;
Fig. 2 is a sectional view of the sliding part of Example 1
of this invention;
Fig. 3 is a plan view of the sliding part as shown in Fig.
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Fig. 4 is a sectional view of the sliding part of Example 2
of this invention;
Fig. 5 is a sectional view of the sliding part of ~xample 3
of this invention;
Fig. 6 is an enlarged sectional view taken along the line
VI-VI of Fig. 5;
Fig. 7 is an enlarged sectional view taken along the line
VII-VII of Fig. 5;
Fig. 8 is a sectional view of the sliding part of Example 4
of this invention;
Fig. 9 is an enlarged sectional view taken along the line
IX-IX of Fiy. 8; and
Fig. 10 is an enlarged sectional view taken along the line
X-X of Fig. 8.
The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments
of the invention and, together with the description, serve to ex-
plain the principles of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The sliding part of this invention is produced in the fol-
lowing manner. At first, a shaft is fitted into a bearing and
rotatably or reciprocatably supported by the bearing, primarily
in the ,axial direction. The bearing may be separate and indepen-
dent or integral with the machine proper. Next, a monomer or a
low-viscosity prepolymer of a suitable resin, such as polyamide
resin, urethane resin, epoxy resin or pPlyester resin, which may
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be incorporated with a polymerization initiator according to
need, is poured into the clearance between the shaft and the
bearing surface of the bearing. The monomer or prepolymer is
polymerized or cured by heating or irradiation. A resin lining
is thus formed on the bearing surface in the existing clearance
between the shaft and the bearing surface of the bearing. Prior
to the pouring of a monomer, the bearing should be provided with
proper masking excluding the bearing surface, because it is dif-
ficult to remove the unnecessary resin lining after polymeriza-
tion. For the uniform, smooth polymerization of the monomer, it
may be desirable to preheat the shaft and bearing to a tempera-
ture suitable for polymerization prior to the pouring of the
monomer. In addition, it is also desirable to apply a proper
primer to the bearing surface of the bearing and a proper mold
release to the shaft. The primer ensures the firm adherence of
the resin lining to the bearing surface of the bearing. The
polymerization initiator shoulcl be properly selected according to
the monomer used. For example, Eor caprolactam (monomer or
nylon-6), lactam anion and acyl lactam are recommended.
The polymerization of the monomer is usually accompanied by
a certain degree of molding shrinkage. This molding shrinkage
gives rise to a very small amount of clearance between the shaft
and the resin lining when the resin lining is formed. The amount
of clearance is as Eollows in the case where the resin lining is
made of nylon-6. The molding shrinkage of nylon-6 is 14 to 16%
(by volume) and it corresponds to a linear shrinkage of 4 to 5%
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across the thickness or cross-section when nylon-6 is used as a
thin film. If the clearance between the shaft and the bearing
surface is about 0.2 mm and the resin lining of nylon-6 is formed
in the clearance, the shrinkage of nylon-6 is about 8 to ~0 um.
It follows, therefore, that a very small amount of clearance
(about 8 to 10 um) is formed between the shaft and the resin lin-
ing. Such a small anmount of clearance will be possible only
with with extremely accurate machining. According to the present
invention, the high precision clearance can be obtained easily
even though the shaft and the bearing are characterized by low
dimensional accuracy. The sliding part of the present invention
is formed in situ,and according to the method of the invention,
it is not necessary to select a shaft and a bearing that mate
with each other. In addition, it is not necesary to machine the
shaft and the bearing to high accuracy to achieve a close fit.
In spite of the good sliding characteristics, resin linings
have not been effectively utilized for sliding parts that gener-
ate significant frictional heat resulting ~rom repeated sliding
motion because of the following disadvantages. Resins undego a
great amount of creep or deformation at high temperatures, and
they exhibit low thermal conductivity, which is responsible for
their low critical PV value. In this invention, these disadvan-
tages are eliminated. The resin lining produced in accordance
with this invention in the form of a thin film between the shaft
and the bearing has a greatly increased compression strength
resulting from the support provld~d by the bearing metal. In the
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case of resin lining made of nylon-6, the compression strength
remarkabl~ increases if the lining is thinner than about 0.6 mm,
as shown in Fig. 1. In addition, such a thin resin lining per-
mits rapid heat dissipation and consequently provides an improved
critical PV value. Thus the sliding part of this invention has
high performance. That is the resin lining fully utilizes the
sliding characteristics of the resin; the resin lining is greatly
improved in compression strength and resistance to deformation;
and the resin lining permits rapid heat dissipation, providing an
improved critical PV value. The sliding part of the invention is
produced simply by pouring a monomer into the clearance between
the sliding interfaces, which results in low production cost.
The sliding part of this invention may be advantageously applied
to various functional parts where sliding motion frequently and
repeatedly takes place, such as a crank shaft and crank journal
bearing, cam shaft and cam-shaft journal bearing, and transmis-
sion.
According to the method of this invention, the resin lining
is formed in situ by monomer casting. Since the resin lining is
in the form of a thin layer, a sliding part with high accuracy
and high performance can be produced regardless of the
dimensional accuracy of the associated shaft and bearing. In
adidtion, the monomer casting can be accomplished without the
application of pressure and heat, and consequently the sliding
part can be produced easily and at a low cost.
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The invention is described with reference to a slide spline
consisting of an internal spline and an external spline. Nylon
monomer is poured into the clearance between the two components
and cured therein so that a resin lining is formed on either of
the two components. In the preferred slide spline, at least
either the internal spline or external spline is provided with a
groove to receive excess monomer so that no flash is formed. The
absence of flash eliminates the need for fabrication operations,
such as deflashing, which impairs the product precision and slide
performance.
S PEC I F I C EXAMP LES
EXAMPLE 1
In Fi~s. 2 and 3, there is shown an external spline 1 and an
internal spline 2 which is fitted into and reciprocatably sup-
ported by the external spline. There is also shown a resin lin-
ing 3 of nylon-6 formed on the inner surface 4 of the external
spline 2. A centering pin 5 and centering hole 6 are provided at
an end of the internal spline 2.
The sliding part in this example was produced as follows:
First, the external spline 1 was coated with a primer and the in-
ternal spline 2 was coated with a release agent. The external
spline 1 and the internal spline 2 were preheated to 130 to 160C
within which temperature range the monomer of nylon-6 poly-
merizes. A proper amount of the monomer of nylon-6 containing
the polymerization initiator (lactam anion and acyl lactam) was
poured into the external spline 1, and then the internal spline 2
: . . . , . . . - . . .
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was fitted into the external spline 1, whereby the clearance (t =
about 0.2 mm) between the external spline and the internal spiine
was filled with the nylon monorner. The nylon monomer was poly-
merized at a temperature of 130 to 160C. This resulted in the
formation of a resin lining 3 on the surface 4 of the external
spline 1. The sliding part thus produced allowed the internal
spline 2 to slide on the resin lining 3 without any play.
EXAMPLE 2
In this example, the sliding part of the invention was
applied in the prodiction of a manual transmission gear, as shown
in Fig. 4. This gear has a bearing 7, a shaft 8 fitted into the
bearing and rotatably supported by the bearing, and a resin lin-
ing 3 of nylon-6 which is formed on the bearing surface 9 of the
bearing 7 in the same manner as in Example 1. This sliding part
exhibited outstanding sliding performance without any play.
EXAMPLE 3
In this example, the sliding part of the invention was
applied in the production of a slide spline 11 as shown in Figs.
5 to 7. This slide spline has an external spline 12 and an in-
ternal spline 13 slidably fitted into the external spline 12.
The external spline 12 has a cylindrical shape with a bottom 12a.
The inner surface of the cylinder has spline serrations 14
extrending in the longitudinal direction. The spline serrations
14 are defined by squares 15 and trapezoids 16 projected and re-
cessed alternatively at regular intervals on the periphery. The
bottom 12a of the cylinder is connected to a rod 12b having an
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end attached to an additional component (not shown). A groove 17
as best shown in Fig. 5, is formed at the upper inside o~ the ex-
ternal spline 12 and serves as a well for excess resin.
The internal spline 13 has a cylindrical shape with a base
attached to an additional component (not shown) through the fix-
ing member 18. The external surface of the cylinder has spline
serrations 19 extending in the longitudinal direction. The
spline serrations 19 are defined by squares 20 and trapezoids 21
projected and recessed alternately at regular intervals on the
periphery.
The internal spline 13 is fitted into the external spline 12
so that a clearance 22 is formed between the spline serrations 14
and the spline serrations 19. This clearance is filled with
nylon-6 forming the resin lining 23 to reduce frictional resis-
tance. The resin lining is formed on either the spline ser~a-
tions 14 of the external spline 12 or the spline serrations 19 of
the internal spline 13.
Prior to the formation of the resin lining 23, a release
agent is applied to either the spline serrations 14 of the
exernal spline 12 or the spline serrations 19 of the internal
spline 13, according to which side is to constitute the substrate
for the resin lining. The clearance 22 bewtween the spline ser-
rations 14 and the spline serrations 19 is then filled with the
resin lining material, which is molten nylon. The molten nylon
Eills the clearance completely and an excess 24 of the molten
nylon stays in the groove 17, which serves as a well. This
arrangement prevents formation of flash 30, as shown in Fig. 2.
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The resin lining material in the clearance 22 adheres to
either the spline serrations 19 or the spline serrations 14
depending upon which of these components is not coated with a re-
lease agent. The resin lining material shri.nks during curing to
form a very small gap that permits the mutual sliding motion of
the two splines.
EXAMPLE 4
In this~example, the sliding part of the invention was
applied in the production of a slide spline, as shown in Figs. 8
to 10. This slide spline is identical to that of Example 3, ex-
cept that the groove 77 serving as a well for excess resin lining
material is formed at the upper portion of the internal spline,
