Tensioning apparatus for applying a tension to elongate metal elements, a machine for manufacturing a reinforced metal netting comprising same, and a method for manufacturing a reinforced metal netting

Abstract

A tensioning apparatus (200) is configured to apply a tension to elongate metal elements (20) which are supplied to a weaving machine (10) for manufacturing metal nettings (12) for geotechnical protection. The tensioning apparatus (200) comprises a tensioning device (228) having a group of drums (230), about which one or more coils of the elongate metal elements (20) to be placed under tension are wound. There are provided tensioning members (250) which keep the coils in contact with the drums (230) in such a manner as to adjust the friction between the elongate metal elements (20) and the drums (230) themselves so as to generate an opposing force counter to the pulling action which is applied by the weaving machine (10) and which tends to unwind the elongate metal elements (20) from the drums (230) of the tensioning device (228).

Description

[0001] TENS IONING APPARATUS FOR APPLYING A TENS ION TO ELONGATE METAL ELEMENTS WHICH ARE SUPPLIED TO A WEAVING MACHINE FOR MANUFACTURING METAL NETTINGS FOR GEOTECHNICAL PROTECTION

[0002] Field of the invention

[0003] The present invention relates to the field of protective or retaining metal nettings in the geotechnical field, which are used, for example , for constructing protection barriers against rockfalls , avalanches or snow falls , for bark-like coverings of rocky walls in order to contain detachments of rocks , for three-dimensional stabili zation of soil , scarps , levees , embankments , tunnels and road constructions , for constructing retaining walls for embankments , for protecting banks of water basins , for constructing weirs and other debris-protection barriers along rivers and streams and hydraulic structures in general , for constructing gabions and other products made of metal nettings , and any other use of the generally known geotechnical type .

[0004] The present invention has been developed with particular regard for a tensioning apparatus for flexible , fili form metal elements which are supplied to a machine for manufacturing a metal netting for protection or containment of the type mentioned above .

[0005] Technological background

[0006] Several types of retaining or protective metal nettings are known for use in the geotechnical field . Among them, particular relevance is attributed to woven metal nettings made by interweaving metal wires which form the mesh of the netting . The wires are wound one about the other in a unidirectional sense in the so-called nodes of the netting . Depending on the number of windings which a wire carries out with respect to another wire in the node of the netting, the nettings may have single, double or triple twists. In doubletwist nettings of the known type, the wires are twisted unidirectionally around each other in a clockwise or counterclockwise direction in the various nodes so as to form the mesh of the netting, which are typically hexagonal. These nettings can be used as such, for example, in order to form protection barriers against falling rocks or to restrain snow or avalanches, while in other cases such nettings are used to construct retaining or protective manufactures, such as, for example, gabions made of metal netting, or soil consolidation structures, such as the product known by the commercial name Terramesh® by Officine Maccaferri S.p.A. The wires used to construct the above-mentioned nettings can have a protective covering, for example, the known covering based on zinc or zinc / aluminium, known as Galfan®, or a plastics coating of the metal wire, such as, for example, the polymer covering known under the commercial name Polimac® by Officine Maccaferri S.p.A.

[0007] It is also known to reinforce the double-twist metal nettings with additional flexible elements and / or with elements having a greater resistance than the other wires of the netting. Examples of such nettings reinforced by ropes or by wires with a greater strength are described in WO 2005 / 038143, WO 2011 / 030316 and WO 2018 / 146516 by the same Applicant. When using these nettings, for example, known by the commercial names of SteelGrid HR® and MacArmour® by Officine Maccaferri S.p.A., it is particularly advantageous to make the flexible reinforcing elements, whether wires or metal ropes, as rectilinear as possible so that, when the netting is urged by an impact, the flexible reinforcing elements, whether wires or ropes, immediately become tensioned before the other wires which form the netting. Furthermore, the more taut are the flexible reinforcing elements in the protection netting, the more the width of the netting remains identical to the nominal production width . I f , however, the flexible reinforcement elements which are woven in the netting remain undulating, the tensioning thereof under force brings about a constriction in terms of width of the netting, with the result that greater quantities of netting are needed to cover the same surface-area to be protected .

[0008] In order to supply wires to machines of various types by maintaining a correct and uni form tension thereof , it is known to use various types of braking systems . For example , it is known to subj ect the wire to a constant braking force by braking the supply roller of the coil from which the wire is taken . This system can be used with di f ficulty when manufacturing protection netting for the geotechnical sector because the wire coils are very heavy and bulky and, furthermore , it would be di f ficult to coordinate the braking systems of all the coils with each other so that the tension is substantially the same for all the reinforcement wires or ropes of the netting . In a di f ferent manner, a netting in which the various reinforcement wires or ropes would not be uni formly taut would take up a distorted and non-uni form formation .

[0009] In other known systems , the wire to be kept under tension passes about one or more redirection pulleys with a small diameter, which apply a speci fic friction against the wire , braking it . These systems are often complex to adj ust precisely and in such a manner that all the reinforcement wires or ropes of a netting are subj ected to the same constant and uni form tension .

[0010] Statement of invention An obj ect of the present invention is to overcome the disadvantages of the prior art by providing a tensioning apparatus for reinforcement wires or ropes which are supplied to a weaving machine for metal netting for geotechnical protection which allows the application of a tension to the reinforcement wires or ropes which are supplied to the weaving machine . Another obj ect is to ensure that the tension applied to the reinforcement wires and ropes of the metal netting is constant and uni form over time . Another obj ect is to provide a tensioning apparatus which is simple , ef ficient , economical and reliable over time .

[0011] These obj ects and other obj ects are achieved with a tensioning apparatus having the features indicated in the appended claims .

[0012] The invention also relates to a machine and a method for constructing protection netting having the features claimed below .

[0013] According to a first aspect , there is described a tensioning apparatus which is configured to apply a speci fic tension to elongate metal elements which are supplied to a weaving machine for manufacturing metal nettings for geotechnical protection . Below, the term "geotechnical protection" is intended to be understood to include all the speci fic areas of application of the field to which the invention relates as indicated above . The tensioning apparatus may comprise a tensioning device which provides for a group of drums , about which one or more coils of the elongate metal elements to be placed under tension are wound . The tensioning apparatus is further provided with tensioning members which are configured to keep the coils in contact with the drums in such a manner as to adj ust the friction between the elongate metal elements and the drums . In this manner, there is generated an opposing force which acts counter to the pulling action which is applied by the weaving machine and which tends to unwind the elongate metal elements from the drums of the tensioning device . The elongate metal elements to which the tension is applied by such a tensioning apparatus are the reinforcement elements which thereby remain more extended with respect to the other fili form metal elements which form the mesh of the netting .

[0014] According to a speci fic aspect , the drums on which the elongate reinforcement metal elements of the geotechnical protection netting are wound are rotatable drums . In particular, the drums are all fixed to a rotatable tensioning shaft which ensures that the drums all rotate in a synchronous manner so as to apply a uni form tension to all the elongate reinforcement metal elements which are wound thereon .

[0015] According to a speci fic aspect , the position of each drum may be adj ustable along the longitudinal axis of the shaft so as to adapt to di f ferent configurations and measurements of the reinforced metal netting . It is possible not only to adj ust the position of the drums on the tensioning shaft , but also to add or subtract drums as desired .

[0016] According to a preferred aspect , the rotatable tensioning shaft may be provided with a braking device which is provided to selectively decelerate and / or brake the rotation thereof with a speci fic force , thereby acting counter to the pulling action applied by the netting manufacturing machine which takes the elongate metal elements from the respective supply coils . The term "decelerate" is intended to be understood to mean reduce the speed while the term "brake" is intended to be understood to mean moderate the speed so that it does not increase .

[0017] In a preferable but non-limiting manner, the braking device can comprise at least one brake disk which is mounted on the shaft in a coaxial manner . There is also provided at least one brake calliper which can be controlled in order to selectively clamp the brake disk in order to brake and / or decelerate the rotation of the shaft on which the drums are mounted . The brake may be of the type with automatic, semiautomatic or manual actuation .

[0018] According to a di f ferent aspect , there is described a machine for manufacturing a reinforced metal netting which comprises a plurality of metal wires which are interlaced with each other and with metal ropes in order to define the mesh of the netting . The machine may comprise , upstream of a weaving device , a tensioning apparatus which is of the type indicated above and which is provided to apply a greater tension to the metal ropes which are supplied to the machine so as to keep the metal ropes more rectilinear than the metal wires in the formation of the mesh of the reinforced netting .

[0019] According to yet another aspect , there is described a method for manufacturing a metal netting for geotechnical protection, wherein there are interlaced with each other in a weaving machine metal wires which are intercalated with metal ropes , and wherein the metal ropes are supplied to the weaving machine by applying thereto an opposing force counter to the pulling action with which the weaving machine takes the metal ropes being supplied . Preferably, the opposing force which is applied to the metal ropes is brought about by the friction of the metal ropes on respective tensioning surfaces . According to another preferable aspect , the tensioning surfaces are defined by the cylindrical covering of drums about which some coils of the metal ropes are wound .

[0020] Brief description of the drawings

[0021] Additional features and advantages will be appreciated from the following detailed description of a preferred embodiment with reference to the appended drawings which are given purely by way of non-limiting example and in which :

[0022] - Figure 1 is a view of a known machine for weaving a metal protection netting;

[0023] - Figure 2 is a detailed view of a known machine for weaving a metal protection or containment netting which is provided with woven reinforcement ropes which are intercalated with the metal wires of the netting;

[0024] - Figure 3 is a plan view of a rope tensioning apparatus according to the invention which can be used for supplying the ropes and metal wires to the known machine of Figure 2 ;

[0025] - Figure 4 is a view of a detail of Figure 3 drawn to an enlarged scale ; and

[0026] - Figure 5 is a cross-section along the marked plane V-V of Figure 3 .

[0027] Detailed description

[0028] In the following embodiments , there are described features which allow the invention to be carried out . The features described can be combined with each other in various manners and are not necessarily limited to the precise embodiment to which the drawings and the relevant description refer . In other words , a person skilled in the art of the field who reads the following description will know how to obtain the information items which are advantageous for knowing the way to carry out one or more of the features described by combining it with one or more of the other features described without the particular formulation of the description, paragraphs , terms or drawings constituting a limitation on the possibility of isolating one or more of the features described and illustrated in order to combine them with one or more of any of the other features described and illustrated . In greater detail , in the present description there should be understood to be expressly described any combination of any two features which are expressly described, even in the case in which the features are individually extracted from the speci fic context in which they can be beside or combined with other, di f ferent features , taking into account the competences and knowledge of a person skilled in the art in the field, who understands the possibility of functionally combining the features without it being necessary to functionally apply the other, di f ferent features . Unless otherwise speci fied, each and any element , member, means , system, component , obj ect which is described and illustrated in the present description must be understood to be individually described and autonomously able to be modi fied and able to be separated from and / or combined with any and each other element , member, means , system, component , obj ect which is described and illustrated . The materials , forms and functions described and illustrated do not limit the present invention but are only set out to allow a person skilled in the art to understand and carry out the invention according to preferred though non-exclusive embodiments .

[0029] Now with reference to Figure 1 , there is schematically illustrated a known machine for manufacturing a metal protection or containment netting 1 for geostructural uses . The machine comprises a weaving mechanism 2 which provides for alternately interlacing a series of metal wires which are supplied from coils 3 with similar metal wires which are removed from rods 4 which are intercalated with the metal wires from the coil 3 . The resultant netting 3 , which may be of the type with double twists with hexagonal mesh netting, passes around a drum or beam 5 in order to be subsequently wound in a roll 6 . The development of the present invention relates to a reinforced netting, wherein a number of the wires which are supplied from the coils 3 are replaced by a more resistant wire or, more preferably, by a rope or cable , which generally has a thickness and resistance which are greater than the other metal wires which form the netting .

[0030] Known solutions for constructing a reinforced netting are described in the documents WO 2005 / 038143 , WO 2011 / 030316 and WO 2018 / 146516 by the same Applicant , which are incorporated herein by reference in their entirety in order to describe features both of the reinforced netting and of the installations for the manufacture thereof .

[0031] Figure 2 is a perspective , partially sectioned view of a portion of a machine 10 for manufacturing a protection netting 12 , particularly a metal protection netting in the field of civil works , such as rockfall barriers , snow barriers , anti-debris weirs for water courses , bark-like coverings and other works for the protection of rocky escarpments or terrain, and the like . In greater detail , the protection netting 12 comprises an assembly of metal wires 14 which are interlaced with each other in order to form a series of mesh 16 . In the embodiment illustrated in the Figures , the mesh 16 are of virtually hexagonal shape . The dimensions of the hexagonal mesh are generally known and standardi zed in the field of double-twist metal netting even i f naturally, in accordance with the configuration of the machine 10 , it is possible to construct hexagonal mesh of any type and kind, with a given proportion between width and height which in the field is generally, even i f in a non- limiting manner, around values between approximately 0 . 70 and approximately 0 . 85 , for example , - at least nominally - approximately 0 . 75 ( for mesh of 60 x 80 mm) , approximately 0 . 80 (mesh of 80 x 100 mm) and approximately 0 . 83 (mesh of 100 mm x 120 mm) .

[0032] The metal wires 14 are generally arranged in the direction of the length thereof in a preferential longitudinal direction of the protection netting 12 . The metal wires 14 are interlaced in wire interlacing portions 18 which are defined by the sections of the respective metal wires 14 which are twisted around each other more than once , in a unidirectional twisting direction, that is to say, in a single direction, clockwise or counter-clockwise , for each wire interlacing portion 18 . This type of interlacing which is defined as being "double-twist" is particularly resistant and stable and allows the production of protection netting with secure and resistant mesh . There are intercalated between the assembly of metal wires 14 , at predetermined, preferably regular intervals , metal ropes 20 with a greater resistance and preferably with a greater diameter with respect to the metal wires 14 .

[0033] In the embodiment of the reinforced netting of Figure 2 , as in the other reinforced netting of the known documents mentioned above , it is particularly advantageous for the metal ropes 20 to have a progression which is rectilinear as far as possible , although slightly undulating, with respect to the undulating progression of the metal wires 14 which form the mesh of the reinforced netting 12 so that the metal ropes 20 contribute predominantly to the resistance of the protection netting 12 following an impact on the netting itsel f , for example , by rocky material of a landslip . The example of Figure 2 clearly shows that the metal wires 14 adj acent to the metal rope 20 are wound around it in rope interlacing portions 22 which are defined by the sections of the metal wires 14 which are re-twisted more than once around the rope in a unidirectional twisting direction, that is to say, in a single direction, clockwise or counter-clockwise , for each rope interlacing portion 22 . The metal wires 14 are thereby interlaced with the metal rope 20 , which has transverse undulations with respect to the preferential longitudinal direction which are far less pronounced than those of the metal wires 14 and in particular is virtually rectilinear or has barely pronounced undulations . Therefore , the metal wires 14 form a so-called "hal f mesh" 24 which can take up, in the protection netting in which the metal wires which are interlaced with each other form hexagonal mesh, the characteristic form of a semi-hexagon .

[0034] The protection netting 12 which may be constituted by metal wires 14 constructed, for example , from common steel , for example , with a diameter of from 2 to 3 mm or greater, for example , also up to from 4 to 5 mm, is flexible and readily transportable . Naturally, the wires 14 can be completely or partially replaced by thin metal ropes having, for example , a diameter of approximately from 2 to 5 mm, which is far less than the diameter of the greatest and strongest metal ropes 20 .

[0035] The metal wires 14 and the greatest metal ropes 20 can be covered by a protective covering, for example , a covering made of plastics material which prevents or at least reduces the corrosion of the wires and / or ropes . The metal ropes 20 preferably have a total external diameter, including the potential protective covering, of from approximately 4 mm to approximately 6 mm and above , sometimes greater than 8 mm, for example , between 9 and 12 mm, preferably approximately of 10 mm, naturally except for the typical dimensional tolerances in the field of manufacture of metal ropes .

[0036] As can be seen in Figure 2 , the machine 10 comprises a drum or beam 32 which is mounted with means which are not illustrated in the fixed housing of the machine so as to be able to rotate , in a manner synchronous with the speed of the interlacing means of the wires 14 , at a constant speed in the direction of the arrow 34 about the axis T thereof . Radial proj ections or pins 38 proj ect outwardly from the curved face 36 of the drum . These pins are ordered in rows which extend in a direction parallel with the axis T and are arranged at identical angular intervals . In each row, the pins 38 are arranged with constant spacing and two successive rows are staggered relative to each other by a hal f-pitch in an axial direction . These pins are used to form the netting with hexagonal mesh and to retain a portion of the netting which is already formed in the direction of the discharge of the machine .

[0037] The interlacing and / or interconnection means of the metal wires and the ropes comprise a series of pairs of first guide devices , which are spaced part from each other and coaxial and which are arranged in parallel rows with respect to the axis of the drum 32 at one side of the plane of symmetry tangent to the cylindrical periphery of the beam 32 . The pairs of guide members are arranged in radial planes with respect to the beam and the pitch thereof is identical to the pitch of the pins 38 . The interlacing and / or interconnection means of metal wires and ropes further comprise a series of pairs of second guide devices which are spaced part from each other and coaxial and which are arranged at the other side of the plane of symmetry tangent to the drum 32 . Each pair of second guide devices is arranged specularly opposite, with respect to the plane of symmetry, one of the pairs of first guide devices . The pairs of first and second devices are simultaneously movable in an alternating manner by hal f a pitch in opposite directions parallel with the axis of the drum 32 . During use , the rotation about the axis thereof of the guide devices generates the interlacing of the wires while the movement in a manner parallel with the axis of the drum 32 of the pairs of first and second guide devices in the opposite direction generates the hexagonal mesh . The interlacing means are naturally coordinated in terms of the movements with the movement of the beam 32 so as to carry out the weaving of the netting overall .

[0038] In greater detail , under the drum 32 there are provided two pairs of bars 40 , 42 and 44 , 46 which are parallel with the axis T and which act as a support for rotatable semi- cylindrical bodies 60 , 62 , 64 and 66 ; the function of the semi-cylindrical bodies is to twist with each other the wires and the ropes in pairs in order to produce the netting 12 .

[0039] The bars 40 , 42 and 44 , 46 have in cross-section a U-shaped profile rotated through 90 ° . The bars are positioned in pairs with the respective open edges of the U' s facing each other and located in a vertical plane of symmetry tangent to the periphery of the drum 32 ; the bars 40 and 42 form an upper pair and the bars 44 and 46 form a lower pair . Naturally, the terms "upper" and " lower" indicate the position in which the bars are arranged in the embodiment of Figure 2 . In fact , however, it is not excluded that they may be arranged di f ferently, for example , with the wires and the ropes which slide mainly in a hori zontal direction and in a vertical direction, as illustrated in Figure 2 . More generally, an "upper" bar is downstream in the working direction with respect to a corresponding " lower" bar, independently of the height at which it is located .

[0040] The pairs of bars 40 , 42 and 44 , 46 are supported by elements 50 , 52 , 54 , 56 which form part of the fixed housing of the machine 10 . Furthermore , they can move in a direction parallel with the direction of the axis T . The upper bars 40 and 42 are similar to the bars 44 and 46 of the lower pair of bars . At the edges of each of the bars 40 , 42 , 44 , 46 , there are formed semi-cylindrical seats with an axis perpendicular to the axis T , in each of which there is received a respective semi-cylindrical rotatable body 60 , 62 , 64 , 66 . The distance between each seat and the adj acent seat in the same bar is substantially equal to the distance between the pins 38 .

[0041] The semi-cylindrical rotatable bodies 62 which are received in the upper bar 42 are aligned with the semi-cylindrical rotatable bodies 66 of the lower bar 46 and each have a respective through-hole 72 , 76 having an axis parallel with the axis of the corresponding semi-cylindrical rotatable body . The through-holes 72 , 76 are also aligned . The holes 72 , 76 are passed through by wires 14 to be supplied to the netting in a formation, as described in greater detail below .

[0042] In the region of the position in which it is desirable to insert a rope 20 into the netting 12 , there are provided upper semi-cylindrical rotatable bodies 160 , 162 and lower semi-cylindrical rotatable bodies 164 , 166 which are preferably of a di f ferent type from the ones used for the passage of the wires 14 and which allow the passage of the ropes with a greater diameter than the wires 14 . There can be mounted under each semi-cylindrical body 60 and 160 which is carried by the upper bar 40 a cylindrical container 90 which contains a predetermined length of wire 14 which is wound helically . The wires 14 leave the containers 90 at the top, pass through the through-holes 72 and supply the netting machine for forming the netting . During use , the cylindrical containers 90 rotate about the adj acent wires 14 or about the ropes 20 .

[0043] The pairs of bars 40 , 42 and 44 , 46 are connected to movement mechanisms which allow at the same time the two bars 42 , 46 one above the other and the two bars 40 , 44 one above the other to move in translation in the same direction parallel with the axis T of the drum 32 but with opposite orientations , respectively . The movement mechanisms are configured so that each semi-cylindrical body which is carried by the same bar can be moved in translation from a position in which it faces a first semi-cylindrical body of the bar facing towards it to a second position in which it faces a second semi-cylindrical body which is adj acent to the first semi-cylindrical body . Furthermore , the semi- cylindrical rotatable bodies are connected by means of racks , such as the ones 100 , 102 visible in Figure 2 , to rotation mechanisms which rotate them in pairs in order to interlace two adj acent wires 14 with each other or to twist a wire 14 with a rope 20 and thereby to generate a portion which is twisted in order to gradually define the mesh of the protection netting 12 .

[0044] In order to be able to tension the ropes 20 , there is provided a tensioning apparatus 200 which is arranged upstream of the machine for forming the netting, between the machine itsel f and the supply coils of the wires 14 and the ropes 20 . The tensioning apparatus 200 is fixed to the ground in order to withstand the forces applied to the wires 14 and the ropes 20 , as will be better understood in the description below . The tensioning apparatus 200 comprises an inlet zone 202 , to which the wires 14 and the ropes 20 are supplied, and a discharge zone , from which the wires 14 and the ropes 20 are discharged in order to be supplied to the machine 10 . Figure 3 illustrates a particular form of this tensioning apparatus 200 when viewed from above . The arrow A indicates the supply direction of the wires 14 and the ropes 20 from the supply coil to the machine for forming the netting . In the particular form illustrated in the Figures , to be considered as a merely exemplary and non-limiting form of the invention, there are provided eleven ropes 20 which are spaced apart in groups of three adj acent wires 14 . Naturally, the invention may be modi fied and adapted to any other type of configuration of supply of wires 14 and ropes 20 . For example , the number of wires 14 and / or ropes 20 may be di f ferent from that illustrated, as the number of adj acent wires 14 spaced apart by the ropes 20 may be di f ferent and do not necessarily have to be separated by an identical number of wires 14 , even i f a regular configuration of the intervals between ropes is preferable in order to provide a speci fic uni formity of performance levels over the entire width of the finished product .

[0045] In the inlet zone 202 , the tensioning apparatus 200 is provided with an inlet comb 206 which is mounted on a support 218 . The teeth 208 of the inlet comb 206 keep the wires 14 and the ropes 20 separate from each other and aligned at predetermined spacings . The inlet comb 206 is composed of a series of rods 212 which are preferably vertical and fixed to a transverse bar 214 . Tubes 216 which reduce the friction of the wires 14 and the ropes 20 on the teeth 208 are mounted on the rods 212 in a rotatable and movable manner . Downstream of the inlet comb 206 , in a state mounted on the same support 218 , there is arranged an inlet deviating roller 220 which is rotatable and movable on supports 222 and which redirects the wires 14 and the ropes 20 by directing them from the top of the inlet zone 202 downwards , where the outlet zone 204 is located . In the outlet zone there is provided an outlet comb 224 which is similar to the inlet comb 206 . Downstream of the outlet comb 224 there is mounted an outlet deviating roller 226 which is similar to the inlet deviating roller 220 and from which the wires 14 and ropes 20 are supplied to a lower portion of the machine 10 , and are further redirected where applicable by one or more other deviating rollers in order to rise again in a state facing the cylindrical containers 90 , as described above and illustrated in Figure 2 .

[0046] In the section between the inlet deviating roller 220 and the outlet deviating roller 226 , the wires 14 run in a rectilinear manner and without any impediments . In the same section between the inlet deviating roller 220 and the outlet deviating roller 226 , however, the ropes 20 are involved with a tensioning device 228 which is provided to apply thereto a speci fic additional tension . The tensioning device 228 comprises an assembly of drums 230 , about which a number of coils of the ropes 20 , preferably two or three coils , are wound . There are provided on the sides of the drums 230 lateral shoulders 232 which delimit the cylindrical covering 234 on which the coils of the ropes 20 are wound . The ropes 20 are kept in an aligned position with respect to the drums 230 by means of guide wings 233 . The cylindrical covering of the drums 230 can be processed or covered with material which increases the friction of the ropes 20 . The drums 230 are mounted on a tensioning shaft 236 which is rotatable on supports 238 . Preferably, the supports 238 are also arranged, in addition to at the end of the tensioning shaft 236 , in an intermediate zone thereof in order to prevent it from deflecting under the load applied by the pulling action on the ropes 20 . The drums 230 are fixed to the tensioning shaft 236 in adj ustable positions along the axis thereof so as to reflect the number and position of the ropes 20 used for manufacturing the speci fic product . As indicated above , the particular example shown in the Figures provides for eleven ropes 20 which are distributed uni formly, for which reason there are also eleven drums 230 which are further distributed uni formly along the tensioning shaft 236 . Naturally, the number of ropes and corresponding drums may vary on the basis of the type of metal netting which is intended to be constructed, for example , on the basis of the width of the netting and the interval ( s ) between one rope and another .

[0047] There is mounted at one of the two ends of the tensioning shaft 236 a braking group 240 which is configured to brake the rotation of the tensioning shaft 236 which is brought about by the movement of the ropes 20 which pull the drums 230 which are fixedly j oined to the tensioning shaft 236 so as to apply a predetermined tension to the ropes 20 as a result of the friction of the given on the drums 230 . The braking group 240 may comprise a brake disk 242 which is fixed in a coaxial manner to the end of the tensioning shaft 236 . A brake calliper 244 , for example , a pneumatic, hydraulic or electrical calliper, and where applicable with manual actuation, may be actuated in order to clamp as desired the walls of the brake disk 242 so as to act counter to the rotation of the tensioning shaft 236 and therefore of the drums 230 , on which the twisting of the ropes 20 are provided in order to thereby dynamically tension the ropes 20 themselves . The clamping force of the brake calliper 244 may be fixed and predetermined or may be automatically adj usted in order to keep constant the tension of the ropes 20 . In order to automatically adj ust the braking of the tensioning shaft 236 by the braking group 240 , there may be used an electronic control system (not illustrated) which can receive , for example , a signal which indicates the rotation speed of the tensioning shaft 236 or the torsion force to which it is subj ected and to consequently adj ust the clamping force of the brake calliper 244 on the brake disk 242 . The actuation of the brake can be of the automatic, semiautomatic or manual type .

[0048] The tensioning apparatus 200 further comprises tensioners 250 which act on the ropes 20 upstream of the tensioning device 228 in order to maintain a speci fic clamping of the loops provided at the ropes 20 on the drums 230 . As Figure 5 shows more clearly, each rope 20 passes through a corresponding tensioner 250 which acts by redirecting to a greater or lesser extent the rectilinear path of the rope 20 . The rope 20 passes between a group of fixed idle wheels 252 and an opposite group of movable idle wheels 254 . In the exemplary embodiment illustrated, there are provided three fixed idle wheels 252 which are mounted on a fixed support 256 having the rotation axes thereof parallel and aligned one after the other with predetermined spacings in the sliding direction of the rope 20 . There are further provided two movable idle wheels 254 which are mounted on a movable support 258 , having the rotation axes thereof parallel and aligned in the sliding direction of the rope 20 . The axes of the two movable idle wheels 254 are intercalated with the axes of the fixed idle wheels 252 so that , by the movable support 258 approaching the fixed support 256 , the rope 20 is redirected from the rectilinear configuration and constrained to bend, forming more or less pronounced undulations about the opposite wheels 252 , 254 . The approach and movement apart of the movable support 258 from the fixed support 256 can be brought about manually, for example , by rotating a screw type adj ustment member 260 , or automatically with a pneumatic, hydraulic or electrical control .

[0049] In order to manufacture a reinforced netting, the wires 14 and the ropes 20 are supplied by the respective coils to the machine 10 , making them pass through the tensioning apparatus . The wires 14 pass into the spaces assigned to them between two teeth 208 of the inlet comb 206 , are curved above the inlet deviating roller 220 and continue in a rectilinear state until passing into the corresponding spaces between two teeth of the outlet comb 224 before becoming curved upwards , passing around the outlet deviating roller 226 in order to be supplied to the machine 10 .

[0050] The ropes 20 also pass into the spaces assigned to them between two teeth 208 of the inlet comb 206 and are curved above the inlet deviating roller 220 in order to be directed towards the outlet comb 224 and the deviating roller 226 in the same manner as the wires 14 . However, before reaching the outlet comb 224 , the ropes 20 are initially introduced into the tensioners 250 in order then to continue by winding over a speci fic number of coils , preferably two or three , on the drums 230 of the tensioning device 228 .

[0051] When the machine 10 is put into operation in order to weave the wires 14 and the ropes 20 and to construct the reinforced netting, it takes the quantity of wires and ropes required by pulling them from the respective coils . The unwinding of the wires 14 from the coils is carried out without any particular impediments while the unwinding of the ropes 20 from the respective coils is involved with the tensioning ef fect which is applied thereto mainly by the tensioning device 228 . In particular, the machine 10 encounters a speci fic resistance to pulling the ropes 20 for constructing the reinforced netting . This resistance encountered while taking the ropes 20 keeps them under tension during weaving so that they remain virtually rectilinear during the formation of the mesh of the netting, as illustrated in Figure 2 . The tension of the ropes 20 depends to the maximum extent on the friction applied during the sliding of the ropes 20 to the cylindrical covering of the drums 230 , which also depends , in addition to on the respective materials , particularly on how much the loops on the drums 230 are tensioned and how much more the movement of the drums 230 is decelerated or braked with respect to the sliding of the ropes 20 . The clamping of the loops of the ropes 20 on the drums 230 is mainly adj usted by the tensioners 250 while the relative speed of the sliding of the ropes on the drums is adj usted by the intensity of braking applied by the braking group 240 to the rotation of the tensioning shaft 236 .

[0052] Naturally, the principle of the invention remaining the same , the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention .

Claims

CLAIMS1. A tensioning apparatus for applying a tension to elongate metal elements (20) which are supplied to a weaving machine for manufacturing metal nettings for geotechnical protection, comprising a tensioning device (228) having a group of drums (230) , about which one or more coils of the elongate metal elements to be placed under tension are wound, tensioning members (250) keeping the coils in contact with the drums in such a manner as to adjust the friction between the elongate metal elements and the drums so as to generate an opposing force counter to the pulling action which is applied by the weaving machine and which tends to unwind the elongate metal elements from the drums of the tensioning device (228) .

2. A tensioning apparatus according to claim 1, wherein the drums (230) are rotatable.

3. A tensioning apparatus according to claim 2, wherein the drums (230) are all fixed to a rotatable shaft (236) so as to be rotatable with synchronous movement.

4. A tensioning apparatus according to claim 3, wherein the position of each drum (230) is adjustable along the longitudinal axis of the shaft.

5. A tensioning apparatus according to claim 3 or claim 4, wherein the rotatable shaft (236) is provided with a braking device (240) which is provided to selectively decelerate and / or brake the rotation of the shaft.

6. A tensioning apparatus according to claim 5, wherein the braking device (240) comprises at least one brake disk which is mounted on the shaft in a coaxial manner, at least onebrake calliper being able to be controlled in order to selectively clamp the brake disk in order to brake and / or decelerate the rotation of the shaft on which the drums are mounted .

7. A machine for manufacturing a reinforced metal netting (12) which comprises a plurality of metal wires (14) which are interlaced with each other and with metal ropes (20) in order to define the mesh of the netting, comprising, upstream of a weaving device, a tensioning apparatus according to any one of the preceding claims which is provided to apply a tension to the metal ropes (20) which are supplied to the machine so as to keep the metal ropes more rectilinear than the metal wires (14) in the formation of the mesh of the reinforced netting.

8. A method for manufacturing a reinforced metal netting (12) for geotechnical protection, wherein there are interlaced with each other in a weaving machine metal wires (14) which are intercalated with metal ropes (20) , and wherein the metal ropes are supplied to the weaving machine by applying thereto an opposing force counter to the pulling action with which the weaving machine takes the metal ropes being supplied.

9. A method according to claim 8, wherein the opposing force which is applied to the metal ropes (20) is brought about by the friction of the metal ropes on respective tensioning surfaces .

10. A method according to claim 9, wherein the tensioning surfaces are defined by the cylindrical covering (234) of drums (230) about which one or more coils of the metal ropes (20) are wound.

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