Combing machine and method for operating a combing machine

Description

[0001] The invention relates to a combing machine and a method for operating a combing machine according to the preamble of the independent patent claims.

[0002] In the classic combing process, e.g. according to Heilmann, cotton is pulled from a lap and fed to a pair of grippers by means of a feed roller. When the grippers are retracted, they are closed and hold a front end section of the cotton protruding from the grippers in the form of a fiber tuft. The fiber tuft protruding from the grippers is combed out by the circular comb arranged below the grippers. The grippers are then moved to a front, open position, whereby the tear-off rollers feed a previously combed-out fiber tuft with its rear end section by rotating backwards towards the front end section of the cotton clamped by the grippers. The fiber tuft combed out by the circular comb lies down on this rear end section and is pulled together with it into the clamping point of the tear-off rollers, as the tear-off rollers change direction of rotation again.During this rotation, where the angle of rotation is approximately twice as large as the previous reverse rotation, the fiber tuft is torn from the cotton lying in the nipper unit. The rear end of the torn fiber tuft is pulled through the top comb.

[0003] The detachment rollers perform a piling motion, whereby during a reverse rotation they return an end section of the fiber tuft removed during the previous combing cycle. The beginning section of the fiber tuft is placed on this end section and, after a reversal of rotation, soldered together by the pressure of the two detachment rollers. The detachment rollers must not only change their direction of movement twice during each combing cycle, but also rotate a shorter distance during the return run than during the forward run. A cam disc, cam disk, or cam groove is often used for this movement of the detachment rollers, which are firmly coupled to the pincer movement via a gear system. This back-and-forth piling motion of the detachment rollers, when the adjacent combing heads are geared together and have combing cycle rates of over 400 per minute, places extreme stress on the shafts, leads to significant vibrations in the combing machine, and consumes a lot of energy.The drive motors for the detaching rollers must be very powerful and also require high-performance servo converters to power the motors. The constant acceleration and deceleration results in high power losses, which are reflected in the combing machine's energy consumption and, for combing cycles exceeding 500 per minute, require water cooling of the electric motors. This makes the motors very expensive.

[0004] WO 2013 / 182260 A1 discloses a combing machine with a drive device for generating a pilger-step motion for the detachment rollers of the combing machine. The combing machine comprises a first electric motor rotating with uniform motion and a second electric motor equipped with operating means subject to a unidirectional motion law with acceleration and deceleration phases. Both the first and second motors are engaged at all times and rotate continuously in the same direction. Their rotational movements are combined by means of a differential device to achieve a resulting "pilger-step"-type motion on the detachment rollers.In order to increase the degree of freedom in the design of the movement curve of the detaching rollers and to increase the efficiency of the combing machine, the second electric motor is a servo motor which converts a uniform movement of the first electric motor into a non-uniform rotary movement and which is connected to an electronic control and / or regulating device.

[0005] Based on this known prior art, it is the object of the invention to provide a combing machine and a method for combing out short fibers, with which these disadvantages are reduced.

[0006] The invention is solved by the features of claim 1 and claim 10. Advantageous developments of the invention are defined in the subclaims.

[0007] The invention relates to a combing machine with several combing heads, wherein at least one batt sliver is unwound from a lap roll at each combing head and fed to a feed cylinder and a nipper unit, the noils are combed out of the batt sliver by means of a top and round comb and sucked off, and the resulting fiber web is formed into a fiber sliver by means of a funnel, which is stretched with the other fiber slivers of the other combing heads to form a single fiber sliver.

[0008] The invention includes the technical teaching that a first pair of tear-off rollers and a second pair of tear-off rollers are arranged downstream of the nipper unit, wherein the first pair of tear-off rollers is designed to execute a reciprocating rotary movement for a soldering and tearing process of a fiber tuft to a fiber web, and that the second pair of tear-off rollers is designed to execute a rotary movement in a constant direction of rotation, so that a loop of the fiber web is formed between the pairs of tear-off rollers, which loop changes in length during a combing cycle. The loop forms a material buffer of fiber web, which compensates for the different rotary movement and rotation speed of the pairs of tear-off rollers without destroying the soldered fiber tuft to the fiber web. The loop must be long enough that no tensile stress or stretching occurs on the soldered fiber web. This depends on the feed amount and, among other things,on the diameters of the detachment rollers. This allows the first pair of detachment rollers to maintain the pilger-step motion, thus preserving the classic combing process, including the tongs' movement and gear arrangement. Only the movement and thus the drive of the second pair of detachment rollers is changed, as they have a constant direction of rotation. The motor for the second pair of detachment rollers can be smaller and designed without water cooling, making the combing machine more cost-effective and energy-efficient.

[0009] Accordingly, the combing method according to the invention is designed such that a fiber tuft is torn from the batting band by means of a first pair of tear-off rollers arranged downstream of the nipper unit and soldered to a fiber web by means of a reciprocating rotary movement, wherein a second pair of tear-off rollers following in the fiber transport direction executes a rotary movement in the fiber transport direction in a constant direction of rotation, wherein a loop of the fiber web formed between the pairs of tear-off rollers changes in length during a combing cycle. Due to the different direction of rotation and speed of the pairs of tear-off rollers, a material buffer is created by the formation of a loop, with which a constant direction of rotation of the second pair of tear-off rollers is possible, although the first pair of tear-off rollers continues to execute a pilgrim step movement and thus counteracts the movement of the second pair of tear-off rollers.

[0010] Preferably, the rotational movement of the second pair of take-off rollers is constant throughout all combing cycles. This allows a simpler drive motor, designed as a servomotor with a significantly lower drive power, to be used for the second pair of take-off rollers. Since the resulting forward movement of the tear-off roller pairs must be absolutely identical to avoid consuming the loop size, the drive motors of the first pair of tear-off rollers and the drive motors of the second pair of tear-off rollers must run synchronously. However, the drive motor for the second pair of tear-off rollers can be designed more simply, with lower power and without active cooling.

[0011] Alternatively, the rotational movement of the second pair of break-off rollers can be uneven during a combing cycle while maintaining the same direction of rotation. The second pair of break-off rollers varies their rotational speed while maintaining the same direction of rotation, allowing the loop length between the break-off roller pairs to be kept more constant. This reduces the pulsating formation of the loop in length between a maximum and a minimum.

[0012] Preferably, the loop with its greatest length is formed at a first reversal point of the first pair of tear-off rollers, from which point the pair of tear-off rollers moves the fiber web back towards the nipper unit in the opposite direction to the fiber transport direction.

[0013] Preferably, the loop with its smallest length is formed at a second reversal point of the first pair of tear-off rollers, from which point the pair of tear-off rollers again moves the fiber web away from the gripper unit in the fiber transport direction. The difference in the angle of rotation between the two pairs of tear-off rollers is still large enough that no tensile stress or stretching acts on the fiber web between the two pairs of tear-off rollers.

[0014] In a preferred embodiment, the loop is formed at the beginning of the combing process by stopping the first pair of tear-off rollers and rotating the second pair of tear-off rollers against the fiber transport direction. The uncombed sliver is first guided through the nipper unit to behind the second pair of tear-off rollers and through the funnel to the take-off rollers. Only then can the loop formation be initiated via the combing machine's control system. The uncombed fiber sliver must then be removed according to the uncombed length after the combing machine has started.

[0015] Alternatively, the second pair of tear-off rollers can be stationary or rotate only slowly in the fiber transport direction, while the first pair of tear-off rollers feeds the uncombed lap sliver only in the fiber transport direction until the second pair of tear-off rollers can pick up the lap sliver and the loop is formed. With the direction of rotation remaining constant, the speed difference between the first pair of tear-off rollers and the second pair of tear-off rollers is crucial.

[0016] After the loop formation is completed, the first pair of tear-off rollers conveys the fiber web in the fiber transport direction and the second pair of tear-off rollers, which reverses the direction of rotation, also conveys the fiber web in the fiber transport direction.

[0017] Preferably, the formation and position of the loop can be improved by a device in which the loop is formed between the upper tear-off rollers or between the lower tear-off rollers using an air flow. At a combing speed of over 500 loops per minute, loop formation is a highly dynamic process in which small disturbances, such as fiber adhesion to the tear-off rollers, can interrupt the process or cause the resulting fiber web to become uneven or damaged.

[0018] Further measures improving the invention are described in more detail below together with the description of a preferred embodiment of the invention with reference to the figures.

[0019] They show: Fig. 1 is a schematic side view of a combing head of a combing machine according to the prior art; Fig. 2a is a view of the tear-off roller movement with a movement diagram in an initial position according to the invention; Fig. 2b is a view of the tear-off roller movement with a movement diagram during the formation of a loop or a buffer according to the invention; Fig. 2c is a view of the tear-off roller movement with a movement diagram after the formation of a loop or a buffer according to the invention.

[0020] Below, with reference to the Fig. 1 the state of the art and the Figures 2a to 2c Preferred embodiments of the combing machine according to the invention are explained below. Identical features in the drawings are provided with the same reference numerals. It should be understood that the drawings are merely simplified and, in particular, are not drawn to scale.

[0021] In Figure 12 shows a combing head 20 according to the prior art, of which at least eight are mounted on a combing machine. For reasons of clarity, the exemplary embodiment is shown and described using only one combing head 20, with the details shown being installed on each of these combing heads, except for the common drive units and the sliver deposit. The combing head 20 consists, among other things, of two lap transport rollers 2, 3, on which a lap roll 1 with a winding tube lies and from which the lap sliver 4 is unwound by a tensile load from a feed roller 7. The lap transport rollers 2, 3 can be driven individually or both together. The design of the lap transport rollers 2, 3, whether they are only rotating and not driven, or individually or both driven, is not relevant to the invention.

[0022] The batting sliver 4 is transferred to a feed cylinder 7 of a nipper unit 5. The nipper unit 5 can be moved back and forth via levers and driven via a shaft 6, which is connected to a gear 17. According to the example shown, the nipper unit 5 is in a forward position and transfers the combed-out fiber tuft to a subsequent pair of detaching rollers 10, 12, the first in the fiber transport direction. A circular comb 8 is rotatably mounted below the nipper unit 5, which, via its comb segment, combs out the fiber tuft presented by the closed nipper. The circular comb 8 is also drive-connected to the gear 17. A ratchet wheel (not shown) is attached to the feed cylinder 7. This ratchet wheel is rotated step by step by the back and forth movement of the nipper unit 5 by a pawl (also not shown), thereby feeding the batting sliver 4 to the jaws of the nipper for combing.During operation, the batting sliver 4 is continuously unwound over the lap transport rollers 2, 3 by the rotational movement generated by the batting reel 1 and reaches the feed cylinder 7. The batting is then fed via the feed cylinder 7 to the jaws of the nipper unit 5 for combing and then delivered to the first pair of tear-off rollers 10, 12 in the fiber transport direction. The fiber tuft delivered in this way is finally pulled through the top comb 9 and soldered to the preceding fiber tuft. The resulting fiber web 14 is transferred via a second pair of tear-off rollers 11, 13 in the fiber transport direction. The fiber web 14 created here, which consists of individual soldered pieces of fiber tuft, is pulled through a funnel 15 by means of take-off rollers 16 and formed into a fiber sliver 21. It is then fed to a drafting system (not shown) together with the fiber slivers also formed on the other combing heads.The web emerging from the drafting system is gathered into a fiber sliver, the so-called combing machine sliver, and transferred to a sliver depositor for depositing in a can.

[0023] In this prior art, the nipper unit 5 is moved into a forward, open position, whereby the tear-off rollers 10, 12 convey a previously combed-out fiber tuft with its rear end section by a reverse rotation towards the front end section of the batt clamped by the nippers. The tear-off rollers 11, 13 perform the same movement, so that the fiber web 14 is moved back a short distance. The fiber tuft combed out by the circular comb 8 lies on this rear end section and is pulled together with it into the clamping point of the tear-off rollers 10, 12, since the tear-off rollers 10, 12 and 11, 13 change direction of rotation again. During this rotation, in which the angle of rotation is approximately twice as large as the previous reverse rotation, the fiber tuft is torn away from the batt lying in the nipper unit 5. The rear end of the torn fiber beard is pulled through the top comb 9.The detachment rollers 10, 12, 11, 13 perform a pilgrim-step motion, returning an end piece of the fiber tuft removed during the previous combing cycle during a reverse rotation. The beginning piece of the fiber tuft is placed on this end piece and, after a reversal of rotation, is soldered together by the pressure of the two detachment rollers 10, 12. The detachment rollers 10, 12, 11, 13 must not only change their direction of movement twice during each combing cycle, but must also rotate a shorter distance during the return run than during the forward run.

[0024] Figure 2aThe left-hand illustration shows the initial state of the movement of the detaching rollers 10, 12 and 11, 13 according to the invention, in which the batting sliver 4 clamped by the nipper unit 5 runs into the first pair of detaching rollers 10, 12 in the fiber transport direction (arrow) and is arranged between the pairs of detaching rollers 10, 12 and 11, 13 as a taut fiber web 14. This initial state is initiated once at the beginning or each time the combing machine is started. In the corresponding movement diagram on the right, the angles of rotation of the detaching rollers are entered on the ordinate and the time on the abscissa. By way of example, in the movement diagram the combing machine is operated with a combing cycle rate of 20 per minute, so that one combing cycle lasts 3 seconds. In a value range from 1 to 3, a single combing cycle 30 is carried out completely.This means that in the motion diagram, the rotational movement of the pairs of detachment rollers 10, 12 and 11, 13 during three combing cycles 30 is shown on the abscissa from 0 to 10, and the start of the comber during startup with the formation of the loop 32 or buffer is shown in the range from 0 to 1. With a combing backlash of 500 rpm, the same division of the diagram would show 75 combing cycles over 9 seconds, each with the same curve shape. The movement of the second pair of detachment rollers 11, 13 in the fiber transport direction is shown as a solid line, and the movement of the first pair of detachment rollers 10, 12 is shown as a dashed line. With a value on the abscissa of 0, both pairs of detachment rollers 10, 12 and 11, 13 have a rotation angle of 0°. In this initial state, the tear-off rollers 10, 12 and 11, 13 are stationary.

[0025] Figure 2bshows the formation of a buffer or a loop 32 of the fiber web 14 between the pairs of tear-off rollers 10, 12 and 11, 13. The first pair of tear-off rollers 10, 12 is stationary and does not rotate, while the second pair of tear-off rollers 11, 13 is rotated back by an angle of approximately -150° in this illustration, so that a loop 32 with a length over the distance between the tear-off rollers 10, 12 and 11, 13 to each other of a total of 60 mm is formed. In this embodiment of the Figure 2bAt a rotation angle of 150°, the currently formed loop 32 has a length of approximately 33 mm. This position shown is at a value of 0.5 s in the movement diagram. The size of the loop 32 depends on the rotation angle of the detachment rollers 11, 13 and their diameter and can vary depending on the combing machine type. The setting via the size of the return travel of the detachment rollers 11, 13, i.e. the amount by which the second pair of detachment rollers 11, 13 is turned back, also depends on the feed amount set on the nipper unit 5 and can therefore vary. In this exemplary embodiment, the outer diameters of the lower rollers 10, 11 are approximately 25 mm and the outer diameters of the upper rollers 12, 13 are approximately 24.5 mm. Only the tear-off rollers 10 and 11 are driven, whereas the tear-off rollers 12 and 13 are pressed onto the lower tear-off rollers 10 and 11 and run along with them due to friction.

[0026] In the Figure 2cthe buffer or loop 32 is almost completely formed from the fiber web 14. At this point in time, it is sufficient to start the combing process. When the detachment rollers 11, 13 return by 270°, the loop 32 can be up to 60 mm and can therefore sag between the detachment rollers 10, 12 and 11, 13 in the form shown. The loop 32 then grows in length briefly and reaches its maximum in the difference in angle of rotation between the reversal point U1 of the detachment rollers 10, 12 and the continuous rotation of the detachment rollers 11, 13. The arrow in the movement diagram shows exactly the reversal point of the rotational movement of the detachment rollers 11, 13 or the starting point of the renewed rotational movement of the detachment rollers 10, 12, which are still stationary at this point in time but now resume the rotational movement.The loop 32 of the fiber web 14 serves to compensate for the different rotational directions of the tear-off roller pairs 10, 12 and 11, 13, i.e., in particular, the return movement of the first pair of tear-off rollers 10, 12 for tearing and subsequently soldering the fiber tuft against the fiber transport direction. As can be seen from the motion diagram, the first pair of tear-off rollers 10, 12 continue to perform the classic pilgrim step motion according to the prior art, whereas the second pair of tear-off rollers 11, 13, after reversing the direction, perform a linear rotational movement that can be constant in speed.

[0027] The rotational movement of the detachment rollers 10, 12 from the abscissa value 1 s up to the reversal point U1 is in the fiber transport direction (arrow), i.e., towards the detachment rollers 11, 13, so that the batting sliver 4 is pulled through the detachment rollers 10, 12 and the soldered fiber tuft is compacted. From the reversal point U1, the rotational direction of the detachment rollers 10, 12 reverses against the fiber transport direction, so that the combed-out end of the fiber tuft, or in this illustration the batting sliver 4, is conveyed to the nipper unit 5 to start a new soldering process. The rotational movement of the detachment rollers 10, 12 back is almost 270° and reduces the loop 32 or the buffer, so that the fiber web 14 is arranged almost straight between the detachment rollers 10, 12 and 11, 13. The reversal point U2 shows this, since the distance in the movement curve of the diagram between the tear-off rollers 10, 12 and 11, 13 is minimal.After the reversal point U2, the tear-off rollers 10, 12 rotate again so that the fiber web 14 is conveyed in the fiber transport direction (arrow) and the loop 32 increases in size again until the end of the combing cycle 30, during which the fiber tuft is soldered and then torn off from the nipper unit 5. With the rotation angle differences 31, which are represented by vertical arrows between the curves of the tear-off rollers 10, 12 and the tear-off rollers 11, 13, the size or length of the loop 32 is represented by means of the outer circumference of the tear-off rollers 10, 11. It can be seen in this motion diagram that the tear-off rollers 10, 12 with the steep curves experience very high acceleration and deceleration, thus constantly changing their speed and direction of rotation (pilgrim step). In this embodiment, the tear-off rollers 11, 13 rotate in only one direction at a constant speed during the combing process.Only when the combing machine is started, during combing, do the tear-off rollers 11, 13 rotate backwards to form the first loop 32.

[0028] It is possible to operate the tear-off rollers 11, 13 at a non-uniform speed while maintaining a constant direction of rotation. During the return travel of the tear-off rollers 10, 12 between the reversal points U1 and U2, the tear-off rollers 11, 13 can rotate more slowly, and from the reversal point U2 onward, they can rotate more quickly again. Ultimately, however, the embodiment disclosed here is the more energy-efficient form for operating the tear-off rollers 11, 13.

[0029] The Figures 2b and 2cThe loop 32 or buffer of the fiber web 14 shown here hangs down between the tear-off rollers 10 and 11. Depending on the air flow, the loop 32 can also form between the tear-off rollers 12 and 13. Air blowing from above or below between the pairs of tear-off rollers 10, 12 and 11, 13 can promote loop formation, since the distances between the pairs of tear-off rollers 10, 12 and 11, 13 are very small.

[0030] The invention has the advantage that only a first pair of detachment rollers 10, 12 performs the pilgrim step motion, while the second pair of detachment rollers 11, 13 performs a constant rotational motion. The power loss for driving the second pair of detachment rollers 11, 13 is thus reduced, thereby lowering the energy consumption of the combing machine. For the second pair of detachment rollers 11, 13, water cooling of the drive motors can be eliminated, and the drive motor can be designed with a significantly lower drive power.

[0031] To prevent loop 32 from being built up or reduced as a material buffer, both tear-off roller pairs 10, 12 and 11, 13 must perform the same resulting forward movement, i.e., the same resulting angle of rotation. Depending on the design of the combing machine, loop 32 can also be made smaller than in this example. This can be influenced by the spacing between the tear-off roller pairs 10, 12 and 11, 13, their diameter, the feed amount, and other factors.

[0032] According to the invention, after the loop 32 has been formed, the second tear-off roller pair 11, 13 rotates in the same direction, i.e., a constant rotational movement. This rotational movement can preferably have the same speed (constant, consistent rotational movement), which achieves the greatest effect in terms of energy savings. However, the rotational movement of the second tear-off roller pair 11, 13 can also vary in speed, which can positively influence loop formation and make the resulting fiber web 14 more uniform. Reference symbol

[0033] 1Cotton roll 2Roll transport roller 3Roll transport roller 4Cotton band 5Tong unit 6Shaft 7Feed cylinder 8Circular comb 9Fixing comb 10Tear-off roller 11Tear-off roller 12Tear-off roller 13Tear-off roller 14Fiber pile 15Funnel 16Take-off rollers 17Gearbox 18Motor 19Control system 20Combing head 21Fiber band 30Combing cycle 31Torsion angle difference 32Loop U1Turning point U2Turning point

Claims

1. Combing machine having a plurality of combing heads (20), wherein at each combing head (20) at least one lap sliver (4) is unwound from a lap roll (1) and supplied to a feed cylinder (7) and a nipper unit (5), the noils are combed out of the lap sliver (4) by means of a top comb and a circular comb (9, 8) and are extracted by suction, and the resulting fibre web is shaped by means of a funnel (15) into a fibre sliver which is drawn with the other fibre slivers of the other combing heads to form a single fibre sliver, wherein there are arranged downstream of the nipper unit (5) a first pair of detaching rolls (10, 12) and a second pair of detaching rolls (11, 13), wherein the first pair of detaching rolls (10, 12) is configured to perform a reciprocating rotational movement for a process of piecing a fibre tuft onto and detaching it from a fibre web (14), characterized in that the second pair of detaching rolls (11, 13) is configured to perform a rotational movement in a uniform direction of rotation so that a loop (32) of the fibre web (14) forms between the pairs of detaching rolls (10, 12 and 11, 13), the length of which loop changes during a combing cycle.

2. Combing machine according to claim 1, characterised in that the second pair of detaching rolls (11, 13) is configured to convey the fibre web (14) with a constant uniform rotational movement.

3. Combing machine according to claim 1, characterised in that the first pair of detaching rolls (10, 11) is configured to form the loop (32) with its greatest length at a reversal point (U1), after which the pair of detaching rolls (10, 12) moves the fibre web (14) contrary to the fibre transport direction towards the nipper unit (5) again.

4. Combing machine according to claim 1, characterised in that the first pair of detaching rolls (10, 11) is configured to form the loop (32) with its smallest length at a reversal point (U2), after which the pair of detaching rolls (10, 12) moves the fibre web (14) in the fibre transport direction again away from the nipper unit (5).

5. Combing machine according to claim 1, characterised in that, at the beginning of the combing process, the first pair of detaching rolls (10, 12) is stationary and the second pair of detaching rolls (11, 13) performs a rotational movement contrary to the fibre transport direction, so that a loop (32) forms between the pairs of detaching rolls (10, 12 and 11, 13).

6. Combing machine according to claim 5, characterised in that, when loop formation is complete, the first pair of detaching rolls (10, 12) is configured to convey the fibre web (14) in the fibre transport direction and the second pair of detaching rolls (11, 13) is configured to reverse its direction of rotation and convey the fibre web (14) in the fibre transport direction.

7. Combing machine according to claim 1, characterised in that the second pair of detaching rolls (11, 13) is configured to be operated in a uniform direction of rotation with a different rotational speed, or speed.

8. Combing machine according to claim 1, characterised in that each pair of detaching rolls (10, 12; 11, 13) is driven by means of a separate servomotor, wherein the servomotors are synchronised in order to generate an identical resulting forward movement.

9. Combing machine according to any one of claims 1 to 8, characterised in that, by means of a device for supplying air between the pairs of detaching rolls (10, 12 and 11, 13), the loop (32) is formed between the detaching rolls (10, 11) or between the detaching rolls (12, 13).

10. Method for combing a lap sliver (4) by means of a combing machine having a plurality of combing heads (20), wherein at each combing head (20) a lap sliver (4) is unwound from a lap roll (1) and supplied to a feed cylinder (7) and a nipper unit (5), noils are combed out of the lap sliver (4) by means of a top comb and a circular comb (9, 8) and are extracted by suction, and the resulting fibre web (14) is shaped by means of a funnel (15) into a fibre sliver (21), wherein there are arranged downstream of the nipper unit (5) a first pair of detaching rolls (10, 12) and a second pair of detaching rolls (11, 13), wherein the first pair of detaching rolls (10, 12), by means of a reciprocating rotational movement, detaches a fibre tuft from the lap sliver (4) and pieces it onto a fibre web (14), characterised in that the second pair of detaching rolls (11, 13) performs a rotational movement in a uniform direction of rotation in the fibre transport direction, wherein the length of a loop (32) of the fibre web (14) formed between the pairs of detaching rolls (10, 12 and 11, 13) changes during a combing cycle.

11. Method for combing according to claim 10, characterised in that the rotational movement of the second pair of detaching rolls (11, 13) is constant over all the combing cycles (30).

12. Method for combing according to claim 10, characterised in that the rotational movement of the second pair of detaching rolls (11, 13) during a combing cycle (30) is non-uniform.

13. Method for combing according to claim 10, characterised in that the loop (32) is formed with its greatest length at a reversal point (U1) of the first pair of detaching rolls (10, 11), after which the pair of detaching rolls (10, 12) moves the fibre web (14) contrary to the fibre transport direction towards the nipper unit (5) again.

14. Method for combing according to claim 10, characterised in that the loop (32) is formed with its smallest length at a reversal point (U2) of the first pair of detaching rolls (10, 11), after which the pair of detaching rolls (10, 12) moves the fibre web (14) in the fibre transport direction again away from the nipper unit (5).

15. Method for combing according to claim 10, characterised in that the loop (32) is formed at the beginning of the combing process in that the first pair of detaching rolls (10, 12) is stationary and the second pair of detaching rolls (11, 13) performs a rotational movement contrary to the fibre transport direction.

16. Method for combing according to claim 14, characterised in that, when loop formation is complete, the first pair of detaching rolls (10, 12) conveys the fibre web (14) in the fibre transport direction and the second pair of detaching rolls (11, 13) reverses its direction of rotation and conveys the fibre web (14) in the fibre transport direction.

17. Method for combing according to any one of the preceding claims, characterised in that the loop (32) is formed between the detaching rolls (10, 11) or between the detaching rolls (12, 13) by means of an air flow.