GB1604239A - Apparatus for use in compression of material - Google Patents

Description

(54) APPARATUS FOR USE IN COMPRESSION OF MATERIAL (71) We, NATIONAL RESEARCH DEVELOPMENT CORPORATION of Kingsgate House, 66--74 Victoria Street, London, S.W.1., a British Corporation, established by Statute, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to apparatus for compressing material and has particular, but not exclusive, application to compressing straw into bales.

In known baling machines for compressing and baling straw, a pick up on a propelled, usually tractor driven, machine collects straw from the ground and the straw is transferred by an auger or other conveying device into an input opening of a compression chamber, which usually extends longitudinally of the machine. The straw is periodically taken up by a compression piston and driven along the compression chamber. The compression chamber conventionally is of rectangular crosssection having parallel side walls and top and bottom walls which converge towards each other along the length of the chamber. However, baling machines have been proposed in which the side walls converge and the top and bottom walls are parallel (see U.S.A.

Patent Specification Number 2,576,784).

There is no end wall to the compression chamber for the compression piston to bear against, the compression of the straw taking place instead by virtue of the resistance to the movement of the straw between the converging walls due to frictional contact with the walls defining the compression chamber. Periodically the column of compressed straw in the compression chamber is separated and tied in convenient lengths to provide bales.

It is known that the sliding resistance in the movement of straw or other non-comminuted crop material being compressed in the compression chamber varies with the type of crop, the dampness of the crop and other factors.

Where, for example, straw being compressed is wet, both the coefficient of friction between the straw and the side walls and the compressive resistance of the straw increases and hence the resistance offered to the compressing piston is much greater. Unless an adjustment is made to the machine, this results in a higher density of the compressed bale, and in some circumstances, can result in breakdown of the machine due to drive line overload or jamming of the straw in the com- pression chamber. It is therefore conventional practice to provide means for adjusting the degree of convergence of and the spring resistance to divergence of the converging walls, usually a manually operated control operating through a lead screw to vary the angle of convergence. Thus, in the most common baling machines, the operator of the machine will judge from observation of the crop and density of the compressed bales, the setting required for the converging walls. However, such manual adjustment by judgement of the operator normally results in less than optimum efficiency in the compression of the straw.

Operators tend to err on the safe side in setting the walls at a degree of convergence less than the maximum which could be utilised.

The reason for this is to avoid overload or jamming should a quantity of wet material find its way into the compression chamber.

The bales thus produced are erefore not as dense or uniform as could be obtained in optimum conditions by the machine.

In order to try to alleviate this problem, it has been proposed in the past to provide an automatic control of the degree of convergence of the convergent walls by attaching to the machine a sensor coupled between one of the convergent walls and a fixed wall of the compression chamber, the sensor being arranged to detect the outward movement of the convergent walls under the influence of the compressed straw. In such an arrangement, the convergent walls have a certain degree of freedom to move outwardly under excess pressure of the compressed straw and it is this movement which is detected by the sensor. A hydraulic ram is provided to control the degree of convergence of the convergent walls and is so coupled to the output of the sensor as to relax the said walls in circumstances of excess outward pressure by the straw. However, such an automatic arrangement is, in effect, only an overload release mechanism, since the sensor does not measure compression of the straw or resistance to moved ment in the longitudinal direction along the chamber but only measures the effects of over compression by outward movement of the compression plates.

Various proposals have been made to automatically adjust the degree of convergence betwen converging walls of the compression chamber of baling machines to provide bales of constant density. In particular, U.S.A.

Patent Specification Number 2,796,825 describes a baler in which the degree of convergence is adjusted in response to the weight of the compressed bales and U.S.A. Patent Specifications Numbers 2,576,784 and 2,708,872 describe balers in which the degree of convergence is adjusted in response to the resistance of the partially compressed straw to penetration. However, none of said proposed balers are entirely satisfactory in that inter alia they provide adjustment in response to the result of changes in resistance offered to the compressing piston and not in response to a cause of said changes, namely friction.

It is known from German Offenlegungsschrift Number 1,802,438 to briquette comminuted harvested crops by pressing them through a compression chamber having a crosssection which is automatically enlarged when the resistance to a compression piston exceeds a predetermined threshold value. In the briquetting machine described, the compression chamber is of generally square cross-section and is formed by a pair of opposed channel members. These members are maintained in parallel relationship by means of a parallel gram linkage and normally abut each other to provide a closed cross-section to the channel.

One of the members is secured to a pivoted lever for movement therewith and the lever is spring-biased to maintain the members in their normal abutting relationship. If the spring tension is exceeded during the pressing operation, the lever is pivoted forwardly in the direction of material movement, the resultant forward movement of the member fixed thereto causing the parallelogram linkage to move the members apart thereby increasing the cross-sectional area to relieve the excess pressure. Whilst the compression of crops passing through the chamber is automatically limited by the spring tension, the principle purpose of the parallelogram linkage is to provide an overload safety device in the event of excessive applied pressure. The arrangement of said linkage cannot automatically compensate for variations in coefficient of friction in the pressed material to maintain substantially constant compressive force because the rate of increase in spring tension increases with the angle of deviation of the lever whilst the rate of increase in separation of the channel members decreases with increased angle of deviation. Accordingly, the compressive force exerted by the channel members on material passing through the compression chamber increases with increased spacing between said members. Moreover, the briquetting apparatus is not intended to vary the spacing between the channel members about a median distance, the normal operating mode of the said members being in their mutually abutting condition. In the context of the particular application of the present invention to baling straw and other non-comminuted stalks and fibres, it is of significance that the briquetting apparatus is intended to produce blocks of a few inches, typically about 5 inches square compressed to about 24 to 30 pounds per cubic foot density whereas straw bales are consider ably larger typically 14 to 16 X 18 X36 to 44 and compressed to about 6 to 10 pounds per cubic foot density.

U.S.A. Patent Specification Number 2,711,687 discloses a baler in which the degree of convergence is adjusted in response to changes in the friction between the hay being compressed and a sensor plate set in the side of the bale chamber. The sensor plate has a degree of freedom to move longitudinally along the bale chamber and is coupled by a mechanical linkage to a clutch element. When the sensor plate has been moved by a change of friction beyond a predetermined position the clutch element is brought into engagement with a constantly rotating drive motor which effects a variation in the convergence of the walls of the bale chamber. The apparatus of this USA specification provides only a very coarse control of the degree of compression and cannot provide a uniformly compressed bale. Further more the apparatus is excessively complicated, which brings problems of maintenance in farm conditions, and is more expensive than would be justified in, for example, baling straw.

UK Patent Specification No. 662,390 discloses a hay baling machine in which an upper compression plate of a compression chamber is pivoted by a pair of link arms which are attached to outwardly extending support arms outside the bale chamber. A tension spring urges the compression plate against the direction of movement of the crop, and the effect of the pivotal linkage is to also apply a biasing force inwardly to the crop being compressed. Movement of the compression plate downstream with the crop being compressed brings some variation of the angle of the compression plate, but this change of convergence angle is made relative to a fixed lower compression plate, so that overall an asymmetic compression effect is exerted on the crop relative to the horizontal centre line of the bale chamber.

It is an object of the present invention to provide a relatively simple and inexpensive compression apparatus, especially for baling, which relies upon a mechanical linkage to vary the resistance to compression in response to changes in the sliding resistance of the material being compressed, and to effect the variation in a balanced manner.

According to the present invention there is provided apparatus for compressing material comprising main frame means, a pair of spaced apart opposed wall members mounted on the main frame means and relatively movable to vary mutual convergence therebetween, the wall members being adapted to co-operate with conveying means for forcing material between said pair of wall members in the direction of convergence to compress the material therebetween, at least a first one of the said wall members being mounted for longitudinal movement to and fro generally in the direction of material flow in response to changes in sliding resistance between the longitudinally movable member and the material and for pivotal movement to vary the degree of the said mutual convergence, biasing means urging said wall members towards greater convergence and urging said first member in the opposite direction to the direction of material flow, and guide means for constraining angular movement of the wall members relative to each other by an extent dependent upon the position of the first wall member in the direction of material flow in such a manner that movement of the first wall member to or fro in the direction of the material flow causes angular motion to vary the degree of the said mutual convergence to compensate at least in part for the said changes in sliding resistance during compression of material, in which both the first and second wall members are pivotally mounted relative to the main frame means so as to allow in operation substantially equal angular movement of the first and second wall members relative to the main frame means during said variation of mutual convergence.

In particularly preferred arrangements according to the invention, the said biasing means applies a force along a direction relative to the various pivot axes such as to exert a turning effect on the first wall member urging the wall members to greater convergence, and the arrangement being such that in operation movement of the first wall member in the direction of crop movement changes the relationships between the direction of the biasing force and the various pivot axes in such a manner as to increase the turning effect of any force applied by the biasing means.

Preferably the guide means are arranged to guide relative movement between the wall members in such a manner as to tend to maintain substantially constant the resistance to the passage of material between the wall members.

The apparatus may include in the apparatus conveying means for forcing material between said pair of wall members.

It is also provided in particularly preferred arrangements according to the invention that the said guide means comprises first coupling means coupling said first wall member to said main frame means in such a manner as to allow longitudinal and pivotal movement of the first wall member, and second coupling means coupling said first and second wall members together in such a manner as to allow angular movement of the wall members relative to each other, and also to allow angular movement of both wall members relative to the main frame means.

Preferably only a first of the said pair of wall members is mounted for reciprocal and pivotal movement.

Preferably the guide means includes or con sists of a pivotted arm linkage, but the guide means may include or consist of guide track means, and may comprise both a pivotted arm linkage and a guide track means.

Where only the first wall member is reciprocally movable, the first wall member is prb ferably pivotally coupled by a pivotted arm linkage at least partially to the second wall member.

Preferably the said second coupling means comprises a first sub-frame which is pivotally connected by first pivot means to the first wall member and is pivotally connected by second pivot means to the second wall member, the pivot axes of the said pivot means being parallel to each other and substantially perpendicular to the direction of material flow to permit movement of the first wall member both pivotally, and generally, in the direction of the movement of material. Preferably each sub-frame comprises a pair of parallel arms spaced transversely apart with the wall members aligned between them. Preferably said second pivot means is positioned in normal operation downstream of said first pivot means.

Preferably the first coupling means comprises a further sub-frame which is pivoted to the first wall member by a further first pivot means, and which is pivoted to the main frame means by a further second pivot means, the pivot axes of the said further pivot means being parallel to one another and generally substantially perpendicular to the direction of material flow to permit movement of first wall member both pivotally and generally in the direction of movement of material. Preferably the further sub-frame comprises a further pair of arms spaced transversely apart with the first and second wall members aligned generally between them.

In a preferred arrangement the said main frame means may comprise a further pair of wall members which together with said first pair of wall members define a compression chamber through which the material is forced by the conveyor means, said further subframe being pivotted to said further wall members. Preferably said further second pivot means is positioned in normal operation downstream of said further first pivot means. Also preferably the first mentioned sub-frame is positioned down stream of the said further sub-frame, and the distance between the pivot axes of the first mentioned first and second pivot means is greater than the distance be- tween the pivot axes of the said further first and second pivot means.

As has been mentioned, the guide means may comprise guide track means along which at least part of each reciprocally movable wall member is constrained to mn. Conveniently the said guide uack means may be mounted on the said main frame means.

The guide track means may comprise a pair of opposed channel-shaped guide members mounted on the main frame means, said main frame means comprising a further pair of wall members which together with the first pair of wall members define a compression chamber through which material is forced by the conveyor means. Conveniently the guide track means comprises a first guide track portion aligned substantially parallel to the path of material being compressed through the apparatus, and a second guide track portion aligned at an angle of inclination to the path of material being compressed through the apparatus. Preferably said second guide track portion is position downstream of said first guide track portion.

Also, as has been mentioned, the guide means may comprise a combination of guide track means and pivotted arm linkage. The guide means may comprise a guide track portion and a pivotted arm linkage portion, both constraining movement of the or each reciprocally mounted wall member, said pivotted arm linkage portion being positioned downstream of said guide track portion.

Preferably the bias of the said biassing means mav be effected by one or more coil springs acting between the said pair of wall members.

The said pair of opposed wall members may comprise bars or plates or other elements constraining the material for compression.

Usually they will be mounted at their upstream ends relative to material flow. Although the said pair of opposed wall members can be side walls of a compression chamber, it is preferred that they constitute top and bottom walls Oc the chamber. It is especially preferred that the first wall member constitutes the top v'all.

The conveying means conveniently is a reciprocating piston pressing material in the downstream direction although other means of forcing material between the pair of wall members can be used.

As mentioned previously, the invention has particular, although not exclusive, application to baling machines and it is preferred therefore that the apparatus of the invention should be incorporated in or be in operative association with a baling machine, especially a straw baling machine.

The following is a description by way example only and with reference to the drawings of embodiments of the invention. In the drawings:- Figure 1 is a side view of a straw baler in accordance with a preferred embodiment of the invention; Figure 2 is a perspective view from above of the baler of Figure 1 with the side walls shortened for clarity; Figure 2(a) is a perspective view of a modification of the baler shown in Figs. 1 and 2; Figure 3 is a view corresponding to Figure 1 of a baler in accordance with another preferred embodiment of the invention; Figure 4 is a view corresponding to Figure 2 of the baler of Figure 3; and Figure 5 is a view corresponding to Figure 2 of a baler in accordance with yet another preferred embodiment of the invention.

Referring first to Figures 1 and 2, a bale chamber 1 has an opposed pair of fixed side walls 2, 3 extending rearwardly of the main frame of a baling machine (not shown) about an orifice through which straw is pushed by a reciprocating piston (not shown). The bale chamber 1 also has top and bottom walls 4, 5 of channel section. The bottom wall 5 is pivoted to the main frame for angular movement in the vertical plane by a rod 6 rotatably received in lugs 7 at respective sides of the chamber 1. The top wall 4 is mounted at its forward end for pivotal movement in the vertical plane and reciprocal movement hori zontal y in the direction of the longitudinal axis of the chamber. The mounting comprises a transverse cross member 8 which protrudes at the respective sides of the top wall 4. The end portions of the cross member 8, are of reduced diameter and are rotatably received in cooperating holes at the upper end of respective arms 9. The outer extremities of the cross member 8 are threaded and receive respective locating nuts 10. The lower end of each arm 9 is pivotally attached to a respective plate 11 secured to the respective side walls 2, 3 by means of a pin 12 extending from the plate 11 and rotatably received in a co-operating hole in the arm 9. The outer end of each pin 12 is threaded and receives a locating nut 13.

The top wall 4 is biased forwardly and downwardly by means of coil springs 14 at respective sides of the bale chamber 1. The springs 14 act between a bracket 15 secured to the respective side walls 2, 3 and a bar 16 threadably received in a hole at the respective end of a further cross member 17 mounted on top wall 4. The other end of the bar 16 is shaped to provide a handle 16 permitting rotation of the bar to adjust the length of, and hence the force applied by, the spring 14.

The top and bottom walls 4, 5 are joined by an arm 18 of adjustable length which is pivoted at its upper end to a cross member 19 mounted on the top wall 4 and at its lower end to a cross member 20 attached to the bottom wall 5. The manner of attachment to the arm 18 of the respective cross member is as described above in connection with the pivotal connection between the forward cross member 8 and the arms 9. The arm 18 is formed of two elongate members 18a, 18b having a plurality of longitudinally spaced holes through which bolts 21 are passed to connect the members together.

In use, straw is pushed by the piston through the orifice of the baler and into the forward end of the bale chamber 1. The partially compressed straw frictionally engages the top wall 4 and thereby urges the wall rearwardly in opposition to the bias of the spring 14. When the sliding resistance of the straw increases, the top wall 4 will be moved rearwardly.

Similarly, when the sliding resistance decreases, the top wall 4 will move forwardly in response to the spring bias. In order to compensate for such changes in resistance the angle of convergance between the top and bottom walls 4, 5 is varied by the arm 18. Thus, when the top wall moves rearwardly said arm operates to increase the vertical distance between the cross-members 19 and 20 and thereby to decrease the degree of convergence of the top and bottom walls. Said movement will reduce the resistance to movement of straw through the bale chamber and thereby compensate for the frictional and/or compressive resistance changes. When the top wall moves forwardly, the arm 18 will reduce the vertical distance between the cross members 19 and 20 and correspondingly reduce the degree of convergence of the top and bottom walls. Said movement will increase the resistance to passage of straw through the bale chamber.

Figure 2(a) shows a perspective view of a modification of the baler shown in Figures 1 and 2. The construction and operation of the baler shown in Figure 2(a) are generally the same as those of the baler shown in Figures 1 and 2, and like reference numerals are used to indicate like elements. The modification lies in the provision in the baler of Figure 2(a) of adjustable rear side links 18 which are adjustable by rotation of upper bolt leads.

Also, the coil springs 14 in Figures 1 and 2 are replaced by double coil springs 14 in Figure 2(a).

Referring now to Figures 3 and 4, apparatus in accordance with a second preferred embodiment differs from that of Figures 1 and 2 in the manner in which the top wall 4 is mounted at its forward end and is biassed forwardly. In particular, the respective ends of the forward cross member 8 bear rollers, which are located in tracks 31 mounted on top of the respective side walls 2, 3 for pivotal and reciprocal movement therein. The intermediate cross member 17 is omitted and the springs 14 are mounted on the rearward cross mem ber 19 to which the arm 18 is pivotally attached. The same reference numerals are used in Figures 3 and 4 as are used to identify corresponding parts in Figures 1 and 2.

The manner of operation of the embodi ment of Figures 3 and 4 is substantially iden tical with that of Figures 1 and 2 and therefore will not be described.

A modification applicable to embodiments of the invention is illustrated, only diagram matically to illustrate general principles, in Figure 5, which is a view corresponding to Figure 2 of a baler in accordance with the invention. The same reference numerals are used in Figure 5 as in the other figures to identify corresponding parts. In this modi- fication the forward cross-member 8 of the top wall 4 has end rollers 30 located in tracks 31 mounted on top of the respective side walls 2, 3. Similarly, the rearward cross < nember 19 has end rollers 50 which are located in tracks 51 mounted on top of the respective side walls 2, 3 and inclined upwardly in the rearward direction. The tracks 31, 51 are mounted for angular adjustment in the vertical plane, for example about pivot points at their upstream ends to vary the change in convergence of the top and bottom walls resultant upon movement along the tracks.

The top wall 4 is biassed forwardly by adjustable tension rubber compression springs 52 acting between a seat at the forward end of respective rods 53 and a fixed member 54.

The rods 53 are secured to and extend forwardly from the cross-member 8 and are slidably received through respective elongated holes in the member 54. Said member 54 extends across the bale chamber 1 and is mounted on the top of the side walls 2, 3.

Operation of the baler of Figure 5 is substantially as described above with reference to Figures 1 and 2 except that the pivotal movement is constrained by the tracks.

All three apparatus described with reference to the drawings, provide a simple and effective manner of compensating for changes in coefficient of friction of straw being compressed in a bale chamber. In particular variations in moisture content are readily compensated for in response to changes in frictional drag on the top wall.

It will be appreciated that the invention is not restricted to the particular details described above with reference to the drawings but that numerous modifications and variations can be made to those details without departing from the scope of the invention.

WHAT WE CLAIM IS:- 1. Apparatus for compressing material comprising main frame means, a pair of spaced apart opposed wall members mounted on the main frame means and relatively movable to vary mutual convergence therebetween, the wall members being adapted to cooperate with conveying means for forcing material between said pair of wall members in the direction of convergence to compress the material therebetween, at least a first one of the said wall members being mounted for longitudinal movement to and fro generally in the direction of material flow in response to changes in sliding resistance between the longitudinally movable member and the material and for pivotal movement to vary the degree of the said mutual convergence, biasing means urging said wall members towards greater convergence and urging said first member in the opposite direction to the direction of material flow, and guide means for constraining angular movement of the wall members relative to each other by an extent dependent upon the position of the first wall member in the direction of material flow in such a manner that movement of the first wall member to or fro in the direction of the material flow causes angular motion to vary the degree of the said mutual convergence to compensate at least in part for the said changes in sliding resistance during compression of material, in which both the first and second wall members are pivotally mounted relative to the main frame means so as to allow in operation substantially equal angular movement of the first and second wall members relative to the main frame means during said variation of mutual convergence.

2. Apparatus according to Claim 1 in which the said biasing means applies a force along a direction relative to the various pivot axes such as to exert a turning effect on the first wall member urging the wall members to greater convergence, and the arrangement being such that in operation movement of the first wall member in the direction of crop moved ment changes the relationships between the direction of the biasing force and the various pivot axes in such a manner as to increase the turning effect of any force applied by the biasing means.

3. Apparatus according to Claim 1 or 2 in which said guide means are arranged to guide relative movement between the wall members in such a manner as to tend to maintain substantially constant the resistance to the passage of material between the wall members.

4. Apparatus according to Claim 1, 2 or 3 in which said apparatus includes conveying means for forcing material between said pair of wall members.

5. Apparatus according to any of Claims 1 to 4 in which said guide means comprises first coupling means coupling said first wall member to said main frame means in such a manner as to allow longitudinal and pivotal movement of the first wall member, a

Claims (25)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   numerous modifications and variations can be made to those details without departing from the scope of the invention.

   WHAT WE CLAIM IS:- 1. Apparatus for compressing material comprising main frame means, a pair of spaced apart opposed wall members mounted on the main frame means and relatively movable to vary mutual convergence therebetween, the wall members being adapted to cooperate with conveying means for forcing material between said pair of wall members in the direction of convergence to compress the material therebetween, at least a first one of the said wall members being mounted for longitudinal movement to and fro generally in the direction of material flow in response to changes in sliding resistance between the longitudinally movable member and the material and for pivotal movement to vary the degree of the said mutual convergence, biasing means urging said wall members towards greater convergence and urging said first member in the opposite direction to the direction of material flow, and guide means for constraining angular movement of the wall members relative to each other by an extent dependent upon the position of the first wall member in the direction of material flow in such a manner that movement of the first wall member to or fro in the direction of the material flow causes angular motion to vary the degree of the said mutual convergence to compensate at least in part for the said changes in sliding resistance during compression of material, in which both the first and second wall members are pivotally mounted relative to the main frame means so as to allow in operation substantially equal angular movement of the first and second wall members relative to the main frame means during said variation of mutual convergence.
2. 2. Apparatus according to Claim 1 in which the said biasing means applies a force along a direction relative to the various pivot axes such as to exert a turning effect on the first wall member urging the wall members to greater convergence, and the arrangement being such that in operation movement of the first wall member in the direction of crop moved ment changes the relationships between the direction of the biasing force and the various pivot axes in such a manner as to increase the turning effect of any force applied by the biasing means.
3. 3. Apparatus according to Claim 1 or 2 in which said guide means are arranged to guide relative movement between the wall members in such a manner as to tend to maintain substantially constant the resistance to the passage of material between the wall members.
4. 4. Apparatus according to Claim 1, 2 or 3 in which said apparatus includes conveying means for forcing material between said pair of wall members.
5. 5. Apparatus according to any of Claims 1 to 4 in which said guide means comprises first coupling means coupling said first wall member to said main frame means in such a manner as to allow longitudinal and pivotal movement of the first wall member, and second coupling means coupling said first and second wall members together in such a manner as to allow angular movement of the wall members relative to each other and also to allow angular movement of both wall members relative to the main frame means.
6. 6. Apparatus according to Claim 5 in which the said second coupling means comprises a first sub-frame which is pivotally connected by first pivot means to the first wall member and is pivotally connected by second pivot means to the second wall members, the pivot axes of the said pivot means being parallel to each other and substantially perpendicular to the direction of material flow to permit movement of the first wall member both pivotally and generally in the direction of the movement of material.
7. 7. Apparatus according to Claim 6 in which said sub-frame comprises a pair of parallel arms spaced transversely apart with the wall members aligned between them.
8. 8. Apparatus according to Claim 6 or 7 in which said second pivot means is positioned in normal operation downstream of said first pivot means.
9. 9. Apparatus according to Claim 6, 7, 8 or 9 in which the first coupling means comprises a further sub-frame which is pivoted to the first wall member by a further first pivot means and which is pivoted to the main frame means by a further second pivot means the pivot axes of the said further pivot means being parallel to one another and generally substantially perpendicular to the direction of material flow to permit movement of first wall member both pivotally and generally in the direction of movement of material.
10. 10. Apparatus according to Claim 9 in which the further sub-frame comprises a further pair of arms spaced transversely apart with the first and second wall members aligned generally between them.
11. 11. Apparatus according to Claim 10 in which the said main frame means comprises a further pair of wall members which together with said first pair of wall members define a compression chamber through which the material is forced by the conveyor means, said further sub-frame being pivoted to said further wall members.
12. 12. Apparatus according to any of Claims 9 to 11 in which said further second pivot means is positioned in normal operation downstream of said further first pivot means.
13. 13. Apparatus according to any of Claims

    9 to 12 in which the first mentioned sub-frame is positioned downstream of the said further sub-frame, and the distance between the pivot axes of the first mentioned first and second pivot means is greater than the distance between the pivot axes of the said further first and second pivot means.
14. 14. Apparatus according to any preceding claim in which the guide means comprises guide track means along which at least part of the first reciprocally movable wall member is constrained to run.
15. 15. Apparatus according to Claim 14 in which the said guide track means are mounted on the said main frame means.
16. 16. Apparatus according to Claim 14 or 15 in which the guide track means comprise a pair of opposed channel-shaped guide members mounted on the main frame means, said main frame means comprising a further pair of wall members which together with the first pair of wall members define a compression chamber through which material is forced by the conveyor means.
17. 17. Apparatus according to Claim 14, 15 or 16 in which said guide track means comprises a first guide track portion aligned substantially parallel to the path of material being compressed through the apparatus, and a second guide track portion aligned at an angle of inclination to the path of material being compressed through the apparatus.
18. 18. Apparatus according to Claim 17 in which said second guide track portion is positioned downstream of said first guide track portion.
19. 19. Apparatus according to any of Claims 14 to 18 in which said guide means comprises a guide track portion, and a pivotted arm linkage portion both constraining movement of the or each reciprocally mounted wall member, said pivotted arm linkage portion being positioned downstream of said guide track portion.
20. 20. Apparatus according to any preceding claim in which said bias is effected by one or more tension or compression springs, acting between the said pair of wall members.
21. 21. Apparatus according to any preceding claim in which said bias is effected by one or more hydraulic rams acting between the said pair of wall members.
22. 22. Apparatus according to any preceding claim in which said bias is effected by pressure accumulator means acting between the said pair of wall members.
23. 23. Apparatus according to any preceding claim in which the conveying means is a reciprocatory piston arranged to compress material by reciprocating along the direction of material travel between the said pair of wall members.
24. 24. Apparatus according to any preceding claim forming part of or in operative association with a baling machine for collecting a crop, compressing the crop and producing tied bales of the crop.
25. 25. Apparatus for compressing material substantially as hereinbefore described with reference to Figures 1 and 2, or Figure 2(a), or Figures 3 and 4, or Figure 5, of the accompanying drawings.