BACKGROUND ART There are known baling presses for compressing waste material, such as paper and cardboard packaging, into bales for more compact storage and disposal. Such presses typically comprise a chamber having a reciprocating piston therein to compress materials inserted into the chamber through an inlet chute. Bales are formed progressively by new material being compressed against the last formed bale. Such compression is achieved by means of a choking system restricting the material from egressing from the chamber. After a bale of a predetermined size has been formed, it is usually tied with baling wire and a new bale is commenced.

The known presses also include a choke mechanism to hold the last formed bale while the piston pushes newly inserted materials against it. This choke only allows the last formed bale to move once a predetermined compaction pressure has been achieved.

There are two basic types of known choke mechanisms. One type uses a single hydraulic ram, usually located on the top of the choke assembly and standing vertically. The hydraulic ram activates a scissor-type linkage that produces a contracting horizontal action on the wall panels of the choke chamber as the hydraulic ram is extended vertically. On occasions the base of the hydraulic ram is also used to create a downward force on the roof section of the choking chamber.

This type of known mechanism is unduly complex in construction, thereby resulting in high construction costs and servicing requirements.

The second known type of choking mechanism

relies on short hydraulic rams [one or more on each side] located on outside of the choke panels. These rams create a choke action by pushing the choke panels horizontally towards each other, thereby causing the area within the choke panels to contract. This type of choke mechanism is also relatively expensive to construct and service.

Secondly, this known choke mechanism has an inherent disadvantage if the choke chamber is short, as required where space restrictions so require. The choking action becomes quite unstable as the choke panels can be displaced off centre, e.g. by the material on one side of the chamber being more or less dense than the material on the other side of the chamber. Consequently, the bales formed by the choke mechanism can easily become "banana" shaped.

The known baling presses are also provided with unduly complex wire tying mechanisms for the bales. A typical wire tying mechanism has complex spring loaded "flicker" guides through which the tying wire travels and which work to allow the tying wire to be moved aside as the needle [used to hook onto the wire and pull it through for tying] passes the wire. These spring loaded flicker assemblies then flick the wire back into the hook so that the wire can be loaded in the tying action for tying off each bale.

It is an object of the present invention to provide an improved baling press which overcomes or ameliorates the abovedescribed disadvantages, or which at least provides the consumer with a useful choice.

SUMMARY OF THE INVENTION In one broad form, the present invention provides a baling press of the type comprising a load chamber adapted to receive material to be compressed into bales by a piston mechanism reciprocating within the chamber, and a choke mechanism including a choking chamber at an outlet end of the load chamber for frictionally restraining movement of material therethrough such that

the piston mechanism may compress further material against the restrained material, characterised in that the choke mechanism includes a pair of opposed choking panels at least one of which is movable, and at least one pair of hydraulic cylinders, each hydraulic cylinder having its ends connected respectively to the opposed panels.

Typically, each choking panel is hinged at its end proximal to the load chamber. Preferably, the hydraulic cylinders are provided at the distal end of the choking panels.

In a preferred embodiment, the choking panels are side walls of the choking chamber, hinged about respective vertical axes. Each side wall is provided with top and bottom brackets extending inwardly and orientated perpendicularly to the plane of the side wall. A first hydraulic cylinder has its ends pivotally connected to the top brackets, while a second hydraulic cylinder has its ends pivotally connected to the bottom brackets. In this manner, by contraction of the hydraulic cylinders, the side walls can be brought together to grasp the compressed material therebetween.

Advantageously, the hydraulic cylinders are "floating", i.e. not fixed to the frame of the press. This arrangement of the hydraulic cylinders with the brackets being perpendicular to the plane of the side walls creates a self-centering stabilising effect, thereby avoiding the problem of curved bales in short and otherwise unstable choke chambers.

In an alternative embodiment, the choking panels are top and bottom walls of the choking chamber, hinged about respective horizontal axes.

The baling press is suitably provided with electrical and hydraulic controls so that the compressed material is held by the choke mechanism only for as long as it is necessary. Normally, the side walls of the choke mechanism grasp and hold compressed material to enable the piston mechanism to compress further material against it and thereby complete the bale or form a new bale. However,

when the pressure in the piston mechanism exceeds a predetermined limit, the hydraulic cylinders on the side walls are released momentarily, allowing the compressed material held within the side walls to slip a little further outwardly. This, in turn, allows more material to be compressed against the held material until the piston pressure rises above the predetermined limit, at which time the material held within the side walls of the choke mechanism will again be permitted to slip a little more outwardly. In this manner, the bales are progressively formed, yet in a highly compressed state.

In another embodiment of the invention, the choking panels are located at the top and bottom of the choke chamber, and the hydraulic rams are located at the sides. One choke panel, usually the top panel, is mechanically adjustable to provide a fixed amount of choke restriction to the bale. Once the choke panel has been mechanically adjusted to provide the desired amount of choke restriction, it is fixed, and the other choke panel, usually the bottom panel, is moved by the hydraulic rams.

In this alternative embodiment, the hydraulic rams are not floating, but rather are fixed to the frame of the baling press by pins at their top ends. The bottom ends are connected to respective opposite sides of the bottom choke panel. In this manner, by contraction of the hydraulic cylinders, the bottom panel can be brought closer to the top panel to grasp a bale of compressed material therebetween and effect a choking function.

Preferably, the baling press also comprises a wire tying mechanism for binding the bales. In the preferred embodiment, a respective conduit is provided for each baling wire. (Typically, each bale is tied by three or more wires) . The conduits not only facilitate the feeding of the wire but also serve to protect the wire.

They also provide alignment of the wire, and serve to locate the wire within a predetermined area necessary to ensure that each wire will be engaged by a respective needle used in the wire tying mechanism.

The use of the tube to locate the wire within the predetermined area, and thereby engage the respective needle, relies on the inherent spring in the tying wire to flick the wire into the needle hooks to complete the tying cycle.

In order that the invention may be more fully understood and put into practice, a preferred embodiment will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a general perspective view of a baling press according to one embodiment of the invention, Fig. 2 is a schematic sectional view of the baling press of Fig. 1, Figs. 3A and 3B are front and side elevations of the operative end of a needle about to engage a baling wire, Fig. 4 is a perspective view of the platen of the piston mechanism within the baling press of Fig. 1, and Fig. 5 is a perspective view of part of a choking mechanism according to another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT As shown in Fig. 1, a baling press 10 comprises a load chamber 11 having a piston mechanism (not shown) which reciprocates therein. Material inserted into a feed chute 12 falls into the chamber 11 where it is compressed by the piston mechanism into bales. Such material typically comprises waste paper, cardboard, waste packaging, and/or other dry materials.

The piston is normally driven hydraulically by a pump which is powered by an engine or motor located within housing 13 in this embodiment. The housing 13 also contains the electronic and hydraulic control mechanisms for the baling press. Another housing 14 contains the

needles and wire tying mechanism used for binding the bales with wire, as will be described below.

A choke mechanism 15 is provided at the outlet end of the load chamber 11. The choke mechanism includes a choking chamber designed to hold a newly compressed material so that additional material can be compressed against it by the piston mechanism to complete a bale or form a fresh bale.

The choke mechanism 15 comprises a pair of side walls 16, 17, each of which is hinged at its end proximal to the chamber 11 so that the wall may pivot about a vertical axis. Each wall 16, 17 has a post at its distal end. The posts have respective upper brackets 16A, 17A and lower brackets 16B, 17B, extending inwardly and perpendicularly to the respective side walls 16, 17.

The choke mechanism also comprises a pair of hydraulic cylinders 18A, 18B. (For clarity, the hose connections to the cylinders are omitted). The upper cylinder 18A has its opposite ends pivotally connected to the brackets 16A and 17A. Similarly, the lower cylinder 18B has its opposite ends pivotally connected to the brackets 16B and 17B.

The hydraulic cylinders 18A, 18B are connected only to the side walls 16, 17 (via the brackets) . That is, the hydraulic cylinders 18A, 18B are not fixed to the frame of the baling press, but are "floating". The described construction provides a self-centering stabilising effect to the choke mechanism 15. Although both side walls 16, 17 are pivotable, the contraction of the hydraulic cylinders 18A, 18B imparts a centering or aligning influence on the side walls so that the bales will be pushed out of the baling press in a straight formation.

As shown in Fig. 2, when the baling press is in operation, recently compressed material is held between the side walls 16, 17. The side walls 16, 17 are brought together by pistons 18A, 18B, and frictionally retain the material between them. This enables the reciprocating

piston in chamber 11 to compress newly added material against the compressed material and thereby complete a bale or form a new bale.

As the piston attempts to compress more material into the same volume, the pressure in the hydraulic piston ram increases. Once the pressure rises above a predetermined level (typically around 1200 psi), an electro-hydraulic control circuit releases the pressure in the hydraulic cylinders 18A, 18B for a fraction (typically a millisecond) thereby momentarily releasing the material held between the side walls 16, 17. The material slips forward, allowing a little extra space for the bale being formed.

Every time the ram pressure rises above the predetermined level, the material held within the side walls 16, 17 is momentarily released (to allow it to slip forward), then grasped again. In this manner, a bale is formed progressively, with uniformly compressed material.

At start-up, there will be no material in the choke mechanism to provide a reaction to the piston mechanism. An optical sensor (not shown) is provided to detect the absence of material at the entrance to the choke mechanism, e.g. at start-up. If there is no material present, the ram is permitted to reciprocate until the compressed material accumulates and passes through to the choke mechanism. If however, there is no movement of the bale counter wheel 24 after a predetermined number of piston strokes, the ram is disabled to avoid the risk of malfunction.

The baling press 10 also comprises a wire tying mechanism to bind the bales with wire. As shown in Fig. 2, three wires 20 are drawn from respective rolls and passed around rollers 30 and 31. The three wires 20 then pass through respective spaced tubes 22 located under the baling press 10. The tubes 22 are typically metal pipe sections with slightly flared ends to facilitate the feeding of the wires into the tubes. Fig. 2 depicts the baling press in operation, with a bale already formed. The

wires 20 extend out of the tubes 22 and pass under the bale. Grooves are suitably provided in the top and bottom walls of the choke mechanism (see Fig. 1) to accommodate the wires.

A second set of three wires 21 are drawn from individual rolls, pass around rollers 32, 33 and 34, and alongside the top of the bale (where they have been joined previously to the respective wires 20).

When a bale of predetermined length has been formed (determined by a measuring wheel 24 which is in contact with the top of the bale being formed and is turned by the travel of the material through the choke mechanism), the bale is bound by the wires.

In the bale binding procedure, the material in the bale is held in a compressed state by the piston mechanism. Three needles 23 pass through respective vertical through-holes in the platen 25 (Fig. 4) of the piston mechanism and engage respective wires 20 at the outlets of the tubes 22 at the location marked "A". The needles then draw the wires 20 upwardly to the point marked "B" where the wires 20 are each joined to respective wires 21 in two locations, and cut between the two joins. The outermost join closes the wire loop around the bale. The innermost join forms a loop which is pushed outwardly by the new bale to be formed. The abovedescribed procedure is known in the art, and need not be described in detail in this application.

Known wire tying mechanisms normally comprise a complex arrangement of wire guides, flicker assemblies and sensors to ensure that the wires are engaged by the needles 23. The baling press of the described embodiment obviates the need for such complex arrangements, as the wires are located by their respective tubes 22.

As shown in Figs. 3A and 3B, each wire 20 is located within a respective tube 22. Hence, the position of the wire at the outlet of each tube 22 is constrained to be within a distance corresponding to the internal diameter of the tube 22.

When the needle 23 is brought down, the wire 22 is deflected (to the right as shown in Fig. 3A) by the oblique face 23A of needle 23. As the needle 23 continues downwardly to its lowest position, the tension in each wire 20 draws the wire back to a centre position where it is hooked in the recess 23B of needle 23. The hooked wire 20 is then drawn upwardly as the needle 23 rises, to be joined with respective wire 21.

Since each wire 20 is constrained to be within the horizontal distance corresponding to the internal diameter of the tube 22 (Fig. 3A), the wire 20 will always be engaged by the oblique face 23A of the needle point, and thereafter hooked by the needle. This simple, yet reliable, arrangement obviates the need for complex wire feed and flicker mechanisms, thereby reducing manufacturing costs and service requirements.

As shown in Fig. 4, the platen 25 forms part of the piston mechanism (not shown) used to compress the material into bales. The platen 25 is provided with vertical through-holes 26 for passage of the needles 23 during the wire tying procedure. The through holes 26 are grooves or slots which are open to the front face of the platen 25. Although the grooves are thin (typically a few millimetres wide), with known platens it has been found that material [typically flat cardboard and paper] can slide across the face of the piston and into the grooves and interfere with the proper operation of the needles 23.

The platen 25 of the preferred embodiment is provided with lips 27 at the outer edges of the grooves 26. These lips 27 formed raised edges at the slit openings of the grooves, so that material moving along the face of the platen is deflected away from the slit openings, thereby minimising the risk that material will enter the grooves 26.

Fig. 5 illustrates the choking panels of another embodiment of the invention. In this embodiment, the choking panels 30, 31 are the top and bottom walls of the choking chamber. The top wall 30 is mechanically

adjustable but otherwise fixed. The bottom wall 31 is hinged at its inner end 32 to the frame of the baling press 10. The bottom panel 31 is hinged about a horizontal axis. A pair of hydraulic cylinders 33 are provided at the outer end of the bottom panel 31, on opposite sides thereof. (For clarity, only one hydraulic cylinder is shown in Fig. 5). The bottom ends of the hydraulic cylinders 33 are pivotally connected to opposite sides of the bottom panel 31, while the upper ends of the hydraulic cylinders 33 are pivotally connected to the frame of the baling press. The bottom panel 31 can be pivoted up and down about its hinge axis by the hydraulic cylinders 33 to grasp and release a bale located in the choking chamber between the panels 30, 31.

The foregoing describes only some embodiments of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention.

For example, the choking panel in Fig. 1 may form the top and bottom walls of the choking chamber, and the choking panels of Fig. 5 form the side walls of the choking chamber instead.

In an additional improvement, the baling press 10 is provided with hard wearing slide rails on the bottom face of the chamber. The slide rails protect the bottom face of the load chamber from wear and tear from the reciprocating movement of the piston. Furthermore, when necessary, the slide rails can be easily replaced.

Sensors may also be provided to detect the end of a wire from a coil, to thereby indicate to an operator that a fresh coil is required.

In some instances, flat cardboard may slide under the platen. To avoid this problem, the floor of the chamber may be provided with an undulating profile. In one embodiment, three flat steel strips, approximately 65mm wide and 10mum high, are placed longitudinally on the floor of the chamber 11, in a parallel, spaced-apart configuration. These flat strips may suitably be located

under the grooves 26 in the platen. Corresponding recesses are formed in the bottom of the platen 15 to accommodate the flat bars. In this manner, the floor will have a castellated transverse profile, thereby avoiding the problem of flat sheets of cardboard being sandwiched between the floor of the chamber and the platen. In a variation of this floor arrangement, several round sections (approximately 12mm diameter) are laid longitudinally along the floor to provide an undulating profile.