Transport belt for transporting a fiber strand to be condensed

A transport belt of a ring spinning machine for transporting a fiber strand to be condensed over a suction slit of a condensing zone is provided with a perforation or perforations for a suction air stream which suctions the fiber strand. The transport belt comprises a nonperforated area which permits a friction drive, and also an effective area containing the perforation, the width of the effective area being larger than the width of the suction slit. For example, the transport belt comprises a skeleton belt forming a supporting structure with a close-meshed woven fabric applied thereto.

BACKGROUND AND SUMMARY OF THE INVENTION
 This application claims the priority of German application 198 37 179.9,
 filed Aug. 17, 1998, the disclosure of which is expressly incorporated by
 reference herein.
 The present invention relates to a transport belt for transporting a fiber
 strand to be condensed over a suction slit of a condensing zone, said belt
 having a perforation for a suction air stream which sucks the fiber
 strand.
 In U.S. Pat. No. 5,600,872 a transport belt of this type is described,
 which is designed like a drafting apron, but made of a material which has
 a greater elastisicity than is usual in the case of drafting aprons. The
 transport belt comprises centrical holes arranged in travel direction,
 through which holes the suction air stream enters. The size of the
 perforations determines to what degree the fiber strand is bundled
 transversely to the transport direction in the condensing zone. The
 transport belt is guided during operation over a suction slit, which
 extends in transport direction and which is essentially wider than the
 perforation.
 The condensing of an already drafted, yet still spinning twist-free fiber
 strand serves the purpose of rolling outwardly projecting edge fibers
 around the core strand, so that a better material utilization is permitted
 and that the fiber strand is less hairy before being imparted a spinning
 twist. This results in a smoother and more tear resistant yarn.
 It has been shown that it is not favorable when the clearance of the
 perforation holes alone determines the degree of condensing. The diameter
 of the holes would have to be so large that the air entering though the
 perforations would become inhomogenous.
 It is an object of the present invention to make the condensing effect not
 exclusively dependant on the clearance of the perforation, but rather to
 chose a perforation with which a homogenous as possible suction air stream
 can be achieved.
 This object has been achieved in accordance with the present invention in
 that the transport belt comprises a non-perforated area which permits a
 friction drive, and an effective area containing the perforation, which
 effective area is wider than the width of the suction slit.
 In contrast to prior art, the clearance of the perforation holes no longer
 determine the condensing effect, but rather the suction slit located under
 the transport belt. The width of the suction slit is somewhat wider than
 the width of the condensed fiber strand. The effective width of the
 perforation is in contrast significantly wider, namely so wide that the
 suction slit can, if required, be arranged under the perforation slightly
 transversely to the transport direction, in order that the fiber strand to
 be condensed is imparted an additional, slight false twist. In the case of
 such an embodiment the perforation can be so close-meshed that a
 completely homogenous suction air stream arises.
 The transport belt can consist of a flexible apron looped around a drive
 roller, which apron comprises a plurality of centrical rows of holes. A
 thin steel belt of, for example, 0.4 mm thickness can be provided, which
 comprises a centrical perforation produced by means of etching.
 Particularly advantageous is, however, a skeleton type supporting
 structure for a transport belt, on which only a very thin perforated tape
 is applied in the central area. This centrical placed perforated tape can
 consist of a particularly thin and close-meshed woven or knitted fabric.
 In a variation of the embodiment according to the present invention, the
 perforated tape is welded or adhered to the skeleton-like supporting
 structure. Alternatively, the perforated tape can be applied to the
 skeleton belt in an interchangeable way.
 It is important that the perforation is as closely meshed as possible,
 while on the other hand the perforated area should be significantly wider
 than the fiber strand to be condensed. The perforation serves only for the
 generating of a suction air stream, which effects the pneumatic
 condensing. The degree of condensing is however determined by the suction
 slit located under the transport belt.

DETAILED DESCRIPTION OF THE DRAWINGS
 In the embodiment of the present invention according to FIGS. 1 and 2, only
 the area of a front roller pair 2 of a drafting assembly 1 of a ring
 spinning machine is shown. The front roller pair 2 comprises in a known
 way a driven bottom cylinder 3 which extends in machine longitudinal
 direction, on which bottom cylinder 3 one top roller 4 per spinning
 station is flexibly pressed. Further, an apron pair of the drafting
 assembly 1 can be recognized, which apron pair is arranged upstream of the
 front roller pair 2, and which apron pair consists of a bottom apron 5 and
 an upper apron 6.
 In the drafting assembly 1 a sliver or roving 7 is drafted in transport
 direction A to the desired degree of fineness. Downstream of the front
 roller pair 2 a finished drafted apart from a slight subsequent
 draft-fiber strand 8 exists, which is guided through a condensing zone 9.
 In the condensing zone 9, still outwardly projecting edge fibers are to be
 rolled around the core strand under a light tension draft, so that the
 fiber strand 8 is bundled, becomes less hairy and is overall smoother and
 more tear resistant after a spinning twist has been imparted.
 A transport belt 10 serves to transport the fiber strand 8 through the
 condensing zone 9, which transport belt 10 is provided centrically with a
 perforation 11. The perforation 11 serves to suction the fiber strand 8 to
 the transport belt 10 by means of a suction air stream.
 The perforation 11 is limited to a centrical effective area 12 of the
 transport belt 10. This effective area 12 is laterally defined by a
 non-perforated area 13,14, which has an exclusively reinforcing function
 and which supports the friction drive of the transport belt 10.
 A delivery roller pair 15 ends the condensing zone 9 on its exit side,
 which delivery roller pair 15 comprises a driven bottom roller 16 and a
 top roller 17 pressed thereon. The top roller 17 is driven by the bottom
 roller 16 and drives in turn the transport belt 10 which is looped around
 the top roller 17 by means of friction.
 The delivery roller-pair 15 forms a twist block to the onset of spinning
 twist in the yarn 18 to be spun, which yarn 18 is guided in delivery
 direction B to a ring spindle. The condensing zone 9 is thus free of any
 spinning twist and is essentially free of draft.
 The transport belt 10 comprises in its effective area 12 a plurality of
 centrical rows 19 of holes, whereby the effective area 12 is in its
 entirety so wide, that a suction slit 20 located thereunder is completely
 covered. The fiber strand 8 is transported by means of the transport belt
 10 over the suction slit 20, which is disposed slightly transversely to
 the transport direction A. The suction slit 20 is itself somewhat wider
 than the finished drafted fiber strand 8.
 The transport belt 10 slides between the front roller pair 2 and the
 delivery roller pair 15 over a hollow profile 21 of the suction device.
 The suction slit 20, disposed slightly transversely, is directed towards
 the transport belt 10, so that under the effect of the inclination of the
 suction slit 20 and the transport direction of the transport belt 10, the
 fiber strand 8 is imparted a slight false twist during condensing.
 The hollow profile 21 is connected to a suction supply 22, which leads to a
 vacuum source (not shown).
 Deviating from the above described prior art, the diameter of the holes of
 the perforation 12 no longer determines the degree of condensing, but
 rather the position and the dimensions of the suction slit 20 do. The
 perforation 12 should be as close-meshed as possible and ensure a
 homogenous suction air stream.
 In the Figures described below the same reference numbers will be used as
 before, insofar as components having identical functions are involved. A
 repeat description is therefore omitted.
 The embodiment of the present invention according to FIGS. 3 and 4 differs
 from the previous design essentially in that now a transport belt 23 is
 provided, which is no longer looped around a transport roller. In place of
 the delivery roller pair 15 as shown in FIGS. 1 and 2, a nipping roller 24
 is provided in the embodiment according to FIGS. 3-and 4. The transport
 belt 23 runs around a hollow profile 21, which may extend over a plurality
 of spinning stations. The outer contour of the hollow profile 21 is in the
 form of a sliding surface for the transport belt 23. The nipping roller 24
 presses the fiber strand 8 to be condensed against the transport belt 23
 and this in turn on the hollow profile 21, which is part of a suction
 device. The pressure of the nipping roller 24 is effected along a nipping
 line 26, which here also is effective as a twist block against the
 spinning twist in the yarn 18.
 The condensing zone 9 is located now between the front roller pair 2 of the
 drafting assembly 1 and the nipping line 26. This design has the advantage
 that the suction slit 25 applied to the hollow profile 21 can now be
 guided up to the nipping line 26. The transport belt 23 itself is driven
 by means of friction by the nipping roller 24, which in turn is driven by
 means of a drive belt 29 by the top roller 4.
 In the embodiment according to the present invention as shown in FIGS. 3
 and 4, the perforation 11 is provided only over an effective area 12 in
 the centrical area of the transport belt 23. The width of the effective
 area 12 is so chosen, that it completely covers the suction slit 25. Thus
 the diagonal, the width and the length of the suction slit 25 determine
 here also the condensing effect, while the perforation 11 of the transport
 belt 23 primarily ensures as homogenous a suction air stream as possible.
 The transport belt 23 has, as can be seen in particular in the enlarged
 representation in FIG. 5, a skeleton-like supporting structure 30, on
 which a thin perforated tape 31 is applied centrically by means of welding
 or adhering. This perforated tape 31 is made for the purpose from a
 close-meshed woven or knitted fabric, preferably very thin polyamide
 filaments. The perforated tape 31 can thus be applied to the
 non-perforated areas 13 and 14 of a more stable supporting structure.
 In order that the perforation 11 of the perforated tape 31 is completely
 effective, the supporting part of the transport belt 23 is provided with
 very wide longitudinal slits 33, which are broken by cross-pieces 32 for
 the purpose of reinforcement.
 In a variation of the present invention shown in FIG. 6, a transport belt
 34 is provided, which takes the form of a very thin steel belt 35. The
 thickness of the steel belt 35 can measure, for example, 0,4 mm. The steel
 belt 35 comprises a centrical perforation 36, which is produced by
 etching. The edges of the transport belt 34 comprise again each a
 non-perforated area 13,14.
 In a particularly advantageous embodiment of the present invention as shown
 in FIG. 7, a transport belt 37 is provided, which has a non-perforated
 area 13,14 at the edges and an effective area 12 in a central area, the
 effective area 12 comprising a perforation 11. The transport belt 37 is
 produced as a so-called skeleton belt 41, which has primarily a supporting
 function and which furthermore serves the friction drive. This skeleton
 belt 41 is provided in the central area with a plurality of longitudinal
 slits 39 arranged one after the other in a row, and which are broken by
 cross-pieces 40.
 A thin, close-meshed woven fabric 38 of polyamide filaments is secured to
 the skeleton belt 41 in an exchangeable way. The exchangeability can be
 achieved in that the woven fabric 38 comprises coated edge zones 42 and
 43, with which the woven fabric 38 can be sealed or secured in some other
 way onto the skeleton belt 41 which is adapted to receive these coatings.
 The strength of the seal need only be such that the woven fabric 38 can be
 transported with the skeleton belt 41 during operation. The woven fabric
 38, when it is worn down, can be easily removed from the skeleton belt 41
 to be replaced by a new one.
 The perforation 11 of the woven fabric 38 is located to a great extent in
 the area of the longitudinal slits 39, which are completely covered by the
 woven fabric 38. It has been shown, that the cross-pieces 40 do not impair
 the quality of the yarn in any way.
 Here also the width of the effective area 12 is chosen that the suction
 slit, located under the transport belt 37, is completely covered. The very
 close-meshed, thin woven fabric 38 permits a particularly homogenous
 suction air stream, while the condensing effect is determined by the
 position and the arrangement of the suction slit 20 or 25.
 The foregoing disclosure has been set forth merely to illustrate the
 invention and is not intended to be limiting. Since modifications of the
 disclosed embodiments incorporating the spirit and substance of the
 invention may occur to persons skilled in the art, the invention should be
 construed to include everything within the scope of the appended claims
 and equivalents thereof.