Slab preheating plant for semi flat steel product in continuous and high temperature type

Abstract

To provide a slab preheating plant in a continuous and high temperature type for preheating a flat steel product.SOLUTION: A slab preheating plant in a continuous type is provided with: a transportation line (10) configured to transport semi flat steel products from an inlet (2) to an outlet (3) of the preheating plant (1); and a plurality of heating facilities (20,30, 41, 42, 43, 44, 45, 46, 47, 48) arranged along the transportation line (10) to heat the semi flat steel products from an entrance temperature (Te) to a specific final temperature (Tf). The plurality of heating facilities includes a first induction furnace (20) and a second induction furnace (30) placed between the inlet (2) and the outlet (3) along the transportation line (10) in order as well as at least one of electric resistance radiation furnaces (41, 42, 43, 44, 45, 46, 47, 48).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a continuous (high capacity) and high temperature (which can exceed 1150° C.) preheating plant for flat steel semi-finished products (slabs).

[0002] The preheating plant according to the invention is particularly suitable for operation in mass production of slabs based on small batches, which are characterized by high dimensional variability, while maintaining high energy efficiency. [Background technology]

[0003] Increasing atmospheric emissions of carbon dioxide from industrial and anthropogenic sources are considered one of the most important causes of the greenhouse effect, which is increasing global temperatures and, therefore, of ongoing climate change.

[0004] Carbon dioxide (CO2) is a naturally occurring compound normally present in the atmosphere; it is produced by the respiration of most living organisms and, together with water contained in the atmosphere in gaseous (vapor) or liquid (cloud) form, contributes to the greenhouse effect. While the Earth's water content remains fairly constant over time, carbon dioxide concentrations can change due to natural causes (e.g., temperature changes due to solar activity or volcanic eruptions) or anthropogenic causes (mainly related to the burning of fossil fuels such as coal and natural gas).

[0005] From prehistoric times to the present, atmospheric carbon dioxide concentrations have risen from approximately 280 ppm to over 420 ppm. This increase is linked to the expansion of industrial activity, and atmospheric carbon dioxide concentrations can only be reduced by influencing industrial processes. This goal is implemented in the Kyoto Protocol, established in 1995 and implemented since 2005, which requires industry to completely eliminate carbon-emitting sources in the long term.

[0006] In industrial preheating plants intended to preheat semi-finished products to the temperatures required for rolling processes or other high-temperature plastic deformation processes, the complete elimination of CO2 emissions can basically be achieved in two different ways:

[0007] The first method is to replace fossil fuels with alternative carbon-free fuels (typically hydrogen) obtained through CO2-free production pathways.

[0008] The second method is to replace combustion with another heat source, usually electricity.

[0009] The first approach is to replace carbon-based fuels with pure hydrogen (i.e., the only fuel that does not emit carbon dioxide). Burners that use hydrogen or a mixture of natural gas and hydrogen as the combustion source have already been developed and are currently on the market. However, to produce hydrogen, some of the fossil fuel-free energy is lost during the conversion, and production efficiencies are typically in the range of 0.5 to 0.8.

[0010] The second method involves industrial processes aimed at directly converting electricity into heat. Specifically, the process involves: (A) Induction heating (B) Direct resistance heating (C) Radiant resistance heating

[0011] [(A) Induction heating] In induction heating, heat is generated directly in the material by the action of eddy currents.

[0012] When a workpiece is exposed to an alternating magnetic field, eddy currents (alternating currents, sinusoidal currents) are generated near its surface. The current flow inside the workpiece causes internal heating according to Joule's law.

[0013] Induction heating has the advantage of being very fast and efficient even at low temperatures.

[0014] However, such a technique has several technical problems.

[0015] The first problem is that the construction of induction heating equipment inevitably leaves gaps between the coils, where the workpiece rests on rollers that ensure its forward movement. Especially in the case of hot, flat workpieces (e.g., slabs), the hot material radiates a lot of energy into the air, which significantly reduces energy efficiency.

[0016] Additionally, coils, rollers, and other elements may require water cooling, further reducing efficiency.

[0017] Typical overall efficiencies for induction heating starting from room temperature semi-finished products are 80% when heating to 350°C, 55% when heating to 700°C, 45% when heating to 1000°C, and less than 40% when heating to 1200°C (common rolling temperatures).

[0018] The second problem is that although induction coils can heat the material quickly, they do not provide sufficient temperature uniformity across the slab to allow a direct rolling pass. In fact, a sufficient waiting time is required to achieve adequate temperature uniformity across the thickness of the slab.

[0019] The above two problems make it impossible to use induction heating as the sole heating source in preheating plants for flat steel semi-finished products.

[0020] [(B) Direct resistance heating] Direct resistance heating consists of passing a high current through the workpiece by direct contact with electrical resistance elements (terminals), one of which acts as an anode and the other as a cathode.

[0021] This system requires a gripper design that provides sufficient contact area with all edges of the workpiece so that current can flow through all sections of the workpiece.

[0022] The advantages of this system are that each semi-finished product can be heated in a relatively short time, heating is more uniform than with induction heating (as the current passes through the entire internal section), and overall efficiency is 70% to 80%.

[0023] However, this technique also has some technical problems.

[0024] The first problem is that although the heating process is rapid, it takes a significant amount of time to set up the equipment to handle the semi-finished products, and the overall production rate is slower than with conventional furnaces or induction heating systems.

[0025] A second problem is that heating flat steel semi-finished products (especially slabs) requires clamping systems that are difficult to design and implement.

[0026] The above two problems make it impossible to apply direct resistance heating to high-production preheating plants for flat steel semi-finished products.

[0027] [(C) Radiant resistance heating] Radiant resistance heating consists of using an electrical resistance element to heat an enclosed heating chamber (e.g., an "electric furnace") lined with refractory insulating material. This results in both the resistance and the refractory surface heating to high temperatures, which radiate the energy into the workpiece. Electrical resistance elements made of heat-resistant, electrically conductive material (both metallic and ceramic) may be embedded in a refractory sheet, thereby forming a "radiant panel."

[0028] This type of technology has traditionally been applied in laboratory and small furnaces, but due to several issues, it has rarely been applied to continuously operating high-production furnaces. The advantage of a fully sealed and insulated chamber is that it can achieve excellent efficiency (80%-85%).

[0029] However, this technique also has some technical problems.

[0030] The first problem is that the power density of radiant panels (radiant resistive panels) is lower than the power density generated by the aforementioned power-to-heat conversion systems or conventional combustion burners. For example, data showing this is available, such as the power density of metal resistive panels (e.g., Fe-Cr-Al) of 20-30 kW / m. 2 and the power density of ceramic resistive panels (e.g., MoSi2) is 120-150kW / m 2 and the power density of the heating furnace equipped with a combustion burner is 150 to 200 kW / m 2 The following points can be mentioned.

[0031] Radiant preheating is inherently slower than the other two methods mentioned above, and is made even slower by the limited power density compared to conventional combustion furnaces, which tends to result in longer electric resistance preheating furnaces and larger plant sizes.

[0032] However, this at least has the advantage of providing better temperature uniformity within the workpiece.

[0033] The second problem is that in conventional combustion furnaces, the combustion products contribute to an inert, non-oxidizing atmosphere, with an O2 content typically below 1%. However, in the absence of combustion, the free atmosphere present in electrically heated furnaces can increase oxidation of the semi-finished products, especially for carbon and low-alloy steels.

[0034] The third problem is that in a typical steel slab rolling mill, the lengths of the slabs fed into the furnace vary widely, resulting in a significant decrease in the furnace filling rate and a drop in efficiency.

[0035] The fourth problem is that in plate rolling mills that handle a wide variety of slabs with different shapes and steel grades, as well as small batches of slabs with similar characteristics, the typical large chamber of a walking beam furnace or a moving hearth furnace does not offer much flexibility in accommodating different batches or providing optimal heating conditions for each batch, since slabs of different thicknesses and steel grades are placed side by side. Alternatively, to achieve optimal heating conditions for each batch, air gaps must be formed in the furnace to separate slabs with different shapes and compositions, which reduces the packing rate and reduces efficiency.

[0036] The fifth problem is that the thermal cutting of the daughter slab can cause the alloy steel slab to crack. When heat is supplied to the cutting zone of a cold slab, high stresses are generated, causing cracks in the slab itself, leading to waste of the rolled parent slab and a decrease in yield.

[0037] The sixth problem is that in these types of sheet metal rolling plants, the slabs may have a combination of large thickness (more than 200 mm) and high temperature (more than 1150°C), so the roller furnace heating solution is not applicable.

[0038] Finally, a seventh problem is that the resistive heating panels that form the first insulating layer within the furnace cannot be removed from the outside of the furnace for replacement.

[0039] For these reasons, currently available technical solutions are not suitable for application in preheating plants for flat steel semi-finished products (slabs).

[0040] Therefore, in the field of preheating plants for flat steel semi-finished products (slabs), there is still an unmet need to replace combustion-based heating devices with electric devices, in particular radiant resistance heating devices. Summary of the Invention

[0041] It is therefore an object of the present invention to eliminate or at least mitigate the above-mentioned problems associated with the prior art by providing a continuous, high-temperature preheating plant (continuous high-temperature preheating plant) for flat steel semi-finished products (slabs) that is more compact than conventional plants while using radiant resistance heating devices to ensure high energy efficiency.

[0042] A further object of the present invention is to provide a continuous high-temperature preheating plant for flat steel semi-finished products (slabs) which makes it possible to avoid the occurrence of cracks in the slabs after cutting, without compromising the compactness of the preheating plant.

[0043] A further object of the present invention is to provide a continuous high-temperature preheating plant for flat steel semi-finished products (slabs) which is highly energy efficient even when the characteristics of the semi-finished products to be treated vary widely.

[0044] A further object of the present invention is to provide a continuous high temperature preheating plant for flat steel semi-finished products (slabs) which is operationally simple to manage.

[0045] A further object of the present invention is to provide a continuous high-temperature preheating plant for flat steel semi-finished products (slabs) which allows the processing of slabs with a combination of large plate thickness and high rolling temperatures. [Brief explanation of the drawings]

[0046] The technical features of the present invention can be clearly understood from the content of the appended claims, and the advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which one or more embodiments of the present invention are shown by way of non-limiting examples only.

[0047] [Figure 1] 1 is a simplified schematic plan view of a continuous high-temperature preheating plant for flat steel semi-finished products (slabs) according to a first embodiment of the present invention; FIG. [Figure 2] FIG. 5 is a schematic plan view showing, in a simplified form, a preheating plant for flat steel semi-finished products (slabs) according to a second embodiment of the present invention. [Figure 3] 3 is an elevation view of a portion of the preheating plant of FIG. 1 or 2 for a moving hearth type electric resistance radiant furnace. FIG. [Figure 4] 4 is a cross-sectional view of the part of the preheating plant of FIG. 1 for a plurality of electric resistance radiant furnaces of the moving hearth type, taken along the line IV-IV in FIG. [Figure 5] 5 is a detailed view of FIG. 4 showing an enlarged view of the internal passage portion of the movable hearth type electric resistance radiation furnace. [Figure 6] 5 showing the furnace structure at the top and side. [Figure 7] 7 is a cross-sectional view of the furnace of FIG. 5 taken along line VII-VII of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0048] With reference to the drawings, a continuous high-temperature preheating plant 1 for flat steel semi-finished products according to the invention is generally designated by the reference number 1 .

[0049] The preheating plant 1 is configured to operate continuously and is therefore an industrial plant capable of handling high production flows, as opposed to batch furnaces or laboratory plants.

[0050] The term "high temperature" means that the preheating plant 1 is potentially capable of temperatures above 1150°C, although it can also operate at lower temperatures.

[0051] In particular, the preheating plant 1 is intended for processing slabs. In the following description, the term slab is used as a synonym for flat steel semi-finished products.

[0052] A slab is a flat semi-finished product, generally with a thickness of at least 50 mm and a width at least twice the thickness. It has a rectangular cross section with rounded corners. The ratio of the long side to the short side of the slab cross section is at least 2 but less than 4.

[0053] Slabs come in a variety of lengths and are made of a variety of steel grades, each of which requires specific optimum heating conditions.

[0054] Generally, slabs are obtained by hot cutting (perpendicular to the longitudinal direction) a long, flat semi-finished product. Hereinafter, the term "parent slab" is used to identify the original slab before cutting, and the term "child slab" is used to identify the individual slabs obtained by cutting the parent slab.

[0055] On the slab, one longitudinal axis can be identified.

[0056] The preheating plant 1 is intended to preheat the slabs to the temperature required for the rolling process or other hot plastic deformation process, in particular the slabs being hot rolled to obtain sheet metal.

[0057] According to a general embodiment of the present invention, the preheating plant 1 comprises a conveying line 10 configured to transport a flat semi-finished product (parent slab) from an inlet 2 to an outlet 3 of the preheating plant 1, and a plurality of heating devices 20, 30, 41, 42, 43, 44, 45, 46, 47, 48 arranged along the conveying line 10 to heat the semi-finished product (slab) from an inlet temperature Te to a predetermined final temperature Tf.

[0058] Advantageously, if the heating device is not provided with its own internal transport means, the movement of the semi-finished products (slabs) inside the heating device may be carried out by a conveying line 10 or by transport means integrally provided in the heating device itself.

[0059] In particular, as shown in Figure 2, the conveying line comprises a number of connecting sections 10a, 10b, 10c, 10d between the various devices that make up the preheating plant 1. Preferably, such connecting sections consist of roller conveyor devices.

[0060] 1 and 2, the plurality of heating devices include a first induction furnace 20, a second induction furnace 30, and at least one electric resistance radiation furnace 41, 42, 43, 44, 45, 46, 47, and 48. The first induction furnace 20, the second induction furnace 30, and the at least one electric resistance radiation furnace 41, 42, 43, 44, 45, 46, 47, and 48 are arranged in this order along the conveying line 10 between the entrance 2 and the exit 3.

[0061] Induction furnaces and electric resistance radiant furnaces are essentially known to those skilled in the art and will not be described in detail except for details that differ from conventional configurations.

[0062] According to a further aspect of the present invention, the preheating plant 1 includes a cutting device 50. The cutting device 50 is configured to cut the initial flat steel semi-finished product MS (i.e., the "parent slab") in a transverse direction (transverse direction) so as to obtain a plurality of cut segments (hereinafter also referred to as "child slabs" for simplicity) CS made up of flat steel semi-finished products (flat steel semi-finished products) shorter than the initial flat steel semi-finished product MS.

[0063] Cutting devices for flat steel semi-finished products are also known per se to those skilled in the art and will not be described in detail except for those details which differ from conventional constructions.

[0064] The cutting device 50 is disposed between the first induction furnace 20 and the second induction furnace 30 .

[0065] In use, the first induction furnace 20 is configured to preheat each flat steel semi-finished product MS introduced into the preheating plant 1 from the inlet temperature (Te) to a predetermined first intermediate temperature T1m (to prepare it for cutting in the cutting device 50), while the second induction furnace 30 is configured to preheat each cut segment (i.e., child slab) CS (discharged from the cutting device 50) from the first predetermined intermediate temperature T1m to a predetermined second intermediate temperature T2m.

[0066] In use, the at least one electric resistance radiant furnace 41, 42, 43, 44, 45, 46, 47, 48 is configured to complete preheating of a child slab CS from the second predetermined intermediate temperature T2m to the predetermined final temperature Tf.

[0067] According to the invention, a continuous, high-temperature preheating plant 1 for flat steel semi-finished products (slabs) uses radiant resistance heating devices to ensure high energy efficiency, while being more compact than conventional plants.

[0068] More specifically, this effect is achieved by combining induction furnaces and electric resistance radiant furnaces in a specific arrangement, whereby two induction furnaces provide heat to the slab in the initial stage and at least one electric resistance radiant furnace provides the final stage heating.

[0069] Part of the heat required for the preheating operation is provided by an induction furnace (which is less energy efficient but faster than an electric resistance furnace), resulting in less energy efficiency but more compactness for the same amount of heat provided.

[0070] In fact, such a configuration of the preheating plant 1 makes it possible to prioritize compactness of the preheating plant 1 at the expense of energy efficiency during the sizing stage, or conversely, prioritize energy efficiency at the expense of compactness, depending on whether the second intermediate temperature T2m increases or decreases.

[0071] In fact, induction furnaces are less efficient than electric resistance radiant furnaces, but they have a faster processing speed. Therefore, for the same final temperature Tf and the same characteristics of the slab to be processed, the higher the second intermediate temperature T2m, the greater the proportion of heat supplied by the induction furnace and the smaller the proportion of heat supplied by the electric resistance radiant furnace relative to the total required heat. As a result, the preheating plant 1 can be made more compact, although energy efficiency is sacrificed.

[0072] Conversely, if the final temperature Tf and the characteristics of the slab to be treated are the same, the lower the second intermediate temperature T2m, the smaller the proportion of the heat supplied by the induction furnace and the larger the proportion supplied by the electric resistance radiant furnace relative to the total required heat. As a result, the preheating plant 1 becomes less compact and its energy efficiency improves.

[0073] Preferably, the inlet temperature Te is ambient temperature (20°C).

[0074] Preferably, the second intermediate temperature T2m is 300° C. or higher and 800° C. or lower, and is appropriately selected depending on whether priority is given to compactness of the preheating plant 1 or to energy efficiency.

[0075] Advantageously, the first intermediate temperature T1m is selected depending on the characteristics of the material of the semi-finished product to be cut by the cutting device 50.

[0076] By preheating the low temperature (parent) slab to temperatures above 300-350°C, thermal shock can be minimized and crack formation during thermal cutting can be avoided.

[0077] According to the preheating plant 1 of the present invention, the cutting device 50 is arranged between the first induction furnace 20 and the second induction furnace 30, so that the occurrence of cracks in the (sub) slab after cutting can be avoided without compromising the compactness of the preheating plant 1. The heat provided by such a furnace, although inefficient, is quickly utilized without compromising the compactness of the preheating plant 1.

[0078] Preferably, the preheated slabs are fed directly into the electric resistance radiant furnace 40 so that the energy already supplied is conserved and CO2 emissions are reduced. For this purpose, the section of the conveying line between the second induction furnace 30 and the electric resistance radiant furnace 40 is preferably insulated to reduce heat loss.

[0079] Advantageously, the at least one electric resistance radiation furnace 41, 42, 43, 44, 45, 46, 47, 48 defines a furnace axis X, and the cutting segment (child slab) CS is movable along the furnace axis X between the furnace entrance 40a and the furnace exit 40b with the aid of a moving means.

[0080] 4 and 5, each of the at least one electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, and 48 defines a tunnel 400 therein extending between a furnace entrance 40a and a furnace exit 40b along the furnace axis X so as to define (constitute) a heating chamber of the furnace itself. The cutting segment (child slab) CS can be moved along the tunnel 400 (heating chamber) with the aid of the moving means.

[0081] Advantageously, as shown in particular in Figures 5, 6 and 7, the tunnel 400 is bounded on its top and sides by resistive heating panels (electrical resistive heating panels) 401, 402, 403.

[0082] Preferably, each of said resistive heating panels 401, 402, 403 is removable to facilitate maintenance of the preheating plant 1.

[0083] Preferably, to facilitate maintenance of the electric resistance radiant furnace, the upper part of the electric resistance radiant furnace is configured with a plurality of covers 420 that are removable from a lower structure 430, as shown in FIG.

[0084] Preferably, as shown in Figure 3, the at least one electric resistance radiant furnace 41, 42, 43, 44, 45, 46, 47, 48 is made up of a number of modular units 410, 411, 412, ..., 410n arranged next to one another along the furnace axis X. This allows the preheating plant 1 to be expanded by adding additional modular units to increase the heat capacity.

[0085] Advantageously, the at least one electric resistance radiant furnace 41, 42, 43, 44, 45, 46, 47, 48 may be divided into a number of heating zones over its entire length along the furnace axis X. The heating zones communicate with one another and are thermally adjustable independently of one another. Each of the heating zones defines a temperature control zone. This allows the preheating plant 1 to achieve a high degree of precision in temperature control and to adapt to the specific characteristics of the semi-finished products to be preheated.

[0086] Advantageously, the at least one electric resistance radiant furnace 41, 42, 43, 44, 45, 46, 47, 48 is provided with sealed doors at the inlet 440 and outlet 450 and with an internal pressurization system 500 for injecting an inert gas (e.g., nitrogen) into the furnace chamber, thereby avoiding the free air inside the electric resistance radiant furnace from causing oxidation of the semi-finished products, especially in the case of carbon steels and low-alloy steels.

[0087] Preferably, the tunnel 400 of the at least one electric resistance radiation furnace 41, 42, 43, 44, 45, 46, 47, 48 has a minimum cross-sectional area (passage cross-section) that can accommodate the passage of semi-finished products (cut segments, i.e., child slabs) in order to reduce heat loss and increase furnace efficiency.

[0088] In particular, the tunnel 400 of the at least one electric resistance radiant furnace 41, 42, 43, 44, 45, 46, 47, 48 has a passage cross-sectional area (passage cross-section) sized to allow one semi-finished product (slab) to pass through at a time, i.e., multiple slabs can flow in a single file along the tunnel 400.

[0089] Preferably, as shown in particular in Figures 3 and 4, the at least one electric resistance radiant furnace 41, 42, 43, 44, 45, 46, 47, 48 is a furnace of the moving hearth type.

[0090] The furnace 40 may be a roller furnace. However, due to the potential combination of slab thickness and heating temperature (final temperature Tf), it is highly preferable to select a moving hearth furnace, since rollers with sufficient strength and heat resistance cannot be applied. Furthermore, even if such rollers were applicable, they would necessarily need to be cooled, which would reduce the efficiency of the furnace.

[0091] The furnace 40 may be a walking beam furnace. However, since a walking beam furnace requires a cooling element that reduces the efficiency of the furnace, it is highly preferable to select a moving hearth furnace that does not include a cooling element. Furthermore, a moving hearth furnace provides an excellent support base for the slab, allowing for more stable processing of slabs of moderate length and width.

[0092] Advantageously, in the case of a furnace of the movable hearth type, the electric resistance radiant furnace is provided with a water seal arranged between the fixed hearth part 460 and the movable hearth part 470 to ensure sealing between the internal furnace chamber and the external environment.

[0093] Above, the presence of at least one electrical resistance radiant furnace is mentioned.

[0094] According to a highly preferred embodiment of the invention shown in Figures 1 and 2, the preheating plant 1 comprises a plurality of electric resistance radiant furnaces 41, 42, 43, 44, 45, 46, 47, 48, each of which defines a furnace axis X. Cutting segments (child slabs) CS are movable along the furnace axis X between a furnace inlet 40a and a furnace outlet 40b with the aid of a moving means (preferably a movable hearth system).

[0095] The electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, and 48 are inserted into the transfer line 10 after (downstream from) the second induction furnace 30 and in parallel with each other.

[0096] In fact, the presence of several electric resistance radiant furnaces not only increases the capacity of the preheating plant 1 in terms of the volume of production to be processed, but also its adaptability to productions in which the characteristics of the semi-finished products to be processed vary greatly, both in terms of length and quality of the metal.

[0097] Advantageously, the temperature of each of the electric resistance radiant furnaces 41, 42, 43, 44, 45, 46, 47, and 48 can be adjusted independently of the other electric resistance radiant furnaces 41, 42, 43, 44, 45, 46, 47, and 48. This allows the cut segments (child slabs) CS of the semi-finished product processed in the electric resistance radiant furnaces 41, 42, 43, 44, 45, 46, 47, and 48 to be discharged in a state preheated to a final temperature Tf different from the cut segments CS of the semi-finished product processed in the other electric resistance radiant furnaces 41, 42, 43, 44, 45, 46, 47, and 48.

[0098] Such a multi-furnace configuration allows the preheating plant 1 to maintain high energy efficiency even if the characteristics of the semi-finished products to be treated vary greatly.

[0099] In fact, each electric resistance radiant furnace may be dedicated to a specific type of slab (length and metal quality).

[0100] This allows for efficiency benefits such as significantly higher furnace loading, efficient management of small batches of slabs of similar quality, and optimal heat treatment of each type of slab in the presence of a wide variety of slabs.

[0101] Advantageously, each of said electric resistance radiant furnaces 41, 42, 43, 44, 45, 46, 47, 48 may have the features described above in relation to said at least one electric resistance radiant furnace.

[0102] As shown in Figures 1 and 2, the first induction furnace 20 defines a first furnace axis X1. Along this first furnace axis X1, a flat steel semi-finished product MS (parent slab) can be moved between a furnace entrance 20a and a furnace exit 20b with the aid of a moving means (preferably, a roller conveyor device). Similarly, the second induction furnace 30 defines a second furnace axis X2. Along this second furnace axis X2, a cut segment (child slab) CS can be moved between a furnace entrance 30a and a furnace exit 30b with the aid of a moving means (preferably, a roller conveyor device).

[0103] Preferably, the first induction furnace 20 and the second induction furnace 30 are arranged on the transfer line 10 so that their respective furnace axes (first furnace axis X1 and second furnace axis X2) are parallel to each other.

[0104] In particular, as will be described in more detail below, the two induction furnaces (first induction furnace 20 and second induction furnace 30) may be arranged relative to one another such that their respective furnace axes (first furnace axis X1 and second furnace axis X2) are offset or aligned.

[0105] According to a highly preferred embodiment shown in FIG. 2, the first induction furnace 20 and the second induction furnace 30 are arranged offset from one another on two parallel sections of the conveying line 10 and are interconnected by the cutting device 50.

[0106] Advantageously, the cutting device 50 is arranged to process the flat steel semi-finished product MS (parent slab) and the child slabs obtained by cutting with their respective longitudinal axes oriented parallel to the furnace axes (first furnace axis X1 and second furnace axis X2) of the two induction furnaces (first induction furnace 20 and second induction furnace 30).

[0107] In this case, the conveying line 10 comprises a first transfer means 11 configured to transfer the flat steel semi-finished product MS (parent slab) discharged from the first induction furnace 20 into the cutting device 50, and a second transfer means 12 configured to transfer the cut segment (child slab) CS produced by cutting the flat steel semi-finished product MS and discharged from the cutting device 50 to the entrance of the second induction furnace 30.

[0108] More specifically, according to the embodiment shown in FIG. 2, the electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, and 48 are arranged so that their respective furnace axes X are parallel to each other and to the furnace axes (first furnace axis X1 and second furnace axis X2) of the two induction furnaces (first induction furnace 20 and second induction furnace 30).

[0109] In this case, the conveying line 10 is equipped with a first manipulator means (first automatic operating means) 110 configured to transport one sub-slab discharged from the second induction furnace 30 to the entrance of any one of the electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, 48, and a second manipulator means (second automatic operating means) 120 configured to transport one sub-slab discharged from any one of the electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, 48 to the exit 3 of the preheating plant 1.

[0110] According to an alternative embodiment shown in FIG. 1, the first induction furnace 20 and the second induction furnace 30 are arranged on two sections of the conveying line 10, aligned in a straight line and interconnected by the cutting device 50.

[0111] In this case, the cutting device 50 is arranged to process the flat steel semi-finished product MS (parent slab) and the cut segment (child slab) CS obtained by cutting with their respective longitudinal axes aligned with the furnace axes (first furnace axis X1 and second furnace axis X2) of the two induction furnaces (first induction furnace 20 and second induction furnace 30).

[0112] More specifically, according to the embodiment shown in FIG. 1, the electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, and 48 are arranged so that their respective furnace axes X are parallel to each other and perpendicular to the furnace axes (first furnace axis X1 and second furnace axis X2) of the two induction furnaces (first induction furnace 20 and second induction furnace 30).

[0113] In this case, the transfer line 10 includes a connection section 13 extending from the furnace outlet 30b of the second induction furnace 30 to the furnace inlets 40a of all of the electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, and 48, and a rotation device 130 arranged on the connection section 13. The rotation device 130 is configured to rotate each of the child slabs on the rotation device 130. This allows each of the child slabs to reach the inlet of one of the electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, and 48 with its longitudinal axis aligned with the furnace axis X of that electric resistance radiation furnace.

[0114] More specifically, according to the embodiment shown in FIG. 1, the conveying line 10 includes a child slab recovery section (cut segment recovery section) 14 extending from the furnace outlets 40b of all the electric resistance radiation furnaces 41, 42, 43, 44, 45, 46, 47, 48 to the outlet 3 of the preheating plant 1.

[0115] Advantageously, both the plant configuration with the rotating device 130 (FIG. 1) and the plant configuration in which all furnaces have parallel axes (FIG. 2) are configured in such a way that the cross section through which the semi-finished products are inserted through the coils of the induction furnace and the cross section of the tunnel of the electric resistance radiant furnace are always as constant as possible, regardless of the furnace type, which allows maximizing the filling factor of the two types of furnaces.

[0116] Preferably, the preheating plant 1 is equipped with an automatic control system 200 based on a material tracking program and a number of sensors for identifying the position of each slab over time.

[0117] In particular, the automatic control system 200 is configured to control the first manipulator means 110 to place (position) each slab at the entrance of the desired furnace, and to control the second manipulator means 120 to pick up each slab at the exit of the furnace where it has been treated and to transport the slab to the exit 3 of the preheating plant 1.

[0118] The present invention makes it possible to achieve several of the advantages already mentioned.

[0119] The high-capacity preheating plant 1 for flat steel semi-finished products (slabs) according to the present invention uses radiant resistance heating devices to ensure high energy efficiency, while being more compact than conventional plants for the same amount of heat transferred to the semi-finished products.

[0120] The continuous high-temperature preheating plant 1 for flat steel semi-finished products (slabs) according to the invention makes it possible to avoid the occurrence of cracks in the slabs after cutting, without compromising the compactness of the plant.

[0121] The continuous, high-temperature preheating plant 1 for flat steel semi-finished products (slabs) according to the invention has a high energy efficiency, even if there are large variations in the characteristics of the semi-finished products to be treated.

[0122] The continuous, high-temperature preheating plant 1 for flat steel semi-finished products (slabs) according to the invention is operationally simple to manage.

[0123] The continuous high-temperature preheating plant 1 for flat steel semi-finished products (slabs) according to the invention allows the processing of slabs with a large thickness combined with high rolling temperatures.

[0124] Therefore, the present invention as devised above achieves the above-mentioned predetermined objects.

[0125] Of course, in practice, shapes and configurations different from those disclosed above may be adopted without departing from the scope of protection of the present invention.

[0126] Furthermore, all details may be replaced by technically equivalent elements and any size, shape and material may be used as required.

Claims

1. A continuous, high-temperature preheating plant (1) for preheating flat steel semi-finished products, comprising: a conveying line (10) configured to transfer the flat steel semi-finished products from the inlet (2) to the outlet (3) of the preheating plant (1); a plurality of heating devices (20, 30, 41, 42, 43, 44, 45, 46, 47, 48) arranged along the conveying line (10) for heating the flat steel semi-finished products from an inlet temperature (Te) to a predetermined final temperature (Tf); The plurality of heating devices include a first induction furnace (20), a second induction furnace (30), and at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) arranged in sequence along the conveying line (10) between the inlet (2) and the outlet (3); The preheating plant (1) comprises a cutting device (50) configured to cut the initial flat steel semi-finished product (MS) into a plurality of cut segments (CS) consisting of flat steel semi-finished products having a predetermined length shorter than the length of the initial flat steel semi-finished product, The cutting device (50) is disposed between the first induction furnace (20) and the second induction furnace (30); the first induction furnace (20) is configured, in use, to preheat each of the flat steel semi-finished products (MS) introduced into the preheating plant (1) from the inlet temperature (Te) to a predetermined first intermediate temperature (T1m); the second induction furnace (30) is configured, in use, to preheat each of the cut segments (CS) from the first predetermined intermediate temperature (T1m) to a second predetermined intermediate temperature (T2m); the at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) is configured, in use, to complete preheating of the cut segments (CS) from the second predetermined intermediate temperature (T2m) to the predetermined final temperature (Tf); A preheating plant characterized by:

2. The inlet temperature (Te) is ambient temperature. A preheating plant according to claim 1.

3. The second intermediate temperature (T2m) is 300°C or higher and 800°C or lower. A preheating plant according to claim 1 or claim 2.

4. the at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) defining a furnace axis (X); Along the furnace axis (X), the cut segments (CS) of the flat steel semi-finished products are movable between a furnace entrance (40a) and a furnace exit (40b) by a moving means. A preheating plant according to any one of claims 1 to 3.

5. the at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) defines a tunnel therein extending along the furnace axis (X) between the furnace inlet (40a) and the furnace outlet (40b) so as to define a heating chamber of the furnace itself; the cutting segment (CS) is movable along the tunnel by the moving means; A preheating plant according to claim 4.

6. The tunnel is bounded at its top and sides by electric resistance heating panels (401, 402, 403); Each of said electrical resistance heating panels (401, 402, 403) is preferably removable. A preheating plant according to claim 5.

7. The at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) is composed of a plurality of modular units (410, 411, 412, ..., 411n) aligned with one another along the furnace axis (X). A preheating plant according to any one of claims 4 to 6.

8. the at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) is divided along its length into a plurality of heating zones along the furnace axis (X); the plurality of heating zones are in communication with one another and are thermally adjustable independently of one another; Each of the heating zones defines a temperature control zone. A preheating plant according to any one of claims 4 to 7.

9. The at least one electric resistance radiation furnace (41, 42, 43, 44, 45, 46, 47, 48) is provided with sealing doors at the furnace inlet and the furnace outlet, and is provided with an internal pressurization system for injecting an inert gas into the furnace chamber. A preheating plant according to any one of claims 4 to 8.

10. the tunnel of the at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) has a passage cross-section large enough to pass one of the cutting segments at a time; A preheating plant according to any one of claims 5 to 9.

11. The at least one electric resistance radiant furnace (41, 42, 43, 44, 45, 46, 47, 48) is a moving hearth type furnace. A preheating plant according to any one of claims 1 to 10.

12. a plurality of the electric resistance radiation furnaces (41, 42, 43, 44, 45, 46, 47, 48) each defining a furnace axis (X); The cutting segment (CS) is movable along the furnace axis (X) between a furnace entrance (40a) and a furnace exit (40b) by a moving means; The electric resistance radiation furnaces (41, 42, 43, 44, 45, 46, 47, 48) are inserted into the conveying line (10) so as to be parallel to each other downstream of the second induction furnace (30). A preheating plant according to any one of claims 1 to 11.

13. the temperature of each of the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48) can be adjusted independently from that of the other electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48) so that the cut segments (CS) treated in each of the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48) can be preheated to a final temperature (Tf) different from that of the cut segments (CS) treated in another of the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48) and discharged. A preheating plant according to claim 12.

14. The first induction furnace (20) defines a first furnace axis (X1), and flat steel semi-finished products (MS) can be moved along the first furnace axis (X1) between a furnace entrance (20a) and a furnace exit (20b) by a moving means; The second induction furnace (30) defines a second furnace axis (X2), along which the cut segments (CS) of the flat steel semi-finished products are movable between a furnace entrance (30a) and a furnace exit (30b) by a moving means. A preheating plant according to any one of claims 1 to 13.

15. The first induction furnace (20) and the second induction furnace (30) are arranged on the transfer line (10) such that the first furnace axis (X1) and the second furnace axis (X2) are parallel to each other. A preheating plant according to claim 14.

16. the first induction furnace (20) and the second induction furnace (30) are arranged in two parallel sections of the conveying line (10), offset from each other, and interconnected by the cutting device (50); the cutting device (50) is arranged to process the flat steel semi-finished products (MS) and the cut segments (CS) with their respective longitudinal axes parallel to the first furnace axis (X1) and the second furnace axis (X2); The conveying line (10) comprises a first transfer means (11) configured to transfer the flat steel semi-finished products (MS) discharged from the first induction furnace (20) to the cutting device (50), and a second transfer means (12) configured to transfer the cut segments (CS) generated by cutting the flat steel semi-finished products (MS) and discharged from the cutting device (50) to a furnace entrance of the second induction furnace (30).

16. Preheating plant according to claim 15.

17. the electric resistance radiation furnaces (41, 42, 43, 44, 45, 46, 47, 48) are arranged such that their furnace axes (X) are parallel to each other and to the first furnace axis (X1) and the second furnace axis (X2); The transfer line (10) comprises a first manipulator means (110) configured to transfer one cut segment (CS) discharged from the second induction furnace (30) to a furnace inlet of any one of the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48), and a second manipulator means (120) configured to transfer one cut segment (CS) discharged from any one of the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48) to the outlet (3) of the preheating plant (1).

17. Preheating plant according to claim 16.

18. The first induction furnace (20) and the second induction furnace (30) are arranged in two sections of the conveying line (10), are arranged in a straight line, and are interconnected by the cutting device (50); the cutting device (50) is arranged to process the flat steel semi-finished products (MS) and the cut segments (CS) with their respective longitudinal axes aligned with the first furnace axis (X1) and the second furnace axis (X2); 16. Preheating plant according to claim 15.

19. The electric resistance radiation furnaces (41, 42, 43, 44, 45, 46, 47, 48) are arranged so that their furnace axes (X) are parallel to each other and perpendicular to the first furnace axis (X1) and the second furnace axis (X2), The conveying line (10) a connecting section (13) extending from a furnace outlet of the second induction furnace (30) to reach the furnace inlets of all of the electric resistance radiation furnaces (41, 42, 43, 44, 45, 46, 47, 48); and a rotating device (130) arranged on the connecting section (13), the rotating device (130) is configured to rotate the individual cut segments (CS) on the rotating device (130) so that the longitudinal axis of each cut segment (CS) is aligned with the furnace axis (X) of any one of the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48) and the cut segments appear at the furnace entrance of the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48).

19. Preheating plant according to claim 18.

20. The conveying line (10) comprises a cut segment recovery section (14) extending from the furnace outlets of all the electric resistance radiant furnaces (41, 42, 43, 44, 45, 46, 47, 48) to the outlet (3) of the preheating plant (1).

20. Preheating plant according to claim 19.

21. an automatic control system (200) for identifying the position of each of the flat steel blanks and / or the cut segments based on a material tracking program and a plurality of sensors; A preheating plant according to any one of claims 1 to 20.

Images