Note: Descriptions are shown in the official language in which they were submitted.
7~3
Descri~e~ion
An Improved Track Joint
and Method of Assembl_n Same
Technical Field
This invention relates `generally to endless
track chains for track-type vehicles and, more
particularly, to the pivot joints of such track chains.
Backqround Art
Endless track chains are used to support and
propel track-type vehicles and are subjected to severe
loads and an adverse environment in such use. Such
track chains are constructed from a plurality of
articulately coupled link sections, each having a pair
of links, a pin, and a bushing. The pin of each link
section is pivotally mounted through the bushing of the
preceding link section so as to provide a hinge or
pivot joint between each of the a~joining sections 3f
the chain. Because of the adverse, highly abrasive
environment in which track chain operates, it is highly
advantageous to minimize internal wear by sealing and
lubricating such hinge joints. The seals used to seal
such joints are typically annular face type seals which
are mounted within a seal cavity defined by a
counterbore in the pin ends of the links, the adjoining
end face of the bushing, and a thrust ring. One
function of the thrust ring is to act as a spacer for
limiting the inward movement of the pin links as they
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are pressed onto the ends of the pin during assembly.
Duriny such assembly, the links are pressed onto the
pins until they are solid against the thrust rings
which~ in turn, are solid against the opposite ends oE
the bushing. This produces a tight joint, or a joint
with no axial gaps between the assembled components o~
the joint. Those skilled in track art will appreciate
that very large capacity hydraulic presses, presses of
up to 300 ton capacity, are used to assemble the links
onto their respective pins and bushings, the press fit
connection therebetween being the principle means for
retaining the track components together during
operation.
Because of the nigh press forces used to
assemble the track for retention purposes, there has
been a tendency for the joints to become locked-up
during the assembly process due to a retention in the
joint of a cornpressive assembly load after the assembly
is completed The residual compressive load acting on
the mating thrust surfaces of the joint may be of a
sufficient magnitude to cause galling of such thrust
surfaces and to generate sufficient fric-tional heat
during the initial operation of the track joint to
injure and even melt portions of the joint seals. Such
damage to the track joint may lead to premature seal
failure, loss of lubricant, and other deleterious
affects, resulting in increased operating costs and
downtime.
The present invention is directed to over-
coming one or more of the problems set forth above.
Disclosure of the Invention
In accordance with one aspect of the presentinvention, a track joint is provided with a controlled
running clearance between opposing thrust surfaces of
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the joint by a method including the steps of applying a
controlled interstice producing membrane to at least
one of the thrust surEaces of the joint and then
assembling the joint by exerting an axial compressive
~orce sufficient to compressively load the membrane
between relatively pivotal members of the joint. The
membrane has a thickness of betweell ,001 to .010 inches
and of a material which is readily pulverizable by
grinding.
~pon being ground away during the initial
pivotal movements of the track joint, a controlled
narrow interstice is provided between the thrust
surfaces so as to unlock the joint and allow
substantially free pivotal movement thereof during
further operation o the joint.
Brief Description of the Drawings
Fig. 1. is a cross-sectional view of a track
chain joint illustrating an embodiment of the present
invention;
Fig. 2 is a greatly enlarged fragmentary
sectional view illustrating the interstice producing
membrane immediately aEter the assembly of the joint;
Fig. 3 is a view similar to Fig. 2, but after
destruction o~ the membrane upon initial pivotal
movement of the joint; and
Fig. 4 is an isometric view oE a ring membrane
illustrating one of the preferred embodiments of the
present invention.
sest Mode For Carrying Out the Invention
Referring more particularly to the drawings, a
hinge or pivot joint 10 of an endless track chain 12 is
depicted in cross-section in Fig. i. A pair of such
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chains 12 are used to support and propel a track-type
vehicle (not shown) and are subjected to severe loads
and adverse environment in such use. Each track chain
12 is constructed from a plurality oE like link
sections 14, each having its opposite ends pivotally
~oined by a like plurality of pivot joints 10 to a
succeeding and preceding link section. In Fig. 1, a
bushing end 16 of one link section and a pin end 1~ of
another link section make up one of the pivot joints
10. Those skilled in the art will appreciate that each
link section 14 has identical components. However,
some of the same components in the adjoining sections
shown in Fig. 1 are given different numbers herein Eor
the sake of clarity. sushing end 16 includes a bushing
15 20, a right-hand link 22, and a left-hand link 24. The
links and bushing are connected together into a unitary
structure by each of the links 22 and 24 being pressed
onto a respective one of the opposite end portions of
the bushing 20. The bushing 20 has opposite end faces
26 and 28, each of which serves as a sealing and thrust
surface, as will hereinafter be more fully described.
Each pin end 18, as shown in Fig. 1, includes
a pin 30, a right-hand link 32, and a left-hand link
34. Pin 30 is disposed through and pivotally mounted
25 within the bushing 20, The opposite end portions 36,38
of the pin 30 extend from the bushing 20 an~ are
pressably mounted within the links 32,34.
Means 40 for sealing and lubricating the joint
10 include a pair of seals 42 and a lubricant filled
30 reservoir 44 in pin 30. A cross hole 46 communicates
the reservoir 44 to the interface between the pin 30
and the bushing 20. The reservoir 44 is pre~erably
closed by a plug 48.
Each seal 42 is disposed within an inwardly
facing counterbore 50 provided in each of the links 32
and 34. Each counterbore 50 has a bottom wall 52 which
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is disposed in an opposing relationship to its
respective bushislg end face 26,28. Each bottotn wall
52, lilse end Eaces 26,28, also serves as a thrust
surEace, as will hereinafter be described.
As further illustrated in ~iy~ 1, joint 10
also includes thrust means 54 for -transferring axial
loads which are exerted on the chain 12 during use
between adjourning link sections 14 which are exerted
on the chain during its operational use. Thrust means
54 also functions as a positive stop for positioning
the links 32,34 as they are pressed onto the opposite
end portions 36,38, respectively, of the pin 30 during
assembly of the track chain. In sealed and lubricated
track, as shown herein, the thrust means 54 also
control the axial compression of the seals 42 which
control is necessary for the proper functioning oE the
seals. In such a sealed and lubricated joint, this is
customarily accomplished b~ use of a pair of annular
spacers or thrust rings 56. One of ~he thrust rings 56
is concentrically disposed within each of the seals
42. Each thrust ring 56 has a thrust surface 58 at
each end thereof. One of such thrust surfaces 58 is
disposed in an opposing relationship with a respective
one of the thrust surfaces 52 of the counterbore 50 and
the other is disposed in an opposing relationship to a
respective one of the thrust surfaces 26,28 of the
bushing 20,
A controlled interstice producing membrane 60
is interposed each set of opposing thrust surfaces for
relieving the joint 10 of any residual compressive
loads which may become locked-up in the joint during
the assembly process. As best shown in Fig. 2,
membrane 60 is preferably affixed to the thrust
surfaces 58 of the thrust rings 56. Each membrane 60
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is provided with a material thickness oE between .001
to .010 inches (.025 to .254 mm). The use of a
membrane with a thickness of greater than .010 inches
~.254 mm) may create an undue amount of end play in the
joint, as well as produce a sufficient amount of debris
therein to prevent adequate access of lubricating oil
to the seals. On the other hand, a membrane of a
thickness less than .001 inches (.025 mm) is not
sufficient to reliably unlock the joint. A membrane 60
with a material thickness of between .003 to .005
inches (.076 to .127 mm) has been found to be
preferable, with a thickness of approximately .004
inches (.102 mm) having been used with satisfactory
results.
It is also desirable that the membrane 60 be
of a material which is readily pulverizable by grinding
to facilitate its disintegration upon the initial
pivotal movement of the joint after assembly. A
material which is relatively weak in shear is,
therefore, preferred. While the membrane 60 is
subjected to high compressive loads, sometimes as high
as 130,000 psi, it has been discovered that a material
with a similarly high compression modulus is not
likewise re~uired. This is believed to be because the
member 60 is so thin, paticularly in comparison to its
compressible area, that material is not extruded from
between the thrust surfaces when compressed, as would
occur if it were much thicker.
As shown in Fig. 4, the membrane 60 is
preferably in the form of a thin ring which is secured
to each of the ends of the thrust rings by any suitable
adhesive. In this form, a membrane made of a cellulose
paper has been used with satisfactory results. The
membrane 60 may also take the form of a thin coating
covering the entire surface of the thrust ring. In
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this form, a coating of perfluoroalkoxy (PE`A) has been
used with satisEactory results. Such PFA coating may
be applied to the thrust riny by any well-known process
which provides sufficient adherence between the coating
and the thrust ring and which produces a coating with a
uniform thickness of between .003 to .004 inches.
Industrial Applicability
Track joint 10 is preEerably assembled by
means of a track press (not shown) of any conventional
design. As is well-known in the track art, such track
presses are very powerful hydraulic devices, normally
with a 150 to 290 ton capacity. Some newer track
presses, however, have a 300 ton capacityO Thus, it is
readily apparent that large compressive forces are
exerted on the components of the track joint 10 during
the assembly process which preferably occurs in the
following sequence. ~irst, the left and right-hand
links 22,24 are pressably forced onto the opposite ends
of the bushing 20 so as to form a unitary structure
thereof. Second, the pin 30 is centrally placed within
the bushing 20. A clearance fit is provided between
the pin 30 and the bushing 20 to permit free pivotal
movement therebetween. Third, the thrust ring 56 with
the membranes 60 attached thereto are placed about
their respective pin end portion~ 36,38 which protrude
from the opposite ends of the bushing 20. A seal 42 is
mounted within the counterbore 50 of the links 32,34
2rior to the links being positioned adjacent to their
3~ respective ends of the pin 30. By means of the track
press, the links 32,34 are forced onto their respective
pin end portions 36,33 until the joint becomes solid,
e.g., there is no axial clearance between the links
32,34, thrust rings 56, and bushing 20.
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In practice, the press force applied to the
links 32,34 is much greater than the nominal Eorce
required to assemble such links onto the pin 30. The
application of a greater than nominal force is required
to insure proper assemblage of all joints, each of
which may require a different assembly force due ~o
- variations in manufacturing tolerances and the like.
For example, a particular joint may require a nominal
assembly force of 60 tons, while an actual assembly
force oE 100 tons would be applied thereto to insure
the complete assemblage of every link onto every pin 30
of a track chain.
The application of this amount of excessive
force on the joint can and frequently does produce a
compressive load which becomes locked into the joint
after the assembly process is completed. Such a
residual load, due to friction between the mating
thrust surfaces of the joint, restricts the normal free
pivotal movement of the joint. If of sufficient
magnitude, such compressive loads can cause galling of
the thrust surfaces and generate sufficient frictional
heat to injure, and possibly melt, the synthetic
plastic materials of the seals in certain areas. The
interstice producing membrane 60 advantageously
eliminates this residual compressive load in the joint,
thereby eliminating the deleterious consequences
thereof. This is accomplished by the membrane 60
sacriEicially selE-destructing upon the initial pivotal
movements of the joint after the joint is assembled.
3~ The membrane 60, in effect, is pulveri~ed, preferably
into fine particles, by being ground between the thrust
surfaces during such initial pivotal movements. The
fine particles are then removed from between the thrust
surfaces by entering into solution with or by being
flushed away by the
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lubricatin~ oil. The disappearance of the membeane 60
between the mating thrust suraces of the joint
produces a controlled interstice or running clearance
62, as shown in Fig. 3, between such thrust surfaces
which is sufficient to unlock the joint and allow the
free pivotal movement thereof. However, no significant
looseness is produced in the joint upon the
disappearance of the membrane 60 due to its minimally
controlled thickness.
Other aspects, objects, and advantages of this
invention can be obtained from a study of the drawings,
the disclosure, and the appended claims.
