Title of Invention

A PROCESS AND APPARATUS FOR CONDENSING A DRAFTED FIBRE STRAND .

Abstract

This invention relates to a process and apparatus for condensing a drafted fibre strand in a condensing zone arranged downstream of a front roller pair of a drafting apparatus, in which process, the fibre strand is transported through the condensing zone by means of an air permeable transport means moving over a suction device, wherein the fibre strand, on reaching the condensing zone, has the same direction of motion as the transporting means and wherein a sufficient amount of the fibres located in the fibre strand are nipped by the front roller pair during condensing.

Full Text

The present invention relates to a process and apparatus for condensing a drafted fibre strand in a condensing zone arranged downstream of a front roller pair of a drafting apparatus, in which process the fibre strand is transported through the condensing zone by means of a perforated, suctioned transport means. The present invention relates further to an apparatus for condensing a drafted fibre strand in a condensing zone arranged downstream of a front roller pair of a drafting unit, said apparatus comprising a stationary sliding surfaced, which has a suction slit extending essentially in the direction of the motion of the fibre strand, also comprising a perforated transport belt located between the fibre strand and the sliding surface, which transport belt transport the fibre strand over the sliding surface, the speed of said transport belt corresponding to at least the peripheral speed of the front roller pair, and also comprising a nipping roller bordering the condensing zone on its exit side. Such condensing apparatuses are used in addition to drafting apparatuses of textile machinery, especially ring spinning machines, for improving the quality of the spun yarn. A process and an apparatus of this type is prior art in Indian Patent 185214. The condensing zone is bordered on its entry side as well as on its exit side by a nipping point, namely on the entry side by the nipping point of the front roller pair and on its exit side by a nipping point defined by the nipping roller, whereby the nipping roller presses against a driven bottom roller. The distance between the two nipping points is given in the known publication as l.S times that of the fibre length. A light tension draft is provided in the condensing zone, that is the nipping roller has a somewhat higher circumferential speed than the front roller pair. On reaching the condensing zone, the direction of motion of the fibre strand differs from the direction of motion of the transport belt. A similar apparatus is prior art in German published patent application 197 22 528. According to this publication, the suction zone of the condensing zone is limited to between 10 and 25 mm, in order that, in the case of reduced suction performance, an improved condensing effect is attained. However, the distance between the nipping points is significantly larger than the suction zone and also larger than the fibre length. In the case of the latter publication, the matter of the airways of the transport belt becoming clogged with time is addressed. As a remedy, the suggestion is made to design the perforations of the transport belt as edge—free. In the case of the known apparatus there is the risk that despite everything, fibre fly and trash can collect between the stationary sliding surface and the moving supporting surface of the transport belt. This trash build-up comes about, for example, in that individual fibres of the fibre strand to be condensed, in particular the shorter fibres, can insert themselves inwards with their front ends in the area of the suction slit in through the perforations of the transport belt. These fibres project then partly into the suction slit, namely until the suction slit has been passed. In the most favourable case, the relevant fibre can be cut off at the end of the suction slit and the cut-off end is suctioned off. In the least favourable case, the fibre end is simply turned over, so that it is not suctioned off, but rather is transported further with the transport belt, thus lying partly between the supporting surface and the sliding surface. This fibre can tear at any time, and can settle, in the form of dust, anywhere on the supporting surface or on the sliding surface, in particular in the case of sticky fibres containing honeydew. This results in time in varying condensing effects from spinning station to spinning station, so that at the exit side nipping points, varyingly condensed fibre strands are delivered. The condensing of a drafted fibre strand, namely in an area to which the spinning twist is not yet retroactive, serves the purpose of bundling the fibre strand in its cross section and to make it less hairy overall. This results, after the spinning twist has been imparted, in a smoother yarn with a higher tear resistance. When, however, the desired condensing effect does not occur at even one spinning station due to an impaired condensing zone, a so-called Moire effect occurs in the later fabric, which can render it a reject product. It must be ensured, therefore, that the condensing effect at the individual condensing zones of the spinning stations is constantly maintained. It is an object of the present invention to ensure that the perforations of the transport belt do not become clogged, and that in the area between the supporting surface of the transport belt and the stationary sliding surface no small deposits can form. This object has been achieved in the process in accordance with the present invention in that the fibre strand has the same direction of motion as the transporting means when it reaches the condensing zone, and in that a sufficient amount of fibres located in the fibre strand continues to be nipped by the front roller pair during condensing. The transport means has thus in the case of long fibres in the condensing zone - in the same direction - the same or a greater speed than the front ends of the fibres, which thus cannot insert themselves in the first place into the perforations of the transporting means. In the case of short fibres, however, it is sufficient when as high a percentage as possible of fibres are still controlled by the front roller pair as soon as the front ends are seized by the suction. This object has been achieved in relation to the apparatus in accordance with the present invention in that the distance between the nipping points defined by the front roller pair on the one side and by the nipping roller on the other side is, in any case, not very much greater than the average staple length of the fibres located in the fibre strand. This reliably prevents the fibres in the condensing zone from being seized by the suction force at their fronts ends and crawling forwards on the transport belt. The suction of the front end of the fibres into the perforations is thus effectively prevented. In the case of short stapled material to be spun, the distance between the nipping points measures advantageously between 20 and 27 mm. The smaller value is selected for synthetic fibre material, in particular for viscose fibres. In an embodiment of the present invention, the suction slit arranged directed against the transport belt has a shaft-like opening. Experience has shown that in the case of such openings of suction tubes in general, almost no fibres collect there. The shaft-like opening may taper in suction direction, which results in an acceleration of the suctioned fibres. In contrast, in the case of a suction slit in a metal sheet, in which the height of the suction slit corresponds to the thickness of the metal sheet, the risk of clogging, caused by increased turbulences, would arise. The shaft-like opening is formed for the purpose by an exchangeable fitted window. The suction slit can then be adapted easily to various fibre materials. In a further embodiment of the present invention, the front roller pair can have a bottom roller which is provided on its periphery with a profiling, which is disposed with a light pressure on the transport belt outside of the condensing zone. BRIEF DESCRIPTION OF THE DRAWINGS These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings wherein: Figure 1 is a part intersectional side view of an arrangement according to the present invention, Figure 2 is a view in the direction of the arrow II of Figure 1 onto the condensing zone, Figure 3 is a view similar to Figure 1 in another embodiment of the present invention, Figure 4 is a view in the direction of the arrow IV of Figure 3 onto the condensing zone. DETAILED DESCRIPTION OF THE DRAWINGS Of the drafting apparatus 1 of a spinning station of a ring spinning machine, only the front roller pair 2 and the apron roller pair 3 arranged upstream thereof are shown in Figures 1 and 2. The front roller pair 2 comprises a driven bottom roller 4, which extends over a plurality of spinning stations, and also comprises a pressure roller 5 arranged to each spinning station. In a similar way, the apron roller pair 3 comprises a driven bottom roller 6, and also a pressure roller 7 per spinning station. In addition, a bottom apron 8 and an upper apron 9 can be seen. In the drafting apparatus 1, a sliver or a roving 10 is transported in transport direction A in a known way and is drafted to the desired degree of fineness. Directly downstream of the nipping point 11 of the front roller pair 2, a drafted, but still twist-free fibre strand 12 is present. A condensing zone 13 is arranged downstream of the drafting apparatus 1, said condensing zone 13 comprising a device for condensing the fibre strand 12. This device comprises a hollow section 14, which extends over a plurality of spinning stations. The outer contour of the hollow section 14 comprises a stationary sliding surface 15, to which a transporting means in the form of a transporting belt is arranged to each spinning station. The transport belt 16 belonging to the condensing zone 13 is designed in an air-permeable way, and consists preferably of a fine-pored woven fabric of polyamide threads. The transport belt 16 transports the fibre strand 12 to be condensed through the condensing zone 13 and over a suction slit 17 of the sliding surface 15. The suction slit 17 is somewhat wider than the condensed fibre strand 12 and is arranged at a slight slant in direction of motion B of the fibre strand 12, so that the fibre strand 12 is imparted a light false twist during condensing. The suction slit 17 extends to a nipping point 18, which is formed between a nipping roller 19 and the sliding surface 15 of the hollow section 14, and which borders the condensing zone 13 on its exit side. The Downstream of the nipping point 18, a thread 20 is present to which the spinning twist is imparted. The nipping roller 19 serves as a twist block for the spinning twist, so that the fibre strand 12 is twist-free in the condensing zone 13. Downstream of the nipping point 18, the thread 20 is fed in delivery direction C to a ring spindle (not shown). The hollow section 14 comprises per machine section an opening 21, which is connected with a vacuum source (not shown) by means of a suction tube 22. Thus a suction effect acts through the perforated transport belt 16 onto the fibre strand 12 to be condensed. The nipping roller 19 is connected to a drive, which is derived by means of a transfer roller 23 from the pressure roller 5 of the front roller pair 2. The peripheral speed of the nipping roller 19 is slightly greater than the peripheral speed of the front roller pair 2. The transport belt 16 is provided on its side facing away from the fibre strand 12 with a bearing surface, which slides on the stationary sliding surface 15. There is a risk here that fibre fly and trash will settle between the bearing surface and the sliding surface 15. The front ends of individual fibres, in particular the shorter fibres, can namely project through the perforations of the transport belt 16 into the suction slit 17. When such fibres turn over at the end of the suction slit 17, that is when they are leaving the condensing zone 13, they then reach the area between the bearing surface of the transport belt 16 and the stationary sliding surface 15. This leads after a time to an impairment of the condensing effect of the respective condensing zone 13. In order to avoid this disadvantage it is provided that when the fibre strand 12 reaches the condensing zone 13, it takes the same direction of motion B as the transport belt 16. Thus the front ends of the fibres cannot reach the area of the perforations in the first place. In addition it is provided that most of the fibres located in the fibre strand 12 continue to be nipped by the front roller pair 2 during condensing. The front roller pair 2 thus controls the speed of the fibre strand 12 when it reaches the condensing zone 13 and holds the fibre strand 12 back somewhat, while the transport belt 16 runs at a slightly higer speed. These measures also prevent the front ends of the fibres from inserting themselves into the perforations of the transport belt 16. The distance a between the two nipping points 11 and 18 is so selected that it is at most insignificantly larger, but preferably smaller, than the average staple length of the fibres located in the fibre strand 12. Thus the fibres leaving the nipping point 11 are prevented from crawling forward on the transport belt 16 under the effect of the suction action and thus from entering the perforations. The suction slit 17 aligned against the transport belt 16 comprises a shaft-like opening 24, which tapers slightly in suction direction. Experience has shown that such openings 24 in general are not clogged by fibre fly. It is provided that in the area of the suction slit 17 a window is fitted on the hollow section 14, so that the condensing zone 13 can, if required, be adapted to the fibre material to be spun. The bottom roller 4 is provided on its periphery with a profiling 26, which is disposed with light pressure on the transport belt 16. Thus the bottom roller 4 serves to a certain extent as a cleaning roller, which continuously cleans the transport belt 16 of any adhering fibre fly outside of the area of the condensing zone 13. In Figures 3 and 4, a further embodiment of the invention is shown in somewhat enlarged dimensions. Insofar as the same components as above are involved, the same reference numbers are used, so that a repeat description is omitted. In the embodiment shown in Figures 3 and 4, a somewhat differently designed hollow section 27 is provided, which again extends over a plurality of spinning stations and which is connected by means of a suction opening with a vacuum source in a way not shown. The hollow section 27 faces the condensing zone 13 with a sliding surface 28, on which the perforated transport belt 16 again slides and which transports the fibre strand 12 through the condensing zone 13. A suction slit 29 per spinning station is located in the sliding surface 28, which suction slit 29 in the present case extends exactly in the direction of motion B of the fibre strand 12, that is, it does not extend diagonally. This has been proved favourable in the case of some fibre materials, for example, long staple fibre material. The opening 30 of the suction slit 29 is here also in the form of a chimney-like shaft, so that there is no tendency for fibre fly or the like to settle at this point. The chimney-like shaft graduates into a greatly enlarged cross section of the hollow section 27. In this embodiment of the present invention, an exchangeable window 31 is also fitted onto the hollow section 27, which window surrounds the suction slit 29 on all sides. On the side of the transport belt 16 facing away from the window 31, the condensing zone 13 is shielded by a non- contact cover 33 between the pressure roller 5 and the nipping roller 19, so that a blower which travels along the ring spinning machine does not disturb the fibre strand 12 to be condensed. On the side facing away from the condensing zone 13, the contour of the hollow section 27 is provided at the point where the transport belt 16 slides with longitudinal grooves 32 or with another type of diagonal knurling or fluting. In addition to the profiling 26 of the bottom roller 4 already described, which engages from below at the transport belt 16, the transport belt 16 cal be freed of anv adherina fibre fly from the inside. WE CLAIM: 1. A process for condensing a drafted fibre strand in a condensing zone arranged downstream of a front roller pair of a drafting apparatus, in which process the fibre strand is transported through the condensing zone by means of an air permeable transport Means Moving over a suction device, wherein the fibre strand, on reaching the condensing zone, has the same direction of motion as the transporting means and wherein a sufficient amount of the fibres located in the fibre strand are nipped by the front roller pair during condensing. 2. An apparatus for condensing a drafted fibre strand in a condensing zone arranged downstream of a front roller pair of a drafting unit, said apparatus comprising: -a stationary sliding surface, which has a suction slit extending essentially in the direction of the motion of the fibre strand, - a perforated transport belt located between the fibre strand and the sliding surface, which transport belt transports the fibre strand over the sliding surface, the speed of said transport belt corresponding to at least the peripheral speed of the front roller pair, - and a nipping roller bordering the condensing zone on an exit side thereof, wherein the distance (a) between the nipping points (11,18) defined on the one hand by the front roller pair (2) and on the other hand by the nipping roller (19) essentially corresponds to the average staple length of the fibres located in the fibre strand (12). 3. An apparatus as claimed in claim 2, wherein the distance between the nipping points (11,18) measures between 20 to 27 mm. 4. An apparatus as claimed in claim 2 or 3 wherein the suction slit (17; 29) aligned against the transport belt (16) comprises a shaft-like opening (24; 30). 5. An aparatus as claimed in claim 4, wherein the shaft-like opening (24;30) is formed by an exchangeable fitted window (25; 31). 6. An apparatus as claimed in any one of the previous claims 2 to 5, wherein the front roller pair (2) comprises a bottom roller (4) having a profiling (26) on its periphery, which bottom roller (4) is disposed outside of the condensing zone (13) with a light pressure on the transport belt (16). 7. An apparatus as claimed in any one of the claims 2 to 6, wherein the sliding surface (28) is arranged on a suctioned hollow section (27) which is looped by the transport belt (16) and the hollow section (27) is provided with longitudinal grooves (32) or the like which rub against the transport belt (16). 8. An apparatus as claimed in any one of the previous claims 2 to 7 wherein the condensing zone (13) is shielded by a non- contact cover (33). This invention relates to a process and apparatus for condensing a drafted fibre strand in a condensing zone arranged downstream of a front roller pair of a drafting apparatus, in which process, the fibre strand is transported through the condensing zone by means of an air permeable transport means moving over a suction device, wherein the fibre strand, on reaching the condensing zone, has the same direction of motion as the transporting means and wherein a sufficient amount of the fibres located in the fibre strand are nipped by the front roller pair during condensing.

Documents:

94-cal-2000-granted-abstract.pdf

94-cal-2000-granted-assignment.pdf

94-cal-2000-granted-claims.pdf

94-cal-2000-granted-correspondence.pdf

94-cal-2000-granted-description (complete).pdf

94-cal-2000-granted-drawings.pdf

94-cal-2000-granted-examination report.pdf

94-cal-2000-granted-form 1.pdf

94-cal-2000-granted-form 18.pdf

94-cal-2000-granted-form 2.pdf

94-cal-2000-granted-form 26.pdf

94-cal-2000-granted-form 3.pdf

94-cal-2000-granted-form 5.pdf

94-cal-2000-granted-form 6.pdf

94-cal-2000-granted-priority document.pdf

94-cal-2000-granted-reply to examination report.pdf

94-cal-2000-granted-specification.pdf

94-cal-2000-granted-translated copy of priority document.pdf