Note: Descriptions are shown in the official language in which they were submitted.
CA 02567494 2006-11-24
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Power Transmission Belt and Method
This application is a divisional of application
Serial No. 2,453,899, filed on July 17, 2002.
Field of the Invention
The invention relates to power transmission belts
having a low cordline and a method of producing same.
Background of the Invention
It is known in the art to make power transmission
belts from elastomeric materials having an embedded tensile
member. The belts may describe a multi-rib, toothed or v
type profile. The belts run in pulleys having a cooperating
profile.
It is known that the tensile cord in power
transmission belts is generally disposed in an elastomeric
matrix. In particular, on multi-ribbed belts the tensile
members are disposed in the body of the belt. This form of
construction places an increased lever arm on the belt rib
which is supported by the tensile members. The amount of
force exerted is in direct proportion to the radial distance
from the center of the tensile cord line to the bearing
surface of the mating pulley. A longer lever arm length
diminishes the operating life of the belt.
The method of fabrication of the belt determines,
in part, the location of the tensile cord. In the case of
ground belts, a belt slab is molded and vulcanized on a
mandrel. The belt slab is then removed and the multi-rib
profile is then ground into the belt slab. Since the
grinding operation cannot be completely controlled, some
allowance must be made in the location of the tensile cord
to prevent it from being cut by the grinding
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operation. This results in the tensile cord line being a
larger than preferred distance from a rib apex.
Representative of the art is U.S. patent no.
3,820,409 to Meadows which discloses a v-belt having a
plurality of closely spaced supporting cords arranged
transverse to and on at least one side of the load
carrying cord.
What is needed is a belt having a significantly
reduced distance from a tensile cord to a rib apex. What
is needed is a belt having a significantly reduced
distance from a tensile cord to a rib/ 'illey interface.
What is needed is a belt having an overcord layer
disposed in an elastomeric layer overlying a tensile cord
for controlling a tensile cord location during molding.
The present invention meets these needs.
Summary of the Invention
The primary aspect of the invention is to provide a
power transmission belt having a significantly reduced
distance from tensile cord to a rib apex.
Another aspect of the invention is to provide a
power transmission belt having a significantly reduced
distance from a tensile cord to a rib/pulley interface.
Another aspect of the invention is to provide a
power transmission belt having an overcord layer disposed
in an elastomeric layer overlying a tensile cord for
controlling a tensile cord location during molding.
Other aspects of the invention will be pointed out
or made obvious by the following description of the
invention and the accompanying drawings.
The invention comprises a belt having a plied
construction overlying tensile cords. An elastomeric
layer overlies an overcord which overlies yet another
elastomeric layer which in turn overlies a tensile cord.
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The overcord layer supports the tensile cords during molding
thereby stabilizing a cordline position. This construction
results in a significantly reduced distance from a tensile
cord centerline to a rib apex and rib/pulley interface in a
multi-ribbed belt.
According to an aspect of the invention, there is
provided a belt comprising: a first elastomeric layer; a first
cross-cord layer bonded to the first elastomeric layer;
tensile members extending along a longitudinal axis of the
belt; and a second elastomeric layer bonded to the cross-cord
layer and overlaying the tensile members; the belt further
comprising a multi-ribbed profile; and a third elastomeric
layer bonded to the second elastomeric layer, the multi-ribbed
profile being defined in the third elastomeric layer; wherein
the second elastomeric layer extends between the tensile
members and forms lobes disposed between the tensile members
and a rib apex of the ribbed profile, the lobes being
substantially parallel to the tensile members.
Brief Description of the Drawings
Fig. 1 is a cross-sectional view of the prior art.
Fig. 2 is a cross-sectional view of the inventive belt.
Fig. 2A is a detail of Fig. 2 after the molding operation.
Fig. 3 is a chart of test results for the inventive belt.
Fig. 4 depicts high load life test results for the inventive
belt.
Fig. 5 depicts a high temperature durability life for the
inventive belt.
Fig. 6 is a cross-sectional view of a -d dimension.
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Fig. 7 is a side view of a belt section.
Fig. 8 depicts conventional overcord construction.
Fig. 9 depicts overcord construction for the inventive belt.
Detailed Description of the Preferred Embodiment
Fig. 1 is a cross-sectional view of the prior art.
The prior art construction comprises an overcord A,
undercord B and tensile cords C. The cord line centerline
is shown at a given distance d from an apex of a multi-
ribbed profile. The cordline must be at a sufficient
distance d from the rib apex to avoid being damaged when the
multi-rib profile is ground into the belt. Tensile cords C
are embedded in elastomer material D.
Fig. 2 is a cross-sectional view of the inventive
belt. Belt 100 comprises a plurality of layers. Undercord
14 comprises a multi-ribbed profile in the
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preferred embodiment. In operation, belt 100 engages
pulley P.
More particularly, layer 10 comprises gum or fiber-
loaded elastomeric material. Overcord or cross-cord 11
comprises a cross-cord layer. The cross-cord layer
supports tensile cord 13 during the molding and curing
process, maintaining a proper cordline location within
the belt body. Cross-cord 11 may comprise woven or non-
woven material.
Cross-cord layer 11 is substantially non-porous,
preventing a significant amount of layer 10 from
penetrating through layer 11 during the molding process.
This has the effect of layer 11 supporting tensile cord
13 thereby controlling a uniform tensile cord centerline
, CL location.
A thin layer of gum 12 is applied between layer 11
and the tensile cord 13. Cords 13 extend along a
longitudinal axis of the belt. Although in the preferred
embodiment the gum 12 layer is applied between layer 11
and tensile cords 13, gum 12 may also be applied between
tensile cords 13 and undercord layer 14 so long as cords
13 are encapsulated by gum 12 during molding.
Undercord 14 comprises an elastomeric material
having a fiber loading. In an alternate embodiment it may
also comprise pure elastomeric without fiber loading,
i.e., a gum layer. The fiber loading for layer 10 and 14
may be in the range of .1 to 20 parts per hundred. The
fibers may comprise any known in the art, including by
way of example cotton, PTFE, and aramid.
Jacket 15 may be included and may comprise woven or
non-woven material in order to establish a coefficient of
friction.
Manufacturing.
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The inventive belt is constructed in a process of
sequential application of each layer on a build drum. The
belt is fabricated by molding using an expanding membrane
that presses the belt slab into a ribbed outer shell. In
this process the belt is built-up on a mandrel having an
expandable member on the surface of the mandrel. During
molding and curing the expandable member presses the belt
build into an outer shell mold. Use of the cross-cord
overcord ply 11 stabilizes the tensile cordline 13
position, resulting in a precisely controlled cordline
position. This allows the tensile cord 13 to be placed
closer to a rib apex 16, and thereby closer to a
rib/pulley interface RP significantly increasing
operating life. By comparison, prior art cordlines are
at a greater distance from a rib apex and rib/pulley
interface, resulting in a shorter operational life.
In particular, a first elastomeric layer 10 of a gum
elastomeric or fiber-loaded material is plied on the
mandrel. Next, a cross-cord layer 11 is applied. Due to
the flow characteristics of the gum during molding, the
cross-cord layer 11 can be butt-spliced by stitching the
ends of the ply together or left with a gap as described
in Fig. 9.
Next, a second elastomeric layer comprising a thin
ply of gum stock 12 is applied over the cross-cord ply
11. Layer 12 is solely made of rubber stock in the
preferred embodiment. Next, the tensile members or cords
13 are wound over the gum stock ply. Next, the third
elastomeric layer comprising a fiber-loaded undercord ply
14 is applied. Finally, a ply of non-woven material 15
is applied to the surface of the undercord ply. Non-
woven material 15 may comprise cellulose or non-cellulose
------------ ------------
----based mate ia1s. - -
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Use of the build and process results in the final
cord position remaining stable and significantly closer
to a rib apex 16 and rib/pulley interface RP. In
particular, during the inverted molding operation the
belt build, and cord 13 in particular, is spiraled onto
an expanding membrane positioned in a build drum. During
molding the expanding membrane or bag pushes the belt
build into the mold shell ribs.
In the prior art during a forming sequence the cord
13 tended to either distort or pull down into the first
available support layer. The resulting misalignment of
the cords caused them to have differing loads, thereby
decreasing the operational life.
In the inventive belt and process, the support to
prevent this occurrence is provided by cross-cord layer
11. In this manner the cord 13 is supported causing
cordline CL to be placed more precisely and closer to the
rib/pulley interface RP.
This construction also has a significant advantage
over the fabrication method wherein a belt profile is
ground into the cured belt build. In the case of a
ground belt the cord line must be located a greater
distance from a rib apex 16 to avoid having the cord
inadvertently damaged by the grinding operation. In the
instant molded construction, the cord line is much closer
to the apex.
The disclosed construction of the inventive belt
places cordline CL at a lesser radial distance d above an
rib apex 16 and rib/pulley interface RP (d2) as compared
to prior art belts. Positioning the cordline in this
manner provides superior dynamic performance, see Fig. 3.
The range of radial distance d in the inventive belt is
such that an outer surface of tfie c d i3 is
approximately .000" to .050" above the rib apex 16. It
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is also possible for the cordline distance d to be
negative such that an outer surface of the cord is below
the rib apex, effectively placing cord 13 partially or
totally within the ribs, see Fig. 6. The distance of a
cord centerline relative the rib apex is in the
approximate range of -.040" to .000". The negative
value, for example, -.040", indicates the cord is "below"
the rib apex such that the cord is set within the ribs,
see Fig. 6, a cross-sectional view of a -d dimension.
In the preferred embodiment the range of d is
approximately between .010" and .015" above the rib apex
for a cord 13 having a diameter of approximately .040".
In the case where radial distance d is equal to .020", a
tensile cord 13 is at the surface of layer 14 at a rib
apex 16. The cord diameter given herein is for
illustrative purposes only and may be varied depending
upon the needs of a user and operating conditions of the
belt.
As previously noted, the disclosed construction of
the inventive belt has the effect of reducing a distance
d2 from a rib/pulley interface RP to the belt cordline
CL. Reduction of distance d2 causes a reduction of the
magnitude of the deflection of the rib as the belt
engages a pulley. More particularly, during operation as
a belt engages a pulley the rib elastomeric material
deflects in response to the torque being transmitted to
the pulley. The deflection is along a longitudinal axis
and is relative to a point on the tensile cord. See Fig.
7.
Fig. 7 is a side view of a belt section. A
represents a point on a tensile cord 13. C represents a
point on a pulley engaging surface of a rib 14. When the
- -belt - unde-r-
p u l l e y - deflects such that point C deflects to point B through a
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distance D3. The magnitude of distance D3 is a function
of d2 as described herein. As d2 is increased, so is D3.
Conversely, as d2 is decreased, D3 is decreased.
Excessive deflection, D3, causes premature belt failure
by rib cracking. Reduction of deflection D3 during
operation by significantly reducing d2 significantly
increases the life span of the inventive belt.
Fig. 2A is a detail of Fig. 2. The belt cross-
section is such that elastomeric layer 12 has been
pressed between and through the tensile cords 13 forming
lobes 120. Lobes 120 run parallel to and along a length
of the tensile cords, substantially parallel to a
longitudinal axis. Layer 11 is also pressed adjacent to
the tensile cords and bears upon a thin remaining portion
of layer 12 upon cords 13. Lobes 120 comprise
elastomeric from layer 12. Lobes 120 provide support and
cushion for the cords during operation.-
Fig. 3 is a chart of test results for the inventive
belt. As shown in Fig. 3, reducing the average distance
between a rib apex 16, and thereby rib/pulley interface
RP, and the cordline CL significantly increases belt
life. For example, belt life for a belt having an average
tensile cord centerline to rib apex radial distance d of
approximately .042" is 100 hours as compared to 280 hours
for a belt having an average tensile cord centerline to
rib apex radial distance d of approximately .032".
Fig. 4 depicts high load life test results for the
inventive belt. The inventive belt exhibited
significantly improved high load life. The high load
test comprises running a belt at approximately 4900 RPM
under approximately 264 pounds total tension at a
temperature of approximately 85 . The inventive belt
operated approximately 280 hours o failure while a belt
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having a higher cordline location operated less than 150
hours to failure, an improvement of 86%.
Fig. 5 depicts a high temperature durability life
for the inventive belt. The inventive belt exhibits
significantly improved high temperature durability. The
high temperature durability test comprises a running a
belt on a three point drive at approximately 13000 RPM
under approximately 282 pounds total tension at a
temperature of approximately 250 F. The inventive belt
operated approximately 390 hours to failure while a belt
having a standard cordline operated 250 hours to failure,
an improvement of 56%.
Fig. 8 depicts conventional overcord construction.
Overcord layer C is joined at a lap joint. An end of the
lap joint overlays the lower portion by an amount OL.
This "high spot" creates a bump that can cause noise
during operation in the case of use of the belt with a
backside idler.
Fig. 9 depicts overcord construction for the
inventive belt. As described elsewhere in this
specification, layer 10 overlays cross-cord layer 11. D
depicts the build drum upon which the belt is layed-up
during fabrication as described elsewhere in this
specification. Ends 11A and 11B of layer 11 may be
configured in a butt splice and/or stitched to each
other. However, in the preferred embodiment, during
fabrication on the build drum a slight gap G may be
present between the ends 11A and 11B, allowing an end 11A
to be stitched into layer 10 instead of to the opposite
end 11B. During vulcanization, the material of layer 10
then flows together across the gap creating a seamless
joint. A seamless joint eliminates any noise that might
--be paused by the "belt traveling over a backside idler.
Consequently, fabricating the belt with a gap on the
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overcord is an improvement over a prior art belt where a
gap on the overcord layer would cause noise in the case
of use of a backside idler because the prior art belts
require the ends of the overcord layer to be closely
controlled. The inventive belt does not require the ends
of layer 11 to be precisely cut and layed-up also
resulting in decreased fabrication costs.
Although a single form of the invention has been
described herein, it will be obvious to those skilled in
the art that variations may be made in the construction
and relation of parts without departing from the spirit
and scope of the invention described herein.
