WO1983000473A1

WO1983000473A1 - Packing and compacting apparatus

Info

Publication number: WO1983000473A1
Application number: PCT/GB1982/000248
Authority: WO
Inventors: Thomas Henry Gardner; Gareth Dietlof John Whitehead
Original assignee: Thomas Henry Gardner; Gareth Dietlof John Whitehead
Priority date: 1981-08-06
Filing date: 1982-08-06
Publication date: 1983-02-17
Also published as: AU8764782A

Abstract

Apparatus for compacting and packing material such as shredded newspaper includes a horizontal chamber (1) into which the material falls and compactor ram (2) which is reciprocated within the chamber. A hinged tailgate (4) is pivoted about a transverse axis into an open position, forming a continuation of the chamber when the material has been compacted, and the compactor ram (2) then makes an extended stroke to discharge the compacted material from the chamber. The material is discharged into a bag (8) which lines a pivoted skip (9) mounted on a trolly (12), the skip having mechanically or hydraulically operated bag retaining and closing means to close the mouth of the bag prior to sealing.

Description

"Packing and Compacting Apparatus" This invention relates to the compacting of material such as shredded newspaper.

A known method and apparatus for compacting light¬ weight flexible and inelastic material such as shredded newspaper, described for example, in the applicants'

U.K. Patent specification 2040794, utilises a compaction ram which compacts the material into a chamber, usually by making a number of reciprocating strokes, and a discharge ram which pushes the compacted material from the compaction chamber while the face of the compacting ram acts as one wall of the chamber. With this arrangement the compacting ram and the discharge ram are arranged with their axes mutually perpendicular and the compacting ram compacts the material against a fixed wall of the compaction chamber opposite the face of the ram.

An object of the present invention is to provide an improved compacting apparatus in which the compaction and discharge of the material takes place in a single direction, utilising a single ram, with advantages both as regards the space taken up by the apparatus and the overall cost.

According to the present invention there is provided an apparatus for compacting material such as shredded newspaper, comprising a horizontal chamber into which the material falls and a compactor ram which is reciprocated within the chamber, characterised in that the apparatus further includes a hinged tailgate at the end of the chamber opposite the ram and actuator means, operable when the material in the chamber reaches a desired degree of compaction, to pivot the tailgate about a transverse axis in one wall of the chamber between a compaction position in which the tailgate blocks the outlet of the chamber and an open position in which the tailgate forms, in effect, a continuation of the said one wall of the chamber, and means for initiating an extended stroke of the compactor ram to discharge the compacted material from the chamber when the tailgate is in the open position. Compaction in this case takes place against the tailgate, which is disposed in its compaction position during the compaction stroke or strokes of the ram. The compactor ram also serves to discharger the compacted material from the chamber by making an extended stroke after the material has been compacted. Although the apparatus of the present invention is particularly suited to the compaction of shredded paper for the production and packing of animal bedding, the apparatus is also applicable generally to the compaction of other materials preparatory to baling or packing. Preferably the material to be compacted is delivered to the compacting chamber through an entry port in an upper wall of the chamber, the compactor ram having a vertical compacting wall and an adjoining horizontal baffle surface which extends rearwardly from the upper edge of the compacting wall such that it blocks the entry port when the compactor ram completes a forward compacting stroke.

The apparatus is preferably automatic or semi¬ automatic in operation. Thus the tailgate may be hinged in an upper wall of the compacting chamber and may be movable by means of an hydraulic actuator, the compactor ram being also movable by means of an hydraulic actuator which includes a pressure switch responsive to the hydraulic pressure in the compactor ram actuator to initiate opening movement of the tailgate actuator when a predetermined threshold compacting pressure is reached. Once the pressure switch indicates that a desired degree of compaction has been reached it may initiate a discharge stroke of the compactor ram, while at the same time causing opening movement of the tailgate actuator.

The apparatus of the present invention is prefer- -ably used for the loading of compacting material into bags or sacks. Although such loading could be carried out automatically, a preferred embodiment of the invention, for use in the packing of shredded paper and like material, utilises manual means for the placement of empty bags or sacks to be filled and the removal and sealing of the filled bags. In a preferred embodiment, therefore,the apparatus further provides a collection sk,ip for the compacted material which is located at the delivery outlet of the compacting chamber, the skip having means for releasably retaining the open end of a bag which lines the skip for the reception of the compacted material. The skip may be supported upon trunnions for pivotal movement about a horizontal transverse axis between a loading position in which the skip is horizontal and is an effective continuation of the compacting chamber, so that the bag lining the skip can receive a load of compacted material discharged from the chamber, and a bag closing position in which the skip is upright with the open end of the bag uppermost to facilitate closure and sealing of the open end of the bag.

The means for releasably retaining the open end of the bag may be purely mechanical. For example, these means may be constituted by or carried by doors hinged to opposite sides of the open end of the skip, the doors being movable by means of a mechanical operating linkage between open positions in which the mouth of the bag is held open for loading and closed positions in which the doors at least partially close the bag. The skip may be mounted upon a trolley which is movable along guides towards and away from the delivery end of the compacting chamber, pivotal movement of the skip from its loading to its bag closing position being effected when the trolley has been moved along the guides to a stop, the movement of the trolley against the stop being effected by the discharge - 4 - of compacted material intc the lined skip from the compacting chamber. The movement of the trolley against the stop may serve to trip automatic operation of the operating linkage of the retaining doors to move the latter into a closed position _ before the skip is tipped into its upright position, either by powered actuator means or manually.

The operating linkage for the retaining doors may include a spring-loaded -overcentre trip lever which is moved into the door closing position when the trolley engages the stop. Once the doors have been moved into their closed positions, upon filling of a bag, the bag may be released manually from the retain- -ing means and the mouth of the bag closed and sealed while the open end of the bag is firmly gripped by the closed doors. Thereafter the door may be opened by manual operation of the trip lever and the bag containing the compacted material may be removed from the skip, through an open side of the skip. In a preferred practical embodiment of the invention the means for releasably retaining the open end of the bag comprise hydraulically operated retainer means arranged adjacent the mouth of the skip to be operated automatically following the discharge of the compacted material into the bag to at least partially close the mouth of the bag and retain the material therein during subsequent sealing of the bag, prior to the removal of the bag from the skip.

In a preferred embodiment of the invention the bag retainer means comprise at least one hydraulically operated pressure plate pivotally mounted at the mouth of the skip. Alternatively the retainer means may comprise retractable fingers movable by respective hydraulic actuators. Where the tailgate is hydraulically operated the retainer means may be actuated by hydraulic pressure derived from the tailgate actuator. In a preferred embodiment of the invention the operation of the retainer means is controlled by a valve which is tripped by a sensor responsive to the operation of the tailgate to discharge the material from the compaction chamber.

Although the placement of the bags to be filled may be carried out .automatically, a preferred embodiment of the invention uses bag retaining means onto which bags to be fjelled are fitted manually, the filled bags being removed from the retaining^'means semi-automatically.

In this embodiment of the invention the compacted material is discharged through a duct provided with means for releasably retaining the open end of the bag into which the material is discharged by the discharge stroke of the compactor ram. The means for releasably retaining the open end of the bag preferably comprises a portable frame which fits over and is releasably supportable on the duct, the frame having fingers projecting downstream in the direction of discharge of the compacted material, the fingers being arranged to retain the open end of the bag by friction.

The bag retaining frame may have two portions which are resiliently biased relative to each other to urge at least two of the fingers away from each other to exert a friction grip on the bag. In this case the apparatus may further include a jig into which a said frame may be placed when empty, the jig having pedal-operated means for compressing the frame to move the said fingers towards each other so as to allow a bag to be fitted over the fingers. This greatly facilitates the attachment of an empty bag to the frame, prior to the mounting of the frame on the discharge duct.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic longitudinal sectional view of a compacting and packing apparatus for shredded paper, according to one embodiment of the invention; Figure 2 is a diagrammatic perspective view of a - collection skip utilised with the apparatus illustrated in Figure 1 ;

Figures 3 and 4 are diagrammatic plan views of the underside of the collection skip shown in Figure 2, illustrating the door operating linkage with the doors in their open positions and closed positions respectively;

Figures 5 and 6 are respective diagrammatic perspective views of two alternative collection skips with hydraulic bag retainer means , for use with the apparatus illustrated in Figure 1 ;

Figure 7 is a diagrammatic perspective view showing part of the discharge duct of the apparatus and a bag retaining frame, and

Figure 8 is a diagrammatic illustration of a jig for use in fitting a bag to the retaining frame shown in Figure 7.

The illustrated apparatus has a horizontal compacting chamber 1 defined by steel plates which are preferably welded together to form a chamber of rectangular cross section. A compactor ram 2 is mounted for horizontal reciprocation within the chamber 1 by means of an hydraulic actuator 3 mounted externally of one end of the chamber 1. A hinged tailgate 4 is mounted adjacent the other end of the compacting chamber 1 for pivotal movement about a horizontal transverse axis in the upper wall of the chamber 1 between a vertical compaction position, illustrated in Figure 1 , in which the tailgate blocks the outlet of the chamber 1, and a horizontal open position, shown in ghost outline, in which the tailgate 4 forms in effect a continuation of the said upper wall of the chamber 1. Movement of the tailgate 4 is effected by means of a double acting hydraulic ram 5 mounted on top of the compacting chamber 1. Material tobe compacted, which in this example is in the form of shredded or diced newspaper for use as animal bedding, enters the compacting chamber 1 through an entry port 6 in the upper wall of the chamber 1. The compactor, ram 2 has a vertical face which acts as a compacting wall and an adjoining hor- -izontal baffle surface 7 which extends rearwardly from the upper edge of the compacting face so as to block the entry port 6 when the compactor ram completes a forward compacting stroke. When the com- -pactor ram 2 subsequently retracts the baffle surface 7 moves rearwardly and- allows material which has collected on the surface 7 _ during the forward stroke of the ram 2 to fall into the compacting chamber 1. Compaction of material in the chamber 1 is effected by a number of successive reciprocating strokes of the compactor ram 2 with the tailgate 4 in its compaction position. These strokes continue until the hydraulic back pressure in the compactor ram actuator 3 reaches a predetermined threshold, sensed by a pressure switch (not shown) , indicating a desired degree of compaction of the material in the chamber 1. Upon being tripped the pressure switch initiates operation of the tailgate actuator 5 to raise the tailgate 4 into its open position, and also initiates an extended stroke of the compactor ram 2 to cause the compacting face of the ram to move through the compacting chamber 1 , past the open tailgate 4 to discharge the compacted material into a plastic bag 8 supported at the delivery outlet of a discharge duct 23 which is, in effect, a continuation of the compacting chamber 1. The bag - 5 - 8 is located in a collection skip 9.

The collection skip 9 is supported upon trunnions 10 for pivotal movement about a horizontal transverse axis between a loading position, illustrated in Figure 1 , in which the skip 9 is horizontal — and forms an effective continuation of the compacting chamber 1 , as illustrated in Figure , so that the bag 8 lining the skip can receive directly from the compacting chamber a load of compacted material pushed from the chamber 1 by the ram 2 and a bag closing position, shown in ghost outline in Figure , in which the skip is substantially upright, with the open end of the bag 8 uppermost to facilitate manual closure and sealing of the bag. The trunnions 10 are supported by cradle arms 11 of a trolley 12 which is movable along fixed guide rails 13 towards and away from the delivery end of the compacting chamber 1. Pivotal movement of the skip 9 from its loading position to its bag closing and sealing position may be effected automatically when the trolley 12 is moved along the guide rails 13 under the action of the compacted material displaced into the bag 8 by the compacting ram 2. Such pivotal movement may be initiated automatically when the trolley 12 engages a stop on the guide rails 13.

The open end of the plastic bag 8 which lines the skip 9 is releasably retained upon lugs 14A or other suitable shaped formations carried by two doors 14 hinged to opposite sides of the open end of the skip 9. The doors 14 are movable by means of a mechanical operating linkage between open positions, shown in Figures 1 and 3, in which the mouth of the bag is held open for loading,and closed positions, illustrated in Figure 4, in which the doors 14 partially close the skip 9 and hold the mouth of the bag 8 firmly against the contents of the bag, facilitating disengagement of the open end of the bag 8 from the lugs 14A and the subsequent closure and sealing of the bag manually.

As illustrated in Figures 3 and 4, the hinged doors 14 are movable in unison by means of an operating linkage which includes a spring-loaded overcentre trip lever 15 pivoted to the base, of the skip 9 about a pivot pin 16 intermediate the end of the lever 15. One end of the lever 15 connected to the two doors 14 by means of respective^ links 17, while the other end of the lever 15 projects laterally beyond the skip 9 and carries a trip arm 18 which engages a striker (not shown) fixed relative to the guide rails 13 when the trolley 12 is displaced against the stop. A tension spring 19 acts upon the trip lever 15 and main- -tains the lever 15 in the position illustrated in Figure 3 in which the doors 14 are open. hen the trip arm 18 engages the striker upon rearward movement of the horizontal skip 9 upon the trolley 12 the lever 15 is displaced so that the spring 19 passes through an overcentre position in relation to the pivot pin 16. This causes the spring 19 to urge the doors 14 into the closed position, illustrated in Figure 4, in which the loaded bag 8 can easily be disengaged from the retaining lugs 14A carried by the doors 14 and the bag then closed and sealed, the skip 9 having in the meantime been moved into its vertical position for bag closure. The closed and sealed bag 8 can then be removed from the skip 9 through an open side (shown uppermost in Figure 2) , which, when the skip is in its upright bag closing position, is open towards the machine operator.

Tilting movement of the skip 9 about the axis of the trunnions 10 from the horizontal loading position to the vertical bag closing position may be effected by means of a pedal lever 20 fixed to the rear end of the skip 9 and positioned so as to be readily operable by a foot of the machine operator. When the trolley 13 carrying the skip 9 is pushed into its rearward position against the stop the pedal 20 is depressed to tilt the skip 9 into its vertical position, after the doors 14 of the skip have been closed by operation of the trip lever 15 as described previously.

The skip 9 may, in an alternative embodiment of the invention, be tipped automatically into its bag closing and sealing position when the trolley 12 advances to the rearward stop upon completion of the discharge stroke of the compacting ram 2.

Referring to Figure 1 ,- it will be noted that the top and bottom walls of the compacting chamber downstream of the entry port 6 are fitted with spring- loaded fingers 21 of wedge profile which act as non¬ return 'elements to prevent substantial rearward expansion of the compacted material between successive compacting strokes of the ram 2. The ram 2 itself is formed with a cam surface 22 to depress the fingers 21 as the ram 2 retracts through the chamber 1 , following an ejection stroke, to return to its initial position for the commencement of another compaction sequence. Figure 5 illustrates an alternative form of bag unloading skip 9 equipped with hydraulic bag retaining means. The two opposite vertical walls of the skip 9 are equipped with two coaxial opposed pairs of bag retainer fingers 24 in place of the doors 14. The fingers 24 have rounded ends and are carried by respective hydraulic actuators 25 which are mounted on the outside of the skip 9 with their axes perpendicular to the direction of movement of the compactor ram 2. The fingers 24 occupy retracted positions when the skip 9 receives a load of compacted paper from the compacting chamber 1 , as shown in Figure 1. The hydraulic actuators 25 of the fingers

^V'^I?0 24 are connected through a non return valve NRV to the hydraulic actuator 5 of the tailgate 4 (Figure 1 ) . When the pressure in the actuator 5 builds up following the extended stroke of the latter which expels the compacted material this pressure is transmitted to the actuators 25 through the valve NRV and a control valve CV, the latter being opened when the ram 2 trips a limit switch {not shown) at the end of its ejection stroked The actuators 25 thereupon extend the fingers 24 to the positions shown in Figure 5, in which the fingers partially close the open end of the bag 8, retaining the compacted contents therein as the skip 9 tilts into the upright position prior to the closing and sealing of the bag 8, an operation which may be effected manually or automatically.

Once a bag 8 has been sealed the fingers 24 are retracted, for example by manual operation of the control valve CV to relieve the pressure in the actuators 25. Retraction of the fingers 24 may be effected by spring-loading of the actuators 25, or hydraulically in the case of double acting actuators 25. The closed and sealed bag 8 can then be removed from the skip 9 through an open side of the latter (shown uppermost in Figure 2) which, when the skip is in its upright bag closing position, is open towards the machine operator.

In the embodiment illustrated in Figure 2 tilting of the skip 9 about the axis of the trunnions 11 from the horizontal loading position to the vertical bag closing position may be effected by means of a pedal lever 20 fixed to the rear end of the skip 9 and positioned so as to be readily operable by a foot of a machine operator. When the trolley 13 carrying the skip 9 is pushed into its rearward position against the stop the pedal 20 is depressed to tilt the skip 9 into its vertical position, after fingers 24 have been extended as described previously. An alternative version of the skip 9, illustrated in Figure 6 , is arranged to be tipped automatically into its upright bag closing and bag sealing position when the trolley 13 advances to the rearward stop upon completion of the discharge stroke of _ the compacting ram 2. In this case tipping of the skip 9 is effected by means of an hydraulic actuator 26. The hydraulically operated bag retaining elements in this case take the form of two pressure plates 27 pivotally mounted at the mouth of the skip 9 for angular movement in a common plane about respective pivot axes parallel to the direction of discharge of the material into the skip 9. The pivotal movement of the two pressure plates 27 is effec- -ted by means of a double acting hydraulic ram 28 housed below the mouth of the skip 9 and connected to the tailgate actuator 5 through a non-return valve. The two pressure plates 27 are so profiled that when they are-moved pivotally towards each other by means of the ram 28 they engage the mouth of the bag 8 (not shown in Figure 6} and partially close the bag, retaining the compacted material in the bag and preparing the latter for complete closure and sealing when the skip 9 is subsequently tipped into its upright position by means of the actuator 26.

Each individual empty bag 8 to be filled with compacted material is supported at the outlet end of the discharge duct 23 in a releasable manner, so that when the compacted material is discharged from the chamber 1 and through the duct 23, the bag 8 is released into the skip 9. Figure 7 illustrates one form of bag retaining means comprising a portable frame 30 which is releasably supported upon laterally outwardly projecting external lugs 31 adjacent the outlet of the discharge duct 23. For this purpose the frame 30 has, on opposite sides, opposing pairs of hook elements 29 which can be placed on the lugs 31 and by means of which the frame 30 is supported in a generally vertical plane against movement in the direction of the longitudinal axis of the discharge duct 23. The frame 30 is provided with four bag retaining fingers 32-35 extending generally parallel . to the longitudinal axis of the duct 23 and projecting downstream in the direction of discharge of the compacted material. The fingers are arranged in two pairs 32, 33, and ,34, 35 on opposite sides of the frame 30, laterally outwardly of opposite vertical side walls of the discharge duct 23. The open mouth of a bag 8 is supported on the four fingers 32-35 by friction, and is pulled off these fingers when the compacted material is pushed by the discharge stroke of the ram 2 into the bag 8 lining the skip 9.

To ensure good frictional grip between the retaining fingers 32-35 and the bag 8 the fingers 32-35 are coated with plastics material or rubber. In addition, one finger of each pair of fingers 32, 33 and 34, 35 is spring loaded away from the other. Thus in the illustrated embodiment the fingers 32, 34 of each pair are supported on respective sliders 36, 37 which slide within respective tubular bores of the frame 30 and which are urged by internal compression springs (not shown) away from the other fingers 33, 35 of the respective pairs, the fingers 33, 35 being attached to the frame 30 by welding.

In order, to fit an empty bag 8 onto the retaining frame 30 the latter is first unhooked from the lugs 31 and then placed in a compression jig 40, illustrated diagrammatically in Figure 8. In the compression jig 40 the frame 30 is supported with the fixed fingers 33, 35 in abutment with respective stops while the movable fingers 32, 34 are engaged by a displaceable member 41 which is laterally movable, against the action of tension springs 42, by means - 14 - of cables 43 attached to a pivoted foot pedal lever 44. The arrangement is such that when the pedal 44 is_. depressed the displaceable member 41 is drawn by the cables 43 against the action of the biasing springs 42 to cause the fingers 32, 34 to move towards the fingers 33, 35 respectively, compressing the respective springs within the frame 30. With the pedal 44 depressed a bag 8 is fitted over the four fingers 32, 35 and the pedal is then released, causing the two pairs of fingers 32, 33 and 34, 35 to spread apart and thereby retain the bag 8 on the frame 30. The frame 30 ,with the bag 8 attached thereto, can then be replaced on the discharge duct 23 by re-engagement of the hook members with the lugs 31 , preparatory to the reception of a load of compacted material from the duct 23.

Claims

1. Apparatus for compacting material such as shredded newspaper comprising a horizontal chamber (1) into which the material falls and a compactor ram (2) which is reciprocated within the chamber, characterised in^" that the apparatus further includes a hinged tailgate (4) at the end of the chamber (1) opposite the ram and actuator means, (5) operable when the material in the chamber reaches a desired degree of compaction, to pivot the tailgate (4) about a transverse axis in one wall of the chamber between a compaction position in which the tailgate blocks the outlet of the chamber and an open position in which the tailgate forms, in effect, a continuation of the said one wall of the chamber, and means for initiating an extended stroke of the compactor ram (2) to discharge the com- -pacted material from the chamber when the tailgate is in the open position.

2. Apparatus as claimed in Claim 1, in which material to be compacted is delivered to the compacting chamber (1) through an entry port (6) in an upper wall of the chamber, the compactor ram (2) having a vertical compacting wall and an adjoining horizontal baffle surface (7) which extends rearwardly from the upper edge of the compacting wall such that it blocks the entry port when the compactor ram completes a forward compacting stroke.

3. Apparatus as claimed in Claim 1 or Claim 2, in which the tailgate (4) is hinged in an upper wall of the compacting chamber (1) and is movable by means of an hydraulic actuator (5) , the compactor ram (2) being also movable by means of an hydraulic actuator (3) which includes a pressure switch responsive to the hydraulic pressure in the compactor ram actuator to initiate opening movement of the tailgate actuator (5) when a predetermined threshold compacting pressure is reached.

4. Apparatus as claimed in any one of the Claims 1 to 3, and further including a movable collection skip

(9) for the compacted material, located at the delivery outlet of the compacting chamber (1) , the skip having means for releasably retaining the open end of a bag (8) which lines the skip for the reception of the compacted material.

5. Apparatus as claimed in Claim 4 , in which the skip (9) is supported upon trunnions (1 ) for pivotal movement about a horizontal transverse axis between a loading position in which the skip (9) is horizontal and is an effective continuation of the compacting chamber (1), so that the bag (8) lining the skip can receive a load of compacted material discharged from the chamber, and a bag closing position in which the skip (9) is upright with the open end of the bag uppermost to facilitate closure and sealing of the open end of the bag (8) .

6. Apparatus as claimed in Claim 4 or Claim 5, in which the means for releasably retaining the open end of the bag are carried by or constituted by doors (14) hinged to opposite sides of the open end of the skip (9) the doors being movable by means of a mechanical operating linkage (15-17) between open positions in which the mouth of the bag (8) is held open for loading and closed positions in which the doors at least partially close the bag.

7. Apparatus as claimed in Claim 6, in which the skip (9) is mounted upon a trolley (12) which is movable along guides (13) towards and away from the delivery end of the compacting chamber (1) , pivotal movement of the skip (9) from its loading to its _ bag closing position being effected when the trolley . has been moved along the guides to a stop, the movement of the trolley (12) against the stop being effected by the discharge of compacted material into the lined skip from the compacting chamber (1 ) .

8. Apparatus as claimed in Claim 6 or Claim 7, in which the movement of the trolley (12) against the stop trips automatic operation of the operating linkage (15-17) of the retaining doors (14) to move the latter into the closed position before the skip (9) is tipped into its upright position.

9. Apparatus as claimed in Claim 8, in which the door operating linkage includes a spring-loaded over- -centre trip lever (15) which is moved into the door closing position when the trolley (9) engages the stop.

10. Apparatus for compacting and packing material such as shredded newspaper comprising a compactor ram (2) arranged for reciprocation in a compaction chamber

(1) , and characterised by a hinged hydraulically operated tailgate (4) forming a wall of the compaction chamber (1) opposite the compactor ram (2) , control means for opening the tailgate (4) when a predetermined degree of compaction has been reached and for causing the compactor ram (2) to make an extended stroke to discharge the compacted material into a bag (8) lining a collection skip (9) , and hydraulically operated - 18 - retainer means (24; 27) arranged adjacent the mouth of the skip to be operated automatically following the discharge of the compacted material into the bag (8) to at least partially close the mouth of the bag and retain the material therein during subsequent sealing of the bag, prior to the removal - of the bag from the skip.

11. Apparatus according, to Claim 10, in which the retainer means comprise at least one hydraulically operated pressure plate (27) pivotally mounted at the mouth of the skip (9) .

12. Apparatus according to Claim 1, in which the retainer means comprise retractable fingers (24) movable by respective hydraulic actuators (25) .

13. Apparatus according to Claim 1 , Claim 2, or Claim 3, in which the retainer means (24; 27) are actuated by hydraulic pressure derived from the hydraulically operated tailgate (4) .

14. Apparatus according to any one of the preceding claims, in which the compacted material is discharged from the compaction chamber (1) through a duct (10) provided with means (30) for releasably retaining the open end of the bag (8) into which the material is discharged by the discharge stroke of the compactor ram (2) .

15. Apparatus according to Claim 14, in which the means for releasably retaining the open end of the bag comprises a portable frame (30) which fits over and is releasably supportable on the duct (10), the frame having fingers (32-25) projecting downstream in the direction of discharge of the compacted material. the fingers being arranged to retain the open end of the bag by friction.

16. Apparatus according to Claim 15, in which the frame (30) has portions which are resiliently biased_ relative to each other to urge at least two of the fingers (32, 33 ; 34, 35) away from each other to exert a friction grip on the bag.

17. Apparatus according to Claim 16, including a jig (40) into which the bag retaining frame (30) may be placed when empty, the jig having pedal-operated means (41-44) for compressing the frame to move the said fingers (32, 33; 34, 35) towards each other so as to allow a bag (8) to be fitted over the fingers.