GB2061340A

GB2061340A - Method and apparatus for continuously S-Z stranding electrical cable cores

Info

Publication number: GB2061340A
Application number: GB8017523A
Authority: GB
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1979-10-24
Filing date: 1980-05-29
Publication date: 1981-05-13
Also published as: GB2061340B; IN152523B; SE8007431L; FR2467909B2; NL8005822A; SG5584G; IT1145277B; NL188715B; NL188715C; JPH02270225A; BR8006745A; DD154559A6; AR222902A1; JPH0325883B2; SE462068B; IT8049215A0; FR2467909A2

Abstract

The invention is concerned with a continuous cable core stranding technique, wherein thick cable cores are concentrated into a bundle or bunch at a first stranding point, and hauled off therefrom by one or more gripping jaw or tong haul-off assemblies, which rotate about the bundle axis to S-Z strand the cores and which retain the stranded material in a torsion free state over a predetermined distance. From these retaining means, the material is advanced to a second stranding point. According to the invention, the interval (l) between the end of the retaining means and the second stranding point is an even-number multiple of (i.e. at least twice) the storage length, the latter being the distance lsp from the beginning to the end of the one or more haul-off assemblies mentioned above. This measure makes it possible to minimise "waviness" in the cable core bundle or bunch. The cores concentrated into a bundle or bunch at the first stranding point may, immediately after leaving the latter, be wrapped with one or more retaining helices, whereby deviations of the stranded elements from their desired positions in the stranded assembly may be minimised, even with stranding elements of large cross-section. <IMAGE>

Description

SPECIFICATION Method and apparatus for continuously stranding electrical cable cores This invention relates to a method of continuously stranding linearly extended material comprising shaped strands which are either solid or composed of individual filaments, wherein the shaped strands are drawn off individually from stationarily mounted supplies for stranding as desired by a stranding apparatus revolving with changing direction and/or speed of rotation, and wherein the shaped strands are brought together at a first stranding point to form a bundle or bunch, and are thereafter held as a bundle or bunch in a stretched state during passage along a predetermined path extending to a second stranding point, being stranded together during the period in which they are so held during passage along the said predetermined path.

The invention also relates to an apparatus suitable for use in a method as mentioned above, comprising shaped-strand supplies and a stranding apparatus fed thereby, the latter having a first and a second stranding point between which are one or more gripping jaw or tong assemblies, disposed consecutively along the path of the material in the case of more than one thereof, and the bundle or bunch comprising the shaped strands being (in use of the apparatus) gripped by the said one or more assemblies, which (in use) travel along in the axial direction with the material and revolve whilst travelling along in the axial direction.

More specifically, the invention is concerned with a method and an apparatus for the continuous stranding, effected with alternating lay direction, of electrical cables or lines comprising cores of large cross-section, either solid or assembled from individual wires, these cores being hauled off individually from stationarily mounted supplies, concentrated into a bundle or bunch at a first stranding point, and thereafter stranded in the stretched condition within a prescribed path whilst travelling along the prescribed path, which is limited by a second stranding point; within said path, the material is stored in the stretched condition along a predetermined shorter path, and, after leaving the first stranding point, the bundle or bunch is frictionally gripped on all sides and retained along a length which amounts to only a fraction of the storage length, whilst during its retention the section between the first stranding point and the retaining means is stranded and said stranded section continues to be retained in a torsion-free state in said stranded condition whilst travelling along the storage length, before it is fed to the second stranding point after the stranded cores have been released from the retaining means.In this manner it is possible to apply the so-called SZ stranding technique, which has been practised for a long time in telecommunication cable and heavy-current line technology, even for stranding elements of large cross-section and hence considerably higher moments of resistance.

However, a disadvantage has been encountered in as much as cable cores produced as described in the last preceding paragraph sometimes exhibit a waviness in the bundle or bunch of cores, which, although it has no influence upon the operational reliability of the cable, nevertheless frequently gives the latter an untidy external appearance.

It is an object of the invention, in a first aspect thereof, to make it possible to produce cables which are satisfactory even externally from cores of large cross-section, without having to sacrifice an economic utilisation of the SZ stranding technique.

According to the invention, in a first aspect thereof, a method as specified in the last preceding paragraph but two is characterised in that the interval between the end of the retaining means and the second stranding point is an evennumber multiple of the storage length, but is at least twice the storage length. The invention is based upon the discovery that a bundle or bunch of shaped strands of large cross-section stranded in the SZ mode acquires a waviness in the direction of its longitudinal axis, in a stranding method with storage, if a stranding point (this being a fixed point) is arranged at too short an interval from the store outlet.The functional principle of a stranding machine with storage which has a periodically alternating direction of rotation of the store relies upon a two-fold twisting of the shaped strands, the first twisting occurring on entering the stranding store, and the second occurring on leaving the store. Whereas the first twisting is possible without side effects, it becomes apparent in connection with the second twisting, which is applied to an already stranded bundle or bunch, that the stranding necessary for the shortening of the length of lay, in the case of large cross-sections, no longer occurs solely internally within the stranded bundle or bunch, but also affects the bundle or bunch as a whole.The second twisting can thus generate a waviness in the bundle or bunch, and this, apart from impairing the external appearance of the product, may hinder the induction of the cable into a cable duct; also an after-straightening might for instance be necessary when working with cable platforms, and winding on cable drums could be adversely affected.

However, if the second twisting occurs over a length /with a complete sequence of twists with S and Z lays, the length / corresponding to twice the storage length, then the twisting over that length, mathematically considered, is equal to zero, i.e., what is stranded in along e.g. and S-stranded section is stranded out again along a Z-stranded section. The waviness of the length considered is then a minimum. Now if, according to the invention, the S and Z-stranded length I is prolonged by an integral multiple, then the waviness in the increased length considered tends towards zero.

In applying the invention, it has therefore been found particularly advantageous if the stranded bundle or bunch, after leaving the retaining means, passes through a sheathing installation before the second stranding point is reached.

During the passage through the sheathing installation, at least an inner sheath producing a rounded effect may conveniently be extruded on to the stranded bunch. It will be understood that one or more other operational steps, by themselves or additionally, may be carried out (included) along said path. Thus it has sometimes been found advantageous to provide the stranded bundle or bunch, before the extrusion of the inner sheath just mentioned, with banding, which may be in the form of the familiar retaining helix. A marking of the core assembly can also be provided, in a method according to the invention, before the bundle or bunch of stranded cores reaches the second stranding point.

The invention also includes an apparatus comprising means for performing a method according to the invention, characterised in that the retention and stranding are effected by one or more revolving gripping jaw or tong haul-off assemblies. It is to be understood that these are arranged along the storage path, surrounding the stranded bundle or bunch and travelling together with the material in the axial direction.In this case the gripping elements rotate about the longitudinal axis during the travelling together with the stranded material, the first and last gripping element being utilised to effect stranding between itself and the stranding point, and, in a continuous cycle, surrendering this function of effecting stranding to the next, and the latter in turn to the next, the initially first, then second etc., gripping element, by a continuing retention of the bundle or bunch, ensuring a torsion-free guidance of the latter in the course of the storage phase.

However, it has been found particularly convenient if the retention and stranding of a bundle or bunch comprising shaped strands of large cross-section is effected by two gripping jaw or tong haul-off assemblies arranged consecutively in the direction of passage and revolving in the same direction and at the same speed. Preferably, carriages of the said assemblies are secured to chains, and form, conjointly with the latter, a chain caterpillar on both sides of the stranded bundle or bunch, and, in each pair of these carriages, one carriage is provided with a bolt positioned so as to travel around the operative circuit of the carriage, and the other carriage is provided with a recess so positioned and dimensioned as to cooperate with this bolt, by receiving the bolt to form a positive connection between the two carriages.This measure ensures positive synchronism between the said carriages, so that the stranded bundle or bunch is always gripped on all sides simultaneously, and can be guided in a torsionfree state during the stranding.

The invention will be explained more fully with reference to the accompanying diagrammatic drawings, in which: Fig. 1 is a side view showing equipment employed in accordance with the invention, in a first aspect thereof, Fig. 2 is a side view, on an enlarged scale, of a haul-off assembly included therein, and Fig. 3 is a side view showing equipment employed in accordance with the invention, in a second aspect thereof, described below.

In Fig. 1, cores 50, which may be, e.g., sectorshaped cores of a power transmission cable, which are required to be stranded, are hauled off from stationarily mounted-supplies (not shown), and fed to a stranding nipple 53 through guide rollers 52, which also serve to straighten the cores 50 (the rollers 52 may thus belong to roller straightening machines). In the nipple 53, the cores are concentrated into a bundle or bunch and fed to a stranding device 54 disposed downstream of it in the direction of travel. The device 54 comprises at least one revolvable gripping jaw or tong haul-off assembly, and, as actually illustrated in Fig. 1, it comprises two such assemblies, consecutively connected, as shown at 55 and 56.

Fig. 2 shows details of one of these assemblies.

As may be seen from this figure, its gripping jaws or tongs surround the concentrated bundle or bunch pf sector-shaped cores, and simultaneously rotate in a direction of rotation alternating at intervals of time, so that, in each rotation, the section of the concentrated bundle or bunch which is present between the stranding nipple 53 and the first gripping jaws or tongs of the haul-off assembly 55 undergoes a stranding. With steady revolution, in the SZ mode, the next gripping jaws or tongs of the haul-off assembly 55, and then those of the haul-off assembly 56, grip the stranded material positively and frictionally, and guide it in a torsion-free state through the stranding store constituted by the two haul-off assemblies.Now in order to ensure that the products thus produced can be further processed satisfactorily, and are subject to no waviness due to the stranding operation, a schematically indicated sheathing installation 57 is employed, this being disposed adjacently to the haul-off assembly 56. It may be constituted, e.g., by a spinner, to apply a banding, and an extruder, to apply a packing or inner sheath, and also a cooling trough.

Only downstream of the sheathing installation 57 is there a stationarily mounted haul-off device 58, which may be in the form of a caterpillar hauloff device. The haul-off device 58 also provides a second stranding point of the stranding apparatus.

By the choice of an interval, between this and the haul-off assembly 56, of at least 2n x 15p, where n is an even number and 15p is the storage length, it is ensured that the waviness of the stranded bundle 59 tends towards zero, i.e., in principle no waviness is present even with large crosssections. The stranded material, provided at least with an inner sheath, is then wound via a deflector roller 60 on to a winding drum 61. It will be understood that the caterpillar haul-off device 58 may be followed by further processing stations, in a continuous succession, so that, e.g., an armouring is applied, and immediately after this a mechanically strong outer sheath is extruded on.

Fig. 2 illustrates a haul-off assembly 55 or 56 on a larger scale than Fig. 1. It incorporates carriages 62 for the gripping jaws or tongs, these carriages 62 being secured by means of straps 63 to chains 64 of a chain transmission 65. Two driving motors are shown at 66, and the bunch or bundle to be stranded is shown at 67.

To obtain a synchronism between associated upper and lower carriages 62, so as to ensure operational reliability, a positive coupling of paired carriages is provided for. This positive coupling results from the provision on each upper carriage of a bolt 68, prefereably elastic, e.g., made of hard polyethylene, which is positioned on the operational circuit 69 of the upper carriages, and from the provision on each lower carriage of a recess 70, which is so positioned and dimensioned as to cooperate with the bolt 68 of the upper carriage of the pair concerned, by receiving this bolt to form a positive connection between the two carriages.

Because the carriages 62 are secured to the chains 64 by straps 63, the positive coupling must occur in a radially outward prolongation of the strap centre 71. The bolt 68 and the recess 70 are then in principle part of the chain transmission, forming a toothed drive system.

The attainment of synchronism by means of this simple positive connection makes it possible to omit lateral gearing, and thereby permits an equal-sided mass disposition on the haul-off assembly concerned. Furthermore, this construction permits the parallel wiring of the armatures in the two driving motors 66, and thereby makes it possible to employ a relatively simple electronic control system. In this way two individual chain transmissions of 3 haul-off assembly can be brought into synchronism with the smallest possible expenditure in respect of mechanical and electronic equipment.

We now turn to a second aspect of the invention.

From the foregoing description, it will be appreciated that the invention, in its first aspect, makes it possible to avoid the waviness mentioned, by the selection of the stated interval between the end of the retaining means and the second stranding point.

However, if stranding elements of large crosssection are used, e.g., cores produced from individual wires, i.e., elements which are inherently flexible, or those which owing to some other specific construction exhibit a low rigidity compared to solid constituent strands, difficulties may sometimes arise during the formation of the stranded assembly, in that the stranding elements may not occupy, or may not always occupy, the desired position in the stranded assembly.

It is therefore an object of the invention, in a second aspect thereof, to enable the measures described earlier herein to be employed for the continuous stranding of any desired cores of large cross-section.

According to the invention, in a second aspect thereof, the cores concentrated into a bundle or bunch at the first stranding point, immediately after leaving the first stranding point, are continuously wrapped as a bundle or bunch conjointly with one or more retaining helices. The application of the one or more retaining helices and the twisting occur simultaneously, so that the one or more retaining helices are wound on to a twisted core bundle or bunch. The one or more retaining helices therefore fix the configuration of the bundle or bunch.

The "banding" or "winding" of stranded elements is known per se; it is resorted to after the stranding of individual elements in order to obtain secure cohesion. On the other hand, in order to improve the method according to the first aspect of the present invention, it is intended that a bundle or bunch should be fixed with at least one retaining helix simultaneously with the twisting of the individual cores.

Insulating materials familiar in cable manufacture may be employed for wrapping the bundle or bunch with at least one retaining helix.

These materials may have the shape of a band or strip, or of any desired other profile, preferably of low height. If there are particularly stringent demands in respect of tensile strength, then correspondingly tension-resistant materials will be adopted, e.g., based on polytetrafluoroethylene or polyamide. In this context a braided or woven fabric, e.g., a lattice weave, of these materials, which is cut into the form of a band and applied spirally on to the gathered bundle or bunch, has been found particularly suitable.

In order to perform a method according to this second aspect of the invention, it is convenient to make use of a reverse winder of flat or central construction disposed between the first stranding point and a haul-off assembly effecting the stranding. Such a winder, having a very small overall length, permits a minimum interval between the first stranding point (stranding nipple) and the haul-off assembly effecting the stranding.

The stranding or twisting of the individual elements may be effected by means of a rotary gripping jaw or tong haul-off assembly, as already described in respect of the first aspect of the invention. However, a rotary belt caterpillar hauloff assembly, or a rotary chain caterpillar haul-off assembly may also be found advantageous, particularly for "flexible" conductor strands.

It is further advantageous, particularly to make possible a compact production installation, to accommodate a straightening device (roller straightening machine, which can be used to straighten cores hauled off from stationarily mounted core supplies), a stranding nipple providing the first stranding point, and a winder for the one or more retaining helices, in a single housing. It is also convenient to employ a straightening device having longitudinal mobility with respect to the stranding nipple This can have a striking effect upon the stranding process in the stranding nipple. An optimum selection of the entry angle of the individual cores can be achieved by this means.

The second aspect of the invention will be explained more fully with reference to Figure 3 of the accompanying diagrammatic drawings. Figure 3 shows an installation for stranding cores of large cross-section, e.g., cores of "low tension" distribution cables in the 1 kV service voltage range.

In Figure 3, cores 101 are constituted e.g. by mutually stranded individual wires (multiple-wire sector conductors); they are therefore flexible stranding elements in the generally accepted sense. Said cores 101 are hauled off, in the number prescribed for the finished product concerned, from stationarily mounted supplies, not shown, and fed through a roller straightening device 102, which is followed by a further device comprising "prestranding" rollers 103, to a stranding nipple 104. The core inlays (fillers) and wedge gussets often incorporated in such cables may likewise enter with them. Immediately behind the stranding nipple, i.e., whilst the stranding process of the individual cores is still proceding, the bunch is wrapped with preferably two retaining helices 106. A reverse winder 105 of the known flat construction is employed for this purpose.Next the bunched strand comprising the stranded cores provided with the wrappings enters a gripping jaw or tongs haul-off means 107 revolving in an alternating direction of rotation (SZ). The stranding bundle or bunch is twisted along the path between the stranding nipple 104 and the first gripping element of the haul-off means 107.

After leaving the haul-off means 107, the stranded bundle or bunch comprising the cores 101 travels through a sheathing line 108, in which it is given e.g., an inner and an outer protective sheath. During this stage also the stranded bundle or bunch twists from the haul-off means 107 as far as a haul-off caterpillar 109 of the sheathing line; therefore any second twisting which would give rise to waviness in the shaped strand is eliminated. Beyond the haul-off caterpillar 109, the stranded and sheathed stranded bundle or bunch (cable) 111 runs on to a cable drum 110.

By a "stranding point", we mean, in the present description and claims, a point of transition from a non-rotating system (e.g. a non-rotating conductor supply means) to a rotating system (here a stranding device), or, conversely, a point of transition from a rotating system (stranding device) to a non-rotating system (e.g. a haul-off device or collecting drum).

Claims

1. Method of continuous stranding, effected with alternating lay direction, of electrical cables and lines comprising cores of large cross-section, either solid or assembled from individual wires, these cores being hauled off individually from stationarily mounted supplies, concentrated into a bundle or bunch at a first stranding point, and thereafter stranded in the stretched condition within a prescribed path whilst travelling along the prescribed path, which is limited by a second stranding point; the material being stored in the stretched condition, within said path, along a predetermined shorter path; the bundle or bunch, after leaving the first stranding point, being gripped frictionally on all sides and retained along a length which amounts to only a fraction of the storage length, and being stranded during the retention of the section of the bundle or bunch between the first stranding point and the retaining means, and said stranded section continuing to be retained in a torsion-free state in said stranded condition whilst travelling along the storage length, before, after the stranded cores have been released from the retaining means, it is fed to the second stranding point; characterised in that the interval between the end of the retaining means and the second stranding point is an even-number multiple of the storage length, but is at least twice the storage length.

2. Method according to claim 1, characterised in that, after leaving the retaining means, the stranded bundle or bunch passes through a sheathing installation before the second stranding point is reached.

3. Method according to claim 2, characterised in that at least an inner sheath producing a rounded effect is extruded on to the stranded bundle or bunch during its passage through the sheathing installation.

4. Method according to claim 3, characterised in that the stranded bundle or bunch is provided with banding before the extrusion of the inner sheath.

5. Apparatus comprising means for performing a method according to claim 1, characterised in that the retention and stranding are effected by a revolving gripping jaw or tong haul-off assembly.

6. Apparatus comprising means for performing a method according to claim 1, characterised in that the retention and stranding are effected by two gripping jaw or tong haul-off assemblies arranged consecutively in the direction of passage and revolving in the same direction and at the same speed.

7. Apparatus according to claim 6, characterised in that carriages of the said assemblies are secured to chains, and form, conjointly with the latter, a chain caterpillar on both sides of the stranded bundle or bunch, and, in each pair of these carriages, one carriage is provided with a bolt so positioned as to travel around the operational circuit of the carriage, and the other carriage is provided with a recess so positioned and dimensioned as to cooperate with this bolt, by receiving the bolt to form a positive connection between the two carriages.

8. Method according to claim 1, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

9. Apparatus according to claim 6, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

10. Electrical cables and lines produced by a method according to claim 1, 2, 3, 4 or 8, or by means of an apparatus according to claim 5, 6, 7 or9.

11. Method according to claim 1, characterised in that the cores concentrated into a bundle or bunch at the first stranding point, immediately after leaving the first stranding point, are continuously wrapped as a bundle or bunch conjointly with one or more retaining helices.

12. Method according to claim 11, characterised in that one or more insulating profile bands or strips are used as the one or more retaining helices.

13. Method according to claim 11, characterised in that one or more braided or woven fabrics are used as the one or more retaining helices.

14. Method according to claim 13, characterised in that one or more lattice weaves of tension-resistant insulating material are used as the one or more retaining helices.

1 5. Apparatus comprising means for performing a method according to claim 11, characterised in that a reverse winder of flat or central construction is disposed between the first stranding point and a haul-off assembly effecting the stranding.

1 6. Apparatus according to claim 15, characterised in that the said haul-off assembly is a rotary gripping jaw or tong haul-off assembly.

17. Apparatus according to claim 15, characterised in that the said haul-off assembly is a rotary belt caterpillar haul-off assembly.

1 8. Apparatus according to claim 15, characterised in that the said haul-off assembly is a rotary chain caterpillar haul-off assembly.

1 9. Apparatus according to claim 15, characterised in that a straightening device, a stranding nipple and a retaining helix winder are accommodated in a single housing.

20. Apparatus according to claim 19, characterised in that the straightening device is longitudinally mobile with respect to the stranding nipple.

21. Method according to claim 11, substantially as described with reference to Figure 3 of the accompanying drawings.

22. Apparatus according to claim 1 5, substantially as described with reference to Figure 3 of the accompanying drawings.

23. Electrical cables and lines produced by a method according to claim 11,12,13, or 21, or by means of an apparatus according to claim 15, 16, 17, 18, 19, 20 or 22.