Note: Descriptions are shown in the official language in which they were submitted.
- CA 022248~0 l997-l2-l5
BELT CLEANER FOR REMOVING FINES FROM GRANULAR MATERIAL
FIELD OF THE INVENTION
The present invention relates to screens and other apparatus
for removing fines from a flow of larger material in general and to apparatus
for removing fines from wood chips and similar materials in particular.
BACKGROUND OF THE INVENTION
In the manufacture of paper from wood, logs and sawmill wastes are
reduced to wood chips. The wood chips are then further processed either
by chemical digestion or mechanical commutation or a combination of
,o chemical and mechanical means into wood fibers. Any grit in the form of
sand commingled with the wood chips can produce severe wear of the
downstream wood chip processing machinery. Furthermore, very small
particles of wood and dirt are detrimental to the quality of the paper formed
from the wood chips. It is therefore desirable to remove as much sand, dirt
and other materials not containing useful fiber from the chips before they
are further processed.
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Various screen have been used to perform this task. Yet screens with
very small holes rapidly become clogged with particles and lose their
effectiveness. Screens with larger holes are less likely to become clogged,
yet the larger holes allow particles containing useful amounts of fiber to be
5 lost through the screen.
Wave screens utilize a screen which is beaten from below to cause
the wood chips to bounce off the screen. This bouncing facilitates removal
of sand and fines which drop through the screen. Wave screens have
beaters which rub the bottom of the screen, and thus suffer from wear
10 produced by the beaters grabbing particles which are passing through the
screen and pushing them against the sides of the screen holes and across
the screen bottom. Wave screens also consume considerable energy
because they must keep the entire scrèen's bed load suspended about the
screen to be effective.
Existing screening devices for removing small roughly spherical
particles from larger objects such as wood chips can suffer from problems of
screen clogging, high energy use, screen wear and loss of useful material
through the screen.
What is needed a device for removing fines from a flow of material
20 which is energy efficient and of low maintenance cost and can be tailored to
remove fines of a selected size.
SUMMARY OF THE INVENTION
The apparatus of this invention employs a moving endless belt which
is positioned at an inclined angle with respect to the horizontal. A flow of
25 material is supplied to the inclined surface of the belt. The belt is inclined
sufficiently so that the material tumbles down the incline. The belt is driven
so that it moves up the incline. The surface of the belt is textured and thus
contains small pockets into which particles fall and are held against
downward motion along the incline. The larger particles in the material
30 cascade down the belt and are collected for further processing. The small
CA 02224850 1997-12-1~
particles, which are entrained in the pockets formed by the texture on the
belt's surface, move up the incline with the belt and are removed from the
belt when it reverses direction at the top of the incline. Removal of the fines
from the belt are facilitated by an agitator which vibrates the belt as it
reverses direction and moves down the incline. The size of the particles
removed can be controlled by increasing the size of the pockets formed by
texturing the belt's surface. The angle of inclination can also be varied to
optimize the motion of the large particles down the inclined belt. The
apparatus of this invention is particularly suitable for removing sand and
10 fines from wood chips. However it could be used to remove broken glass
from municipal trash by choosing an angle of inclination and a texture on the
belt which will hold broken glass but allow larger items of trash to cascade
down the inclined belt.
It is a feature of the present invention to provide an apparatus for
cleaning wood chips.
It is another feature of the present invention to provide an apparatus
which can be selectively designed to remove particles of varying types from
a flow of material.
. It is a further feature of the present invention to provide an apparatus
which can separate broken glass from municipal trash.
It is a yet further feature of the present invention to provide a process
for separating dirt, sand, dust, spherical particles, wood fines, and pins,
from a flow of material such as wood chips and municipal trash.
It is a still further feature of the present invention to provide a process
and apparatus for preparing wood chips used in the construction of particle-
board by removing fines from the chips.
Further objects, features and advantages of the invention will be
apparent from the following detailed description when taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 is a side elevational cross-sectional view of the belt cleaner of
this invention.
FIG. 2 is an isometric view, partially cut-away in section, of the of the
belt cleaner of FIG. 1.
FIG. 3 is an enlarged detail view of the belt surface of the belt
cleaner of FIG.1 showing the belt surface about three times life size.
FIG. 4 is an enlarged detail view of an alternative embodiment belt
surface showing the belt surface about one and one-half life size.
FIG. 5 is an enlarged detail view of a further alternative belt surface
showing the belt surface about four times life size.
FIG. 6 is a detail view of yet another alternative belt surface showing
the belt surface about twice life size.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring more particularly to FIGS.1-6 wherein like numbers refer
to similar parts, a belt cleaner 20 is shown in FIGS.1 and 2. The belt
cleaner 20 is useful for separating sand, dust, and fines 22 from wood chips
24. The belt cleaner 20 can be used with a wide variety of materials, for
example broken glass can be removed from municipal waste. The cleaner
20 employs an endless belt 26 which travels between an upper roll 28 and a
lower roll 30. The upper roll 28 and lower roll 30 are mounted to a frame 32.
As shown in FIG. 2, the lower roll 30 is mounted at both ends by a screw
jack bracket 33 which adjusts the tension in the belt 26 by moving lower roll
bearings 35 towards or away from the upper roll 28. The rolls 28, 30 are
crowned in order to keep the belt centered on the rolls 28, 30. As shown in
FIG. 2, the crowning of the rolls is exaggerated for purposes of illustration.
The frame 32 is mounted to a shaft 34 which is supported on bearings 36
which are mounted by supports 38 to a support structure 39. The shaft 34
and the bearings 36 allow the angle ~ of the frame 32 and the looped belt
26 to be adjusted with respect to the support structure 39.
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As the belt 26 moves between the lower roll 30 and the upper roll 28
it defines an upwardly sloping upwardly facing substantially planar surface
40. A motor 42 turns a drive belt 44 and a speed reducer 46 which engages
and rotates the upper roll and thereby advances the endless belt 26. The
5 belt 26 is driven to move upwardly so that the upwardly facing surface 40 of
the belt 26 is constantly moving upwardly from the lower roll 30 towards the
upper roll 28. Material 24 in a hopper 48 is distributed along a chute 50 by
a twelve inch pitch distribution screw 52 which has a six inch distribution slot(not shown) which distributes the material 24 along the width of the chute
10 50. The chute 50 is angled downwardly amount thirty-hve degrees from the
vertical. The angle of the chute 50 is chosen for use with a particular
material 24 to be sufficiently steep so the material 24 will readily slide down
the chute's surface 53. For reliable operation thè surface 53 of the chute 50
should be very smooth or polished and with some materials low frequency
15 vibration of the chute may facilitate materials sliding along the chute 50.
From the chute 50 the material 24 is distributed along the width of the
belt 26 onto the upwardly moving planar surface 40. The surface 40 of the
belt is inclined roughly sixty degrees from the horizontal at the angle a. The
distributed material cascades down the inclined planar surface 40 of the belt
20 26. The cascading action of the material results in rolling, bouncing motion
of the material down the surface 40 so that fines and dirt are jarred loose
from the wood chips 24. The material 24 is encouraged to cascade by the
velocity with which it initially strikes the surface 40. The sliding action along
the chute surface 53 combined with a short free-fall of four to six inches
25 onto the surface 40 of the belt 26 produces the initial velocity which
encourages the material 24 to tumble or cascade down the inclined surface
40 of the belt 26.
The angle o. which the surface 40 of the belt makes with the
horizontal is chosen to enable and facilitate the tumbling action of the
30 material. This angle a is related to the so-called angle of repose of the
material being cleaned. The angle of repose is a characteristic of granular
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materials and depends on the material type and the distribution of particle
sizes. The angle of repose of a particular material is found by measuring
the angle a heap of the material makes with the horizontal. The angle of
repose is the steepest angle which a particular material will assume when
5 poured into a pile. Because the surface 40 is inclined at a steeper angle
then the angle of repose of the material 40 it will not remained in one
position on the belt 26 and therefore will not move upwardly with the belt.
The belt has an exterior surface 54 and an inner surface 56. The
exterior surface 54 is textured as shown in the approximate 3X scale
10 illustration of FIG. 3. The textured surface 54 has a multiplicity of pockets58 of varying sizes formed by ridges 60 and bumps 62. Grooves 65 which
for clarity of illustration are shown only on a portion of the belt shown in FIG.
3 cover the ridges 60 arid bumps 62 of the belt 26. The complex surface
texture makes a multiplicity of sites for holding a range of particle sizes.
15 Small particles or fines 22 which are jarred loose during the cascading
action of the larger material 24 down the inclined surface 40 become
trapped in the pockets 58 and grooves 65 and thus move with the belt 26 as
it moves up towards the upper roll 28.
As the belt moves over the upper roll 28 it reverses direction and
20 begins to move downwardly towards the lower roll 30. The downwardly
moving side 63 of the belt 26 faces downwardly. Gravity in combination with
an agitator 64 or cleaning means, removes the fines 22 contained in the
pockets 58 formed by the textured surface 54 of the belt 26. As shown in
FIGS. 1 and 2, the agitator 64 consists of a shaft with three bars 66 which
25 impinge against the interior surface 56 of the downward moving side 63.
The agitator is driven by a belt 68 driven off the shaft 70 on which the upper
roll 30 is mounted.
The belt 26 as it moves up between the lower roll 30 and the upper
roll 28 to form the inclined surface 40 must be supported to maintain a
30 planar surface which facilitates the cascading of the material 24 down the
inclined surface 40. Support of the belt facilitates individual wood chips or
CA 022248~0 l997- l2- l~
the like bouncing against the rigidly supported belt 26. The belt support is
provided by a metal plate 72 which is connected to the sides 74 of the frame
32. The sides 74 are joined by a tubular subframe 73. The metal plate is
rigidified by transverse framing 75. A low friction plastic plate 76
5 constrùcted of ultra high molecular weight plastic (UHMW) is attached to the
to the metal plate 72.
The cleaner 20 has an upper cover 78 and a lower cover 80. The
upper cover 78 has an opening 82 through which the chute 50 delivers the
wood chips 24. The upper cover 78 retains the material 24 on the belt 26 as
10 it cascades down the inclined surface 40. The upper cover 78 also supports
side baffles 79, as shown in FIGS. 1 and 2, which extend from an inner
surface 81 of the upper cover 78 towards the belt 26 and parallel to the
edges 83 of the belt 26. The baffles 79 keep the material 24 on the planar
surface 40 of the belt 26
An outfeed plate 84 is positioned above and tangent to the lower
roller 30 so the wood chips 24 cascade down onto the outfeed plate 84
where they are removed from the cleaner 20 and can be collected for further
processlng.
The ouffeed plate comprises a planar extension member positioned
20 adjacent the lower support and and thus forms a substantially contiguous
extension of the planar surface of the belt so that wood chips tumbling down
the planar surface of the belt are directed along the planar extension.
The lower cover 80 forms an inner surface 86 against which fines 22,
which may consist of dust, dirt, sand, (or whatever is being removed or
25 cleaned from the material 24) is collected. The fines 22 travel down the
cover inner surface 86 and leave the belt cleaner along a chute 88. The
fines are collected for disposal or further processing. Because the inner
surface 86 forms a sliding surface it may benefit from being polished or
subjected to low frequency vibration to assure material does not become
30 stuck on the surface 86.
CA 022248~0 1997-12-15
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Many different belt textures can be used to clean or process different
materials. For example alternative belt texturing 90 is textured as shown in
the approximately 1.5X scale illustration of FIG. 4 and appears to have
special utility in removing pins from wood chips. The textured belt 90 has
hexagonally close packed cones 92 topped by small cylin~rical protrusions
94. Pins are small slivers of wood which contain some useful fiber. It can
be desirable to remove pins if paper of the highest strength is required.
Another alternative belt texturing 96 is shown at approximately 4X
scale in FIG. 5. This texturing 96 is similar to the material shown in FIG. 3
10 but has finer pockets 98 and might have greater utility in removing sand or
dust from sawdust from sawdust.
Yet another alternative belt texturing 100 is shown at a scale of
approximate 2X in FIG. 6 This texturing may be useful in removing larger
grains of material such as broken glass from municipal trash.
Belting material such as shown in FIGS. 34 can be obtained from a
distributor such as Empire Rubber located at 88 Southeast Taylor, Portland,
Oregon 92714. Manufacturers of such belting material include Fabreeka
International of Strughpon Massachusetts and Habasit Belting of Chamblee
Georgia. Belting material is typically manufactured of rubber compounds
20 but additional durability may make polyurethane or other high durability
plastic desirable or necessary for a practical belting material.
The agitator 64 could be replaced by agitators of various design or
could be replaced or supplemented by a rotating brush. Other possible
means for cleaning the texturing of the belt include vacuuming or blowing
25 the fines from the belt. Even a high pressure water spray might be effective
with some materials.
When wood chips are processed it may be desirable to avoid chips
which are excessively wet or excessively dry, a typical moisture content of
the wood chips may be about fifty percent moisture content.
The angle of repose of a material can be measured in a number of
ways. The so-called external angle of repose is the angle between a line of
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repose of loose material and a horizontal plane. A poured angle of repose is
obtained when a pile of solid is formed, drained angle results when solids
are drained from a bin. Typically the drained angle of repose and the
poured angle of repose are approximately the same but for material with a
5 wide size distribution the drained angle wil~ be greater than the poured
angle. Other related angles are the angle of slide which is the angle of a
plate on which a material will slide. For the belt cleaner 20 the important
relationship between the material being cleaned and the belt is that the
material cascade or slide down the belt while the belt is moving upwardly.
10 Therefore the angle of repose is herein defined as that angle at which,
dependent on the belt surface properties and the type of material being
cleaned, a particular material will move down a particular belt under the
influence of gravity while the belt'is moving upwardly. For some materials
and some belt surfaces that angle will be approximately sixty degrees from
15 the horizontal.
It is understood that the invention is not limited to the particular
construction and arrangement of parts herein illustrated and described, but
embraces such modified forms thereof as come within the scope of the
following claims.
