Stranding apparatus and method

Abstract

 Stranding apparatus includes input and output nipples (3), (4) longitudinally spaced along the wires (1) etc to be stranded. The nipples (3), (4) allow twisted wires to pass therethrough but inhibit the transfer of torque from one side to the other. One or more rotating stranding heads (5) are provided and the apparatus is periodically adjusted between a first condition in which the stranding heads inpart a twist to the wires, and a second condition in which they allow the wires (1) to pass therethrough substantially unaltered. The apparatus may be adjusted by varying the tension of the wires (1) periodically between a level at which the wires are gripped by the stranding heads, and one at which they slip across untwisted. Additionally or alternatively the stranding heads are moved periodically between an engaged position (11) and a disengaged position (10).

Description

[0001] This invention relates to the stranding together of stranding elements into twisted bunches. By the term stranding element, there is herein meant any flexible elongate elements such as ropes, wires, cables and the like.

[0002] The invention particularly relates to S-Z stranding wherein the elements are given alternately a left hand lay and a right hand lay. As the overall average lay of the resulting product is substantially zero, it is not necessary for the pay off apparatus or take up apparatus to rotate.

[0003] The most commonly used S-Z stranding apparatus produces the change in lay by means of a stranding head repeatedly changing its direction of rotation. As the inertia of any stranding head is quite considerable, such apparatus is relatively slow. In addition the engine or gear system repeatedly changing the direction of rotation is subject to great wear leading to frequent maintenance being required. U.K. Patent No: 1391356 describes an S-Z stranding machine which avoids changing the direction of rotation of the stranding head by periodically moving a torsion block longitudinally along the stranding elements. However as before, a body having a large inertia is being repeatedly changed in direction. The apparatus is therefore liable to produce relatively long sections of untwisted wire as the torsion block is being slowed and reversed. This deficiency is recognised in U.K. Patent No: 2018845 describing modifications to the above described apparatus.

[0004] It is an object of the present invention to provide S-Z stranding apparatus which overcomes, at least in part, the above-mentioned disadvantages.

[0005] Accordingly there is provided apparatus for the stranding together of stranding elements drawn from a supply at a haul-off speed, the apparatus comprising input and output nipples longitudinally spaced along the stranding elements, the nipples being adapted to allow twisted stranding elements to pass therethrough but to inhibit the transfer of torque thereacross; a rotating stranding means positioned between the input and output nipples; and reciprocating means for perodically adjusting the apparatus between a first condition in which the stranding means imparts a twist to the stranding elements, and a second condition in which the stranding means allows the stranding elements to pass therethrough substantially unaltered. The stranding means is required to rotate in one direction only, conveniently with a constant rotational speed, and no movement of the stranding means is required longitudinally of the stranding elements.

[0006] Preferably the reciprocating means adjusts the apparatus with a period related to the haul-off speed. Therefore the lay/unit length which is a function of both the haul-off speed and the period of the reciprocating means, may be accurately controlled. Thus as the haul-off speed varies, the period of the reciprocating means varies, to maintain constant the required lay/unit length.

[0007] Preferably the stranding means comprises one or more stranding heads, each of the one or more stranding heads comprising one or more twisting members rotatably driven about the axis of the stranding elements. Each stranding head conveniently comprises at least two twisting members, adapted to engage opposite sides of the stranding elements.

[0008] In one arrangement the stranding means comprises a single stranding head and the reciprocating means adjusts the apparatus with a period substantially equal to the time taken for the stranding elements to travel from the input nipple to the stranding head. This prevents excessive overwinding of the stranding elements, where one lay is added to the elements only to be subsequently unwound and rewound with an opposite lay. In addition substantially no parallel sections will be produced between the regions of "S" and "Z" lay. Conveniently the stranding head is positioned substantially nearer to one of the input or output nipples than to the other. Preferably the stranding head is positioned nearer to the output nipple, thereby increasing the time taken for the stranding elements to travel from the input nipple to the stranding head and hence the period of the reciprocating means.

[0009] According to an alternative arrangement the stranding means comprises first and second stranding heads spaced one from the other between the input and output nipples. Where the period of the reciprocating means is to be related to the haul-off speed, the reciprocating means adjusts the apparatus with a period substantially equal to the time taken for the stranding elements to travel between the first and second stranding heads. The provision of first and second stranding heads further serves to reduce overwinding of the stranding elements. With the period of the reciprocating means related to the time taken for the stranding elements to travel between the first and second stranding heads, no unnecessary winding of the stranding elements takes place.

[0010] There is conceivably provided one or more intermediate stranding heads positioned between the first and second stranding heads. This arrangement allows the distance between the first and second stranding heads, and hence the period of the reciprocating means, to be increased whilst maintaining uniform rotation of the stranding elements therebetween. As the distance between the first and second stranding heads increases, it may become necessary to confine the stranding elements therebetween within a rigid sleeve in order to prevent excessive lateral movement, known as "whip".

[0011] The reciprocating means preferably comprises tension control means for periodically adjusting the tension of the stranding elements between a first level wherein the tension is relatively high such that the rotation of the stranding means imparts a twist to the stranding elements, and a second level wherein the tension is relatively low such that the stranding elements pass therethrough substantially unaltered. At the higher level of tension the stranding elements are gripped and twisted by the stranding means, whereas at the lower level of tension the stranding elements merely slip over the stranding means without being rotated thereby. By periodically varying the tension above and below the level at which slippage occurs, a selective twisting of the stranding elements can be achieved without any movement or change of direction of the stranding means.

[0012] The tension control means conveniently comprises a member around which the stranding elements pass, the member being moveable laterally with respect to the longitudinal axis of the stranding elements passing thereacross to adjust the tension thereof. The member is conveniently mounted on a dancer arm the position of which is controlled by biasing means such as a pneumatic cylinder. By adjusting the force exerted by the biasing means between a high and low value, the tension of the stranding elements can be correspondingly varied.

[0013] Alternatively or additionally to the tension control means, the reciprocating means includes means for periodically moving the stranding means between an engaged position in which it imparts a twist to the stranding elements, and a disengaged position in which it allows the stranding elements to pass therethrough substantially unaltered. In this arrangement the only reciprocating movement of the stranding means is over the small distance required for it to travel between its engaged and disengaged positions. Where the stranding means comprises one or more stranding heads, each comprising one or more rotatable twisting members, the twisting members are mounted so as to be moveable laterally of the stranding elements between the engaged and disengaged positions. Where the apparatus employs first and second stranding heads spaced one from another, the heads are mounted to be moveable between their engaged and disengaged positions substantially in synchrony. Similarly if one or more intermediate stranding heads are present, they are also arranged to be moved between their engaged and disengaged positions substantially in synchrony.

[0014] One or both of the input and output nipples conveniently comprises at least three roller elements disposed two on one side of the stranding elements and one on the other side thereof, the roller elements co-operating to inhibit the transfer of torque on the stranding elements across the nipple. Preferably the roller elements include a groove in which the stranding elements are received. Alternatively, one or both of the input and output nipples comprises at least three curved skid surfaces, as opposed to roller elements.

[0015] The invention further resides in a method of stranding together stranding elements incorporating apparatus as above described. In particular a method for the stranding together of stranding elements in which the stranding elements are drawn from a supply at a haul-off speed comprises inhibiting the transfer of torque along the stranding elements at two spaced positions with input and output nipples, the nipples allowing twisted stranding elements to pass therethrough; periodically twisting the stranding elements with rotating stranding means; and periodically adjusting the apparatus between a first condition in which the stranding means imparts a twist to the stranding elements and a second condition in which the stranding means allows the stranding elements to pass therethrough substantially unaltered.

[0016] The apparatus is preferably adjusted by periodically adjusting the tension of the stranding elements between a first level wherein the tension is relatively high such that the rotation of the stranding means imparts a twist to the stranding elements, and a second level wherein the tension is relatively low such that the stranding elements pass therethrough substantially unaltered. Alternatively or additionally the apparatus is adjusted by periodically moving the stranding means between an engaged position in which it imparts a twist to the stranding elements, and a disengaged position in which it allows the stranding elements to pass therethrough substantially unaltered. Preferably the apparatus is adjusted, whether by means of varying the tension of the stranding elements or by means of moving the stranding means, with a period related to the haul-off speed.

[0017] The invention further extends to a stranding line including two or more sets of the above described apparatus, whether in series or in parallel one with the other.

[0018] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of one embodiment of stranding apparatus according to the invention;

Figures 2 and 3 are schematic views of a twisting head for use in the apparatus of Figure 1, the twisting head being shown in its disengaged and engaged positions respectively;

Figure 4 is a schematic diagram of an input or output nipple of the apparatus of Figure 1;

Figure 5 is a graphical representation of the lay of elements stranded by the apparatus of Figure 1;

Figure 6 is a schematic diagram of an alternative embodiment of stranding apparatus in accordance with the invention;

Figure 7 is a graphical representation of the lay of elements stranded by the apparatus of Figure 6; and

Figure 8 is a schematic diagram of another alternative embodiment of stranded apparatus in accordance with the invention.

[0019] Referring to Figure 1, stranding elements such as wires 1 are fed in the direction of the arrow A to stranding apparatus shown generally at 2. The apparatus 2 comprises an input nipple 3 and an ouput nipple 4, spaced one from the other along the wire 1. Between the nipples 3 and 4 is a twisting head 5 rotating at a constant speed about the longitudinal axis of the wire 1, as shown by the arrow B.

[0020] The twisting head 5 is shown in more detail in Figures 2 and 3. The head 5 comprises a cylindrical cage 6 within which is housed two wheels 7, one mounted on each side of the central axis through which the wires 1 pass. The cage 6 and the wheels 7 are rotatably driven about the longitudinal axis of the wires by means of a motor (not shown). Guides 8 and 9 help achieve the correct positioning of wires 1 on entering and leaving the twisting head 5.

[0021] The wheels 7 are movable laterally of the wires 1 by means of a pneumatic system (not shown). Figure 2 shows the wheels in their disengaged position 10 wherein they do not contact the wires 1 which are thus allowed to pass through the twisting head unaltered. Figure 3 shows the wheels in their engaged position 11 in which they contact the wires and impart a twist thereto.

[0022] Figure 4 shows the configuration of the input nipple 3 and output nipple 4, which are identical one to the other. The nipple comprises three rollers 12 disposed two on one side of the wires and one on the other side thereof. The rollers 12 in combination prevent rotational torque on the wire 1 from being transferred from one side of the nipple to the other. However, twisted wire is allowed to pass thereacross without being significantly untwisted. As with the twisting head 5, guides 15 and 16 control the entry and exit of the wire 1.

[0023] The operation of the apparatus of Figure 1 will now be described. With parallel wire passing through the stranding apparatus 2, the stranding head 5 is moved to its engaged position 11. Positive lay twists will start to build up over the relatively large distance L between the input nipple 3 and the head 5, whilst negative lay twists will be built up over the smaller distance x between the head 5 and the output nipple 4. Exiting from the output nipple 4 will be negative lay twists built up over region x, beginning to fall off as wires with positive lay enter region x from L. This is the area shown as P in Figure 5.

[0024] When a net twist of e.g. 0.5 positive lay wire has been built up in region L, the twisting head is moved to its disengaged position 10. This allows the region of positive lay wire to pass through to the output nipple 4 as depicted by the area Q in Figure 5. When the last of the positive lay wire has reached the head 5 and parallel wire is in the region L, the head returns to its engaged position and the cycle is repeated. In this way regions of wire with alternating positive and negative lay are produced as depicted in Figure 5.

[0025] Figure 6 shows an alternative embodiment of stranding apparatus incorporating two twisting heads. As before, an input nipple 3 and an output nipple 4 are spaced along the wires 1, which are fed from a supply at constant velocity. A measuring wheel 22 measures the length of wires 1 entering the input nipple 3. A first twisting head 20 is positioned adjacent the input nipple 3, whilst a second twisting head 21 is positioned adjacent the output nipple 4. First and second heads 20 and 21 are both as previously described with reference to Figures 2 and 3. Between the heads 20 and 21 is a tube 23 in which the wires 1 are constrained to prevent excessive "whip" on rotation thereof.

[0026] The twisting heads are rotatably driven from a common shaft 24 which is itself driven by a motor 25 by means of a belt and pulley system 26. Timing and control of the stranding apparatus is carried out by a control unit 27.

[0027] The operation of the apparatus of Figure 6, which incorporates two twisting heads, will now be described. With parallel wire passing through the apparatus, twisting heads 20 and 21 are simultaneously moved to their engaged positions and negative lay twists will start to emerge from the apparatus, being built up between the second head 21 and the output nipple 4. This is the region R shown in Figure 7.

[0028] Between the first and second twisting heads, the wires will rotate without any change in their lay. Therefore firstly parallel wire, followed by the start of the positive lay region built up between the input nipple 3 and the first head 20 will pass through the tube 23 between the first and second twisting heads. When the positive lay region reaches the second twisting head 21, both heads are moved to their disengaged positions and wire with a positive lay emerges from the apparatus. This is the region S in Figure 7. Parallel wires will now be passing along the tube 23 and when this parallel region reaches the second head 21, both heads return to their engaged positions and the cycle is repeated.

[0029] The wire emerging with alternate regions of positive and negative lay as shown in Figure 7, is not subject to any overwinding - i.e. wire given first a lay in one direction and then subsequently unwound and given a lay in the reverse direction. Thus no unnecessary or unproductive working of the wire takes place.

[0030] Although apparatus according to the invention produces very little parallel wire between the regions of S-Z twist, some unravelling of the wires at the intersections is to be expected when the bunched wires are put under tension. This can be counteracted by passing the wires over a castellated roller to produce small indents in the wires thereby locking them one to another. The castellated roller may be located such as to be permanently in engagement with the wires, or alternatively may be brought into engagement only when intersections between S-Z twist are passing thereby.

[0031] Additionally or alternatively, unravelling of the wires may be compensated for by adding an extra degree of twist to regions adjacent the intersections. This may conceivably be achieved by temporarily slowing the passage of wires through the one or more twisting heads, just as they are to be moved between their engaged and disengaged positions. Momentary slowing of the wires can be achieved by passing them around a pulley which is movable between off-line and in-line positions. During the normal twisting of the wires the pulley moves slowly to its off-line position. Just as the one or more twisting heads are to be moved between their engaged and disengaged positions, the pulley moves quickly in-line, momentarily slowing the passage of the wires and producing a degree of extra twisting adjacent the S-Z intersections. Furthermore, unravelling of the wires may be reduced or even eliminated by ensuring that the twisted wires emerging from the apparatus are taken up under low tension conditions.

[0032] Figure 8 shows an alternative embodiment of stranding apparatus in which the lateral movement of the wheels 7 is replaced by a tension control unit shown generally at 30. The wires are passed over in input wheel 31 and then travel over a tension pulley 32 laterally displaced from the main longitudinal axis of the apparatus. The tension pulley 32 is located at one end of a cantilevered dancer arm 33, pivotally mounted on support 34. The other end of the the dancer arm 33 is biased by means of a gas cylinder 35 driven by a source of compressed air 36. The input and output nipples 3 and 4, and the first and second twisting heads 20 and 21, are disposed as before.

[0033] In the apparatus of Figure 8, the wires 1 are fed at constant velocity and the twisting heads 20 and 21 are continually in the engaged position with the wheels 7 in contact with the wires. The operation of the appartus is essentially the same as that of the apparatus of Figure 6, except that the effect of the twisting heads, is governed by the tension control unit 30. With the gas cylinder 35 exerting a relatively high bias on the dancer arm 33, the tension applied to the wires 1 is sufficient to cause them to be gripped and twisted by the rotating wheels 7. This is equivalent to the twisting heads 20 and 21 being in their engaged position as described with reference to Figure 6.

[0034] When it is required to change the lay of the wires, the gas cylinder 35 is switched to exert a relatively low bias on the dancer arm 33. This results in a much lower tension of the wires 1 allowing them to slip over the rotating wheels 7 without being twisted thereby. This is equivalent to the twisting heads 20 and 21 being moved to their disengaged position as described with reference to Figure 6. Indeed both an adjustment of the tension by the control unit 30 and lateral movement of the wheels 7 may be employed in combination, if desired.

[0035] In order to isolate any variations in the tension of the wires being input to the apparatus, it may be advisable to employ a tension control capstan (not shown) situated prior to the input wheel 31. The capstan is driven at a speed governed by the position of the arm 33. In the event of an undesired change in the tension of the input wires, the dancer arm 33 will be moved causing a corresponding change in the speed of the capstan to counteract the change in tension. In this way the tension of the wires entering the twisting heads 20 and 21 is carefully controlled.

Claims

1. Apparatus for the stranding together of stranding elements (1) drawn from a supply at a haul-off speed, the apparatus comprising input and output nipples (3) (4) longitudinally spaced along the stranding elements (1), the nipples (3) (4) being adapted to allow twisted stranding elements to pass therethrough but to inhibit the transfer of torque thereacross; and a rotating stranding means (5; 20, 21) positioned between the input and output nipples, characterised in that there is provided reciprocating means for periodically adjusting the apparatus between a first condition in which the stranding means imparts a twist to the stranding elements, and a second condition in which the stranding means allows the stranding elements to pass therethrough substantially unaltered.

2. Apparatus according to Claim 1 characterised in that the reciprocating means adjusts the apparatus with a period related to the haul-off speed.

3. Apparatus according to Claim 1 or Claim 2 characterised in that the stranding means comprises one or more stranding heads (5; 20, 21), each of the one or more stranding heads comprising one or more twisting members (7) rotatably driven about the axis of the stranding elements.

4. Apparatus according to Claim 2 and 3 characterised in that the stranding means comprises a single stranding head (5) and the reciprocating means adjusts the apparatus with a period substantially equal to the time taken for the stranding elements (1) to travel from the input nipple (3) to the stranding head (5).

5. Apparatus according to Claim 3 or Claim 4 characterised in that the stranding means comprises first and second stranding heads (20, 21) spaced one from the other between the input and output nipples (3, 4).

6. Apparatus according to Claim 5 when appendant to Claim 2 characterised in that the reciprocating means adjusts the apparatus with a period substantially equal to the time taken for the stranding elements (1) to travel between the first and second stranding heads (20, 21).

7. Apparatus according to any of Claims 1 to 6 characterised in that the reciprocating means comprises tension control means (30) for periodically adjusting the tension of the stranding elements (1) between a first level wherein the tension is relatively high such that the rotation of the stranding means (5;20, 21) imparts a twist to the stranding elements, and a second level wherein the tension is relatively low such that the stranding elements pass therethrough substantially unaltered.

8. Apparatus according to Claim 7 characterised in that the tension control means (30) comprises a member (32) around which the stranding elements (1) pass, the member (32) being moveable laterally with respect to the longitudinal axis of the stranding elements passing thereacross to adjust the tension thereof.

9. Apparatus according to any of Claims 1 to 8 characterised in that the reciprocating means includes means (5; 20, 21) for periodically moving the stranding means between an engaged position (11) in which it imparts a twist to the stranding elements, and a disengaged position (10) in which it allows the stranding elements to pass therethrough substantially unaltered.

10. A method for the stranding together of stranding elements in which the stranding elements (1) are drawn from a supply at a haul-off speed; characterising by the steps of inhibiting the transfer of torque along the stranding elements (1) at two spaced positions with input and output nipples (3, 4), the nipples allowing twisted stranding elements to pass therethrough; periodically twisting the stranding elements (1) with rotating stranding means (5; 20, 21); and periodically adjusting the apparatus between a first condition in which the stranding means imparts a twist to the stranding elements (1) and a second condition in which the stranding means (5; 20, 21) allows the stranding elements to pass therethrough substantially unaltered.

11. A method according to Claim 10 characterised in that if it includes the step of periodically adjusting the tension of the stranding elements (1) between a first level wherein the tension is relatively high such that the rotation of the stranding means (5; 20, 21) imparts a twist to the stranding elements, and a second level wherein the tension is relatively low such that the stranding elements pass therethrough substantially unaltered.

12. A method according to Claim 10 or 11 characterised in that in includes the step of periodically moving the stranding means (1) between an engaged position (11) in which it imparts a twist to the stranding elements (1), and a disengaged position (10) in which it allows the stranding elements (1) to pass therethrough substantially unaltered.

13. A stranding line characterised in that it includes two or more sets of apparatus acording to any of claims 1 to 9.

Drawing