NZ195534A

NZ195534A - Stranding machine with central bobbins

Info

Publication number: NZ195534A
Application number: NZ195534A
Authority: NZ
Inventors: M Sarracino
Original assignee: Pirelli Cavi Spa
Priority date: 1979-12-12
Filing date: 1980-11-12
Publication date: 1984-07-06
Also published as: GB2064611A; BR8008139A; SE8008684L; AU532071B2; AR223258A1; FI803638L; GB2064611B; NO157185B; DK532880A; JPH0128153B2; DE3046940A1; DK156837B; CA1126711A; IT7907219A0; AU6423780A; FR2471439A1; SE462878B; IT1165923B; ES498314A0; DE3046940C2

Description

1955 34 Priority Datejs): : J . 7.^.

Compfste Specification FiSacS: PP Class: .P.°.7&3l°.Z Publication Date: ..0.6 JUL J984..

P.O. Jei£*na!, Mo: ..

No.: Date: NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION /-Vi? , "®8C }' "STRANDING MACHINE PROVIDED WITH CENTRAL BOBBINS" 31/We, INDUSTRIE PIRELLI S.p.A., an Italian company, of Piazzale Cadorna, 5 Milan - Italy hereby declare the invention for which / we pray that a patent may be granted to dcdc/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - 195534- The present invention relates to a stranding machine which comprises a plurality of bobbins rotatably mounted about an axis of the machine, which bobbins are used both for the stranding and to wind up fresh wire upon themselves.

Machines of this type are employed to strand several wires together or to strand several wires about a central core, as for instance a rope, the conductor of an electric cable, or a similar element of considerable length progressing in the direction of its axis. In general, such a machine comprises a plurality of hollow shafts aligned with one another on the machine axis, each rotatably mounted in a support and driven into rotation by a motor, at least one pair of bobbins disposed on each shaft, and a paying-off arm for each bobbin.

During the stranding operation, the wire of one bobbin of each pair is paid-off by the associated paying-off arm (which in this phase is secured fast with the rotating shaft) and, by mens of a system of pulleys, this paid-off wire is guided through the plurality of hollow shafts towards a stranding station, tension being applied to the wires to draw them from their bobbins. The second bobbin of each pair is driven into rotation to be rewound with fresh wire, so that these bobbins can subsequently be used for the stranding phase when the wires on the first bobbins are exhausted.

In machines of this kind, it is necessary to impart to the wire a correct paying-off tension and to provide convenient tension regulation systems; also it is important to apply a braking force when the machine stops, stronger N.Z. FA". '- ;\T G'~r ICE JAN 1984 105534- than that exerted in the paying-off phase, so as to stop the bobbin at the same moment as the machine is stopped.

In fact, when the sense of bobbin rotation in the paying-off phase is the same as that of the paying-off arm, so that the latter is always dragging the bobbin into rotation, the absolute speed of the bobbin is equal to the arm speed (for instance of the order of 600-700 r.p.m.) plus the paying-off speed, for instance of the order of 50 r.p.m.

On the contrary, when the sense of bobbin rottion in the paying off phase is opposite to that of the paying-off arm, the absolute speed of the bobbin is equal to the arm speed minus the paying-off speed, but is still very high.

Therefore, in the above described machines it is necessary to provide a system which, besides placing the wire under tension is able to subject the bobbin to a strong braking torque when the machine stops, because the rotation of the bobbin depends not only on the paying-off speed but also upon the dragging-speed which is ten or more times higher than the paying-off speed.

The provision of a satisfactory solution is made more difficult by the need of further complying not only with the working conditions of the machine to obtain a good stranding, but also with those caused by stopping the machine no matter for what reason; this must be ensured by means which are able to allow an automatic change from the light tension exerted on the wire being paid off to a strong braking action necessary to stop the bobbin, and a further feature must be the possibility of a quick release of the bobbin to enable it N.Z. PATENT?:-;-ICE 2 5 JAN 1984 19553-1 to pass from the stranding phase to the rewinding phase.

Further, the solution must be suitable for a simple and economic applicaton to a large number of bobbins, which number is sometimes considerable, comprising for instance 18 pairs of bobbins or even more.

It is moreover to be noted that in the above machines the speeds involved lead to problems caused by high centrifugal forces which could compromise or handicap the means foreseen to regulate the wire tension during pay-off and to brake the bobbins.

An embodiment of the invention to be described herein ensures an intermediate braking of the bobbins when the machine stops, a regulated tension of the wire during stranding which can be applied to all the bobbins mounted on the hollow shaft in central position and a quick release of the bobbin brakes for their subsequent rewinding.

In accordance with the present invention, there is provided a stranding machine comprising a plurality of pairs of bobbins, used alternately to strand and to wind up fresh wire and each pair rotatably mounted on a hollow shaft itself rotatably mounted on a support, with a pair of discs rotatably mounted on each shaft axially inwards of the associated pair of bobbins, each of said discs being driven by the shaft when the respective bobbin is in the stranding phase and carrying a paying-off arm with a paying-off pulley for use in guiding the paid-off wire towards and into the hollow shaft where it is subjected to tension and drawn through said shaft towards a stranding station, the machine -f a P; - o < further comprising connection means operative in the stranding phase to regulate relative rotary movement between each bobbin and its disc and brake the former relative to the latter when the machine stops, and means to release each bobbin from its disc to prepare it for the subsequent phase of rewinding with fresh wire.

Preferably, said connection means comprises a band brake wrapped about a brake drum coupled to respective bobbin, the band ends being respectively connected to a point on respective disc and to a first spring arranged to apply maximum braking torque, means for adjusting the tension of the wire being paid-off and comprising a system of levers subjected to the wire tension acting on a pulley carried on a first side of one lever of the system and to a contrasting action of a second spring upon the second end of the lever, and an element able to transmit a wire tension, higher than the contrasting force of said second spring, from the lever system to the band brake, to vary the braking action of the band on the bobbin drum and to adjust to a constant value the tension of the wire being paid off.

Preferably, the means for releasing each bobbin from its disc when the machine is stopped comprises a device carried by the disc and arrange to tension the first spring during the stranding phase and able to remove the tension of said first spring when the machine is stopped.

The main aspects of the embodiment to be described herein are a brake band connection between each bobbin and its disc, a device for adjusting the tension acting in the N.Z. PATE.MY OFFICE 25Jki'^U / / r a > _L& stranding operation, and a releasing device for the immediate conversion of the bobbin from the stranding phase to its rewinding with new wire.

The brake band connection, associated with the tension adjusting system, results in a wire tension of constant value in the relative movement between the bobbin and the disc, in particular, owing to the above described features, during the transitory step preceding the machine stop, the action exerted by the element transmitting the wire tension on the band brake is progressively reduced, thus giving rise to a progressively increased braking action of the first spring, up to elemination of the relative movement between the disc and the bobbin.

The releasing device completes the brake band connection since in the stranding phase it has the task of loading the first spring; when the machine stops, the relative approach of the ends of each first spring permits the disengagement between the disc and the bobbin.

Preferably, particularly to reduce the effect of centrifugal force on the wire tension adjusting system, in the lever system the lever axis and the axis of rotation of ' the pulley on that lever are disposed radially to the axis of rotation of the machine.

According to a preferred feature, the wire being paid-off, before passing to said one pulley of said lever system, travels over a return roller disposed parallel to the bobbin axis, immediately outside a flange of that bobbin.

An embodiment of the present invention will now be N.Z. PATi'rr •:r:-!CP 25 JA:v 1S5534- described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 is a diagrammatic side elevational view of a stranding machine, shown for simplicity's sake with only two pairs of bobbins; FIGURE 2 is a front view of a disc adjacent one of the bobbins and showing a wire tension adjusting means, a bobbin braking means and a bobbin release device; FIGURE 3 is a longitudinal partial view of the machine illustrating a detail of the wire tension adjusting means; FIGURE 4 is a partial perspective view of the machine showing the path of the wire from a bobbin to the interior of the associated hollow shaft; and FIGURE 5 is a view illustrating details of the bobbin releasing device.

The invention is applicable to machines for applying one-layer strands or several-layer strands wound in alternate senses and/or with different pitches. The particular embodiment shown comprises a machine 1 (Figure 1) used for example to strand several wires 2 about a central core 3 or to form a screening layer about a central core 3 formed by the conductor, and its insulation, of a power cable.

The machine comprises several units 4, of a number equal to the number of wires to be stranded; each of these units comprises a hollow shaft 5 (Figures 1 and 3) mounted rotatably in a central support 6, a pair of bobbins 7,8 mounted rotatably on the shaft 5 at opposite sides of the support and used alternatively to wind fresh wire upon 7 N.z. pat?' -;- c. . - 1 2 5JAfr:.,wv:. themselves or to strand wire onto the core 3, their roles being alternated in successive operating phases, a pair of discs 9, 10 rotatably mounted on the shaft 5 at the opposite sides of the support, axially inwards of the bobbins, a paying-off arm 11 carried by each disc and having a pulley 12 to pay off wire from the bobbin and to guide it to a further pulley 13 secured to and rotating with the shaft 5 (which pulley 13 guides the wire into the end of the shaft 5), a single dispenser 14 (Figure 1) to supply the fresh wire selectively either to bobbin 7 or bobbin 8, and means for driving the bobbins in the winding up phase.

The units 4 of the machine 1, and for simplicity only two such units are shown, have their respective shafts 5 axially aligned and spaced apart so as to allow an advantageous connection between the end of the wire paid off from bobbin 8 in the stranding phase and the leading end of the wire of adjacent bobbin 7' of the adjacent units 4, which bobbin 71 has received fresh wire via dispenser 14 during the stranding phase of bobbin 8.

An auxiliary shaft 15 is mounted on supports 6, and by means of gears or otherwise drives the shafts 5 into rotation and the discs 9, 10 associated therewith by suitable means in the stranding phase of the respective bobbins.

All the units 4 (figure 1) are situated between a core paying-off stand or drum 16 and a final station 17 which comprises a perforated plate 18, for the passage of the wires 2 through respective perforations, which plate 18 rotates with the shaft 5 of the last unit 4, a die 19 secured to a JM' str ' ?5534=- base 20 and conventional tensioning and collection means (not illustrated).

Therefore the wires and the core are drawn through the plurality of shafts 5 by the application of a drawing force of tension exerted by the tensioning means.

If the machine is used to form a multi-layer strand, for instance a two-layer strand, the machine units are divided into two successive groups, one for each layer, each group having units whose rotation senses and speeds are equal to or different from those of the units of the other group, depending on whether the two layers have alternate laying senses or not, each group being moreover provided with its own perforated plate 18 and associated die.

The dispenser 14 for selectively winding up fresh wire on one bobbin or the other and the system for imparting motion to the bobbins in the winding up phase may be that which is described in our New Zealand patent 195078 which can be swung through an angle of 180° from one bobbin to the other, and is reciprocably movable in a direction parallel to the machine axis with a stroke corresponding to the distance between the two flanges of each bobbin; an end pulley 22, able to guide the wire coming from a feeding drum and onto the machine bobbin, is carried by the arm 21 so as to reciprocate therewith. The drive for bobbins in the winding phase may be effected by a central shaft, positioned between the discs 9, 10 and driven by a motor independent of the main shaft 5, and two side shafts, assembled rotatably on In such case, the dispenser 14 compries an arm 21 i G Q /f _L o o O tyr- the discs and connected to gears of the bobbins; in particular claw clutches may be provided between the side shafts and the central shaft, as explained in detail in our above-mentioned patent application.

A description will now be given of a braking means between each bobbin and its disc, for use in the stranding phase regulate the tension in the wire, and to brake the bobbin relative to the disc when the machine stops, and also of means able to disengage the bobbin from the disc to prepare for rewinding with new wire. These various means, being identical for each bobbin of unit of the machine, are described with reference to bobbin 8 and to disc 10 of Figure 1.

Referring to Figure 2, a band brake 23 is provided to act on bobbin 8, together with a lever system 24 sensitive to variations in tension of the wire paid-off from bobbin 8, and an element 25 connected between the lever system 24 and the band 23 for transmitting a change in the tension of the wire being paid-off which is higher than a pre-established value in order to vary the braking force of the band on the bobbin, adjusting therefore to a practically constant value the tension of the wire paid off.

The band 23 is wrapped around a predetermined proportion of the periphery of brake drum 26 of the bobbin, one end 27 of the band being fixed to disc 10 and the other end 28 being subjected to the action of a first spring 29 having such a characteristic and applied to the disc 10 in such a manner as to transmit to the band 23 a braking torque able to stop the 195534- bobbin loaded with the wire and rotating at the rated speed, at the same moment at which the machine is stopped.

Preferably, as shown, a plate 30 is rotatably mounted about a pin 31 parallel to the disc axis and secured to the disc 10: the plate 30 is connected to diametrically opposite points to a first end 32 of spring 29 (the second end 33 of which is secured to a part 34 carried by the disc 10) and to an end 35 of the element 25 transmitting the sensed variations of the wire tension from the lever system 24 to the band 23.

The plate 30 carries moreover the end 28 of band 23, the connection being made to the same side of the plate with respect to the pin) as the side to which the spring 29 is connected.

By means of this arrangement, the tension in the first spring 29 tends to cause a rotation of plate 30 about its pin 31, the sense of rotation (as shown in Figure 2) being such as to wrap closely the band 23 around the brake drum and to impart the maximum braking torque.

The release of this braking action depends on the action exerted on plate 30 by element 25 in accordance with the oscillations of system 24 providing the wire tension adjustment, which will now be explained in detail.

Substantially the lever system 24 depends on the use of a lever, having a rotation pin on a support fast with the disc 10, and with opposite ends respectively subjected to the action of the wire and to that of a contrasting spring.

The spring has pre-established characteristics so that N.Z. PATc -iT c::rE -11~ 25 JAK' f?f-4 1. D d 3 4- it ensures an unvaried position of the lever as long as the wire does not exceed a pre-established tension; in the contrary case, the oscillation of the lever acts on the transmission element 25 and the bobbin is released to bring again the wire tension to a practically constant value. Several forms of the wire tension adjusting system can be provided in accordance with this principle: the preferred form will be described herebelow.

A lever 36 has a pin 37 mounted in a support 38 (see Figure 3,4) extending in a direction substantially parallel to the bobbin axis; the end 39 of the lever carries a pulley 41 having an axis of rotation 42, whilst the end 40 is instead subjected to the action of a second spring 43 having the above-mentioned function and shown in Figure 2. The pin 37 of the lever is directed radially to the bobbin axis (see Figures 3,4) so that the lever can swing along planes orthogonal to this direction, with the advantageous result not to be subjected to the influence of centrifugal forces which might otherwise compromise the adjusting system.

The second spring 43 has one end 44 connected to a fixed point on the disc 10 and its other end 45 is fixed to a further lever 46 (Figures 2,3) pivotal about a pin 47 disposed orthogonal to the disc 10 and secured thereto, end 48 of lever 46 being associated at 48' to lever 36 by means of connections (not shown) comprising a pin slidable in accordance with the oscillations of the system provided at the forked end 40 of lever 36.

The position of end 44 of the spring 43 could be 19553 4r variable on the disc 10 in order to vary its loading; regulation means of conventional type (not illustrated) may be provided for this purpose.

The lever 46 is connected (Figure 2) to the end 49 of the transmission element 25. The element 25 may, as in the embodiment shown, be flexible and transmit only tension forces; for instance, it may be a metal or nylon string whose end 49 is connected to the lever 56, at the opposite side of pin 47 from spring 43. The use of a flexible string instead of a rigid element is an advantage: flexible, the string can follow a curved path by passing for instance over a pulley 25' carried by the disc 10 (Figures 2,5) permitting an easy arrangement of both springs within the space defined by the string itself; substantially, in this case, the two springs can be situated very near to the centre of rotation of the disc, reducing therefore the influence of centrifugal forces and affording the advantage of a correct braking of the bobbin.

The path of travel of the wire from the bobbin during stranding will now be described.

The wire 2 being drawn from the bobbin at first passes over a return roller 50 (Figure 4), which is rotatably mounted on a shaft 11 forming the paying-off arm, the roller 50 being disposed parallel to the bobbin axis and immediately outside flange 51 of the bobbin 8: then the wire passes around pulley 41 of lever 36, and then it passes around a pulley 52 of the shaft 11, rotatably mounted independent of roller 50; then the wire passes over pulley 13 which is N.Z. PAT: 25JA(V!^4 secured to the shaft 5 and then through the shaft towards the stranding station.

Thus the wire 2 instead of passing directly from the bobbin to the pulley on the paying-off arm and then directly to the pulley on the shaft 5f namely instead of following a practically rectilinear path, travels along a broken line, substantially deviating several times, hence with a reduction of the maximum radius of rotation of the machine owing to the presence of the return roller, over which the wire passes to and from pulley 41, and with the consequent possibility of increasing the machine speed because - the radial dimensions being reduced - the problems regarding balance and structure are more limited, so that a lesser power loss due to aerodynamic resistance is achieved.

Means for releasing the bobbin from its disc to prepare it to be reloaded with new wire will now be described. Said means (Figures 2,5) comprise a device 53 permanently secured to disc 10 and rotated with the latter even during the stranding phase. The device 53 acts on one of the two ends of the first spring 29 of the band brake 23 and is based on the principle of stretching said spring during the stranding-phase and of allowing a contraction of the spring, with release of the brake when the machine stops.

As shown, the device 53 acts on the second end 33 of spring 29 and comprises a peg 54 disposed in a seat 55 on the disc, intended to receive the end of the peg pushed by a small spring 56. This peg is situated at the end of a lever 57 having a rotation pin 58 fixed to the disc, and end 33 of "" 155534- spring 29 being connected to said lever 57 at a point opposite the peg; the device further comprises a handle 58' to rotate the lever in clockwise direction (with reference to Figure 2), thus releasing spring 29 and the band brake 23.

The operation of the machine will now be described, starting from the arrangement of Figure 1, in which the bobbins 7, 7' and 8, 8' of the units of machine 1 work in the winding phase and in the stranding phase, respectively.

During the reloading with new wire, the disc 9 of bobbin 7 is secured - for instance by a pin - to the central support 6 with an appropriate orientation in which the paying-off arm 11 is directed downwards and to avoid interference with the wire dispenser 14. The bobbin 7 is driven into rotation by the motor provided for re-winding with wire from a feeding drum and/or reel, a regulating action of the turns being wound being carried out by dispenser 14 which reciprocates the moving arm 21 and the pulley 22 at a speed correlated, at a pre-established rate, to the speed of rotation of bobbin 7. The winding up of new wire on bobbin 7' is carried out in an analogous manner.

In the stranding phase, disc 10 of bobbin 8 is connected - for instance by a pin - to an appropriate flange (not shown) of shaft 5, which is driven into rotation by the auxiliary shaft 15, and the transmission means for reloading this bobbin with new wire is interrupted.

The bobbin 8 is drawn into rotation about shaft 5 in consequence of the tension applied to the wire 2 by the tensioning means and said wire 2 is guided from the bobbin to -15- N.Z.P.".". - , • the interior shaft 5 at first over the return roller 50 (Figure 4) then over pulley 41 of the adjusting lever 36, then over pulley 52 at the end of roller 50 and finally over pulley 13 rotating with shaft 5.

Simultaneously with wire 2, the cable core 3 passes through shaft 5; also this core is subjected to the tension exerted by the tensioning means and is drawn from the paying-off stand 16, through the hollow shafts 5 of all units 4 of the machine, towards the stranding station 18-19.

Still considering the stranding phase, the tension of wire 2 passing over pulley 41 and the swinging lever 36 is balanced by the reaction force of the spring 43 (Figure 2); the tension resulting from said balance, through the metal string 25, exerts a reducing action on the braking of band 23 exerted by spring 29 around the brake drum of the bobbin 8.

When the machine stops for any reason, disc 10 is braked separately by a suitable brake, for instance pneumatically actuated, but bobbin 8 tends still to rotate relative to its disc 10. Consequently, a slackening of the wire takes place, so that the action exerted by the wire on the band brake 23 through the pulley 41 and the swinging lever 36 and intended-to reduce the braking action is eliminated; therefore the brake, no longer subjected to the tension exerted"on the element 25, may apply its maximum torque, giving rise to a close synchronism between disc 10 and bobbin 8 until their relative movement is nullified.

The operation of bobbin 8* in the stranding phase takes place analogously to that of bobbin 8.

N.2. PAT" C K f ~ O ft ±_<j Ovkj qr~ In the intermediate steps, the inversion in the functions of the bobbins of a same unit occurs as follows. When the machine is stopped, the bobbin 7 is disengaged from the re-winding motor and disc 9 is coupled to a suitable flange of shaft 5 for rotating the disc 9 by shaft 5: then the end of the wire on bobbin 7 is connected to the end of the wire on the bobbin, just exhausted, which is carried by the adjacent unit of the next downstream unit 4.

An analogous procedure is used to prepare for use in stranding the bobbins which have just been reloaded with wire in the preceding phase * Then the bobbin 8, just exhausted, is prepared to be reloaded with new wire. This is carried out by operating handle 58' (Figures 2,5) of device 53, to remove peg 54 from its seat 55 on disc 10 (Figure 5), and release spring 29 to release braking band 23 from its effect on the bobbin. Then, with bobbin 8 free to rotate, the following operations are carried out: first disc 10 is rotated to a position such that the paying-off arm 11 does not interfere with the position to be taken by dispenser 14 with its wire-guiding arm 21, then the arm 21 is swung through 180° until pulley 22 is aligned with bobbin 8, the disc 10 is locked to the support 6 and the wire rewinding motor is coupled to bobbin 8; finally the wire coming from the feeding drum or reel is guided around pulley 2 2 and onto bobbin 8 and the reloading of bobbin 8 is started.

In particular, the embodiment described has the advantage that the bobbin braking elements namely the two N.z.P; "17~ 195534- springs and the brake band, are arranged in a position extremely near to the respective disc, without any excessive deviation in axial direction, so that, together with the other parts of the machine, they enable the provision of many pairs of bobbins (i.e. many units 4) in a relatively reduced area. ^ f OT

Claims

WHAT WE CLAIM IS:

1. A stranding machine comprising a plurality of pairs of bobbins, used alternately to strand and to win<4 up fresh wire and each pair rotatably mounted on a hollow shaft itself rotatably mounted on a support, with a pair of discs rotatably mounted on each shaft axially inwards of the associated pair of bobbins, each of said discs being driven by the shaft when the respective bobbin is in the stranding phase and carrying a paying-off arm with a paying-off pulley for use in guiding the paid-off wire towards and into the hollow shaft where it is subjected to tension and drawn through said shaft towards a stranding station, the machine further comprising connection means operative in the stranding phase to regulate relative rotary movement between each bobbin and its disc and brake the former relative to the latter when the machine stops, and means to release each bobbin from its disc to prepare it for the subsequent phase of rewinding with fresh wire.

2. A stranding machine as claimed in claim 1, in which said connection means comprises a band brake wrapped about a brake drum coupled to respective bobbin, the band ends being respectively connected to a point on respective disc and to a first spring arrangement to apply maximum braking torque, means for adjusting the tension of the wire being paid-off and comprising a system of levers subjected to the wire tension acting on a pulley carried on a first side of one lever of the system and to a contrasting action of a second spring upon the second end of the lever, and an element able -19- M.Z. patf; - • 105534- to transmit a wire tension, higher than the contrasting force of said second spring, from the lever system to the band brake, to vary the braking action of the band on the bobbin drum and to adjust to a constant value the tension of the wire being paid-off.

3. A stranding machine as claimed in claim 1 or 2, in which the means for releasing each bobbin from its disc when the machine is stopped comprises a device carried by the disc and arranged to tension the first spring during the stranding phase and able to remove the tension of said first spring when the machine is stopped.

4. A stranding machine as claimed in claim 2, in which, in the lever system arranged to regulate the wire tension, the axis of said one lever and the axis of rotation of the pulley which is carried by that lever are disposed in a radial direction with respect to the hollow shaft.

5. A stranding machine as claimed in claim 2, comprising a return roller disposed parallel to the axis of each bobbin immediately outside a flange of that bobbin, for the wire to pass over in passing from the bobbin to the pulley of said lever.

6. A stranding machine as claimed in claim 5, in which each said roller is freely rotatably mounted on a shaft carried by the associated disc.

7. A stranding machine as claimed in claim 6, in which the free end of each roller shaft carries a freely rotatable pulley around which is passed the wire passing from said one pulley of the lever system. -20- N.Z. FAT'-'^T G; . " S ! jArn-~" 1 C: PS r V A ^ tvr *•/ KfJ *•} -

8. A stranding machine as claimed in claim 7, in which the wire passing from said pulley on the roller shaft is directed towards a pulley fast with the hollow shaft and from thence, in axial direction, into the hollow shaft and towards the stranding station.

9. A stranding machine as claimed in claim 2, in which the band brake comprises a plate rotating about a pin parallel to the hollow shaft and carried by the disc, said plate respectively carrying to opposite sides of that pin, a first end of the first spring to second end of which is fixed to a point on the disc, and an end of the element for transmitting the wire tension from the lever adjusting system to the brake band, one of the two ends of the band being connected to the plate on the same side (with respect to the pin) as the first spring.

10. A stranding machine as claimed in claim 2, in which said element for transmitting the wire tension between the lever adjusting system and the band brake is a flexible element.

11. A stranding machine as claimed in claim 10, in which said element is a metal string.

12. A stranding machine as claimed in claim 11, in which the spring follows a deviating path and the first and the second spring are disposed adjacent the centre of rotation of the disc.

13. A stranding machine as claimed in claim 3, in which the device carried by the disc to release the bobbin acts on an end of the first spring opposite to the end carried by a -21- N.Z.7. 25 JAN 1984 195534- plate rotating about a pin on the disc, an end of the band being connected to said plate at the same side thereof with respect to that pin, and an end of the element transmitting the wire tension between the lever system and the band brake being connected to the plate at its opposite side with respect to the pin.

14. A stranding machine as claimed in claim 13, in which said device comprises a peg to which is connected the end of said first spring and a seat on the disc for receiving the peg.

15. A stranding machine as claimed in claim 14, in which said peg is disposed at the end of a lever having its fulcrum on the disc and the first spring is applied to that lever at its opposite end, with respect to the peg, the latter being urged into its respective seat by a further spring.

16. A stranding machine as claimed in claim 1, in which said connection means and said means to disengage the bobbin from the disc are provided for each bobbin of each pair, alternatively employed to strand and to wind up new wire, which are rotatably mounted said hollow shaft itself rotatable about a central support between the discs of each ■ pair, the length of said hollow shaft being substantially equal to the distance between the outer flanges of the two bobbins and said plurality of pairs being situated on a plurality of hollow shafts aligned to one another.

17. A stranding machine as claimed in claim 16, comprising, in combination with the means to disengage each bobbin from its disc to prepare it for the winding up phase, means for -22- N.2. 19553^ guiding the fresh wire from a feeding drum or reel towards that bobbin of the machine.

18. A stranding machine as claimed in claim 17, in which, for each pair of bobbins, a single said guiding means is provided, comprising an arm positioned between the respective two discs and swingable between the bobbins alternately used in the winding up phase.

19. A stranding machine as claimed in claim 18, in which for each pair of bobbins an individual motor is provided independent of the hollow shaft drive means, and which is able todrive either bobbin for the winding up phase and to drive said guiding means.

20. A stranding machine as claimed in claim 1, further comprising means for feeding the core of an electric power cable (comprising a conductor and its insulation) into and through said hollow shafts and means to receive a cable provided with a screening layer formed by the wires paid off from the bobbins and stranded about said core.

21. A stranding machine substantially as herein described with reference to the accompanying drawings. INDUSTRIE PIRELLI S.p.A. By His/Their authorised Agenfs, A- J. ^PARK & SON Peiv -23- ^^TOfFlCE 2 5 JAN 1984