Rolling apparatus and corresponding method

Abstract

Rolling apparatus (10) for rolling a metal product (P), initially in the form of wire rod or wire, comprising a rolling unit (16) with at least one rolling cassette (18) configured to reduce the sizes of the section of the metal product (P) through a substantially radial compression, and a lubrication device (15) configured to atomize oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the surface of the metal product (P).

Description

[0001] “ROLLING APPARATUS AND CORRESPONDING METHOD”

[0002] FIELD OF THE INVENTION

[0003] The present invention concerns a rolling apparatus and a corresponding method for rolling wire rods or wire products in order to obtain a metal wire, which can for example be used in the aeronautical, medical, automotive, construction, industrial, agricultural and livestock breeding sectors, in small metal parts, fences or other.

[0004] The present invention is applied mainly, although not exclusively, in processes for the post-treatment of metal material essentially coming from hot rolling processes, in order to obtain particular mechanical properties of resistance and workability, as a function of the specific intended use.

[0005] BACKGROUND OF THE INVENTION

[0006] It is known that long products such as wire rods, which are obtained from hot rolling processes downstream of a continuous casting, are often used as starting products in the next supply chain in order to obtain final products with desired sizes and mechanical properties.

[0007] Drawing apparatuses that use, as a metal product at entry, wire rods wound into coils and disposed on special feeding reels to obtain a final product with a different and desired size and section are known.

[0008] In these apparatuses, a wire rod is made to pass cold through holes of decreasing diameter (dies), so as to reduce the sizes of its section to those desired.

[0009] Drawing generally requires a preliminary phosphating treatment, in which phosphate granules, generally zinc and calcium, are deposited on the wire rod at entry. Phosphating gives the wire rod corrosion resistance. In addition, the phosphate granules increase the wire rod’s surface roughness, promoting the deposit of lime, improving the adhesion of the lubricant added subsequently. The lubricant is generally a powder lubricant, for example a calcium or sodium stearate.

[0010] These powder lubricants can contaminate the environment. Expensive suction, purification and disposal systems are used to partly reduce this contamination, which, in addition to weighing on the overall plant costs, do not completely solve the problem.

[0011] During the drawing passes, friction and surface temperature increase. This leads to an increase in the work hardening, and consequently in the yield strength, on an external surface of the metal product. For example, in the case of high carbon steel wire rods, the steel of the metal product’s surface can become martensitic and therefore be harder than the internal material. Consequently, the internal part of the metal product can deform more easily than the external part: this increases the risk of micro-cracks and breaks, both during drawing and also in any subsequent working steps.

[0012] Drawing also causes a worsening of the metal product’s microstructure, since it causes an elongation of the grains of the crystalline structure that makes the product very rigid, and therefore hinders a stranding or similar subsequent working.

[0013] Rolling apparatuses comprising a plurality of rolling units, each of which is provided with at least one pair of rolling rolls, or rings, are also known. The rolls are reciprocally disposed in such a way as to define a passage channel through which, during use, the metal product being worked is made to pass.

[0014] The passage channel between one working unit and the next progressively decreases until it reaches the final thickness / size to be given to the metal product, which at the end of the process will have the form of a metal wire.

[0015] The aforementioned phosphating and lubrication treatments with powder lubricants are also necessary in the case of cold rolling. Furthermore, due to the type of process it is currently very difficult, or even not feasible, to roll wire rods made of high carbon or cobalt content steel, titanium and its alloys, hardened nickel-based superalloys, hardened cobalt-based superalloys and other materials also obtained by sintering the powders, in order to obtain respective metal wires. In fact, the product could suffer from crack formations during working or brittle fracture phenomena.

[0016] There is therefore the need to perfect an apparatus and method for rolling wire rods that can overcome at least one of the disadvantages of the state of the art.

[0017] In particular, one purpose of the present invention is to provide a rolling apparatus which, starting from wire rods or wire products made of high or low carbon content steel, titanium alloys, tungsten molybdenum alloys, nickel chromium alloys, cobalt molybdenum alloys, enriched titanium stainless steel, stainless steel with low or high chromium percentage and other materials, and having a thickness, or nominal diameter, between 2 mm and 18 mm, depending on the type of product, is able to produce metal wires having a thickness, or nominal diameter, comprised between approximately 0.8 mm and approximately 11 mm, which requires low energy input, which does not release contaminants into the environment and which is therefore eco-sustainable. For example, the starting product can have, in the case of a product in the form of wire rod, a thickness, or nominal diameter, between approximately 5.5 mm and approximately 18 mm, while in the case of a wire product the thickness, or nominal diameter, can be between approximately 2 mm and approximately 10 mm.

[0018] Another purpose of the present invention is to provide an apparatus as above, which allows to obtain metal wires having physical properties favorable for a subsequent stranding.

[0019] Another purpose is to perfect a method for rolling metal products, such as wire rods or wire products, that is able to achieve a significant reduction in thickness even on materials that typically present work hardening problems.

[0020] 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.

[0021] SUMMARY OF THE INVENTION

[0022] 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.

[0023] In accordance with the above purposes and to resolve the technical problem described above in a new and original way, also achieving considerable advantages compared to the state of the prior art, an apparatus for rolling a metal product, initially in the form of wire rod or wire, according to the present invention comprises a rolling unit with at least one rolling cassette configured to reduce the sizes of the metal product’s section through a substantially radial compression.

[0024] In accordance with one aspect of the present invention, the rolling apparatus comprises a lubrication device configured to atomize oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the surface of the metal product with the function of lubricant.

[0025] Doing so achieves the advantage of avoiding the use of solid lubricants, such as calcium or sodium stearates, which have a strong environmental impact. This also allows to eliminate expensive suction systems necessary for working apparatuses that use solid lubricants. Furthermore, liquid lubricants do not require phosphating to adequately adhere to the metal product’s surface, therefore it is possible to avoid both phosphating and also a prior chemical pickling, thus avoiding the economic, environmental and safety costs associated therewith.

[0026] The rolling apparatus can comprise, immediately upstream of the lubrication device, a mechanical pickling device, configured to mechanically remove the oxides present on the surface of the metal product. The oil or water-oil emulsion or colloidal dispersion in water have the additional function of protecting the pickled surface of the metal product from moisture.

[0027] Some embodiments described here also concern a method for rolling a metal product comprising:

[0028] - making the metal product available in the form of wire rod or wire;

[0029] - lubricating the metal product, on the surface of which oil, or a water-oil emulsion or a colloidal dispersion in water is atomized, by making it pass through a lubrication device;

[0030] - rolling the metal product by making it advance continuously through a rolling unit, which reduces the sizes of the metal product’s section through a substantially radial compression, until it takes the form of a metal wire.

[0031] The method can also provide, before rolling, to pickle the metal product with a mechanical pickling device, which mechanically removes the oxides present on the surface of the metal product. The lubrication as above can occur immediately after the pickling.

[0032] DESCRIPTION OF THE DRAWINGS

[0033] 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:

[0034] - fig. 1 is a schematic representation of a drawing apparatus according to the state of the art;

[0035] - fig. 2 is a schematic representation of a drawing apparatus according to the present invention;

[0036] - fig. 3 is a comparison of the results of tensile tests carried out on two metal products obtained with the apparatuses of fig. 1 and fig. 2, respectively;

[0037] - fig. 4 is a comparison of exit temperature measurements carried out on two metal products obtained with the apparatuses of fig. 1 and fig. 2, respectively.

[0038] 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.

[0039] 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.

[0040] DESCRIPTION OF SOME EMBODIMENTS

[0041] A brief description of a drawing apparatus 1 10 according to the state of the art is given with reference to fig. 1 , with the sole purpose of exposing its limitations, which are overcome by the present invention (described further below). The drawing apparatus 110 is configured to work a metal product P in the form of a wire rod to obtain a metal wire with smaller sizes.

[0042] The term metal product P is understood here as the metal product being worked, which is initially in the form of a wire rod or wire, and at the end of the method carried out with the drawing apparatus 110 (or with a rolling apparatus 10 according to the present invention described further below) is in the form of a metal wire.

[0043] The drawing apparatus 110 comprises a cold drawing unit 116, having a plurality of dies 118 with decreasing diameters and a plurality of drawing members 119. The drawing apparatus 110 is configured to make the metal product P pass through the dies 118 so as to reduce the sizes of its section. The drawing members 119 are configured to keep the metal product P under tension and draw it through the dies 118. An exit winding device 114 can be provided at exit from the drawing unit 116 to collect the drawn metal product P.

[0044] Each die 118 is generally preceded by a lubrication device 117, configured to lubricate the metal product P with powder lubricants, such as calcium stearate, sodium stearate or suchlike. Powder lubricants are harmful to the environment and require the use of suction, purification and disposal systems, which make the drawing apparatus 110 expensive and complex and do not completely eliminate the risks of environmental contamination.

[0045] In addition, powder lubricants impose limits on temperature and, consequently, speed of advance of the metal product P. In fact, the strong friction between the surface of the metal product P and each die 118 causes high temperatures, which are higher the higher speed of advance of the metal product P is. At too high temperatures, powder lubricants can char and detach from the metal product P. The lack of lubrication can lead to excessive vibrations and consequent breakages in the dies 118.

[0046] To facilitate the adhesion of the powder lubricants to the surface of the metal product P, the drawing unit 116 is preceded by a phosphating line 115, configured to phosphate the surface of the metal product P. Phosphating requires that the surface of the treated metal product P be extremely clean, therefore the phosphating line 115 is preceded by a mechanical pickling device 112 and comprises a chemical pickling device 120 and a washing device 121 upstream of a phosphating device 122 configured to carry out the actual phosphating.

[0047] The chemical pickling device 120 is configured to clean the surface of the metal product P, for example with the use of a strong acid such as hydrochloric or sulfuric acid. Chemical pickling is expensive and involves safety and environmental risks, both during the process and also for the disposal of its waste products.

[0048] The washing device 121 is configured to wash the metal product P after the chemical pickling.

[0049] A similar washing device 121 can be provided downstream of the phosphating device 122 and be configured to wash the metal product P after phosphating.

[0050] The phosphating line 115 also comprises a pre-lubrication device 123, configured to treat the phosphated metal product P with lime (calcium carbonate), borax (sodium tetraborate pentahydrate) or similar substances, so as to prepare an external surface of the metal product P for the subsequent lubrication described above. This pre-lubrication treatment can give a base which improves the adhesion of the above mentioned powder lubricant. The phosphating line can also comprise a drying device 124 configured to dry the metal product P after this pre-lubrication treatment.

[0051] The drawing apparatus 110 can also provide at least one intermediate winding device 113 interposed between the phosphating line 115 and the drawing unit 116, configured to act as a “buffer” for the accumulation of the phosphated metal product P, so that it is possible to adjust the speed at which the metal product P is fed to the drawing unit 116.

[0052] A rolling apparatus 10 according to the present invention has a simpler and more compact structure than the drawing apparatus 110 according to the state of the art, as visible in fig. 2.

[0053] The rolling apparatus 10 is configured to work the metal product P, initially in the form of a wire rod or wire, to obtain a metal wire with smaller sizes.

[0054] The metal product P can be made of a material selected from a group comprising a high or low carbon content steel, titanium alloys, tungsten molybdenum alloys, nickel chromium alloys, cobalt molybdenum alloys, enriched titanium stainless steel, stainless steel with low or high chromium percentage.

[0055] For example, the metal product P can be made of a non-magnetic material for hot rolling (since characterized by high work hardening if worked cold), chosen in a group comprising nickel alloys type Inconel® 625 (Ni Cr Mo + Nb), titanium alloys type Grade 5 (Ti 6 Al 4V) or Grade 23 (Ti 64V ELI), cobalt alloys type F76 (Co Cr Mo) or F562 (Co Ni Cr Mo), Cr Co Ni alloy in equal parts.

[0056] At entry into the rolling apparatus 10 the metal product P can be in the form of a wire rod and have an initial thickness, or nominal diameter, comprised between approximately 5.5 mm and approximately 18 mm, or it can be a wire metal product P with an initial thickness, or nominal diameter, of between approximately 2 mm and approximately 10 mm. In addition, at the end of the rolling, that is, at exit from the rolling apparatus 10, the product thus obtained can be in the form of a metal wire which can have a final thickness, or nominal diameter, comprised between approximately 0.8 mm and approximately 11 mm. We must clarify that the initial and final thickness, or nominal diameter, sizes of the metal product should not be considered in any way limiting the present invention’s scope of application.

[0057] According to some embodiments, the metal product P can have a round, oval, square, rectangular, hexagonal, octagonal, half-round section, or similar or comparable shapes. In the case of a metal product P with a round section, the initial and final thicknesses are substantially equivalent to the diameter of the circular section.

[0058] The rolling apparatus 10 can comprise, in succession along a work axis X of the metal product P, a lubrication device 15 and a rolling unit 16.

[0059] The lubrication device 15 can be configured to atomize oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the surface of the metal product P. The oil used can be an oil, for example synthetic, with low viscosity grade. The water-oil emulsion can for example be a water-soluble graphite oil. The colloidal dispersion in water can for example be a colloidal dispersion of graphite in water. The atomized oil or emulsion or dispersion can perform the function of lubricant, for example to lubricate a subsequent rolling process.

[0060] The use of liquid lubricants (possibly atomized) is much less problematic in terms of environmental impact compared to the use of solid lubricants, and it does not require suction systems. In addition, liquid lubricants do not require phosphating to properly adhere to the surface of the metal product P. As a result, both phosphating as well as a previous chemical pickling can be avoided, therefore the rolling apparatus 10 is simpler, more compact and more economical than the drawing apparatus 110, the metal product P to be worked and the initial and final diameters being equal. Avoiding chemical pickling also allows to avoid the economic, environmental and safety costs associated with the use of strong acids.

[0061] The rolling apparatus 10 can comprise, immediately upstream of the lubrication device 15, a mechanical pickling device 12.

[0062] The mechanical pickling device 12 can be configured to mechanically remove any oxides present on the surface of the metal product P, for example by abrasion.

[0063] The lubrication device 15 can be located immediately downstream of the mechanical pickling device 12, so that the atomized oil, or emulsion, or dispersion can perform the additional function of protecting the pickled surface of the metal product P from moisture.

[0064] The rolling unit 16 comprises at least one rolling device, or cassette 18, configured to reduce the size of the section of the metal product P through a substantially radial compression of the metal product P, for example by means of one or more pairs of rotating rolls.

[0065] The rolling unit 16 can comprise a plurality of rolling cassettes 18. The rolling unit 16 preferably comprises between one and sixteen rolling cassettes 18.

[0066] The rolling unit 16 can comprise at least one drawing member 19, configured to keep the metal product P under tension and draw it through each rolling cassette 18. Preferably, the rolling unit 16 comprises a drawing member 19 downstream of each rolling cassette 18.

[0067] In some embodiments, the rolling unit 16 can comprise at least one other lubrication device 17, configured to atomize oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the surface of the metal product P. Other lubrication devices 17 can be provided at the entry of the rolling unit 16 and / or at half-way of the rolling unit 16 and / or at regular intervals along the rolling unit 16. In some embodiments, each rolling cassette 18 is preceded by a respective other lubrication device 17.

[0068] An exit winding device 14 can be provided at exit from the rolling unit 16 to collect the rolled metal product P.

[0069] The rolling apparatus 10 can also provide at least one intermediate winding device 13, for example two intermediate winding devices 13, interposed between the lubrication device 15 and the rolling unit 16, configured to function as a “buffer” for the accumulation of the phosphated metal product P, so that it is possible to adjust the speed at which the metal product P is fed to the rolling unit 16.

[0070] Some embodiments described here also concern a method for rolling a metal product P.

[0071] The method provides to make a metal product P available, for example in the form of a wire rod, with an initial thickness, or nominal diameter, comprised between approximately 5.5 mm and approximately 18 mm, or a wire metal product P with an initial thickness, or nominal diameter, of between approximately 2 mm and approximately 10 mm.

[0072] The method provides to roll the metal product P by making it advance, in a continuous manner, along the work axis X through the rolling unit 16, which reduces the sizes of the section of the metal product P through a substantially radial compression until it takes the form of a metal wire, for example having a final thickness, or nominal diameter, comprised between approximately 0.8 mm and approximately 11 mm.

[0073] The metal product P, which enters in the form of a wire rod or wire, is introduced into the rolling unit 16, where the drawing members 19 draw it through the at least one rolling cassette 18.

[0074] The rolling can provide a plurality of successive rolling passes, corresponding to the subsequent passage of the metal product P through the plurality of rolling cassettes 18.

[0075] Before rolling, the metal product P can be pickled with a mechanical pickling device 12, which mechanically removes any oxides present on the surface of the metal product P.

[0076] According to one aspect of the method, after the mechanical pickling, before the metal product P is made to advance through the rolling unit 16, the metal product P is lubricated by making it pass through a lubrication device 15, which atomizes oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the pickled surface of the metal product P in order to protect and lubricate said surface.

[0077] This lubrication can take place immediately after the mechanical pickling, in order to guarantee the protection of the pickled surface.

[0078] Optionally, when it advances in the rolling unit 16, the metal product P can be further lubricated by one or more other lubrication devices 17, which atomize oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the surface of the metal product P.

[0079] Some embodiments provide to further lubricate the metal product P with a respective other lubrication device 17 before each rolling pass of the plurality of subsequent rolling passes.

[0080] We must clarify that the properties of the metal wires obtained through rolling are more favorable for typical subsequent working, such as stranding, compared to the properties of the metal wires obtained through drawing. In fact, with drawing, the decrease in the diameter of the metal product P occurs by subjecting the external surface of the metal product P to strong friction, causing a faster advance of the internal material of the metal product P relative to its surface, and an elongation of the material’s grains. As a result, the material of the external surface of the drawn metal product P is harder than the internal material, and the elongated grains make the metal product P very rigid, opposing the torsion required in the stranding processes.

[0081] Instead, with rolling, the decrease in the diameter of the metal product P occurs through a substantially radial compression of the material of the metal product P, so that the metal product’s granules are not deformed, unless only in a small part. The rolled metal product P is much more malleable, with the strength being equal, compared to a drawn metal product, favoring the stranding processes.

[0082] Fig. 3 shows the results of tensile tests carried out by the Applicant on two metal products P consisting of the same material and in the example initial form of wire rod with the same shape and diameter, one subjected to one, two, three, four or five drawing passes, the other subjected to one, two, three, four or five rolling passes with the rolling apparatus 10 described above. As can be seen, the yield strength of the drawn metal product P (long dash line) tends to remain constant or decrease after the fourth drawing pass, which indicates a worsening of malleability. On the other hand, in the face of reductions in the cross-section area of comparable magnitude (line with triangles and short dashes for the rolled metal product P, line with “+” shaped crosses, dash and two points for the drawn metal product P), the yield strength of the rolled metal product P (dotted line with “X” shaped crosses) is systematically higher or comparable to the yield strength of the drawn metal product and tends to grow linearly, guaranteeing the good malleability properties of the rolled metal product P are maintained.

[0083] Furthermore, the strong friction typical of drawing implies high exit temperatures from the die 118. As can be seen in fig. 4, the exit temperatures from the die 118 after a first, second, third, fourth or fifth drawing pass (solid line with circles) are of the order of approximately 145°C - 210°C for a speed of advance of the metal product P of 5 m / s. This makes it necessary to provide a cooling system to cool the drawing members 119. Instead, the exit temperatures from the rolling cassette 18 are of the order of 165°C - 195°C both at a speed of advance of the metal product P of 5 m / s (dashed line with squares), and also at a speed of advance of 6 m / s (dotted line with rhombi), so that the magnitude of the cooling of the drawing members 19 can be reduced, with considerable energy savings, and the speed of advance of the metal product P can be increased, achieving greater productivity.

[0084] It is clear that modifications and / or additions of parts may be made to the rolling apparatus 10 and to the method as described heretofore, without thereby 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 some specific examples, a person of skill in the art will be able to achieve other equivalent forms of rolling apparatus and corresponding method, having the characteristics as set forth in the claims and hence all coming within the field of protection.

[0085] 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. Rolling apparatus (10) for rolling a metal product (P), in the form of wire rod or wire, comprising a rolling unit (16) with at least one rolling cassette (18) configured to reduce the sizes of the section of said metal product (P) through a substantially radial compression, characterized in that it comprises a lubrication device (15) configured to atomize oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the surface of the metal product (P).

2. Rolling apparatus (10) as in claim 1, characterized in that it comprises, immediately upstream of said lubrication device (15), a mechanical pickling device (12), configured to mechanically remove the oxides present on the surface of said metal product (P), said oil or water-oil emulsion or colloidal dispersion in water having the additional function of protecting the pickled surface of said metal product (P) from moisture.

3. Rolling apparatus (10) as in any claim hereinbefore, characterized in that said rolling unit (16) comprises at least one other lubrication device (17), configured to atomize oil, or a water-oil emulsion, or a colloidal dispersion in water, onto the surface of said metal product (P).

4. Rolling apparatus (10) as in any claim hereinbefore, characterized in that said rolling unit (16) comprises between one and sixteen rolling cassettes (18).

5. Rolling apparatus (10) as in claim 4, characterized in that said rolling unit (16) comprises a plurality of rolling cassettes (18), each preceded by a respective other lubrication device (17).

6. Method for rolling a metal product (P) comprising:- making the metal product (P) available in the form of wire rod or wire;- lubricating the surface of said metal product (P) by atomizing oil, a water-oil emulsion or a colloidal dispersion in water, as it passes through a lubrication device (15);- rolling said metal product (P) by making it advance continuously through a rolling unit (16), which reduces the sizes of the section of said metal product (P) through a substantially radial compression, until it takes the form of a metal wire.

7. Method as in claim 6, characterized in that immediately before said lubrication it comprises pickling, with a mechanical pickling device (12), for the mechanical removal of the oxides present on the surface of said metal product (P).

8. Method as in claim 6 or 7, characterized in that it provides to further lubricate said metal product (P), with a respective other lubrication device (17), before each subsequent rolling pass corresponding to the subsequent passage of the metal product (P) through a plurality of rolling cassettes (18) of said rolling unit (16).

9. Method as in claim 6, 7 or 8, characterized in that said metal product (P) which is initially made available can be in the form of wire rod with an initial thickness, or nominal diameter, comprised between approximately 5.5 mm and approximately 18 mm, or it can be in the form of wire with an initial thickness, or nominal diameter, of between approximately 2 mm and approximately 10 mm, and, after rolling, said metal wire has a final thickness comprised between approximately 0.8 mm and approximately 11 mm.

10. Method as in any claim from 6 to 9, characterized in that said metal product (P) is made of a material chosen from a group comprising a high or low carbon content steel, titanium alloys, tungsten molybdenum alloys, nickel chromium alloys, cobalt molybdenum alloys, enriched titanium stainless steel, stainless steel with low or high chromium percentage.

11. Method as in any claim from 6 to 10, characterized in that said metal product (P) is made of a material chosen from a group comprising nickel alloys type Inconel® 625 (Ni Cr Mo + Nb), titanium alloys type Grade 5 (Ti 6 Al 4V) or Grade 23 (Ti 6 4V ELI), cobalt alloys type F76 (Co Cr Mo) or F562 (Co Ni Cr Mo), Cr Co Ni alloy in equal parts.

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