Note: Descriptions are shown in the official language in which they were submitted.
CA 02243259 1998-07-15
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~ APPARATUS AND METHOD FOR CURING ENDLESS RUBBER TRACK
BACKGROl,IND OF THE INVENTION
s 1. Field of the Invention
The present invention relates to elastic endless crawlers or tracks for
earth-moving machines, agricultural equipment and the like, in which the track
is assembled over drive wheels.
2. Deacri:ction of the Prior Art
Vehicles such as earth-moving machines and agricultural equipment are
constructed with endless tracks which are driven by drive wheels. The track or
belt is assembled over a plurality of wheels, at Least one of which is a drive
wheel, and is engaged by the drive wheel. Increasingly, vehicles used in
agric.utture are driven by track systems because the tracks have higher
traction
in soil and cause less ground compaction than vehicles equipped with
conventional, pneumatic tires. As a result of this renewed interest in track
systems, many improvements in such systems have recently been implemented.
One such improvement, set forth in U.S. Patent No. 5,279,378 sets forth
2 o a vehicle having an endless belt with a highly tensioned elastomeric
exterior
surface which provides improved frictional coupling between its interior
surface
and the drive wheel. The improvement is directed to belt tensioning aspects of
the invention. The improvement discloses an endless belt comprised of at least
one reinforcing flament wrapped substantially parallel to the longitudinal
axis of
~ 2 s the chassis.
Other improvements, such as described in U.S. Patent No. 5,295,741,
No. 4,678,244 and No. 4,057,302 are directed at improving the coupling
befinreen the interior surface of the track and the drive wheel of the
vehicle.
Whine many belts or tracks utilize rubber lugs to accomplish the coupling,
such
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as set forth in U.S. Patent No. 5,279, 378, these improvements utilize core
bars,
typically of a mater'sal of a different composition than the rubber track, to
improve
coupling.
While some of these improvements are effective, the methods for
s manufacturing reinforced, endless rubber track for propulsion of
agricultural or
earth-moving vehicles is both expensive and time-consuming.
Some methods and apparatus ace available for making V-belts which may
also be applicable to tractor treads or belts. The description of such
apparatus
and methods is set forth in Patent No. 2,867,845 and No. 4,861,403. However,
Z o because of the Large differences in the sizes of V-belts, which are small,
typically
having widths measured in inches and fractions thereof, compared to the rubber
track utilized in earth-moving vehicles, typically having widths measured in
feet,
simple scate up of V-belt technology may not always be practical and may not
yietd usable rubber track because of the size differences.
U.S. Patent No. 2,867,845 depicts apparatus and method for forming a
continuous V-belt. The V-belt is formed in segments and has lugs formed on
one side. While such a method and apparatus are suitable for forming
continuous V-belts, there are probtems with applying these methods to the
manufacture of the large tracks required for agricultural or earth-moving
2 o equipment. When the V-belts are manufactured in segments and vulcanized in
the molds, the segments have parting fines therebetween which are undesirable.
Because the segments are individually formed, with each segment vulcanized,
the rubber between the segments is not vulcanized across the parting lines,
resulting in a discontinuous region. This discontinuous region has less
strength
25 than the surrounding vulcanized, cross-linked region. if the tracks are not
vulcanized in the mold during forming, but rather fom~ed as green rubber belts
and vulcanized separately after fomling, then another time-consuming operation
2
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. is required to vulcanize the rubber after the green belt is formed.
Furthermore,
since the green rubber belt is vulcanized after molding, the rubber belt no
tonger
being contained by the mold during heating and pressurization, the likelihood
of
distortion and belt of the belt as a result of out-of-tolerance conditions is
s significantly increased.
U.S. Patent No. 4,8fi1,403 is similar to the method of Patent No.
2,8Ei7845, but differs in that a fabric-reinforced double toothed belt is
fom~ed.
As one side of the belt is formed with teeth, it is partially vulcanized. In a
subsequent operation, the second side of the belt is formed with teeth, and
then
to the entire belt is vulcanized.
The present invention is directed to an improved rubber track made in
accordance with an improved method and with improved apparatus, overcoming
the deficiencies and short-comings of the prior art methods and apparatus for
producing endless track.
SUMMARY OF THE 1NYENTtON
The present invention provides novel apparatus and a novel method for
manufacturing an endless rubber track for large vehicles such as tractors or
earth-moving machines. A plurality of sprocket-engaging core bar inserts are
2o disposed in the inner portion or inner diameter of the endless rubber track
to
engage the power drive mechanism of the vehicle. Rubber tread is disposed on
the outer portion or external diameter of the rubber track. Although the
rubber
track is made in segments, it is completely vulcanized, and does not have
discontinuous, unvulcanized regions between vulcanized segments, such as is
' 25 found in the prior art.
To provide such a tread, a first mold assembly having an inner mold half
and an outer mold half is provided. The inner mold half has a cavity patterned
3
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in the form of the interior of the rubber track which is to be produced, while
the
outer mold half has a cavity patterned in the form of the exterior of the
rubber
track which is to be produced, the motd cavities being the negative
impressions
of the rubber track. Each of the mold halves also contain cooling channels
located on the ends of the mold so that each end can be cooled and maintained
at a temperature tower than the mold interior. Formable material, when placed
in the mold, will fill the mold cavity taking the shape of the track. The mold
assembly also includes a removable subplate which is positioned between the
inner mold half and the outer mold half. The subpiate is essentially a flat
plate.
zo Positioning means is also provided to properly orient the mold halves in
relation
to themselves and to the subptate.
A first quantity of green rubber of a desired composition is provided. The
green rubber, in the fom~ of a slug, is positioned adjacent the inner mold
half of
the fast mold assembly. The green rubber may occupy a substantial portion of
s5 the cavity of the inner mold half.
The subplate is then positioned adjacent to the green rubber so that the
green rubber is between one face of the subplate and the inner mold half.
A second quantity of green rubber of a desired composition is positioned
adjacent a second face of the subplate which is opposite the first subplate
face
2 o and the inner mold half. The composition may be the same as or different
than
the composition of the first quantity of rubber. The outer mold half is then
positioned adjacent the second quantity of rubber so that the rubber is
between
the second face of the subptate and the outer mold half.
The first mold assembly is then heated to a temperature sufficient to
25 soften the green rubber. Simultaneously, pressure is applied to the mold
assembly sufficient to completely flow the green rubber into the mold
cavities.
However, the temperature is held within a range sufficiently low such that
rubber
4
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vulcanization will not occur, yet sufficiently high such that rubber flows
relatively
easily under the applied pressure. After the green rubber has flowed to
completely fill the cavities of the mold halves, the inner and outer molds
halves
are separated and the subpiate is removed from between the mold halves.
An endless green rubber belt, in the shape of a loop, which may be
formed by any conventional process, is now positioned between the inner and
outer mold halves, substantially in the region previously occupied by the
subplate. The green rubber belt may include any known reinforcement such as
steel cord or other reinforcing material, as is well known in the art. The
rubber-
Z o filled mold halves are closed against a portion of the green rubber belt.
Cooling
water is supplied to the cooling channels of the mold halves. The assembly is
then heated to an elevated temperature. However, the cooling water cools the
ends or outer portions of the mold halves for a predetermined length L, white
a
central portion of the mold assembly is unaffected by the cooling for a
i5 predr~termined length P. The temperature is raised suffrciently high to
vulcanize
the rubber in the central portion of the mold assembly for the predetermined
length P, yet sufficient cooling is provided so that the rubber in the end
portions
are not vulcanized. A very thin transition zone of partially vulcanized rubber
may
exist between the vulcanized portion and the end portion. Simultaneously,
2 o pressure is applied to the assembly. The assembly is held under pressure
at
temperature for a time sufficient to permit essentially the complete
vulcanization
of the: rubber along predetermined length P. Upon removal of the pressure and
separation of the mold halves, the endless belt has a rubber track segment
formed thereon. The rubber track segment has a vulcanized central portion of
' 25 lengi:h P and a substantially green rubber track segment outer portions
each
having a length L. This process is then repeated using the fast mold assembly
at a predetermined distance Q along the endless green belt from the formed
5
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rubber track segment until the green belt has a plurality of formed rubber ,
segments separated by the predetermined distance Q.
A second mold assembly having an inner mold half and an outer mold '
half is provided. The inner mold half has a cavity similar to that of the
first mold
assembly patterned in the form of the interior of the rubber track which is to
be
produced, white the outer mold half has cavity also similar to that of the
fast
mold assembly patterned in the form of the exterior of the rubber track which
is
to be produced. The mold halves of the second mold assembly, however, do
not contain cooling channels as do the rnoid halves of the first mold
assembly.
1o Formable material, when placed in the mold will fill the cavity taking the
shape
of the track. The second mold assembly also includes a removable subplate
which is positioned between the inner mold half and the outer mold half. The
second mold assembly subplate has three distinct regions, two outboard or end
portions extending toward the edges of the subplate and a central portion
extending between the outboard or end portions. The central portion is a
substantially flat plate having a predetermined length Q, corresponding to the
distance between the formed rubber segments made using the first mold
assembly. Each of the outboard or end portions is at least equal to, and
preferably greater than the Length L, which dimension t_ corresponds to the
2 0 length of the unvulcanized portions of the formed rubber segments. Each of
the
outboard or end portions of the subpiate has an inner portion patterned in the
form of the interior portion of the rubber track, and an outer portion
patterned in
the form of the exterior portion of the rubber track. When the subplate is
assembled between the mold halves, the outboard or end portions engage the
corresponding portions of the mating inner mold half and outer mold half
cavities, filling the cavities. Thus, when assembted between the mold halves,
the subplate assures that the formabte material fills the central portion of
the
s
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mold assembly while preventing material from entering the cavities positioned
adjacent the outboard or end portions of the subplate. Positioning means is
also
provided to properly orient the mold halves in relation to themselves and to
the
removable subptate.
s A third quantity of green rubber having the same composition as the first
quantity of green rubber is positioned adjacent the inner mold half of the
second
mold assembly. By calculation and careful subsequent measurement, the
amount of green rubber supplied can be sufficient to fill the inner mold half
cavity
opposite the central portion of the subplate, with Tittle or no overage or
waste.
to A first side of the subplate is positioned adjacent to the third quantity
of
green rubber utilizing positioning means, to thus assure that the subplate
outboard portions properly mate with the corresponding cavities in the mold
half.
A fourth quantity of green rubber having the same composition as the first
quantity of green rubber is positioned adjacent a second side of the subplate.
15 Again, the quantity of rubber supplied is sufficient to fill the mold
cavity of the
outer mold opposite the central portion of the subplate, with Tittle or no
overage
or waste.
The outer mold half is assembled over the fourth quantity of green rubber,
Again, positioning means is utilized to assure that the subplate outboard or
end
2 o portions properly mate with the corresponding cavities in the outer mold
half.
The second mold assembly is now heated to raise the temperature of the third
and fourth quantities of green rubber sufficiently to soften the rubber, but
not so
high as to cause the rubber to vulcanize. Simultaneously, pressure is applied
to the second mold assembly so the rubber readily flows to fill the inner and
25 outer mold cavities opposite the centrat portion of the subpiate. The
outboard
or end portions of the subptate fill the inner and outer moil half cavities
adjacent
to its central portion, and thereby prevent the flow of rubber into the
cavities in
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the outboard portions ofi the mold. Subsequent to this molding operation, the
,
inner and outer mold halves are separated from the mold and the subplate is
removed.
Next, a portion of the green belt lying between the formed rubber track
segments made using the ftrst mold assembly is positioned between the second
mold assembly halves. The length of the green belt Q corresponds to the length
Q of the central portion of the second mold cavities filled with green rubber.
The
outer portions of the mold halves, having a length equal to or greater than L,
overlap the green rubber portions L of the fomled rubber track segments made
using the first mold assembly. These portions L of the formed rubber track
segments ace substantially unvuicanized, but may include the thin transition
zone of partially vulcanized rubber. Preferably, the outer portions of the
mold
halves are of a length greater than L, so that at least a portion of the
overlapped,
formed rubber track segments made during the prior operation with the f rst
mold
s5 assembly includes rubber which was completely vulcanized in the first mold.
This vulcanized rubber, positioned in the cavities of the outer portions of
the
second mold assembly adjacent the unvulcanized rubber, serves as packing to
prevent movement of the green rubber from the central portion during
subsequent operations.
2o The second mold assembly, with the green belt and substantially
unvulcanized portions of the formed rubber track segment sandwiched
therebetween, is closed and heat is applied to raise the temperature of the
rubber above the vulcanization temperature, while pressure is applied to the
assembly. The green rubber positioned between the mold halves is now
25 vulcanized, producing a fusty vulcanized track segment. The mold halves can
.
then be removed and the process repeated. After this process is repeated at
each of the green belt segments of predetermined length Q, a complete endless
s
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~ vulcanized rubber track having no discontinuous regions is produced.
One of the major advantages of a rubber track produced in the apparatus
of thf: present invention and by the process of the present invention is that
although the rubber track is formed in segments, the rubber between the
s segments is vulcanized, that is, properly cross-linked, eliminating the
weak,
discontinuous region as found in prior art processes in which the segments
them:aelves are vulcanized, but wherein the cross-linking does not extend
across
the parting line. This weak region having been eliminated, the vulcanized
rubber track of the present invention is not prone to a failure across the
weak
to region.
Other features and advantages of the present invention will
become apparent from the following more detailed description of the preferred
embodiment, taken in conjunction with the accompanying drawings, which will
illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWIN S
Figure 1 is a side view of a core bar insert;
Figure 2 is a side cross-sectional view of the first motd assembly;
Figure 3 is a sectional view of the first mold assembly along fines 3-3 of
2 o Figure 2;
Figure 4 is a side cross-sectional view of the second mold assembly;
Figure 5 is a sectional view of the second mold assembly along fines 5-5
of Figure 4;
Figure 6 is a side cross-sectional view of the first mold assembly with
2 s green rubber slugs positioned above and below the subplate prior to
molding;
Figure 7 is a view of a green rubber belt positioned between the mold
halves of the first mold assembly, the green rubber belt being viewed on edge,
9
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and the mold halves shown in cross-section positioned on either side of the
belt; .
Figure 8 is a schematic of a partially compteted endless track;
Figure 9 is a side cross-sectional view of the second mold assembly with '
green rubber stags positioned above and below the subplate prior to molding,
while Figure 9A is a side cross-sectional view of the same second mold
assembly after molding;
Figure 10 is a view of a partially completed endless track viewed on its
edge with the second mold assembly in position on either side of the track
prior
to final molding and vulcanization;
so Figure 11 is a cross-sectional view, viewed along the longitudinal axis of
the assembly, of a preferred embodiment of the first mold assemblies of the
present invention, loaded with rubber slugs, the molds being in a horizontal
position;
Figure 12 is a cross-sectional view, viewed along the longitudinal axis of
the assembly, of a preferred embodiment of the first mold assemblies of the
present invention, loaded with rubber slugs, the molds having been pivoted
90°
from their prior horizontat position;
Figure 13 is a cross-sectional view, viewed along the longitudinal axis of
the assembly, of a preferred embodiment of the first mold assemblies of the
2 o present invention, with molded green rubber, in a vertical position with
mold
halves retracted and subptates removed;
Figure 14 is a view of a preferred embodiment of the present invention
with a green rubber belt positioned between the mold halves of a pair of first
mold assemblies, the green rubber belt being shown on edge;
Figure 15 is a view of a green rubber belt positioned between the mold
halves of a pair of first mold assemblies filled with molded green rubber, the
mold assemblies shown in cross-section and the green rubber belt being shown
io
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on edge;
Figure 16 is a view of the partially completed rubber track of Figure 15
with two segments positioned opposed to one another, the green belt being
shovm on edge;
s Figure 17 is a cross-sectional view, viewed along the longitudinal axis of
the assembly, of a preferred embodiment of the second mold assemblies of the
present invention loaded with green rubber and in a horizontal position;
Figure 18 is a sectional view of a preferred embodiment of the second
mold assemblies of the present invention loaded with green rubber after
pivoting
to the assemblies 90°, the longitudinal axis of the assemblies being
vertical;
Figure 19 is a sectional view of a preferred embodiment of the present
invention showing the partially completed rubber track and the green belt,
vievtved on edge and positioned between a pair of second mold assemblies, the
longitudinal axis of the mold assemblies being parallel to the belt edge.
L5
DETAILED DESCRIPTION OF THE PREFERRED EMEODIMENTS
The present invention is directed to a novel method and apparatus for
marn~facturing an endless rubber track. The rubber track is characterized by a
belt positioned between the sprocket-engaging inner surface and the treaded
2 0 outeir surface.
Preferably, the belt is continuous and does not include a splice. In an
optio~nai configuration, the track is further characterized by the inclusion
of hard,
spro~:,ket-engaging core bar inserts extending inward of the inner surface of
the
rubber track for engaging the tractor drive mechanism.
2s The belt is positioned between the inner and outer portion of the rubber
track;. The belt may be fom~red by any process well-known in the art. Although
a continuous steel belt is preferred for the main cord, a fabric belt may also
be
I1
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used. In addition to the belt main cord, the belt preferably includes at least
one
bias ply. When a bias ply is included, it is positioned at an angle of t 30-
60° to
the main cord, and preferably at an angle of t45° to the main cord. It
is '
understood, however, that a bias ply is not required to be assembled to the
main
cord. The belt may be comprised solely of the main cord. The belt is initially
formed as a green rubber belt, which is made by any process well known in the
art.
In the optional configuration, core bar inserts are fabricated into the track
as part of the manufacturing process. The core bar insert 60 has a shape such
1o as shown in Fig. 1 and is made of a hard material. In a preferred
embodiment,
each core bar insert 60 is made from an ultrahigh molecular weight plastic
such
as polyethlene. Each core bar insert 60 has a modified U-shape. Two legs 62,
64 extend downward from a head 66 of each core bar insert 60. Each leg is
inclined at an angle of from 50-85° degrees from the top surface. In a
preferred
15 embodiment, such as shown in Figure 1, the legs of the core bars are formed
by compound angles. Each leg has a first or upper portion 68 which is inclined
at an angle 70 of about 50-75° from head 66. The lower portion 72 of
each leg
is inclined at an angle 74 which is greater than angle 70, and preferably of
from
about 70-85° from head 66.
2 o Legs 62, 64 and a portion of head 66 of each core bar insert 60 are
embedded in the elastic rubber track. A portion of core bar insert head 66 is
not
embedded in the elastic rubber track and forms anti-detracking protrusion 76
which extends from the inner circumferential surface of the rubber track.
Optionally, portions of the core bar legs may extend outward from the track.
25 That is to say, the edges of the legs 62, 64 may be exposed white a
substantial
portion of the legs are embedded in the rubber track, as shown by the dashed
fines in Figure 1. An example of a core bar insert may be found in U.S. Patent
is
SUBSTITUTE SHEET (RULE 26)
CA 02243259 2005-07-18
No. 5,295,741. The major difference between the core bar insert 60 of the
present invention and prior art core bar inserts is the configuration of core
bar
insert 60. Prior art core bar inserts are held in place by wings which are
embedded in the elastomeric track material. The result is that the core bar
insert
shape is complex, while the size is large relative to the track. This prior
art core
bar insert can be very heavy when the material of construction is an iron-
based
alloy. Alternatively, when the material of construction is a lightweight
material, for
example polyethylene, the wings are fragile and are easily overloaded in their
thin
sections. Core bar inserts 60 of the present invention are positioned in the
rubber
track by legs 62, 64 extending into the elastomeric track material. The angles
70
and 74 formed by the legs are sufficient to assure that the core bar inserts
are
captured by the track and held in place by friction between the rubber of the
track
and the material of the insert. Among the benefits are more flexibility in
choosing
the materials of construction for the core bar inserts. Additionally, because
of
their simpler configuration, core bar inserts 60 of the present invention are
cheaper and easier to manufacture and assemble into the track, as will become
evident. In a preferred embodiment, an ultrahigh molecular weight plastic such
as polyethylene, is the preferred material of construction for core bar insert
60.
The track, typically including core bar inserts 60, is prepared in a novel and
unconventional manner. At least two mold assemblies are required for the
preparation of the track.
Referring now to Figure 2, the first mold assembly 102 is comprised of a
pair of mold halves, an inner mold half 104, an outer mold half 106 as well as
a
removable subplate 108. Inner mold half 104 is a pattern which will form the
interior portions of a segment of the rubber track. That is, when material
fills
inner mold half cavity 110, the material will have the shape of the rubber
track
13
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interior portion, also referred to as the sprocket engaging surface. Outer
mold
half 106 is a pattern which wilt form the exterior portion of a segment of the
rubber track, also referred to as the treaded surface. That is, when material
fills '
the outer mold half cavity 112, the material will have the shape of the rubber
track exterior portion. Removable subplate 108 is a substantially flat plate
which
is positioned between mold halves 104, 106 and preferably which has a surface
finish smoother than either of mold halves 104, 106. Mold halves 104, 106
include cooling channels 114 positioned between mold ends 116, 118 and
insulation 119 located at interior positions 120, 122, the centerlines of
which are
to shown as dotted lines located at a preselected inboard location from mold
ends
116, 118. Cooling channels 114 and insulation 119 are provided so that cooling
wafer may be circulated to keep the mold halves cool from the mold ends 116,
1'18 to the interior positions, as wilt be discussed. The insulation prevents
the
cooling water from adversely affecting the portion of the track between the
dotted lines 120, 122.
Mold assembly 102 also include positioning means to properly locate
inner mold half 104 in relation to outer mold half 106. Referring to Figure 3,
inner mold half 104 includes pins 124 which pass through apertures 126 in
subplate 108 and extend into bores 128 in outer mold half 106. It is
understood
2 o that the pin/aperture/bore 124/126/128 system is but one positioning means
for
locating the inner motd half 104, outer mold half 106, and subpiate 108. Any
other suitable system for locating these elements in proper relation to one
another may be used.
Inner mold half further includes notches 130, one notch 130 being present in
2s each lug cavity 132. Notch 130 is dimensioned to receive at least the head
66
of core bar insert. Notch 130 extends about 1-20 millimeters, and preferably
from 1-2 millimeters, inward from the bottom of lug cavity 132.
14
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Referring now to Figa.tre 4, the second mold assembly 142 is comprised
of a pair of mold halves, an inner mold half 144 an outer mold half 146 and a
removable subplate 148. Inner mold half 144 is a pattern which will form the
Interior portions of a segment of the rubber track. That is, when material
fills
inner mold half cavity 150, the material will have the shape of the rubber
track
interiior portion.
Outer mold assembly 146 is a pattern which will fiorm the exterior portion
of a segment of the rubber track. That is, when material fills the outer mold
half
cavity 152, the material wilt have the shape of the rubber track exterior
portion.
Zo Removable subplate 148 has a surtace finish which is smoother than
either of mold Naives 144, 146. Subplate 148 has a central portion 174 with a
preselected length Q which is a substantially flat plate. Subptate 148 also
has
two ~~utboard or end portions 176, 178. Each of these subplate portions 176,
178 has an inner portion 180 having the conftguration of the interior, or
sprocket
i5 engaging, portions of a rubber track segment and an outer portion 182
having
the configuration of the exterior,or treaded surface, portion of a rubber
track
segment. These subplate outboard portions extend from mold ends 156, 158
to the central portion 174, a distance at least as great as, and preferably
greater
than the distance from mold ends 116, 118 to interior portions 120, 122 of
inner
2 o mold half 104 and outer mold half 106 of first mold assembly 102. Each
subptate outboard or end portion 176, 178 extends for a distance greater than
1/4 of a pitch, and in a preferred embodiment, from 1-2 pitches of the rubber
track interior portion, each pitch being equal to the distance between the
centers
of adjacent lugs, shown as r in Figure 4. Subplate outboard or end portions
176,
25 178 fill inner mold half cavity 150 and outer mold half cavity 152 for a
length as
great as or greater than the length L, and preferably for 1-2 pitches of the
interfor
portion of the rubber track, as shown in Figure 4 when removable subplate 748
is
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is assembled to mold half cavities 150, 152 of second mold assembly 142.
Thus, in the preferred embodiment each of the outboard or end portions of the
rubber track extends for a length of 1-2r, where r is one pitch of the
interior
portion of the rubber track. Subpiate portions 176, 178 may be manufactured
s as portions of subplate 148, for example, aluminum or machined tool steel.
In
a preferred embodiment, subplate portions 176, 178 are manufactured from
vulcanized butyl rubber and assembled onto metallic subplate 148. A butyl
rubber composition is preferred since, upon application of heat, it will
expand to
completely seal lug cavities 172 and tread cavities 214 without damaging the
1o motd. Additionally, the butyl rubber is easily removable and reptaceable as
it
wears and ages.
Referring now to Figure 5, mold assembly 142 also include positioning
means to properly locate inner mold half 144 in relation to outer mold half
146.
Inner mold half 144 includes pins 164 which pass through apertures 166 in
15 subplate 148 and extend into bores 168 in outer mold half 146. It is
understood
that the pin/aperturelbore 164/166/168 system is but one positioning means for
locating mold halves 144, 146, in relation to subplate 148 and to each other.
Any other suitable system for locating these elements in proper relation to
one
another may be used.
2 o Referring back to Figure 4, inner mold half further includes notches 170,
one notch 170 being present in each lug cavity 172. Notch 170 is dimensioned
to receive core bar insert head 66 and Legs. Notch 170 extends about 1-20
millimeters, and preferably 1-2 millimeters, inward from the bottom of lug
cavity
172.
2s Using first mold assembly 102 and second mold assembly 142, track is
prepared in the following manner. Referring now to Figure 6, core bar inserts
60 are inserted so that heads 66 are positioned in notches 130 of lug cavities
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132 of inner mold half 104. A first green rubber slug 190 is positioned in
inner
mold cavity half 110. There is sufficient rubber in green rubber slug 190 to
completely fill inner mold half cavity 110.. Subplate 108 is positioned over
first
green rubber slug 190, utilizing positioning means. A second green rubber slug
s 192 is positioned over subpfate 108. Outer mold half 106 is positioned over
second rubber slug 192 utilizing positioning means. Sufficient rubber is
present
in sec;ond rubber slug 192 to completely fill outer mold half cavity 112.
The amounts of rubber utilized in green rubber slugs 190, 192 are
obtained by determining the volume of rubber required for the respective mold
so half cavities 110, 112. Then, by carefully weighing the rubber, the proper
amount of green rubber for rubber slugs 190 and 192 can be provided with very
little overage or waste, which, if present, can be readily removed.
The first mold assembly 102, with rubber slugs 190, 192 inserted therein,
is heated to an elevated temperature in the range of 50-140°C which is
sufficient
is to cause the rubber to soften. However, the temperature is not so high so
that
the rubber will vulcanize. This temperature may be achieved by any
conventional techniques, such as by providing electrical resistance heaters
within the mold or placing the rubber mold assembly in an oven held at a
temperature of 50-140°C, although the preferred method is introducing
steam
2 o into steam channels built into the mold assembly (not shown) as is well
known
in the art. Pressure in the range of about 100-300 kilopascals (about 14-50
psi)
is also applied perpendicular to mold halves 104, 106 substantially in the
direction of the arrow as shown in Figure 6. The heat and pressure applied to
mold assembly 102 are sufficient to cause green rubber slugs 190, 192 to flow
2s and fill mold half cavities 110, 112. After the green rubber is flowed into
the
mold, taking the shape of the mold cavities, and preferably, while mold
assembly
102 is still hot, inner mold half 104 and outer mold half 106 are separated so
that
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subpiate 108 can be removed. Because subptate 108 has a smoother surface
finish than either of mold halves 104, 106, the green rubber will remain in
the
mold halves, allowing easy separation pf removable subplate. '
Referring now to Figures 2 and 7, a green belt 194 is placed between
s inner mold half 104 and outer mold half 106 of first mold assembly 102,
which
now has green rubber ftliing the mold cavities. The longitudinal axis of the
first
mold assembly is parallel to the length of the belt in the region of interest,
the
belt being viewed on edge in Figure 7. The mold halves are properly located
utilizing positioning means as previously discussed, and the rubber containing
i o mold halves are closed about green belt 194, preferably while the molded
green
rubber is still hot. The initial placement of green belt 194 between the mold
Naives is at an arbitrary position A as shown in Figure 7. Cooling water is
then
supplied to cooling channels 114. The temperature of the assembly is now
raised to an elevated temperature sufficient to vulcanize the rubber in the
mold
is assembly and the belt while pressure is applied. The temperature is in the
range of 145-180oC, and preferably 155-165°C. However, the cooling
water in
cooling channels 114 is adjusted so that rubber is not vulcanized between mold
ends 116, 118 and insulation 119 for a distance L in both the inner mold half
and
outer mold half 106. Length L extends for a distance greater than or equal to
2 0 ll4r, and preferably, preselected length L extends from the mold end to
the
insulation for a length of 1 r to 2r, where r is one pitch of the rubber track
interior
portion. A thin region of partially vulcanized (partially cross-linked) rubber
may
occur in the vicinity of insulation 119. However, the rubber is fully
vulcanized in
the first mold assembly between interior positions 120 and 122. The amount of
25 cooling water required will depend on the size of the mold assembly and the
actual temperature at which vulcanization will be pertormed. However, as is
apparent to one skiiled in the art, the required cooling water flow can be
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determined for each moil design at a selected vulcanization temperature. The
result is a rubber track segment 196 at position A which is vulcanized
befinreen
interior positions 120 and 122, but which is still green for a length L at
exterior
positions from 716 to 120, 116 to 122, 118 to 120 and 118 to 122.
s Once Position A is established, the above procedure utilizing frrst mold
assembly is repeated at positions C, E and G, as illustrated in Figure 8, so
that
a belt segment having a plurality of vulcanized portions, shown at positions
A,
C, E. and G, and adjacent green portions, shown at positions B, D, F and H, is
formed, the respective belt segments indicated as 196, 198, 200 and 202. Each
to segment is separated from the other segments by a preselected distance Q
equal to the length of the central portion 174 of subplate 148. It will be
understood by those skilled in the art that although the procedure is repeated
four times in the illustrated example, the procedure may be successfully
emp~ioyed by dividing the track into fewer or more sections, as desired.
15 Belt positions B, D, F and H as illustrated in Figure 8, are, at this
point,
simply green belt segments with no tread. The green belt segments 197, 199,
201, 203 at positions B, D, F and H have the same length as the central
portion
174 of removable subplate 148 of second mold assembly 142.
Rubber track segments are provided for belt positions B, D, F and H in
20 the following manner. Referring now to Figure 9, core bar inserts 60 are
inserted into inner mold half 144 so that heads 66 are positioned into notches
170 of tug cavities 172. A third green rubber slug 210 is positioned in inner
mold
half 144. Subplate 148 is positioned over green rubber slug 210 utilizing
positioning means so that green rubber slug 210 is positioned in inner mold
half
25 cavity 150 between subplate outboard or end portions 176, 178 and under
central portion 174 utilizing positioning means. There is sufficient rubber in
green rubber slug 210 to completely fail inner mold half cavity 150 between
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subplate outboard or end portions 176, 178. A fourth green rubber slug 212 is
positioned over subplate central portion 174. Outer mold half 146 is
positioned
over fourth rubber slug 212 utilizing positioning means so that rubber slug is
positioned in outer mold half cavity 152 between subptate outboard or end ,
portions 176, 178. There is sufficient rubber in rubber slug 212 to completely
fill
outer mold half cavity 152 between subplate outer portions 176, 178. The
amounts of rubber utilized in green rubber slugs 210, 212 are determined in
the
same manner as the amount of rubber used in green rubber slugs 190, 192.
The second mold assembly 142, with rubber slugs 210, 212 inserted
so therein, is heated to an elevated temperature in the range of 50-
140°C which is
sufFcient to cause the rubber to soften. However, the temperature is not so
high
so that the rubber will vulcanize. This temperature may be achieved by any
conventional techniques, such as by providing electrical resistance heaters
within the mold or placing the rubber mold assembly in an oven at a
temperature
Zs in the range of 50-140°C, although the preferred method is
introducing steam
into steam channels built into the mold assembly (not shown). Pressure is also
applied perpendicular to mold halves 144, 146 substantially in the direction
of
the arrows as shown in Figure 9. The heat and pressure applied to mold
assembly 142 are sufficient to cause green rubber slugs 210, 212 to flow and
2 o fill mold half cavities 150, 152. The subplate outboard or end portions
176, 178
extend into lug cavities 172 and tread cavities 214 so as to prevent the flow
of
the softened rubber into the mating portions of the inner and outer mold
halves
144, 146, as shown in Figure 9A. After the green rubber has taken the shape
of the mold cavities adjacent subplate central portion 174, and preferably,
while
25 mold assembly 142 is still hot, inner mold half 144 and outer mold half 146
are
separated so that subplate 148 can be removed. The surface roughness of
mold halves 144, 146 facilitates the removal of smooth subptate 148 without
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disturbing rubber in cavities in the mold halves.
Referring now to Figure 10, a green belt segment, for example segment
197, located at position B is placed between inner mold half 144 and outer
mold
half 146 of second moid assembly 142. Second mold assembly 142 includes
green rubber filling the mold cavities which were adjacent subplate central
portion 174. However, mold cavities 216, 218, which were adjacent subplate
outboard or end portions 176, 178, are empty. As inner mold half 144 and outer
mold half 146 close about green best segment 197, inner and outer mold half
asse~mbiies 144, 146 overlap portions of adjacent rubber track segments,
rubber
to tracEc segment 196 at Position A and rubber track segment 198 at Position
C.
Empty cavities 216, 218 of inner and outer mold half assemblies 144, 146
capture end portions of each of rubber track segments 196, 198.
As can be seen by reference to Figures 2, 4 and 10, empty moil cavities
216, 218 which extend for a length greater than length L on either side of
filled
mold cavities of mold assembly 142, capture unvulcanized portions of rubber
track segments 196, 198, which extend a distance L, preferably about 1 to 2
pitches of the inner mold assembly, as well as adjacent vulcanized portions of
rub6~er track segments 196, 198.
The cavities of mold assembly 142 now capture all of the remaining green
2 0 or u~nvuicanized rubber as well as the green belt between the inner and
outer
mold halves. immediately adjacent to the captured green rubber, at either end
a portion of vulcanized rubber is also captured. The temperature of motel
assembly 142 is then raised to a temperature sufficient to vulcanize the green
rubber in mold assembly 142 and green belt positioned between inner and outer
mofc~ halves 144, 146, while pressure is applied. The temperature is in the
range of 145-180°C, and preferably from 155-165°C. The pressure
is held in the
range of 100-300 kilopascals. As the green rubber is vulcanized at elevated
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temperature and pressure, the vulcanized rubber captured at either end of the
mold assembly 142 acts as packing to prevent movement or flow of the green
rubber during the curing operation. After the rubber is vulcanized, the inner
and
outer mold halves are removed and the operations utilizing mold assembly 142
are repeated for green belt segments 199, 201, 203 at positions D, F and H.
Upon completion, a fully vulcanized endless rubber track is produced.
A preferred system for manufacturing rubber track, referred to as the dual
press system, utilizes two pair of presses to manufacture an endless rubber
track. Referring to Figure 11, a pair of first mold assemblies 102 is viewed
in
io cross section along the longitudinal axis of the assembly, that is the
longitudinal
axis of the assembly runs into and vut of the plane of the Figure. The
assemblies are each loaded with ftrst green rubber slugs 190 and second green
rubber slugs 192 and shown positioned horizontally on a support 221. Each
inner mold half 104 includes amts 222 which are connected to a pivot means
224 such as a pivot pin. After first green rubber slugs 190 are loaded into
inner
mold half 104 by a slug server, not shown, removable subplates 108 are
positioned over slugs 190. Second green rubber slugs 192 are loaded onto
subptates 108 by a slug server and outer mold halves 106 are positioned over
slugs 192. The assemblies are then pivoted 90° about pivot means 224 so
that
2 o first mold assemblies are in a vertical position on support 221 as shown
in
Figure 12. Pressure is then applied by press means 226, such as for example,
hydraulic presses, in a horizontal direction perpendicular to the faces of
outer
mold halves 106 and along the mold longitudinal axis as shown in Figure 12,
while heat is applied to first mold assemblies 102 to cause the green rubber
to
flow in accordance with the method previously set forth. The molds are then
opened and subplates 108 are removed, for example, with an overhead lifting
device as shown in Figure 13.
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Referring now to Figures 14 and 15, green rubber belt 194 is positioned
befinreen mold halves 104, 106. In these views, the belt is shown on edge, the
belt being parallel to the longitudinal axis of each mold half in the area of
interest. The belt may be positioned on a belt holder or hanger which lowers
the
s belt. However other methods for positioning the belt between the mold halves
may also be utilized. Once green rubber belt 194 is captured in mold
assemblies 102 at positions W, Y. cooling water is applied to mold halves as
previously discussed and pressure is applied by hydraulic presses 226 as the
temperature is raised, to vulcanize portions of the green rubber between the
z o mold halves as previously discussed, to form rubber track segments at 230,
234.
The centrat portions of the rubber track segments are vulcanized while the
outer
portions of the rubber track segments are green rubber, as previously
discussed.
After mold halves 104, 106 are removed, a partially completed track such as
shown in Figure 16 having rubber track segments 230, 234 at positions W, Y
15 and green belt segments 232, 236 at positions X, Z is produced.
Rubber track is provided to green belt segments 232, 236 in a similar
manner. Referring to Figure 17, a pair of second mold assemblies 142 is viewed
in cross section along the longitudinal axis of the assembly, that is, the
longitudinal axis of the assembly runs into and out of the plane of the
Figure.
2 o The assemblies are loaded with third green rubber slugs 210 and fourth
green
rubber slugs 212 and shown horizontally positioned on a support 221, which
may be the same support depicted in Figure 11, or may be a separate support.
Each of inner mold halves 144 includes arms 222 which are connected to pivot
means 224, such as a pivot pin. After third green rubber slugs 210 are loaded
25 into inner mold half 144 by a slug server, removabte subpiates 148 are
positioned over slugs 210. Fourth green rubber slugs 212 are loaded onto
subpiates 148 by a slug server and outer mold halves 146 are positioned over
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slugs 212. The assemblies are then pivoted 90° about pivot means 224 so
that
the second mold assemblies are in a vertical position on support 221 as shown
in Figure '! 8, wherein the assemblies are shown positioned on the support,
with
the longitudinal axes of each of the mold assemblies parallel to the mold
cavity
patterns of the exterior tread cavities and the interior lug cavities.
Pressure is
then applied by hydraulic presses 226 in a horizontal direction as shown in
Figure 16, while heat is applied to second mold assemblies 142 to cause the
green rubber to flow in the manner previously set forth for mold assemblies
142.
Subptates 148 are removed, as for example by an overhead crane. See, for
example, Figure 13.
Referring now to Figure 19, the partially completed track having rubber
track segments 230, 234 is positioned so that green belt segments 232, 236 are
between inner mold halves 144 and outer mold halves 146. The inner and outer
mold halves overlap rubber track segments 230, 234 as previously described for
~.5 second mold assembly 142. Pressure is applied across the faces of outer
mold
halves 146 substantially in the direction shown in Figure 19, forcing inner
mold
halves 144 together, and temperature in second mold assemblies 142 is raised
to vulcanize the green rubber within them. After vulcanization is complete,
the
mold halves are removed and a completed, vulcanized rubber track is produced.
The invention in its broader aspects is not limited to the specific
embodiments shown and described. Departures may be made therefrom
without departing from the principles of the invention and without
sacrifiicing its
chief advantages.
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