Method and arrangement in connection with reverse stranding

Abstract: The invention relates to a method and an arrangement in connection with reverse stranding, comprising drawing conductors (4) through a stationary divider means (5), peripheral tubes (8) peripherically surrounding a central tube (7) and twistable around the central tube recurrently in opposite directions and a twisting means (6) rotatable in opposite directions, into a stranding nozzle or similar. To achieve longitudinal strip winding, a strip (12) is fed into the central tube (7). The strip (12) is guided to pass through the rotatable twisting means (6) and further between the desired conductors (4) ahead of the stranding nozzle or similar (9), the stranding nozzle or similar (9) bending the edges of the strip (12) in the desired direction.

Description: THIS INVENTION relates to a method of forming a cable by reverse stranding, comprising the steps of drawing conductors through a stationary divider means, through peripheral tubes peripherally surrounding a central tube and which peripheral tubes are twistable around the central tube recurrently in opposite directions and through a twisting means rotatable alternately in opposite directions, into a stranding nozzle. The term "conductors" as used herein is intended to include filaments, conductor elements, bundles of conductors, optical fibres or the like. The invention also relates to apparatus for forming a cable by reverse stranding. A wide variety of methods and arrangements are known for reverse stranding. The solution disclosed in U.S. Patent 4974408 may be mentioned as an example of such prior art solutions. US-A-4974408 discloses a method and apparatus for forming a cable by reverse twisting in which conductors are drawn through a stationary holeplate or divider, through peripheral flexible pipes which surround a central tube and through twisting means in the form of a holeplate rotatable alternately in opposite directions. From the twisting means, the conductors pass through a nipple. A core element is fed axially through the central tube and through the nipple, the conductors being laid around the core element as they pass through the nipple. The solution disclosed in this U.S. Patent operates completely faultlessly in most circumstances, but if one desires to manufacture block-insulated cables, PCM cables for instance, by means of such an arrangement, then said solution cannot be used as such, as the feed of a strip serving as an intermediate shield in the cable cannot be realised with said apparatus. The block-insulated cables referred to above are digital cables usually employed for duplex data transmission, and therefore the discrete main blocks are separated from one another by an S-shaped metallic intermediate shield. The intent is to correct near-end crosstalk, since both transmission directions use the same frequency band and, furthermore, the difference in level between the output and input is great. Several different solutions have been developed for the longitudinal strip winding of a block-insulated cable. The solution described in U.S. Patent 4428787 may be mentioned as an example of an arrangement for longitudinal strip winding known in this field. The solution of this U.S. Patent is intended only and exclusively for carrying out longitudinal strip winding; for instance stranding cannot be performed by means of this arrangement. GB-2120836 discloses a method of and apparatus for forming a cable in which two groups of conductors are separated by a longitudinally extending strip which is longitudinally folded so as to have approximately an S-shape in cross-section. The strip is fed through the middle of a shaping die which has peripheral holes for the conductors and the shaped strip and conductors pass to a rotating finishing die where the conductors and the strip come together. The drawback of the prior art has been the large quantity of devices required in the manufacture of cables of the above type. Heretofore it has not been possible to perform reverse stranding and longitudinal strip winding with the same equipment. Furthermore, it has been difficult to connect the strip winding to other steps. This has increased the costs and complicated the production. It is the object of the invention to provide a method and an arrangement wherewith the drawbacks of the prior art can be eliminated. According to one aspect of the invention there is provided a method of forming a cable by reverse stranding comprising the steps of: drawing conductors through a stationary divider means, through peripheral tubes which surround a central tube and which tubes are twistable around the central tube recurrently in opposite directions and through twisting means rotatable alternately in opposite directions, and into a stranding nozzle, and rotating the twisting means alternately in opposite directions; characterised by feeding a longitudinally extending strip into the central tube in a downstream direction, guiding the strip through the rotatable twisting means and between the conductors upstream of the stranding nozzle to twist the strip alternatively in opposite directions upon alternate rotation of the twisting means in opposite directions; and, wherein subsequent to guiding and twisting the strip, the stranding nozzle bends the edges of the strip which serves as an intermediate shield in the cable. According to another aspect of the invention, there is provided reverse stranding apparatus for forming a cable comprising a stationary divider means for conductors to be stranded to form a cable, the divider means being disposed at the upstream end of a central tube, twisting means rotatable alternately in opposite directions and disposed downstream of the divider means, said central tube being rotatable recurrently about its longitudinal axis, alternately in opposite directions, peripheral tubes peripherally surrounding the central tube and twistable recurrently in opposite directions, the central tube and the peripheral tubes being disposed between the divider means and the twisting means and being arranged to bear against one another during twisting of the conductors, the peripheral tubes being suitable for guiding therethrough conductors to be stranded, characterised by means for feeding a rectilinear strip for use as an intermediate shield into said central tube, a twisting member fixed to said twisting means and having a slot, the apparatus including a rotatable stranding nozzle, said twisting member being rotatable with said twisting means alternately in opposite directions and being located to twist and guide the strip between the conductors upstream of the rotatable stranding nozzle to segregate groups of conductors on opposite sides of said strip in said cable said stranding nozzle (9) being suitable for bending the edges of the strip (12) in the desired direction. The advantage of the invention lies above all in that the strip winding, stranding and binding can be combined in a second line, for instance a sheathing line. A further advantage is that the strips can be continued with a tape paster during the run, or the run can be performed with continued strip coils joined together in a separate step. A further advantage is that on account of prolonged upturns, a combined stranding, strip winding and binding speed would permit higher line speeds than is typically permitted by the output of the plastic press. Still another advantage of the invention is its simplicity and suitability for use in connection with existing equipment. Thus putting the invention into use is advantageous. Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing in which Figure 1 is an example of a typical PCM cable in a schematic perspective view, Figure 2 is a schematic elevational view of the arrangement of the invention, Figure 3 is a schematic elevational sectional view of the passage of the strip within the central tube, and Figures 4 to 6 show alternative embodiments of an essential detail of the arrangement of Figure 2 in views seen in the running direction of the strip. Figure 1 is a schematic representation of an example of a block-insulated cable, wherein the individual main blocks 1, 2 are separated from one another by an S-shaped metallic intermediate shield 3. Figure 2 is a schematic representation of an arrangement in accordance with the invention, wherewith block-insulated cable can be produced in a simple way. Figure 2 shows a preferred embodiment of the arrangement of the invention. The embodiments of this figure include a stationary divider means 5 disposed at the upstream end for the conductors 4 to be stranded with said arrangement, a twisting means 6 disposed at the downstream end, and a medially disposed central tube 7 rotatable recurrently about its longitudinal axis in opposite directions and peripheral tubes 8 being twistable recurrently in opposite directions and peripherally surrounding the central tube 7, the central tube and the peripheral tubes being disposed between the divider means and the twisting means. The central tube 7 and the peripheral tubes 8 are pressed against each other at least during the twisting step of the conductors, and the conductors 4 are adapted to pass through the peripheral tubes 8 and a strip 12 is adapted to pass through the central tube 7. The term conductor in this context refers to filaments, conductor elements, bundles of conductors, quads, optical fibres and other similar elements. When a reverse-stranded product is manufactured with the apparatus of Figure 2, the conductors to be stranded are drawn through the divider means 5 into the peripheral tubes 8 and further through the twisting means 6 out for instance into a stranding nozzle 9 disposed downstream of the twisting means in the running direction of the conductors, the nozzle having a tapering opening wherein the stranded conductors are pressed tightly against one another, thus forming a reverse-stranded product. Any conventional binding device or other similar apparatus 10 may be used for the binding. The divider means and the twisting means may be for instance apertured disks, each having a central bore for the central tube 7 and a plurality of bores, peripherally spaced at regular intervals and radially distanced from the central bore, for the peripheral tubes 8 and for the stranded conductors 4 to be drawn through the peripheral tubes. The stationary divider means 5 at the upstream end for the conductors is fixedly secured to the support structure of the reverse stranding apparatus, and the twisting means 6 at the downstream end for the conductors is journalled to the support structure of the reverse stranding apparatus. The twisting means 6 is fitted with a rotatable drive of its own, preferably with a chain gear, gear transmission, or cogged belt driven electric motor whose speed of rotation can be regulated and reversing automation realized relatively simply. The peripheral tubes 8 may be formed from thin tubes made from a torsion-elastic material, said tubes being attached to the bores of both the divider means 5 and the twisting means 6, so that the tubes form a tube sheath around the central tube 7. The peripheral tubes may be manufactured from polyamide or polytetrafluoroethylene, for instance. During the twisting step of the conductors 4 to be stranded, the peripheral tubes 8 are twisted to the external surface of the central tube 7 on account of the rotating motion of the twisting means 6. To compensate the increasing tensile stress generated by the twisting of the peripheral tubes, the ends of the peripheral tubes are secured to at least the bores of the divider means 5 in an axially resilient manner. Furthermore, it is expedient to bind the peripheral tubes elastically with one another, which eliminates the drawbacks of centrifugal force. The structural details relating to peripheral tubes have been described in U.S. Patent 4 974 408, for instance. In the embodiment of Figure 2, the upstream end of the central tube 7 has been fitted in the central bore of the stationary divider means 5 as a part rotatable relative to said divider means, and fitted with a journalling 11 withstanding axial loads. The downstream end is rigidly secured to the central bore of the twisting means 6. In this embodiment, the rotating and twisting movements of the central tube 7 and the peripheral tubes 8 are generated by the twisting means 6. The central tube may be manufactured for instance from steel, but it should be noted that steel is not the only possible material, since the central tube may also be a torsion-elastic tube manufactured from a plastic material. The construction and operation of the central tubes have been described in U.S. Patent 4 974 408, for instance. This patent also otherwise discloses technology relating to reverse stranding apparatus. In accordance with an essential feature of the invention, a strip 12 serving as an intermediate shield 2 separating the main blocks in a completed cable as shown in the example of Figure 1 is fed into the central tube 7. The strip 12 is guided to pass through the rotatable twisting means 6 and is further guided between the desired conductors 4 ahead of the stranding nozzle or similar 9. In accordance with the invention, the stranding nozzle or similar 9 bends the edges of the strip 12 in the desired direction. Thus, by means of the invention the stranding and longitudinal strip winding of the main blocks can be combined, so that the middle portion of the S remains between the main blocks and the edges thereof are bent around them invariably in the same direction. The strip types used may be paper, plastic or metal strips or combinations thereof. The strip pay-offs offs may be braked coils, several of which may be disposed adjacently on one shaft. The strips on the coils are joined together: when one is finished the strip will shift to an adjacent coil. In the case of large-diameter coils, driven pay-offs are used. The strip 12 is guided from the pay-off into the central tube 7, as set forth previously. The diameter of the central tube is equal to or greater than the width of the strip 12. In some cases, the strip can be bent preliminarily into the shape of an S or a V, thus enabling the use of a smaller-diameter central tube 7. The diameter of the central tube is greater than the diameters of the peripheral tubes. As stated previously, the strip 12 is guided between the desired blocks, i.e. bundles constituted by conductors 4, ahead of the stranding nozzle or similar 9. The guiding is effected by means of a slot 13 provided in a twisting member carried by the rotatable twisting means 6. The twisting member having the slot 13 may for instance be a wearing plate 14 fixed to the rotatable twisting means 6. Figures 4 to 6 show some possible shapes for the slot. Thus the slot 13 may have a wide variety of configurations. In Figures 4 to 6, the different variants of the slot are indicated by the reference numerals 13a, 13b and 13c. Reverse stranding, for instance SZ stranding, inherently involves reciprocating rotation of the twisting means 6, and in consequence the strip 12 will also be twisted up to the guides at the pay-off. The twisting of the strip 12 takes place protected within the central tube 7, as shown in Figure 3. On account of the length of the tube packet, there is a sufficient reserve length maintaining the pitch of twist of the strip 12 sufficiently high. The rotatable stranding nozzle 9 may be a separate device disposed for instance ahead of the binding device 10. However, the strip winding, stranding and binding may also be performed in a rotatable nozzle of the binding device 10. While rotating, the stranding nozzle 9 bends the edges of the strip 12 passing therethrough in the desired direction. Consequent upon the SZ stranding mode, the speed of rotation of the stranding nozzle 9 must always be higher than the speed of rotation of the rotatable twisting means 6. The examples set forth above are in no way intended to restrict the invention, but the invention may be modified fully freely within the scope of the claims. Thus it is to be understood that the arrangement of the invention or its details need not necessarily be exactly as shown in the figures, but other solutions are possible as well. For instance, the number of peripheral tubes may be selected in accordance with current need, etc. The stranding nozzle and the twirling member of the binding device may be rotated by any suitable power source, and any suitable transmission mechanism may also be used in these details. Any suitable reel arrangements, and also power sources in some embodiments, may be used as strip feeding means, as stated previously. Also the slot may be shaped at will in accordance with current need.

Claims: A method of forming a cable by reverse stranding comprising the steps of: drawing conductors (4) through a stationary divider means (5), through peripheral tubes (8) which surround a central tube (7) and which tubes (8) are twistable around the central tube (7) recurrently in opposite directions and through twisting means (6, 14) rotatable alternately in opposite directions, and into a stranding nozzle (9), and rotating the twisting means (6, 14) alternately in opposite directions; characterised by feeding a longitudinally extending strip (12) into the central tube (7) in a downstream direction, guiding the strip (12) through the rotatable twisting means (6, 14) and between the conductors (4) upstream of the stranding nozzle (9) to twist the strip alternatively in opposite directions upon alternate rotation of the twisting means in opposite directions; and, wherein subsequent to guiding and twisting the strip (12), the stranding nozzle (9) bends the edges of the strip which serves as an intermediate shield in the cable. A method according to claim 1 including providing a slot (13) in the rotatable twisting means (6, 14) and guiding the strip (12) between the conductors (4) by means of the slot (13). A method according to claim 1 including rotating the stranding nozzle (9) at a higher speed than the twisting means (6, 14). Reverse stranding apparatus for forming a cable comprising a stationary divider means (5) for conductors (4) to be stranded to form a cable, the divider means (5) being disposed at the upstream end of a central tube (7), twisting means (6) rotatable alternately in opposite directions and disposed downstream of the divider means (5), said central tube (7) being rotatable recurrently about its longitudinal axis, alternately in opposite directions, peripheral tubes (8) peripherally surrounding the central tube (7) and twistable recurrently in opposite directions, the central tube (7) and the peripheral tubes (8) being disposed between the divider means (5) and the twisting means (6, 14) and being arranged to bear against one another during twisting of the conductors, the peripheral tubes (8) being suitable for guiding therethrough conductors to be stranded, characterised by means for feeding a rectilinear strip (12) for use as an intermediate shield into said central tube (7), a twisting member (14) fixed to said twisting means (6) and having a slot (13), the apparatus including a rotatable stranding nozzle (9), said twisting member (14) being rotatable with said twisting means alternately in opposite directions and being located to twist and guide the strip (12) between the conductors (4) upstream of the rotatable stranding nozzle (9) to segregate groups of conductors on opposite sides of said strip (12) in said cable said stranding nozzle (9) being suitable for bending the edges of the strip (12) in the desired direction. Apparatus as claimed in claim 4 wherein said twisting member comprises a wear plate (14) provided with said slot (13). Apparatus as claimed in claim 4 including means for rotating said stranding nozzle at a speed higher than the speed of rotation of said twisting means.

Inventors: KARHU RAIMO, KARHU, RAIMO
Applicants: MAILLEFER NOKIA HOLDING, NOKIA-MAILLEFER HOLDING S.A.
Application year: 1992
Main classification: H01B13
IPC codes: H01B13