Production line and method for automatically producing threadlike metal products

Abstract

A production line (10) for automatically producing metal products in the form of strands or single wires. The production line (10) comprises feed devices (19, 21) configured to feed a plurality of wires to form a strand or a single wire, and a drawing unit (22) disposed downstream of the feed devices (19, 21) and comprising two drawing pulleys configured to receive, wound on them one or several times, the strand or the single wire coming from the feed devices (19, 21).

Description

[0001] “PRODUCTION LINE AND METHOD FOR AUTOMATICALLY PRODUCING THREADLIKE METAL PRODUCTS”

[0002] FIELD OF THE INVENTION The present invention concerns a production line and an associated method for automatically producing threadlike metal products, for example made of steel, such as single wires, or strands, intended as ropes or cables, consisting of several wires intertwined with each other, possibly on a central core, which can consist of one of the wires. By way of a non-limiting example, the production line and the method according to the present invention can be applied in the field of mechanical processing to transform raw products, or semi-finished products, into other more specific products, which can then be used in the construction sector in general, or in various civil infrastructures, such as for example low relaxation steel wires and strands for prestressed reinforced concrete and structural reinforcement. BACKGROUND OF THE INVENTION

[0003] To date, production lines are known in which, by means of substantially cold mechanical processing, or mechanical processing with some heat treatment, it is possible to produce threadlike metal products, such as wires and strands, in particular made of low relaxation steel for prestressed reinforced concrete and structural reinforcement.

[0004] It is known that high carbon steel wire, either on its own or braided in the form of a strand of two or more wires, according to techniques known to the people of skill in the art, can be used as structural reinforcement in a wide field of applications, such as large industrial or civil engineering works, such as for example beams for structures of buildings, in particular multi-story ones, pylons, bridges, tensile structures, port docks, highway barriers, high-speed railway sleepers, reinforced concrete pipes, giant suspension cables for cable stayed bridges, or suchlike. To effectively fulfil the load and reinforcement functions, the steel wire has to have low relaxation characteristics when subjected to the continuous application of strong axial loads, particularly when coupled with concrete. To obtain this type of wire, it is known to subject it to a stress relieving treatment, subjecting it to a load equal to about 40% of the breaking limit while it is heated to a temperature of about 400°C, with subsequent rapid cooling. The same Applicant has successfully designed, perfected, built and installed two different production lines for automatically producing threadlike metal products: a first, about 90 m long called “PC WIRE”, for producing single wires starting from a motorized bobbin from which a raw wire, with a diameter comprised between about 3 mm and about 12 mm, is pulled by a single drawing unit to be subjected to mechanical and thermal processing which stabilize it, so that it can then be wound into a strapped spool; a second, about 110 m long called “PC STRAND”, for producting strands consisting of a plurality of wires, for example seven, coming from corresponding bobbins associated with a stranding machine and pulled together by a first drawing unit, after the wires themselves have been braided together to form the strand, which is then subjected to an indentation step and other processes in order to stabilize it, so that it can be finally wound into bobbins by means of special winding devices. In the first known production line, the processing speed at which the wire travels reaches 500 m / min, which allows to achieve high productivity, that is, from about 1400 to over 5000 kilograms mass per hour (kg / h), which corresponds to between approximately 10,000 and over 36,000 nominal tons per year (t / y), depending on the diameter of the wires produced. In the second known production line, on the other hand, the processing speed at which the strand travels is lower, since the weight of the strand per linear meter is greater than that of the single wire, and reaches 170 m / min, which in any case allows to obtain a high productivity, that is, from about 1,000 to over 113,000 kilograms mass per hour (kg / h), which corresponds to between approximately 7200 and over 81 ,000 nominal tons per year (t / y), depending on the diameter of the strands produced. In the two above mentioned known production lines, considering the high operating speeds and the traction forces applied to the wires / strands, the drawing units and their sizing become particularly important. In particular, each of them comprises a pair of drawing wheels, called capstans, on the peripheral and grooved surface of which the wire, or strand, is made to pass. In addition, a single electric motor is connected to one of the two drawing wheels, which becomes a drive wheel, while the other remains driven. More in detail, in the first known production line each drawing wheel has a very large external diameter, from about 3 m to about 5 m, while in the second known production line each of the four drawing wheels, that is, two for each drawing unit, has a slightly smaller external diameter, from about 1.5 m to about 2.5 m.

[0005] Until now, precisely because of the different characteristics of the single wires and strands, and therefore because of the different traction forces at play, which can reach about 255000 N, especially for strands, it has not been possible to provide a single production line for these threadlike metal products which is versatile, that is, which can be used to selectively and alternatively produce both types of products.

[0006] There is therefore the need to provide a production line and perfect a method for automatically producing threadlike metal products, which can overcome at least the above disadvantages that exist in the state of the art.

[0007] To do this, it is necessary to solve the technical problem of creating drawing groups that allow for the choice of drawing both a single wire and also a strand at high speed, that is, up to at least 500 m / min, depending on the diameter of the wire or of the strand, guaranteeing at the same time a high productivity, at least equal to, or higher than, that of the two known production lines disclosed above.

[0008] One purpose of the present invention is to provide a production line and perfect a method for automatically producing threadlike metal products, with which it is possible to produce, automatically and as required, single wires or strands. Another purpose of the present invention is to provide a production line and perfect a method for automatically producing threadlike metal products, which are reliable and highly efficient, and which allow to have high productivity, that is, up to approximately 5000 kilograms mass per hour (kg / h) for single wires, or up to approximately 11300 kilograms mass per hour (kg / h) for strands. The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

[0009] SUMMARY OF THE INVENTION

[0010] The present invention is set forth and characterized in the independent claims. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

[0011] In accordance with the above purposes and to resolve the technical problem disclosed above in a new and original way, also achieving considerable advantages compared to the state of the prior art, a production line according to the present invention, for automatically producing metal products in the form of single wires or strands, comprises: feed means configured to feed a single wire or a plurality of wires to form a strand; at least a first drawing unit disposed downstream of the feed means and comprising two drawing pulleys configured to receive, wound on them one or several times, the single wire or the strand coming from the feed means.

[0012] In accordance with one aspect of the present invention, the two drawing pulleys are connected to two respective electric motors which can be energized together or independently of each other, as a function of the tractive force to be applied to the single wire or to the strand.

[0013] In accordance with another aspect of the present invention, the production line comprises a control unit configured to selectively energize both, or only one, of the electric motors.

[0014] In accordance with another aspect of the present invention, the two drawing pulleys have the same external diameter and the shafts of the electric motors are mechanically connected to each other, in such a way that the drawing pulleys rotate at the same peripheral speed, which substantially, or nearly, corresponds to the drawing speed of the products when at least one of the electric motors is energized, or even only one of them is energized. In accordance with another aspect of the present invention, the mechanical connection between the shafts of the electric motors comprises two driving pulleys each attached to one of the shafts and connected to each other by means of a drive

[0015] In accordance with another aspect of the present invention, each of the drawing pulleys is shaped in such a way as to have on its periphery a plurality of circular grooves preferably equidistant from each other and each having a V-shaped cross section, with a flaring angle comprised between about 25° and about 50°, preferably about 38°.

[0016] In accordance with another aspect of the present invention, the depth of each of the circular grooves is such as to house the strand between its walls, regardless of its diameter; moreover, the radius of curvature of the bottom of each of the circular grooves is substantially equal to half the diameter of the single wire.

[0017] In accordance with another aspect of the present invention, the production line also comprises treatment means disposed downstream of the first drawing unit and configured to carry out at least mechanical and thermal processing on the products.

[0018] In accordance with another aspect of the present invention, the treatment means comprise, in sequence, one or several of: an indenting apparatus; a post-forming apparatus; a washing apparatus; heating means; a cooling unit.

[0019] In accordance with another aspect of the present invention, the production line also comprises a second drawing unit disposed downstream of the treatment means and substantially the same as the first drawing unit.

[0020] In accordance with another aspect of the present invention, a method for automatically producing metal products, in the form of single wires or strands, comprises a feeding step in which the above mentioned feed means feed a single wire, or a plurality of wires, to form a strand, and a winding step, in which the single wire or the strand coming from the feed means is wound one or several times on two drawing pulleys of the above mentioned first drawing unit; moreover, the method also comprises a driving step, in which the two electric motors, each connected to one of the two drawing pulleys, are both energized, or only one of them is energized, as a function of the tractive force to be applied to the single wire or to the strand.

[0021] In accordance with another aspect of the present invention, when only one of the two above mentioned electric motors is energized, the other non-energized electric motor acts as a current generator, since the shafts of the electric motors are mechanically connected to each other.

[0022] DESCRIPTION OF THE DRAWINGS

[0023] These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

[0024] - fig. 1 is a block diagram of a production line according to the present invention, for automatically producing threadlike metal products;

[0025] - fig. 2 is a lateral view of a first portion of the production line of fig. 1; - fig. 3 is a lateral and partly sectioned view of a second portion of the production line of fig. 1;

[0026] - fig. 4 is a top view of a part of the second portion of the production line of fig. 3;

[0027] - fig. 5 is an enlarged and sectioned detail of a part of a drawing pulley of the production line of fig. 1 ;

[0028] - fig. 6 is a lateral view of a third portion of the production line of fig. 1 ;

[0029] - fig. 7 is a lateral and partly sectioned view of a fourth portion of the production line of fig. 1. We must clarify that the phraseology and terminology used in the present description, as well as the figures in the attached drawings also in relation as to how described, have the sole function of better illustrating and explaining the present invention, their purpose being to provide a non-limiting example of the invention itself, since the scope of protection is defined by the claims. To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can be conveniently combined or incorporated into other embodiments without further clarifications.

[0030] DESCRIPTION OF AN EMBODIMENT OF THE PRESENT INVENTION With reference to fig. 1, a production line 10 according to the present invention for automatically producing metal products 11 (figs, from 3 to 7), for example made of steel, and threadlike, that is, in the form of strands 12 (fig. 5) formed by braiding multiple wires 13 or a single wire 15, comprises a plurality of operating units 16 (fig. 1), installed on a base 18 (figs. 2, 3, 6 and 7), for example consisting of a floor of a suitable establishment, and aligned in sequence along a longitudinal axis X (figs, from 1 to 4, 6 and 7), preferably horizontal.

[0031] The operating units 16 comprise (from left to right in fig. 1): a feed apparatus 19 for feeding the wires 13; a stranding machine 20 for forming the strands 12; a single feed bobbin 21 for feeding the single wire 15; a first drawing unit 22; a first measuring device 23; an indentation apparatus 25; a post-forming apparatus 26; a washing apparatus 29; heating means 30; a cooling apparatus 31 ; a second drawing unit 32; an apparatus 33 for winding the single wire, or the strand, such as for example a winding apparatus known in the sector by the name of “dancer” 33; and a collection unit 35. The production line 10, in its extension along the longitudinal axis X, is about

[0032] 120 m long.

[0033] All of the operating units 16 are controlled by a control unit 36, for example of the electronic and programmable type, which together with a plurality of sensors and other detection devices, of a known type and not shown in the drawings, constitute the control means of the production line 10.

[0034] The feed apparatus 19 and the single feed bobbin 21 constitute the feed means of the production line 10. The feed apparatus 19 can be of any known type whatsoever and contains a plurality of feed bobbins 38 (fig. 2), for example between two and eighteen, in particular seven in the embodiment shown here, of which one is central and the other six are disposed interwoven around it. Each feed bobbin 38 can contain, wound into coils, a wire 13 (fig. 5) having a certain diameter DI comprised, for example, between 2 mm and 10 mm, and with a length of a few thousand meters.

[0035] The stranding machine 16 (figs. 1, 2 and 3) can be of any known type whatsoever, it is disposed close to the exit of the feed apparatus 19 and configured to receive the plurality of wires 13 (fig. 5) and transform them into a strand 12 having a certain diameter D2, for example from about 4 mm to about 25 mm, and a certain programmable pitch.

[0036] The single feed bobbin 21 (figs. 1, 3 and 4) can be of any known type whatsoever, and the single wire 15 is wound onto it, which substantially has the sizes of one of the wires 13. The single feed bobbin 21, if necessary, is able to be selectively displaced laterally with respect to the longitudinal axis X, for example when the production line 10 is used to produce the strands 12.

[0037] The first drawing unit 22 is disposed inside a first cavity 39 (figs. 3 and 4) created in the base 18, with a parallelepiped shape and having, for example, sizes of about 7.5 m x 5 m and a depth of about 3 m. Service steps 40 (fig. 4) are present to access the bottom of the first cavity 39. The first drawing unit 22 comprises two identical drawing pulleys 41 and 42 (figs. 3 and 4), mounted rotatable around two horizontal axes of rotation Y1 and Y2, which are substantially perpendicular to the longitudinal axis X, although on different planes. In fact, the axis of rotation Y1 of the first drawing pulley 41, that is, the one positioned closest to the single feed bobbin 21, is lower (fig. 3) by about 400 mm compared to the axis of rotation Y2 of the other, or second, drawing pulley

[0038] 42. The external diameter D3 of the two drawing pulleys 41 and 42 is advantageously about 3 m and the center distance between the two axes of rotation Y1 and Y2 is about 3.5 m. In a new and original way, the two drawing pulleys 41 and 42 are connected, or attached, respectively, to the shafts of two electric motors 43 and 44 (fig. 4), coaxial to the axes of rotation Y1 and Y2. Furthermore, the shafts of the two electric motors 43 and 44 are mechanically connected to each other, for example by means of a drive belt 45 (fig. 4) and two driving pulleys 46 and 48, with a smaller diameter than that of the two drawing pulleys 41 and 42, so that the latter rotate at the same peripheral speed, which substantially or almost corresponds to the drawing speed Vt (fig. 3) of the products 11, when the two electric motors 43 and 44 are energized, or only one of them is energized, as will be described in detail below.

[0039] Each of the two drawing pulleys 41 and 42 is shaped in such a way as to have a plurality of circular grooves 49 (fig. 5) on its periphery, for example five in the embodiment shown here, preferably equidistant from each other and each having a V-shaped cross section, with a flaring angle a comprised between about 25° and about 50°, preferably of about 38°. The depth P of each circular groove 49 is such as to house the strand 12 between its walls, regardless of its diameter D2, and is for example comprised between about 26 mm and about 34 mm, preferably of about 30 mm. The radius of curvature of the bottom of each circular groove 49 is substantially equal to half the diameter DI of the single wire 15. In this way, advantageously, the drawing pulleys 41 and 42 can draw the products 11, be they strands 12 or single wires 15, without creating reciprocal sliding between them, thus guaranteeing a high precision drawing.

[0040] The two drawing pulleys 41 and 42 (figs. 3 and 4) have the function of horizontal axis capstans, and the strand 12 or the single wire 15 is wound onto them, as in a block, making it pass with several turns, for example five, from one circular groove 49 to the adjacent one, starting from one of the two outermost circular grooves 49. In this way, also by sizing the two electric motors 43 and 44 so that they have a relatively low power, for example of about 220 KW, that is, about half the power of the production lines of the prior art, it is possible to exert on the strand 12 or on the single wire 15 a tractive force F of up to over 255000 N, at a drawing speed Vt variable from about 80 m / min to about 170 m / min for the strand 12, and from about 90 m / min to about 420 m / min for the single wire 15. By way of example, the two electric motors 43 and 44 are commanded by the control unit 36 so that the tractive force F applied on the strand 12, or on the single wire 15, by the first drawing unit 22 is approximately equal to a value comprised between 40% and 45% of their breaking load.

[0041] Advantageously, the two electric motors 43 and 44 can be commanded by a single electric inverter of a known type, for example of 440 KW.

[0042] The first measuring device 23 (figs. 3 and 4) can be of any known type whatsoever and comprises, for example, load cells not shown in the drawings and configured to measure the load present on the strand 12 or on the single wire 15 immediately downstream of the first drawing unit 22 and before the subsequent processing.

[0043] The indenting apparatus 25 (fig. 3) can be of any known type whatsoever and is configured to create a plurality of teeth, or ridges, on the peripheral surface of the strand 12 or single wire 15.

[0044] The post-forming apparatus 26 is configured to perform, in a known manner, a post-forming treatment on the strand 12 or on the single wire 15, for example an operation of alignment of the strand 12 or of the single wire 15.

[0045] In its final part, the post-forming apparatus 26 comprises a second measuring device 50, also of a known type and comprising for example other load cells not shown in the drawings, which is configured to measure the load present on the strand 12 or on the single wire 15 after the indentation operation carried out with the indentation apparatus 25 and the elongation that the strand 12 or the single wire 15 undergoes during this indentation operation, which is of the order of about 1% to 1.5%.

[0046] The washing apparatus 29 can be of any known type whatsoever and is configured to wash the strand 12 or the single wire 15 downstream of the indenting and post-forming operations.

[0047] The heating means 30 (figs. 1 and 6) comprise a heating furnace 30, for example an induction furnace, which can be of any known type whatsoever, for example modular and selectively and alternately mobile along the longitudinal axis X between a first position A (fig. 6) and a second position B, and vice versa, and it has the function of carrying out a heating operation of the strand 12 or of the single wire 15, for example at a temperature comprised between about 350°C and about 410°C, in order to stabilize them. The cooling unit 31 can be of any known type whatsoever and is configured to cool the strand 12 or the single wire 15, after the heating and stabilization operation.

[0048] The indentation apparatus 25, the post-forming apparatus 26, the washing apparatus 29, the heating means 30 and the cooling unit 31 together constitute the treatment means 51 (fig. 1) of the products 11.

[0049] The second drawing unit 32 (figs. 1 and 7) is substantially the same as the first drawing unit 22, except for the fact that the axes of rotation of the two drawing pulleys, designated as 41 A and 42 A (fig. 7), lie on a same plane parallel to the longitudinal axis X, so it is not described in detail again. The second drawing unit 32 is installed in a second cavity 52 (fig. 7) created in the base 18 and substantially the same as the first cavity 39.

[0050] The winding apparatus 33 can be of any known type whatsoever, for example a so-called “dancer” that uses the principle of inertia compensation and effectively absorbs any tension imbalances and guarantees constant winding tension. The tension is adjusted and maintained thanks to a feedback of its own up and down movement, through an encoder and a pneumatic cylinder controlled by a proportional valve modifying the weight force.

[0051] The collection unit 35 is configured to collect, for example in the form of bobbins, or spools, the strand 12 or the single wire 15 after the processing cycle is complete. For example, the collection unit 35 comprises a pair of reels 53 which can be of any known type whatsoever.

[0052] The operation of the production line 10, which corresponds to the method for automatically producing the products 11 , essentially comprises the following steps, for example coordinated and commanded by the control unit 36:

[0053] - a feeding step, in which the feed means, consisting of the feed apparatus 19 and the single feed bobbin 21, feed a plurality of wires 13 to form a strand 12 or a single wire 15;

[0054] - a winding step, in which the strand 12 or the single wire 15, coming from the aforementioned feed means, is wound one or more times on the two drawing pulleys 41 and 42 of the first drawing unit 22; and

[0055] - a driving step, in which the two electric motors 43 and 44 are both energized, or only one of the two is energized, as a function of the tractive force F to be applied to the strand 12 or to the single wire 15.

[0056] Moreover, when only one of the two electric motors 43 or 44 is energized, the other electric motor 44 or 43, not energized, advantageously acts as a current generator, or dynamo, precisely because the shafts of the two electric motors 43 and 44 are mechanically connected to each other, as described above. This current can be used at this time, or accumulated for later use.

[0057] It will be apparent to the people of skill in the art that the new and original solution of having the two drawing pulleys 41 / 41 A and 42 / 42 A connected to two respective electric motors 43 and 44, which can be energized independently of each other, or together, as a function of the tractive force F to be applied to the strand

[0058] 12 or to the single wire 15, makes the production line 10 very versatile and brings considerable advantages in terms of reliability and productivity. The latter, in fact, is of the order of about 11300 kilograms mass per hour (kg / h) for the strands 12, and about 5000 kilograms mass per hour (kg / h) for the single wires 15. In the preparation of the wire rod or starting metal product, the wire can be pickled with hydrochloric / phosphoric acid or with mechanical cleaning. It is then coated with zinc and calcium phosphate crystals in order to improve corrosion resistance and the friction coefficient, favoring cold-drawing or cold-rolling. The electrochemical deposit is about 6 mm / m2, which corresponds to 0.03 mm of thickness. After the cold drawing / rolling step, with a section reduction of about 85%, the remaining phosphate crystals covering the wire pass, in accordance with the stabilization process, into the furnace at 410°C with an elongation of 1% / 1.5%, reducing the anti-corrosion property. The step with hopeite is completely dehydrated at a temperature of 240°C and from 250°C to 600°C, and a consistent loss of weight of the phosphate crystals occurs. For this purpose, a corrosion protection system can be provided with an emulsion (water-oil with about 8 / 12% oil), which covers the strand or wire for about 0.05 mm, before the final winding, with great energy savings. The corrosion protection device can be any, for example a vacuum generator that, by exploiting the Venturi effect, when the compressed air passes it sucks the emulsion which, mixing with the air, is sprayed onto the material being processed. The device allows to dose the compressed air being expelled and the amount of emulsion required by the diameter of the strand or wire and by the production speed. It is clear that modifications and / or additions of parts or steps may be made to the production line 10 and to the method for automatically producing threadlike metal products as described heretofore, without departing from the field and scope of the present invention, as defined by the claims. It is also clear that, although the present invention has been described with reference to a single specific example, a person of skill in the art will be able to achieve other equivalent forms of production line 10 and method for automatically producing threadlike metal products, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby. In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the claims.

Claims

CLAIMS1. Production line (10) for automatically producing metal products (11) in the form of single wires (15), or strands (12), comprising: feed means (19, 21) configured to feed a plurality of wires (13) to form a single wire (15), or a strand (12); at least a first drawing unit (22) disposed downstream of said feed means (19, 21) and comprising two drawing pulleys (41, 42) configured to receive, wound on them one or several times, said single wire (15) or said strand (12), characterized in that said two drawing pulleys (41, 42) are connected to two respective electric motors (43, 44) which can be energized independently of each other, or together, as a function of the tractive force (F) to be applied to said strand (12) or to said single wire (15).

2. Production line (10) as in claim 1, characterized in that it comprises a control unit (25) configured to selectively energize both, or only one, of said electric motors (43, 44).

3. Production line (10) as in claim 1 or 2, characterized in that said two drawing pulleys (41, 42) have the same external diameter (D3) and the shafts of said electric motors (43, 44) are mechanically connected to each other, in such a way that said drawing pulleys (41, 42) rotate at the same peripheral speed, which substantially, or nearly, corresponds to the drawing speed (Vt) of said products (11) when said electric motors (43, 44) are energized, or even only one of them is energized.

4. Production line (10) as in claim 3, characterized in that said external diameter (D3) is 3 m.

5. Production line (10) as in claim 3 or 4, characterized in that the mechanical connection between said shafts of said electric motors (43, 44) comprises two driving pulleys (46, 48) each attached to one of said shafts and connected to each other by means of a drive belt (45).

6. Production line (10) as in any claim hereinbefore, characterized in that each of said drawing pulleys (41, 42) is shaped in such a way as to have on its periphery a plurality of circular grooves (49) preferably equidistant from each other and each having a V-shaped cross section, with a flaring angle a comprised between about 25° and about 50°, preferably of about 38°.

7. Production line (10) as in claim 6, characterized in that the depth (P) of each of said circular grooves (49) is such as to house said strand (12) between its walls,regardless of the diameter (D2) of the latter, and in that the radius of curvature of the bottom of each of said circular grooves (49) is substantially equal to half the diameter (DI) of said single wire (15).

8. Production line (10) as in any claim hereinbefore, characterized in that it comprises treatment means (50) disposed downstream of said first drawing unit(22) and configured to carry out at least mechanical and thermal processing on said products (11).

9. Production line (10) as in claim 8, characterized in that said treatment means (50) comprise, in sequence, one or several of: an indenting apparatus (25); a post- forming apparatus (26); a washing apparatus (29); heating means (30); a cooling unit (31).

10. Production line (10) as in claim 8 or 9, characterized in that it comprises a second drawing unit (32) disposed downstream of said treatment means (50) and substantially the same as said first drawing unit (22).

11. Method for automatically producing metal products (11) in the form of single wires (15), or strands (12), comprising a feeding step in which feed means (19, 21) feed a single wire (15), or a plurality of wires (13), to form a strand (12), and a winding step, in which said single wire (15), or said strand (12), coming from said feed means (19, 21) is wound one or several times on two drawing pulleys (41, 42) of a drawing unit (22), characterized in that it comprises a driving step, in which said two electric motors (43, 44), each connected to one of said two drawing pulleys (41, 42), can be energized independently of each other, or together, as a function of the tractive force (F) to be applied to said single wire (15) or to said strand (12).

12. Method for automatically producing metal products (11) as in claim 11, characterized in that when only one of said two electric motors (43, 44) is energized, the other non-energized electric motor acts as a current generator, since the shafts of said electric motors (43, 44) are mechanically connected to each other.

Images