TECHNICAL FIELD
The present invention relates to a conveyor belt cleaner and tensioning
arrangement, and in particular to a conveyor belt cleaner and tensioning arrangement
wherein the scraper blades of the conveyor belt cleaner have a blade face which
provides initial and subsequent full-face contact with the conveyor belt and wherein the
scraper blades maintain a substantially constant cleaning angle with the surface of the
conveyor belt and engage the conveyor belt with a substantially constant scraping
pressure during the wear life of the scraper blades.
BACKGROUND ART
Conveyor mechanisms utilize an endless conveyor belt to transport bulk
material, such as sand, gravel, coal and other bulk materials, from one location to
another. Such a conveyor utilizes a rotating drum at each end of the moving belt. As the
bulk material is discharged from the moving conveyor belt, a portion of the bulk
material often remains adhered to the outer surface of the conveyor belt. Conveyor belt
cleaners, including one or more scraper blades, are used to scrape the adherent material
from the belt on its return run and thereby clean the belt. The scraper blades of a
conveyor belt cleaner are removably attached to a rotatable cross shaft that extends
transversely across the width of the conveyor belt. A tensioning device is attached to the
cross shaft and applies a rotational biasing force to the cross shaft which in turn rotates
the tips of the scraper blades into scraping engagement with the conveyor belt.
Scraper blades made for contacting the belt on the curvature of the discharge
pulley were previously made such that just the scraping edge of the blade face surface
initially engaged the conveyor belt, rather than the entire or full blade face surface,
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when installed. This edge contact type of blade design cleans with high efficiency when
new, but after the blade wears for a short period of time cleaning effectiveness is lost.
Scraper blades that provide full-face contact between the face surface of the blade and
the conveyor belt, such as those of the present invention, can be designed to maintain
constant cleaning efficiency over their wear life. Full-face contact blades extend the life
of the scraper blade, particularly on high speed conveyors because a full-face contact
blade has more mass to absorb the heat of friction generated with the rotating belt. Fullface
blades reduce a problem known as feathering which occurs with primary cleaner
blades when just the scraping edge engages the belt.
The present invention also enables a scraper blade to operate with a substantially
constant cleaning angle and scraping pressure. The tips of primary scraper blades
engage the curved surface of the conveyor belt at the head pulley of the conveyor and
form a cleaning angle between the conveyor belt surface and the front surface of the
scraper blade at the scraping edge of the front surface. The tip of each scraper blade
also includes a scraping surface that engages the surface of the conveyor belt. The
scraping surface engages the surface of the conveyor belt with a scraping pressure that
is approximately equal to the scraping force with which the scraper blade engages the
conveyor belt divided by the area of the scraping surface of the scraper blade.
During operation, the scraping edge and the scraping surface of each scraper
blade wears due to its scraping engagement with the moving conveyor belt coated with
abrasive bulk solids. The tensioner rotates the cross shaft and the scraper blades to
maintain the scraper blades in biased scraping engagement with the conveyor belt. As
the scraper blades wear and are rotated into continuing engagement with the conveyor
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belt, the orientation of the scraper blades with respect to the conveyor belt changes,
which typically causes a change in the cleaning angle between the surface of the
conveyor belt and the front surface of the scraper blade at the scraping edge, and a
change in the scraping pressure with which the scraper blade engages the conveyor belt.
In order to maintain optimum cleaning of the surface of the conveyor belt, and to
achieve maximum scraper blade life and performance, the cleaning angle between the
scraper blades and the conveyor belt surface, and the scraping pressure with which the
scraper blades engage the conveyor belt, should remain substantially constant during the
wear life of the scraper blades as the scraper blades wear and are rotated into continuing
engagement with the conveyor belt. One approach to partially solving this problem is
shown in U.S. Pat. No. 4,917,231 owned by the applicant herein.
DISCLOSURE OF THE INVENTION
The present invention relates to a tensioner for a conveyor belt cleaner including
a rotatable support frame having a central axis and a scraper blade attached to the
support frame for cleaning a conveyor belt. The tensioner comprises a first mounting
member adapted to receive a first end of the support frame and operatively attach the
support frame to a stationery support, the first mounting member comprising a fixing
element movable between a first position configured to enable the scraper blade to
communicate with the conveyor belt and a second position configured to secure the
blade assembly in a position rotated away from the conveyor belt. A second mounting
member is adapted to be attached to the support frame for conjoint rotation with the
support frame about the central axis. Additionally, an actuator is operatively attached to
the mounting member and is configured to selectively apply a rotational biasing force to
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the mounting member and rotate the support shaft and the scraper blade about the
central axis.
In a preferred embodiment, the fixing element comprises a set screw and the first
mounting member comprises a bearing bracket with a hub for receiving the first end of
the support frame, wherein the hub comprises an aperture positioned transverse to the
central axis for receiving the set screw. The set screw is configured to selectively
engage the support frame to maintain the scraper blade in a first position in
communication with the conveyor belt and to maintain the scraper blade in a second
position rotated about the central axis, away from the conveyor belt.
The actuator comprises a locking nut and an adjustment nut mounted on a shaft
operatively connected to the second mounting member. Alternatively, the actuator may
comprise a turnbuckle operatively connected to the second mounting member, a toggle
mechanism or other device commonly used for linear actuation.
The tensioner further comprises a resilient biasing member having a first end
and a second end operatively connected to the actuator, the second end of the biasing
member being movable with respect to the first end of the biasing member. As the
actuator applies force to the biasing member, a biasing force is stored in the biasing
member, the stored biasing force biasing the scraper blade into continuing engagement
with the conveyor belt as the scraper blade wears without any additional force being
applied to the biasing member by the actuator member. In a preferred embodiment of
the present invention, the biasing member comprises a spring.
The second mounting member comprises a pulley. A connector comprises a
first end operatively associated with the actuator, a second end operatively associated
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with the pulley, and central portion there between. The pulley comprises a socket
adapted to releasably hold the second end of the connector and a peripheral groove
adapted to releasably hold the central portion of the connector.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 shows a front elevation view of a conveyor belt cleaner and tensioner in
accordance with a preferred embodiment of the present invention;
Figure 2 shows a second perspective view of the conveyor belt cleaner and
tensioner in accordance with a preferred embodiment of the present invention;
Figure 3 shows a side elevation view of a chute wall associated with the
conveyor belt cleaner and tensioner in accordance with a preferred embodiment of the
present invention;
Figure 4 shows a first perspective view of components of the conveyor belt
cleaner and tensioner in accordance with a preferred embodiment of the present
invention;
Figure 5 shows a side elevation view of components of the conveyor belt cleaner
and tensioner in accordance with a preferred embodiment of the present invention;
Figure 6 shows a third perspective view of components of the conveyor belt
cleaner and tensioner in accordance with a preferred embodiment of the present
invention;
Figure 7 shows a front elevation view of a component of the conveyor belt
cleaner and tensioner in accordance with a preferred embodiment of the present
invention;
7
Figure 8 shows a perspective view of a component of the conveyor belt cleaner
and tensioner in accordance with a preferred embodiment of the present invention;
Figure 9 shows a perspective view of assembled components of the conveyor
belt cleaner and tensioner in accordance with a preferred embodiment of the present
invention;
Figure 10 shows a front elevation view of assembled components of the
conveyor belt cleaner and tensioner in accordance with a preferred embodiment of the
present invention;
Figure 11 shows a perspective view of assembled components of the conveyor
belt cleaner and tensioner in accordance with a preferred embodiment of the present
invention;
Figure 12 shows a front elevation view of assembled components of the
conveyor belt cleaner and tensioner in accordance with a preferred embodiment of the
present invention;
Figure 13 shows a perspective view of assembled components of the conveyor
belt cleaner and tensioner in accordance with a preferred embodiment of the present
invention;
Figure 14 shows an exploded view of a conveyor belt cleaner in accordance with
a preferred embodiment of the present invention;
Figure 15 shows a perspective view of the conveyor belt cleaner in accordance
with a preferred embodiment of the present invention;
8
Figure 16 shows a perspective view of assembled components of the conveyor
belt cleaner and tensioner in accordance with a preferred embodiment of the present
invention;
Figure 17 shows a perspective view of a component of the tensioner in
accordance with a preferred embodiment of the present invention;
Figure 18 shows a perspective view of a component of the tensioner in
accordance with a preferred embodiment of the present invention;
Figure 19 shows a perspective view of a component of the tensioner in
accordance with a preferred embodiment of the present invention;
Figure 20 shows a side elevation view of a component of the tensioner in
accordance with a preferred embodiment of the present invention;
Figure 21 is a diagram illustrating the operation of a conveyor belt cleaner and
tensioner in accordance with a preferred embodiment of the present invention;
Figures 22 and 23 are perspective views of a component of the conveyor belt
cleaner in accordance with a preferred embodiment of the present invention;
Figures 24a and 24b are elevation views of a component of the conveyor belt
cleaner in accordance with a preferred embodiment of the present invention.
MODES FOR CARRYING OUT THE INVENTION
The conveyor belt cleaner and tensioner arrangement 10, as shown in Figures 1
and 2 is adapted for use in connection with a conveyor mechanism. The conveyor
mechanism includes a rotatable endless conveyor belt 12 having an outer surface 14 that
is adapted to transport bulk material. The bulk material is discharged from the conveyor
9
belt 12 at a generally cylindrical head pulley 16 about which the conveyor belt 12 is
partially wrapped. The rotatable head pulley 16 and the discharge end of the conveyor
belt 12 may be located within a conveyor chute 18 or an open frame structure which
forms part of the conveyor mechanism. The conveyor chute 18 includes a first chute
wall 20 and a spaced apart and generally parallel second chute wall 22. The first and
second chute walls 20, 22 form a chamber 24 located there between in which the head
pulley 16 and discharge end of the conveyor belt 12 are located.
The conveyor belt cleaner and tensioner arrangement 10 includes a conveyor
belt cleaner 26 and one or more conveyor belt cleaner tensioners 28. As shown in
Figures 1 and 2, the conveyor belt cleaner and tensioner arrangement 10 includes a first
conveyor belt cleaner tensioner 28. However, a second conveyor belt cleaner tensioner
(not shown), constructed substantially identical to the first tensioner may also be
utilized, either on the same side as the first tensioner or on the opposite side of the
conveyor belt.
As shown in Figures 14 and 15, the conveyor belt cleaner 26 of the present
invention comprises a support frame 30, mounting bar 32, and one or more full face
contact scraper blade assemblies 34 comprising a blade support 68 and scraper blade 70.
The support frame 30 consists of a cross shaft 36 having a first end 38, a second end 40,
a central portion 42, and a longitudinal support frame axis of rotation 44 extending from
the first end 36 through the second end 40. The first and second ends 38, 40 are adapted
to fix the conveyor belt cleaner 26 in close proximity to the conveyor belt 12 either by
the first and second ends 38, 40 extending through bores 23 (Figure 3) in the conveyor
chute walls 20, 22 and being received by bearing brackets 42 (Figures 1 and 2),
10
described in detail below, or by the first and second ends 38, 40 being received by a
stationery structure (not shown) adapted to secure the support frame 30 in position.
A mounting member comprising a bearing bracket 42, as is shown in Figures 7,
9 and 10, is adapted to be connected to the first end 38 of the support frame 30 to secure
the support frame 30 in position. A second mounting member (not shown) is located on
the opposite chute wall 22 to receive and secure in place the second end 40. The
bearing bracket 42 includes a base plate 44 having a plurality of apertures 46
corresponding to a plurality of apertures 47 (Figure 3) in the conveyor chute wall 20 for
affixing the bearing bracket 42 to the conveyor chute wall 20, or other stationery
structure, with screws, pins or other like fasteners. A hub 48 extends from the front
surface of the base plate 44 and includes a bore 50 that extends through the hub 48 and
base plate 44 to form a central channel 52 through the bearing bracket 42. The channel
52 is adapted to receive an end 38 or 40 of the support frame 30. An aperture
comprising an internally threaded bore 54 extends through the wall of the hub 48 and is
configured to receive a set screw 56 to facilitate securing of the support frame 30 within
the central channel 52.
Mounted within the hub 48 is a rotatable bearing 58 having an inside diameter
adapted to receive the end 38 or 40 of the support frame 30 and progressively
decreasing outside diameters creating a curved exterior surface 60 (Figure 8) with
respect to the central axis of the bearing 58. In this manner, the bearing 58 has the
geometry of a plain spherical bearing. The curved exterior surface 60 of the bearing 58
enables it to freely rotate within the central channel 52 of the bearing bracket 42. Upon
manipulation of the bearing 58 into the desired position, the bearing 58 is secured into
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place with the set screw 56 in the hub 48. The bearing 58 may be composed of nylon,
urethane, hardened rubber, plastic or any other suitable material that will enable the set
screw 56 to securely hold the bearing 58 in place. Use of a polymer or plastic material
in the bearing also aids in shock absorption and noise reduction.
The multi-position, rotatable bearing 58 enables the bearing bracket 42 to be
fastened to a chute wall 20 or other stationery structure to form an angle (the mounting
angle) other than 90° with the support frame 30. The mounting angle is limited by the
interior diameter of the hub 48 and the length of the hub 48. Preferably the mounting
angle of the bearing bracket 42 to the chute wall 20 is 90° ± 5°.
Referring back to Figures 14 and 15, a mounting bar 32 adapted to receive the
blade assembly 34 is mounted to the central portion 42 of the support frame 30 by any
suitable means. Preferably the mounting bar 32 is secured to the support frame 30 by
welding. However, it is contemplated that other means, including glue, other adhesives
or clamps may be used to secure the mounting bar 32 to the support frame 30. As seen
in Figures 3 and 6, at least one of the chute wall bores 23 further comprises a
rectangular keyway 66 in communication with the bore 23. The keyway 66 is
configured to accommodate the size of the mounting bar 32 to enable the support frame
30-mounting bar 32 assembly to insert through the chute wall 20 and into the conveyor
chamber 24 (Figures 1 and 2).
A blade assembly 34, comprising a blade support 68 and scraper blade 70, is
removably attached to the mounting bar 32. A shoulder bolt 72 and lynch pin 74 secure
the blade assembly 34 to the mounting bar 32. As is seen in Figures 22 and 23, the
blade support 68 is a substantially W-shaped member preferably formed from 14 gauge
12
or 2 mm thick galvanized steel or stainless steel. The blade support comprises a first,
second, third, and fourth sidewall 71, 73, 75, 77. The first and second sidewall 71, 73
and third and fourth 75, 77 sidewall are connected by web portions 78, 80 at the lower
edge of each sidewall forming a first and second upwardly opening outer channel 82,
84. The second and third sidewalls 73, 75 are connected by a web portion 86 at the
upper edge of each sidewall, forming a downwardly opening central channel 88. The
central channel 88 is configured to receive the mounting bar 32 (Figures 14 and 15) in a
tongue and groove or telescoping arrangement.
The scraper blade 70, as best seen in Figures 24a and 24b, includes a scraper
portion 90 that extends outwardly from a base portion 92 to a scraping tip 197. The
base portion 90 comprises a first and second leg portion 94, 96 and a central channel 98,
mirroring the profile of the blade support 68 for removable attachment to the blade
support 68. The scraper portion 90 and base portion 92 extend between a generally
planar left sidewall surface 200 and a generally planar right sidewall surface 202. The
base portion 92 includes a generally planar basewall 204a, 204b having a front edge 206
on the first leg portion 94 and a rear edge 208 on the second leg portion 96. The scraper
portion 90 and base portion 92 are primarily formed from an elastomeric material such
as urethane or rubber.
The blade assembly 34 and scraper blade 70 described herein are exemplary in
nature. Any suitable blade assembly and scraper blade can be used with the tensioner
arrangement 10 described herein.
The scraping tip 197 of the scraper blade 70 includes a generally linear scraping
edge 198. The scraper blade 70 further includes a front surface 210 extending from the
13
front edge 206 to the scraping edge 198, forming a distal edge of the front surface 210
and a rear surface 212 that extends from the rear edge 208 to a distal edge 214. A blade
face surface 216 extends between the distal scraping edge 198 and the distal edge 214.
The blade face surface 216 is curved to conform to the curvature of the conveyor belt 12
(1, 2 and 21) such that the entire blade face surface 216 will engage the belt in full-face
contact.
The portion of the front surface 210 that extends along the scraper portion 90, is
preferably formed to have a configuration that provides a substantially constant cleaning
angle between the front surface 210 at the scraping edge 198 as the scraper portion 90
wears down during use and the scraper blade 70 is radially adjusted along the
longitudinal axis 44 (Figures 14 and 15) to remain in full face scraping engagement with
the conveyor belt. A configuration for the front surface that provides a substantially
constant cleaning angle is disclosed in U.S. Patent Nos. 4,917,231 of Martin
Engineering Company and 6,439,373 also of Martin Engineering Company. Both of
which are incorporated herein by reference.
The scraper portion 90 also includes a plurality of elongated ridges 218A-D
which extends across the front surface 210. The ridges 218A-D respectively indicate
when the scraper portion 90 has been worn down such that 25%, 50%, 75% and 100%
of the total wear volume of the scraper portion 90 has been worn away. The ridges
218A-D may also be formed as grooves.
Referring to Figure 1, 5, 11-13 and 19, the conveyor belt cleaner tensioner 28
includes a mounting member such as pulley 114. The pulley 114 has a generally
circular peripheral edge 116 including a circular groove 117 and at least one internally14
threaded bore 118 for receiving a set screw 120. A central bore 122 (Figures 19 and 20)
extends from the front surface to the rear surface of the pulley 114. The central bore
122 is sized such that the first end 28 of the support frame 30 fits closely within the bore
122. Tightening of the set screw 120 couples the pulley 114 and support frame 30
together for conjoint rotation. The pulley 114 also includes a transverse channel 124 on
the periphery of the pulley 114, the channel having a substantially C-shaped crosssection
and defined by a channel wall portion 126 and a first and second inwardly
facing lip portion 128, 130. The intersection of the groove 117 and transverse channel
124 forms a socket 132 adapted to securely receive the first end 134 (Figure 18) of a
connector 136, preferably an elongate flexible cable.
The cable 136 (Figure 18) may be made from wire rope, chain, nylon rope and
other types of materials that provide sufficient flexibility and tensile strength. The cable
136 includes a first end and a second end 134, 138 and a central portion 139 there
between. The first end 134 of the cable 136 includes an enlarged, bulbous stop member
140 configured to insert within and be retained by the socket 132 (Figures 19, 20). The
second end 138 of the cable 136 mates with the first, channeled end 142 of an elongate
tensioner shaft 144.
Referring to Figures 1, 2, 5 and 16, the tensioner 28 includes a biasing member,
such as a coil spring 146 having a first and second end 148, 150. The first end 148 of
the spring 146 sits on the horizontal, landing portion 152 of an L-shaped bracket 154
(Figures 16 and 17) mounted to the conveyor chute wall 20 or another stationery
structure. Apertures 156 in the vertical, mounting portion 158 of the bracket correspond
to apertures 160 (Figure 3) on the chute wall 20 to facilitate mounting of the bracket 154
15
to the chute wall 20 by any suitable means, such as screws or rivets. An annular
compression disc 162 located at the second end 150 of the spring 146 enables even
distribution of the tensile force exhibited by the spring 146 during operation of the
tensioner. In this arrangement, the second end 150 of the spring 146 is movable with
respect to the first end 148 along a central axis extending through the center of the
spring 146.
The externally-threaded, second end 163 (Figure 18) of the elongate tensioner
shaft 144 extends through an aperture 164 (Figure 17) in the landing portion 152 of the
bracket 154, through the center of the spring 146 and extends through the compression
disc 162 at the disc aperture 165 (Figure 16). An actuator member 166 mounts on the
second, externally-threaded end 163 of the elongate shaft 144. In a preferred
embodiment, the actuator member 166 comprises a washer 168, adjustment nut 170 and
locking nut 172 positioned in a “double nutting” arrangement. Alternatively, the
actuator member may comprise a turnbuckle or toggle mechanism (not shown)
interposed between the first end of the biasing member 148 and the second end 138 of
the cable 136 (Figure 18).
Referring back to Figures 1 and 2, in operation, the support frame 30-mounting
bar 32 assembly is fabricated and inserted through the chute wall 20 (Figure 3 and 6)
associated with the keyway 66. The first and second ends 38, 40 of the support frame
30 come to rest outside of the conveyor chamber 24 (Figure 1), and the central portion
42 of the support frame 30, with the affixed mounting bar 32, comes to rest within the
chamber 24. As is seen in Figure 4, the bearing bracket 42 is inserted over the first end
38 of the support frame 30 and mounted to the chute wall 20 in a position enabling
16
coaxial alignment of the central channel 52 in the bearing bracket 42 and the chute wall
bore 23 (Figures 3 and 6).
Once the bearing bracket 42 is mounted, the set screw 56 in the hub 54 (Figures
9 and 10) may be tightened to secure the bearing 58 and support frame 30 together and
to hold the support frame 30 in a maintenance position. Releasing the set screw 56 and
disengaging it from secure contact with the bearing 58 enables the support frame 30 to
rotate freely with the bearing 58.
A second bearing bracket (not shown) may be inserted over the second end 40 of
the support frame 30 and mounted on the opposite chute wall 22. Alternatively, any
mounting member with a central channel adapted to securely receive the second of the
support frame 30 may be utilized.
In the single tensioner embodiment described herein, the tensioner assembly 28
prevents excess lateral movement of the support frame 30 along its longitudinal axis and
away from the chute wall 20. Continued lateral movement of the support frame 30
towards the opposing chute wall 22 is restricted by the tensioner 28 coming into contact
with the bearing bracket 42.
At the non-tensioner end, a set collar (not shown) is supplied to prevent excess
lateral movement of the second end 40 of the support frame 30 towards the opposite
chute wall 20. The set collar has an inner diameter that is slightly larger than the outer
diameter of the support frame 30. Preferably, the outer diameter is approximately 76.2
mm (3 inches) and the width of the set collar is 22.2 mm (7/8 inch). A 12.7 mm (½
inch) set screw extending through the periphery of the set collar engages the support
frame and locks the support frame and set collar enabling conjoint rotation and lateral
17
movement. Lateral movement of the support frame 30 towards the opposing chute wall
20 is restricted by the set collar coming into contact with the bearing bracket on the
chute wall 22.
One or more blade assemblies 34 are removably fastened to the mounting bar 32
by fasteners extending through the aligned through holes in the blade assembly 34 and
mounting bar 32, as previously described above in connection with Figure 14 and 15.
The blade assembly or assemblies 34 are thereby selectively removable and replaceable
on the support frame 30.
Referring to Figures 1, 2 and 5, a conveyor belt cleaner tensioner 28 is attached
to the first end 38 of the support frame 30 extending through the bearing bracket 42.
The pulley 114 is slid over the first end 38 of the support frame 30 which extends
through the central channel 52 of the bearing bracket 42. The central bore 122 (Figure
19) of the pulley 114 receives the first 38 end of the support frame 30. A set screw 120
(Figure 12) is inserted within the bore 118 (Figure 12) on the periphery of the pulley
114 and is tightened to couple the pulley 114 and support frame 30 for conjoint rotation.
Referring to Figures 11-13, the cable 136 is inserted within the groove 117
around the periphery of the pulley 114 by first aligning the stop member 140 at the first
end 134 of the cable 136 with an end of the transverse channel 124 and aligning the
cable 136 in a position extending radially away from the center of the pulley 114. The
cable 136 is then slid into position within the groove 117 by sliding the stop member
140 within the transverse channel 124 with the cable 136 traveling within the opening at
the top of the channel. When the stop member 140 is received by the socket 132, the
cable 136 is laid within the peripheral pulley groove 117.
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The second end 138 of the cable 136 mates with the channeled, first end 142 of
the tensioner shaft 144. The threaded, second end 163 of the shaft 144 extends upwards
from the pulley 114, through the aperture 164 (Figure 17) in the bottom of the L-bracket
154, previously mounted to the chute wall or other stationery support. The spring 146 is
seated with the first end 148 on the landing 152 of the L-bracket 154 and with the shaft
144 extending though the interior of the spring 146. The threaded, second end 163 of
the shaft 144 extends through the aperture 165 (Figure 16) in compression disc 162 atop
the second end 150 of the spring 146. Inclusion of the compression disc 162 enables the
shaft 144 and spring 146 to align coaxially.
The tensioner actuator 166 mates with the threaded, second end 163 of the shaft
144 extending above the compression disc 162. Tension is applied to the shaft 144 and
cable 136 by tightening the adjustment nut 170 to compress the spring 146 and securing
the adjustment nut 170 in position by tightening the locking nut 172 until it abuts the
adjustment nut 170. As is shown in Figures 1, 2 and 5, the spring 146 and actuator 166
extend generally coaxially with one another and are disposed in a generally vertical
orientation. However, if desired, the spring 146 and actuator 166 may be positioned in a
generally horizontal orientation or at any other angle in between.
Referring to Figures 1, 14, 15, 24 and 25, initially the support frame 30 and
blade assembly 34 of the conveyor belt 12 cleaner are located such that the blade face
surface 216 of the scraper blade 70 is in full-face contact or engagement with the outer
surface 14 of the conveyor belt 12. The actuator 166 may then be selectively rotated
with respect to the tensioner shaft 136 such that the spring 146 will become compressed
between the annular compression disc 162 and landing 152 of the L-bracket 154
19
creating a stored biasing force within the compressed spring 146. The spring 146
applies a tensile biasing force to the tensioner shaft 144 and cable 136 which in turn
applies a rotational biasing force to the pulley 114 and to the support frame 30.
As the scraper portion 90 wears down through scraping engagement with the
rotating conveyor belt, the distal edge 198 of the front surface 210 becomes relocated
along the front surface 210. The scraping angle defined between a first line passing
through the distal edge 198 of the front surface 210 that is tangential to the conveyor
belt 12 and a second line extending through the distal edge 214 that is generally
tangential to the front surface 210 will remain substantially constant as the scraper blade
wears down and is rotated about the axis 44 into continuing full-face contact with the
conveyor belt 12 due to the configuration of the front surface 210.
As the distal scraping edge 110 of the front surface 104 of the scraper blade 70,
the distal edge 112 of the rear surface 106, and the scraping tip 100 wears down through
scraping engagement with the rotating conveyor belt 12, the compressed spring 146 will
expand or elongate. The spring 146 will rotate the pulley 114 and the support frame 30
about the longitudinal axis 44 to maintain the newly formed distal edges 110, 112 and
blade face surface 108 of the worn scraper blade 70 in biased, full-face scraping
engagement with the conveyor belt 12. The spring is adapted to rotate the support
frame 30 and the scraper blade 70 through a selected angle about the longitudinal axis
44 over the wear life of the scraper blade 70.
The tip surface 197 of the scraper portion 90 has a width that extends between
the left sidewall surface 200 and the right sidewall surface 202. The blade face surface
216 also has a height that extends between the distal edge 214 of the rear surface 212
20
and the distal edge or scraping tip 198 of the front surface 210. Therefore the blade face
surface 216 therefore has a surface area defined by the width and height of the blade
face surface 216. The spring 146 applies a rotational biasing force to the pulley 114 and
to the support frame 30 which rotates the blade face surface 197 into full-face
engagement with the conveyor belt 12 with a scraping force that is generally normal to
the surface of the conveyor belt 12. The blade face surface 216 is thereby pressed
against the surface of the conveyor belt 12 with a scraping pressure that is equal to the
scraping force divided by the area of the blade face surface that is engaging the surface
of the conveyor belt 12.
To maintain efficient cleaning of the conveyor belt 12, the scraping pressure
with which the blade face surface 216 engages the conveyor belt should remain
generally constant through the wear life of the scraper blade 70. The portion of the rear
surface 212 that extends along the scraper portion 90 is configured and located with
respect to the portion of the front surface 210 that extends along the scraper portion 90
such that the average scraping pressure between the blade face surface 216 and the
conveyor belt 12 remains substantially constant over the wear life of the scraper portion
90 as the scraping tip 198 of the scraper portion 90 wears down toward the base portion
92.
As illustrated in Figure 21, when the center of the blade face surface 216 of the
scraper portion 90 engages the outer surface 14 of the conveyor belt 12 at position “A,”
the tensile biasing force (TA) applied by the spring 146 to the cable 136 and to pulley
114 is equal to the spring constant of the spring 146 (which may be in pounds per inch)
multiplied by the distance the spring is compressed by the actuator (not shown). This
21
tensile biasing force TA creates a moment (M44) about the longitudinal axis 44 that is
equal to the tensile biasing force TA multiplied by the radius (rp) from the longitudinal
axis 44 to the center line of the cable located within the groove (not shown) of the
pulley 114. The moment M44 created about the longitudinal axis 44 by the spring 146 is
resisted by an equal and opposite moment equal to the length of a radius (RA) extending
from the longitudinal axis 44 to the center of the blade face surface 216 multiplied by a
force (FA) that is generally perpendicular to the radius RA. Radius RA is calculated by
calculating the arc angle of the blade face surface 216 and then dividing the arc angle by
two to determine the point where the average radius of the scraper 70 contacts the belt
surface 14. This radius is used as the blade contact surface lever arm.
Force FNA is the component of the force FA that is normal to the surface 14 of
the conveyor belt 12. Force (FNA) is divided by the area of the blade face surface 216 to
obtain the scraping pressure with which the tip surface 216 engages the conveyor belt
12. Radius RA is calculated for every 5° of wear of the scraper blade 70. This enables
calculation of an appropriate spring constant to maintain a constant scraping pressure
throughout the wear life of the scraper blade 70. Through an iterative process the
contact areas, lever arms and spring constants are selected which result in a constant
cleaning pressure over the wear life of the scraper blade 70, to the extent practical. One
embodiment uses a nine inch radius as an eighteen inch diameter pulley diameter is
among the larger diameters to be used in such common applications. By basing the
design on the maximum radius, the contact for smaller diameters will initially be a point
of contact at RA. The contact will quickly become full surface as the blade wears and
adapts to smaller diameters.
22
Another embodiment would use a radius of twelve inches to allow for larger
diameter pulleys and corresponding belt surface diameters. Likewise the radius used for
designing the blade geometry could start at any diameter depending on the application.
As the scraper portion 90 wears down toward the mounting base 92, the spring
146 will elongate to rotate the scraper portion 90 into continuing engagement with the
conveyor belt 12 and the blade face surface 216 will move from position A as shown in
Figure 21 to position B. As the spring 146 elongates, it will provide a tensile force TB
to the cable 136 and the pulley 114 that is smaller than the tensile force TA. The tensile
force TB will create a smaller moment about the longitudinal axis 44 than the tensile
force TA as the radius RP of the pulley 114 remains constant. In addition, as the scraper
portion 90 wears down, the length of the radius RB from the longitudinal axis 44 to the
center of the blade face surface 216 at position B will be shorter than the radius RA. The
angle at which each radius RA and RB is located with respect to the curved surface of the
conveyor belt 12 also changes as the scraper portion 90 moves from position A to B.
This results in a change in the force FNB that is normal to the surface of the conveyor
belt 12 that resists the biasing force created by the spring 146 at position B from the
force FNA at position A.
As the scraping force FNB has changed from the scraping force FNA, the area of
the blade face surface 216 must accordingly change to maintain a constant scraping
pressure. As the width of the blade face surface 216 remains substantially constant as
the scraper portion 90 wears down, the height of the blade face surface 216 between the
distal edge 198 of the front surface 210 and the distal edge 214 of the rear surface 212
(which generally corresponds to the thickness of the scraper blade) must change as the
23
scraper portion 90 wears down to maintain a substantially constant full-face scraping
pressure between the blade face surface 216 and the conveyor belt 12.
The shape of the front surface 210 and of the rear surface 212 of the scraper
portion 90 are respectively configured and located with respect to one another such that
a substantially constant scraping pressure will be maintained between the blade face
surface 216 and the surface 14 of the conveyor belt 12 as the scraper portion 90 wears
down and is rotated into continuing full face engagement with the conveyor belt 12 by
the spring 146. The scraper portion 90 provides a substantially constant cleaning angle
between the front surface 210 and the conveyor belt 12, and provides a substantially
constant scraping pressure between the blade face surface 216 and the conveyor belt 12,
as the scraper portion 90 wears down during use with conveyor belt 12 having a radius
R1 of approximately 225 mm (9 inches) or less. Although a preferred embodiment of
the present invention has been described with a conveyor belt 12 having a radius R1 of
approximately 225 mm (9 inches) or less, it is contemplated that as described in U.S.
Patent Nos. 4,917,231 of Martin Engineering Company and 6,439,373 also of Martin
Engineering Company, both patents of which are incorporated herein by, when the
conveyor belt head pulley 16 has a radius R1 ranges of approximately 600 to 1200 mm
(12 to 24 inches) and 1200mm (24 inches) or larger, the same principles apply.
A preferred scraping pressure is approximately 19 Kpa (2.75 pounds per square
inch). As used herein, a substantially constant scraping pressure may deviate up to plus
or minus fifteen percent from the average scraping pressure over the wear life of the
scraper portion 90, and a substantially constant scraping angle may deviate up to plus or
minus fifteen percent from the initial scraping angle. The initial scraping angle is
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preferably within the range of approximately 25° to 60° with a preferred angle of 40°.
The configuration of the front surface 210 is an involute curve. The rear surface 212 is
determined by the contact area needed to maintain substantially constant cleaning
pressure. To accommodate manufacturing of the molds a tolerance of the curved
surfaces of plus or minus one-quarter (0.25) inch, and preferably plus or minus one
tenth (0.1) inch, of the true path is desired. These tolerances still enable a substantially
constant cleaning angle and a substantially constant full-face scraping pressure to be
maintained in practice.
The radius Rp of the pulley 114 is substantial similar to the radius of the support
frame 30, and is preferably only slightly larger than the outer radius of the support
frame 30. The small pulley radius design enables the scraper blade 70 to be design for
full wear across 45° of rotation between a first position where the unworn, unused
scraper blade 70 communicates with the conveyor belt 12 and a second position where
the worn, used scraper blade 70 communicates with the conveyor belt 12.
Additionally, by keeping the pulley radius Rp small, 45° of rotation requires less
linear travel of the actuator 166 and translates into less compression of the spring 146.
In the present inventive tensioner, 45° of rotation in the pulley 114 results from
application of a rotational biasing force to the pulley 114 that is derived the linear
biasing force generated by compression of the spring 146. The spring 146 must be
preloaded with an actuator generated force equal to biasing force required when the
scraper blade 70 is 100% worn. In this embodiment the preload distance is
approximately 10 mm (0.39 inches) from the resting position of the spring. An
additional compression of 25 mm (0.98 inches) is required to conjointly rotate the
25
pulley and support frame between the first and second positions, resulting in a total
spring travel of 35 mm (1.38 inches). In contrast, certain prior art tensioners require as
much as 150 mm (5.9 inches) of total spring travel. Of the many beneficial aspects of
the present inventive tensioner, its compact dimensions contribute to a small overall
footprint. Additionally, the compactness of the tensioner leads to added safety since the
movement of the tensioner is as little as approximately 35 mm (1.38 inches). In the
event of a failure, there will be very little inertia stored in the connector 138.
Belt cleaner blades can be caught by obstructions on the belt or defects in the
belt surface and pulled through in the direction of travel at the speed of the belt. With
prior tensioner designs this may present a hazard to those inspecting or adjusting the
belt cleaner. The present design is a safety improvement over prior designs in that there
are no protruding fasteners or levers attached to the support shaft of the belt cleaner.
The small diameter of the pulley mounted on the belt cleaner shaft reduces the distance
the pulley will travel if the belt cleaner blades are pulled through. The flexible
connection means between the pulley and the biasing spring reduces the chance of
injury, when compared to a fixed lever arm, should the blade be pulled through.
Various features of the invention have been particularly shown and described in
connection with the illustrated embodiments of the invention, however, it must be
understood that these particular arrangements merely illustrate, and that the invention
must be given its fullest interpretation within the terms of the appended claims.

We claim:
1. A tensioner for a conveyor belt cleaner including a rotatable support frame having a
central axis and a scraper blade attached to the support frame for cleaning a conveyor
belt, the tensioner comprising: a first mounting member adapted to receive a first end of
the support frame and to operatively attach the support frame to a stationery support, the
first mounting member comprising a fixing element movable between a first position
enabling the support frame to freely rotate about the central axis and a second position
selectively securing the support frame in a position wherein the scraper blade is rotated
away from the conveyor belt and prevented from rotating back into scraping
engagement with the conveyor belt surface; and an actuator operatively attached to the
support frame to apply a rotational biasing force to rotate the support frame and the
scraper blade about the central axis.
2. The tensioner of claim 1 wherein the fixing element comprises a set screw.
3. A tensioner for a conveyor belt cleaner including a rotatable support frame having a
central axis and a scraper blade attached to the support frame for cleaning a conveyor
belt, the tensioner comprising: a first mounting member adapted to receive a first end of
the support frame and to operatively attach the support frame to a stationery support, the
first mounting member comprising a fixing element movable between a first position
configured to enable the scraper blade to communicate with the conveyor belt and a
second position configured to secure the scraper blade in a position rotated away from
the conveyor belt, the fixing element comprising a set screw and the first mounting
member comprising a bearing bracket with a hub for receiving the first end of the
support frame, wherein the hub comprises an aperture positioned transverse to the
central axis for receiving the set screw; a second mounting member adapted to be
attached to the support frame for conjoint rotation with the support frame about the
central axis; and an actuator operatively attached to the second mounting member and
configured to selectively apply a rotational biasing force to the second mounting
member and thereby rotate the support frame and the scraper blade about the central
axis.
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4. The tensioner of claim 3 wherein the actuator comprises an adjustment nut and a
locking nut mounted on a shaft operatively connected to the second mounting member.
5. The tensioner of claim 3 wherein the actuator comprises a turnbuckle operatively
connected to the second mounting member.
6. The tensioner of claim 3 wherein the actuator comprises a toggle clamp operatively
connected to the second mounting member.
7. The tensioner of claim 3 wherein the second mounting member comprises a pulley.
8. The tensioner of claim 3 further comprising a connector comprising a first end
operatively associated with the actuator, a second end operatively associated with the
second mounting member, and central portion there between.
9. The tensioner of claim 8 wherein the second mounting member comprises a socket
adapted to releasably hold the second end of the connector and a groove adapted to
releasably hold the central portion of the connector.
10. The tensioner of claim 8 wherein the connector comprises a wire rope.
11. The tensioner of claim 8 wherein the connector comprises a cable.
12. The tensioner of claim 3 further comprising a biasing member having a first end and
a second end, the second end operatively connected to the actuator and being movable
with respect to the first end of the biasing member.
13. The tensioner of claim 12 wherein the biasing member is configured to store a
biasing force generated by the actuator, and wherein the biasing member is further
configured to release the biasing force to bias the scraper blade into continuing
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engagement with the conveyor during the wear life of the scraper blade without
additional force being generated by the actuator.
14. The tensioner of claim 12 wherein the biasing member comprises a spring.
Dated this 15th day of March, 2012.