Method and machine for tamping a track

Abstract

The invention relates to a method and machine for tamping multiple sleepers (4) of a track (3) laid successively in a ballast bed (2) by means of a tamping assembly (7), comprising multiple independently height-adjustable tamping units (14) arranged successively in a working direction (25) and having tamping tines (22) that can be provided relative to one another, wherein, during a tamping cycle, the tamping tines (22) of a front tamping unit (14) and the tamping tines (22) of a rear tamping unit (14) are lowered into the ballast bed (2) to different depths (Ti, T2, T3), wherein the tamping assembly (7) is moved onwards for the next tamping cycle in the working direction and by a number of sleepers (4) that is lower than the number of successively arranged tamping units (14). In this way, the successively arranged tamping units (14) tamp the same sleeper (4) multiple times in different depth zones (Ζ1, Z2, Z3) of the ballast bed (2).

Description

Technical field

[0001] The invention relates to a method for tamping several sleepers of a track laid one behind the other in a ballast bed using a tamping unit comprising several tamping units arranged one behind the other in a working direction and independently height-adjustable, with tamping picks that can be adjusted relative to one another. The invention also relates to a machine for carrying out the method. State of the art

[0002] To restore or maintain a specific track alignment, ballasted tracks are regularly treated with a tamping machine. The tamping machine travels along the track and raises the track bed, consisting of sleepers and rails, to a target level using a lifting / aligning unit. The new track alignment is then fixed by tamping under the sleepers with a tamping unit. This unit comprises tamping tools with tamping picks, which, during the tamping process, vibrate and are drawn into the ballast bed, aligning themselves with each other. This process pushes the ballast under each sleeper and compacts it.

[0003] Track tamping machines, in particular, utilize tamping units to simultaneously tamp multiple sleepers. The resulting high processing speed allows for the complete tamping of a track during short track closures. Modern tamping machines are also characterized by low wear on both the tamping unit and the ballast.

[0004] From AT 513 034 A1, a method and a generic machine with at least two tamping units arranged one behind the other are known. Each tamping unit is height-adjustable and arranged in a common mounting bracket. A tamping cycle begins with the simultaneous lowering of the tamping units. This simultaneous lowering of adjacent tamping units for tamping sleepers adjacent in the longitudinal direction of the machine occurs with a time delay. This particularly facilitates the insertion of immediately adjacent tamping picks into a common sleeper compartment. Such a device is also known from DE 1985337U or DE 952644C. Description of the invention

[0005] The invention is based on the objective of improving a method of the type mentioned above in such a way that high-quality tamping results are achieved, particularly when the track is raised significantly and when it is being relaid. A further objective of the invention is to provide a correspondingly improved machine.

[0006] According to the invention, these problems are solved by the features of claims 1 and 9. . Dependent claims specify advantageous embodiments of the invention.

[0007] The system is designed so that during a tamping cycle, the tamping picks of a front tamping unit and the tamping picks of a rear tamping unit are lowered to different depths in the ballast bed. For the next tamping cycle, the tamping unit is advanced in the working direction by a number of sleepers that is less than the number of tamping units arranged in series. In this way, the tamping units arranged in series repeatedly tamp the same sleeper at different depths within the ballast bed. The result is homogeneous compaction of the entire ballast layer beneath the respective sleeper.

[0008] A sleeper-by-sleeper approach results in a more uniform compaction process. Furthermore, the ballast load is reduced because a different ballast layer is dynamically compressed in each tamping cycle. This prevents hollow sections, especially in cases of significant track elevation. Since only one tamping pass is required even for larger elevation changes, time is saved by eliminating the need for reversing and repeated ramp formation required for separate tamping operations.

[0009] When more than two tamping units are arranged in series, it is advantageous to specify approximately uniformly graduated immersion depths. Furthermore, it is beneficial if the tamping picks of the leading tamping unit are lowered into the gravel bed to a greater immersion depth than the tamping picks of the unit behind it.

[0010] According to the invention, the sleepers and the rails attached to them of the track are lifted by means of a lifting unit before tamping, with the respective immersion depth being predetermined depending on a lifting value. A change in the lifting value leads to a change in the gradation of immersion depths in order to achieve optimized compaction of the ballast bed.

[0011] A further improvement involves operating each of the tamping units arranged in series with its own vibration parameters for applying vibration to the tamping picks and / or its own positioning parameters for the positioning movement of the tamping picks. Specifically, a separate vibration frequency, vibration amplitude, and positioning time can be defined for each tamping unit. The tamping picks of each of the tamping units arranged in series are thus set into vibration and positioned relative to each other independently. This takes into account the different properties of the gravel in the individual bedding layers and the varying pick counterforces resulting from the different immersion depths.

[0012] To fix a raised track section in its position over a large area, it is advantageous to tamp several sleepers positioned directly behind one another simultaneously using multiple tamping units during a tamping cycle. This is achieved by having adjacent tamping picks from tamping units arranged directly behind one another plunge into the same sleeper bay. A compact multi-sleeper tamping unit (in-line unit) with tamping units that are narrow in the longitudinal direction of the machine is used for this purpose.

[0013] In a further development of this method, several tamping units arranged in immediate succession are lowered sequentially during a tamping cycle. The tamping picks entering the same sleeper bay thus do not strike the ballast surface simultaneously. One tamping pick penetrates the ballast bed first, setting the surrounding ballast grains into vibration. The tamping pick lowered after a delay then encounters the already mobilized ballast grains, significantly reducing the penetration resistance. This reduces wear on both the tamping units and the ballast grains.

[0014] Advantageously, during a tamping cycle, at least two sleepers positioned one behind the other are tamped in two layers of the ballast bed at different depths by lowering the tamping picks of a rear tamping unit to a first immersion depth and by lowering the tamping picks of a front tamping unit to a second immersion depth.

[0015] One variant involves assigning different immersion depths to all tamping units arranged in series. This results in tamping in more than two different depth zones of the gravel bed when more than two tamping units are arranged in series. This variant is particularly useful in loose gravel beds and with high heave rates.

[0016] Another variant involves tamping units arranged in series forming a lowering group, which are lowered to a common immersion depth. Each lowering group compacts the ballast layers under several sleepers simultaneously in the same depth zone of the ballast bed. For example, two lowering groups, each with two tamping units arranged in series, are used. Tamping then takes place in two depth zones, with the tamping unit advancing two sleepers after each tamping cycle.

[0017] For multiple tamping operations on each sleeper with small gradations in depth zones, it is advantageous if the tamping unit is advanced by one sleeper division after each tamping cycle using a drive mechanism. In this way, the ballast layer under each sleeper is tamped in successive steps by each of the tamping units arranged in succession.

[0018] A machine according to the invention comprises a tamping unit for simultaneously tamping several sleepers of a track positioned one behind the other by means of several tamping units arranged one behind the other with respect to a longitudinal direction of the machine. Each tamping unit includes a tool carrier that is height-adjustable by means of a height-adjusting drive, on which opposing tamping tools are mounted. These tamping tools can be set into vibration by means of drives and can be positioned relative to each other. The machine is configured to carry out one of the described methods such that all height-adjusting drives are connected to a common control unit and that different lowering values ​​are stored in the control unit for the height-adjusting drives of the tamping units arranged one behind the other. Thus, the tamping operations of the tamping units arranged one behind the other are coordinated by means of the control unit.

[0019] Advantageously, each height actuator is coupled with a displacement measuring device connected to the control unit. Each displacement measuring device provides a position signal for the height of an associated tool carrier, allowing the lowering to a predefined immersion depth to be controlled. In a simpler version, the different lowering values ​​are stored as graduated activation time intervals for the height actuators. For hydraulic height actuators, the flow rate of a hydraulic fluid can also be used as a measure for the lowering of the associated tool carrier.

[0020] A further improvement involves assigning a vibration drive to each tamping unit and coupling opposing tamping tools to their assigned vibration drive via auxiliary drives. In particular, each vibration drive can be controlled separately, allowing each tamping unit to operate with its own vibration frequency and amplitude.

[0021] Furthermore, it is advantageous if each of the tamping units arranged in series has its own pressure stage of a hydraulic pressure system for actuating the auxiliary drives. In this way, the actuation process of each tamping unit can be adapted to the depth zone of the ballast bed being worked.

[0022] Advantageously, several tamping tools arranged side-by-side, transverse to the machine's longitudinal direction, along with their associated auxiliary drives, form an auxiliary group, with each auxiliary group being controllable uniformly via the control unit. This applies to the tamping units arranged side-by-side, which tamp a sleeper on both sides of the track's rails. During operation, the auxiliary groups are controlled together to ensure a uniform compaction process along a sleeper.

[0023] According to the invention, a lifting unit is arranged upstream of the tamping unit, wherein a lifting value predetermined for the lifting unit is supplied to the control device of the tamping unit. In this way, the lowering values ​​can be adapted to the currently predetermined lifting value. Brief description of the drawings

[0024] The invention is explained below by way of example with reference to the accompanying figures. These show, in schematic representation: Fig. 1 Machine with tamping unit Fig. 2 Tamping unit for simultaneously tamping three sleepers in side view Fig. 3 Tamping process with tamping unit according to Fig. 2 Fig. 4 Tamping unit in front view Fig. 5 Tamping process with tamping unit for simultaneously tamping four sleepers Fig. 6 Tamping process with tamping zone profile according to the prior art Fig. 7 Tamping process with tamping zones of different depths Description of the embodiments

[0025] The in Fig. 1 The machine 1 shown is designed as a track tamping machine for the simultaneous tamping of three sleepers 4 embedded in a ballast bed 2 of a track 3. The machine 1 comprises a machine frame 6 supported on rail bogies 5, on which a tamping unit 7 is mounted. The machine 1 also includes a lifting / aligning unit 8 for lifting and aligning the track grid formed from sleepers 4 and rails 9. A measuring system 10 records the current rail position.

[0026] The tamping unit 7 is attached to the machine frame 6 by means of an adjusting device 11. It comprises a unit frame 12 with guides 13 and several tamping units 14, as shown in Fig. 2 The following is shown. In a variant not shown, each tamping unit 14 is assigned its own aggregate frame 12. Each tamping unit 14 comprises a tool carrier 15, which is mounted on the associated guides 13 in a height-adjustable manner by means of a height adjustment drive 16. On the respective tool carrier 15, opposing tamping tools 18 are pivotably mounted in a machine longitudinal direction 17.

[0027] Furthermore, a vibration drive 19 is arranged on each tool carrier 15, to which the tamping tools 17 are coupled via auxiliary drives 20. In an alternative embodiment (not shown), a hydraulic cylinder is arranged between the tool carrier 15 and the respective tamping tool 17, which is configured as both a vibration drive 19 and an auxiliary drive 20. The hydraulic cylinder is pressurized with pulsating hydraulic pressure to generate the vibration. During an auxiliary operation, the pulsating hydraulic pressure superimposed on the auxiliary pressure generated by the hydraulic cylinder.

[0028] Each tamping tool 18 comprises a pivoting lever 21 with an upper and a lower lever arm. The pivoting lever 21 is mounted on the associated tool carrier 15, with the upper lever arm connected to the associated auxiliary drive 20. Two tamping picks 22 are usually attached to the free lower lever arm.

[0029] The height actuators 16 can be controlled by means of a common control unit 23, in which different lowering values ​​for the individual tamping units 14 are stored. A displacement measuring device 24 is assigned to each height actuator 16 to detect the height position of the respective tool carrier 15. This device comprises, for example, a cable with a cable pull sensor. Alternatively or additionally, position detection is integrated into the height actuator 16, for example, as displacement measurement of a piston in a hydraulic cylinder.

[0030] During a tamping cycle, the height actuators 16 are controlled by the control unit 23 based on the different lowering values. For example, the respective lowering value specifies how long a control valve of the height actuator 16, designed as a hydraulic cylinder, is open. A piston stroke of the corresponding hydraulic cylinder or a distance to be achieved between the tool carrier 15 and the machine frame 6 can also be defined as a lowering value.

[0031] Furthermore, it is advantageous to establish a control loop for each specified lowering value. The control unit 23 generates a control signal for the respective height actuator 16. The resulting position of the tool carrier 15 or the tamping pick 22 is continuously recorded by the displacement measuring device 24 and compared with the specified lowering value.

[0032] In a further development step, the resistance of the tamping picks 22 upon contact with the ballast bed 2 is recorded. For this purpose, each tamping unit 14 is equipped with appropriate sensors. For example, an acceleration sensor is arranged on each tamping tool 18. The downward stroke of each tamping pick 22 from the point of contact with the ballast bed 2 is derived from the recorded acceleration. This directly yields the corresponding immersion depth T1, T2, T3, based on a common height reference R. In addition to a predefined upper limit of the ballast bed 2, the height of the individual tamping units 14 in their raised position can serve as a height reference R.

[0033] A tamping cycle is divided into several phases. In a first phase, the tamping unit 7 is positioned over the sleepers 4 to be tamped. Specifically, the tamping picks 22 are positioned over the sleeper bays located between the sleepers 4. In a second phase, the tool carriers 15 with the tamping tools 18 attached to them are lowered. During this process, the vibrating tamping picks 22 penetrate the ballast bed 2. According to the invention, the tamping units 14 arranged one behind the other are given staggered lowering values, so that the corresponding tamping pick ends reach different immersion depths T1, T2, T3, as shown in Fig. 3 depicted.

[0034] During a third phase, the tamping picks 22 of the opposing tamping tools 18 are aligned. Depending on the immersion depth T1, T2, T3, different depth zones Z1, Z2, Z3 of the ballast bed 2 are compacted. The extent of each depth zone Z1, Z2, Z3 is determined by the dimensions of the pick plates arranged at the ends of the tamping picks. Specifically, the pick plates transfer the kinetic energy of the tamping tools 18 to the ballast grains located in the respective depth zone Z1, Z2, Z3. This causes the ballast grains to vibrate and assume a fluid-like state. The result is a denser packing and a displacement of the ballast grains beneath the respective sleeper 4.

[0035] The height of the respective ballast plate is sensibly taken into account when determining the immersion depths T1, T2, and T3. The resulting depth zones Z1, Z2, and Z3 are defined such that the lowest depth zone, Z3, reaches the lower boundary of a loose ballast layer. The height of this loose ballast layer depends on the condition of the track (new or existing), the amount of new ballast, and the degree of track bed lift. The minimum immersion depth, T1, is chosen so that the uppermost depth zone, Z1, extends below the associated sleeper.

[0036] In a fourth phase of the tamping cycle, the tamping picks 22 are retracted by means of the auxiliary drives 20 and pulled out of the ballast bed 2 by raising the tool carriers 15. As soon as the tamping picks 22 are raised above the top of the sleepers, the tamping unit 7 is moved forward in a working direction 25 and a new tamping cycle begins.

[0037] In Fig. 3 Three consecutive tamping cycles are shown, each at the end of the third phase. During the first tamping cycle in the upper image, three thresholds 4 are tamped sequentially in different depth zones Z1, Z2, and Z3, shown in hatched areas. The front tamping unit 14 is lowered to the lowest depth zone Z3. The middle tamping unit 14 tampers the middle depth zone Z2, and the rear tamping unit 14 tampers the uppermost depth zone Z1, which is located directly below the threshold 4.

[0038] For the next tamping cycle in the middle image, the tamping unit 7 is moved forward by one sleeper increment t in the working direction 25. The middle tamping unit 14 then tamps under the sleeper 4, which was previously tamped by the front tamping unit 14. Thus, the ballast bed 2 under this sleeper 4, after having been processed in the lowest depth zone Z 3, is now processed in the middle depth zone Z 2. The rear tamping unit 14 then tamps the corresponding sleeper 4 in the third, uppermost depth zone Z 1. Beneath all sleepers 4 that have already been completely tamped, there is a compaction zone V, which is formed by the three superimposed depth zones Z 1 - Z 3.

[0039] The respective compaction range V thus results from the specified different immersion depths T 1 - T 3, which result from the lowering values ​​for the individual tamping units 14 stored in the control device 23.

[0040] In the exemplary version in Fig. 4 It is evident that each rail 9 of track 3 is assigned two separately lowerable tamping units 14. Thus, the tamping assembly 7 comprises four tamping units 14 arranged side by side in each row. In a simplified variant not shown, each rail 9 is assigned a combined tamping unit 14 with tamping tools 18 on the inside of the rail and tamping tools 18 on the outside of the rail. The tamping units 14 arranged side by side in a row are provided for tamping under a sleeper 4. These tamping units 14 form auxiliary groups whose tamping picks 22 are lowered to a common immersion depth T1, T2, T3 and positioned together.

[0041] Fig. 5 Figure 1 shows a tamping process with four tamping units 14 arranged in series. Two front tamping units 14, or rows, are combined to form a front lowering group 26, and two rear tamping units 14, or rows, are combined to form a rear lowering group 26. Both lowering groups 26 are lowered to different tamping depths T1 and T2 during a tamping cycle. The front lowering group 26 works the ballast bed 2 in a lower depth zone Z2. The upper depth zone Z1, located directly under the sleepers 4, is worked by the rear lowering group 26.

[0042] After an initial tamping cycle in the upper image, the tamping unit is moved forward by two sleeper divisions t. Thus, here too, the number of sleepers 4 by which the tamping unit 7 is moved in the working direction 25 is less than the number of tamping units 14 arranged in series. For forward movement in the working direction 25, the machine 1 includes a drive 27, which is controlled by a machine control 28. Advantageously, the machine control 28 is coupled with the control device 23 to automatically coordinate the lifting and lowering movements of the tamping units 14 and the forward movement of the tamping unit 7.

[0043] In the lower image of the Fig. 5 The subsequent tamping cycle is shown at the end of the third phase. The rear lowering group 26 completes the compaction in the compaction zones V below the corresponding sleepers 4. The front lowering group 26 begins the tamping of two further sleepers 4 in the lower depth zone T 2. This process combines zone-by-zone tamping with an increased processing speed due to the cyclical forward movement by twice the sleeper spacing t.

[0044] In an alternative method, it can be advantageous to reduce the cyclical forward movement to a sleeper spacing t and to provide four more finely graduated immersion depths. This variant is advantageous in the case of large track surface heaves or new track laying with a relatively loose ballast bed 2. In this way, high-quality compaction of a compaction zone V with a large vertical extent is achieved.

[0045] In a further development of the method according to the invention, the different immersion depths T1-T3 are specified depending on a lifting value. The lifting value is also supplied to the control unit 23 of the tamping unit 7 for controlling the lifting / aligning unit 8. In an alternative embodiment, a current actual lifting value is recorded by means of the measuring system 10 and reported to the control unit 23.

[0046] For example, for immersion depths T1-T3, larger increments are chosen for higher lift values ​​in order to increase the compaction range V in the vertical direction. In particular, the formation of lowering groups 26 depending on the specified lift value is useful. For example, the lift value determines which of the two methods described above is used with the tamping unit 7 for the simultaneous tamping of four sleepers 4. Either two immersion depths T1 and T2 are specified for two lowering groups 26, or four more finely graduated immersion depths are specified.

[0047] A conventional tamping process with a tamping unit for the simultaneous under-tamping of three sleepers 4 is in Fig. 6 As shown, according to the state of the art, all tamping picks 22 are lowered to a common immersion depth T and positioned in a depth zone. Then the tamping unit 7 is moved forward by three sleeper divisions t. Thus, after one pass, all sleepers 4 are only tamped once.

[0048] A so-called multiple tamping method is also known, in which the tamping picks 22 are lowered and positioned in the same sleeper bays two or more times before proceeding to the next sleepers 4. In this method as well, the tamping picks 22 always operate in the same depth zone, without affecting the size of the compaction area V.

[0049] In contrast, in Fig. 7A method according to the invention is illustrated. Here, different, approximately uniformly graduated immersion depths T1-T3 are provided. Each sleeper 4 is tamped successively in three different depth zones Z1-Z3. The sleeper 4 under the foremost tamping unit 14 is first tamped in the deepest zone Z3. Two sleeper divisions t opposite the working direction 25, the final compaction takes place under the corresponding sleeper 4. In this way, a ramp-like, graduated structure of the compaction zones V is created over three sleepers 4. The height of the compaction zone V is significantly greater than in a conventional method. Furthermore, the uniform compaction profile results in a particularly homogeneous and stable ballast bed 2 and a durable track alignment.

[0050] In addition, the compaction energy is adapted to the respective bedding layer. Advantageously, each tamping unit 14 is operated with its own vibration and pressure parameters. A deeper bedding layer, for example, is subjected to greater vibration energy because the risk of lateral displacement of the ballast is lower. Furthermore, a higher pressure may be beneficial because there is greater counter-pressure in the deeper layer. In any case, the compaction processes taking place across several sleepers 4 in different depth zones T1-T3 are coordinated with one another. Thus, the method according to the invention results in a uniform compaction of the ballast bed 2 both vertically and in the working direction 25.

Claims

1. A method for tamping a plurality of sleepers (4) of a track (3) positioned one behind the other and supported in a ballast bed (2) by means of a tamping unit (7) comprising a plurality of tamping unit segments (14) arranged one behind the other in a direction of work (25) that are independently adjustable of each other in height and have tamping tines (22) that can be squeezed towards each other, wherein during a tamping cycle, the tamping tines (22) of a front tamping unit segment (14) and the tamping tines (22) of a rear tamping unit segment (14) are lowered into the ballast bed (2) at different penetration depths (T1, T2, T3) and the tamping unit (7), in order to start a next tamping cycle, is moved further in the direction of work (25) by a number of sleepers (4) which is less than the number of tamping unit segments (14) arranged one behind the other, characterised in that the sleepers (4) and rails (9) of the track (3) fixed thereon are lifted by means of a lifting unit (8) before tamping and the respective penetration depth (T1, T2, T3) is predefined in relation to a lifting value.

2. A method according to claim 1, characterised in that each of the tamping unit segments (14) arranged one behind the other is operated with separate vibration parameters for an application of vibration to the tamping tines (22) and / or separate squeezing parameters for a squeezing movement of the tamping tines (22).

3. A method according to claim 1 or 2, characterised in that a plurality of sleepers (4) positioned directly one behind the other is tamped simultaneously during a tamping cycle by means of a plurality of tamping unit segments (14), with adjacent tamping tines (22) of tamping unit segments (14) arranged directly one behind the other penetrating the same sleeper crib.

4. A method according to one of the claims 1 to 3, characterised in that a plurality of tamping unit segments (14) arranged directly one behind the other is lowered at staggered intervals during a tamping cycle.

5. A method according to one of the claims 1 to 4, characterised in that, during a tamping cycle, at least two sleepers (4) positioned one behind the other are tamped in two layers of the ballast bed (2) having different depths by lowering the tamping tines (22) of a rear tamping unit segment (14) to a first penetration depth (T1) and by lowering the tamping tines (22) of a front tamping unit segment (14) to a second penetration depth (T2).

6. A method according to one of the claims 1 to 5, characterised in that different penetration depths (T1, T2, T3) are predefined for all tamping unit segments (14) arranged one behind the other.

7. A method according to one of the claims 1 to 5, characterised in that tamping unit segments (14) arranged one behind the other form a lowering group (26) that is lowered to a common penetration depth (T1, T2, T3).

8. A method according to one of the claims 1 to 7, characterised in that, after a tamping cycle, the tamping unit (7) is moved forward by one sleeper spacing (t) by means of a traction drive (27).

9. A machine (1) with a tamping unit (7) for the simultaneous tamping of a plurality of sleepers (4) of a track (3) positioned one behind the other by means of a plurality of tamping unit segments (14) arranged one behind the other in a longitudinal direction of the machine (17), each tamping unit segment (14) comprising a tamping tool carrier (15) adjustable in height by means of a height-adjustment drive (16), with opposing tamping tools (18) being mounted on the tamping tool carrier which can be set in vibration via drives and can be squeezed towards each other, characterised in that the machine (1) is adapted to carry out a method according to one of the claims 1 to 8 in such a way that all height-adjustment drives (18) are connected with a shared control equipment (23), that different lowering values are stored in the control equipment (23) for the height-adjustment drives (16) of the tamping unit segments (14) arranged one behind the other, and that a lifting unit (8) is arranged upstream of the tamping unit (7), and a lifting value that is predefined for the lifting unit (8) is fed into the control equipment (23) of the tamping unit (7).

10. A machine (1) according to claim 9, characterised in that each height-adjustment drive (18) is coupled to a distance measuring equipment (24), and each distance measuring equipment (24) is connected to the control equipment (23).

11. A machine (1) according to claim 9 or 10, characterised in that a vibration drive (19) is assigned to each tamping unit segment (14), and that opposing tamping tools (18) are each coupled to the associated vibration drive (19) via squeezing drives (20).

12. A machine (1) according to one of the claims 9 to 11, characterised in that each of the tamping unit segments (14) arranged one behind the other is assigned a separate pressure stage of a hydraulic pressure system for the application to the squeezing drives (20).

13. A machine (1) according to one of the claims 9 to 12, characterised in that several tamping tools (18) arranged next to each other crosswise to the longitudinal direction of the machine (17), together with the associated squeezing drives (20), form a squeezing group that can be actuated by means of the control equipment (23).

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