MACHINE AND METHOD FOR HELICALLY WINDING A WIRE ABOUT A RING-SHAPE CORE

Abstract: A stranding machine (1) for stranding a wire (W) around a core (C) comprises: a support frame (2), means (3) for guiding and supporting the core (C), means (5) for holding the wire (W), allowing the wire (W) to advance towards a combining point (P) with the core (C), and a pulling unit (4) for advancing the core (C) along an annular path. The means (3) for guiding and supporting the core (C) are arranged around the annular path so as to cause the core (C) to adopt a loop-shaped configuration. The stranding machine (1) further comprises kinematic means (12) for moving the means (5) for holding the wire (W) around the annular path with an interlinked rotary movement. This enables a helical winding of the wire (W) to be formed around the core (C).

Description: MACHINE AND METHOD FOR HELICALLY WINDING A WIRE ABOUT A RING-SHAPE CORE DESCRIPTION The present invention relates to a stranding machine for stranding at least one wire around a core, the machine comprising a support frame, means for guiding and supporting a core, means for holding at least one wire to be arranged around the core, and a pulling unit for advancing the core. The invention also relates to a method of forming a loop of stranded wire and of forming a net in which the meshes are formed by the above-mentioned loops linked together. Within the scope of the present invention, the term "stranding" is used to indicate the technique of combining one or more wires by winding them in a helix around a support wire called the core. The term "splicing" is used to indicate the technique of securing the end of a cord or of a wire in place by inserting it between the wires or between the turns of a strand. It has been known for some time to use protective nets to achieve an effective restraint and barrier effect against falling stones and the like. Clearly, for these applications, there is a great need to produce very strong nets which can withstand large stresses. For these applications, as well as for applications of other types, it is particularly advisable to use metal nets in which the meshes are formed by loops linked together . In order to satisfy the above-mentioned requirement, it is fundamental to be able to close the linked loops without the closure means or the closure technique used constituting a weak point, that is, a point of structural failure of the protective net. In this connection, it is pointed out that the solution of closing the loops constituting the meshes of protective nets by twisting the ends of the wire of each loop together so as to connect them is not satisfactory since it cannot withstand large loads. Similarly, the solution of joining the ends of the loops by welding is unsatisfactory both because of the cost and the complexity involved in the operation of welding each mesh, and because of the reduction in the strength characteristics of the material constituting the loop as a result of local heating due to the welding. A protective net the meshes of which are formed by loops of steel wire linked together is known from US patent 5,597,017. In greater detail, each loop is formed by a single metal wire wound so as to form a plurality of parallel turns which are held close together by means of two or more clamping clips. This net, however, has the disadvantage that the clips used to hold together the turns of wire making up the individual loops are subject to breakage, causing structural failure of the protective net. In fact, the clips may break or be removed as a result of possible impacts against rocks or of impacts due to falling stones. In both cases, the turns of each loop would no longer be held together and, under the effect of the load, the wire of which the turns were made would no longer be able to hold together the loops linked thereto, giving rise to structural failure of the protective net. In fact, since the wires do not co- operate with one another, their strength is equal to that of a single wire. Moreover, when the net is subjected to load, the wire constituting the turns of each loop is put under tension, that is, it is in a state of one-dimensional stress. The breaking load of each loop, and hence the breaking load of the protective net, is consequently limited substantially to the tensile breaking load of the wire constituting the loops, multiplied by the number of whole turns of which each loop is composed. It is hardly necessary to point out that the breaking load of a strand constituted by several wires stranded together is undoubtedly greater than the sum of the breaking loads of the wires constituting the strand. However, although stranding machines can form a strand having a length of several metres , the problem remains of how to connect the ends of a short length of strand to one another in a simple and strong manner so as to form a closed loop without giving rise to the above-mentioned problems . The problem upon which the present invention is based, is that of devising a stranding machine which has structural and functional characteristics such as to satisfy the above-mentioned requirements and at the same time to avoid the problems referred to, as well as to devise a method of forming a closed loop of stranded wire which is extremely strong. This problem is solved by a stranding machine according to Claim 1. The means for holding the wire preferably move around a point on the annular path with a substantially planetary movement to avoid giving rise to twisting in the wire during winding. According to a further aspect, it is necessary to produce a loop of wire which has good strength characteristics. This is achieved by a method according to Claim 28 . Further characteristics and the advantages of the stranding machine according to the invention will become clear from the following description of a preferred embodiment thereof, given by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 is a perspective view of the front portion of a stranding machine according to the invention, Figure 2 is a perspective view of the rear portion of the stranding machine of Figure 1, Figure 3 is a lateral plan view of the stranding machine of Figure 1, Figure 4 is a front plan view of the stranding machine of Figure 1, Figure 5 is a perspective view of a loop of stranded wire formed with the stranding machine of Figure 1, Figure 6 is a net formed by a plurality of loops according to Figure 5, linked together, Figures 7 and 8 are perspective views of the wire used to form the stranded loop of Figure 5 during various stages of the formation of the loop . With reference to the drawings, a stranding machine according to the invention for stranding at least one wire W around a core C is generally indicated 1. The following description will refer, in non- limiting manner, to a single steel wire W to be arranged around a core C which, as will become clearer from the following description, is formed, at least in a starting phase, by suitable bending of a starting end portion of the wire W, so as to close it onto the wire itself. The core C is formed in a single piece with the wire W. The stranding machine 1 comprises a support frame 2 which extends from a base and supports the components of the machine . The stranding machine 1 comprises : - means 3 for guiding and supporting the core C, - a pulling unit 4 for advancing the core C during the stranding operation, - means 5 for holding the wire W, the means 5 allowing the wire W to advance towards a point P at which it is combined (or stranded) with the core C, and drive means kinematically connected to the components of the stranding machine 1 in order to operate them during the stranding operation. The means 5 for holding the wire W comprise a wire- holder 13 which, in the embodiment shown, is in the form of a hollow cylindrical body extending along a predetermined axis Z-Z and having a lateral opening or window 28 from which the wire W emerges. According to the invention, the means 3 for guiding and supporting the core C are arranged so as to define a closed annular path around which the core is arranged, the core itself adopting a loop-like configuration. The guide and support means 3 are preferably arranged so as to define a circle. In the embodiment shown, the means 3 for guiding and supporting the core comprise a plurality of rollers defining a roller bed 6 extending along a predetermined circular arc of the annular path and a wire-guide channel 7 positioned above the roller bed 6 in a diametrally opposed portion of the annular path. Both the wire-guide channel 7 and the roller bed 6 are positioned so as to be on the inside of the annular path. The diameter D of the annular path is defined by the distance between the roller bed 6 and the wire-guide channel 7. As stated, the annular path is thus a circle of diameter D contained in a vertical plane. The inside diameters of the stranded loops to be formed, for example of 0.43 m, is thus substantially equal to the diameter D of the annular path. The roller bed 6 defines a cradle which extends around the lower inner portion of the annular path. The rollers may be covered with rubber or another equivalent material, and the portion of the wire-guide channel which is intended to come into contact with the steel wire is preferably covered with a material having a low coefficient of friction such as, for example, Teflon™. Alternatively, the wire-guide channel 7 may be replaced by one or more rollers, or by a sliding surface. The pulling unit 4 comprises an endless chain 8 (i.e. a chain having the ends jointed together to form a loop) supported for rotation by a plurality of sprockets 10 supported by the frame 2. In conventional manner, one of the sprockets is kinematically connected to an electric motor 9 so as to be driven, enabling the chain 8 to be rotated. The chain 8 has a portion which is arranged around the annular path so as to be in contact with the core C so that the core is dragged along with the rotating chain and advanced around the annular path. In the embodiment shown in the drawings, the above- mentioned portion of the chain 8 is on the outside of the annular path and is positioned in the region of the roller bed 6. In the lower portion of the annular path, the core C therefore passes between the roller bed 6 and the chain 8 associated therewith. A chain-tensioner 14 is associated with the chain 8 and allows the chain to vary the space occupied by the loop of wire being formed, the cross-section of which increases as a result of the deposition of the wire W around the core C. The surfaces of the links of the chain 8 which are intended to come into contact with the core C are preferably covered with rubber or another equivalent material. This prevents direct contact between the wire and the links of the chain 8 and at the same time increases the coefficient of friction between the wire W and the links of the chain 8 so as to increase the dragging effect. In the initial portion of the roller bed 6, identified with reference to the direction of advance of the core C along the annular path (anticlockwise in Figure 3) , there is a lateral plate 11 which prevents the core C from escaping from the roller bed sideways, that is, from slipping off the rollers. Advantageously, the stranding machine 1 comprises kinematic means 12 for causing the means 5 for holding the wire W and, in particular, the wire-holder 13, to move around the annular path with an interlinked rotary movement . Whilst the core C is forced to advance along the annular path (with an anticlockwise direction of rotation with reference to Figure 3) , the interlinked rotary movement of the wire-holder 13 consequently enables the wire W to be wound in a helix around the core C, that is, it enables the wire W to be stranded around the core C. The combination of the advancing movement of the core along the annular path and of the interlinked rotary movement of the wire-holder 13 thus enables a stranded loop of wire W to be formed. The kinematic means 12 preferably enable the wire- holder 13 to be moved around a point R on the annular path with a substantially planetary movement composed of: - a first rotary movement which takes place about a predetermined axis of rotation X-X (the interlinking axis) and is interlinked with the annular path, and - a second rotary movement of the wire-holder 13 which takes place about a second axis of rotation Y-Y (the axis of revolution) and which has an opposite direction of rotation (in the clockwise direction indicated by the arrow T of Figure 4) to the first rotary movement . The two above-mentioned rotary movements of the wire-holder 13 are preferably synchronized with one another so as to avoid twisting of the wire about its own axis during the winding of the wire W in a helix around the core C. Basically, for each complete revolution of the wire-holder 13 about the interlinking axis X-X, that is, about the point R on the annular path, the wire- holder 13 is simultaneously rotated about itself in the opposite direction by one turn, consequently moving with plain motion. In the embodiment shown in the drawings , the second axis of rotation Y-Y extends through the wire-holder 13 so that the second rotary movement consists of a revolution of the wire-holder about itself . The above-mentioned planetary movement is therefore composed of a rotary movement of the entire wire-holder 13 about the interlinking axis X-X, and a simultaneous and opposite revolving movement of the wire-holder 13 about itself, about the axis Y-Y (the axis of revolution) . The point R on the annular path about which the interlinked rotary movement of the wire-holder 13 takes place is positioned upstream of the combining point P, with reference to the direction of advance of the core C along the annular path. The wire W can thus be caused to reach the combining point P in a manner such as to be arranged around the core C, arriving substantially tangentially relative to the core along a stranding axis K-K. The stranding axis K-K and the interlinking axis X- X are therefore different. In the embodiment shown in the drawings, the interlinking axis X-X and the stranding axis K-K are coplanar and perpendicular to one another. In the embodiment shown, the interlinking axis X-X extends through the point R so as to be tangential to the annular path (Figure 3) . The axis Y-Y about which the wire-holder 13 rotates about itself is preferably parallel to the interlinking axis X-X. In the embodiment shown, the kinematic means 12 comprise: - a ring gear 15 which is positioned so as to be interlinked with the annular path and is connected to the support frame 2 so as to be rotatable about the interlinking axis X-X; the wire-holder 13 is associated with the ring gear 15 so as to be rotatable about the second axis of rotation Y-Y which, as indicated above, is parallel to the axis X-X, - a first gear train 16 kinematically connecting drive means 18 to an external set of teeth of the ring gear 15 in order to rotate the ring gear 15 about the interlinking axis X-X, and - a second gear train 19 kinematically connecting the ring gear 15 to the wire-holder 13 in order to bring about the second rotary movement of the wire-holder 13 about the axis of revolution Y-Y, resulting in the plain motion of the wire-holder 13 about the interlinking axis X-X. The ring gear 15 has an external set of teeth 27 and comprises a hub 20 which in turn bears an external set of teeth 24. So that the interlinking axis X-X is tangential to the annular path at the point R and, at the same time, also coincides with the axis of rotation of the ring gear 15, the hub 20 of the ring gear is hollow axially to allow the core C to extend through it. The circular continuity of the ring gear 15 is interrupted by a slot 21 which also extends radially through the hollow hub 20. The slot 21 enables the loop of stranded wire to be passed through the ring gear 15 when, upon completion of the stranding operation, it is necessary to remove the stranded loop 33 from the machine 1. The first gear train 16 comprises two pinions 22 which engage the outer set of teeth 27 of the ring gear 15 at two different points thereof . The two pinions 22 are connected to one another by an idler gear 23. This ensures both correct transmission of the drive from the drive means 18 to the ring gear 15 and a uniform transmission ratio between them, in spite of the discontinuity due to the presence of the slot 21. In the embodiment shown, the second gear train 19 is in the form of an epicyclic gearing which takes the motion from the ring gear 15 and ensures de-twisting of the wire W. For this purpose, the second gear train 19 comprises two pinions 25 which mesh with different points on the external set of teeth 24 formed on the hub 20 of the ring gear 15. The two pinions 25 are connected to one another by an idler gear 26. The stranding machine 1 also comprises a unit for shaping the wire W, which is indicated 29 in the drawing and, with reference to the direction of advance of the core C around the annular path, is positioned immediately downstream of the point P at which the wire W is combined with the core C. The shaping unit 29 positions the wire W relative to the core C, possibly moving the turns of wire W already arranged around the core C in order to make room for the portion of wire which is being arranged. The shaping unit 29 also allows only the quantity of wire W necessary to cover the helix along which the wire W is arranged around the core C to be advanced towards the combining point P . In the embodiment shown in the drawings, the shaping unit is of the type with pulleys of which two are fixed pulleys 30 and one is a pulley 31 which swings away from and towards the wire W. The grooves of the pulleys enable the position adopted by the wire W during its deposition around the core C to be arranged in a manner such that the strand being formed has a substantially circular cross-section. The stranding machine 1 preferably also comprises a unit (not shown in the drawing) for splicing the end of the wire W between the other turns of the stranded loop 33. The wire-holder 13 is positioned with the axis Z-Z of the cylindrical body arranged transversely (perpendicularly in the embodiment shown in the drawing) relative to the axis X-X of the ring gear 15. The wire- holder 13 is associated with the ring gear 15 so as to be rotatable about itself about the axis of revolution Y-Y which is parallel to the interlinking axis X-X. As stated, the axis of revolution Y-Y is therefore perpendicular to the axis Z-Z of the cylindrical body of the wire-holder 13. The wire-holder 13 can house a length of wire W, for example, 7.5 m long, which is sufficient to form the stranded loop 33. The length of wire W to be inserted in the wire-holder is preferably shaped like a helical spring (Figure 7) . The lateral opening 28 of the wire-holder 13 faces towards the point P at which the wire W is combined with the core C. The opening 28 is formed in a cylindrical side wall of the cylindrical body and enables the wire W to emerge from the wire-holder 13 already facing the combining point P. The above-mentioned positioning of the wire-holder 13 and of its lateral opening 28 advantageously enables the wire W which has already emerged from the wire-holder 13 to be wound back into it. This prevents the portion of wire disposed between the wire-holder 13 and the combining point P from forming a bend during the interlinked rotary movement of the wire-holder 13 around the annular path. It should, in fact, be borne in mind that, during the rotary movement of the wire-holder 13, the distance between the lateral opening 28 and the combining point P is variable (see Figure 3) and, as stated above, the shaping unit 29 allows only the quantity of wire necessary to cover the helix in which the wire W is arranged around the core C to be advanced. Clearly, a bend formed by the wire W would create problems caused by the wire interfering with the walls of the machine during the interlinked rotary movement and the formation of a bend would lead to a continual and undesired variation of the angle at which the wire W reaches the point P at which it is combined with the core C. Moreover, the formation of a bend in the wire would hinder the correct deposition of the wire W around the core C at the combining point P. To favour the recovery of the wire W by the wire- holder 13, the latter is movable angularly about the axis Z-Z of the cylindrical body through a predetermined, limited angle α, by way of example, of between 15° and 20°. This rotation of the wire-holder 13 prevents the wire from sticking relative to the wire-holder 13 instead of being rewound inside it. In the embodiment shown in the drawings, the wire- holder 13 is supported for rotation at its ends by two opposed prongs of a fork 32 the stem of which extends in the direction of the axis of revolution Y-Y. The stem of the fork 32 in turn is supported by the ring gear 15 so as to be rotatable about the axis of revolution Y-Y and is kinematically connected to the second gear train 19 in order to be rotated. Two stop elements associated with the prongs of the fork 32 ensure that the amplitude of the rotation of the wire-holder 13 about the axis Z-Z is limited to the desired angle α. In a more simplified embodiment than the preferred embodiment described above, the wire-holder 13 may be associated with the ring gear 15 so asto be idle relative to the ring gear 15, that is, to be free to rotate about the axis of revolution Y-Y, for example, owing to the interposition of a rolling bearing, and may have its centre of gravity offset, that is, eccentric, relative to the axis of revolution Y-Y. By virtue of the fact that the centre of gravity of the wire-holder is eccentric relative to the axis of revolution, the wire-holder can thus always be kept oriented in the same manner by its own weight during the rotation of the ring gear 15 about the interlinking axis X-X. This de-twists the wire, that is, prevents twists in the wire due to the interlinked rotary movement, without the use of the second gear train. In this case, however, it is preferable to associate with the wire-holder or, more precisely, with the prong of the fork which supports it, known means for eliminating swinging movements of the wire-holder due to the inertial forces which act on the wire-holder as a result of the rotation of the ring gear. The stranding machine 1 also comprises conventional means for regulating the speed of the drive means 18 relative to the speed of advance of the core C around the annular path, imposed by the pulling unit 4. This enables the speed of the planetary movement of the wire- holder 13 to be synchronized relative to the speed of advance of the core C around the annular path in order to form around the core C a helical winding of the wire W having the desired pitch. The operation of the machine 1 is described below with reference to a starting condition in which the wire- holder 13 contains a length of wire W wound in a helix as indicated above and a starting end portion of the length of wire projects from the lateral window 28. Purely by way of indication, the length of wire is 7.5 m long and is constituted by a steel wire having a diameter of 0.0035m. The starting end portion of the wire W is arranged around the annular path, starting from the shaping unit 29 (in an anticlockwise direction with reference to Figure 3) . The starting end portion of the wire W thus passes between the roller bed 6 and the pulling unit 4 and through the wire-guide channel 7 until it reaches the point P at which it is fixed to the wire W. This starting end portion of the wire W thus forms the core C around which the remaining portion of the wire W is to be stranded (Figure 8) . The starting end of the wire W may be fixed to another point on the wire so as to form a closed loop constituting the core C by means of a known fastening technique . The fastening may be achieved with the use of a clamping element such as a clip or a lead seal, or by shaping a portion of the wire W in a loop, or even by shaping the starting end of the core C as a hook. The pulling unit 4 then causes the core C to advance around the annular path (in the anticlockwise direction indicated by the arrow F in Figure 3) . Since the wire W is fastened to the core C, the advance of the core along the path causes the wire W to be drawn from the wire- holder 13. The wire-holder 13 at the same time moves with a planetary movement around the point R of the annular path. As stated above, the planetary movement is composed of a rotation of the wire-holder 13 about the point R (in the clockwise direction indicated by the arrow H of Figure 4) and a simultaneous and opposed revolving rotary movement (in the anticlockwise direction indicated by the arrow T of Figure 4) of the wire-holder 13 about the axis Y-Y. The transmission ratio selected for the second gear train 19 is such that, for each complete rotation of the wire-holder 13 about the point R on the annular path, the wire-holder performs substantially one complete revolution about the axis Y-Y coinciding with the stem of the fork 32. The wire W drawn along by the core C is consequently arranged in a helix around the core C. The shaping unit 29 in wholly conventional manner arranges or positions the wire W during its deposition around the core C, possibly moving the turns of wire W already arranged around the core C to make room for the portion of wire which is being wound. The shaping unit 29 then sends back the excess wire W, allowing only the quantity of wire W necessary to cover the helix along which the wire is arranged around the core to advance towards the combining point P. When all of the wire W has been arranged (wound) around the core C, the stranding machine 1 is stopped and, after the tail end of the wire W has been secured, the stranded loop 33 can be removed from the guiding and support means 3 by virtue of the slot 21 in the ring gear 15 and in the hub 20. The tail end of the wire W can be secured with the use of the splicing unit with which the stranding machine 1 is provided. Alternatively, the splicing may be performed outside the machine 1. If a stranded loop 33 is to be formed in a manner such that it is linked with one or more stranded loops 34 already formed so as to form a net, it suffices to position the already-formed loops 34 straddling the cradle defined by the roller bed 6 before arranging the core C around the annular path. When the core C is then arranged around the annular path, it interlinks the loops 34 already formed. Naturally, the stranding machine 1 can produce a closed loop formed by two or more wires stranded together or in successive steps. Similarly, instead of using a wire W, it is possible to use a strand or several strands simultaneously. The stranding machine 1 may be mounted on wheels or on a track perpendicular to the interlinking axis X-X so as to be movable sideways. This enables the stranding machine to be moved along the protective net 35 which is being constructed, whilst the net 35 is kept hanging in a fixed position. The method of forming a loop of stranded wire according to the invention, comprises the steps of: - arranging a core of wire around an annular path, - providing at least one length of wire which is to be stranded with the core and which has a starting end and a tail end, fastening the wire to the core at a combining point, - advancing the core around the annular path, at the same time moving the wire which has not yet been stranded around a point on the annular path with an interlinked rotary movement so as to form a helical winding of the wire around the core . After the wire has been wound in a helix, its tail end is secured to the turns of wire of the loop formed. The tail end of the wire is preferably secured by being spliced between the turns of wire of the stranded loop 33. The splicing may advantageously be performed by replacing a portion of the starting end of the wire with a tail end portion thereof . This is done by removing a portion of wire from the turns of the stranded loop 33, starting from the starting end of the wire W, that is, a starting portion of the core C, and inserting the tail end of the wire in its place by splicing. The core C of the stranded loop 33 is thus formed by a portion of the starting end and by a portion of the tail end of the wire, respectively. The stranding operation is preferably performed starting with a length of wire to be stranded, arranged in the form of a helical spring (Figure 7) . The core is advantageously formed in a single piece with the wire, the core being formed by an end portion of the wire which is arranged around the annular path so as to form a loop closed onto itself by fastening. Alternatively, the core may be formed by a wire separate from the wire to be stranded. Preferably, the wire to be stranded around the core arrives at the combining point so as to be substantially tangential to the core and, during the stranding, is rotated about itself with an opposite direction of rotation to that of the interlinked rotary movement about the point on the annular path. This prevents twists arising in the wire due to the interlinked rotary movement . This is particularly advantageous when the wire to be stranded is made of steel . The stranded loop 33 may be formed by the stranding of two or more wires or of one or more strands, simultaneously, or in successive steps. In order to form a net 35 in which the meshes are formed by a plurality of stranded loops linked together, it suffices to prepare one or more stranded loops 34 in accordance with the method indicated above and to form a further stranded loop 33, causing the core of the latter to extend through the loops 34 prepared. The further loop formed is thus linked with the stranded loops 34 prepared. The stranded loops may also be formed with a wire or thread of a material other than steel such as, for example Nylon™. The protective net formed by the method according to the invention may also be used for uses other than those indicated in the initial part of the description. Thus, for example, the net may be used to protect marine fish farms from intrusion by seals or killer whales. Naturally, the diameter of the stranded loops should be selected on the basis of the specific requirements to be satisfied. As can be appreciated from the foregoing description, the stranding machine according to the invention has structural and functional characteristics such as to satisfy the above-mentioned requirements and at the same time to solve the problems referred to. In fact, the loop formed is constituted by several turns of wire which are stranded together and which do not require elements such as clamping clips and the like to keep them close together. Moreover, the stranded loop can be closed onto itself by splicing the tail end of the wire between the other turns of the loop. When the stranded loop produced by the stranding machine and by the method according to the invention is subjected to load and hence to tensile stress, the wire constituting the turns is pulled onto itself, closing up the turns to a greater extent and preventing the wire from slipping. The wire therefore advantageously works in torsion and not simply in tension as in the non- stranded loops of the prior art . The planetary movement of the wire-holding means relative to the annular path and to the core prevents the wire arranged in a helix from generating twisting tensions during the stranding. With the stranding machine according to the invention, it is possible to produce a stranded loop easily, quickly and at low cost. Another advantage of the stranding machine according to the invention lies in the fact that it can produce a stranded loop linked with other loops. A further advantage of the stranding machine according to the invention lies in the fact that it can be automated. The method according to the invention enables stranded loops with good strength characteristics to be produced easily and in an economically advantageous manner . With the method according to the invention it is possible to produce protective nets in which the meshes are formed by stranded loops linked together without the need to use retaining elements such as clips, clamps and the like to join the meshes or to hold together the wires of which they are composed. Naturally, in order to satisfy contingent and specific requirements, an expert in the art may apply to the above-described stranding machine and to the production method many modifications and variations, all of which, however, are included within the scope of protection of the invention as defined by the appended claims . Thus, for example, as an alternative to the arrangement described, the stranding machine may be supported from above, so as to be suspended, instead of being supported by a base. This leaves the space beneath the machine free, preventing the meshes of the protective net being formed from interfering with the base . This same advantage may be achieved with a C-shaped base. The ring gear 15 may be formed in a manner such as to be divisible into two or more parts joined together releasably. In this case, in order to remove the loop of stranded wire from the machine, it is necessary to split the ring gear . The shaping unit may, for example, be formed by a die which can be divided into two halves . A wire-holder comprising an open reel instead of a closed cylindrical body may be used. The wire-holder may be replaced by a bobbin or by a reel. The above-mentioned recovery of the wire by the wire-holding means may be performed by spring or friction devices or by other functionally equivalent devices. The two gear trains may be replaced, at least partially, by functionally equivalent mechanical transmission means such as, for example, toothed belt or chain transmissions.

Claims: CLAIMS 1. A stranding machine (1) for stranding at least one wire (W) around a core (C) , comprising: - a support frame (2) - means (3) for guiding and supporting a core (C) , - means (5) for holding at least one wire (W) to be arranged around the core (C) and connected to the core, the holding means (5) allowing the wire (W) to advance towards a point (P) at which it is combined with the core (C) , and - a pulling unit (4) for advancing the core (C) , characterized in that: - the means (3) for guiding and supporting the core (C) are arranged around an annular path so as to cause the core (C) to adopt a loop-shaped arrangement, the stranding machine (1) comprises kinematic means (12) for moving the means (5) for holding the wire (W) around the annular path with an interlinked movement, - the pulling unit (4) brings about the rotary advance of the core (C) around the annular path and the dragging of the wire (W) towards the point (P) at which it is combined with the core (C) so as to produce a stranded loop (33) formed by the at least one wire (W) arranged in a helix around the core (C) . 2. A stranding machine (1) according to Claim 1, in which the means (5) for holding the wire (W) move around a point (R) on the annular path with a substantially planetary movement composed of : - a first rotary movement about an interlinking axis (X-X) , the first rotary movement being interlinked with the annular path, - a second rotary movement of the means (5) for holding the wire (W) about itself, about a second axis of rotation (Y-Y) , the second rotary movement having an opposite direction of rotation to that of the first rotary movement . 3. A stranding machine (1) according to Claim 2, in which the first and second rotary movements of the means (5) for holding the wire (W) are synchronized so as to prevent twisting of the wire (W) about its own axis. 4. A stranding machine (1) according to Claim 1, comprising means for regulating the speed of the interlinked movement of the means (5) for holding the wire (W) relative to the speed of advance of the pulling unit (4) in order to form around the core (C) a helical winding of the wire (W) having a predetermined, uniform pitch. 5. A stranding machine (1) according to Claim 2, in which the kinematic means (12) comprise: - a ring gear (15) which is kinematically connected to the support frame (2) so as to be rotatable about the interlinking axis (X-X) and is positioned in a manner such as to be interlinked with the annular path, the means (5) for holding the wire (W) being associated with the ring gear (15) so as to be rotatable about the second axis of rotation (Y-Y) , a first gear train (16) which kinematically connects the ring gear (15) to a first drive means (18) in order to bring about the first rotary movement of the means (5) for holding the wire (W) . 6. A stranding machine (1) according to Claim 5, in which the kinematic means (12) comprise a second gear train (19) , which kinematically connects the ring gear (15) to the means (5) for holding the wire (W) in order to bring about the second rotary movement of the means (5) for holding the wire (W) and to prevent twisting of the wire (W) . 7. A stranding machine (1) according to Claim 5, in which the means (5) for holding the wire (W) are supported by the ring gear so as to be freely rotatable, the means for holding the wire having a centre of gravity which is eccentric relative to the second axis of rotation. 8. A stranding machine (1) according to Claim 7, in which means are associated with the means for holding the wire, to eliminate swinging movements of the means for holding the wire due to inertial forces during the rotation of the ring gear. 9. A stranding machine (1) according to Claim 5, in which the interlinking axis (X-X) and the second axis of rotation (Y-Y) are parallel to one another. 10. A stranding machine (1) according to Claim 2, in which the point (R) on the annular path is positioned upstream of the combining point (P) , with reference to the direction of advance of the core (C) along the annular path. 11. A stranding machine (1) according to Claim 5, in which the interlinking axis (X-X) coincides with the axis of the ring gear (15) and is tangential to the point (R) on the annular path. 12. A stranding machine (1) according to Claim 5, in which the ring gear (15) comprises an external set of teeth (27) . 13. A stranding machine (1) according to Claim 5, in which the ring gear (15) can be split to allow the stranded loop (33) to be removed from the guide and support means (3) . 14. A stranding machine (1) according to Claim 12, in which the ring gear (15) is interrupted by a slot (21) for allowing the stranded loop (33) to be removed from the guide and support means (33) and extracted from the stranding machine (1) , the first gear train (16) comprising at least two pinions (22) meshed with the external set of teeth (27) of the ring gear (15) at different points thereof. 15. A stranding machine (1) according to Claim 14, in which the at least two pinions (22) are connected by an idler gear (23 ) . 16. A stranding machine (1) according to Claims 11 and 14, in which the ring gear (15) comprises a hollow hub (20) through which the core (C) can extend, and in which the slot (21) also extends to the hollow hub (20) . 17. A stranding machine (1) according to Claim 6, in which the second gear train (19) comprises at least two pinions (25) meshing with a set of teeth (24) of the ring gear (15) at different points thereof. 18. A stranding machine (1) according to Claims 16 and 17, in which the pinions (25) mesh with an external set of teeth (24) formed on the hollow hub (20) of the ring gear (15) . 19. A stranding machine (1) according to Claim 1, in which the means (5) for holding the wire (W) comprise a wire-holder (13) which can recover the portion of wire (W) unwound from the wire-holder during interlinked movement thereof . 20. A stranding machine (1) according to Claim 19, in which the wire-holder (13) comprises a cylindrical body extending along a predetermined axis (Z-Z) and having a lateral opening (28) allowing the wire (W) to emerge. 21. A stranding machine (1) according to Claim 20, in which the opening in the cylindrical body faces towards the point (P) at which the wire (W) is combined with the core (C) . 22. A stranding machine (1) according to Claim 20, in which the axis (Z-Z) of the wire-holder (13) is transverse the axis of the ring gear (15) . 23. A stranding machine (1) according to Claim 21, in which the wire-holder (13) is movable angularly through a predetermined angle (α) about its own axis (Z-Z) . 24. A stranding machine (1) according to Claim 1, in which the pulling unit (4) comprises a dragging unit with a driven chain (8) acting on the loop-shaped core (C) . 25. A stranding machine (1) according to Claim 1, in which the means (3) for guiding and supporting the core (C) comprise a plurality of rollers arranged around the annular path in order to guide the wire (W) . 26. A stranding machine (1) according to Claim 1, in which the means (3) for guiding and supporting the core (C) comprise a roller bed (6) . 27. A stranding machine (1) according to Claim 26, in which the roller bed (6) is positioned on the inside of the annular path. 28. A stranding machine (1) according to Claim 26, in which the annular path is arranged in a vertical plane and the roller bed (6) is positioned around the lower portion of the annular path. 29. A stranding machine (1) according to Claim 1, comprising a unit (29) for shaping the wire (W) , the unit (29) being positioned downstream of the combining point (P) , with reference to the direction of advance of the core (C) along the annular path. 30. A stranding machine (1) according to Claim 1, comprising a unit for splicing a tail end of the wire (W) between the turns of the stranded loop (33) . 31. A method of forming a loop of stranded wire, comprising the steps of : - arranging a core (C) of wire (W) around an annular path, - providing at least one length of wire (W) which is to be stranded with the core (C) and which has a starting end and a tail end, - fastening the at least one wire (W) to the core (C) at a combining point (P) , - advancing the core (C) around the annular path, moving the at least one wire (W) around a point on the annular path with an interlinked rotary movement so as to wind the wire (W) in a helix around the core (C) . 32. A method of producing a loop of stranded wire according to Claim 31, comprising the step of securing the tail end of the wire (W) . 33. A method of producing a loop of stranded wire according to Claim 32, in which the step of securing the tail end of the wire (W) comprises the splicing of the tail end of the wire (W) between the turns of stranded wire (W) of the loop. 34. A method of producing a loop of stranded wire according to Claim 31, in which the step of securing the tail end of the wire (W) comprises the step of removing a portion of wire (W) from the turns of stranded wire (W) , starting from the starting end of the wire (W) and inserting the tail end of the wire (w) in its place by splicing. 35. A method of forming a loop of stranded wire according to Claim 31, in which the length of wire (W) to be stranded is arranged in the form of a helical spring. 36. A method of forming a loop of stranded wire according to Claim 31, in which the core (C) is formed in a single piece with the wire (W) , the core (C) being formed by a portion of the starting end of the wire (W) arranged around the path to form a loop closed onto itself by fastening. 37. A method of forming a loop of stranded wire according to Claim 31, in which the wire (W) arrives at the combining point (P) in a manner such as to be substantially tangential to the core (C) . 38. A method of forming a loop of stranded wire according to Claim 31, in which the wire (W) is rotated about itself with an opposite direction of rotation to that of the interlinked rotary movement of the wire (W) about a point on the annular path, preventing twisting of the wire (W) due to the interlinked rotary movement. 39. A method of forming a loop of stranded wire according to Claim 31, in which the wire (W) is made of steel. 40. A method of forming a net (35) in which the meshes are formed by a plurality of linked loops formed by the method according to any one of Claims 31 to 39, comprising the steps of : - preparing one or more stranded loops (34) by the method according to any one of Claims 31 to 39, - forming a further stranded loop (33) by the method according to any one of Claims 31 to 39 after interlinking the core (C) of the further stranded loop (33) to be formed with the one or more stranded loops (34) prepared, by causing the core (C) to extend through the loops .

Inventors: RUSSO VITALIANO, RUSSO, VITALIANO
Applicants: RUSSO VITALIANO, S I C MILANO S R L, RUSSO, VITALIANO, S.I.C. MILANO S.R.L.
Application year: 2000
Main classification: B21F31
IPC codes: B21F27, B21F37, B65H81, D07B5, E01F7