WEB TAKE-OFF FOR A CARDING MACHINE

Abstract: A web take-off device, particularly for use at the doffer (10) of a card, for transferring the web (16) on the doffer (10) to the sliver delivery rollers (24, 26) at which the web (16) has the form of a sliver, the sliver delivery rollers (24, 26) possibly being preceded by a trumpet (22), characterised by a detaching device (28) which operates continually at least at creep speed and is arranged immediately adjacent the doffer (10) to transfer the web (16) preferably directly to a means which forms a sliver, the means possibly including a trumpet (22). The detaching device is preferably in the form of a separation roller (30) provided with longitudinal grooves (38) and generates pulse-like air flows which assist the separation.

Description: Web Take-Off for a Carding Machine The present invention relates to a web take-off device, in particular for use at the doffer roll of a card for transfer of the fibre web on the doffer roll to the sliver delivery rollers at which the fibre web has the form of a sliver. A condenser trumpet may be provided upstream from the sliver delivery rollers. The invention also relates to a method for transferring the fibre web on the doffer roll of a card to the fibre sliver delivery rollers. A web take-off device of this kind is known from several specifications. For example, in a very old British patent specification 9854 from the year 1843 a web take-off device is described comprising a hollow tube with arms on its outer periphery: The device has to be driven at a high speed. The tube should thereby collect air from its open ends and should distribute this air through holes in the tube wall into a space formed by an outer tube or an outer casting within which the tube with the arms rotates. The air stream is blown out through an opening or a slit along the tube over the full width of the doffer roll and should release the fibre web without requiring the cooperation of the usual hacker or doffer comb. The extreme edges of the arms can possibly act on the outer cotton fibres in order to reinforce the function. It is not known whether the device suggested in the old British specification was ever used in practice. In any event, in the course of further developments of cards and web take-off devices for cards, doffing combs were used over a long period, for example as referred to in US Patent 2,364,50 of Jan 11 , 1881 and as seen in US patent specification 3,196,492 from the year 1962. As described in this specification, the fibre web is transferred to a guide plate after the doffing comb, and the guide plate is specially formed so that it guides the fibre web released by the doffing comb from the doffer roller into a trumpet provided at one side of the card. The doffing comb comprises a reciprocable element, that is an element which operates in discontinuous manner. Such devices were firmly established in the practice of carding at relatively low operating speeds. A doffer comb of this kind is also integrated into the web take-off device according to US PS 5,432,981 of 18. July 1995. In that case, a web take-off device is proposed in which a roller provided with teeth cooperates with the doffer roller of a card in order to release or separate the fibre web from the doffer roller and to transfer it to a collecting belt which feeds the fibre web further: The belt can represent a condensing device. In order to ensure the function of this arrangement, a doffer comb is suggested which co¬ operates with the toothed roll at low speeds and ensures the separation of the fibre web from the toothed roller. Accordingly, the removal roller is a roller having a clothing provided with special teeth. The patent specification explains that the web take-off device of the kind proposed therein is designed to operate both at high operating speeds and also at low operating speeds during running up of the card. A relatively complex arrangement has been accepted in order to ensure the function over a wide range of speeds. Thus, a toothed roller is required and is to be fitted with a special clothing. Such clothings are relatively expensive and require precise adjustment. In order to achieve the required function of the toothed roller, and to prevent the fibre web released from the doffer roller forming a lap on the toothed roller at low delivery speeds, the reciprocable doffer comb must be provided and this represents a relatively expensive component. The control of the web take-off device with various modes of operation in dependence on the speed with which the web take-off device operates represents a considerable control expenditure. Finally, a collecting belt arrangement is also required, which at the same time is to have a convergent formation and can only be realised with relatively expensive means. French Patent of Addition 81598 (Addition to French Patent 1 301 384) describes very briefly an arrangement in which a pulsed air flow is to be used to release the web from the doffer roller. It is not at all clear how the arrangement would operate in practice. The web appears to be totally unsupported on its side facing away from the air stream but a rotating smooth roll is provided to contact the web on the face acted on by the pulsed air flow. In one embodiment, a nozzle blows air into a narrow gap between the smooth roll and the doffer, while in another embodiment the web leaves the doffer almost at a tangent and is drawn upwardly against the underside of the smooth roll. The French specification is directed to many other aspects of a carding machine and provides no indication of the performance of the delivery section. Especially there is no indication as to how the web is condensed to a sliver. The object of the present invention is to deal with some of the above problems and to provide a web take-off device which operates reliably, in particular at creep speed, that is during running up of the card. The web take-off device preferably comprises few, relatively inexpensive components and preferably does not require considerable control expense. It should furthermore be assured that the fibre web is transferred reliably to the sliver delivery rollers without any special risk of the fibre web catching in the web take-off device or forming a lap thereon. In order to achieve this object by means of a device, it is proposed that a web detaching device is disposed immediately adjacent the doffer roll in order to release the fibre web from the doffer roll. The detaching device preferably operates continually at least at creep speed. The detaching device preferably transfers the fibre web immediately to a means adapted to form a sliver. The sliver-forming means can possibly include the trumpet which is normally provided before the sliver delivery rollers. The detaching device preferably comprises a separating or detaching roller which is provided with grooves. The grooves, which in the region of the doffer roll are moving in the opposite direction relative to the doffer roller, act pneumatically and possibly mechanically on the fibre being transported on the clothing of the doffer roller in the region of the detaching device. The detaching device thus releases the fibre web from the doffer roller and transfers it to the sliver-forming means. The detaching device preferably comprises a fan which either replaces or supplements the grooved roller in order to create or to reinforce the pneumatic action on the fibre web in the region of the detaching device. The detaching device is preferably provided (at least in the region of the doffer roller) with a casing which cooperates with the grooves and which converts the air carried along with those grooves into an air stream which separates the fibre web pneumatically from the doffer roller. This air stream can operate in particular in a pulse¬ like fashion. On the side of the detaching device running towards the doffer roller, the casing preferably forms a converging gap with the detaching device, that is it forms a condenser which in the region of the doffer roller increases the speed of flow of the air dragged along by the separating roller and delivered thereby. In order to reinforce the air stream it is useful to provide the casing with a rounded mouth formation in the region of the air inflow of the condenser. On the other hand, on the side of the detaching device at which it is moving away from the doffer roller, the casing should lie close to the detaching device in order to prevent as far as possible carrying along of air (and therefore undesired carrying along of fibres) on this side. In contrast to the old British patent specification 9854 of 1843, the air is not drawn first through a hollow shaft of the separating roller in order to be passed through holes provided in the tube wall into the working region of arms on the separating roller. Instead, the air flow created by the surface of the roller itself is exploited in order to generate the required air stream. This has, amongst other things, the advantage that the air is distributed evenly along the separating roller so that a uniform action on the fibre web is obtained. This uniformity cannot be achieved reliably in the arrangement according to the old British specification; rather, in that case, at higher operating speeds (which in any event were not attainable by cards at that time) a disturbing influence on the fibre web would have to be anticipated. Furthermore, an additional means is provided in accordance with the present invention, namely means for converting the fibre web taken off the doffer roller to a sliver. This means, which preferably includes a guide surface, may cooperate with the separating roller to release the fibre web from the doffer roller during running up of the card and at creep speed, and to guide the web away from the doffer roller. A guide surface can also assists the operator in feeding the sliver into the sliver delivery rollers, which possibly can take place via the trumpet. The trumpet can be provided as an element of a guide plate at the delivery end thereof. At higher operating speeds, a guide plate can prevent flapping, and an undesirable tearing or ripping of the fibre web in the region between the doffer roll and the sliver delivery rollers. The guide surface assists collecting of the thin fibre web to a sliver. It also reduces unwanted air streams in the web collecting region. The sliver forming means according to this invention differs from the arrangement in French Patent 8 159 8 in its performance of the above functions and in its mode of cooperation with the detaching device. Within limits, the speed of the separating roller can be selected independently of the speed of the doffer roller, being preferably driven by its own independent motor. The speed of revolution of the separating roller can be set as a parameter in itself and can adopt various values in dependence upon the rate of revolutions of the card or of the doffer roller. Since the association of the separating roller with the sliver forming means is constant in all operating conditions, there is no need for complicated controls in a solution according to the invention. The fibre web is released reliably from the doffer roll during threading up of the card in creep speed, and can be collected by an operator at the end of a convergent guide and can be fed into the trumpet or between the sliver delivery rollers, without the risk that the operator comes into contact with the separating roller and is thereby injured. The separating roller is enclosed for the greater part by the casing. The casing on both sides of the detaching device preferably forms a housing enclosing the detaching device with an air inflow opening which preferably lies opposite the envelope or outer surface of the separating roll. At least one fan can be mounted on the housing at the location of the air inflow opening. A fan of this kind serves the purpose of blowing air at high pressure into the housing thus reinforcing the action of the separating roller. It is, however, conceivable to forego the use of a separating roller and simply to guide the air stream generated by the fan into the region of the web take-off on the doffer roller and to effect the web take¬ off simply by means of this air flow, which possibly can be modulated in order to enable a pulse-like operation in such a case also. Particularly preferred embodiments of the separating roller are defined in claims 10 to 12. As can be seen from claim 12, the smallest spacing of the outer edges of the grooves from the points of the clothing on the doffer roll can lie in the region of 0.1 to about 3 mm. At the lower limit of this spacing, the outer edges of the grooves also exert a mechanical action on the fibres projecting from the fibre web, thus assisting the release of the fibre web from the doffer roll. The sliver-forming means preferably comprises a guide having side portions which may project from a floor region, and which converge towards one another in a direction away from the doffer roller in order to assist in gathering the fibre web from a width corresponding at least substantially to the length of the doffer roller into a width corresponding at least substantially to the infeed width of the sliver delivery rollers or of the trumpet upstream from these rollers. The height of the side portions may increase in a direction away from the doffer roller. In this way, the fibre web is well guided while it is being collected to a sliver. The side portions can prevent the formation of laterally directed air flows which could disturb the coherence of the web. Furthermore, a kind of open trough may be formed so that air contained in the fibre web can escape therefrom without difficulty in an upward direction. The guide may be formed in a region adjacent to the doffer roll with a strip-like section which extends at least substantially parallel to the surface of the doffer roll. The section may join by way of a curve into a floor of the guide leading to the delivery rollers. By this means, the fibre web is guided gently in the critical region at the position in which it is released from the doffer roll Side portions of the guide are preferably provided in the region of the curved portion or up to the strip-like section and thus they are able to prevent to a large extent air streams flowing parallel to the doffer roller, that is directed towards its axial ends In any event, the doffer roller should be provided with a cover at least in the region in front of and behind the position of transfer to the detaching device This cover and the casing on the side of the detaching device running towards the doffer roller, preferably converge to an edge in the region of the converging space formed between the doffer roll and the detaching device The parts forming this edge can possibly be formed by a single element This special formation assists the creation of pulse-like air flows which reinforce the separation function It also prevents escape of the air in the axial direction relative to the doffer Preferred embodiments of the web take-off device according to the invention are to be seen in claims 13 to 23 A special method for transfer of the fibre web lying on the doffer roll of a card to the sliver delivery rollers can be seen from claims 24 to 32 The invention will be explained in further detail by reference to the drawings, in which Fig 1 shows a schematic side view of a conventional carding machine, also shown Fig 2 shows a schematic side view of a web take-off device according to the invention Fig 3 shows a section on the lines II-II through a web take-off device according to Fig 2 in a plane parallel to the axis of rotation of the separation roller, Fig 4 is a plan view of the guide of Fig 2 and Fig 3 viewed in the direction of the arrow III in Fig 2, Fig. 5 is a diagrammatie side view for purposes of general explanation, Fig. 6 is a plan view of the arrangement shown in Fig. 5, Fig. 7 is a side view similar to Fig. 2 showing an alternative detaching device, Fig. 8 is a plan view similar to Fig. 6 of an alternative embodiment, Fig. 9 is a plan view of yet a further embodiment Fig. 10 A and B are side views similar to Fig. 2 of a further embodiment in two different states, and Fig. 11 is a side view of a self-threading trumpet. The carding unit shown in Fig. 1 comprises a feed chute 220 which receives fibre material (flocks) from a schematically illustrated flock transport system 222. The chute eliminates the transport air to form a batt 224 which is passed to the feed device 226 of the card 228. The card itself is of conventional design with a licker-in 230, (main) cylinder 232, revolving flats assembly 234 and a doffer 10, which forms part of a delivery section 238 having a drive unit 280. The delivery section forms a sliver 240 which is passed to a coiler 242 where the sliver is deposited in coils in a can 244. In Figure 2, the doffer roller is illustrated at 10, and it rotates in the direction of the arrow 12, being provided on its radially outer surface with a conventional doffer clothing 14. The doffer carries on the clothing 14 a fibre web 16 which it has previously doffed from the main cylinder of the card. This web 16 is separated at a position 18 which extends over a small circumferential region of the doffer 10 and the web is guided via a guide 20 to a condenser trumpet 22 arranged immediately before a pair of sliver delivery rollers 24,26. These rollers are preferably of the well-known step-roller kind. A web detaching device 28 is located at the separation position 18, and comprises in this example a separation roller 30 which is driven by a motor 32 (Fig. 3) and rotates at a high rate of revolutions in the direction of the arrow 36 around an axis of rotation 34. The direction of rotation 36 of the separation roller 30 therefore corresponds to the direction of rotation 12 of the doffer 10 so that the surfaces of the two rollers are moving in opposite directions relative to each other at the separation position 18. As can be seen from the Figures, the separation roller 30 has longitudinal grooves 38 in its surface. These grooves preferably extend over the complete length of the separation roller, that is in the direction of the width of the card. However, it can be advantageous to arrange that the grooves do not run out over the axial ends of the separation roller but they are limited in that region by a radially extending flange. In this way, unnecessary lateral air flows can be prevented at the axial ends of the separation roll. In this embodiment, the separation roller is driven by its own motor 32, so that the speed of rotation of the separation roller can be set independently of the speed of rotation of the doffer of the card and can also be varied within a broad range. However, it is also possible to drive the separation roller by a gear transmission from another drive motor of the carding machine. Above the separation roller 30 there is a first casing 40 which is formed e.g. of sheet material and which comprises a section 42 extending downwardly and to the left at an inclination (Fig. 2) and passing via a rounded inflow edge 44 into a curved section 46 which forms a converging gap 50 with the envelope surface of the separation roller 30. The narrowest portion of the gap 50 is located shortly before the separation location 18. The section 46 forms with the cover 52 of the doffer roll, with which it is connected, a wedge-shaped portion. The casing 40 and the cover 52 can advantageously be provided by a single element having a corresponding formation, for example an elongated profile. On the other side of the separation roller 30, there is also a casing 54 which, starting from bevelled end edge 56, runs through a rotation angle of approximately 90° around the envelope surface of the separation roller and then continues vertically upwards where it is connected to the section 42 of the casing 40 by way of a horizontal section 58 and a further vertical section 59. In this way, the two casings 40 and 54 form a kind of housing around the separation roller, the axial ends 60 and 62 of the housing (shown only in Fig. 3) being closed and the bearing 64,66 for the shaft 68 of the separation roller 30 being carried thereby. The drive motor 32 for the separation roller 30 is fixed to the side wall 62. A fan 70 is mounted on the horizontal section 58 of the casing 54, that is on the housing of the web detaching device 28. Fan 70 is provided with its own drive motor 72 (Fig. 3). The fan 70, which is driven in the direction of rotation 74 by the motor 72, delivers an air flow through an air inflow opening 76 (Fig. 3) in the horizontal section 58 of the housing. The fan can be designed as an axial, radial or lateral flow blower. In a first embodiment the guide 20 is formed in the manner illustrated in Fig. 2 and 3. It thus comprises a floor plate 80 and two side plates 82 and 84. In the region below the separation roller and adjacent to doffer roller 10, the floor 80 runs by way of a curved section 86 into a strip 88 which extends parallel to the surface of the doffer roller 10 over its complete width. The strip 88 defines a lower edge of the position 18 and the upper edge is defined by the casing 40 and cover 52. From Fig. 3 it can be seen that the side portions or side wings 82,84 of the guide 20 converge in a direction away from the doffer roller and thus continually gather the fibre web which first has the working width of the doffer roller. The side portions thus collect fibre web 16, in cooperation with the floor 80, from an extended, narrow cross section in the region of the doffer roll 10 into a somewhat rectangular or rounded cross section at the exit from the guide 20, where the transverse dimension of the fibre web corresponds approximately to the infeed diameter of the trumpet 22. The mode of operation of the illustrated arrangement is as follows: When the card is switched on it goes through a running-up routine including a period at the so-called creep speed, for example according to EP 978 101 749 of 4.4.97. However, the separation roller 30 can be driven at a relatively high speed, sufficient to generate a web detaching airstream as further described below. The surface speed of the separation roller 30 should be matched to the surface speed of the doffer 10 so that the web is not torn or otherwise disturbed. The separation roller has a diameter in the region of 30 to 150 mm. Due to the grooved form of the separation roller 30, this acts as a scoop wheel and carries a significant air flow along with it. This generator effect is reinforced in that the gap 50 gradually gets smaller and the flow is facilitated by the rounded inflow edge 44. The feeding effect is also reinforced by the action of the fan 70. In the region of the apex 15 of the wedge the individual grooves of the separation roller form pockets with the casing 40. These pockets contain air at a somewhat raised pressure. When the pockets move past the apex, they are exposed in sequence and a pulse-like flow is generated in the convergent space in the direction of the doffer roller, this flow favouring the separation of the fibre web 16 from the doffer roll. If the longitudinal edges of the grooves 38 run past the clothing of the doffer roller 10 with a relatively narrow spacing, they are able to act mechanically for example on projecting fibre portions and thus to generate an additional force on the fibre web favouring the separation of the web from the doffer roll. The edge 56 of the casing 54 lies relatively close to the envelope surface of the separation roller and prevents the separation roller carrying air with it in significant quantities in this region. This also prevents fibres moving into the region between the end edge 56 and the separation roller and forming a blockage there. Instead, the bevelled end edge 56 ensures that the web glides in a gentle manner onto the guide 20. As a result of this arrangement, the outflowing air first moves past the end edge 56 parallel to the floor region 80 of the guide thus guiding the movement of the fibre web away from the doffer 10 at the take¬ off point 18 and along the guide. In this way, the separation of the fibre web from the doffer roll at the position 18 arises by the pneumatic action of the separation roller 30 possibly aided by mechanical action. Because the guide 20 has a convergent formation, the cross section of the fibre web is increasingly changed until at the end of the guide 20 there is a web which can be grasped by an operator and fed into the trumpet 22. In this trumpet, air is pressed out of the web and the end of the sliver formed in this way is caught in the convergent gap (nip) of the delivery rollers 24,26 so that these rollers can exert a mechanical drawing off force on the web. Although the web is still a relatively weak structure, there is adequate fibre to fibre friction to ensure that the fibres are drawn off in the form of a coherent structure from the doffer roller 10 by means of the fibre delivery rollers 24,26. The control unit of the card now accelerates the rotation of the delivery rollers 24,26, the rotational speeds of the other rollers of the card being raised simultaneously until they have achieved the normal operational speed. The rotational speed of the separating roller 30 may be maintained constant at this phase of running up, but preferably it is raised according to a predetermined program. There are indications, however, that the separating roller can be stopped when the card has reached its operational speed. The function of the separating roller can be reinforced by the fan 70. This means that when the separation action of the separating roller 30 does not seem adequate, an increased air flow can be achieved by switching on the motor 72, since then the fan 70 also operates and, acting as a precompressor, ensures an increased air flow to the separation roller. It also conceivable to forego the use of the separation roller itself and to use only the fan to effect separation of the fibre web 16 from the doffer roller. In this case also the fan could be switched off if the separation function operates satisfactorily at normal operating speeds of the card. The arrangement illustrated especially in Fig. 2 and 3 enables not only a satisfactory operation but also an exceptionally short web take-off arrangement. This gives a compact and low cost structure for the take-off device, as indicated by the plan view shown in Fig. 4. As shown there, the side portions 82,84 form an angle A in range 140° to 180° in the region of the trumpet. The new web take-off process comprises two steps, namely: - detaching (or releasing, or separating, or stripping) the web from the doffer, and - forming a sliver. The step of forming a sliver can be divided into two stages, namely: - gathering (or collecting) the web, and - condensing the gathered web into a sliver. According to the invention, the sliver-forming stages (gathering and condensing) follow directly after detaching. Condensing can be carried out by substantially conventional means, e.g. by a condenser trumpet followed by delivery/withdrawal rolls generating a tensile force drawing the gathered fibre material through the trumpet. The condensing means (trumpet) is preferably located very close to the location at which the web detaches from the doffer. This distance can for example be less than 200 mm. There may, however, be more than one condenser, for example, two condenser trumpets might be provided in succession, the first condenser serving primarily to expel air from the fibre structure and the second serving to further compact the elongate fibre structure. The condensing means may be self-threading, but that is not essential. The delivery (or withdrawal) means preferably follows immediately on the (last) condensing means, but there may be a space between them depending upon the geometry of the sliver path after it leaves the condensing means. The resultant sliver is in any event a compact, elongate structure with adequate tensile strength for coiling and further processing, e.g. in drawframes (not shown). The web leaving the doffer, on the other hand, is in the form of a fine veil or gauze spread out over the whole working width of the machine. The strength of the web at the detaching location is due wholly to fibre/fiber friction within this fine veil. It depends on the number of fibres per unit area of web and the degree to which they have been compacted, which in turn depends on the transfer of fibres from the main cylinder to the doffer. However, many other parameters also exert an influence on the web strength at this stage, e.g. the degree of random orientation/parallisation of the fibres in the web, the degree of crimp of the fibres, the presence/absence of lubricants ... In conventional carding machines, this web is transported in web form over relatively long distances. Depending on the geometry of the delivery section, the web in the conventional card may have to be protected (e.g. against disturbing airstreams) and/or supported (e.g. against the influence of gravity). The need for such protection and/or support is much reduced in a card according to the invention, but it can nevertheless be needed depending upon the material to be processed. In order to prepare the web for condensing, e.g. by drawing it through a condensing trumpet, the web must first be gathered, preferably in an orderly fashion. In the gathering stage, the number of fibres per unit area and fibre/fibre friction are both increased. Gathering can be effected by moving the edge zones of the web towards the center thereof. In the preferred arrangement, the gathering procedure can involve folding of partly gathered edge zones onto a central zone. This can be performed immediately prior to condensing, and suitable guide means can be provided to cause the desired folding action. In any event, the gathering step now has to be performed in the relatively short space remaining between the detaching location and the condensing means, and it must therefore begin immediately after the web has been detached from the doffer. On the other hand, the withdrawal force generated by the delivery rollers is now transmitted back (through fibre/fibre friction) into the web between the condensing means and the doffer and it also now exerts a gathering action. In all forms of web gathering equipment, the handling of the edge zones is of special significance, particularly in the vicinity of the detaching location (furthest from the condensing means). Support and/or protection for the web is less important in web zones closer to the condensing means. For example, if the condensing means is positioned in the middle of the working width, the central web zones undergo less diversion in their passage to the condensing means, and they are supported on both sides by the web edge zones. Depending on the strength of the web, it may be desirable in a card according to the invention to provide full support for the web between the doffing location and the condensing means, or only edge support, possibly only in the region of the doffing location, or it may not be necessary to provide any support at all. If the edge regions are not strong enough to withstand the drawing (gathering) forces imposed on them, it may be desirable to provide a forwarding means to reduce the tensile forces exerted on the web as it gathers. The region between the detaching location and the condensing means is preferably substantially enclosed in a housing. The condensing means may provide an outlet from this housing. The housing (or part thereof) may be openable, preferably by swinging about a horizontal axis, to enable inspection and / or threading up („piecing" or „piecening"). The delivery means (e.g. rollers) has to be designed to develop a tensile force on the sliver it draws out of the condensing means. This force should be sufficient to generate a predetermined minimum draft ratio between the delivery means and the location at which the web detaches from the doffer, e.g. a draft in the range 1 to 2. The distance between the delivery (or withdrawing) rollers and the detaching location can be made so short, and there may be so few intervening elements, that part of the tensile force exerted by the delivery rollers is effective also (during normal operation) to assist in detaching the web from the doffer. This effect cannot of course be relied upon prior to threading of the sliver through the delivery rollers, so that a detaching means is required at least for generating a positive detaching action as preparation for threading up. The detaching force needed at that time is also relatively large because the doffer is rotating at a relatively low rate of revolutions, so that centrifugal force urging the web off the doffer is relatively low. The detaching means preferably functions without requiring contact of the web with any moving parts, but the detaching force is preferably exerted close to the doffer surface. The detaching means is therefore preferably a pneumatic device, in particular a device adapted to generate a pulsating airflow. This airflow can be generated by a rotating or a reciprocating means. The overall arrangement is preferably such as to enable the detaching airflow to escape without disturbing the web passing to the condensing means, and the previously mentioned housing should be arranged to enable such escape. The detaching device is also preferably designed to stabilise the detaching "plane" within a defined detaching region of the doffer circumference during normal operation. This detaching region then has a predetermined relationship to the gathering and condensing stages. In other words, the detaching device is preferably arranged to ensure that detaching is effected as far as possible over the whole width of the doffer along a "line" (in a "plane") and that as far as possible, this line or plane does not "wander" (back and forth) relative to the circumference of the doffer. This function has to be fulfilled for various processed materials (cotton from various sources, synthetics of various types, blends ....) and also for varying types and conditions of doffer clothing (for example with or without plasma coated teeth, with varying degrees of "aggressivity" of the basic clothing design, and for conditions ranging from "sharp" to "worn"). In any event, the arrangement may be such that the detaching effect generated by the detaching device is variable so that it can be coordinated with the prevailing operating conditions. Various alternative embodiments, beginning with a diagrammatic representation (Fig. 5), will now be described to expand on the immediately preceding remarks. As far as possible, the reference numerals used in Figs. 5 and the subsequent figures correspond to those used in in the description of the embodiment according to Figs. 2 to 4. The principle represented in Figs. 5 and 6 is that the condensing means (here in the form of a trumpet 22) followed immediately by the stepped rollers 24,26, is located as close as possible to the circumference of the doffer 10 with the minimum of intervening elements. The nip of the rollers 24,26 represents a means generating a withdrawing force drawing the fibre material through the trumpet 22 in normal operation and delivering the resulting sliver. The nip of the rollers may be spaced from the detaching region 18 by a distance in the range 25 to 160 mm., and preferably in the range 30 to 120 mm. The drive 280 (Fig. 1 ) for the delivery section of the card may comprise a drive motor MD for the doffer and another drive motor MW for the withdrawal/delivery rollers 24,26. The drive may be controllable, for example by a programmable controller (not shown) for the machine as a whole, to generate a draft (expressed as the ratio of the linear - circumferential - speeds) in the range 1 ,05 to 1 ,6, preferably 1 ,1 to 1 ,3, between the withdrawal/delivery unit 24,26 and the doffer (region 18). A space 99 must be left to enable a detaching means (indicated by the arrow 28A) to operate on the web 16 carried by the doffer 10 at least during the threading up operation, but preferably also during normal operation. The preferred form of detaching means is "non mechanical" (i.e. it does not involve a clothed detaching roller or belt, on which the web must be carried). Instead, the preferred embodiment comprises an air stream flowing in a direction substantially opposite to the direction of rotation of the doffer and directed against the surface of the doffer over the whole working width thereof. The airstream can be generated by a permanent or periodic high or low pressure (suction or injector). In this way, it is possible to generate a detaching effect not simply at the envelope surface of the doffer, but within the doffer clothing 14 itself. This is especially advantageous in the edge zones. The detaching device (not specially illustrated in Fig. 5) should be controlled so that it is set in operation simultaneously with or before setting in operation of the doffer 10. Thus, as soon as the doffer 10 begins to produce a web 16, the web end 16A (Fig. 5) will be stripped off the doffer as cleanly as possible by the action of the detaching device. For this purpose, it is desirable to create a detaching action effective between the web and the underlying surface of the doffer roller 10, i.e „ within" the doffer clothing. It is not possible to generate such an action mechanically. The web has to be detached uniformly over the full working width of the card (doffer), which can be more than one metre. The infeed end of a conventional sliver condensing trumpet usually has a diameter not greater than 40 mm. The element receiving the web in Figs. 5 and 6 has a portion 22 corresponding to the conventional condensing trumpet. However, the web has to be gathered together in an orderly fashion before it can run through the portion 22. This statement applies especially to the edge zones Z1 , 22 (Fig. 6), which have to be diverted particularly sharply in order to reach the trumpet portion 22. Accordingly, the trumpet 22 in Figs. 5 and 6 has been provided with wing- sections 20W (Fig. 6) which both support and protect the fibre material being dragged into the central region of the trumpet. The wing-like sections 20W together form a kind of trough opening towards the doffer 10. The device is therefore similar to the kind of device shown for example in DE-B-2711619, differing significantly, however, in its position immediately adjacent the doffer 10. The lower lip of this trough is preferably formed with a section 21 converging along a curve with the adjacent surface of the doffer, so that the web 16 transfers smoothly from the doffer clothing 18 to the trumpet. It is particularly important to provide a positive detaching action when the newly formed web on the doffer has to be detached for threading into the trumpet 22 and the draw-off rolls 24,26. Without such a positive action, there is practically no reason for the web to leave the surface of the doffer, because the doffer itself is rotating at relatively low revs. On the other hand, at operating speed (after threading up has long been completed and a sliver is running through the trumpet 22 and the rolls 24,26) the rate of rotation of the doffer will be relatively high, so that centrifugal force will be tending to urge the web off the doffer. Further, the web still on the doffer clothing is subjected to a draw-off force transmitted by fiber-to-fiber friction from the sliver being forwarded by the rolls back via the gathering web to the detaching region. Accordingly, the need for a positive detaching action is reduced at operating speed, and it may be possible in some operating circumstances to draw the web off the doffer simply by means of the draw-off force generated by the rolls 24,26, or to provide positive detachment only in the edge regions. However, the preferred solution does not rely on such effects, which are likely to be variable in dependence upon many operating parameters which cannot be taken fully into account at the time the machine is designed. Accordingly, Fig. 7 shows an alternative form of detaching device 28 with at least one fan 70 blowing air into a convergent trough 101 the lower end of which merges into a slit 102 extending across the full working width of the doffer. The slit 102 has a slot-like mouth 104 directed against the surface of the doffer at the detaching location 18. The trough and the slot are formed between two profiled elements 106,107 defining opposite sides thereof, element 107 also forming part of the casing of the doffer 10. The outer element 106 carries in the slit region a flap 108 pivotable about an axis 109 mounted in the element 106. A suitable actuator can be provided to pivot the flap back and forth through a small angle as indicated by the dotted lines in Fig. 7, thereby creating a pulsating effect in the airflow forced through the slit 102 and the mouth 104 by the fan 70. This actuator could, for example, be in the form of a vibrator. Alternatively, the device 28 could be designed as a fluidic vibrator (or "flip-flop"), for example as generally shown in DE-B- 2628120. Fig. 7 also illustrates a modified form of web guide 20A comprising in this case a pair of channel- or trough-like members 120, only one of which can be seen in the view shown in Fig. 7. The illustrated member 120 is provided at one side of the doffer, being mounted on a carrier 121 secured to the machine housing 122, as will be described later in the text. The other member (not seen in Fig. 7) is correspondingly mounted at the other side of the doffer. During normal operation, each member 120 extends inwardly from its respective end of the doffer 10 towards the middle thereof, and also at an angle towards the sliver withdrawing unit (not shown in Fig. 7, but apparent from the very similar embodiment illustrated in Fig.8). However, each member 120 is short relative to the working width of the doffer (as also seen in Fig. 8), so that the two guide members 120 only form a pair of guide "shoulders" in the immediate region of the doffer, and especially in the edge zones thereof. The open channels or troughs presented by the members 120 to the doffer 10 receive the web stripped from doffer at the detaching location 18 by the pulsating airstream. In this case, the guide 20 (the shoulders 120) does not perform any function in relation to the stripping action. The casing 124 of the doffer can be formed with an edge 125 defining one border of the detaching location 18, the other border being defined by the mouth 104. The housing 122 may be mounted pivotably on a horizontal shaft (not shown) below the level of the illustration in Fig. 7, enabling the assembly including guide shoulders 120 to be swung away from the doffer for inspection purposes, the doffer 10 being then still largely separated from the web collecting area by the casing 124. It will be appreciated that this embodiment provides no support for the web in the central zones thereof, as can be clearly seen in the embodiment according to Fig. 8, which is similar in this respect. Fig. 8 also shows the condensing trumpet 22 of the sliver withdrawing and delivery unit which is also mounted in the housing 122, forming a sliver exit therefrom. The sliver leaving the housing 122 can be diverted at a guide 128, depending on the geometry of the sliver path to the coiler (Fig. 1 ). The web collecting region within the housing is thus substantially enclosed by the latter. In the embodiment of Fig. 8, the carriers 121 are formed as sliders, running in rebates 126 provided in the side walls 127 of the housing 122. It is therefore possible to move the guide shoulders away from the doffer, for example during threading up, without having to move the whole of the housing 122 relative to the doffer. It should be recognised that two airstreams interact at the detaching location 18, namely - the airstream generated by the detaching device 28 in order to give a stripping action at location 18, and - the airstream carried along by the doffer 10 at its own periphery. Turbulence can arise in the interaction region and this could disturb the detaching and/or gathering operations. It is therefore important to confine the airflows at the detaching location by providing suitable constraining surfaces on the casing 124 of the doffer 10, on the guide 20 and/or on the detaching device 28 to ensure that the degree of turbulence is maintained below a level at which it interferes with an acceptable detaching action and/or to protect the web from turbulence that may arise. Figure 8 also shows two fans 70 mounted one on each side of the central region of the doffer. This modification can be used in an embodiment according to Fig. 7 (without any rotating parts in the detaching device) or in an embodiment according to Fig. 2 (with a rotary air pulse generator). The modification has the advantage of a more even supply of detaching air over the working width. It can be adapted if necessary to provide for preferential air supply in the sensitive edge zones. Figure 9 is a view similar to Fig. 8 of an embodiment which is useful where the web has inadequate strength or coherence in its edge zones. In this case, belts 130 are provided to exert a forwarding effect on the web edges feeding them (and possibly also supporting them) in their passage to the sliver withdrawal device. Fig. 9 assumes that the belts are required over the full distance from the edge zones of the doffer to the withdrawal unit, but that may not be necessary as the strength of the partly-gathered web nearer the withdrawal unit will be higher than the strength of the web in the edge zones nearer the doffer. The belts 130 can therefore possibly be made shorter than those illustrated, while still giving an adequate forwarding effect. Figs. 10 A and B illustrate further modifications on the basis of a detaching device 28 as shown in Fig. 2 in combination with slidable guide shoulders 120 as shown in Fig. 8. The guide shoulders 120 are in this case joined by a strip 132 in the immediate vicinity of the doffer, forming a guide and transfer lip similar to the lip 86 shown in Fig. 2. The sliver withdrawal and delivery unit 134 comprises the trumpet 22, the roller pair 24,26 and a carrier 136 therefor. Carrier 136 also supports the motor (not shown) for driving the roll pair 24,26. Carrier 136 is itself mounted in an end wall 137, which is mounted at each end (near respective side walls 127) on a lever 138 pivotable about an axis 139 fixed relative to the side walls 127. The carrier 136 or the end wall 137 is fitted with a handle 140 by means of which the wall 137, carrier 136 and unit 134 can be pivoted about axis 139 out of their normal operating position (Fig. 10, in which the housing is "closed") into an "open" position (Fig. 11 ). This enables the sliders 121 to be moved along the rebates 126, giving access to the detaching location. For threading up the trumpet 22 and rolls 24,26 it is not necessary to shift the guide 20 out of its operating position (illustrated in Fig. 10B), but only to open the housing by pivoting the end wall and the parts carried thereby. The web detached at location 18 can now be grasped by the operator, gathered to an extent adequate to enable feed of at least part of the web into the trumpet 22 and hence to the rotating rolls 24,26, whereupon the rolls will draw the remainder of the web into the trumpet, completing the gathering action. The housing can then be "reclosed" with the sliver running from the outlet of the roll pair. A gap 142 (Fig. 10A) is left between the end wall 137 and the casing 54 of detaching device 28, enabling the detaching air to flow upwards out of the web collecting region. However, the guide shoulders 120 (Fig. 10) or the side portions 82,84 (Fig. 3) direct the detaching air exhaust towards the central zones, further assisting gathering of the web into the central zone aligned with the trumpet 22. These side guides can also perform a further useful function. Instead of allowing the web to simply form "pleats" in the direction of movement towards the outlet and then squashing these pleats together "concertina-fashion", the edge zones of the web can be made to curl over as indicated diagrammatically in Fig. 3 so that they are effectively folded onto the central zones as the fibre structure is drawn through the trumpet 22. It should, however, be emphasised, that this has practically no effect upon the orientation of the fibres in the fibre structure - they remain in their orientation largely in the direction of movement. The curling over of the edges does however give a desirable macro-structure within the resulting sliver. The space below the web collecting region can be left free to receive web remnants which may be left after threading up, but the arrangement should be such as to enable easy cleaning of this space. Finally, Fig. 11 illustrates a self-threading trumpet 22A, cooperating with a withdrawal roller pair 24,26. The trumpet 22A is provided with air passages (jets) 144 leading from respective inlets near the infeed end of the trumpet to respective outlets in the apex region. There may be many such jets distributed around the circumference of the trumpet, only two being shown in Fig. 11. The jets are connected at their inlet ends to a manifold (not shown) which in turn is connected to a source of pressurised air (for example fan 70) by way of a selectively operable valve (also not shown). The jets may extend in a spiral-fashion around the trumpet-body, thus creating a rotating airflow which helps to thread the web end into the nip of the rolls. The lower roll can be moved away from the upper roll (as indicated by the arrow B in Fig. 11 ) to aid threading up. When the valve is operated to pressurise the manifold, air is blown through the passages 144 and exits from the outfeed end of the trumpet through the nip between the roller pair. This creates a suction effect at the infeed region of the trumpet (injector effect) and this in turn can be adequate to drag some fiber material into the roller nip. It is not necessary to pull the whole end of the web into the nip by means of suction. Provided a minimum amount of fibre material is present in the nip, the tensile force exerted on that material by the nip will drag in further material, so that finally the web will settle into its designed gathering pattern and will then run normally through the trumpet and the nip. The valve may be operated manually, or it could be operated by a programmable control system. The valve can be operated in response to opening the nip by separating the nip rolls as described above, the nip being reclosed after a predetermined time adequate to ensure that fibre material from the web has been urged between the rolls. Statements of Invention. Based on the foregoing description it is possible to define further aspects of the present invention as follows: In a first aspect the invention provides a card with a main cylinder, a doffer, a sliver withdrawal and/or delivery means and a drive. In this first aspect, the spacing of the sliver withdrawal/delivery means from the location at which the web detaches from the doffer is selected less than 200 mm. e.g. in the range 25 to 160 mm., and preferably in the range 30 to 120 mm. The drive may be adapted to generate a draft of less than 2, (e.g. in the range 1 ,05 to 1 ,6 and preferably in the range 1 ,1 to 1 ,3) between the sliver withdrawal/delivery means and the location at which the web detaches from the doffer. Means may be provided to define the detaching location, e.g. by generating a positive detaching action at that location. In a second aspect the invention provides a card with a main cylinder and a doffer, arranged so that fibres transferred from the cylinder to the doffer form a web on the latter, this web being detached from the doffer at a substantially predetermined location thereon. In this second aspect, web gathering means are provided to cause gathering of the web immediately after it has been detached from the doffer. Accordingly, means may be provided to divert at least one, and preferably both edge zones of the web towards the middle thereof immediately after detaching. In a third aspect of the invention, which is however closely related to the second aspect, gathering of a web detached from a doffer involves the step of folding edge zones of the web onto a central zone thereof. A guide for the web may be adapted to exert a corresponding guiding effect on the edge zones of the web as the latter is moving towards a condensing means. This third aspect includes a card sliver having a macro-structure formed by folding edge zones of a web onto central zones thereof. In a fourth aspect the invention provides a card with a doffer and a sliver withdrawal and/or delivery means adapted to exert a drawing force on the web to draw it through a condenser means. In this fourth aspect, the drawing force may be transmitted back into the portion of the web upstream from the condensing means to exert a gathering action thereon, e.g. in the region of the detaching location, especially in the edge zones thereof. In a fifth aspect, which is closely related to the fourth aspect, the invention provides a card with a doffer and a sliver withdrawal and/or delivery means adapted to exert a drawing force on the web to draw it through a condenser means. In this fifth aspect, the drawing force may be transmitted back into the portion of the web upstream from the condensing means to exert a detaching action at the detaching location, where the web is to be released from the clothing of the doffer, especially in the edge zones thereof.

Claims: Patent Claims 1. Web take-off device, particularly for use at the doffer roll (10) of a card, for transferring the fibre web (16) on the doffer roll (10) to delivery rollers (24,26) at which the web (16) has the form of a sliver, the delivery rollers (24,26) possibly being preceded by a trumpet (22), characterised in that a detaching device (28) which is arranged immediately adjacent the doffer roller (10) and operates continuously at least at creep speed, transfers the web (16) preferably directly to a sliver-forming means (20, 22) which possibly comprises the trumpet (22). 2. Web take-off device according to claim 1 , characterised in that the continually operating removal device (28) comprises a separation roller (30) provided with grooves (38) moving in the opposite direction relative to the doffer roll (10) in the region of the roller (10) and acting pneumatically and possibly also mechanically on the web (16) transported on the clothing (14) of the doffer (10) in the region of the detaching device (28) in order to separate the web (16) from the doffer (10) and to transfer it to the sliver-forming means (20, 22). 3. Web take-off device according to claim 1 or claim 2, characterised in that the detaching device (28) comprises a fan (70). 4. Web take-off device according to one of the preceding claims, characterised in that the continually operating detaching device (28) is provided at least in the region of the doffer (10) with casings (40,54) which cooperate with the grooves (38) and convert the air carried along by the grooves (38) into an air stream which separates the web (16) pneumatically from the doffer (10) in particular by means of a pulse¬ like action. 5. Web take-off device according to claim 4, characterised in that on the side of the separation roller (30) leading towards the doffer (10) the casing (40) forms together with the separation roller (30) a converging gap (50), that is a condenser, which raises the flow exit speed in the region of the doffer (10). 6. Web take-off device according to claim 5, characterised in that the casing (40) has a rounded inflow portion (44) in the region of the air inflow side of the condenser. 7. Web take-off device according to claim 4, 5 or 6, characterised in that the casing (54) approaches the detaching device (28) closely on the side of the detaching device (28) at which it departs from the doffer (10) in order to prevent as far as possible on this side carrying along of air and therefore an undesired carrying along of fibres. 8. Web take-off device according to claims 4 and 7, characterised in that the casings (40,54) form on both sides of the separation roller (30) a housing for the separation roller (30) with an air inflow opening (76) preferably lying opposite the envelope surface of the separation roller (30). 9. Web take-off device according to claims 3 and 8, characterised in that the fan (70) is mounted on the housing at the location of the air inflow opening (76). 10. Web take-off device according to one of the preceding claims, characterised in that the grooves (38) have a saw-tooth form in cross section. 11. Web take-off device according to one of the preceding claims, characterised in that the separation roller (30) is relatively small, for example having a diameter in the region of 30 to 150 mm, preferably approximately 70 mm. 12. Web take-off device according to one of the preceding claims, characterised in that the outer edges of the grooves (38) have a minimum spacing from the points of the clothing of the doffer (10) in the range of 0.1 to approximately 3 mm. 13. Web take-off device according to one of the preceding claims, characterised in that the means (20, 22) which forms the sliver comprises a guide having side portions (82,84) converging in a direction away from the doffer (10) in order to assist in the web (16) from a width corresponding at least substantially to the length of the doffer (10) to a width corresponding at least substantially to the infeed width of the sliver delivery rollers (24,26) or the trumpet (22) preceding the sliver delivery rollers (24,26). 14. Web take-off device according to claim 13, characterised in that the height of the side portions (82,84) increases in a direction away from the doffer (10). 15. Web take-off device according to claim 13 or claim 14, characterised in that the means (20, 22) has a strip-like portion (88) in a region adjacent the doffer (10), which section extends at least substantially parallel to the surface of the doffer roller (10) and runs by way of a curve (86) into a floor (80) leading to the delivery rollers (24,26). 16. Web take-off device according to claim 15, characterised in that the side portions (82,84) are provided in the region of the curve (86) or of the strip-like section (88) and in this region substantially prevent flows directed outwardly, (that is parallel to the axis (34) of the separation roller) towards the axial ends of the separation roller (30). 17. Web take-off device according to one of the preceding claims, characterised in that the doffer (10) is provided with a cover (52) at least in the region before and after the transfer position (18) to the removal device (28). 18. Web take-off device according to claims 4 and 15, characterised in that the cover (52) and the casing (40) converge on the side of the separation roller (30) leading to the doffer (10) to an edge edge in the region of the doffer (10) and are possibly formed from sheet material. 19. Web take-off device according to one of the preceding claims, characterised in that the sliver forming means, or guide thereof has side portions (82,84) which form an angle converging in a direction leading away from the separation roller, the angle being in the range between 176 and 140° and preferably approximately 160°. 20. Web take-off device according to one of the preceding claims, characterised in that the side portions (82,84) form a rounded rectangle or an ellipse at their ends remote from the separation roller and form an exit opening with a transverse dimension in the region between 2 and 40 cm and preferably approximately 20 cm. 21. Web take-off device according to one of the preceding claims, characterised in that the side portions (82,84) of the sliver forming means cooperate with a trumpet (22) arranged before the delivery rollers (24,26) and this region is formed as an injector to automatically draw-in the sliver by suction. 22. Web take-off device according to one of the preceding claims, characterised in that the separation roller is formed with grooves (38) which for example exhibit a slight V-shape or a U-shape relative to each other, in order to facilitate gathering together of the web to a sliver. 23. Web take-off device according to one of the preceding claims, characterised in that the floor (80) of guide can either be formed by a continuous sheet or by a sheet formed with one or more openings, or can be absent insofar as the side portions are formed as two gutter-shaped parts facing towards each other. 24. Method for transferring a fibre web (16) on the doffer (10) of a card to the sliver delivery rollers (24,26) at which the web (16) takes on the form of a sliver, the sliver delivery rollers (24,26) possibly being preceded by a trumpet (22), characterised in that a detaching device (28), which is arranged immediately adjacent the doffer (10) and operates continually at least during creep speed operation, transfers the web (16) preferably directly to a sliver-forming means (20, 22), which means possibly includes the trumpet (22). 25. Method according to claim 24, characterised in that the continually operating detaching device (28) comprises a separation roller (30) provided with grooves (38) moving in the opposite direction relative to the doffer (10) in the region of the doffer (10) and acting pneumatically and possibly also mechanically on the web (16) transported by the clothing (14) on the doffer (10) in the region of the detaching device in order to separate the web (16) from the doffer (10) and transfer it to the sliver forming means (20, 22). 26. Method according to claim 24 or 25, characterised in that the continually operating detaching device (28) cooperates at least in the region of the doffer (10) with a casing (40) in order to convert air carried along by the grooves (38) into an air flow, especially pulse-like, which serves pneumatic separation of the web (16) from the doffer (10). 27. Method according to claim 26, characterised in that on the side of the detaching device (28) leading towards the doffer (10) the casing (40) forms with the detaching device (28) a converging gap (50), a condenser, which increases the exit flow speed in the region of the doffer (10). 28. Method according to claim 24,25 or 26, characterised in that the air stream is generated by a fan operating as an alternative or in addition to the separation roller (30). 29. Method according to one of claims 26 to 28, characterised in that the casing (54) approaches the separation roller (30) closely on the side of the separation roller at which it separates from the doffer (10) in order to prevent as far as possible carrying along of air on this side and therefore an undesired carrying along of fibres. 30. Method according to one of claims 24 to 29, characterised in that the separation roller (30) rotates with a high speed, for example with a linear surface speed which corresponds approximately to the linear surface speed of the doffer in normal operation Method according to one of claims 24 to 30, characterised in that the means (20, 22) which forms the sliver compπses a guide having side portions (82,84) converging in a direction away from the doffer (10) and gathering the web (16) from a width corresponding at least approximately to the length of the doffer (10) to a width corresponding at least approximately to the entry width of the sliver delivery rollers (24,26) or of the trumpet (22) preceding the delivery rollers (24,26) A method according to claim 31 , characterised in that by means of the side portions (82,84) flows are substantially prevented in directions parallel to the axis (34) of the separation roller (30) towards the end portions of the separation roller (30)

Inventors: BOSSHARD MARCEL, WUEEST OLIVER, BOSSHARD, MARCEL, WUEEST, OLIVER
Applicants: BOSSHARD MARCEL, RIETER AG MASCHF, WUEEST OLIVER, BOSSHARD, MARCEL, MASCHINENFABRIK RIETER AG, WUEEST, OLIVER
Application year: 1997
Main classification: D01G15
IPC codes: D01G15