CA2454649A1 - Compaction methods and apparatus - Google Patents

Abstract

A compaction apparatus (2) has a screw conveyor (4) for conveying waste material through a passage (6) and compacting it therein. An exit nozzle (10) is arranged to communicate with the passage (6). The nozzle (10) has a transverse internal cross-sectional area which enlarges and reduces respectively in response to increasing and decreasing material pressure.

Description

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 23 September 1993.
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 1'~igh 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 thereof.
However, the known apparatus suffer from the problem that optimal performance can only be achieved ~ ~ 1 ~~ v'18 ~l wo 9a; o~axx . .. j,~.t.~ca~ooi~s~
-z-for one set of opAration conditions such as temperature, volume of waste fed into compactar and ~vpt and densit}~
of wade mato~:i.al. 7s will be appreciated, cost waste compacto:s would in pra.:~ice be exposed to a range ef valises far each condition. For example, a waste compactor which is situated outdoors would be subjected to the extremes of summer and winter temperatures.
..ikewi~e the unifGrmity of volume and type of waste cannot be guaranteed. For exaaple an increase in the Dercentage of fa~.ty or oily substances in the waste aaterial cast rave an adverse effect on the performance of the c:mpactor_ Indeed in experiments czrried cut, the camptction achieved dramatically decreases esF~cially fc: very slippe:y materials. xhe inabi!'ity Z5 to deal with changes in ~:onditions means t.':at eompac:.ors will at one e:ctremE nc;c al4~ays compact material to the c:asired degree if at all and, at the: other extreme, will hale a ten~encr to jaa.
Prior. art i~ kraorn which attempts to address at least certain aspects of this problem. For example, a resiliently.biased trap door can be provide3 at the And of the conveying means which opens only when the pressure on the door exceeds a certain value. In ti.eo~-y, this allows caste material to accurulate so that variations in the volume of waste mater:.al do not affect the pex~formaacs of the coangactar. However, in practice, scch doors remain partially open most of the time which leads to nnsatisiactory results since raaxi.-tum compaction is net achieved. Ferthermore trap doors exert a~ sidways fo=ce which Leads to encourage the break up of the corpacted waste material :~hicr in turn can cause di.'.ficulties with the packaging and/or dist.osal of the material zs wall as increasing the valu:ae of the compacted waste. In any case such compactors are not suited to applications requiring a relatively high degree of compactior. as provides in accordance with embodiments of this invention.

214 ~'! 5'~
~~O 9a/07688 _ PCTlGB93/01995 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 .n achieving successful compaction lies in the ot~_t:At nozzle providing an appropriate degree of back pressure.
This back pressure enhances Lhz compacci.ng actic~ and effectively tones tkae apparatus. It is the loss or reduction of this back pressure which causes the perforaance of the known apparatus to deteriorate.
Conversely, a suirstantial increase in back pressure can cause the apparatus to jam.
Acccrdiag to one aspect of the invention, there is provided compacting apparatus comprising a screw ecnveyor for conveying waste material through a passage and campactiag it therein, and an. exit nozzle communicating with the passage, said nozzle defining so intErnal trarsversa cross-sectiorrl. area which enlar5es and reduces respectively in rpspons~ to increzsira ar<d decreasing material pressure.
By altering the size o~ the outlet opening defined - by the internal transverse cross-sectional area of the nozzle autamatically in response to the volume and/or pressure of matorial flawing therethrough, the nozzle is able to compensate for. changes in carious 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 therethrougly. 3:mbodiments of ~ 35 tht invention may achieve a degree of campaction which is very much larger than that achieved by known prior art a:rangemer~,ts e.3. a 300-a00; increase.
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Thus for a greater range of operating con3itions as compared with the prio: art, the back pressure sill remain above a pzedeterained minimum fer satisfactory operation, and, conversely, excessive back pressures 5 which might cause jamming cf the screw conveyor can be tvoided. This is achieved far more effectively in accordance ;rith the invention as compared with a trap door outlet arrangement and without a sideways force being exerted on the waste or other material being l0 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 ug. If Lhe material remains 15 in the nozzle fcr any length of tine, for example whilst the coapactor is not in usQ, the heated nate-rial has a tsndency to solidify and/or adhere to the walls of the nozzle. Z'he nozzle can thus beco,aa blocYed and the apparatLS then nerds to he dismantled to remove the 20 blockage. It has been found that since the cross-sectional area o' the nozzle is altle to change, at least in preferred er,~odiaents of the present invention there is a self-cleaning and salt-clearing ef4pct which has been found to step or reduce the tendency of material to 25 stick to the nozzle walls.
It shoLld b~ notzd that references to a change in transverse cross-sectional area in the nozzle resulting in a change in tr:e size of the outlet opening defined thereby can refer to changes occurring at substantially 30 a single point, e_g. adjacent the nozzle outlet, or at all goirts 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 35 different points along the length of the no~zlE may change by different amounts. It is thus preferred that the nozzle tapers inwardly (in the flow direction) over ' 21-~ ~?~
U 9~/076tt8 at leapt part of its length and the changes in transverse csoss-sectional area at all points along the tapered regiun aYise froc changes in tt.~ d~ree of taper. It is envisaged that th» 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 14 changes in pressure.
There ara a atraber of ways in which L'~e change in cross-sectional area in response to waste aaterial pressure changes can be achieved. In one embodiment, the nozzle is forme3 of resilient material, or includes 15 a resilient insert, which is biased inward h toward a position of minimum internal cross-section. Tae resilient material responds to charges in pressure such that tha nozzle opening widens as pressure increases to achieve the self tuning effect ss described_ In an alternative preferred eabodimcn~~ the nozzle has a plurality of wall portions which are aovable relative to each o;.her to vary the internal cross-sectional area of t.'~e nozzle. These portions a-a preferably made of a hard wearing material such as steel 25 which can withstand the abrasivQ farces applied by the waste material as i~ passes through the nozzle. For example the nozzle nay comprise two semi-cylindrical portions which together define a generally cylindrical body having a degree of taper depending on the pressure 3~ in the nozzle. These two semi-cylindrical portions are hingedly cos~nacted~togcther at the end region of the nozzle further frog the nozzle outlet. So as to accommodate the change in internal transvease cross-sectional area of the nozzle along at least part of its 35 length, the two cylindrical partions are preferably dimensioned so that one portion is slightly smaller than the other. T:~us w;~en required, parts of one portion can k ~..i p~["(1CB931O1995 w~a ~;~az~ 214 ~ ~ 8 t be reeeived within parts of the other portion.
These portions may be biased using resilient means towards a position is which the tzansverse 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 , sutstantially urif~ra cross-sectional area. Ho: ever, more preferably the semi-cylindrical portions define when biased to the minimum size of outlet opening, a to tapered cylinder waich 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 spar' to thereby increase t:ae internal cross-sectio:~al area of the nozzle at gall pai7ts along the length of the hinged portions.
The resilient means may take any sup=able form and may be in the form of ore or more springs extending around part or all of t.5e circumference of the nezzle.
Alternatively, the resilient means may be in the form of ?0 one or more elastic tensioning barnts 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 -eons may be provided at any suitable position along =he 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 leas: one projection extending outwardly therefzom which retains the resilient means on the nozzle. This projection z.ay 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 214~1~~
H'O 94/076F8 pCT/t:39310199;
- y -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 5 the screw conveyor outlet. The fingers are biased inwardly and are flexed relative to the base Bart to increase or decrease the internal cross-sectional area ' of the nozzle in response to changes it waste material pressure. When the fingers are at their innermost l0 position, it is preferred that there are no gaps between the fingers and that the nozzle tapers toward its outlet. Thus, e3ge to edge abutment of the fingers can define the nozzle s innermost position. As the prevsure in the nozzle increases and the cross-sectional area 15 increases, V-shaped gaps are defined between the fingers. The fingers are biased toward their minimum posirior by resilient means whi~:h could take any of the above described forms. .
The end or end regions of at least one and 2o preferably ail 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 nozale 25 comprises two members each of which takes the form previously described, ie. an annulaz base part having longitudinally extending fingers. One member is arranged insids the other. Consequently the cross-sectional dimensions of the outer member are greater 30 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 tha nozzle is at its minimum, the fingers of the outer member cover the ends of the 35 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 f i -i a:

. ' 214!98 r WQ 9t/076R8 PCT/C893IQ199S-- iB -between the fingers when appropriatej. 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 cuter , member.
The preferred resilient biasing means exerts a very substantial radially inward force on the nozzle -resulting from tensioning bands that typically might namber 20 to 30 exerting a circumferential tension typically of 259 kg per cm of axial length of the nczzle. In the absence of any compacted material within the nozzle to count~ar this farce, the preferred force of nozzle might be damaged i.e. its fingers might be iaploded 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 polyuret~:ane which supports it internally. The plug is ejPCten once compacted material is passed through the nozzle whereafter there will always be compacted material sugporting the nozzle in noriual 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.t:iat she 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 vp 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 eompaetors suffer is that the ~crev conveyor is generally very heavy in order to be sufficiently heavy duty to coapress , ~
2I~~ ~~ t 1f0 9di07G88 PC?/C 89310199 g and compact waste or other material without itself being damaged. In particular, the thickness of the scrzw 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 tteerefor.
According to a second aspect of tha present invention there is provided a screw conveyor in or for a waste compaction apparatus for conveying and co=pressing 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 cf 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 tZ:e larqest amount of pressure as a result o~ the extra force exerte3 by the compacted material.
Typically, the flight will therefare have the greatest thickness at the outlet end of the conveyor with the thickness being least at the inlet end.
Thus wits the embodiments of this aspect of the invention, the thickness of the flight need orly be at the maximum required value rt that part of the screw conveyor which is subjected to the greatest force. 'The other parts of the flight need rot 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 particul:~rly suited to thosa cases whera the farce applied to the screw flight by the material does not increase linearly but rather increases - more quickly, for example where the screw conveyer is . i 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 ix the .

~.~~ lc~~( ' Wo 9a~o~s8E PLT/GB93J019S5~

vicinity o~ the outlet can be ver; large and the additional thickness of the flight is able to compensate for this.
a is preferred that the flight has a relatively large diaa~t~r 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 he taken up by the conveyor.
This then leads to an inwardly tapering portion in which campaction or at least pre-compaction of material taken place.
The thickness of the flight of the screw conveyor may increase uniformly from an inlet end to the cutlet end of the conveyor. Alternatively, the thickness of the flight can be u.-~ifora along most of the length of the screw conveyor with a region of increased t.'~ickness provided only adjacent the outlet end cf the screw conveyor. In a preferred eabodimeat, the thickness of the flight increases in a stepwise fashion frog the inlet. end to the outlet end of the conveyor vi ~h. the first stepped increase preferably being at a point slightly upstream of an inwardly tapering portion of the . flight. This last alternative as preferred as it allows, full advantage to be taken of the invention whilst at the sage time still allowing the device to re mmanufactured relatively easily.
Another prcblem assor_iate9 with the weight of the screw conveyor concerns the provision of sufficient .
support for the conveyor. In the prier urt, such screw conveyors are usually supported by fixz3 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 snppart _ -the screw conveyor along a significant proportion of the length thereof. A mechanical bearing cannot be successfully used to supp~art the outlet en3 of the screw conveyor since this would. partially block the compactor ~t ~~'~~r f 1~C' 94/07688 rCT:G893101995 outlet and interfere with the floe of compacted material which is of course undesirst~le.
According to a third aspect of the invention, there is provided compaction apparatus co>?prising a screw conveyor arranged in t conveying passage and rotatablp supported in relation to the passage :sousing in the region of the inlet end of the conveyor, such support permitting a dagree of transverse movement of the longitudinal axis of the coweyor 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 sl.3nk extension in use being surrounded by a~:~ annulus of compacted material in the downstream compaction chamber, sucix compacted material providing a support bearing neaps for the outlet end of '_he conveyor.
A fourth aspect of ths. invention provides a method of compacting waste or other material, comprising 2o conveying material by a rctating screw conveyor, compacting the materisl in a_compaction chamber located downstream of the screw conveyor, and supporting the outlet end of the screw conveyor during compaction b_f means of an annulus of compacted material which surrounds an axial shank extension of the screw conveyor projecting into the compaction chzmber. The axial shank extension may comprise e.g. 10-30~ of the total leng=h of the screw conveyor.
Since the screw conveyor is, .n 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 t.'~e . - prior art. In a preferred embodiment the inlet end nay - . .-I be supported directly from a drive motor or gear box output shaft withcut the need for costly, heavy duty bearing means to provide additional suppart.~
Since the support for the screw conveyor is , . ,. .. ~. ~. a ,~ _~' j . . ..: t ~~:'...w~....,n.~ . ..:., f.:.. ~ ...

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wa e.ais-.sxx rrrn:gv~iowss~

;reproved in t:. s apect o' the i»vention, a lesser clearance may be left bet:reen the outer edge of the fl:sht and the inner ~all~ of the chanber without the risk of the flight e..~.gagi::a the walls xnc! being duaaQed.
This inproves per:o~ance part-cnlariy with slippery waste which has a ter..~'.encf to recirculate through the .
apparatus by slippi~g past the outer periphery of the conveyor.
Preferably, the axes of the compaction charsber and .9 conveying passage cai:~cide such that when the s:~ank e:ctensi~n is suppcrte3 in use, the axis of the screw cc:veyor and the ~.assage also coincide. Thus the waste support is able to centre the axis of the screw conveyor automatically. The ~:aste caterial acts as a seli-1~ c.-~ntring bearing for the :=ee end of the screw conveyor which is able to c.~.crensate ror wearing of the passage and/or tY.e screw correyor itself .
Preferably, t::e compac;ion cnamber inro which the shank extension extends is cylindrical and may force pare 20 of an. exit nozzle of the apparatus t~hich preferably also inclu3es a tapering cstlet part upstream of the conpaction chamber. The tapering part may be as described in relation to t::e first aspect of the invention.
25 7t is ~3esirable that the inner walls of the passage may be formed so as to resist or prevent conveyed material from rotating abc:a 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 30 the passage. The o- each prominence or rib is preferably adjustab:y mounted on the passage walls, to allow the degree of Frojec:.ion into the passage to be varied. Tho or each proni~ence or rib may be w resiliently mounted. whilat it is preferred that the o_-35 each pra»~inence or rib extends longitudina::y o: the passage, the or sack Yromi:ence or rib may extend along a helical path.
' Such proninences or ribs have a tender=: to damaoe 1 , a ~ ".o ~"o,~ ~ t ~ ~t ~ s ~ PCf/GB93/Ot995 v - 17 -the flight of the screw coweyor if allowed to contact them.
In order to safely transport the waste compactor, it is taerefore preferred that the screw conveyor is S received in a stockir_g of protective material such as suitable plastics so that t:~e 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 cruse the Mocking to be ejected from the apparatus thereafter the compacted material keegs it centered.
Alternatively or additionally, the nozale plug discussed in relation to the first aspect of the invention may surround part of the screw conveyor to initially maintain its axial loeation.
Another problem with known screw conveyors is that they have a tendency to jam when a relatively incompressivle object is fed into the conveyor. Under such circumstances, known screw canveyars attempt to continue to rotate with the motor applying an incseased torque. This puts a strain on the motor ano 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 arr.;nged in a passage;
means for rotating said screw conveyor in a first, compacting and conveying directions means for sensing a jammed condition of said conveyor: and a back chamber arranged at an i~~T;= end region of the screw conveyor for receiving mate~:al causing said jamming, wherein, after a jammed condition has been sensed, said rotatir:3 means is arranged to rotate said screw conveyor in a second, opposite dire:.tion to the first direction and to move said ja»iming a~ateri~: to said back chamber.
~ir.is reversal of direction of rotation of the screw C.fAO 4454649 2004-02-06 WO 94/076$8 PCT/u893/01995~

convEyor allows jamming maternal to re moved back fnto a back chamber where it no lor:gk:r jams the apparatus and can be further dealt with, for example by being tvabled or removed, either manually er automatically, frog the apparatus.
Ti~ere are two main causes of jamming. The fi=st 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 to exrcerbated by conveyors which are tapered and/or which haves decreasing pitch. The second cause of jaaming is material reaching a cowpaction maximum and thus being unable to pass any further along the conveyor.
Accordingly, in a particularly preferred embodiment, the 15 back chamber has tumbling means which is arsanged 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 2o preferably provides a cutting action.
The tumbling means can be of any suitable form and may be part of the screw conveyor itself whicr. has been modified, for ex3aple, by sharpening the flight edges to provide a cutting edge. However, it has been found that 25 a flexihle part secure3 to the .flight perfortls well.
The fle~cible part might be used to mount a hare and rigid cutting member to the shank of the screw conveyor.
Th2 flexible part can be of any suitable material such as polyurethane and, l: used, the cutting member may be 30 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 encoeraqe the break up of material but itself is not damaged by material which cannot easily be broken up, if at all.
35 This is a consequence of the flexible part. The jarssing aaterial can then.be turbled in the back chamber by the rotation of the shaft in the reverse direction and the __ _ .. --_._.. ".:: -.:=:.~'....':?-...'~'.:~:_,...,~___A _- _ .. .

21~~f~~ v WO 94/07688 PCTlGB93/A1995 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 5 initially jammed the compactor.
If the compactor jams again, it is preferred that the ;ramming object be returned to the back chamber where material is again tumbled. The cycle tAen repeats.
After the machine has made any selected number ~f 10 unsuccessful attempts to break up material returned to the back chamber, the material can lae removed manually or automatically dropped into a trough below or behind the chamber from where it can be removed when a wmpaction cycle is completed. At this stage, a warning 15 signal can be given and/or the apparatus can be shut down.
The chamber preferably has a cover which prevents .caste material initially input :into the compactor from entering the chamber. Preferably the cover is movable 20 so as to allow accass 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 preferre3 that 2S when a damming 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 30 one to twenty attempts before the material is taken back to the back chamber and the above procedure followed.
Viewed from a still fuzthe:' aspect the invention . provides a compacting apparatus comprising a rotating screw conveyor a part of which i.s located in a passage ' , 35 which tapers inwardly in the direction of movecent of material being compacted, at least the tapering part of the passage being provided with longitudinally of ! , 21~~~s wo9aio~ss~ , prrecsv3eom~

helically extending sibs to help restrain the material from rotating with the conveyor, the apparatus being adapted to sense a jamming condition t~:erein, whezeupon 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. Trus, in the preferred embo3iment, the material is only taken into t:~e back chamber in extremis, most blockages being able to be cleared by the initial reversal znd retry procedure.
The sensing means may measure any suitable parameter such as the torque applied to the screw conveyor by the motor or the ez:Lrent 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, for«ards direction and preferably also senses if jamming takes pints 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. caste 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 tha accurrence of a t 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,_ard repeating this N'O 9.t/0T68lt , PC'TlGB93/t)1995 - IT -operation up to a predetermined aaximum 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 bP 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 t:~e im ention provides a compacting apparatus having a rotating screw conveyor located in a passage, wherein the passage comprises means to maintain a pre3etenuined maximum fluid level in the base region of the passage.
Such means preferably comprises a fluid outlet at such level, advantageously in the loran 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 pmovides 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 - ~5 received in a passage which has ,a portion of substantially unifors cross-sectional area located beneath a s:aste material inlet hopper and a tapered t s 1~1'094/Oi683 p~j'YG$93101995~
i _ as pcrtion which is at the downstreaae 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 ccmpaction in the passage.

Additionally or alternatively, the pitch of the screw conveyor may decrease toward the outlet of the prssage so as to help obtain sufficient compaction.

Thus the pitch could be relat9.vely large at the beginning of the passage and relatively small at the end of the path. The pitch prefexably decreases si:bstantially continuously ov~:r whole or paa of the length of path.

Of course, the tapering is not essential and sufficient coapaction may be a:chieved in cer-~ain etbodiments which have a screw conveyor passage of uniform cross-section. Likewise, the passage could he 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-section may decrease substantially ccntinuously 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 ccmpaction chamber. Thus, in a preferred embodiment material is compacted as it is moved along by the screw ccnveyor, with further more subs_antial compaction taxing place in the campaction chamber. In practice, _ in such an embodiment the greate.~t amount of coapaction taxes place iomediately downstream of the screw ccnveyor. _ Furthermore, the nozzle does not of course need to be connected directly to the outlet of the conveyor passage. Far example, a second passage may be arranged between the outlet of the screw conveyor and the inlet I
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2~~~~~r !f0 94/07688 FCTIGB93/O1995 of the noazle. This second paasage may be arranged :.o 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 ! 5 . second passage is preferably resisted by friction between the material and the wa?ls of the second passage. This resistance provided may be vazied 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 restauran's and other similar installations. !Compactors embodying the invention also have uses in industrial situations for compacting factory waste. Zt 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 Bother applications where compaction of a material is required. For example, embodiments of the invention can be used on farms or fn factories to provide compactio.n of food products.
embodiments of the invention will now be described by way of example and with reference to the accompanying ., 35 drawings in which:-Figure 1 shows a longitudinal cross sectional view of a compactor;

zm~~g V40 9.t/0:~88 PCT/CB93/01995-Figure la shows an enlarged view of part of the compactor of Figure l:
Figure 2 shows a longitudinal cross sectional view of the compactor of Figure 1 whey filled with waste aaterial; ~ , ' Figure 3 shows a cross-section of the compactor of Figure 1 along line III-III:
Figuse 4 shows a perspecaive view of the nozzle of Figure 1 which has been partially cut away for clarity;
Figure 5 shoes a cross-sectional view of the output end the compactor of Figure a, with the screw conveyor packaged for transportation:
Figure 6 shows a cross-sectional view of the output end of the compactor of Figure l, when filled wish waste is aaterial;
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:
2o Figure 9 shows schematically as arrangement for the bagging of material exiting the compactor of Figure 1;
Figure '.0 shows a schematic view of a back pressure c:~amber for use with the compactor of Figure 1; and . Figure 11 shows a schematic view of a second i 25 eabodiment 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.
30 The passage 6.fs 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 raterial is fed from hopper 16. The size of the hopper 35 15 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 IB (see Figure ->~.~.., , ~1~4'~8 ~~
WO 94107688 PCTlG893lOI995 3), the sides of which also define the hopper 16. The trough opening defines the longitudinally extending opening 24.
The passage,ø also has a second part 20 which is 5 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 10 longitudinal extending ribs 22 which project inwardly inta the passage. These ribs 22 prevent partially compacted material from rotating with the screw conveyor d. Where appropriate the ribs 22 are also able to provide a cutting surface or anvil against which the 15 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) 20 which extend along its length. Th-use 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 25 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 np the matsrial.
Thp screw conveyor 4, which is illustrated in 30 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 35 which corresponds generally to the degree of taper of part 2o of the passage 6. The diameter of tie flight 24 of the scre:r conveyor is selected sueh that mere is _ ,.2 _ 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 5 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 lager.
The pitch of the screw conveyor 4 also varies along its length. In particular the pitch of flight 24 10 decreases in the direction towards the~second tapered part 28. For example the first one and a half turns 34 have a pitch of 400am, the second one ant a half turns 36 a pitch of 20omm whilst the third one and a half turns 38 have a pitch of l0omm ie. giving a pitch ratio 15 of 4:2:1 along the length o.f 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 piteh of the screw conveyor is of course selected depending an 20 the material to be compacted usually as well the degree of compaction required.
The thickness of the flight 24 changes along tile length of the screw conveyor 4 and, in particular, increases as the pitch decreases. In the specific 25 embodiment, about the first one and a half turns 34 have a flight thickness of lZmm, 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 30 subjected go 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 35 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 ' ~ . ... ,..... ..s .: al.~.r;r-.y,p,:.:T; :u.. , , ..
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1f0 94/07688 PCTlGB93/pi995 .. 23 _ 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 f:om the drawings.

The dimensions given in relation to pitch, flight thickness and flight diameter ase included only for 0 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 5 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 conveyer 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 ccnveyor itself is determined by the ratio of the volume ,' . between e the flight turns 34 below the longitudinal opening ', 14 to 25 the volume between the flight turns 38 at the end of passage 6 adjacent the nozzle 10. In a preferred mbodiment, this ratio may be between 4:1 and 10:1 0 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 scrsw conveyor would not have the maximum volume of material required for maximum compaction passing through it at ail 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.

Tha nozzle 10 will now be described in more detail with particular reference to Figures 4, 5 and 5 6. The t nozzle l0 is coupled to the outlet end of passage 6 at he end of section 20 and is surrounded by chamber which allows,any material leaking from the nozzle 10 to . y ~ ..
2144'~~~i wo 94~o~ssa PCT/CB93/0J 995 _ be collected in the chamber 4I. The nozzle is made up of two gain parts 42 and 44. The first part 42 is farmed from a sheet of material such as sheet steel with a thicY~ess 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.
Frog 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 l0. The width of each finger 48 decreases in the direction towards the outlet 52 of the nozzle 10 to thereby define V-shaped gasps (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 dimers~ons. In particular the second part 44 is slightly longer than the first part 42 and has a slightly larger diameter. The first part 42 i s 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 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, 8 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 wanner shown particularly clearly in Figure 4.

Alternatively, a length of elastic tensioning rope may be wound around the nozzle. The lu s S6 i g P reta n the _.
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bands 58 i~ 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 5 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 l0 nozzle l0 increases for example as shown in Figure 6.
In this instance, the force_exerted by the tension hands 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 wag the 15 tapering port:~n of the nozzle 10 is able to regulate itself in resgonse 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 20 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 maxiaua operating positions of the nozzle 10 shown in dotted lines for respective decreases Z5 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 30 bards. 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 35 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 a ) ~ n ~
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of axial thrust which is g~,nerated by the screw during ccmpaction. This counting arrangement permits the leng:tudinal axis of the screw conveyor to pivot very slightly relative to the icagitudinal axis 62 of the passage 6. Thus, if the apparatus 2 is empty the edges of t'e flight 24 of the sc:ew conveyer 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 as axial position in passage 6 by packaging <.~ for ease of transport as sho»-n in Figure 5. '~Jhen -a compactor.2 is first Lsed, ' ~ the cackag:ng 64 is :token up by the action of the screw con'reyor 4 and exits via nozzle 10. Alternatively, the nozzle plug described above may provi3e the desired initial centering effect.
~nen the apparatus 2 is in use, the annulus of movi.~.g compacted waste matorial 65 in the compaction chaser 200 of the nozzle i0 acts as a bearing and supports the third part 3C1 ie. the threadless axial sham: of the screw conveyer 4. It has been found that t?~e screw conveyor 4 is ce!ltred as well as supported by .
the paste 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 :Then the compactor is off, the shat.: 30 is usually supported at both of its ends. Zt _ has also been found that lol 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.ragards the radial location it provide~as-in comparable prior~art arrangements as support is provided at either end of~the shank 30.
The axial location of the screw can cc adjusted to ' accc~modate for wear by inserting s'.?ws of different thiciness between shoulders 225.

21~4~~( WO 94/076AR p~TIGB93I0t995 At the end of the passage 6 adjacent the bearing 60, there is a rear compartment '70. The compar'ment 70 has a movable flsp 71 (see Figures 1, 2 and 3) which is biased in a downward direction to prevent material from the hopper i6 from entering that compartment 70. The flap 71 may be of a flexible material which inherently biases the flap towards the closed position. Idaterial 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 op of a first flexible part 74, which defines a flight, which ca.-i 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 shosrr.) may be provided in a compartment side: wall for the autcmatic removal of material which cannot ~e broken up.
The. rear chamber is further provided with a raised fluid outlet surface 83 provided with a filtering r.zans and allowing fluid to drain frog the apparatus via a drain 80 which is preferably connected to a pump (nr~t 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 ~~11~.~irCA 02454649 2004-02-06 21~'~'~8'?
WO 94107688 p['f/GB93/0199i~

continually wipe the filtering ms:ans clean.
Operation of the apparatus 2 is controlled by a control circuit (not showry, the function of which is now described with reference to Figure 8. Initially, , 5 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 i:he motor 66 from starting under load conditions. The screw conveyor 4 is l0 then driven in the forwards direction.
The control circuit has a sensor (not showny which .
detests 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 15 sensor gives an indication of the torque applied. 1f the torque applied by the aotor 66 exceeds a given value, this is an indication thar_ the screw conveyor 4 is becoming or has become jammed and that the screw conveyor 4 can no longer freely rotate. When this 20 condition is detected, a signal :is sent to the motor 66 which causes the motor 65 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 t?:en drives the conveyor again 25 in the forrards direction. If the torque applied to the motor 66 still exceeds the given value, then the apparatus is still jar.ming and the process is repeated until A equals its preset value, e.g. twenty, or the material passes through the conveyor in which case 30 counter A is reset to zero. In practice, it has besn found that this repeated backward and forward rotrtion 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
35 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 .-2I~~~~~~
VfO 94/076ti8 PCf/G893/OI995 into the rear compartment 70. 7~he 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 matarial can be taken a final time back into the rear compartment 7o, 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 2o 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 fera,ard 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 15. This lid 85 incorporates a conventional safety contact switch (not _.. ._._._ _.._.~. .,.M,~ . , ~,n~~.~.. ,~.~.n.w _,~M, ~~~~,~ ~,~""n~,.
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WO 94/0768tt PLT/G893/01995 _ shown) which when closed allows the motor to drive the screw conveyor and starts the predeterained period of rota=ion for the screw conveyor. However, when the contact switch is open and the lid 86 open, no current 5 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 is the apparatus 2 to allow cleaning. the cleaning system 88 comprises two pipes 90 arranged on opposed walls of the 10 hopper i6. These pipes 90 haves 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 i.t~
15 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 apparar_us to be aerated and prevents the build up of noxious odours or dust.
2o 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 4I in .an axially contracted state. For example a 30m length of packaging material 25 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, a is pushed against 30 the closed end of the tube 104 thereby drawing the packaging material aff 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 35 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 Zl~~~~l VfO 9~I07688 PCilGB93i01995 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 5 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 aFparatus. The position of the cutting edge can be adjusted to either increase or decrease the gap between 1o the cutting edge and the screw. The screw itself may be provided faith 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.
15 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 2o substantia3 compaction takes pace 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 25 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 30 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 was;.a aatezial and degree of compaction desired. In a 35 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 t t 21~4~3~f ~1'O 9d/0?688 pCC/GB93/01995 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 5 compaction achieved by apparatus embodying the present invention may be in the range of I5 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 l0 fingers of the nozzle are preferably sufficiently flexible to conform to a relatively large, incompressible lump of waste being ejected.
The eabodiment described above can be modified so as tc include a back pressure chamber 114, such as shown 15 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 conpaction chamber. In its simplest form, the 20 chamber I14 is a uniform cylindrical tube of circular cross-section through which the waste material passes.
The diameter of the chamber i14, is the same or slightly smaller than that at the outlet end of the passage 6.
Accordingly, as material passes through this chamber 25 1I4, 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 it6 of the chamber. The screw conveyor 4 is forced to convey material against 30 this back pressure which results in further compaction.
The back pressure chamber 114 shown in Figure IO
consists of two portions 118 and 120 which are of approximately the same internal site but which can telescope one within the other to vary the overall 35 length of the chamber 114. Accordingly the total -frictional force and the back pressure generated by the chaaber 114 can be varied.
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A second embodiment of the nozzle will now be described in relation to Figure ll. Nozzle 130 is formed by two portions l32 an3 134 which are each semi-cylindrical. Portion 132 is slightly larger than portion 134 so that the latter portion can, ~f 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 allaws the two portions 132 to and 134 to move toward or away from each other to thereby vary the crass-sectional area of the nozzle 130.
thus the nozzle has a passage which can taper and which can be adjusted to cont:ol the degree of tapering achieved. 1s 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 passfng through the nozzle 130 exceeds a certain value.
2o 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. Thos 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 b,e 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 far the fli~~hts of the screw conveyor and prevent the ribs from fouling the screw conveyor.

., .
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wo 9aio~b8a pctics93io»~, Whilst the Tibs 22 have been shown in the first embodiment as being substantially straight and running along the le:,gth of the passage 6, they could be arranged to define a generally helical path. .
S In addi~ian to the ribs or as an alternative, the inner walls c: 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 iwention, the ' bagging meth:d shown in Figure 9 is dispensed with and the outlet o. the nozzle is connected directed to a waste c.uha w:ich leads directly to a waste bin. As a result of the compaction to which the waste material is subjected, t':e sausage of material emerging from the outlet end o: the nozzle tends to retain its shape.
Accordingly, this material does not tend to stick to the sit~s 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 2o nozzle.
As will he appreciated, although this apparatus has been describe3 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. Ia such cases, some minor codification 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, tte outlet end o~ the nozzle would open into a separate compartment cf 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 he seen Eros the illustrated embodiments, t ~ wo 9s.o~sss 2 ~ 4'~ ~ s ':

- 35 .
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 nozale from yet another. This allows the variaus 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 to biased towards the position which provides greatest compaction. ~xcessive 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 I5 high degree of compaction in comparison with conventional techniques. This permits the apparatus to be relatively snap when desired. Embodiments of the invention may also have low noise levels and accordingly can be used in locations wherw_ such apparatus has not 20 previously been used. The apparatus may be used as a separate device or can be incorporated in equipment which also performs other tasks.
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Claims (15)

1. ~Compaction apparatus comprising a screw conveyor for conveying waste material through a passage and compacting it therein, successive pitches of the screw conveyor defining, with the passage walls, a volume which decreases along at least part of the length of the screw conveyor whereby to cause compaction, and there being resisting means associated with the passage walls along at least the said part of the screw conveyor length, the resisting means, in use, resisting or preventing conveyed material from rotating with the conveyor.

2. ~Apparatus according to claim 1, wherein the inner wall of the passage has at least one prominence or rib which is engageable with material in the passage.

3. ~Apparatus according to claim 2, wherein each prominence or rib is adjustably mounted on the passage walls to allow the degree of projection into the passage to vary.

4. ~Apparatus according to claim 2 or 3, wherein each prominence or rib is resiliently mounted.

5. ~Apparatus according to any one of claims 2 to 4, wherein each prominence or rib extends longitudinally of the passage.

6. ~Apparatus according to any one of claims 2 to 5, wherein each prominence or rib extends along a helical path.

7. ~Apparatus according to any one of claims 1 to 6, wherein the screw conveyor comprises a flight, the thickness of the part of the flight subjected to the greatest force in use being greater than the thickness of other parts of the flight of the conveyor.

8. ~Apparatus according to claim 7, wherein the thickness of the flight increases uniformly from an inlet end toward an outlet end of the conveyor.

9. ~Apparatus according to claim 7, wherein the thickness of the flight increases in a step-wise fashion from the inlet end to the outlet end of the conveyor.

10. Apparatus according to any one of claims 7, 8 or 9, wherein the first increase is substantially at a point at which the flight begins to taper inwardly.

11. Apparatus according to any one of claims 1 to 10, comprising cutting means in the region of the beginning of the tapering portion of the screw, whereby long items may be cut up as they pass through.

12. Apparatus according to claim 11, wherein the cutting means are at a point slightly upstream of an inwardly tapering portion of the flight.

13. Apparatus according to claims 11 or 12, wherein the cutting means comprise a cutting member adjacent the screw.

14. Apparatus according to any one of claims 11, 12 or 13, wherein the cutting means comprise a cutting edge formed on the screw.

15. Apparatus according to any one of claims 1 to 14, wherein the pitch and diameter of the screw conveyor both reduce over at least part of the length of the screw conveyor.