Note: Descriptions are shown in the official language in which they were submitted.
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DRAPER CANVAS WITH A SHAPED EDGE
This invention relates to a header for cutting and transporting a
standing crop with a transverse leading cutter bar and particularly to an
arrangement
which provides a seal between a front edge of a draper canvas and an element
of
the cutter bar and to a draper canvas designed for use with the header.
BACKGROUND OF THE INVENTION
Draper headers generally include a header frame, an elongate cutter
bar along a front edge of the frame including a cutter bar beam which carries
a
plurality of knife guards for guiding reciprocating movement of a sickle knife
across a
front edge of the cutter bar. On the header is also mounted a draper assembly
including a first and second draper guide roller each arranged at a respective
end of
the draper assembly spaced apart along the cutter bar with an axis of each
roller
extending substantially at right angles to the cutter bar, a draper canvas
forming a
continuous loop of flexible material wrapped around the rollers so as to
define a front
edge of the canvas adjacent the cutter bar, a rear edge of the canvas spaced
rearwardly of the cutter bar, an upper run of the canvas on top of the roller
and a
lower run of the canvas below the rollers. The cut crop thus falls rearwardly
onto the
upper run of the canvas and is transported longitudinally of the header.
Generally,
between the draper rollers there is provided a support plate assembly for the
upper
run of the draper canvas to prevent sagging.
The header of this type can be used simply for forming a swath in
which case the material is carried to a discharge opening of the header and
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2
deposited therefrom onto the ground. Headers of this type can also be used for
feeding a combine harvester so that the materials are carried to an adapter
member
positioned at the discharge opening of the header for carrying the materials
from the
discharge opening into the feeder housing of the combine harvester. Yet
further,
headers of this type can be used for hay conditioners in which the material
from the
discharge opening is carried into crushing rolls. It will be appreciated,
therefore, that
the use of the header is not limited to particular types of agricultural
machine but can
be used with any such machine in which it is necessary to cut a standing crop
and to
transport that crop when cut longitudinally of the header for operation
thereon.
The draper canvas normally comprises a fabric which is coated with a
rubber material which is then vulcanized after forming of the fabric into the
required
shape and after attachment thereto of transverse slats.
The arrangement of the above patent has achieved significant success
and has been used for many years. It provides a seal between an under surface
of
a rearwardly extending element of the cutter bar and a front edge portion of
the
upper surface of the canvas.
Also not shown in the above patent is the conventional guiding
arrangement to prevent misalignment of the draper canvas on the rollers and
this is
provided by a bead located on the underside of the canvas which runs in a
groove in
the roller.
One arrangement is shown in US Patent 6,351,931 (Shearer) issued
March 5th 2002 also of the present Assignees. This provides an additional
guide
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3
bead on the outer surface of the canvas which runs in contact with the edge of
the
element of the cutter bar. This arrangement has not been successful and has
not
been adopted since it failed to provide the expected improvements over the
Talbot
and Fox arrangement.
An alternative arrangement is shown in US Patent 7,472,533 (Talbot et
al) issued January 6 2009 also of the present Assignees and originally
published
April 24 2008. This provides a crop harvesting header with a cutter bar and a
draper
canvas with a plurality of transverse slats and a resilient strip across a
front edge of
the outer surface in front of the front end of the slats to cooperate with a
rearwardly
projecting element of the cutter bar extending over the upper run of the
draper
canvas to engage the upper surface of said strip to form a seal to inhibit
entry
between the cutter bar and the draper canvas of materials carried by the cut
crop.
There is also provided a bead on the canvas on the surface opposite the strip
within
the width of the strip. The arrangement can be symmetrical with a strip at
each of
the front and rear edges spanned by the slats extending between them, with
beads
on each edge opposite the front and rear strips respectively.
The disclosures of the above references may be reviewed for details of
the construction not provided herein.
SUMMARY OF THE INVENTION
It is one object of the invention to provide a further design of header
and particularly the draper canvas therefore which can assist in providing a
seal
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between the canvas and the cutter bar.
According to a first aspect of the invention there is provided a draper
canvas for use with a crop header arranged for cutting and transporting a
standing
crop, wherein the header comprises:
a header frame;
an elongate cutter bar arranged along a front edge of the frame;
a knife mounted on the cutter bar for cutting the standing crop;
a draper assembly mounted on the header frame rearwardly of the
cutter bar such that cut crop falls onto the draper assembly for
transportation
longitudinally of the header;
the draper assembly including a first and a second draper guide roller
each arranged at a respective end of the draper assembly spaced apart along
the
cutter bar with an axis of each guide roller arranged substantially at right
angles to
the cutter bar;
wherein the draper canvas forms a continuous loop of flexible material
arranged to be wrapped around the rollers so as to define an upper run of the
draper
canvas on top of the rollers and a lower run of the draper canvas below the
rollers;
wherein the draper canvas includes a front edge of the upper run of the
draper canvas arranged underneath the cutter bar, and a rear edge of the upper
run
of the draper canvas arranged at a position spaced rearwardly of the cutter
bar;
the draper canvas including at least one layer of fabric and a covering
of a rubber material;
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the draper canvas having a main center portion and an edge portion at
least at a front of the main center portion extending up to a front edge of
the draper
canvas;
the draper canvas having an upper surface and a lower surface
5 spaced downwardly from the upper surface;
at least a part of the upper surface of the edge portion at the front edge
of the draper canvas being arranged to engage underneath the cutter bar with
the
lower surface of the edge portion facing away from the cutter bar;
wherein the draper canvas is molded into a shape so that, when lying
unsupported, the edge portion of the canvas is canted upwardly at an angle
relative
to the main center portion;
the upper surface of the canted edge portion being at an angle
upwardly relative to the upper surface of the center portion;
the lower surface of the canted edge portion, when lying unsupported,
being at an angle upwardly relative to the lower surface of the center
portion.
Preferably the canted edge portion is arranged, when unstressed, at
an angle to the main portion lying in the range 0 to 30 degrees and preferably
in the
range 10 to 20 degrees.
The objective of the canted portion is to provide an additional spring
force tending to push the edge portion upwardly against the underside of the
cutter
bar. This can resist the tendency of the edge portion to sag over time to
maintain
the pressure which assists in excluding the dirt and to avoid the development
over
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time of a space between the sagging edge and the cutter bar which can allow
dirt
penetration.
Preferably the draper canvas includes on the upper surface an
additional thickness of rubber material extending along the canted edge
portion such
that the rubber material is thicker at the canted edge portion than on the
main
portion. The additional thickness of rubber material can cover substantially
the
whole of the canted edge portion or it can cover only part of the canted edge
portion
up to the front edge. Preferably the additional thickness of rubber material
is
substantially of constant thickness across the canted edge portion so that its
upper
surface engaging the edge of the cutter bar is flat and parallel to the main
body of
the draper. The additional thickness is relatively thin in comparison with its
width so
that it has a width from the front edge to its rear edge which is greater than
its height
or thickness from the outer surface of the canvas. This provides a seal of
sufficient
width to be effective without interfering with the flexibility of the canvas
to traverse
around the roller. Typically the strip has a width of the order of 25 mm and a
height
of the order of 4 mm.
Preferably the draper canvas includes on the lower surface of the
canted edge portion a bead extending along the canted edge portion which forms
a
V-guide for engagement into a corresponding shaped groove in the guide
rollers.
This v-guide operates at the rear of the canvas with a groove in the rear end
of the
guide rollers but the draper canvas is arranged symmetrically so that it
includes a
canted rear edge portion symmetrical to the canted front edge portion. This
allows
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the canvas to be reversed after a period of wear with the worn front edge
being
replaced by a symmetrical rear edge which is worn in different places due to
the
different functions of the front and rear edges.
The draper canvas includes a first layer of fabric extending across a
full width of the canvas from the front edge to the rear edge and preferably
includes
in a first strip portion at the front edge an additional second layer of
fabric. Generally
in symmetrical manner it includes also a similar strip and the rear edge. The
second
layer of fabric can have a greater tear strength than that of the first layer
of fabric.
However it can also be of the same material with the same properties. The
first strip
portion is wider than the canted edge portion. In this way the two layers of
the fabric
pass through the junction between the canted edge portion and the main body so
as
to assist in maintaining the angle therebetween.
Preferably there is provided a layer of rubber material between the first
and second layers of fabric and the second layer of fabric is on top of the
first layer.
However it can also be below.
As in most canvas constructions of this type, the draper canvas
typically carries a plurality of transverse slats at spaced positions along
the length of
the canvas and integrally formed with the rubber layer. Each slat has a front
end
terminating rearwardly of a rear edge of the canted edge portion and
symmetrically
forwardly of the rear canted edge portion.
As shown in the above patent of Talbot, the draper canvas is
supported at a front edge by the guide rollers and by a front draper support
plate
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extending therealong between the guide rollers and the support plate has a
front
edge thereof recessed rearwardly of the front edge of the upper run of the
draper
canvas such that the upper run of the draper canvas includes a portion thereof
at the
front edge which is cantilevered forwardly of the support plate.
According to a second aspect of the invention there is provided a
draper canvas for use with a crop header arranged for cutting and transporting
a
standing crop
the draper canvas including at least one layer of fabric and a covering
of a rubber material;
the draper canvas being formed to define a main portion extending
across a center and an edge portion at a front edge which is canted upwardly
at an
angle from the main portion;
the draper canvas having a main center portion and an edge portion at
least at a front of the main center portion extending up to a front edge of
the draper
canvas;
the draper canvas having an upper surface and a lower surface
spaced downwardly from the upper surface;
wherein the draper canvas is molded into a shape so that, when lying
unsupported, the edge portion of the canvas is canted upwardly at an angle
relative
to the main center portion;
the upper surface of the canted edge portion being at an angle
upwardly relative to the upper surface of the center portion;
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the lower surface of the canted edge portion, when lying unsupported,
being at an angle upwardly relative to the lower surface of the center
portion.
wherein the draper canvas includes on the upper surface an additional
thickness of rubber material extending along the canted edge portion such that
the
rubber material is thicker at the canted edge portion than on the main center
portion.
It will be appreciated that the term "draper canvas" is a traditional term
based upon the material from which the "canvas" was made but that this term no
longer provides any indication of nor limitation to the use of particular
materials for
the base fabric from which the "canvas" is made. Many synthetic material can
thus
be used. Commonly the canvas is coated with a rubber layer and again many
different resilient coating materials can be used and no limitation is
intended herein
in this regard. The increased thickness at the canted edge portion described
above
can be made of the same material as the remaining rubber covering or may be a
strip of a different material of different chemical structure or of different
characteristics.
While the knife used with the cutter bar is usually of the sickle knife
type including a plurality of knife guards mounted on the cutter bar, other
types of
knife can also be used.
In some embodiments, the cutter bar itself comprises a channel
shaped member which defines the trailing edge as an integral portion of the
cutter
bar itself. In other embodiments, the cutter bar forms in effect a single bar
carrying
the sickle knife with a separate canvas carrier element in the form of a plate
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attached to and carried by the cutter bar. In this latter arrangement, the
trailing edge
can be provided by the edge of the canvas carrier rather than the cutter bar
itself.
However it will be appreciated that in both arrangements the guide bead
engages an
edge which is fixed relative to the cutter bar and thus is guided in position
relative to
5 the cutter bar as it moves along the cutter bar.
Preferably the rear edge of the strip of resilient material at the front
edge is substantially coincident with the rear edge of the cutter bar or the
element
thereof which it engages. This is the intention in order that the sealing
surface be
coincident. However it will be appreciated that the rear edge of the strip can
be
10 slightly retarded from or slightly proud of the rear edge of the element
without
interfering with the operation.
Preferably the rear edge of the strip is in front of the front edge of the
support plate. In this way the strip is cantilevered forwardly of the support
plate and
thus part of the canvas which is free to flex from pressure from the element
of the
cutter bar.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which Figures 1 to 5 are taken from prior
art
patent 7,472,533 cited above and are included for completeness only.:
Figure 1 is a top plan view of the front part of a header of the prior art.
Figure 2 is a cross sectional view along the lines 2-2 of Figure 1
showing the front part of the header and draper canvas.
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Figure 3 is a cross sectional view along the lines 2-2 of Figure 1
showing the rear part of the header and draper canvas and the co-operation of
the
rear guide bead with a groove in the roller..
Figure 4 is a cross sectional view through one edge of the canvas only
taken at location where there is no transverse slat.
Figure 5 is a cross sectional view through one edge of the canvas only
taken at a transverse slat.
Figure 6 is a side elevational view of a draper canvas according to the
present invention to be used in the header described above.
In the drawings like characters of reference indicate corresponding
parts in the different figures.
DETAILED DESCRIPTION
The following description is taken from the above prior art patent. Only
those parts of the header which are of importance to the present invention are
shown in the above figures of the present application and the remaining parts
of the
header including the frame structure, drives, ground wheels and the like are
omitted
as these will be well known to one skilled in the art.
The header therefore comprises a frame, one element of which is
indicated at 10 in the form of a beam extending horizontally and forwardly
from a
rear support frame structure (not shown) to a cutter bar assembly generally
indicated
at 11 for support of that cutter bar assembly. The beam 10 forms one of a
plurality
of such beams arranged at spaced positions along the length of the header
frame so
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as to support the cutter bar assembly 11 as an elongate structure across the
front
edge of the header.
The cutter bar comprises a generally C-shaped beam 12 which
provides structural support for the cutter bar with the C-shaped beam being
welded
to the front ends of the forwardly extending beams 10. The C-shape beam 12
includes a top plate portion 13, a bottom plate portion 14 and a forward plate
portion
which converges from the top and bottom plate portions toward a front apex 16
forming a forward most point of the beam 12. At the apex 16 is welded a
longitudinally extending bar 17 which forms a support for a plurality of knife
guards
10 18 only some of which are shown in Figure 1 for convenience of
illustration. The
knife guards are of course of well known construction and their shape is shown
only
schematically. The knife guards carry a sickle knife assembly 20 having a
longitudinally reciprocating bar 21 driving a plurality of triangular knife
blades 22
which sit on the knife guards and reciprocate back and forth across the knife
guards
15 in a cutting action. Again this construction is well known and therefore
detail is not
necessary.
The cutter bar support beam 12 also carries an elongate angle iron 23
which is welded onto the top plate portion 13 on the underside thereof at the
front
edge thereof with the angle iron extending vertically downwardly and then
forming a
support plate 24 extending forwardly therefrom toward the apex 16.
The draper assembly generally indicated at DA includes a first draper
support roller 30 and a second draper support roller (not shown). One of these
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rollers is driven by a drive motor (not shown) to effect rotation of the
draper in
conventional manner. The draper assembly further includes a draper canvas 32
in
the form of a continuous loop or band of fabric which is wrapped around the
rollers
at respective ends to form an upper run 33 of the draper canvas on top of the
rollers
and a lower run 34 of the canvas underneath the rollers. The rollers are thus
spaced
longitudinally of the cutter bar and arranged with their axes of rotation
parallel and at
right angles to the cutter bar. The draper canvas thus includes a front edge
35 of
the upper run which is adjacent the cutter bar and a rear edge 36 of the upper
run 33
which is remote from the cutter bar and spaced rearwardly therefrom thus
defining
therebetween a flat surface of the upper run for transportation of the crop
longitudinally of the header. The lower run 34 also includes a front edge 37
and a
rear edge. The draper canvas includes a plurality of conventional transverse
slats
39 which assist in carrying the crop along the draper canvas. Each edge of the
draper canvas can include a conventional folded seam so as to define a portion
of
the canvas material which is folded back as indicated at 40 with that folded
back
portion being folded back on top of the fabric layer and bonded to the canvas
by the
vulcanization effect in the manufacture of the canvas.
The upper run of the draper canvas is supported by a support plate
assembly 45 which includes a front plate and includes a center plate and rear
plates
which are not shown for convenience of illustration. The front plate includes
a
horizontal top plate portion 46, shown in phantom in Figure 1, lying
underneath the
upper run of the draper canvas adjacent the front edge for supporting that
front edge
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in sliding movement across the top surface of that plate. The support plate 46
further includes a vertical plate portion, which extends downwardly from a
front edge
of the top plate portion (not shown in the figures). At a bottom edge of the
vertical
plate portion is provided a lower horizontal plate portion thus forming the
front
support plate into a generally C-shape to provide structural strength so that
the
support plate is essentially self supporting mounted on mounting brackets
(also not
shown).
The rollers 30 are carried on the support plate 46. Further details of the
brackets and support elements are described in the above patent of Talbot.
The length of the bracket 25 is arranged so that the front edge 49 of
the support plate is spaced rearwardly from the front edge 35 of the upper run
of the
draper canvas. In addition the front end of the rollers 30 is spaced
rearwardly from
the front edge 35 of the upper run of the canvas. This recessing of the front
edges
of the support plate member and of the rollers provides a portion 70 of the
front edge
of the draper canvas which is cantilevered outwardly beyond the support
provided by
those elements.
The beam 12 of the cutter bar is shaped so that the top plate portion
13 extends rearwardly to a rear edge 71 which overlaps the portion 70. The
rear
edge 71 is located therefore at a position rearwardly of the front edge 35 of
the
draper canvas and in a position forwardly of the front edge 49 of the support
plate
and the front ends 65 of the draper rollers. That portion of the draper canvas
therefore which engages the underside 72 of the top plate portion 13 is
unsupported
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on its underside and is therefore free to flex downwardly should it be
depressed
downwardly by the presence of material collecting on the under surface 72. The
top
plate portion 13 of the beam 12 is substantially horizontal that is parallel
to the
generally horizontal surface of the upper run. The cooperation therefore
between
5 the surface 72 of the upper plate portion 13 and the upper surface of the
draper
canvas at the portion 70 provides a seal which inhibits the tendency of
materials to
pass between the draper canvas and the cutter bar. This seal therefore
inhibits the
build-up of materials inside the C-shape of the cutter bar and between the
draper
canvas upper run and lower run and around the draper rollers which can of
course
10 cause damage.
At the rear edge 36, the draper canvas is guided on the draper roller by
a V groove 30A in the roller 30 into which projects from the back of the
canvas a V-
shaped guide rib 75 which runs along the inner surface of the canvas along its
full
length.
15 The construction of the draper of the present invention as shown in
Figures 4 and 5. Thus the draper of the present invention is symmetrical in
that the
draper can be reversed by rotating the draper so that the front edge is turned
to
become the rear edge and vice versa. Thus only the front edge is shown in
Figures
1, 4 and 5 with it being understood that the rear edge is exactly symmetrical.
Thus
in Figure 4 is shown a portion of the draper canvas which includes a base
layer or
sheet 80 which is formed of a fabric sheet 81 which is folded at its edge 82
to form a
portion 83 which is folded back on top of the layer 81 to form an end edge 84
of the
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folded back portion 83 which lies on top of the fabric of the layer 81 spaced
away
from the edge 82. The canvas carries a coating or infused rubberized layer in
a
conventional manner. At the edge 82 is provided a strip 86 of a resilient
material.
The resilient material is preferably of the same construction as the
rubberized
coating so that it can be vulcanized with the structure of the canvas and
molded in
place as part of the manufacturing process. The strip 86 has a front edge 87
which is
at or immediately adjacent the edge 82 of the base layer of the canvas. In the
embodiment shown the front edge 87 of the strip is immediately coincident with
the
edge 82. The strip includes a rear edge 88 spaced away from the edge 87 into
the
body of the canvas. The strip has an upper surface 89 which is flat and
smooth.
Thus the strip is rectangular with the side edges 87 and 88 being vertical and
the top
surface 89 horizontal. However the strip may be shaped with inclined or
tapered
side edges 87 and 88.
In the example shown the strip has the width of the order of 1" (25mm)
and a height of the order of 1/6" (4.0mm). The strip thus stands up from the
upper
surface of the base layer of the draper canvas that is the upper surface of
the folded
back portion 83.
On the underside of the draper canvas is molded the bead 75 which is
generally V shaped so that the sides are tapered downwardly and inwardly to a
bottom surface 75A which is narrower than the base of the bead. The bead is
located at a position spaced from the edge 82 but underlying the strip 86 so
that the
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edge of the bead is spaced from the edge 82 by a distance less than the edge
88 of
the strip.
As shown in Figure 5 the canvas also carries slats 39 which stand
upwardly from the upper surface of the canvas to a top edge 39A which is at a
height significantly greater than the height of the strip 86. Each slat
extends
transversely across the draper canvas to a position closely adjacent the strip
at the
respective side edges of the canvas. Thus each slat extends to an end edge 39B
which is spaced from the side edge 82 by a distance greater than the spacing
of the
edge 88 of the strip so that the edge 39B of the slat is spaced from the edge
88 of
the strip. The slats 39 are molded integrally with the strip 86 by providing
portions
90 which extend from the edge 39B of the slat to the edge 88 of the strip 86.
These
portions as best shown in Figure 1 have a width equal to the width of the slat
39 to
which they are attached and a height (as shown in Figure 5) equal to the
height of
the strip 86. These portions thus act to integrate the structure so that the
slats
connect into the strip to reduce the tendency of the slats to tear away from
the
canvas since the same resilient material forming the strip extends into the
slat and
thus is resistant to stripping or tearing from the base layer of the draper
canvas, In
the example shown, the bead 75 has a width at its base of the order of 1/2"
(13mm)
and a height from the under-surface of the canvas of the order 1/3" (8mm). The
center of the bead is spaced from the edge 82 by a distance of the order of
2/3"
(16mm). This suitably locates the bead at a position on the canvas for
cooperation
with the groove in the roller at the rear of the canvas as best shown in
Figure 3.
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Turning now to Figure 2, it will be noted that the side edge 88 of the
strip is substantially coincident with the end edge 71 of the plate 13 so that
the whole
of the strip 86 underlies the plate 13. The presence of the strip 86 provides
an
improved sealing effect between the surface 89 of the strip and the surface 72
of the
plate 13 due to an increase in pressure therebetween. In addition the presence
of
the shoulder or edge 88 provides a raised surface standing upwardly from
surface of
the canvas to inhibit the penetration of material into the space between the
surfaces
89 and 72. The surface 89 is formed as a flat surface molded onto the top of
the
resilient strip so that the surface 89 can be formed if required. Also it is
or can be
smoother than the surface of the canvas itself to provide an improved contact
surface engaging the surface 72.
It will be noted in Figure 2 that the bead 75 at the front edge is located
at a position spaced forwardly of the edge 49 of the support plate and
forwardly of
the end of the roller. Thus the bead 75 at the front edge of the canvas has no
effect
since it is engaging no component of the roller or support plate. However it
will be
noted that the bead 75 at the rear edge is located in engagement with a groove
in
the roller. In this way wear of the structure takes place at the strip 86 at
the front
edge and the bead 75 at the rear edge. These two components are worn in use so
that the strip 86 at the rear edge and the bead 75 at the front edge remain
unworn.
Rotation of the canvas when the wear has become excessive allows therefore the
canvas to continue in use while the strip 86 from the rear edge is moved for
the
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sealing effect at the front edge and the bead 75 is moved to the rear edge for
providing guiding action.
Turning now to the present invention the draper canvas generally
indicated at 100 and generally of the construction as described above for use
in the
header as described above is shown in cross-section at the front edge. It will
be
appreciated that, as previously described, the canvas is symmetrical so that
the rear
edge is exactly symmetrical to enable the canvas to be reversed when partly
worn,
so that the arrangement of the rear edge is not shown since this would be
merely
duplicative.
The draper canvas 100 thus forms a continuous loop of flexible
material arranged to be wrapped around the rollers 30 so as to define an upper
run
of the draper canvas on top of the rollers and a lower run of the draper
canvas below
the rollers and so as to define an outer surface 102 facing outwardly and an
opposed inner surface 103.
The draper canvas, as shown in Figure 2, includes a front edge of the
upper run of the draper canvas arranged underneath the cutter bar, and a rear
edge
of the upper run of the draper canvas arranged at a position spaced rearwardly
of
the cutter bar. In Figure 6, the front edge is shown at 101 and the cutter bar
and its
components are omitted for convenience of illustration.
The draper canvas is formed by a first layer 104 of a first fabric and a
second layer 105 of a second fabric together with a top layer 106 of a
covering of a
rubber material on top of the fabric and a bottom layer 107 below the fabric.
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The first layer 104 of fabric extends across a full width of the canvas
from the front edge to the rear edge so as to define with the top rubber layer
106 and
the bottom rubber layer 107 the main body of the canvas.
The second layer 105 of fabric forms a first strip portion extending from
5 a front edge 108 at the front edge 101 to a rear edge 109. Generally in
symmetrical
manner, as explained above, it includes also a similar second strip at the
rear edge.
In some cases, the second layer 105 of fabric is selected so that it has a
greater tear
strength than that of the first layer of fabric to provide increased strength
particularly
at the strips along the front and rear edges where most of the tension in the
canvas
10 occurs. However the fabrics can be of the same material with the same
properties.
There is also provided a third layer 110 of rubber material between the first
and
second layers of fabric with the second layer 105 of fabric extending on top
of the
third layer 110 and on top of the first layer 104 of fabric.
The rubber is laid in strips into the construction during manufacture
15 and then vulcanized to integrate the structure and bury the fabric layers
in the rubber
material.
The draper canvas is formed in the manufacturing process to define a
main portion 111 extending across a center of the canvas and an edge portion
112
at the front edge 101 which is canted upwardly at an angle A from the main
portion.
20 This angle A is maintained by forming the structure while held at the
required angle
in a molding system so that the vulcanization of the rubber occurs at the
molded
angle and tends to hold the canted portion at this angle, although it can of
course be
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distorted from this unstressed position by downward forces on the portion 112
which
occur as the canvas wraps around the end rollers and as the edge is distorted
downwardly by downward pressure applied by the cutter bar as the edge is held
under the cutter bar.
Thus, as previously described, the canted edge portion 112 is
arranged to engage underneath the cutter bar.
The canted portion thus provides an additional spring force tending to
push the edge portion upwardly against the underside of the cutter bar. This
can
resist the tendency of the edge portion to sag over time to maintain the
pressure
which assists in excluding the dirt and to avoid the development over time of
a space
between the sagging edge and the cutter bar which can allow dirt or crop
penetration.
The fabric 105 is wider than the canted edge portion. In this way the
two layers of the fabric pass through the junction between the canted edge
portion
and the main body so as to assist in maintaining the angle therebetween. That
is
the two layers of fabric are held apart by the layer 110 so that there is a
requirement
to stretch one or both of these fabric layers and/or to compress the rubber
layer in
order to deform the structure out of its canted position.
The angle A is formed in the mold at a bend line 113 to be greater than
0 degrees and typically less than 30 degrees. An angle in the range 10 to 20
degrees has been found satisfactory.
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The draper canvas 100 includes on the upper surface 102 at the
canted edge portion 112 an additional thickness 114 of rubber material
extending
along the canted edge portion 112 such that the rubber material layer 106 is
thicker
at the canted edge portion than on the main portion. The additional thickness
portion 114 covers substantially the whole of the canted edge portion from a
front
edge 115 at the front edge 101 to a rear edge 116 in front of the bend line
113. The
additional thickness portion 114 is substantially of constant thickness across
the
canted edge portion 112 so that its upper surface 117, which engages in
operation
the edge of the cutter bar, is flat and parallel to the main body of the
draper. The
additional thickness is relatively thin in comparison with its width so that
it has a
width from the front edge 115 to its rear edge 116 which is greater than its
height or
thickness T from the outer surface of the canvas, that is the normal thickness
of the
layer 106. This provides a seal with the cutter bar which is of sufficient
width to be
effective without interfering with the flexibility of the canvas to traverse
around the
roller. Typically the strip has a width of the order of 25 mm and a height of
the order
of 4 mm.
The draper canvas includes on the lower surface 103 of the canted
edge portion 112 a bead 120 extending along the canted edge portion which
forms a
V-guide for engagement into a corresponding shaped groove in the guide
rollers.
This v-guide operates at the rear of the canvas with a groove in the rear end
of the
guide rollers but the draper canvas is arranged symmetrically so that it
includes a
canted rear edge portion symmetrical to the canted front edge portion. This
allows
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the canvas to be reversed after a period of wear with the worn front edge
being
replaced by a symmetrical rear edge which is worn in different places due to
the
different functions of the front and rear edges.
The draper canvas carries a plurality of transverse slats 121 at spaced
positions along the length of the canvas and integrally formed with the rubber
layer
106. Each slat 121 has a front end 122 terminating at or just rearwardly of
the bend
line 113.
