FIELD OF THE INVENTION

The present invention concerns an apparatus and a corresponding method for rolling wire rod to obtain a metal wire, for example usable in the aeronautical, medical, automotive, building, industrial, agriculture and livestock fields, in small metal parts, fences or other.

The present invention is applied mainly, although not exclusively, in post treatment processes of metal material essentially coming from hot rolling processes, to obtain particular mechanical properties of resistance and workability, depending on the specific intended use.

BACKGROUND OF THE INVENTION

It is known that long products such as wire rod, which are obtained from hot rolling processes downstream of continuous casting, are often used in the subsequent supply chain as starting products to obtain final products with desired characteristics of size and mechanical properties.

For example, rolling apparatuses or drawing apparatuses are known which use, as the metal product at entry, wire rod wound in coils and disposed on suitable feed reels, to obtain a final product having a different and desired size and section.

With particular reference to rolling apparatuses, these comprise a plurality of rolling units, each of which is provided with at least one pair of rolling rollers, or rings.

The rollers are reciprocally disposed so as to define a passage channel through which, during use, the metal product being worked is made to pass.

The passage channel between one work unit and the next progressively decreases until it reaches the final thickness/size to be conferred on the metal product, which will have the shape of a metal wire at the end of the process. Currently, these post-treatments of the wire rod obtained from previous hot rolling steps are mainly carried out cold, with limited reductions in section, both overall and also for each pass, due both to the state of the material and also to the fact that an excessive number of passes would increase the work-hardening of the final product. Furthermore, during cold rolling, the metal product must be constantly lubricated with powdered lubricants that contaminate the environment. To partly reduce this environmental contamination, expensive suction, purification and disposal plants are used, which, however, not only affect the overall plant costs, but also do not completely solve the problem.

At the end of the process it is therefore necessary to lay the product obtained in suitable annealing furnaces to reduce its fragility. This step increases the production times and does not always allow to obtain a product with the desired mechanical properties.

Furthermore, currently, due to the type of process, it is very difficult, or even not practicable, to roll wire rod made of steel with a high content of carbon or cobalt, titanium and its alloys, superalloys based on work-hardened nickel, superalloys based on work-hardened cobalt and other materials also obtained from the sintering of powders, to obtain respective metal wire. In fact, the product could be subjected to cracks during working or phenomena of fragile breakage.

Rolling apparatuses that work hot are also known, such as the one described in US2004/016478 Al.

There is therefore a need to perfect an apparatus and method for rolling wire rod which can overcome at least one of the disadvantages of the state of the art.

In particular, one purpose of the present invention is to provide a rolling apparatus which, starting from wire rod made of steel with a high content of carbon or cobalt, titanium and its alloys, superalloys based on work-hardened nickel or based on work-hardened cobalt, and other materials also obtained from the sintering of powders, and having a nominal diameter comprised between about 3mm and about 8mm, is able to make metal wire having a nominal diameter comprised between about 0.5mm and about 1.5mm, eliminating the problem of work-hardening of the material.

Another purpose of the present invention is to provide such an apparatus which does not require the presence of an annealing furnace at the end of the line.

Another purpose is to perfect a method for rolling wire rod which is able to achieve a significant reduction in thickness even on materials which typically have problems of work-hardening. Another purpose is to provide an apparatus and a corresponding method for rolling wire rod to produce metal wire which require a low energy supply, which do not release contaminants into the environment and which are therefore environmentally sustainable.

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.

SUMMARY OF THE INVENTION

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.

In accordance with the above purposes, an apparatus for rolling a metal product, initially in the form of wire rod with an initial thickness comprised between 3mm and 8mm, to produce a metal wire with a final thickness comprised between 0.5mm and 1.5mm, comprises a plurality of rolling units disposed aligned along a work axis of the metal product as above.

According to one aspect, the apparatus comprises a main heating furnace disposed upstream of a first of the rolling units and configured to operate with a main power at a main frequency, and a plurality of secondary heating units alternating with the rolling units along the work axis and configured to operate with a secondary power at a secondary frequency in order to take/retum the metal product to a suitable work temperature. The main power is greater than the secondary power and the main frequency is greater than or equal to the secondary frequency.

In accordance with some embodiments, there is provided a method for rolling a metal product which provides to make the metal product available in the form of wire rod having an initial thickness comprised between about 3mm and about 8mm.

The method also provides to continuously and sequentially feed the metal product through the plurality of rolling units disposed aligned along a work axis of the metal product which carry out a progressive reduction in the thickness of the metal product until it is in the form of a metal wire having a final thickness comprised between about 0.5mm and about 1.5mm. According to one aspect, before the metal product is fed through a first of the rolling units, the metal product is made to pass through a main heating furnace which takes the metal product from an ambient temperature to a suitable work temperature, operating with a main power at a main frequency.

Furthermore, when it is fed between one rolling unit and the next, the metal product is made to pass through secondary heating units which keep the metal product at the optimum work temperature, operating with a secondary power at a secondary frequency. The main power is greater than the secondary power and the main frequency is greater than or equal to the secondary frequency.

BRIEF DESCRIPTION OF THE DRAWINGS 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:

- fig. 1 is a schematic lateral view of a rolling apparatus in accordance with some embodiments described here;

- fig. 2 is a top view of fig. 1 ;

- fig. 3 is a schematic front view of two pairs of rollers disposed on orthogonal planes;

- fig. 4 shows a perspective view of the rolling units of the rolling apparatus with which a cooling circuit is associated.

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.

DESCRIPTION OF SOME EMBODIMENTS We will now refer in detail to the possible embodiments of the invention, of which one or more examples are shown in the attached drawings, by way of a non-limiting illustration. The phraseology and terminology used here are also for the purposes of providing non-limiting examples.

A rolling apparatus 10, in accordance with the present invention, is configured to roll a metal product P in the form of wire rod in order to obtain a metal wire having a smaller thickness and certain mechanical characteristics.

Here and hereafter in the description and claims, with the term metal product P we mean the product being worked, which is initially in the form of wire rod and at the end of the process implemented with the rolling apparatus 10 is in the form of a metal wire.

The metal product P is made of a material selected from a group comprising titanium and its alloys, a sintered cobalt-based material and its alloys, a stainless steel enriched with high percentages of chromium, a titanium-enriched stainless steel, a steel with high or low carbon content, nickel based alloys, tungsten.

The metal product P can be made with magnetic or non-magnetic materials.

By way of example, the materials considered can be a material obtained from the sintering of powders (C-Cr-Mo-W-Co-V), titanium and a titanium alloy, a titanium Gr 21 superalloy (Mo-Nb-Mo-Al), a hardened nickel-based superalloy (Co-Cr-Mo-Nb), a hardened cobalt-based superalloy (Ni-Cr-W), and others.

The metal product P, in the form of wire rod, has an initial thickness Si comprised between about 3mm and about 8mm and, in the form of metal wire, has a final thickness Sf comprised between about 0.5mm and about 1.5mm. It should be noted that the initial and final thickness sizes of the metal product should in no way be considered as limiting the applicability of the present invention.

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 thickness Si, Sf is substantially equivalent to the diameter of the circular section.

According to some embodiments, the rolling apparatus 10 comprises a plurality of rolling units 11, each of which is provided with a rolling device 12 having at least one pair of rollers 13.

The rolling units 11 are disposed aligned along a work axis X of the metal product P. In the embodiment shown in figs. 1-2, there are four rolling units 11. However, configurations of the apparatus with a greater or lesser number of rolling units 11 are not excluded. The number of rolling units 11 is in any case smaller than that of traditional cold plants, with the same total reduction ratio of the metal product P between entry and exit.

The configuration with four rolling units 11 is advantageous because the rolling apparatus 10 is extremely compact, with an in-line length of less than 4m, and rolling leads, overall, to a variation in thickness of the metal product P with over 99% reduction.

It should be noted that the rolling apparatus 10 can in any case generally be configured according to the type of material that the metal product P consists of, by varying the reduction of the rolling units and therefore the number of passes to perform the entire rolling.

In the embodiment described here, each rolling device 12 comprises four pairs of rollers 13 disposed alternating on two planes, each plane transverse with respect to the other.

In particular, a first and a third pair of rollers 13 lie on a vertical plane while a second and a fourth pair of rollers 13 lie on a horizontal plane, substantially orthogonal to the vertical plane.

The pairs of rollers 13 are disposed in sequence with vertical-horizontal alternation.

In possible embodiments, the lying planes of the pairs of rollers 13 can be disposed reciprocally inclined by an angle other than 90°.

The pairs of rollers 13 define between them a passage channel 14 (fig. 3) with a decreasing gap along the work axis X and inside which the metal product P pushed/drawn by the rollers 13 slides.

The passage channel 14 is substantially horizontal.

In particular, each rolling device 12 allows to obtain a determinate reduction pitch R.

The reduction pitch R is defined by the ratio between the cross-sectional area of the metal product P at entry and the cross-sectional area of the metal product P at exit from the rolling device 12.

The reduction pitch R is also defined by the ratio between the speed of the metal product P at entry and the speed of the metal product P at exit from the rolling device 12.

Each rolling device 12 is characterized by a percentage reduction pitch R preferably comprised between 58% and 75%, more in particular between about 60% and about 68%. The overall reduction, considered between machine entry and exit, can in any case even reach about 99%.

According to some embodiments, the reduction pitch R of the first rolling device 12 is greater than that of the subsequent ones.

In a possible embodiment, the reduction pitches R of the rolling devices 12 other than the first are practically equal to each other.

According to some embodiments, each rolling device 12 comprises a single drive member 15 connected to the pairs of rollers 13 in a per se known manner, in order to make them rotate. Each pair of rollers 13 is made to rotate with a different speed in order to make the rolling fluid, as a consequence of the elongation of the metal product P due to the reduction in section.

Each drive member 15 is electronically managed in order to drive the rollers 13 in such a way as to determine a controlled slipping component between the rollers 13 and the metal product P being fed. By way of example, each drive member 15 can comprise a direct current motor and transmission means connected to the motor and to the shaft on which the rollers 13 are keyed.

With reference to fig. 4, the rolling apparatus 10 comprises a cooling system 20 to cool the mechanical parts of the rolling units 11. The mechanical parts can comprise at least the supporting blocks of the rollers 13 and any other components which may undergo undue heating caused by the passage of the hot metal product P through the rolling unit 11.

The cooling system 20 is a closed circuit, so there is no direct contact between the refrigerant fluid and the metal product P.

The cooling system 20 comprises delivery 20a and return lines 20b and a heat exchanger 20c. Inside the delivery and return lines 20a, 20b a refrigerant liquid of a type known per se can flow.

Advantageously, the presence of the cooling system 20 allows to work without process interruptions which, in the state of the art, are instead caused, among other factors, by the overheating of some mechanical components.

The rolling apparatus 10 comprises a main heating furnace 16 disposed upstream of the first rolling unit 11 and a plurality of secondary heating units 17 alternating with the rolling units 11 along the work axis X and through which the metal product P being worked passes in order to be taken, or returned, to a suitable work temperature Tw.

The presence of the main heating furnace 16 and of the secondary heating units 17 allows to obtain greater reduction pitches R, because when the material that the metal product P consists of is at the work temperature Tw, it requires less energy to be deformed.

Furthermore, by heating the metal product P, powdered lubricants are not required, which tend to contaminate the work environment.

The main heating furnace 16 is configured to take the metal product P from ambient temperature Ta to a work temperature Tw for the first time. According to some embodiments, the main heating furnace 16 and the secondary heating units 17 are of the induction type.

The main furnace 16 and the secondary heating units 17 preferably operate at very high frequency and low power, and are of the adjustable temperature type so that they can be used for many materials and applications. However, it is not excluded that the main furnace 16 and/or the secondary heating units 17 can also operate at low frequency.

By very high frequency we mean a range in the order of about 400-500 kHz. These frequencies are suitable for non-magnetic materials such as titanium, hardened nickel, stainless steel, hardened cobalt and others. By low frequency we mean a range in the order of about 6-10 kHz. These frequencies are suitable for magnetic materials such as steel with low and high carbon content.

According to some embodiments, the operating frequency of the main furnace 16, or main frequency FI, and of the secondary heating units 17, or secondary frequency F2, can be fixed or adjustable.

The adjustment of the frequency FI, F2 can be based on the type of material that the metal product P consists of, for example magnetic or non-magnetic.

The power of the main heating furnace 16, or main power PI, is greater than the power of the single secondary heating units 17, or secondary powers P2. For example, the power of the main heating furnace 16 is approximately 5-8 times the power of a single secondary heating unit 17.

For example, in the case of induction technology, the main heating furnace 16 can have a main power PI of about 75kW and the individual secondary heating units 17 a secondary power P2 of about lOkW.

In accordance with another example, the main heating furnace 16 can have a main power PI of about 50kW and the single secondary heating units 17 can have a secondary power P2 of about lOkW. With regards to the work frequency, the main heating furnace 16 can work at a main frequency FI of about 400- 500kHz and the single secondary heating units 17 can work with secondary frequencies of about 400kHz.

According to possible embodiments, in correspondence with the entry and/or exit of the main heating furnace 16 and of the secondary heating units 17, the rolling apparatus 10 comprises temperature detection devices configured to detect the temperature of the metal product P.

The rolling apparatus 10 also comprises a central unit which receives the temperature data from the temperature detection devices and manages the power and/or frequency of the main heating furnace 16 and of the secondary heating units 17, in order to maintain a constant temperature of the rolled product P regardless of its varying thickness. In fact, a reduction in the thickness of the metal product P corresponds to a different distribution of the thermal load to be imposed in order to keep its temperature constant.

The rolling is advantageously carried out at temperatures which are kept almost constant.

In a hot plastic deformation, the temperature and state of stress imposed on the metal are such as to lead to a rapid recrystallization during the process (dynamic recrystallization) in order to prevent the establishment of a state of hardening of the metal. Recrystallization replaces the crystal structure with deformed grains with a new series of grains free from stresses and distortions.

On the basis of the materials to be rolled, the treatments to be carried out and the properties to be obtained, the work temperature Tw chosen is in a range comprised between about 700°C-800°C up to about 1200°C.

According to some embodiments, the rollers 13 are made of special materials with low thermal conductivity so as to reduce as much as possible the heat released by the metal product P during working.

By low thermal conductivity we mean a range comprised between about 1 W nr’ K ^-1 and about 2 W-m ^_1 K ^_1 . For example, the rollers 13 can be made with sintered materials, for example sintered ceramic alloys with low thermal conductivity.

According to a preferential embodiment, the rollers 13 are made of yttrium- stabilized zirconium oxide, which has a thermal conductivity of about 2 W rn^ K ¹ , integral or in the form of a compound through matrix and coating.

Upstream of the main heating furnace 17, the apparatus 10 comprises one or more reels 18 on which the metal products P in the form of wire rod are wound into coils. The reels can be of different types on the basis of the weight of the coils to be produced and/or the temperatures at exit from the rolling process.

Downstream of the last rolling unit 11 there is a winding device 19 configured to receive the metal wire produced and wind it into coils.

According to possible embodiments, the rolling of the metal product P can occur in a controlled atmosphere with noble gases, for example Argon or Nitrogen.

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

The method provides to make the metal product P available in the form of wire rod having an initial thickness Si comprised between about 3mm and about 8mm.

The method also provides to continuously feed the metal product P through the plurality of rolling units 11 disposed aligned along the work axis X of the metal product P, which carry out a reduction in the thickness of the metal product P until it is in the form of a metal wire having a final thickness Sf comprised between about 0.5mm and about 1 5mm.

According to one aspect of the method as above, before the metal product P is fed through the first rolling unit 11 , the metal product P is made to pass through a main heating furnace 16 which takes the metal product P from the ambient temperature Ta to a suitable work temperature Tw. Furthermore, when it is fed between one rolling unit 11 and the next, the metal product P is made to pass through the secondary heating units 16 which take the metal product P back to the work temperature Tw.

According to some embodiments, the metal product P is initially in the form of wire rod and is wound on one or more coils disposed on respective reels 18. The metal product P, which enters in the form of wire rod, is unwound, straightened and introduced, for example by means of suitable drawing rollers, into the main heating furnace 16.

The metal product P passes through the rolling units 11 in a continuous manner, inside each of which the thickness of the metal product P is decreased by a percentage reduction pitch R comprised between 58% and 75%, more in particular comprised between about 60% and about 68%.

According to one possible embodiment, the path through which the metal product P passes inside the main heating furnace 16 and the secondary heating units 17 is straight and the pull control, determining the sliding value, is controlled with an electronic system in such a way as to increase the residence time between the rolling units 11, while maintaining the feeding speed unchanged. For example, it is possible to provide that the metal product follows a zigzag shaped path.

According to possible embodiments, the rolling apparatus 10 also comprises an automatic device for unloading the coil of rolled product P. The coil is extracted from the rolling apparatus 10 and cooled in still air to complete the metallurgical transformation (stress relieving). The cooling of the extracted coil occurs while the apparatus continues to work on the next metal product P.

It is clear that modifications and/or additions of parts or steps may be made to the apparatus and method for rolling wire rods as described heretofore, without departing from the field and scope of the present invention as defined by the claims.

In the following claims, the sole purpose of the references in brackets is to facilitate reading and they must not be considered as restrictive factors with regard to the field of protection claimed in the specific claims.