Production line and method for automatically producing threadlike metal products

Abstract

Production line (10) for automatically producing metal products (11), comprising feed devices (19, 38) configured to feed a plurality of wires (13) to form a strand (12), and a subsequent drawing unit (22) configured to receive the strand (12).

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, in particular 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 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 line, about 110 m long called “PC STRAND”, for producing 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 post-forming 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 11,300 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 production of strands, it is known to carry out a post- forming operation upstream of the first drawing unit, the purpose of which is to straighten the strand and make it rectilinear before it enters the first drawing unit. This post-forming operation can be carried out for example by means of rows of staggered rollers between which the single wire slides. Upstream of the first drawing unit there is also a load cell designed to detect the pull of the single wire before it enters into the first drawing unit.

[0005] One problem encountered in carrying out the post-forming operation upstream of the first drawing unit is that the pull transmitted to the first drawing unit is not constant and the product coming out of it often has at least a degree of unsatisfactory straightness, which negatively affects its overall quality.

[0006] Since the drawing unit is located downstream of the post-forming process, this process can generate variations in the pull and therefore incorrect functioning of the first drawing unit.

[0007] Furthermore, the drawing unit with variable pull can also generate operating problems on the post- forming apparatus. For example, it is possible that the rollers of the post-forming apparatus may become excessively worn.

[0008] There is therefore a need to create a production line and to perfect a method for automatically producing threadlike metal products, in particular strands, which can overcome at least the above disadvantages present in the state of the art.

[0009] In particular, one purpose of the present invention is to create a production line and to perfect a method for automatically producing threadlike metal products, with which it is possible to produce, by choice and automatically, strands of high stability and final quality, for example in terms of structural resistance and straightness.

[0010] Another purpose of the present invention is to create a production line and perfect a method for automatically producing threadlike metal products, which are reliable and highly efficient, and which allow to obtain high productivity. Another purpose of the present invention is to create a production line and perfect a method for automatically producing threadlike metal products in which the first drawing unit receives a strand directly from feed means and therefore is not subjected to processes which can negatively impact the pull at entry to this first drawing unit, for example causing a change in the pull. 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.

[0011] SUMMARY OF THE INVENTION

[0012] 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.

[0013] 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 comprises feed means configured to feed a plurality of wires to form a strand and a subsequent first drawing unit configured to receive said strand. According to one aspect of the invention, the production line comprises: a first measuring device configured to detect the pull on the strand as it exits the first drawing unit; a post-forming apparatus substantially configured to confer straightness on said strand; a second measuring device, configured to detect the pull on the strand; and a second drawing unit configured to draw the strand exiting from said post-forming apparatus.

[0014] Advantageously, by placing the post-forming apparatus downstream of the first drawing unit, the first drawing unit is not negatively affected by variations in the pull caused by the post-forming operation. Furthermore, the post-forming apparatus also works effectively, is less affected by wear phenomena compared with what happens in known production lines and allows to obtain a stable strand of high quality and straightness, which substantially does not require further straightening operations before leaving the production line.

[0015] According to another aspect of the invention, the production line comprises a control unit configured to receive the data relating to the pulls, to process them and send an overall pull value for the strand to the second drawing unit.

[0016] According to another aspect of the invention, treatment means configured to carry out at least thermal processing on the strand are provided between the postforming apparatus and the second drawing unit.

[0017] According to another aspect of the invention, the treatment means comprise in sequence heating means configured to stabilize the strand and a cooling apparatus.

[0018] According to another aspect of the invention, the heating means comprise an induction furnace configured to heat the strand to a temperature comprised between approximately 350°C and approximately 410°C.

[0019] According to another aspect of the invention, the heating means are mobile selectively and alternatively along a longitudinal axis of the production line between a first position and a second position and vice versa.

[0020] According to another aspect of the invention, the treatment means comprise an apparatus for washing the strand located upstream of the heating means. According to another aspect of the invention, the production line comprises an apparatus, called “dancer”, located downstream of the second drawing unit.

[0021] According to another aspect of the invention, the production line comprises a collection unit configured to collect, in particular in the form of coils, skeins, or suchlike, the strand at the end of the production cycle.

[0022] Another purpose of the present invention is a method for automatically producing metal products in the form of strands, comprising a step of feeding a plurality of wires to form a strand, drawn by a first drawing unit.

[0023] According to one aspect of the invention, the method also comprises: a step of measuring the pull on the strand by means of a first measuring device; a step of conferring substantial straightness to the strand by means of a post-forming apparatus; a subsequent step of measuring the pull on the strand by means of a second measuring device; and a step of drawing the strand exiting from the postforming apparatus by means of a second drawing unit. DESCRIPTION OF THE DRAWINGS

[0024] 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:

[0025] - fig. 1 is a block diagram of a production line according to the present invention, for automatically producing threadlike metal products;

[0026] - fig. 2 is a lateral view of a first portion of the production line of fig. 1 ;

[0027] - fig. 3 is a lateral and partly sectioned view of a second portion of the production line of fig. 1 ;

[0028] - fig. 4 is a top view of a part of the second portion of the production line of fig. 3; - fig. 5 is an enlarged and sectioned detail of a part of a drawing pulley of the production line of fig. 1 ;

[0029] - fig. 6 is a lateral view of a third portion of the production line of fig. 1 ;

[0030] - 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.

[0031] 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.

[0032] DESCRIPTION OF AN EMBODIMENT OF THE PRESENT INVENTION

[0033] 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, 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.

[0034] The production line 10 can operate to produce the strand 12 or a single wire 15, see in particular fig. 5.

[0035] The production line 10 and in particular the operating units 16 comprise: feed means 19, 38 configured to feed a plurality of wires 13 to form the strand 12 and a first drawing unit 22 positioned downstream of the feed means 19, 38 and configured to receive the strand 12. The production line 10 comprises in sequence: a first measuring device 23 located downstream of the first drawing unit 22 and configured to detect the pull T1 on the strand 12 as it exits the first drawing unit 22; a post- forming apparatus 26; a second measuring device 50, configured to detect the pull T2 on the strand 12 downstream of the post- forming apparatus 26; and a second drawing unit 32 configured to draw the strand 12 exiting the post-forming apparatus 26.

[0036] The operating units 16 can also comprise: a washing apparatus 29; heating means 30; a cooling apparatus 31; a strand winding apparatus 33, such as for example a winding apparatus known in the sector by the name “dancer”; and a collection unit 35. The production line 10, in its extension along the longitudinal axis X, is approximately 120 m long.

[0037] The production line 10 comprises a control unit 36 configured to receive the data relating to the pull Tl, T2, to process them and send an overall pull value T for the strand 12 to a second drawing unit 32 located downstream of the postforming apparatus 26. The pull T is in particular the sum of the pulls T1 and T2.

[0038] All of the operating units 16 are controlled by the 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.

[0039] The feed apparatus 19 and the single feed bobbin 21 constitute the feed means of the production line 10, in order to produce the single wire 15.

[0040] The feed apparatus 19 for the production of the strand 12 can be of any known type whatsoever and contain for example 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.

[0041] The single feed bobbin 21 for the production of the single wire 15 can in practice be one of the feed bobbins 38.

[0042] The feed line 10 can comprise a stranding machine 20 of any known type, disposed close to the outlet 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. For the production of the single wire 15 the stranding machine 20 can be by-passed or said single wire 15 can pass through it remaining unchanged. 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. 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 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. 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.

[0043] 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 oc 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.

[0044] 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.

[0045] 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. More generally and 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.

[0046] The electric motors 43 and 44 can be commanded by a single electric inverter of a known type, for example of 440 KW.

[0047] 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.

[0048] The indenting apparatus 25 (fig. 3) can be of any known type whatsoever and is configured to create a plurality of teeth, or protrusions and / or grooves, on the peripheral surface of the single wire 15. In the production of strands 12, the indenting apparatus 25 can be by-passed or the strand 12 can pass through it remaining unchanged.

[0049] 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. The post- forming apparatus 26 is thus configured to confer straightness on the strand 12 or on the single wire 15.

[0050] The post-forming apparatus 26 is associated with or located upstream of the second measuring device 50, also of a known type and comprising for example other load cells not shown in the drawings. The second measuring device 50 is configured to measure the load present on the strand 12 or on the single wire 15 after the operation carried out with the post-forming apparatus 26 and the elongation that the strand 12 or the single wire 15 undergo, which is of the order of about 1% to 1.5%.

[0051] The post-forming apparatus 26 can be housed on a counter 54, with which the second measuring device 50 can be associated. For example, it can be provided that the counter 54 is a sort of cradle under which the second measuring device 50 is positioned.

[0052] 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. 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 to a temperature comprised between about 350°C and about 410°C, in order to stabilize the strand 12 or the single wire 15.

[0053] The heating means 30 are mobile for example to facilitate and speed up the approach of the single wire 15 to be cooled toward the cooling apparatus 31 and resume the segment not heated during an emergency stop, even in the event of breakage of the single wire 15.

[0054] 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.

[0055] The heating means 30 and the cooling unit 31 together constitute the processing means 51 (fig. 1) of the products 11. The processing means 51 can also comprise the washing apparatus 29.

[0056] 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

[0057] 32 is installed in a second cavity 52 (fig. 7) created in the base 18 and substantially the same as the first cavity 39.

[0058] 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.

[0059] 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. The present method for automatically producing the products 11 essentially comprises the following steps, made in sequence, for example coordinated and commanded by the control unit 36: a step of feeding the plurality of wires 13 to form the strand 12 and of drawing the strand 12 by means of the first drawing unit 22; a step of measuring the pull T1 on the strand 12 downstream of the first drawing unit 22 by means of the first measuring device 23; a step of conferring substantial straightness on the strand 12 by means of the post- forming apparatus 26; a step of measuring the pull T2 on the strand 12 by means of the second measuring device 50; and a step of drawing the strand 12 exiting from the post- forming apparatus 26 by means of the second drawing unit 32. 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.

[0060] 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 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), comprising feed means (19, 38) configured to feed a plurality of wires ( 13) in order to form a strand (12) and a subsequent first drawing unit (22) configured to receive said strand (12), characterized in that it comprises: a first measuring device (23) configured to detect the pull (Tl) on said strand (12) at the outlet of said first drawing unit (22); a post-forming apparatus (26) substantially configured to confer straightness to said strand (12); a subsequent second measuring device (50) configured to detect the pull (T2) on said strand (12); and a second drawing unit (32) configured to draw said strand (12) at exit from said post-forming apparatus (26).

2. Production line (10) as in claim 1, characterized in that it comprises a control unit (36) configured to receive the data relating to said pulls (Tl , T2), process them and send an overall pull value (T) for said strand (12) to said second drawing unit (32).

3. Production line (10) as in claim 2, characterized in that it comprises, between said post-forming apparatus (26) and said second drawing unit (32), treatment means (51) configured to carry out at least thermal processes on said strand (12).

4. Production line (10) as in claim 3, characterized in that said treatment means (51) comprise in sequence heating means (30) configured to stabilize said strand(12) and a cooling apparatus (31).

5. Production line (10) as in claim 4, characterized in that said heating means (30) comprise an induction furnace configured to heat said strand (12) to a temperature comprised between about 350°C and about 410°C.

6. Production line (10) as in claim 4 or 5, characterized in that said heating means(30) are selectively and alternately mobile along a longitudinal axis (X) of said production line (10) between a first position (A) and a second position (B), and vice versa.

7. Production line (10) as in claim 4, 5 or 6, characterized in that said treatment means (51) comprise an apparatus (29) for washing said strand (12) located upstream of said heating means (30).

8. Production line (10) as in claim 2, characterized in that it comprises a winding apparatus (33) located downstream of said second drawing unit (32).

9. Production line (10) as in any claim hereinbefore, characterized in that it comprises a collection unit (35) configured to collect, in particular in the form of coils, skeins, or suchlike, said strand (12) at the end of the production cycle.

10. Method for automatically producing metal products (11), comprising a step of feeding a plurality of wires (13) in order to form a strand (12) drawn by a first drawing unit (22), characterized in that it comprises: a step of measuring the pull (Tl) on said strand (12) by means of a first measuring device (23); a step of conferring substantial straightness to said strand (12) by means of a post-forming apparatus (26); a subsequent step of measuring the pull (T2) on said strand (12) by means of a second measuring device (50); and a step of drawing said strand (12) at exit from said post-forming apparatus (26) by means of a second drawing unit (32).

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