Note: Descriptions are shown in the official language in which they were submitted.
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COMPACTION METHODS AND APPARATUS
This application is a division of Canadian Patent Application Serial No.
2,144,987 which was filed as the Canadian National Phase application of
International
Application No. PCT/GB93/01995, filed September 23, 1993, and published on
April 14,
1994 under International Publication No. WO 94/07688.
The present invention relates to compaction methods and compaction apparatus
and in particular but not exclusively to methods and apparatus for compacting
(i.e.
compressing) waste material. Other applications for the invention include the
compaction of materials used in farming and the food industry. These are not
necessarily
waste materials.
Various types of material, including waste material such as litter and
discarded
packaging material, are bulky but not heavy. It is therefore desirable in
certain
circumstances to compact this material to reduce its volume in order to reduce
transport
costs or the storage space required.
Compacting apparatus is known which has conveying means operable to convey
material along a path, which material is compacted as it moves along the path.
Thus, the
conveying means is arranged so that the density of material passing through
the conveyor
is relatively low at the beginning of the path and relatively high at the end
of the path.
Such compaction can be achieved by using a screw conveyor located in a
passage. Screw conveyors of constant pitch are generally used but in some
arrangements
a screw conveyor having a pitch which is relatively large at the beginning of
the path and
relatively small at the end of the path is used.
These known apparatus sometimes include a tapered portion near or at the
discharge end of the path, for further compaction. The cross-sectional area is
thus
relatively large at the entry to the tapered portion and relatively small at
the exit thereo~
However, the known apparatus suffer from the problem that optimal performance
can only be achieved
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for one set of operation conditions such as temperature,
volume of waste fed into compactor and type and density
of waste material. As will be appreciated, most waste
compactors would in practice be exposed to a range of
values for each condition. For example, a waste
compactor which is situated outdoors would be subjected
to the extremes of summer and winter temperatures.
Likewise the uniformity of volume and type of waste
cannot be guaranteed. For example an increase in the
percentage of fatty or oily substances in the waste
material can have an adverse effect on the performance
of the compactor. Indeed in experiments carried out,
the compaction achieved dramatically decreases
especially for very slippery materials. The inability
to deal with changes in conditions means that compactors
will at one extreme not always compact material to the
desired degree if at all and, at the other extreme, will
have a tendency to jam.
Prior art is known which attempts to address at
least certain aspects of this problem. For example, a
resiliently biased trap door can be provided at the end
of the conveying means which opens only when the
pressure on the door exceeds a certain value. In
theory, this allows waste material to accumulate so that
variations in the volume of waste material do not affect
the performance of the compactor. However, in practice,
such doors remain partially open most of the time which
leads to unsatisfactory results since maximum compaction
is not achieved. Furthermore trap doors exert a sidways
force which tends to encourage the break up of the
compacted waste material which in turn can cause
difficulties with the packaging and/or disposal of the
material as well as increasing the volume of the
compacted waste. In any case such compactors are not
suited to applications requiring a relatively high
degree of compaction as provided in accordance with
embodiments of this invention.
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It has been found by the inventor that the problems
with the prior art arise primarily from the outlet
nozzle of the known apparatus being of rigid
construction and having a constant volume. Whilst the
shape and dimensions of the nozzle can initially be
selected so that the apparatus is able to give good
performance i.e. it is "tuned" for a given set of
conditions, there is no flexibility in the apparatus.
The inventor has found that an important factor in
achieving successful compaction lies in the outlet
nozzle providing an appropriate degree of back pressure.
This.back pressure enhances the compacting action and
effectively tunes the apparatus. It is the loss or
reduction of this back pressure which causes the
performance of the known apparatus to deteriorate.
Conversely, a substantial increase in back pressure can
cause the apparatus to jam.
According to one aspect of the invention, there is
provided compacting apparatus comprising a screw
conveyor for conveying waste material through a passage
and compacting it therein, and an exit nozzle
communicating wi,th the passage, said nozzle defining an
internal transverse cross-sectional area which enlarges
and reduces respectively in response to increasing and
decreasing material pressure.
By altering the size of the outlet opening defined
by the internal transverse cross-sectional area of the
nozzle automatically in response to the volume and/or
pressure of material flowing therethrough, the nozzle is
able to compensate for changes in various conditions and
ensure that an appropriate back pressure is achieved for
a range of operating conditions. The compactor can thus
effectively self-tune in response to the nature and
volume of waste passing therethrough. Embodiments of
the invention may achieve a degree of compaction which
is very much larger than that achieved by known prior
art arrangements e.g. a 300-400% increase.
.=
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Thus for a greater range of operating conditions as
compared with the prior art, the back pressure will
remain above a predetermined minimum for satisfactory
operation, and, conversely, excessive back pressures
which might cause jamming of the screw conveyor can be
avoided. This is achieved far more effectively in
accordance with the invention as compared with a trap
door outlet arrangement and without a sideways force
being exerted on the waste or other material being
compacted.
The ability of the apparatus to respond to changes
in pressure in this way solves another problem from
which prior art compactors tend to suffer. As material
is compacted it is heated up. If the material remains
in the nozzle for any length of time, for example whilst
the compactor is not in use, the heated material has a
tendency to solidify and/or adhere to the walls of the
nozzle. The nozzle can thus become blocked and the
apparatus then needs to be dismantled to remove the
blockage. It has been found that since the cross-
sectional area of the nozzle is able to change, at least
in preferred embodiments of the present invention there
is a self-cleaning and self-clearing effect which has
been found to stop or reduce the tendency of material to
stick to the nozzle walls.
It should be noted that references to a change in
transverse cross-sectional area in the nozzle resulting
in a change in the size of the outlet opening defined
thereby can refer to changes occurring at substantially
a single point, e.g. adjacent the nozzle outlet, or at
all points along all or part of the length of the
nozzle. The changes in cross-sectional area may be the
same along all of the relevant part of the nozzle or, as
is preferred, the transverse cross-sectional areas at
different points along the length of the nozzle may
change by different amounts. It is thus preferred that
the nozzle tapers inwardly (in the flow direction) over
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at least part of its length and the changes in
transverse cross-sectional area at all points along the
tapered region arise from changes in the degree of
taper. It is envisaged that the nozzle may taper
outwardly in an extreme case e.g. to allow a hard plug
of incompressible material to pass through. In a
preferred such embodiment the nozzle is generally
frusto-conical in shape and is adapted such that its
cone angle decreases and increases in response to
changes in pressure.
There are a number of ways in which the change in
cross-sectional area in response to waste material
pressure changes can be achieved. In one embodiment,
the nozzle is formed of resilient material, or includes
a resilient insert, which is biased inwardly toward a
position of minimum internal cross-section. The
resilient material responds to changes in pressure such
that the nozzle opening widens as pressure increases to
achieve the self tuning effect as described.
In an alternative preferred embodiment, the nozzle
has a plurality of wall portions which are movable
relative to each other to vary the internal cross-
sectional area of the nozzle. These portions are
preferably made of a hard wearing material such as steel
which can withstand the abrasive forces applied by the
waste material as it passes through the nozzle. For
example the nozzle may comprise two semi-cylindrical
portions which together define a generally cylindrical
body having a degree of taper depending on the pressure
in the nozzle. These two semi-cylindrical portions are
hingedly connected together at the end region of the
nozzle further from the nozzle outlet. So as to
accommodate the change in internal transverse cross-
sectional area of the nozzle along at least part of its
length, the two cylindrical portions are preferably
dimensioned so that one portion is slightly smaller than
the other. Thus when required, parts of one portion can
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be received within parts of the other portion.
These portions may be biased using resilient means
towards a position in which the transverse cross-
sectional area is at its minimum value along the entire
length of the portions. This may be a position in which
the two semi-cylindrical portions define a cylinder of
substantially uniform cross-sectional area. However,
more preferably the semi-cylindrical portions define
when biased to the minimum size of outlet opening, a
tapered cylinder which tapers inwardly in the direction
toward the end of the nozzle. As increased pressure
occurs in the nozzle, the two semi-cylindrical portions
are forced apart to thereby increase the internal cross-
sectional area of the nozzle at all points along the
length of the hinged portions.
The resilient means may take any suitable form and
may be in the form of one or more springs extending
around part or all of the circumference of the nozzle.
Alternatively, the resilient means may be in the form of
one or more elastic tensioning bands or a length of
elastic material which is wound round part or all of the
length of the nozzle. The resilient means may also take
the form of an elastic sleeving. Of course, the
resilient means may be provided at any suitable position
along the length of the nozzle. The most effective
position is, however, typically at the end region next
to the nozzle outlet.
The nozzle preferably has at least one projection
extending outwardly therefrom which retains the
resilient means on the nozzle. This projection may take
the form of a circumferentially extending lip or
alternatively may take the form of one or more discrete
projections extending from the nozzle. The at least one
projection is arranged at any suitable location on the
nozzle.
In another similar preferred embodiment, the nozzle
comprises a larger number of longitudinally extending
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parts of e.g. steel or other suitably flexible hard
wearing material. These relatively movable parts take
the form of fingers extending generally longitudinally
from an annular base part which may be secured around
the screw conveyor outlet. The fingers are biased
inwardly and are flexed relative to the base part to
increase or decrease the internal cross-sectional area
of the nozzle in response to changes in waste material
pressure. When the fingers are at their innermost
position, it is preferred that there are no gaps between
the fingers and that the nozzle tapers toward its
outlet. Thus, edge to edge abutment of the fingers can
define the nozzle's innermost position. As the pressure
in the nozzle increases and the cross-sectional area
increases, V-shaped gaps are defined between the
fingers. The fingers are biased toward their minimum
position by resilient means which could take any of the
above described forms.
The end or end regions of at least one and
preferably all of the fingers may be provided with
outward projections for retaining the resilient means in
place. Of course the outward projections may be
provided at any other suitable location on the nozzle.
It is particularly preferred that the nozzle
comprises two members each of which takes the form
previously described, ie. an annular base part having
longitudinally extending fingers. One member is
arranged inside the other. Consequently the cross-
sectional dimensions of the outer member are greater
than that of the inner member. It is also preferred
that the fingers of the outer member are slightly longer
than those of the inner member so that when the cross-
sectional area of the nozzle is at its minimum, the
fingers of the outer member cover the ends of the
fingers of the inner member. The two members are
preferably arranged so that a finger of one member
overlaps two fingers of the other member (and the gap
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between the fingers when appropriate). Thus even when
the fingers are in their most expanded state, the waste
is fully contained by the overlapping fingers of the two
members and cannot escape between the gaps of the
fingers. Of course, outward projections for retaining
the resilient means need only be provided on the outer
member.
The preferred resilient biasing means exerts a very
substantial radially inward force on the nozzle -
resulting from tensioning bands that typically might
number 20 to 30 exerting a circumferential tension
typically of 250 kg per cm of axial length of the
nozzle. In the absence of any compacted material within
the nozzle to counter this force, the preferred form of
nozzle might be damaged i.e. its fingers might be
imploded inwardly beyond the intended minimum position
defined by their edge to edge abutment. To avoid this,
a preferred embodiment of the nozzle is initially fitted
with a plug e.g. of polyurethane which supports it
internally. The plug is ejected once compacted material
is passed through the nozzle whereafter there wiil
always be compacted material supporting the nozzle in
normal use of the apparatus i.e. even when it is shut
down a plug of material remains in the nozzle.
In an alternative embodiment, it is envisaged that
the cross-section of the nozzle may be altered by a
servo-controlled motor or the like. The nozzle may be
made up of two or more parts, such as described above.
The parts making up the nozzle may be moved by the motor
under micro-processor control to change the cross-
sectional area of the nozzle in response to pressure
detected, for example at the outlet end of the screw
conveyor. The nozzle opening may also open and close as
a function of screw conveyor torque or drive motor
current, both of which vary in dependence on pressure.
Another problem from which the prior art compactors
suffer is that the screw conveyor is generally very
heavy in order to be sufficiently heavy duty to compress
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and compact waste or other material without itself being
damaged. In particular, the thickness of the screw
conveyor flight is dictated by the maximum force to
which any part of the flight is subjected. The weight
of the screw conveyor can lead to problems with
providing sufficient support therefor.
According to a second aspect of the present
invention there is provided a screw conveyor in or for a
waste compaction apparatus for conveying and compressing
waste or other material, wherein said screw conveyor
comprises a longitudinally extending shank and a flight,
the thickness of the part of flight subjected to the
greatest force in use being greater than the thickness
of the other parts of the flight of the conveyor.
It has been found that the part of the flight
nearest the outlet end of the conveyor tends to be
subjected to the largest amount of pressure as a result
of the extra force exerted by the compacted material.
Typically, the flight will therefore have the greatest
thickness at the outlet end of the conveyor with the
thickness being least at the inlet end.
Thus with the embodiments of this aspect of the
invention, the thickness of the flight need only be at
the maximum required value at that part of the screw
conveyor which is subjected to the greatest force. The
other parts of the flight need not be so thick and
accordingly the weight of the conveyor is reduced
resulting in economies in manufacturing as well as
running of the apparatus.
This arrangement is particularly suited to those
cases where the force applied to the screw flight by the
material does not increase linearly but rather increases
more quickly, for example where the screw conveyor is
tapered towards the outlet and is received in a
correspondingly tapered passage and/or the pitch of the
flight decreases toward the outlet end of the conveyor.
In these cases, the force applied to the flight in the
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vicinity of the outlet can be very large and the
additional thickness of the flight is able to compensate
for this.
It is preferred that the flight has a relatively
large diameter flight in the region where it takes up
material i.e. beneath a hopper so that large discrete
chunks of material and other bulky items can fall
between the flights and be taken up by the conveyor.
This then leads to an inwardly tapering portion in which
compaction or at least pre-compaction of material takes
place.
The thickness of the flight of the screw conveyor
may increase uniformly from an inlet end to the outlet
end of the conveyor. Alternatively, the thickness of
the flight can be uniform along most of the length of
the screw conveyor with a region of increased thickness
provided only adjacent the outlet end of the screw
conveyor. In a preferred embodiment, the thickness of
the flight increases in a stepwise fashion from the
inlet end to the outlet end of the conveyor with the
first stepped increase preferably being at a point
slightly upstream of an inwardly tapering portion of the
flight. This last alternative is preferred as it allows
full advantage to be taken of the invention whilst at
the same time still allowing the device to be
manufactured relatively easily.
Another problem associated with the weight of the
screw conveyor concerns the provision of sufficient
support for the conveyor. In the prior art, such screw
conveyors are usually supported by fixed bearings at one
end of the screw conveyor so that the longitudinal axis
of the conveyor is immovable. The weight of the screw
conveyor requires that the bearings be large and support
the screw conveyor along a significant proportion of the
length thereof. A mechanical bearing cannot be
successfully used to support the outlet end of the screw
conveyor since this would partially block the compactor
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outlet and interfere with the flow of compacted material
which is of course undesirable.
According to a third aspect of the invention, there
is provided compaction apparatus comprising a screw
conveyor arranged in a conveying passage and rotatably
supported in relation to the passage housing in the
region of the inlet end of the conveyor, such support
permitting a degree of transverse movement of the
longitudinal axis of the conveyor in the region of its
outlet end, wherein the conveyor comprises at its outlet
end an axial shank extension which extends into a
compaction chamber located downstream of the screw
conveyor and coaxial therewith, the shank extension in
use being surrounded by an annulus of compacted material
in the downstream compaction chamber, such compacted
material providing a support bearing means for the
outlet end of the conveyor.
A fourth aspect of the invention provides a method
of compacting waste or other material, comprising
conveying material by a rotating screw conveyor,
compacting the material in a compaction chamber located
downstream of the screw conveyor, and supporting the
outlet end of the screw conveyor during compaction by
means of an annulus of compacted material which
surrounds an axial shank extension of the screw conveyor
projecting into the compaction chamber. The axial shank
extension may comprise e.g. 10-30% of the total length
of the screw conveyor.
Since the screw conveyor is, in effect, supported
also at its free, outlet end during use of the
apparatus, the bearing required at the inlet end of the
conveyor need not be as strong as those required in the
prior art. In a preferred embodiment the inlet end may
be supported directly from a drive motor or gear box
output shaft without the need for costly, heavy duty
bearing means to provide additional support.
Since the support for the screw conveyor is
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improved in this aspect of the invention, a lesser
clearance may be left between the outer edge of the
flight and the inner walls of the chamber without the
risk of the flight engaging the walls and being damaged.
This improves performance particularly with slippery
waste which has a tendency to recirculate through the
apparatus by slipping past the outer periphery of the
conveyor.
Preferably, the axes of the compaction chamber and
conveying passage coincide such that when the shank
extension is supported in use, the axis of the screw
conveyor and the passage also coincide. Thus the waste
support is able to centre the axis of the screw conveyor
automatically. The waste material acts as a self- .
centring bearing for the free end of the screw conveyor
which is able to compensate for wearing of the passage
and/or the screw conveyor itself.
Preferably, the compaction chamber into which the
shank extension extends is cylindrical and may form part
of an exit nozzle of the apparatus which preferably also
includes a tapering outlet part upstream of the
compaction chamber. The tapering part may be as
described in relation to the first aspect of the
invention.
It is desirable that the inner walls of the passage
may be formed so as to resist or prevent conveyed
material from rotating about the axis of the passage.
The inner wall of the passage may have at least one
prominence or rib which is engageable with material in
the passage. The or each prominence or rib is
preferably adjustably mounted on the passage walls, to
allow the degree of projection into the passage to be
varied. The or each prominence or rib may be
resiliently mounted. Whilst it is preferred that the or
each prominence or rib extends longitudinally of the
passage, the or each prominence or rib may extend along
a helical path.
Such prominences or ribs have a tendency to damage
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the flight of the screw conveyor if allowed to contact
them.
In order to safely transport the waste compactor,
it is therefore preferred that the screw conveyor is
received in a stocking of protective material such as
suitable plastics so that the screw conveyor cannot move
laterally in the passage to cause damage in transit. To
remove this stocking, the compactor merely needs to be
switched on. The action of the screw conveyor will
cause the stocking to be ejected from the apparatus
thereafter the compacted material keeps it centered.
Alternatively or additionally, the nozzle plug discussed
in relation to the first aspect of the invention may
surround part of the screw conveyor to initially
maintain its axial location.
Another problem with known screw conveyors is that
they have a tendency to jam when a relatively
incompressible object is fed into the conveyor. Under
such circumstances, known screw conveyors attempt to
continue to rotate with the motor applying an increased
torque. This puts a strain on the motor and often is
not sufficient to unjam the apparatus. The apparatus
then will require manual attention to remove the
blockage.
Viewed from a fifth aspect, there is provided
apparatus for compacting waste or other material
comprising: a screw conveyor arranged in a passage;
means for rotating said screw conveyor in a first,
compacting and conveying direction; means for sensing a
jammed condition of said conveyor; and a back chamber
arranged at an input end region of the screw conveyor
for receiving material causing said jamming, wherein,
after a jammed condition has been sensed, said rotating
means is arranged to rotate said screw conveyor in a
second, opposite direction to the first direction and to
move said jamming material to said back chamber.
This reversal of direction of rotation of the screw
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conveyor allows jamming material to be moved back into a
back chamber where it no longer jams the apparatus and
can be further dealt with, for example by being tumbled
or removed, either manually or automatically, from the
apparatus.
There are two main causes of jamming. The first is
that incompressible lumps of material are too large to
pass through the conveyor and have not been broken up by
the previous action of the conveyor. This problem is
exacerbated by conveyors which are tapered and/or which
have decreasing pitch. The second cause of jamming is
material reaching a compaction maximum and thus being
unable to pass any further along the conveyor.
Accordingly, in a particularly preferred embodiment, the
back chamber has tumbling means which is arranged to
attempt to break up the jamming material and/or reduce
its density so that it can be processed through the
compactor in the normal way when the screw conveyor is
again driven in the first direction. The tumbling means
preferably provides a cutting action.
The tumbling means can be of any suitable form and
may be part of the screw conveyor itself which has been
modified, for example, by sharpening the flight edges to
provide a cutting edge. However, it has been found that
a flexible part secured to the flight performs well.
The flexible part might be used to mount a hard and
rigid cutting member to the shank of the screw conveyor.
The flexible part can be of any suitable material such
as polyurethane and, if used, the cutting member may be
formed of, for example, a metal such a steel. The blade
can continue along the path defined by the flight of the
screw conveyor. This blade has been found to encourage
the break up of material but itself is not damaged by
material which cannot easily be broken up, if at all.
This is a consequence of the flexible part. The jamming
material can then be tumbled in the back chamber by the
rotation of the shaft in the reverse direction and the
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blade can attempt to break up or decrease the density of
the jamming material. After a predetermined time, the
screw conveyor is rotated in the forward direction in a
further attempt to process the jamming material which
initially jammed the compactor.
If the compactor jams again, it is preferred that
the jamming object be returned to the back chamber where
material is again tumbled. The cycle then repeats.
After the machine has made any selected number of
unsuccessful attempts to break up material returned to
the back chamber, the material can be removed manually
or automatically dropped into a trough below or behind
the chamber from where it can be removed when a
compaction cycle is completed. At this stage, a warning
signal can be given and/or the apparatus can be shut
down.
The chamber preferably has a cover which prevents
waste material initially input into.the compactor from
entering the chamber. Preferably the cover is movable
so as to allow access to the back chamber to remove
objects therefrom, if necessary. The cover preferably
directly engages the screw conveyor and is flexible so
as not to be damaged on reversal of the screw conveyor.
Additionally, it is particularly preferred that
when a jamming condition is initially sensed, the screw
conveyor is reversed by for example only one or two
revolutions and then the screw conveyor is again rotated
in the forward direction. This step can be repeated any
number of times and for example could be in the range of
one to twenty attempts before the material is taken back
to the back chamber and the above procedure followed.
Viewed from a still further aspect the invention
provides a compacting apparatus comprising a rotating
screw conveyor a part of which is located in a passage
which tapers inwardly in the direction of movement of
material being compacted, at least the tapering part of
the passage being provided with longitudinally or
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helically extending ribs to help restrain the material
from rotating with the conveyor, the apparatus being
adapted to sense a jamming condition therein, whereupon
the rotation of the conveyor is reversed by part of a
turn or a small number of turns before being rotated in
a forwards direction again, such cycle being repeated
one or a predetermined number of times.
In practice we have discovered that with this
arrangement most jamming conditions can in practice be
cleared. Thus, in the preferred embodiment, the
material is only taken into the back chamber in
extremis, most blockages being able to be cleared by the
initial reversal and retry procedure.
The sensing means may measure any suitable
parameter such as the torque applied to the screw
conveyor by the motor or the current fed to the motor
(which is also a measurement of torque). The sensing
means is arranged to sense jamming of the conveyor as it
is rotated in the first, forwards direction and
preferably also senses if jamming takes place whilst it
is rotating in the second, reverse direction whereupon
the direction of rotation is again reversed.
According to yet another aspect of the invention,
there is provided a method of compacting e.g. waste
comprising:
feeding waste material into a compacting screw
conveyor;
rotating the screw conveyor in a first, forward
direction to thereby compact and convey the waste
material;
monitoring the apparatus for the occurrence of a
jamming condition; and
rotating the screw conveyor in a second, reverse
direction after a jamming condition has been detected,
through part of a turn or a small number of turns and
then rotating in the first direction in an attempt to
clear the jamming condition, and repeating this
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operation up to a predetermined maximum number of times
if the jamming condition is not cleared; and after the
predetermined number of attempts, reversing the rotation
of the conveyor for a greater number of turns so as to
move the material causing the jam to a chamber adjacent
the end of the conveyor remote from the waste outlet.
All the above operations can be carried out under
automatic or micro-processor control.
A completely separate aspect of the invention
concerns drainage and lubrication. we have discovered
that for optimum performance with waste material having
a fluid component the fluid level in the base of the
compactor should be controlled to provide a degree of
self-lubrication whilst not being detrimental to the
conveying and compacting action.
Thus, a still further aspect of the invention
provides a compacting apparatus having a rotating screw
conveyor located in a passage, wherein the passage
comprises means to maintain a predetermined maximum
fluid level in the base region of the passage.
Such means preferably comprises a fluid outlet at
such level, advantageously in the form of a raised
horizontal platform having a filtering means. Desirably
part of the screw conveyor provides a wiping action on
the filtering means. In a preferred embodiment, the
outlet is provided in the back chamber described above
and the tumbling means therein provides the wiping
action.
As will be appreciated, compacting apparatus
according to the invention can embody any one or more of
the features described in relation to the various
different aspects.
The following features may also be included in any
embodiments of the invention. The screw conveyor may be
received in a passage which has a portion of
substantially uniform cross-sectional area located
beneath a waste material inlet hopper and a tapered
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portion which is at the downstream end of the conveyor
and tapers inwardly towards an outlet nozzle. The
diameter of screw conveyor preferably reflects the size
of the passage and accordingly is decreased in the
tapered part. This tapering helps to increase the
compaction in the passage.
Additionally or alternatively, the pitch of the
screw conveyor may decrease toward the outlet of the
passage so as to help obtain sufficient compaction.
Thus the pitch could be relatively large at the
beginning of the passage and relatively small at the end
of the path. The pitch preferably decreases
substantially continuously over whole or part of the
length of path.
Of course, the tapering is not essential and
sufficient compaction may be achieved in certain
embodiments which have a screw conveyor passage of
uniform cross-section. Likewise, the passage could be
tapered along the whole of its length. Thus the cross-
section of the passage may be relatively large at the
entry to the passage and relatively small at the outlet.
The cross-sectiQn may decrease substantially
continuously along the whole or part of the length of
the passage.
The exit nozzle preferably includes an inwardly
tapering part connected to the passage via a cylindrical
compaction chamber. Thus, in a preferred embodiment
material is compacted as it is moved along by the screw
conveyor, with further more substantial compaction
taking place in the compaction chamber. In practice, in
such an embodiment the greatest amount of compaction
takes place immediately downstream of the screw
conveyor.
Furthermore, the nozzle does not of course need to
be connected directly to the outlet of the conveyor
passage. For example, a second passage may be arranged
between the outlet of the screw conveyor and the inlet
CA 02454645 2005-09-22
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of the nozzle. This second passage may be arranged so as to
resist movement of material through that second passage, to
further compact material received from the screw conveyor.
The movement of material through this second passage is
preferably resisted by friction between the material and
the walls of the second passage. This resistance provided
may be varied by for example changing the length of that
passage and/or its cross-sectional area. In the former
case, the second passage may be defined by two portions
which may telescope together. In the latter case, the
second passage may, for example, be formed in a manner
described above in relation to the exit nozzle.
Waste compacting apparatus such as described is
suitable both for fixed installations as well as for use in
refuse collection vehicles. The particular.use to which a
waste compactor is put will depend to a certain extent on
the actual dimensions and material of the conveyor and
other parts of the compactor. For example, it has been
found that the compactor is particularly useful for
compacting the waste from restaurants and other similar
installations. Compactors embodying the invention also have
uses in industrial situations for compacting factory waste.
It is also envisaged that waste compactors embodying the
invention will also have applications in the home.
Whilst the invention has been described primarily in
relation to the compaction of waste, embodiments of the
invention can be used for other applications where
compaction of a material is required. For example,
embodiments of the invention can be used on farms or in
factories to provide compaction of food products.
In one aspect, the present invention resides in a
compaction apparatus comprising a screw conveyor arranged
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in a conveying passage and rotatably supported in
relation to the passage in the region of the inlet end of
the conveyor, the conveyor comprising at its outlet an
axial shank extension which extends into a compaction
chamber located downstream of the screw conveyor and co-
axial therewith, the shank extension in use being
surrounded by an annulus of compacted material in the
downstream compaction chamber, such compacted material
providing a support bearing means for the outlet end of
the conveyor.
In another aspect, the present invention resides in a
method of compacting waste or other material, comprising
conveying material by a rotating screw conveyor, compacting
the material in a compaction chamber located downstream of
the screw conveyor and supporting the outlet end of the
screw conveyor during compaction by means of an annulus of
compacted material which surrounds an axial shank extension
of the screw conveyor projecting into the compaction
chamber.
Embodiments of the invention will now be described by
way of example and with reference to the accompanying
drawings in which:-
Figure 1 shows a longitudinal cross sectional view of
a compactor;
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Figure la shows an enlarged view of part of the
compactor of Figure 1;
Figure 2 shows a longitudinal cross sectional view
of the compactor of Figure 1 when filled with waste
material;
Figure 3 shows a cross-section of the compactor of
Figure 1 along line III-III;
Figure 4 shows a perspective view of the nozzle of
Figure 1 which has been partially cut away for clarity;
Figure 5 shows a cross-sectional view of the output
end the compactor of Figure 1, with the screw conveyor
packaged for transportation;
Figure 6 shows a cross-sectional view of the output
end of the compactor of Figure 1, when filled with waste
material;
Figure 7 shows a cross-sectional view of the screw
conveyor of the compactor of Figure 1;
Figure 8 shows a flow diagram illustrating the
control for the screw conveyor;
Figure 9 shows schematically an arrangement for the
bagging of material exiting the compactor of Figure 1;
Figure 10 shows a schematic view of a back pressure
chamber for use with the compactor of Figure 1; and
Figure 11 shows a schematic view of a second
embodiment of the nozzle.
As can be seen from Figure 1 to 7, the waste
compaction apparatus 2 has a screw conveyor 4 which
conveys as well as compacts material along a passage 6
from an inlet 8 to an exit nozzle 10.
The passage 6 is generally cylindrical and has a
first part 12 of generally uniform cross-section. The
first part 12 of the passage has a longitudinally
extending opening 14 through which uncompacted waste
material is fed from hopper 16. The size of the hopper
16 is selected so as to prevent over filling of the
apparatus. In practice, this first part 12 is in the
form of a trough having a rounded bottom 18 (see Figure
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3), the sides of which also define the hopper 16. The
trough opening defines the longitudinally extending
opening 14.
The passage 6 also has a second part 20 which is
tapered in the direction towards the exit nozzle. This
second part 20 thus has a generally frusto-conical
shape.
The inner walls of the passage 6, both in the first
part 12 and the second part 20 are provided with
longitudinal extending ribs 22 which project inwardly
into the passage. These ribs 22 prevent-partially
compacted material from rotating with the screw conveyor
4. Where appropriate the ribs 22 are also able to
provide a cutting surface or anvil against which the
flight 24 of the screw conveyor 4 can act to break the
waste material down into smaller pieces which are more
easily compacted.
The inner walls of the first part 12 of the passage
are provided with two projections 230 (see Figure 3)
which extend along its length. These two projections
230 are arranged to contact the outer periphery of the
screw conveyor to cut up elongate waste material such as
plastics bin liners and the like. This prevents such
material from wrapping itself around the screw conveyor
and causing it to jam. The projections 230 are provided
with a cutting edge for this purpose. The outer
periphery of the screw conveyor may also be provided
with a sharpened edge to cut up the material.
The screw conveyor 4, which is illustrated in
detail in Figure 7 has a first part 26 where the flight
is of uniform diameter. The length of this first part
26 corresponds substantially to the length of the first
part 12 of the passage 6. The flight diameter of the
second part 28 of the conveyor 4 decreases in a manner
which corresponds generally to the degree of taper of
part 20 of the passage 6. The diameter of the flight 24
of the screw conveyor is selected such that there is
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usually a few millimeters clearance between the screw
conveyor 4 and the projecting ribs 22. Typically this
clearance is in the range of 2 to 3mm.
The screw conveyor 4 has a third part 30 in the
form of a shank with no flight which extends into the
nozzle 10. The purpose of this third part 30 will be
described in more detail later.
The pitch of the screw conveyor 4 also varies along
its length. In particular the pitch of flight 24
decreases in the direction towards the second tapered
part 28. For example the first one and a half turns 34
have a pitch of 400mm, the second one and a half turns
36 a pitch of 200mm whilst the third one and a half
turns 38 have a pitch of 100mm ie. giving a pitch ratio
of 4:2:1 along the length of the screw conveyor 4. The
decrease in pitch of the screw conveyor 4 as well as the
tapering of passage 6 enhances the degree of compaction
achieved by the waste compaction apparatus 2. The pitch
of the screw conveyor is of course selected depending on
the material to be compacted usually as well the degree
of compaction required.
The thickness of the flight 24 changes along the
length of the screw conveyor 4 and, in particular,
increases as the pitch decreases. In the specific
embodiment, about the first one and a half turns 34 have
a flight thickness of 12mm, about the second one and a
half turns 36 have a flight thickness of 20mm whilst
about the third one and a half turns 38 have a thickness
of 25mm. Thus, the part of the flight which is
subjected to the greatest force as a result of the
tapering passage and reduced pitch, has the greatest
thickness to withstand that increased force and the
resulting increase in wear. The life of the screw
conveyor 4 is thus increased. Likewise, those parts of
the conveyor which are subjected to least force have the
smallest flight thickness. This results in a useful
reduction in the weight of screw conveyor especially
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since the part 34 of the flight 24 having the least
thickness has the largest diameter. In practice, the
thickness preferably begins to increase slightly
upstream of the tapering part 28, although this is not
appreciable from the drawings.
The dimensions given in relation to pitch, flight
thickness and flight diameter are included only for
illustrative purposes and can be varied in accordance
with the application and size of the apparatus.
The screw conveyor 4 is made from any suitable
material which has the desired strength, rigidity and
resistance to wear for the particular application in
question. For example the screw conveyor 4 may be of
mild steel. Furthermore the shank 40 of the screw
conveyor 4 is hollow so as to further reduce the weight
thereof.
The maximum initial compaction ratio achieved as a
result of material passing through the screw conveyor 4
itself is determined by the ratio of the volume between
the flight turns 34 below the longitudinal opening 14 to
the volume between the flight turns 38 at the end of
passage 6 adjacent the nozzle 10. In a preferred
embodiment, this ratio may be between 4:1 and 10:1 which
latter ratio in practice results in a compaction ratio
of about 7 or 8:1. (Maximum compaction would in
practice be not often achieved since the screw conveyor
would not have the maximum volume of material required
for maximum compaction passing through it at all times.)
The required initial compaction depends on the type of
waste being processed, and different screw conveyors may
be supplied for different applications to provide
optimum performance.
The nozzle 10 will now be described in more detail
with particular reference to Figures 4, 5 and 6. The
nozzle 10 is coupled to the outlet end of passage 6 at
the end of section 20 and is surrounded by chamber 41
which allows any material leaking from the nozzle 10 to
CA 02454645 2005-09-22
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be collected in the chamber 41. The nozzle is made up
of two main parts 42 and 44. The first part 42 is
formed from a sheet of material such as sheet steel with
a thickness of 2 to 3mm which has been rolled up to form
a cylinder and welded to maintain that shape. The base-
portion 46 of the first part 42, which is connected to
the passageway 6, is circular, of substantially constant
cross-section and of unbroken sheet material. This
defines a compaction chamber 200 in which further
substantial compaction of the waste material takes place
upstream of the tapering portion of the nozzle. From
this base portion 46 a plurality of eg. twelve fingers
48 extend, the axis of each finger initially being
generally parallel to the longitudinal axis 50 of the
nozzle 10. The width of each finger 48 decreases in the
direction towards the outlet 52 of the nozzle 10 to
thereby define V-shaped gaps (not shown) between
adjacent fingers 48.
The second part 44 is constructed in a similar
manner to the first part 42, the two parts differing
only in dimensions. In particular the second part 44 is
slightly longer than the first part 42 and has a
slightly larger diameter. The first part 42 is arranged
inside the second with the base portions 46 of the first
and second parts 42 and 44 being welded together. The
two parts 42 and 44 are arranged so that the fingers 48
of one part overlap the gaps between the fingers of the
other part. ie. each finger of one part overlaps two
fingers of the other part.
On the outer surface of the ends 54 of each of the
fingers 48 of the second outer part 44, a lug 56 is
provided. These lugs 56 extend in a generally outward
direction. A number e.g. 20 to 30 of elastic tension
bands 58 are then arranged around the nozzle, in the
manner shown particularly clearly in Figure 4.
Alternatively, a length of elastic tensioning rope may
be wound around the nozzle. The lugs 56 retain the
CA 02454645 2005-09-22
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bands 58 in position around the nozzle. The elastic
tension bands 58 are selected so that when the nozzle is
at minimum cross-sectional area the nozzle 10 has a
tapered portion and the edges of adjacent fingers of
both the first and second parts engage one another to
close the gap between the fingers and define the
smallest nozzle aperture. When the pressure and/or
volume of waste material passing through the nozzle 10
exceeds a certain value, the cross-sectional area of the
nozzle 10 increases for example as shown in Figure 6.
In this instance, the force exerted by the tension bands
58 inwardly is now exceeded by the outward force exerted
by the fingers 48 as a result of the waste material and
an equilibrium position is established. In this way the
tapering portion of the nozzle 10 is able to regulate
itself in response to variations in the pressure and
volume of material passing through the nozzle and other
operating conditions as discussed above. An appropriate
back pressure for satisfactory compaction can be
achieved over a range of operating conditions. Thus
when the apparatus is in use, the average operating
position of the nozzle 10 is as shown in Figure 6 with
the minimum and maximum operating positions of the
nozzle 10 shown in dotted lines for respective decreases
and increases in volume and/or pressure of waste
material. An appropriate resilient restoring force can
be selected in accordance with the expected range of
operating conditions when the apparatus is set up by
adjusting the number and/or strength of the tension
bands. The force is strong e.g. 100 kg for each band.
An ejectable plug (not shown) can initially be provided
to support the nozzle against this force and prevent the
fingers being damaged.
The screw conveyor 4 is supported at one end by a
heavy duty bearing 60 and gearbox connected to the drive
motor 66. The bearing provides radial location at that
end but is principally intended to absorb a high degree
CA 02454645 2005-09-22
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of axial thrust which is generated by the screw during
compaction. This mounting arrangement permits the
longitudinal axis of the screw conveyor to pivot very
slightly relative to the longitudinal axis 62 of the
passage 6. Thus, if the apparatus 2 is empty the edges.
of the flight 24 of the screw conveyor 4 in the tapered
part 20 of the passage 6 rest on the bottom 63 of that
passage as shown in Figure la. In practice, the screw
conveyor 4 is initially maintained in an axial position
in passage 6 by packaging 64 for ease of transport as
shown in Figure 5. When the compactor 2 is first used,
the packaging 64 is broken up by the action of the screw
conveyor 4 and exits via nozzle 10. Alternatively, the
nozzle plug described above may provide the desired
initial centering effect.
When the apparatus 2 is in use, the annulus of
moving compacted waste material 65 in the compaction
chamber 200 of the nozzle 10 acts as a bearing and
supports the third part 30 ie. the threadless axial
shank of the screw conveyor 4. It has been found that
the screw conveyor 4 is centred as well as supported by
the waste material in the compaction chamber 200 so that
the flight 24 no longer contacts the bottom 63 of the
passage 6. Since the waste compactor usually has some
waste in the nozzle, even when the compactor is off, the
shank 30 is usually supported at both of its ends. It
has also been found that by using waste material as a
self-centring bearing, the screw conveyor 4 is able to
compensate for wearing of the flight 24 of the screw
conveyor as well as for wearing of the tapered passage
20. Furthermore, the bearing 60 need not be as strong
as regards the radial location it provides as in
comparable prior art arrangements as support is provided
at either end of the shank 30.
The axial location of the screw can be adjusted to
accommodate for wear by inserting shims of different
thickness between shoulders 225.
CA 02454645 2005-09-22
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At the end of the passage 6 adjacent the bearing
60, there is a rear compartment 70. The compartment 70
has a movable flap 71 (see Figures 1, 2 and 3) which is
biased in a downward direction to prevent material from
the hopper 16 from entering that compartment 70. The
flap 71 may be of a flexible material which inherently
biases the flap towards the closed position. Material
can thus only enter the compartment 70 by reverse
rotation of the screw conveyor 4 which brings material
which is causing a jam from a forward part of the
apparatus 2, for example the tapered part 20 of the
passage 6, back to the compartment 70.
Coupled to the screw is a tumbling means having a
metal blade 72. This blade 72 is made up of a first
flexible part 74, which defines a flight, which can be
of any suitable material, for example polyurethane. The
blade 72 acts against any material brought into the
compartment 70 when the screw conveyor 4 is rotating in
a reverse direction to tumble and break the material up
or increase its volume so that the material can
subsequently pass through the apparatus 2 without
causing jamming. If necessary, access can be obtained
to compartment 70 via flap 71 to remove any offending
object therefrom. Alternatively a door (not shown) may
be provided in a compartment side wall for the automatic
removal of material which cannot be broken up.
The rear chamber is further provided with a raised
fluid outlet surface 83 provided with a filtering means
and allowing fluid to drain from the apparatus via a
drain 80 which is preferably connected to a pump (not
shown). With waste having a fluid component, the height
of fluid in the base of the apparatus is therefore
= controlled to the height of the impermeable step 82
provided at the front end of the outlet surface. A
controlled degree of self lubrication is therefore
provided. Desirably, the resilient part 74 of the
tumbling means engages the outlet surface 83 to
CA 02454645 2005-09-22
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continually wipe the filtering means clean.
Operation of the apparatus 2 is controlled by a
control circuit (not shown), the function of which is
now described with reference to Figure 8. Initially,
when the motor 66 is first started, it rotates the screw
conveyor 4 for a short, predetermined period of time in
the reverse direction so as to relieve pressure on the
screw conveyor, thus preventing the motor 66 from
starting under load conditions. The screw conveyor 4 is
then driven in the forwards direction.
The control circuit has a sensor (not shown) which
detects the amount of current being applied to the motor
66. Since the torque applied to the screw conveyor 4
depends on the current applied to the motor 66, this
sensor gives an indication of the torque applied. If
the torque applied by the motor 66 exceeds a given
value, this is an indication that the screw conveyor 4
is becoming or has become jammed and that the screw
conveyor 4 can no longer freely rotate. When this
condition is detected, a signal is sent to the motor 66
which causes the motor 66 to stop driving the screw
conveyor 4 in the forwards direction and to apply a
reverse drive for a predetermined period of time eg. one
rotation. The motor 66 then drives the conveyor again
in the forwards direction. If the torque applied to the
motor 66 still exceeds the given value, then the
apparatus is still jamming and the process is repeated
until A equals its preset value, e.g. twenty, or the
material passes through the conveyor in which case
counter A is reset to zero. In practice, it has been
found that this repeated backward and forward rotation
is often sufficient to break up or adequately reduce the
density of the material causing the jam.
However, if the apparatus is still jamming after A
has reached its preset value, the screw conveyor is
driven in the reverse direction for a sufficient length
of time so that the material causing the jam is brought
CA 02454645 2005-09-22
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into the rear compartment 70. The screw conveyor 4 is
continued to be rotated in the reverse direction for a
further predetermined time such that the blade 72 can
attempt to break up the jamming material. The motor 66
then drives the screw conveyor 4 in a forward direction
so that the material, if broken up, can progressively be
picked up by the screw and passed therethrough as
before. If however, the material still jams the
conveyor, the screw conveyor is again reversed for a
number of cycles and the entire above process repeated.
The material causing the jam will however only be
brought back into the rear compartment a predetermined
number of times ie. until B reaches its preset value
which for example is 2. After that, the offending
material can be taken a final time back into the rear
compartment 70, the motor is switched off, and a warning
light or alarm activated. The operator is then alerted
to the fact that material is to be removed from the rear
compartment via flap 71. The operator can remove the
material, reset the apparatus and continue compaction.
Alternatively, the material can be ejected
automatically. It has however been found that in
practice there are relatively few objects which can not
be processed by the apparatus and which accordingly need
to be removed manually from the rear compartment 70.
Additionally, the torque sensor is arranged to
detect whether the torque of the screw conveyor when
driven in the reverse direction exceeds a given value.
If the torque exceeds a given limit, the screw conveyor
is then driven in the forward direction.
In the situation where no jamming occurs, the screw
conveyor 4 is rotated in the forwards direction for a
predetermined time and will only start rotating again
when further material is introduced into the hopper 16.
The-apparatus 2 has a lid 86 (see Figure 3) which
covers the opening of hopper 16. This lid 86
incorporates a conventional safety contact switch (not
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shown) which when closed allows the motor to drive the
screw conveyor and starts the predetermined period of
rotation for the screw conveyor. However, when the
contact switch is open and the lid 86 open, no current
is supplied to the motor 66 and the screw conveyor 4
does not rotate to ensure the safety of the operator.
A cleaning system 88 is incorporated in the
apparatus 2 to allow cleaning. The cleaning system 88
comprises two pipes 90 arranged on opposed walls of the
hopper 16. These pipes 90 have a plurality of openings
92 along its length. water mixed with detergent is then
periodically sprayed onto the walls of the hopper 16 to
thereby clean it. The hopper 16 is sprayed during use
eg. every 15 minutes. Excess water is collected in
collecting tray 82 from which it can be drained possibly
by a pump (not shown).
Extracting fan 100 is provided in the hopper which
allows the contents of the apparatus to be aerated and
prevents the build up of noxious odours or dust.
The material exiting nozzle 10 can be formed into
packages 102 such as shown in Figure 9. A long tube 104
of material, such as tubular plastics packaging, is
supported around chamber 41 in an axially contracted
state. For example a 30m length of packaging material
can be accommodated on chamber 41. The tube 104 of
material is supported by a former 108 which may be of
cardboard or any suitable material. The tube 104 of
material is closed at its downstream end by a tie 110.
As material exits from nozzle 10, it is pushed against
the closed end of the tube 104 thereby drawing the
packaging material off the former 108 and encapsulating
the waste material in the drawn off packaging material.
As a result of the compaction to which the material has
been subjected, the waste material tends to maintain its
sausage like form in which it exits the nozzle. When
the package has reached an appropriate length, the tube
104 of packaging material is cut and the ends of the
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packaging material tied off to form a completely
enclosed package 102 which can then be easily disposed
of.
An adjustable cutting plate 220 has a cutting edge
adjacent the screw at the beginning of its tapering
portion for cutting up long items such as wooden poles
and the like so that they can be passed through the
apparatus. The position of the cutting edge can be
adjusted to either increase or decrease the gap between
the cutting edge and the screw. The screw itself may be
provided with a cutting edge on its periphery to assist
the cutting plate 220.
The general operation of the apparatus will now be
described with particular reference to Figures 2 to 6.
The lid 86 is opened and material inserted 'into the
hopper 16. The lid 86 is then closed which enables the
operator to start the motor 66 which rotates the screw
conveyor. Initial compaction takes place in the
tapering portion of the screw, as described above. More
substantial compaction takes place in the compaction
chamber 200, in the region immediately downstream of the
end of the screw.conveyor flight. This is due to the
back pressure established by the nozzle. The action of
the rotating end of the screw is to force material from
a lower pressure upstream region to a higher pressure
region in the chamber 200. It does this by sweeping out
a void space trailing a blunt free end of the screw
which space is filled by new material during one
rotation to be forced into the compaction chamber by the
next. To achieve substantial compaction, the angle of
attack of the end of the screw and the thickness of its
free end are important and the optimum values can be
determined experimentally depending on the type of waste
material and degree of compaction desired. In a
preferred embodiment, the flight thickness and pitch at
the front end of the screw are respectively around 25 mm
and around 80 to the longitudinal axis. The compaction
CA 02454645 2005-09-22
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mechanism operates by twisting and shearing the waste
material and in the preferred embodiment this is such
that the material when compacted loses the ability to
expand back to its original shape or volume. The total
compaction achieved by apparatus embodying the present
invention may be in the range of 15 to 60:1 dependent on
the type of waste and of course the dimensions of the
apparatus.
The region X shown in Figure 6 indicates that the
fingers of the nozzle are preferably sufficiently
flexible to conform to a relatively large,
incompressible lump of waste being ejected.
The embodiment described above can be modified so
as to include a back pressure chamber 114, such as shown
in Figure 10, between the outlet of the passage 6 and
the inlet of nozzle 10. Such a back pressure chamber
114 can be used to increase the degree of compaction
achieved by the apparatus 2 and therefore constitutes a
further compaction chamber. In its simplest form, the
chamber 114 is a uniform cylindrical tube of circular
cross-section through which the waste material passes.
The diameter of the chamber 114 is the same or slightly
smaller than that at the outlet end of the passage 6.
Accordingly, as material passes through this chamber
114, friction is created between the material and the
walls of the chamber 114. This creates a resistance to
the movement of the material resulting in a back
pressure effect at the outlet 116 of the chamber. The
screw conveyor 4 is forced to convey material against
this back pressure which results in further compaction.
The back pressure chamber 114 shown in Figure 10
consists of two portions 118 and 120 which are of
approximately the same internal size but which can
telescope one within the other to vary the overall
length of the chamber 114. Accordingly the total
frictional force and the back pressure generated by the
chamber 114 can be varied.
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A second embodiment of the nozzle will now be
described in relation to Figure 11. Nozzle 130 is
formed by two portions 132 and 134 which are each semi-
cylindrical. Portion 132 is slightly larger than
portion 134 so that the latter portion can, if
necessary, be received in the former. The two portions
132 and 134 are pivotally connected to each other at
136, at the end of the nozzle to be attached to the
passage 6. The pivot 138 allows the two portions 132
and 134 to move toward or away from each other to
thereby vary the cross-sectional area of the nozzle 130.
Thus the nozzle has a passage which can taper and which
can be adjusted to control the degree of tapering
achieved. As with the first embodiment, elastic
tensioning bands or springs 140 can be used to urge the
two portions 132 and 134 together but to allow the two
portions to move away from one another when the volume
and/or pressure of material passing through the nozzle
130 exceeds a certain value.
The ribs 22 on the walls of the passage 6 may be
resiliently mounted thereon. The ribs 22 could be
received in suitably shaped grooves in the walls of the
passage with a resilient material such as rubber between
the ribs and the back wall of the grooves. Thus the
ribs would normally be biased toward a position in which
they project to the greatest extent into passage 6. The
degree of projection of the ribs would then depend on
the volume of material passing through the passage 6.
Alternatively, the ribs 22 may be mounted in grooves on
the passage wall so that the extent to which they
project into the passage 6 can be varied according to
the nature of the;material being compacted and to
compensate for wear. Furthermore, the adjustability of
ribs in the grooves allow the arrangement to be adjusted
to ensure adequate clearance for the flights of the
screw conveyor and prevent the ribs from fouling the
screw conveyor.
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Whilst the ribs 22 have been shown in the first
embodiment as being substantially straight and running
along the length of the passage 6, they could be
arranged to define a generally helical path.
In addition to the ribs or as an alternative, the
inner walls of the passage 6 may be treated so as to
increase the friction between the surface of the passage
and the material conveyed.
In an alternative embodiment of the invention, the
bagging method shown in Figure 9 is dispensed with and
the outlet of the nozzle is connected directed to a
waste tube which leads directly to a waste bin. As a
result of the compaction to which the waste material is
subjected, the sausage of material emerging from the
outlet end of the nozzle tends to retain its shape.
Accordingly, this material does not tend to stick to the
sides of the waste tube leading to the bin, provided
that the waste tube has a diameter which is slightly
larger than the maximum size of the outlet end of the
nozzle.
As will be appreciated, although this apparatus has
been described in relation to a use in a fixed
installation, it is clear that such apparatus is also
suitable for use in vehicles such as refuse collecting
vehicles. In such cases, some minor modification to the
apparatus would be required. Firstly, a device would be
arranged in the upper part of the hopper to force feed
the material into the screw conveyor since the waste is
typically relatively light and bulky. Secondly, the
outlet end of the nozzle would open into a separate
compartment-of the truck where the compacted waste would
be stored. Finally, the back chamber would be arranged
to have a trap door which would open when an object was
retained therein to drop that object into a further
compartment. Thus, continuous operation of the device
can be assured.
As can be seen from the illustrated embodiments,
CA 02454645 2005-09-22
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the apparatus is preferably made of a large number of
parts which can be easily assembled for use. In
particular, the first and second parts of the passageway
are preferably formed from different components and the
extrusion nozzle from yet another. This allows the
various parts to be removed, replaced or adjusted for
maintenance or as a result of to wear. In certain
embodiments it may be appropriate to resiliently mount
all adjustable parts of the apparatus so they may be
biased towards the position which provides greatest
compaction. Excessive compaction will then tend to work
against this resilient bias until a state of balance is
achieved.
Embodiments of the invention may provide a very
high degree of compaction in comparison with
conventional techniques. This permits the apparatus to
be relatively small when desired. Embodiments of the
invention may also have low noise levels and accordingly
can be used in locations where such apparatus has not
previously been used. The apparatus may be used as a
separate device or can be incorporated in equipment
which also performs other tasks.
