Heating furnaces for plants for the production of rolled products

Abstract

A heating furnace (10) for a plant (100) for the production of rolled products (P), said heating furnace (10) comprising a tunnel (11) and a plurality of heating means (20), said heating means (20) comprising a plurality of electrically driven heating elements (23, 24, 25).

Description

[Technical Field]

[0001] The present invention relates to a furnace for a plant for the production of rolled steel products, both in the form of flat plates or strips and in long lengths such as bars, blooms, beam blanks, angles or wire rods. The furnace can be used both in plants where the rolled finished product is obtained continuously and in plants where the rolled finished product is obtained discontinuously, for example starting from a product cast in stages before rolling. The present invention also relates to a plant for the production of rolled products, including the furnace. [Background technology]

[0002] It is known that rolling plants for producing flat or long rolled products have a rolling line with at least one furnace associated with one or more rolling units defining a train of rolling mills, these furnaces generally being located at least upstream of the first rolling unit, also called the roughing mill.

[0003] In endless rolling plants, unlike rolling plants separated from casting, there is a caster upstream of the rolling line that continuously feeds semi-finished steel products downstream. The products are usually cast vertically or semi-vertically and then moved to a horizontal position by means of curved segments and straightening elements. However, there are also vertical casters, where the products at the outlet are turned over once completed for the subsequent rolling process.

[0004] In other known types of rolling plants, the product may be pre-cut to size so that after casting it can be fed intermittently, hot or cold, using suitable equipment or transfer devices to a rolling line that is not directly connected to the caster.

[0005] An example of an endless rolling plant is described in EP 2569104 filed in the name of the applicant. Known endless rolling plants can carry out the rolling process in three ways, depending on whether they are designed for flat or long products:

[0006] That is, in the continuous or endless mode, where the uncut cast product is continuously rolled and, after rolling, it is cut and wound to obtain rolls (in the case of flat products or long, thin products such as wire) or it is cut and then stored / packaged (in the case of long products). A semi-endless mode in which, between the caster and the rolling mill, the cast product is subjected to intermediate cuts so that the rolled product has a rolled length corresponding to an integral multiple, typically 2 to 10 times the length of a single finished rolled product, and the rolled product is then cut to size again before being coiled or stored. It is a discontinuous process, called "coil-to-coil" for flat products or "billet-to-billet" for long products (more commonly called batch), where the cast product is cut before being rolled to have a rolling length corresponding to the length of a single roll (coil-to-coil) or a single bar or coil (billet-to-billet).

[0007] On the other hand, in plants where the caster is separate from the rolling mill, the products to be rolled, such as slabs or billets, come from another plant or from an offline caster and are fed to a section upstream of the furnace. These plants typically operate in coil-to-coil or billet-to-billet mode, working on shorter, and therefore more manageable, products, which are usually coiled independently.

[0008] In other cases, especially in the area of long products, after initial heating these products are welded so that endless rolling can be carried out, and finally the rolled products are separated again based on the desired size or cut to size and then collected.

[0009] In these known plants, the furnace, whether endless or not, has a shape that allows it to define a tunnel, ranging between about 60 meters and about 150 meters, or even between 200 and 300 meters, inside which there are usually both conveying rollers that convey the product to be rolled towards the rolling mill train, and burners, usually powered by fossil fuels such as methane, to heat the product to be rolled.

[0010] In particular, furnaces are known that have an initial portion or section extending about one-third of the total length of the rolled product, in which a greater heating power is supplied to the rolled product to heat it up quickly, often to about 1150° C. to 1180° C. In the remaining portion of the furnace, also known as the maintenance portion or section, the heating power is reduced, but sufficient to maintain and equalize the temperature for subsequent rolling.

[0011] It is also known that in endless rolling plants, one or more heating installations are present between the roughing and finishing stands of a row.

[0012] In the case of endless and semi-endless rolling, the distance between the roughing mill section and the finishing mill section is in a compact arrangement, i.e., in such a way that the product leaving the roughing mill abuts on the finishing mill after a few meters. Thus, rolling occurs in the so-called "tandem" mode, where the half-rolled product is abutted between the head and tail of the roughing mill and the finishing mill simultaneously throughout almost the entire process.

[0013] In particular, due to the high transport speed of the semi-rolled product and the small distance between the roughing mill and the finishing mill, the transport time of the product is short, and as a result the heating device is usually an inductor which can supply high heating power in a very short time.

[0014] On the other hand, in the case of batch-to-batch rolling, the distance between the roughing mill section and the finishing mill section can reach 150 meters. In particular, a heated section known as a Heated Transfer Table (HTT) is usually installed between the two sections. The semi-rolled product leaving the roughing mill is completely contained within the HTT, and rolling in the finishing mill begins after the rolling associated with the roughing mill has finished.

[0015] Since the residence time on the heat transfer table and the transit time are longer than in endless and semi-endless rolling conditions, the heating of the semi-rolled product is carried out by fossil fuel burners with the generation of emissions.

[0016] Furthermore, known furnaces comprise, along the course of their longitudinal axis, both so-called "active" parts or sections in which heating elements, such as burners or possibly inductors, are provided to heat the product to be rolled, and so-called "passive" parts or sections, alternately arranged with the active parts and made of refractory material and devoid of heating elements, to ensure that accumulated heat is dispersed without the need for additional heat input. Typically, the passive parts are located in the last two-thirds of the length of the furnace, but may also be located in the last one-third.

[0017] One drawback of known furnaces is that the use of burners to heat the product to be rolled involves a significant consumption of methane or other fossil fuels, which increases production costs.

[0018] Another drawback is that the use of fossil fuels involves the emission of large amounts of carbon dioxide (CO2) and other exhaust gases, amounting to tens of thousands of tonnes per year, which must be appropriately addressed to minimize the impact on the atmosphere as much as possible, as well as high costs associated with "carbon taxes" that in some cases can have a significant impact on company budgets.

[0019] Furthermore, heating furnaces with fossil fuel burners have low energy efficiency, as approximately 60% of the heating power is lost due to smoke generated in the tunnel and contact between the product being rolled and the transport rollers.

[0020] Among known documents is GB 420485, which describes a heating furnace for pipes, consisting of two longitudinal sections of comparable size, with a total length significantly shorter than conventional furnaces, and equipped with a heating and maintenance tunnel for producing rolled products. This furnace provides for the use of induction-type electric heating means and resistance-type electric heating elements in several sections of the furnace.

[0021] This type of furnace can be operated horizontally or inclined and can be filled with neutral or reducing gases lighter than air to obtain polished pipes at the outlet. Gas or other fuel-based heating methods can also be used in the furnace, and the temperatures reached inside are much lower than those achieved in heating and maintenance furnaces for the production of rolled products.

[0022] The known German patent application DE 19518144 A1 describes a heating furnace interposed between two successive rolling trains and having a longitudinal section with a length ratio of substantially 1:1. An electric heating means, in particular induction heating, is provided in the initial section of the rolling mill, while another type of heating means is provided downstream. The rolling mill is provided with a so-called passive section, i.e., an isolated area lined with refractory material, which maintains and equalizes the heat of the passing products but does not add additional heat.

[0023] In the known German patent application DE 10 2011 004 245 A1, a heating furnace for metal products is described in which there is an induction-type electric heating means corresponding to the inlet longitudinal section and in the downstream longitudinal section there is a heating means which is much longer than the inlet one and which uses gas or other fossil fuels to reach temperatures of more than 1000°C.

[0024] US Patent Application Publication No. 2015 / 321232 describes an apparatus for rolling aluminum sheet, using rollers to roll the hot aluminum sheet. The apparatus includes gas, other fossil fuel, or electrical induction or resistance heating means. The temperatures reached in this apparatus are much lower than those reached in the furnaces used to produce the rolled products mentioned above.

[0025] Therefore, there is a need for a complete furnace for a plant for producing rolled products, which overcomes at least one of the shortcomings of the prior art.

[0026] To achieve this, it is necessary to solve the technical problem of heating the rolled product in a heating furnace efficiently and economically without using fossil fuels, in particular methane.

[0027] It is an object of the present invention to provide a furnace for a plant for the manufacture of rolled products that is highly efficient and eliminates the consumption of fossil fuels and the associated pollutant emissions.

[0028] Another object of the present invention is to provide a furnace for a plant for the production of rolled products that is capable of at least duplicating the heating characteristics of furnaces in the prior art.

[0029] Another object of the invention is to provide a furnace for a plant for the production of rolled products which allows clear savings in terms of energy and costs.

[0030] Applicant has conceived, tested and embodied the present invention to overcome the shortcomings of the prior art and to attain these and other objects and advantages. Summary of the Invention

[0031] The invention is set forth and characterized in the independent claims, while the dependent claims describe other features of the invention or variations of the main inventive idea.

[0032] In order to meet the above-mentioned objectives, to solve the above-mentioned technical problems in a novel and original way, and to obtain clear advantages over the prior art, the present invention relates to a heating furnace for a plant for the production of rolled products, said heating furnace comprising a tunnel and a plurality of heating means.

[0033] According to one aspect of the invention, the heating means comprises an induction electric heating element and a resistance electric heating element, the induction electric heating element being arranged at least in the entrance zone of the tunnel, and the second resistance electric heating element being arranged in the tunnel downstream of the induction electric heating element in the entrance zone. In particular, the induction electric heating element arranged in the entrance zone is adapted to bring the temperature of the rolled product to a value of at least 1100°C, which also serves the purpose of keeping the alloying elements in solution.

[0034] By doing this, at least the benefits of eliminating both the consumption of fossil fuels such as methane and the associated production of carbon dioxide and other combustion gases can be achieved.

[0035] According to another aspect of the invention, the heating furnace includes at least a first section corresponding to the inlet end thereof and having at least a first plurality of the induction heating elements, and a second section located downstream of the first section in the direction of advancement of the product being rolled and having a first plurality of the resistance heating elements.

[0036] According to a preferred embodiment, the first plurality of induction heating elements arranged in the first zone are of the longitudinal flow type.

[0037] According to another aspect of the invention, the pre-rolling temperature in the tunnel is comprised between about 1250° C. and about 1300° C. Furthermore, the first section has a first length such that the first plurality of the induction heating elements use a predetermined nominal power comprised between about 10 megawatts and about 60 megawatts to bring the product to the pre-rolling temperature.

[0038] In particular, each induction heating element is preferably capable of delivering approximately 6 megawatts of power.

[0039] According to another aspect of the invention, the furnace has a total length preferably between about 20 meters and about 300 meters, more preferably between about 40 meters and about 180 meters, and the first section has a first length occupying at least 1 / 5 of the total length.

[0040] According to another aspect of the invention, the second section has a second length greater than the first length, such that the first plurality of resistive heating elements are configured to provide a second predetermined power comprised between about 2 megawatts and about 16 megawatts to maintain and uniformly maintain a maintenance temperature of the rolled product substantially equal to or slightly lower than the pre-rolling temperature.

[0041] According to another aspect of the invention, the second section includes at least one movable part that is movable between a closed position and an open position to allow the product to be rolled to be introduced into the tunnel from another product line.

[0042] According to another aspect of the invention, the second zone has a length and heat capacity that is sized and optimized to perform the function of acting as a buffer for the product to be rolled during the step of carrying out replacement or maintenance operations on the rolling cylinders. In other words, the resistive heating elements are configured to provide a heat input that allows the rolled product to be stopped for the time required to carry out said operations on the cylinders, while in each case maintaining the pre-rolling temperature disclosed above.

[0043] According to another aspect of the invention, the heating furnace further comprises a third section located downstream of the second section in the advance direction of the product to be rolled and containing at least a second plurality of the induction heating elements, the third section having a third length such that the second plurality of the induction heating elements are configured to bring the product to the maximum pre-rolling temperature using a third predetermined power comprised between about 6 megawatts and about 30 megawatts as a function of the mode used (endless or coil-to-coil).

[0044] In particular, the third zone is advantageous and useful for achieving the optimized thermal target of endless rolling, which requires the average temperature of the rolled product to reach 1180°C ± 30°C, corresponding to a surface temperature of approximately 1250°C ± 30°C.

[0045] According to another aspect of the invention, the rolling mill may further comprise a fourth zone located downstream of the third zone in the advance direction of the rolled product and including at least a second plurality of the resistive heating elements, in particular the fourth zone having a fourth length such that the second plurality of the resistive heating elements are configured to maintain and homogenize the temperature reached in the third zone for the rolled product using a fourth predetermined heating power comprised between about 2 megawatts and about 8 megawatts.

[0046] The tunnel includes a plurality of continuous interior insulating panels capable of withstanding pre-rolling temperatures.

[0047] According to another aspect of the invention, the resistive heating elements are arranged alongside or adjacent to each other so as to affect at least half of the internal cross section of the tunnel.

[0048] Furthermore, the resistive heating elements are preferably positioned above and / or below the product to be rolled, or on both sides of the product to be rolled, thereby interposing them between the inner surface of the tunnel and the product to be rolled.

[0049] According to another aspect of the invention, the resistive heating elements are arranged perpendicular to the direction of advancement of the product being rolled.

[0050] According to another aspect of the invention, a plant for the manufacture of rolled products comprises at least one rolling mill train and a heating furnace as described above, arranged upstream of said rolling mill train along the rolling line.

[0051] According to another aspect of the invention, the plant includes a caster upstream of the heating furnace which continuously supplies the product to be rolled, and the plant is capable of carrying out the rolling process at least continuously, i.e. in an endless mode.

[0052] According to another aspect of the invention, the plant includes a pendulum shear located along the rolling line between the caster and the heating furnace for cutting the continuously fed rolled product to a predetermined size, and the plant can perform the rolling process in a semi-endless mode, a coil-to-coil mode, or a billet-to-billet mode.

[0053] According to another aspect of the invention, a feeding device is arranged along the rolling line upstream of the heating furnace for cold feeding the product to be rolled, the rolling mill train includes a plurality of roughing mills arranged near the heating furnace and a plurality of finishing mills arranged downstream of the roughing mills, and the plant includes other heating furnaces as described above arranged between the roughing mills and the finishing mills. These and other aspects, features and advantages of the present invention will become apparent from the following description of some embodiments, given by way of non-limiting example with reference to the accompanying drawings. [Brief explanation of the drawings]

[0054] [Figure 1] 1 is a schematic diagram of a plant for the manufacture of rolled products including a heating furnace according to the invention; [Figure 2] 2 is a schematic diagram of a plant for the manufacture of rolled products according to another embodiment, including the heating furnace of FIG. 1; [Figure 3] 3 is a schematic view of a plant for the manufacture of rolled products according to another embodiment, in which the heating furnace according to the invention is shown in more detail. [Figure 4] 1 is a schematic perspective view of a heating furnace according to the present invention, the heating furnace corresponding to a first operating zone and a third operating zone. [Figure 5] FIG. 10 is a schematic perspective view of a heating furnace according to another embodiment of the present invention, the heating furnace corresponding to the first operating zone and the third zone. [Figure 6] 3 is a schematic cross-sectional view of the furnace according to the present invention, corresponding to a second operating zone. FIG. [Figure 7] 4 is a schematic cross-sectional view of a heating furnace according to another embodiment of the present invention, the heating furnace corresponding to the second operating zone. FIG. [Figure 8] 4 is a schematic cross-sectional view of a heating furnace according to another embodiment of the present invention, the heating furnace corresponding to the second operating zone. FIG. [Figure 9] 1 is a schematic representation of a heating furnace according to the present invention; [Figure 10] FIG. 10 is a qualitative diagram showing the relationship between the heating power and the length of the heating furnace in FIG. [Figure 11] FIG. 10 is a qualitative diagram showing the relationship between the average pre-rolling temperature of the heating furnace in FIG. 9 and the length when coil-to-coil rolling or semi-endless rolling is performed. [Figure 12]FIG. 10 is a qualitative diagram showing the relationship between the surface temperature before rolling and the length of the heating furnace in FIG. 9 when coil-to-coil rolling or semi-endless rolling is performed. [Figure 13] FIG. 4 is a schematic representation of a heating furnace according to another embodiment of the present invention. [Figure 14] FIG. 14 is a qualitative diagram showing the relationship between the heating power and the length of the heating furnace in FIG. [Figure 15] FIG. 14 is a qualitative diagram showing the relationship between the average pre-rolling temperature of the heating furnace in FIG. 13 and the length when endless rolling is performed. [Figure 16] FIG. 14 is a qualitative diagram showing the relationship between the surface temperature before rolling and the length of the heating furnace in FIG. 13 when endless rolling is performed. DETAILED DESCRIPTION OF THE INVENTION

[0055] It must be made clear that the phraseology and terms used in this specification, as well as the symbols in the accompanying drawings, have the sole function of better illustrating and explaining the invention, the scope of protection of which is defined by the claims, and that their function is to provide a non-limiting example of the invention itself.

[0056] For ease of understanding, the same reference numerals have been used wherever possible to identify identical common elements in the drawings, it being understood that elements and features of one embodiment may be conveniently combined or incorporated in other embodiments without further description.

[0057] With reference to FIG. 1, a furnace 10 according to the invention is suitable for use in a plant 100 for the production of flat or long finished rolled products as defined above.

[0058] In the embodiment shown in FIG. 1, the plant 100 is an endless rolling plant, which is configured to carry out the rolling process according to several known modes, including continuous mode, also called endless mode, semi-endless mode, and discontinuous mode, also called coil-to-coil for flat products and billet-to-billet for long products.

[0059] The plant 100 for rolled products comprises a rolling line L upstream of which is arranged a caster 101 which continuously supplies rolled products P, for example slabs in the case of flat products or billets, blooms or beam blanks in the case of long products.

[0060] In particular, when semi-endless rolling or coil-to-coil / billet-to-billet rolling modes are used along the rolling line L, it is possible to sequentially arrange a pendulum shear 102 (see FIG. 1), a heating furnace 10, and a rolling mill train or unit 103 configured to cut the rolled product to size. At the terminal part of the rolling line L, there is a winding / unloading area 104 of known type, where the rolled product passes, for example, through a laminar flow cooler 110 before being wound / unloaded on a plate, and may also pass beforehand through an end area 105 with a rectangular element as shown in FIGS. 1 and 2 to be cut to size.

[0061] The hot rolling mill train 103 comprises a number of rolling mills of known type arranged in succession, each provided with a number of rollers adapted to roll the product to be rolled, and divided into roughing stands 106 arranged near the furnace 10 and finishing stands 107 arranged downstream of the roughing stands 106.

[0062] Moreover, according to another embodiment not shown, intermediate stands, substantially of known type and not shown, can also be provided between the roughing mill 106 and the finishing mill 107. The use of these intermediate stands is particularly advantageous when rolling long products, where there may be 20 or more stands, although when rolling flat products this number is often between 6 and 12.

[0063] Between the roughing mill 106 and the finishing mill 107 there may be a heating device 109, preferably of the induction type, to bring the partly rolled product back to the appropriate temperature, which tends to cool during the rolling process.

[0064] According to another embodiment, as shown in Figure 2, the plant 100 does not have a caster 101 and a pendulum shear 102, but comprises a providing device 112 for cold or hot providing of the product P to be rolled along the rolling line L, upstream of the heating furnace 10. In this case, the product to be rolled is in fact supplied discontinuously along the rolling line L, so that the plant 100 carries out the rolling process exclusively in semi-endless mode and / or coil-to-coil mode.

[0065] Furthermore, as shown in FIG. 3, the plant 100 may have another product line LP arranged parallel to the rolling line L, along which other rolled products P can be rolled.

[0066] The furnace 10 is adapted to define a tunnel 11 having an entry end 12 through which at least one rolled product P can be introduced and an exit end 13 opposite the entry end 12 and facing the rolling mill train 103. The length of the furnace 10 is preferably between about 20 m and about 300 m, and more preferably between about 40 m and about 180 m (see FIG. 3).

[0067] The structure of the furnace 10 is of substantially known type, in particular the tunnel 11 (see Figures 4 to 8) formed by a plurality of successive modules associated with one another, each of which may comprise, for example, an interior or exterior insulating panel 15 capable of withstanding high temperatures above about 1300°C, and a cooling panel 16 (see Figures 5 and 6) of substantially known type outside the insulating panel 15. Preferably, for flat products the tunnel 11 has a substantially rectangular internal cross section, while for long products its internal cross section is approximately square.

[0068] Within the tunnel 11 there are a number of conveying elements 17 defined, for example, by rollers, which are arranged so that the product P is rolled forward from the inlet end 12 towards the outlet end 13 .

[0069] Conveying elements 17 are preferably of the so-called "dry" type, i.e., they are not provided with internal cooling, and in particular they are made of a metallic superalloy, preferably consisting of about 40% to 50% nickel (Ni), about 25% to 35% cobalt (Co), and about 25% to 35% chromium (Cr). It should be understood that according to another embodiment of the invention, conveying elements 17 are conventional cooling rollers.

[0070] According to one aspect of the invention, the heating furnace 10 comprises a plurality of electrically driven heating means 20 arranged in the tunnel 11 for heating and / or maintaining the rolled product P at a predetermined pre-rolling temperature comprised between approximately 1250°C and 1300°C.

[0071] The heating means 20 comprises induction electric heating elements 23, 24 and resistance electric heating elements 25, 26, wherein the induction electric heating element 23 is located in the entrance area of the tunnel 11 and the resistance electric heating element 25 is located in the tunnel 11 downstream of the induction electric heating element 23.

[0072] In particular, an induction type electric heating element 23, which is positioned corresponding to the entrance end of the tunnel 11, is configured to bring the temperature of the rolled or rolled-like product to a value of at least 1100°C.

[0073] According to another embodiment of the present invention, the heating furnace 10 includes at least a first section 21 (see Figures 3, 9 and 13), or induction heating section, extending from the entrance end 12 over approximately 1 / 5 of the total length LC of the tunnel 11, and a second section 22, or active maintenance section, located downstream of the first section 21 in the direction of advancement of the rolled product P.

[0074] The first section 21 has a first length L1 and comprises a first plurality of induction-type electric heating elements 23 (see FIG. 10) configured to bring the rolled product P to a heating temperature using a first predetermined heating power P1 comprised between 6 megawatts and 48 megawatts. In one example, the first length L1 is about 10 meters.

[0075] Generally, the induction-type electric heating elements 23, 24 may use a longitudinal flow induction system, a transverse flow induction system, or a combination thereof, where the terms "longitudinal" and "transverse" are defined relative to the direction of advance of the rolled product P.

[0076] Advantageously, the first plurality of induction type electric heating elements 23, ie those arranged corresponding to the entrance end of the tunnel 11, are of the longitudinal flow type.

[0077] It should be noted that this longitudinal flow induction system mainly heats the outer parts of the rolled product, thus preparing it for subsequent maintenance / heating by means of resistance-type elements 25, 26, and this occurs for a sufficient time for the generated heat to be redistributed by conduction over the entire cross section of the product P.

[0078] In particular, in the case of a longitudinal flow induction system, the induction electric heating elements 23, 24 have multiple coils arranged around the rolled product P (see Figure 4), whereas in the case of a transverse flow induction system, the multiple coils are instead arranged across the rolled products (see Figure 5), i.e. above and below them.

[0079] For example, each induction heating element 23, 24 may provide approximately 6 megawatts of power.

[0080] The second section 22 has a second length L2 (see Figures 3, 9 and 13) and comprises a plurality of resistive electric heating elements 25, such as resistors or heating resistors, configured to actively provide a predetermined second heating power P2 comprised between 2 and 16 megawatts in order to maintain and equalize the temperature of the rolled product P at a maintenance temperature TM substantially equal to or slightly lower than the pre-rolling temperature TP (see Figure 10).

[0081] The length of the second section 22 is determined in an optimized manner to allow maintenance of the rolling mill train 103 without the need to interrupt the operation of the furnace 10. In other words, the heat provided by the resistance element 25 allows the furnace to act as a buffer when the production needs to be stopped during operations to replace or maintain the cylinders.

[0082] In the second section 22, the resistance-type element 25 actively provides heat to the rolled product P, heating it or maintaining it, so that it maintains a temperature suitable for subsequent rolling. For example, the maintenance temperature TM of the rolled product can be considered as an average temperature (see FIG. 11) or as a surface temperature (see FIG. 12), and is approximately 1150°C ± 20°C when considered as an average temperature, and approximately 1250°C ± 20°C when considered as a surface temperature. As an example, the second length L2 is comprised between approximately 70 meters and approximately 80 meters.

[0083] In particular, the resistive electric heating elements 25 are preferably made not of a ceramic alloy but of a specific metal alloy that can withstand the pre-rolling temperatures and the vibrations associated with transporting the rolled product P. Preferably, said metal alloy is a resisthom alloy (FeCrAl).

[0084] As can be seen from FIG. 10, the first power P1 provided to the first zone 21 by the inductive electric heating element 23 is greater than the second power P2 provided by the resistive electric heating element 25.

[0085] For example, the resistive electric heating elements 25, 26 are disposed on corresponding support panels 27 (see FIGS. 5 and 6), with each support panel 27 including a plurality of resistive electric heating elements 25, 26.

[0086] In particular, the resistive electric heating elements 25 , 26 are arranged alongside or adjacent to each other so as to affect at least half of the internal cross-sectional area of the tunnel 11 .

[0087] Preferably, the resistive electric heating elements 25, 26 are located on the upper inner wall, i.e. the ceiling, and on the sides of the tunnel 11, and are aligned substantially parallel to the direction of advance of the rolled product P (see Figure 6).

[0088] According to another embodiment, as shown in Figure 7, the resistive electric heating elements 25, 26 are located on the bottom wall, i.e. on the bottom surface and / or on the side surfaces of the tunnel 11. In this case, each resistive electric heating element 25, 26 located below the rolled product P can be protected by a metal encapsulation, for example by means of a radiant tube, in order to prevent short circuits between adjacent resistive electric heating elements 25, 26 due to the falling of scale on the rolled product P transported by the transport element 17.

[0089] As shown in Figure 8, the resistive electric heating elements 25, 26 can be positioned above or below the rolled product P and can be oriented in a direction different from that shown in Figure 6, i.e., so as to be substantially perpendicular to the direction of advancement of the rolled product P.

[0090] Generally, as shown in Figures 6, 7 and 8, the resistive electric heating elements 25, 26 are interposed substantially between the inner surface of the tunnel 11 and the product P to be rolled.

[0091] Furthermore, thanks to the presence of the resistive electric heating elements 25, 26 along the second section 22, there are no so-called "passive" parts, which are typically found in prior art furnaces and are therefore limited to maintaining the temperature of the material as they are made of refractory material.

[0092] By way of example, there may be between 2 and 5 heating means 20 per square meter in the tunnel 11 .

[0093] The second section 22 advantageously has a movable part 22a that can be moved between a closed position and an open position that allows the introduction of a plurality of rolled products P coming from other product lines LP into the tunnel 11 (see FIG. 2). Preferably, the movable part 22a corresponds to an end of the second section 22.

[0094] As an example, the movable portion 22a has a length comprised between about 25 meters and about 30 meters.

[0095] The arrangement of the resistive electric heating element 25 in the movable part 22a is advantageous in that the movement of the movable part 22a is considerably easier than in the prior art.

[0096] According to another embodiment, as shown in Figure 13, the heating furnace 10 also includes a third section 28, located downstream of the second section 22 in the direction of advancement of the rolled product P, containing at least a second plurality of induction-type electric heating elements 24, for induction heating. The third section 28 has a third length L3 (see Figure 14), such that the second plurality of induction-type heating elements 24 are configured to bring the rolled product P to the maximum pre-rolling temperature TP using a third predetermined heating power P3 comprised between 6 megawatts and 30 megawatts. By way of example, the first length L1 is approximately 5 meters.

[0097] The third zone 28 is particularly advantageous in the case of endless rolling, in which the average temperature of the rolled product P must be approximately 1180°C ± 30°C (see Figure 15) and, correspondingly, its surface temperature must be approximately 1300°C ± 30°C (see Figure 16).

[0098] 14, the first power P1 generated by the inductive electric heating element 23 in the first zone 21 and the third power P3 generated by the inductive electric heating element 24 in the third zone 28 are greater than the second power P2 generated by the resistive electric heating element 25 in the second zone 22. It should be clarified that the first power P1 and the third power P3 may be different from each other or may not be constant values along the lengths L1 and L3 of the first zone 21 and the third zone 28, respectively. Furthermore, the power P2 may have a constant value along the length L2 of the second zone 22.

[0099] According to another embodiment, not shown in the figures, the third section 28, or at least a part of it, is movable between a closed position and an open position which allows rolled products P coming from other product lines to be introduced into the tunnel 11.

[0100] Furthermore, as shown in Figure 3, according to another embodiment of the present invention, the heating furnace 10 further has a fourth section 29 arranged downstream of the third section 28 in the forward direction of the rolled product.

[0101] The fourth section 29 has a fourth length L4 (see FIG. 3) and is provided with a second plurality of resistive electric heating elements 26 configured to maintain and equalize the temperature of the rolled product P reaching the third section 28 by supplying a fourth predetermined heating power P4 comprised between 2 megawatts and 8 megawatts.

[0102] As an example, the fourth length L4 is comprised between about 25 meters and about 30 meters.

[0103] According to the embodiment shown in FIG. 2, the heating furnace 10 is not only arranged upstream of the rolling mill train 103 but also between the roughing mill 106 and the finishing mill 107 .

[0104] The use of an electrically powered heating element 20 has the advantage of eliminating the consumption of fossil fuels and the resulting polluting emissions of carbon dioxide and other exhaust gases.

[0105] This can result in significant cost savings for the plant, taking into account the maintenance costs of the heating elements 20. In fact, thanks to electric operation, there is no need to pay carbon taxes due to pollutant emissions at all.

[0106] It will be apparent that modifications and / or additions to components may be made to the furnace 10 thus far described without departing from the spirit and scope of the present invention as defined by the appended claims.

[0107] Although the invention has been described with reference to some particular examples, it is clear to a person skilled in the art that other equivalent forms of furnaces for plants for the production of rolled products can be realised which have the characteristics set out in the claims and which therefore fall within the scope of protection defined by the claims.

[0108] In the following claims, references in parentheses have the sole purpose of improving readability and shall not be considered as limiting factors with regard to the field of protection defined by the same claims.

Claims

1. A heating furnace (10) for a plant (100) for the production of rolled products (P), comprising: The heating furnace (10) includes a tunnel (11) and a plurality of heating means (20); The heating means (20) includes induction-type electric heating elements (23, 24) and resistance-type electric heating elements (25, 26), The induction electric heating element (23) is arranged at least in the entrance area to the tunnel (11), the second resistive electric heating element (25) is located in the tunnel (11) downstream of the inductive electric heating element (23) in the introduction zone; A heating furnace (10) characterized in that the induction electric heating element arranged in the introduction zone is configured to bring the temperature of the rolled product to a value of at least 1100°C.

2. The heating furnace comprises at least a first section (21) corresponding to the inlet end (12) thereof and having at least a first plurality of said induction heating elements (23); a second section (22) located downstream of the first section (21) in the direction of advancement of the product (P) to be rolled, and having a first plurality of the resistive heating elements (25); The furnace (10) of claim 1, comprising:

3. 3. The furnace (10) of claim 2, wherein the first plurality of induction heating elements (23) are of the longitudinal flow type.

4. the pre-rolling temperature (TP) in the tunnel (11) is comprised between about 1250°C and about 1300°C; the first section (21) having a first length (L1) such that the first plurality of induction heating elements (23) bring the product (P) to be rolled to the pre-rolling temperature (TP) using a first predetermined power (P1) comprised between about 6 megawatts and about 48 megawatts; A heating furnace (10) according to claim 2 or 3.

5. the furnace (10) preferably has a total length (LC) between about 20 meters and about 300 meters, more preferably between about 40 meters and about 180 meters; The first section (21) has a first length (L1) that occupies at least 1 / 5 of the total length (LC), The furnace (10) of claim 4.

6. the second section (22) has a second length (L2) greater than the first length (L1), such that the first plurality of resistive heating elements (25) are configured to provide a predetermined second power (P2) comprised between about 2 megawatts and about 16 megawatts to maintain and uniform the product (P) being rolled at a maintenance temperature (TM) substantially equal to or slightly lower than the pre-rolling temperature (TP). A furnace (10) according to claims 2 and 4.

7. 7. The heating furnace (10) according to claim 6, characterized in that the second section (22) comprises at least one movable part (22a) movable between a closed position and an open position to allow the introduction of the product (P) to be rolled from another product line (LP) into the tunnel (11).

8. 7. The heating furnace (10) according to claim 6, characterized in that the second length (L2) is such that the second section (22) performs a buffer function so as not to lose the temperature of the product (P) being rolled in the event of replacement or maintenance work on the rolling cylinders.

9. The heating furnace (10) further comprises a third section (28) located downstream of the second section (22) in the direction of advancement of the product (P) to be rolled, and in which at least a second plurality of the induction-type electric heating elements (24) are located; the third section (28) having a third length (L3) such that the second plurality of the induction heating elements (24) are configured to bring the product (P) to a maximum pre-rolling temperature (TP) using a third predetermined power (P3) comprised between about 6 megawatts and about 30 megawatts; A furnace (10) according to any one of claims 6 to 8.

10. a fourth section (29) located downstream of the third section (28) in the direction of advancement of the product (P) to be rolled, in which at least a second plurality of the resistive electric heating elements (26) are present; the fourth zone (29) having a fourth length (L4) such that the second plurality of resistive electric heating elements (26) are configured to maintain and homogenize the temperature reached in the third zone (28) for the product (P) to be rolled using a predetermined fourth heating power (P4) comprised between about 2 megawatts and about 8 megawatts; The furnace (10) according to claim 9.

11. the resistive heating elements (25, 26) are arranged side by side or adjacent to each other so as to affect at least half of the internal cross section of the tunnel (11); the resistive heating elements (25, 26) are preferably arranged above and / or below the product (P) to be rolled or on both sides of the product (P) to be rolled, so as to be interposed between the inner surface of the tunnel (11) and the product (P) to be rolled; The furnace (10) of claim 1.

12. A plant (100) for the manufacture of rolled products (P), comprising: at least one rolling mill train (103); 12. A plant (100), characterized in that it comprises a heating furnace (10) according to any one of claims 1 to 11, arranged along a rolling line (L) upstream of the rolling mill train (103).

13. A casting machine (101) is provided upstream of the heating furnace (10) to continuously supply a product (P) to be rolled, 13. The plant (100) according to claim 12, characterized in that said plant (100) is capable of carrying out said rolling process at least continuously, i.e. in an endless mode.

14. a pendulum shear (102) disposed along the rolling line (L) between the caster (101) and the heating furnace (10) for cutting the continuously supplied rolled product (P) to a predetermined size; The plant (100) according to claim 12, characterized in that the plant (100) is capable of carrying out the rolling process in a semi-endless mode, a coil-to-coil mode or a billet-to-billet mode.

15. a feeding device (112) arranged along the rolling line (L) upstream of the heating furnace (10) for cold feeding the product (P) to be rolled; The rolling mill train (103) includes a plurality of roughing mills (106) disposed near the heating furnace (10) and a plurality of finishing mills (107) disposed downstream of the roughing mills (106), 13. The plant (100) according to claim 12, characterized in that the heating furnace (10) according to any one of claims 1 to 11 is arranged between the roughing mill (106) and the finishing mill (107).

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