GB2479974A - Apparatus for compensating for thermally induced nip changes between a clothed cylinder and a neighbouring roll - Google Patents

Abstract

Apparatus on a flat or roller card having a clothed cylinder (4) and a clothed neighbouring roll (5), for example a doffer or licker-in, which co-operate with a working nip (a) at the fibre transfer points, comprises a side member (18a) on each side of the cylinder and fixed on a framework, and a displacement device (26) for the neighbouring roll (5) to set the working nip. To keep the working nip substantially constant the side member (18a, 18b) is coupled to the displacement device (26) by at least one force transmission device (21). A temperature change induced expansion or contraction of the side member (18a) is transmitted via the force transmission device to the displacement device to displace the roll (5) to keep the nip substantially constant. The displacement device may comprise a lever arm (26) pivoted (25) on the frame (24) or a linear slide, Figure 4. The displacement of the roll (5) may be greater than the expansion of the side member by selection of the point of action of the force transmitter (21) on the lever arm or by making the force transmitter from material of higher coefficient of thermal expansion than the side member. Alternatively hydraulic or peltier effect enhanced forced transmitters may be utilised, Figures 6a, 6b and 7.

Description

Apparatus on a flat card or roller card having a clothed cylinder and at least one neighbouring roll The invention relates to an apparatus on a flat card or roller card having a clothed cylinder and at least one clothed neighbouring roll, for example doffer and/or licker-in.

In known cards the licker-in co-operates with the clothed cylinder, and the clothed cylinder co-operates with the doffer, in each case, with a small spacing between their cylindrical surfaces (working nip) at the fibre transfer points, and there is a side member (side screen) arranged on each side of the cylinder and mounted in fixed position on a framework, there being provided a displacement device for the neighbouring roll in order to set a prescribed working nip using a setting device.

In modern high performance carding machines, heating of the components and the associated change in the spacing of the components plays an increasingly important role.

The same is also true of the spacing between the cylinder and the doffer. In order to be able to achieve good quality at a maximum production rate, that spacing must be kept as constant as possible. The continual increase in the production rates of new generations of carding machine also results, however, in more significant differences between the roll nip set when the machine is cold and the roll nip in the warm state. For example, in the field of polyester processing it can sometimes happen that the cold setting required to provide an optimum roll nip when the machine is warm is so large that it is scarcely possible to start spinning properly. In addition, the technological result during the "warm-up phase" is significantly inferior to that when the machine is fully warmed up.

During carding, increasingly large amounts of fibre material are processed per unit of time, which requires higher working component speeds and higher installed performances. The increasing throughput of fibre material (production rate), even when the working surface area remains constant, results in increased generation of heat as a result of the mechanical work. At the same time, however, the technological carding result (sliver uniform-ity, degree of cleaning, nep reduction etc.) is constantly being improved, which requires a greater number of effective surfaces in carding engagement and narrower settings of those effective surfaces, for example fixed flats and/or revolving flats, with respect to the cylinder (tambour) . The proportion of synthetic fibres being processed, which -compared with cotton -generate more heat as a result of friction when in contact with the effective surfaces (clothings) of the machine, is continually increasing. The working components of high performance carding machines are nowadays totally enclosed on all sides in order to conform to the high safety standards, to prevent the emission of particles into the spinning room environment and to minimise the need for servicing of the machines. Grids or even open, material-guiding surfaces allowing exchange of air are largely a thing of the past. The said circumstances markedly increase the input of heat into the machine, while the discharge of heat by means of convection is markedly reduced. The resulting more intense heating of high performance carding machines leads to greater thermo-elastic deformation which, on account of the non-uniform distribution of the temperature field, affects the set spacings of the effective surfaces: the spacings between cylinder and flat, doffer, fixed flats and separation sites become smaller. In an extreme case, the set gap between the effective surfaces can be completely consumed by thermal expansion, so that components moving relative to one another collide, resulting in considerable damage to the affected high performance carding machine.

Accordingly, particularly the generation of heat in the working zone of the carding machine can lead to different degrees of thermal expansion when the temperature differ-ences between the components are too great.

Carding gaps and roll nips on a carding machine are extraordinarily important. The carding quality stands or falls with the exact setting of those gaps (roll nips) Under the action of heat, the rolls expand and the gaps change. In addition to expansion of the rolls caused by centrifugal force, which greatly change the gaps, a high production rate and carding-intensive synthetic fibres additionally give rise to intense heating of the rolls.

Thermally induced changes in the dimensions of the rolls occur. In order to achieve optimum carding quality it is necessary for the roll nips to remain constant during operation. !vConstant!v means in this context that the change in spacing should be preferably less than 0.01 mm.

In a known apparatus (EP 1 300 494 B), a delivery module comprises a support and a feed module comprises a support. The rotational axis of the doffer is fixedly arranged in the associated support and the rotational axis of the licker-in is fixedly arranged in the associated support. The supports each have a pivot axis which joins the respective support to a base plate of the framework.

Each support is able to pivot about the respective axis between a readiness position and a working position. In the working position of the feed module, the licker-in has a prescribed spacing (working nip) at the transfer position relative to the cylinder, while in the working position of the delivery module the doffer has its prescribed spacing (working nip) at the transfer position relative to the cylinder. The adjustment of a module about the respective pivot axis is effected by lever action between the axis and a respective setting location spaced apart from the pivot axis. At each setting location there is an adjusting mechanism (setting device), for example a screw. Any kind of adjustable elements can be provided between the support and a stationary stop on the machine framework. The support structure for the cylinder consists of the afore-mentioned base plate and extends from side to side over the entire working width. A pair of support legs is mounted at each end and each pair of legs carries a respective bearing panel which accommodates the bearings for the cylinder shaft. In this apparatus, a prescribed working nip between the cylinder and the doffer or the licker-in is set once only using the adjusting mechanism (setting device) prior to operation and is retained during operation. The working nip in the cold state is set to be slightly larger and decreases in size to the desired dimension as the temperature of the cylinder and the neighbouring roll increases. A disadvantage is that in the cold state of the machine the working nip is too large and reaches the desired value only on warming up. When the carding machine has to run up from stationary in order to process a certain batch of fibre tufts, the temperatures of the different parts of the machine change continually over a certain period until finally a constant or steady state (operating temperature) is achieved. The "transient" period of those temperature changes is much longer than the run-up period itself. A thermal balance is achieved, for example, only after from 1 to 5 hours. This has the result that the quality of the card sliver in the warm-up phase is relatively poor. In addition, the manufacturing process must be extremely precise. The working nip set is accordingly different in the cold state and in the heated state of the machine. That difference becomes increasingly apparent when different fibre materials are processed, for example cotton or synthetic fibres.

It is an aim of the invention to provide an apparatus of the kind described at the beginning which avoids or mitigates the mentioned disadvantages, which is especially simple in structural terms and which enables the working nip between the neighbouring rolls to be kept substantially constant in any state of operation.

The present invention provides an apparatus on a flat card or roller card having a clothed cylinder and at least one clothed neighbouring roll to or from which fibre material is transferred, which co-operate with one another to define a working nip between their cylindrical surfaces at the location of fibre transfer, and further having a side member arranged on each side of the cylinder and mounted in fixed position on a framework, the apparatus comprising a displacement device for the neighbouring roll, and at least one force transmission means, the side member of the cylinder being coupled to the displacement device by means of said at least one force transmission means, whereby in the event of a change in the temperature of the side member the neighbouring roll is so displaceable during operation that the working nip is kept substantially constant.

As a result of the measures taken according to the invention it is possible, in a structurally simple way, to maintain constant roll nips in carding machines under the action of heat. According to the invention, a displacement device operable by a force transmission means, for example a mechanical coupling, is provided for the neighbouring roll in order to keep the working nip between cylinder and, for example, doffer constant in the event of varying operating conditions. Unlike the known apparatus, the pre-scribed working nip set using the setting device can be retained during operation or in the event of changes in temperature. A further advantage is that (electronic) control measures for adapting to changes in the working nip are avoided, such measures being associated with considerable outlay in terms of equipment and cost.

The neighbouring roll may be, for example, a doffer or a licker-in. The following explanation refers to a doffer as the neighbouring roll, but may be applicable also mutatis mutandis to the case where the neighbouring roll is another roll, especially a licker-in.

By skilful arrangement of the doffer linkage and a compensation element, the invention enables the working nip to be kept as constant as possible. For that purpose, the doffer is accommodated on the carding machine framework in a pivot point. By rotation about that point, the spacing between the centre points of the cylinder and the doffer are changed. The positioning element is linked to the aluminium side screen of the cylinder. Aluminium has a higher thermal expansion coefficient than steel. As a result of the heating of the cylinder and thus also of the side screen, the positioning element and thus also the doffer are pushed away from the cylinder, thereby compens-ating for the increased proximity of the rolls to one another caused by the thermal expansion. Furthermore, that effect can be intensified or weakened by reducing or increasing the distance (leverage) of the positioning element from the pivot point. A further possible way of influencing the intensity of the compensation is to vary the material from which the positioning element is made and therefore the thermal expansion coefficient thereof.

Advantageously, the heat of the cylinder acts on the side screen. Advantageously, the side screen of the cylinder is made of aluminium or an aluminium alloy.

Preferably, the side screen of the cylinder is mechanically coupled to the displacement device.

Advantageously, the side member of the cylinder is force-coupled to the displacement device. Preferably, the side member of the cylinder is coupled to the side member of the neighbouring roll. Preferably, the side member of the cylinder is coupled by means of a spindle or the like to the adjusting device. Preferably, the spindle is a threaded spindle.

Advantageously, the neighbouring roll is mounted so as to be pivotable relative to the fixed cylinder about a fixed pivot point (pivot bearing) . Preferably, the pivot point (pivot bearing) is arranged on the machine framework or on the side screen. Preferably, the neighbouring roll is articulated on the fixed pivot point by means of a rotatable lever element (pivot arm) Advantageously, the force transmission means is articulated on the displacement device or on the pivot bearing. Preferably, the force transmission means, for example rod, spindle or the like, is articulated on the rotatable lever element (lever arm) Advantageously, the neighbouring roll is mounted so as to be displaceable relative to the fixed cylinder.

Advantageously, the rotatable lever element (lever arm) is suspended on the force transmission means. Preferably, the force transmission means is mounted on the side member of the cylinder and on the repositioning device for the neighbouring roll.

Advantageously, the working nip is kept substantially constant by arrangement of doffer and/or licker-in linkage and a compensation element. Advantageously, the force transmission element is linked to the aluminium side screen of the cylinder. Preferably, the cylinder is made of steel.

Advantageously, the distance between the force transmission means articulated on the lever and the pivot point can be reduced or increased. Advantageously, the side screen of the cylinder and the force transmission means are made of different materials. The force transmission means may be made of, for example, steel or aluminium. Advantageously, the thermal expansion coefficient of the material for the force transmission means is greater than that for the side screen of the cylinder. Advantageously, on at least one side of the carding machine the side screen of the cylinder is coupled to the displacement device by means of a force transmission means. Preferably, there is additionally associated with the force transmission means a means for supplying and/or removing thermal energy and the additional means comprises a container, housing or the like having a cylinder piston.

Advantageously, a thermally expansible and contractable medium, for example oil, is associated with the cylinder piston. Preferably, the heat of the side member of the cylinder acts on the oil. Advantageously, the container, the housing or the like is associated with, especially fastened to, the outer side of a side member of the cylinder. Preferably, the additional means is a Peltier element and is associated with the force transmission means.

The invention also provides an apparatus on a flat card or roller card having a clothed cylinder and at least one clothed neighbouring roll, for example doffer and/or licker-in, which co-operate with one another with a small spacing between their cylindrical surfaces (working nip) at the fibre transfer points, having a side member (side screen) arranged on each side of the cylinder and mounted in fixed position on a framework, and having a displacement device for the neighbouring roll in order to set a prescribed working nip using a setting device, wherein the side member of the cylinder is coupled to the displacement device for the neighbouring roll by means of at least one force transmission means and in the event of a change in the temperature of the side member the neighbouring roll is displaceable during operation so that the working nip is kept substantially constant.

Certain embodiments of the invention are described in greater detail below with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic side view of a carding machine which may include an apparatus according to the invention; -10 -Fig. 2 is a side view of a part of a carding cylinder and doffer of a carding machine including an apparatus according to the invention, showing a detail of the respective side screens of the cylinder and the doffer, which are joined by a threaded spindle, the doffer with the associated side screen being able to pivot about a pivot bearing; Fig. 3 is a side view of an apparatus according to a first embodiment of the invention having a carding cylinder with a pivotally mounted doffer, a force transmission means being articulated on the side screen of the cylinder and on the lever element of a pivot bearing; Fig. 4 is a side view of a carding cylinder and a doffer mounted displacably in accordance with a second embodiment of the invention; Fig.5a is a diagrammatic side view of a further embodiment having a carding machine framework on which the side screen of the cylinder is mounted in fixed position and the side screen of the doffer is pivotally mounted; -11 -Fig. 5b shows a diagrammatic section I -I through a side screen of the cylinder and a side screen of the doffer, as well as the coupling of the two side screens by means of a spindle on one side of the carding machine and a corresponding view on the other side; Fig. 6a shows a fluid cylinder (hydraulic force transmission means); Fig. 6b shows the attachment of the housing of the fluid cylinder according to Fig. 6a to the outer surface of the side screen of the cylinder as an additional force trans-mission means; Fig. 7 shows a metal tube as a constituent of the force transmission means, with which, in addition, a Peltier element is associated, and Fig. 8 is a diagrammatic side view of the changes in the diameter of the cylinder and of the doffer in the event of an increase in temp-erature.

With reference to Fig. 1, a carding machine, for example a flat card IC (trademark), made by Trdtzschler GmbH & Co.KG of Manchengladbach, Germany, has a feed roll 1, feed table 2, lickers-in 3a, 3b, 3c, cylinder 4, doffer 5, stripper roll 6, nip rolls 7, 8, web guide element 9, -12 -sliver funnel 10, delivery rolls 11, 12, revolving card top 13 with card top guide rolls 13a, 13b and card flats 14, can 15 and coiler 16. The directions of rotation of the rolls are indicated by curved arrows. Reference letter M denotes the centre point (axis) of the cylinder 4, M2 the centre point of the doffer 5 and M3 the centre point of the licker-in 3c. Reference numeral 4a denotes the clothing and reference numeral 4b the direction of rotation of the cylinder 4. Reference numeral 5a denotes the clothing and 5b the direction of rotation of the dotter 5. Reference letter C denotes the direction of rotation of the revolving card top 13 in the carding position and reference letter C denotes the return transport direction of the card flats 14, with 17', 17'' denoting fixed functional elements. The arrow A indicates the working direction.

In the embodiment of the invention shown in Fig. 2, a side screen 18a of the cylinder 4 and a side screen 19a of the dotter 5 are coupled to one another by means of a threaded spindle 21a (setting spindle) . The threaded spindle 21a is supported by its one end on a flange 22a, stop or the like of the side screen 18a and by its other end on a flange 23a, stop or the like of the side screen 19a. The threaded spindle 21a has a screw thread at each of its two ends, with which nuts are associated, and the flanges 22a and 23a each have through-bores through which the screw threads of the screw spindle 21a pass. A fixed machine framework 24 is provided (see Fig. 5a) on which the fixed side screen 18a is fixedly mounted. The cylinder 4 is likewise in fixed position. In addition, on the machine framework 24 there is mounted in fixed position a pivot bearing 25 about which the doffer 5 and the -13 -associated side screen 18a are able to pivot in the direction of arrows H, I (see Fig. 3) In the embodiment of Fig. 3, the doffer is mounted so as to pivot about a fixed pivot point (pivot bearing 25) on the framework 24 of the machine. The pivot arm 26 of the doffer 5 is linked to one end of a spindle 21, metal bar or the like. The linkage can be effected, for example, by means of a spherical washer, ball cup or the like (not shown) . The other end of the spindle is attached to the side screen 18a by means of the fastening element 22a.

When the side screen 18a expands in the radial direction as a result of heating, the spindle 21 is displaced by substantially the same amount in the direction of arrow D and thus turns the pivot arm 26 about the pivot point 25 in the direction of arrow H. At the same time, the doffer 5 (and therewith the side screen 19a, see Fig. 2) is pivoted by the same amount about the pivot point 25 in the direction of arrow H. In that way, the spacing a between the tips of the clothing 4a of the cylinder 4 and the clothing 5a of the doffer 5 remains constant or largely constant. In a corresponding way, the doffer 5 is pivoted about the pivot point 25 in the direction of arrow I when the side screen 18a contracts in the radial direction as a result of cooling. The spacing a remains constant or largely constant. In each case, the cylinder 4 and the side screen 18a remain in fixed position.

The cylinder 4 and the doffer 5 are provided on their cylindrical surface with pointed clothing 4a and 5a, respectively. For the transfer of the fibres from the cylinder 4 to the doffer 5, crucial importance is attached to the spacing a between the cylindrical surfaces of the two rolls, in addition to other parameters, such as, for -14 -example, the surface speed of the two rolls and the nature of the pointed clothing. Good working ratios between the rolls can be ensured only when the spacing a is kept within exact and very narrow tolerances. In such an arrangement, in the case of roll diameters of about from 0.20 m to 1.5 m and roll widths of up to about 2 m the optimum value for the spacing a lies in a range of about 0.05 mm < a < 0.3 mm, the lower limit of the spacing a not being a technological requirement but being maintained only in order to avoid mutual contact or interference between the clothing tips of the two rolls. There is otherwise a risk of fire and mechanical damage to the expensive pointed clothings. The spacing a is therefore extremely small in comparison with the dimensions of the rolls. The increase in diameter brought about by the rise in roll temperature is, as has been established by experiments, of the order of about 0.08 mm per 10°C rise in temperature. By means of the apparatus according to the invention, an optimum value of the spacing a and of the doffer 5 set in the cold state of the carding machine can be retained during operation.

In the embodiment of Fig. 4, a stationary framework 24 of a flat card or roller card is provided in the form of a frame having four supports (only two are shown) and having two horizontal longitudinal bars (only one is shown) . The two longitudinal bars and the supports are joined together by crossbars (not shown) to form a stable, rigid supporting frame for two rotating rolls 4 and 5 which are equipped with pointed clothing and operate with a small spacing a between them. The cylinder 4 is mounted in fixed position and so as to be rotatable about an axis M1 by means of two supporting elements 26 (of which only -15 -one is shown in Fig. 4), which are screwed tightly to the longitudinal bars by means of screws 25a, 25b, and is driven and rotated in the clockwise direction 4b by means of devices not shown. The cylinder 4 carries pointed clothing 4a on its cylindrical surface. The doffer 5 is likewise mounted so as to be rotatable about its axis N2 by means of two supporting elements 27 (only one is shown) on the longitudinal bars 22 of the framework 20. The supporting elements 27 are not screwed tightly to the longitudinal bars, however, but are guided in such a way that they are displaceable parallel to the axis by a small amount of the order of 1 to 2 mm. By parallel displacement of the supporting elements 27, in the direction of the arrows N, N the spacing between the cylindrical surfaces or clothings 4a and 5a of the rolls 4 and 5 can therefore be kept constant. For that purpose, a spindle 28 couples the supporting element 27 (which contains the rotational bearing for the doffer 5) to a stop 22a on the fixed side screen 18a of the cylinder 4.

In Fig. 5a, a fixed carding machine framework 24 is provided, to which the side screen 18a of the cylinder is attached in fixed position. In addition, the side screen 19a of the doffer 5 and the side screen 20a of the licker-in 3c (not shown in Fig. 5a) are pivotally mounted on the carding machine framework 24 (machine framework) Fig. Sb shows a portion of the cylinder 4 with a cylindrical surface 4f of its wall 4e and cylinder ends 4c, 4d (radial supporting elements) . The surface 4f is provided with a clothing 4a, which in this example is provided in the form of wire with sawteeth. The sawtooth wire is drawn onto the cylinder 4, that is to say is wound around the cylinder 4 in tightly adjacent turns between -16 -side flanges (not shown), in order to form a cylindrical working surface provided with points. Fibres should be processed as evenly as possible on the working surface (clothing) . The doffer 5 (only part of which is shown) is in axially parallel association with the cylinder 4. The spacing between the clothings 4a and 5a is indicated by reference letter a. The transfer of fibres is effected between the clothings 4a and 5a located opposite one another. It is substantially influenced by the position of one clothing with respect to the other and by the clothing spacing a between the tips of the teeth of the two clothings 4a and 5a. The working width L of the cylinder 4 and of the doffer 5 is, for example, 1300 mm or more. The cylinder 4 can, however, become deformed as a result of the drawing-on of the clothing wire, as a result of centrifugal force or as a result of heating caused by the carding process. The journals of the cylinder 4 are mounted in bearings 29a, 29b, which are mounted on the fixed machine framework 24 (see Fig. 5a) . The diameter, for example 1250 mm, of the cylindrical surface 4f, that is to say twice the radius r, is an important dimension of the machine. The side screens 18a, 18b are attached to the machine framework 24. The flanges 22a and 22b are attached to the side screens 18a and 18b, respectively.

The circumferential speed of the cylinder 4 is, for example, 35 m/sec. The side screens 18a and 18b of the cylinder 4 are mechanically coupled by means of spindles 21a and 21b to the side screens 19a and 19b, respectively, of the doffer 5.

Fig. 6a shows a cylinder/piston arrangement suitable for use on certain embodiments of the invention, a fluid 44 having a high volumetric expansion coefficient is -17 -located in a leak-proof container 40. A piston 42, which is spring-loaded, for example by two compression springs 41a, 41b, and has a piston rod 21a, is used for biasing the fluid 44 (overpressure) . When heated, the fluid 44 expands. The projecting piston rod 21a moves outwards.

Connected to a pivotally mounted roll 5, the latter moves away from the cylinder 4 which is mounted in fixed position. When the fluid 44 cools, the process takes place in reverse. The necessary energy for heating the fluid 44 or for withdrawing heat from the fluid 44 is implemented by the side screen 18a to which the container 40 is attached (see Fig. 6b) . The piston rod 21a has, for example, a thread, so that initial setting can be carried out. By the correct choice of fluid, piston surface area, spring-bias and fluid volume, the apparatus is adaptable in respect of adjustment force and adjustment travel. The housing 40 is divided into a housing part 40a in which the compression springs 41a, 41b are located and a housing part 40b in which the hydraulic oil is located. The piston rod 21a and the piston 42 are displaceable in the direction of arrow G in the event of thermal expansion. It should be emphasised that, in the event of a change in the temperature of the side screen 18a, the attachment of the container 40 to the side screen 18a results in a displacement (not sliding) of the piston rod 21a in the direction F or G and thus to a displacement of the side screen 19a with the doffer 5. As a result, the side screen 19a of the doffer 5 is, for example, pivoted (for example as shown in Fig. 2 or Sb) . The hydraulic fluid cylinder 45 shown in Fig. 6a, 6b forms an additional force transmission means. In this embodiment, the apparatus according to the invention and the additional force -18 -transmission means 45 form a combination.

In an embodiment illustrated in Fig. 7, the spindle 21a is in the form of a metal tube. The expandable or contractable body of the spindle 21a is preferably made of a material having a high thermal expansion coefficient and at the same time high strength (for example aluminium) The body shown in Fig. 7 is an aluminium tube (of thermal expansion coefficient = 23.8 10-6 [1/°K]) . Being in the form of a hollow body (tube), the body has as little mass as possible in order that it can be heated and cooled as quickly as possible. Furthermore, it is insulated so that it is not able to give up the supplied heat to the environment. The insulation 30 can be effected externally, for example by means of a foam rubber tube. The connection sites to the surrounding components of the machine, unlike the body of the spindle 21a, are made of a material having a low thermal expansion coefficient in order to withdraw as little heat as possible from the body and likewise to insulate the spindle 21a. Here (low) alloyed steel, for example, is suitable. A Peltier element 46 requires a flat surface for mounting. If a round tube as in Fig. 7 is used, it is necessary to attach an intermediate piece 47 (Peltier attachment) to the tube (for example using heat-conductive adhesive or screws) in order to obtain a flat surface. It is also possible to configure the body of the spindle 21a directly with a flat surface, for example in the form of an extruded aluminium profile. A cooling body 48 is adhesively bonded directly to the Peltier element 46; it can also be attached by clamping. In this arrange-ment, an apparatus according to the invention and the embodiment shown in Fig. 7 having a Peltier element 46 additionally associated with the force transmission means -19 -form a combination. The Peltier element 46 can effect both cooling and heating. This enables additional thermal energy to be supplied and withdrawn in a way that responds very flexibly and quickly to changes in the state of the cylinder 4 and a neighbouring roll (for example doffer 5a or licker-in 3c) In Fig. 8, the diameter of the cylinder 4 in the non-deformed state, for example before start-up of the carding machine at room temperature, is indicated by reference letter D, while the diameter of the cylinder 4 in the state in which it has been deformed by the action of temperature is indicated by D + AD. As a result of the increase in diameter AD, the prescribed working nip a would in the said state be reduced to a spacing a -As a result of the displacement of the neighbouring roll, for example of the doffer 5, in accordance with the invention, that reduction is at least largely compensated.

It can then be the case that the diameter d of the doffer increases to a value d + Ad as a result of heating. The processing of, for example, synthetic fibres is associated with the generation of a considerable amount of heat. The directions of the increases in diameter of the cylinder 4 (or the expansion of the side screen 18a) and of the increase in diameter of the doffer 5 are opposite to one another in the region of the working nip a. In that case, the displacement of the doffer 5 may not be sufficient to keep the prescribed working nip a constant in the event of changes in the cylinder 4 and the doffer 5. Here it can be advantageous for the displacement of the doffer 5 to be increased, for example by an amount Ad. Measures taken to effect such an increase in the displacement of the doffer away from the cylinder 4 can include: a change of the -20 -point of action of the force transmission means on the lever arm, a material for the force transmission means having a higher thermal expansion coefficient than for the side screen 18a, an additional hydraulic force trans-mission means (see Fig. 6a, 6b) or a heating and/or cooling device, for example a Peltier element (see Fig. 7), additionally associated with the force trans-mission means.

The apparatus according to the invention can be used for a working width of the cylinder 4 and the neighbouring roll, for example doffer 5 and licker-in 3c, of 1000 mm or more, as well as for lower working widths.