DETECTION SYSTEM, METHOD FOR DETECTING OF A MELTING CONDITION OF METAL MATERIALS INSIDE A FURNACE AND FOR ELECTROMAGNETIC STIRRING,

AND FURNACE PROVIDED WITH SUCH SYSTEMS

Technical field

The present invention relates to a measuring system and method and to a measuring and stirring system and method for a melting furnace according to the characteristics of the pre-characterizing part of the main claims. Furthermore, the present invention relates to a furnace comprising such systems.

Prior art

In the field of the production of metal products, it is known to use recycled metal materials that are molten in a melting furnace to be then cast into dies or ingot moulds for the purpose of obtaining processable metal elements for making finished or semifinished products. The recycled metal materials are introduced into the melting furnace in the solid state and the supply of energy by the furnace allows reaching the melting temperature of the recycled metal materials, which progressively melt forming metal in the liquid state. During melting and when the molten condition has been reached, the metal in the liquid state is measured in order to identify its chemical composition to then introduce additives for adjusting the composition until reaching the desired composition. For example the metal in the liquid state may be steel. Different types of melting furnaces are known, such as electric arc furnaces (EAF), induction furnaces, burner furnaces. Furthermore it is known to use electromagnetic stirring devices for furnaces, known as stirrers, which, by the generation of electromagnetic fields, induce a movement of the metal in the liquid state, thus facilitating a faster melting of the recycled metal materials, and thus enhancing the electrical efficiency following a better transmission of energy from the electrodes to the metal in the liquid state in the case of EAF furnaces, improving the homogenization of the metal in the liquid state contained in the furnace and thus achieving improved productivity. Patent application WO 201 1 /1 36729 describes a method of probing an electrically conductive material, such as a molten metal or semi-conductor material, contained in a metallurgical vessel. In the method, a measurement signal is acquired from a sensor, which is inserted into the electrically conductive material, during a relative displacement between the electrically conductive material and the sensor. The measurement signal is indicative of electrical conductivity in the vicinity of the sensor. The measurement signal is generated to represent momentary changes of an electromagnetic field around the sensor, which is generated by at least one coil in the sensor. Based on the measurement signal, a signal profile is generated, which is indicative of electrical conductivity as a function of the relative displacement between the electrically conductive material and the sensor. The method enables probing of the internal distribution of the electrically conductive material in the vessel. The signal profile can be analysed to provide information about zones or layers that differ, for example, by composition, degree of melting, degree of mixing.

Patent application US 9 599 401 describes a method and device for controlling a melting and refining process in an electric arc furnace for melting a metal, wherein the electric arc furnace includes molten and solid metal and a slag layer on the surface of the molten metal, wherein an electromagnetic stirrer is arranged for stirring the molten metal. The method comprises the steps of:

- calculating or determining masses of the molten and solid metal at a point of time, wherein the calculation is based on initial values of the molten and solid metal, an arc power supplied to the electric arc furnace, and temperatures of the molten and solid metal;

- determining a stirring power based on the calculated/determined masses;

- supplying the determined stirring power to the electromagnetic stirrer.

Patent application US 201 3/269483 describes an apparatus for the electromagnetic stirring of cast steel in an electric arc furnace in which the apparatus comprises two electromagnetic stirring units, a power supply and a control unit. The electromagnetic stirring units are mounted on an external lower surface of the electric arc furnace on opposite sides with respect to a central position of the external lower surface of the furnace. The power supply is operatively connected to the two electromagnetic stirring units and the control unit is operatively connected to the power supply to control the operation of the two electromagnetic stirring units.

Patent application WO 201 8/096368 describes an apparatus and a method for mixing molten metal. The apparatus comprises an electromagnetic stirrer that comprises a core. The core is provided with two or more teeth, two or more electrically conductive coils and connections for applying a current to the electrically conductive coils. The two or more teeth have a proximal end with respect to the core and a distal end with respect to the core. The distal end of the core defines a terminal face of the tooth in which the terminal face of the tooth for at least one of the teeth is not aligned with the face of the end of the tooth of at least one of the other teeth. In this way the gap between the teeth and the container in which the molten metal has to be stirred can be kept small, also in the presence of curved bases or walls of the container.

Problems of the prior art

As previously explained, the use of electromagnetic stirring devices for furnaces, known as stirrers, is well-known. However, the stirrer cannot be activated arbitrarily during the melting process of the recycled metal materials but it must be activated when the melting process has passed an initial phase and the recycled metal materials are at least partially molten.

At present the decision about the right moment for starting the stirrer during the melting process is made based on preparation recipes of the particular steel formulation being produced or based on complex state models of the melting process that are based on acquisitions of measurements that are mostly of the indirect type, which, introduced into the particular state model of the melting process, provide information about the start of the stirring by means of the stirrer.

However, such methods for establishing the right moment for starting the stirrer are not optimal because they are not based on a direct analysis of the actual melting condition of the recycled metal materials.

Aim of the invention

The aim of the present invention is to provide a detection system and method enabling to establish more precisely the melting condition of recycled metal materials inside a melting furnace for the purpose of establishing the most appropriate moment for enabling an electromagnetic stirrer for a melting furnace.

Another aim of the present invention is to provide a detection and stirring system and method for a melting furnace in which the system and the method allow to establish the melting condition of recycled metal materials inside a melting furnace and, by integrating a detection system and a stirrer, allow to improve the melting process of the recycled metal materials inside the melting furnace.

Concept of the invention

This aim is achieved by the characteristics of the main claim. The sub-claims represent advantageous solutions.

Advantageous effects of the invention

The solution according to the present invention, by the considerable creative contribution the effect of which constitutes an immediate and important technical progress, has various advantages.

Advantageously, the solution according to the present invention allows to obtain a measure of the melting condition of the recycled metal materials inside the melting furnace, thus allowing to establish which actions should be undertaken for the purpose, for example, of starting the stirrer in an optimal moment of the melting process or of postponing or anticipating the addition into the furnace of additional recycled metal materials to be molten or for activating systems for providing heat like the electrodes of arc furnaces or like burners, or for activating oxygen injection nozzles or for adding additives, undertaking slagging actions, etc.

In some embodiments it will be possible to advantageously obtain a mapping of the measurement of the melting condition of the recycled metal materials inside the melting furnace also allowing to know the position inside the furnace of any aggregates or high- mass elements for which it is difficult to achieve a molten state, thus enabling the adoption of suitable adjusting measures, such as an activation of the stirrer intended to induce a displacement of the aggregates or high-mass elements to facilitate their melting or the activation of additional means for providing melting energy that are suitably directed towards the zone of the melting furnace in which such aggregates or high-mass elements are located. Said additional means for providing melting energy may be, for example, orientable burners or oxygen injection nozzles that may be advantageously directed in a more precise way towards the zone of interest.

In an embodiment, thanks to the integration of the detection system of the melting condition and of an electromagnetic stirrer, a whole integrated system is advantageously obtained, which is able to manage in an optimal way the starting of the stirrer and the optional adjustment of its power and frequency parameters as a function of the measurement by the detection system itself.

In general, by the use of an electromagnetic stirrer in a furnace, it is possible to obtain various advantages:

- the melting of the recycled metal materials is more uniform and efficient, with the reduction of “cave-in” phenomena and breaking of the electrodes, limited to the application on electric arc furnaces. The melting of any large-sized metal materials is also facilitated thanks to a better heat distribution and thanks to the establishment of convective heat exchange phenomena in addition to the conductive ones, also reducing the presence of non-molten scrap at the slagging port or at the tapping hole, improving the spontaneous opening rate. Hence, there also is less need for an accurate stratification of the scrap in the furnace charging box;

- the stability of the electric arc is achieved more rapidly and the transmission of energy to the metal in the molten state or“bath” is more efficient, following the reduction in energy losses. Limited to the application on electric arc furnaces, following the improved electrical efficiency, one also obtains lower electric consumptions and the wear of the electrodes is slower as well;

- the increase in the reaction kinetics improves the decarbonization rate of the bath of metal in the molten state by a two factor, reducing oxygen consumption to obtain the same degree of decarbonization. Moreover, the lower oxygen supply reduces the oxidation of Fe and Mn, increasing the final yield and the chemical reduction of the slag, which is less aggressive on the refractory materials, thus extending their useful life, including the refractory materials of the tapping hole. The formation of foamy slag is promoted. The oxygen content at tapping is lower and this causes a reduction in the use of deoxidizers in the ladle.

- the steel bath is homogeneous. The samples taken for the chemical analysis and the temperature measures are representative of the whole molten bath, thus requiring a smaller number of samples. The slag is not overheated or partially molten. The more uniform temperature of the bath and of the slag reduces the wear of the refractory materials.

- the final productivity of the furnace is increased by over 5% thanks to the improvement of the chemical yield and to the reduction in processing times. The opening rate of the porous baffles for blowing gas into the ladle is improved, reducing the risk of nonconnection with the continuous casting sequence. It is thus possible to reduce the formation of swirls during tapping and the passage of the furnace slag in the ladle.

Description of the drawings

Hereinafter a solution is described with reference to the enclosed drawings, which are to be considered as a non-exhaustive example of the present invention, in which:

Fig. 1 is an example view of the detection system and of the electromagnetic stirring system according to the present invention applied in correspondence of the bottom of a melting furnace for recycled metal materials.

Fig. 2 is a schematic sectional view of the detection system and of the electromagnetic stirring system according to the present invention, applied in correspondence of the bottom of a melting furnace for recycled metal materials in which the induced movement of the metal in the liquid state contained in the melting furnace is highlighted.

Fig. 3 is a schematic plan view of the detection system and of the electromagnetic stirring system according to the present invention applied in correspondence of the bottom of a melting furnace for recycled metal materials in which the induced movement of the metal in the liquid state contained in the melting furnace is highlighted.

Fig. 4 is a schematic sectional view of the detection system and of the electromagnetic stirring system according to the present invention, applied in correspondence of the bottom of a melting furnace for recycled metal materials in which the force field intended to induce the movement of the metal in the liquid state contained in the melting furnace is highlighted.

Fig. 5 is a schematic plan view showing the different speeds of induced movement of the metal in the liquid state contained in the melting furnace, obtained by means of the detection system and electromagnetic stirring system according to the present invention, applied in correspondence of the bottom of a melting furnace for recycled metal materials.

Fig. 6 is a schematic view of the detection system and of the electromagnetic stirring system according to the present invention including a respective cooling station and control unit.

Fig. 7 is a schematic sectional view of a first preferred embodiment in which only the detection system according to the present invention is applied in correspondence of the bottom of a melting furnace for recycled metal materials.

Fig. 8 is a schematic sectional view of a first preferred embodiment of the detection system and of the electromagnetic stirring system according to the present invention, applied in correspondence of the bottom of a melting furnace for recycled metal materials.

Fig. 9 is a schematic sectional view of a second preferred embodiment of the detection system and of the electromagnetic stirring system according to the present invention, applied in correspondence of the bottom of a melting furnace for recycled metal materials.

Fig. 10 is a schematic sectional view of a third preferred embodiment of the detection system and of the electromagnetic stirring system according to the present invention, applied in correspondence of the bottom of a melting furnace for recycled metal materials.

Fig. Ί 1 , Fig. Ί 2, Fig. 1 3 schematically show different phases of the detection method according to the invention for establishing the melting condition of the recycled metal materials inside a melting furnace.

Fig. 14 schematically shows an exploded view of an integrated embodiment of stirrer and detection system.

Fig. 1 5 schematically shows an exploded view of an embodiment of the detection system only.

Fig. 1 6 schematically shows an exploded view of an integrated embodiment of stirrer and detection system in which the stirrer and the detection system are made as separate components.

Fig. 1 7 schematically shows a first possible configuration of the detection system.

Fig. 1 8 schematically shows a second possible configuration of the detection system. Description of the invention

The modern melting furnaces of recycled metal materials, such as the electric arc furnaces, known by the acronym of EAF, induction furnaces, burner furnaces, have problems concerning the need of operating with times of tapping from the tapping hole (10) that are as reduced as possible.

The main problems that can be found in the furnace can be, for example, the presence of solid scrap that is difficult to be molten, high levels of FeO and of oxygen in the metal in the liquid state contained in the melting furnace, chemical and thermal stratification of the bath of metal in the liquid state contained in the melting furnace, problems of opening the tapping hole owing to localised solidifications due to non-homogeneity of the temperature of metal in the liquid state contained in the melting furnace, breaking of the electrodes in the case of electric arc furnaces, establishment of “cave-in” and “cold boiling” phenomena.

The solution for simultaneously solving these problems is to increase the kinetics of the system through the stirring of the metal in the liquid state of the steel bath by supplying a flow of inert gas or by using an electromagnetic stirrer.

However, as previously said, it is difficult to precisely establish the most appropriate moment for activating the stirrer in such a way as to start the stirring action induced in the metal in the liquid state of the steel bath.

Therefore, the system according to the invention comprises (Fig. 1 , Fig. 2, Fig. 3, Fig. 4, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 1 0, Fig. 1 1 , Fig. 1 2, Fig. 1 3) a detection system (3) intended to measure the melting condition of the recycled metal materials inside the melting furnace (1 ) thus allowing to decide which actions to undertake to, for example, start a stirrer (2) in an optimal moment of the melting process.

However, in an embodiment (Fig. 7) use can be made only of the detection system (3) intended to measure the melting condition of the recycled metal materials inside the melting furnace thus allowing to decide which actions to undertake to, for example, control the power of the electrodes (4) of the furnace (1 ) or the starting of further devices for providing heat, such as burners or other systems, or to control the addition of additives to the metal in the molten state (5) contained inside the furnace (1 ). Therefore, it should be understood that the detection system (3) for measuring the melting condition inside the melting furnace can also be effectively used without it being combined or integrated with a stirrer (2).

Thus, a component of an embodiment of the system according to the present invention is a stirrer (2) of the electromagnetic type (Fig. 1 , Fig. 2, Fig. 3, Fig. 4, Fig. 6, Fig. 8, Fig. 9, Fig. 1 0, Fig. 1 1 , Fig. 1 2, Fig. 1 3, Fig. 14, Fig. 1 6) which is applied in correspondence of the bottom of a melting furnace (1 ) for recycled metal materials, such as an electric arc furnace, known by the acronym of EAF, an induction furnace, a burner furnace. The detection system (3) can be provided independently of the stirrer (2) or can be provided as a whole integrated detection and stirring system (20), which comprises a detection system (3) and a stirrer (2) as integrated parts of the system with advantages in terms of higher efficiency of the whole system.

In the case of a whole integrated detection and stirring system (20), it will be evident that different embodiments can be provided, such as:

- a first embodiment (Fig. 8) in which the whole integrated detection and stirring system (20) consists of a detection system (3) and a stirrer (2) according to an embodiment in which the detection system (3) and the stirrer (2) are housed within one single body, thus being integral with each other;

- a second embodiment (Fig. 9) in which the whole integrated detection and stirring system (20) consists of a detection system (3) and a stirrer (2) according to an embodiment in which the detection system (3) is housed within a casing of the detection system (1 7) and the stirrer (2) is housed within a casing of the stirrer ( 1 6) and the detection system (3) and the stirrer (2) are positioned on top of each other in a condition of essential contact and are mounted on the furnace (1 ) in such a way that the detection system (3) is between the lower outer wall, i.e. the bottom, of the furnace and the stirrer (2), attached to the stirrer (2). Although in the embodiment shown (Fig. 8) the whole integrated detection and stirring system (20) is represented as mounted spaced apart by a space (S) with respect to the lower outer wall, i.e. the bottom, of the furnace, in different embodiments the whole integrated detection and stirring system (20) may be attached to the bottom of the furnace (1 );

- a third embodiment (Fig. 1 0) in which the whole integrated detection and stirring system (20) consists of a detection system (3) and a stirrer (2) according to an embodiment in which the detection system (3) is housed within a casing of the detection system (1 7) and the stirrer (2) is housed within a casing of the stirrer (1 6) and the detection system (3) and the stirrer (2) are positioned in the vicinity of each other but spaced apart from each other by a distance (D) and are mounted on the furnace (1 ) in such a way that the detection system (3) is between the lower outer wall, i.e. the bottom, of the furnace and the stirrer (2), spaced apart from the stirrer (2) by the distance (D). Although in the embodiment shown (Fig. 9) the whole integrated detection and stirring system (20) is represented as having the detection system (3) and the stirrer (2) that are spaced apart from each other by the distance (D), in different embodiments the stirrer (2) may be attached to the detection system (3) which is in turn attached to the bottom of the furnace (1 ).

In another embodiment (not shown) the detection system (3) may be spaced apart from the bottom of the furnace (1 ) by the space (S), like in the second embodiment (Fig. 9), and at the same time the stirrer (2) may be spaced apart from the detection system (3) by the distance (D), like in the third embodiment (Fig. 1 0).

Expected values for the space (S) between the detection system (3) and the furnace (1 ) may range from 30 to 1 20 mm, preferably from 50 to 100 mm. In the space defined by the space (S) an airflow may pass, for example by means of a forced airflow, for cooling and cleaning purposes.

Expected values for the distance (D) between the detection system (3) and the stirrer (2), if present, may range from 30 to 1 20 mm, preferably from 50 to 1 00 mm. In the space defined by the distance (D) an airflow may pass, for example by means of a forced airflow, for cooling and cleaning purposes.

As far as the whole integrated detection and stirring system (20) is concerned, a cooling station (1 1 ) is present (Fig. 6), which sends a cooling fluid, typically water, towards the stirrer (2) and optionally also towards the detection system (3) and which afterwards, after the fluid has removed heat from the components that are installed in correspondence of the furnace (1 ), recovers the heated fluid. Therefore, the cooling fluid will circulate according to fluid delivery and return directions (1 4) along connection pipes for connection to the whole integrated detection and stirring system (20), for example with the stirrer (2) only or with the detection system (3) only in the absence of the stirrer (2) as a component of an integrated system or with both the stirrer (2) and the detection system (3). Preferably the cooling station (1 1 ) along with the respective fluid connections forms a closed circuit. A fluid control system (1 5) is also present, which for example can be made in the form of a pipe portion provided with fluid measuring and adjusting instruments and connected to a control unit (1 2) by means of a local junction box (1 3). For example the fluid control system (1 5) can be positioned on the fluid return pipe in such a way as to be able to monitor the temperature of the fluid coming out of the stirrer (2) or out of the detection system (3) or both. For example the cooling fluid can be water, preferably demineralized, with a flow rate of 1 5-25 m3/h.

For example the cooling station (1 1 ) can comprise a first pumping unit and an optional second safety pumping unit, one or more filters, a heat exchanger, a tank, and can be provided with an automation switchboard connected to the fluid control system (1 5) for the correct and safe operation of the system components installed on the furnace.

The fluid control system (1 5) for example can comprise a flow adjusting valve, one or more temperature sensors such as thermocouples, a flow meter.

For example, should an overheating of the stirrer (2) be detected, one can interrupt the power supply to the stirrer.

For example, should an overheating of the detecting system (3) be detected, one can increase the flow of cooling fluid, if the detection system (3) is provided with an autonomous cooling circuit. However, embodiments are also provided in which the detection system (3) is not provided with a cooling circuit, also in the embodiments in which the detection system (3) is made as a separate component with respect to the stirrer (2) or in embodiments in which the detection system (3) is present in the absence of a stirrer (2). In the latter case the cooling station (1 1 ) may be absent.

With reference to the stirrer (2), it is installed below the furnace (1 ) and, for example, for a furnace having a capacity of 1 00 tonnes, the stirrer (2) can have indicative dimensions corresponding to a length of about 5300 mm, a width of about 2300 mm, and a weight of about 46 tonnes.

The stirrer (2) is controlled with an alternating current preferably having a current intensity between 1 500 A and 2500 A, preferably of 2000 A, a voltage between 400 V and 900 V, preferably of 650 V, a frequency between 0.1 Hz and 1 .0 Hz, preferably of 0.5 Hz.

For example the stirrer (2) may be supplied through a respective medium voltage switchboard provided with an isolation transformer that supplies a switchboard inside which the inverters generating the driving current of the (Fig. 8, Fig. 9, Fig. 1 0, Fig. 1 4) coils (1 8) of the stirrer (2) are installed. The supply to the coils (1 8) of the stirrer (2) is provided in correspondence (Fig. 1 4) of electrical connections (31 , 32, 33) that in a three-phase supply system may consist of a first electrical connection (31 ), a second electrical connection (32) and a third electrical connection (33).

The cooling station (1 1 ) will be connected to the stirrer (2) in correspondence (Fig. 1 4, Fig. 1 6) of respective couplings (30) of the cooling fluid circuit inside the stirrer (2).

The direction of the stirring induced by the stirrer (2) in the metal in the liquid state of the steel bath is generally such as to obtain a flow of hot metal in the liquid state directed towards the tapping hole (1 0) of the furnace (1 ), in such a way as to move the hot metal in the liquid state according to (Fig. 2) a preferred direction of movement (6) towards such area and to improve the spontaneous opening rate of the tapping hole (1 0), as will be explained in the following of the present description.

Evaluations were made with regard to the fluid dynamics induced by the stirrer (2) in the exemplary case (Fig. 2, Fig. 3, Fig. 4, fig. 5) of a furnace (1 ) having an outer steel wall

(7) having a thickness between 25 and 40 mm and an inner lining of refractory material

(8) having a thickness between 800 mm and 1 000 mm, typically of 900 mm.

The current circulation in the stirrer (2) generates (Fig. 4) an electromagnetic field, which in its turn generates a force field (9) in the metal in the liquid state (5). This is translated into the previously described movement of the metal in the liquid state (5) according to (Fig. 2) a preferred direction of movement (6) towards the area of the tapping hole (1 0) of the furnace (1 ). The stirrer (2) exerts a strong motion on the bottom of the furnace. The movement then generates a recirculation flow of the metal in the liquid state (5) and the colder metal in the liquid state (5) on the bottom of the furnace (1 ) is pushed towards the surface of the bath. The movement action induced by the stirrer (2) on the metal in the liquid state (5) arrives to the limit of the steel-slag interface in correspondence of which (Fig. 3, Fig. 5) the circulation speed induced according to the corresponding direction of movement (6) is still relatively high, being able to change, according to the zone on the surface of the metal bath in the liquid state (5) between U4-U5 speed values that are lower or in the order of 0.1 m/s in the farthest zones from the tapping hole (10) and U1 -U2 speed values that are higher than 0.5 m/s in the zones in which the flow moving away from the tapping hole (1 0) is established, with U3 speed values in the order of 0.3 m/s in the intermediate zones. In Fig. 5 the different grayscale grades represented inside the perimeter of the furnace (1 ) correspond to the grayscale grades represented in the measuring scale on the right, matching the numeral indications U1 -U5, to identify the distribution of speeds.

In correspondence of the bottom of the furnace (1 ) the induced circulation speed values will be higher, until reaching speed values in the order of 0.8 1 m/s.

The stirrer (2) is preferably made (Fig. 1 6) in the form of a sealed closed body made up of a set of closing elements (28) constituting the casing (1 6) of the stirrer (2).

Likewise, the integrated detection and stirring system (20), comprising in one single body both the stirrer (2) and the detection system (3), is preferably made (Fig. 1 5) in the form of a sealed closed body made up of a set of closing elements (28) constituting the casing (1 6).

The casing (1 6) is provided (Fig. 1 4, Fig. 1 6) with the previously described couplings (30) for feeding and taking the cooling fluid of the stirrer (2), which are part of a cooling fluid circuit inside the stirrer (2) consisting of ducts (21 ) of a fluid circuit. A base (34) constitutes the support for mounting at least one series of coils (1 8) of the stirrer each of which preferably consists of an essentially quadrangular winding, according to a plan view, in which the coils develop vertically for a certain height in such a way as to define a closed path of the driving current such as to generate a force field directed according to an orthogonal direction with respect to the quadrangular shape. The coils (1 8) of the stirrer can optionally be further protected by a respective protection capsule (29).

In the embodiment shown, the stirrer (2) comprises one single row of six coils (1 8) of the stirrer, which are arranged after one another according to a direction of development along a longitudinal axis (35) of the stirrer (2) that essentially corresponds to the direction of longitudinal development of the furnace (1 ) or to the preferred stirring direction induced by the stirrer (2) in the metal in the liquid state of the steel bath facing the tapping hole (1 0) of the furnace (1 ).

With reference to the previously defined pushing effect of the hot metal flow in the liquid state in a direction towards the tapping hole (1 0), it is obtained by means of an appropriate phase displacement between the currents that supply the coils (1 8) of the stirrer (2). In particular (Fig. 4), one should consider one of the coils (1 8) of the stirrer defined by way of example as the coil (R) of the stirrer closest to the tapping hole (1 0) to which a current phase displacement of zero is assigned with respect to the currents of the other coils (1 8) of the stirrer such as the following coil (S) closest to the tapping hole (1 0) excluding the coil (R) and for example the following coil (T) closest to the tapping hole (1 0) excluding the coil (R) and the coil (S). By assigning then to the coil (S) a phase displacement of 1 20° and by assigning to the coil (T) a phase displacement of 240°, the sequence of the phase displacements of the coils (R, S, T) that generates the pushing effect of the hot metal flow in the liquid state in a direction towards the tapping hole (1 0) is, for example, as follows: R - T / S - R / T - S, where the minus sign indicates that the coil is run through in the opposite direction, that is to say, an additional phase displacement of 1 80 electrical degrees is applied. Any even permutations of the phase displacements will bring about the same effect.

The coils (1 8) of the stirrer consist of a winding of a hollow copper conductor inside which the cooling water flows. This technology is mainly used to reduce as much possible the amount of water inside the stirrer and thus below the furnace. The stirrer is thus safer if the bottom breaks. Such a technology, which defines the stirrer as“dry type”, also enables simpler maintenance since it does not require a joint external resin treatment of the coils and magnetic pack.

It will be evident to a person skilled in the art that it will be possible to provide alternative solutions with multiple parallel rows of coils (1 8) of the stirrer, alternative solutions with a greater or smaller number of coils (1 8) of the stirrer arranged on one single row of coils or on multiple parallel rows of coils, coils (1 8) of the stirrer each consisting of more than one coil arranged in a reciprocally overlapping condition.

With reference to the detection system (3), as previously explained, it can be an independent system relative to the presence (Fig. 8, Fig. 9, Fig. 1 0) or absence (Fig. 7) of the stirrer (2). In particular, the detection system (3) can be for example:

- integrated (Fig. 8) in one single body along with the stirrer (2) in such a way as to obtain an integrated detection and stirring system (20) in which the detection system (3) and the stirrer (2) are housed in one single body, thus being integral with each other;

- housed (Fig. 7, Fig. 9, Fig. 1 0, Fig. 1 5) within a casing of the detection system (1 7) in such a way as to obtain an integrated detection and stirring system (20) in which the detection system (3) is housed within a casing of the detection system (1 7) and the stirrer (2) is housed within a casing of the stirrer (1 6) and the detection system (3) and the stirrer (2) are positioned on top of each other according to a configuration in which the detection system (3) is intended to be facing the furnace.

In an embodiment, the detection system (3) is based on the use of a measuring technique of the magnetic induction tomographic type.

By means of a series of coils (1 9) of the detection system it is possible to measure and reconstruct a volumetric distribution of the electrical conductivity of the material contained inside the furnace (1 ), which, in general, may consist of a set of metal in the molten state (5) and metal materials not yet molten (36).

The measuring principle is based on the mutual inductance theory associated with the problem of the Foucault's currents or eddy currents.

The measuring method is conceived in such a way that one of the coils of the detection system is used as a transmission coil for generating a measuring field (22) and is conceived in such a way that another one of the coils of the detection system is used to acquire the signal due to the eddy currents generated in the set of metal in the molten state (5) and metal materials not yet molten (36). The detection system (3) comprises (Fig. 1 1 , Fig. 1 2, Fig. 1 3) a measuring device (27), which comprises one or more signal generators (23), one or more transmission systems (24), one or more reception systems (25), a processing system (26). The signal generator (23) provides a sinusoidal signal at a transmission frequency to the transmission system (24) that amplifies the sinusoidal signal to drive the coil (1 9) of the detection system that is used for transmission. One or more coils (1 9) of the detection system are in their turn connected to the reception system (25) for measuring the signals received by said coils following the transmission of the sinusoidal signal and the generation of the eddy currents on the set of metal in the molten state (5) and metal materials not yet molten (36). In an embodiment all the coils (1 9) of the detection system are each alternatively configurable as a transmission coil and as a reception coil in different phases of the measuring method. In a different embodiment there are some coils (1 9) of the detection system configured as transmission coils and there are some coils (1 9) of the detection system configured as reception coils.

The processing system (26) acquires the measuring signals and sends the result of processing to the control unit (1 2), which provides useful information for acting on the melting process in progress, in order to identify any necessary corrective actions on the melting process in progress.

The control unit can also acquire further measuring signals (37) to be used in combination with the measurement performed by means of the detection system (3) to provide more precise information about the melting condition of the recycled metal materials inside the melting furnace (1 ). Such further measuring signals (37) can be acquired by means of sensors (38) or by means of a communication interface (39) with the management system of the furnace (1 ) and of the melting process. For example, the control unit can, for the purpose of providing more precise information about the melting condition of the recycled metal materials inside the melting furnace (Ί ), acquire at least one measuring signal (37) selected from:

- temperature of the set of metal in the molten state (5) and metal materials not yet molten (36) inside the furnace (1 );

- temperature of the metal in the molten state (5) inside the furnace (1 );

- temperature of exhaust gas from the furnace;

- composition or concentrations of exhaust gas from the furnace;

- temperature of cooling water from the electric arc furnace.

Likewise, the method according to the invention can correspondingly provide phases of acquisition of such measuring signals (37).

After establishing which actions should be undertaken based on the measure of the melting condition of the recycled metal materials inside the melting furnace (1 ), the control unit (1 2) can, for example, control one or more actions between:

- starting of the stirrer (2), if present or integrated in the system;

- increase or decrease or anyway adjustment of the systems for providing melting heat, such as an increase or a decrease or anyway an adjustment in the power of the electrodes (4) in case of application on an electric arc furnace, an increase or a decrease or anyway an adjustment in the intensity of the burners;

- increase or decrease or anyway adjustment of gas injection units arranged to supply gas to the molten material, such as oxygen or other gases;

- increase or decrease or anyway adjustment of carbon powder supply units.

Likewise, the method according to the invention can further comprise a control phase of control means for controlling the indicated devices or units, such as systems for providing melting heat for increasing or decreasing or adjusting the heat provided to the set of metal in the molten state (5) and metal materials not yet molten (36) in the furnace (1 ), gas injection units arranged to supply gas to the molten material for increasing or decreasing or adjusting the gas quantity, carbon powder supply units for the supply to the metal in the molten state for increasing or decreasing or adjusting the carbon powder quantity. The control phase of control means of such devices can be a control phase in which the control of the devices occurs based on at least the electrical conductivity or resistivity values of the metal materials inside the furnace (1 ) or based on at least the calculated melting condition of the metal materials inside the furnace (1 ).

In general, the control unit (1 2) can provide control signals (40) to the communication interface (39) with the management system of the furnace (1 ) and of the melting process.

In the case of a detection system (3) made as an independent system with respect to the body of a stirrer (2), the detection system (3) is preferably made (Fig. 1 5, Fig. 1 6) in the form of a sealed closed body made up of a set of cover elements (41 ) constituting the casing (1 7) of the detection system.

In the embodiment shown, the detection system (3) comprises one single row of six coils (1 9) of the detection system, which are arranged after one another according to a direction of development along a longitudinal axis (42) of the detection system (3) that essentially corresponds to the direction of longitudinal development of the furnace (1 ) or to the preferred direction of the stirring induced by the stirrer (2) in the metal in the liquid state of the steel bath facing the tapping hole (1 0) of the furnace (1 ).

It will be evident to a person skilled in the art that it will be possible to provide alternative solutions with multiple parallel rows of coils (1 9) of the detection system, alternative solutions with a greater or smaller number of coils (1 9) of the detection system arranged on one single row of coils or on multiple parallel rows of coils, coils (1 9) of the detection system each consisting of more than one coil arranged in a reciprocally overlapping condition. For example, there may be solutions with (Fig. 1 8) two parallel rows of coils (1 9) of the detection system.

The coils (1 9, 1 9’, 1 9”, 1 9n) of the detection system are made with copper wire wound on a non-magnetic and non-conductive core. It is not necessary to cool the coils, because the current density is low and also the supply of each coil is not continuous. Therefore, in an embodiment, the detection system (3) is made in the form of a body containing the coils (1 9, 1 9', 1 9") of the detection system, wherein the body of the detection system (3) is devoid of a respective cooling system.

In an embodiment the dimensions in length or width of the coils can be substantially comparable to the length of the coils (1 8) of the stirrer (2), if present.

The series of coils (1 9) of the detection system is arranged in the vicinity of the bottom of the furnace (1 ) and, in the preferred embodiment of the present invention, each of the coils (1 9) of the detection system is alternatively used as a transmission coil and as a reception coil, although it will be evident to a person skilled in the art that it will be possible to provide solutions in which a first series of coils (1 9) of the detection system is exclusively intended to be used as a series of transmission coils and a second series of coils (1 9) of the detection system is exclusively intended to be used as a series of reception coils. The first of the two solutions will be described in the following, it being evident that an extension is possible should one consider the second of the two solutions as defined herein.

For example, in a first phase (Fig. 1 1 ), a first coil (1 9') of the detection system is used as a transmission coil and generates a corresponding measuring field (22). One or more second coils (1 9") of the detection system are used as reception coils and receive a corresponding reception signal due to the response to the measuring field (22) induced by the presence of the set of metal in the molten state (5) and metal materials not yet molten (36) inside the furnace (1 ). In general (Fig. 1 3) any generic coil (1 9n) of the detection system in an“n” phase of the measuring process can be used as a transmission coil, while the remaining coils (1 9) of the detection system except for the generic coil ( 1 9n) will be used as reception coils.

With reference to the measurement of the melting condition of the material contained inside the furnace (1 ), which, in general, can consist of a set of metal in the molten state (5) and metal materials not yet molten (36), the detection system (3) measures the electrical conductivity of the material contained inside the furnace ( 1 ), more particularly it measures and reconstructs a volumetric distribution of the electrical conductivity of the material contained inside the furnace (1 ).

The measuring method is based on the injection of a sinusoidal current onto one or more coils (1 9) of the detection system configured as transmission coils. When the sinusoidal current is injected into the coil, it generates a magnetic field in the space, indicated as measuring field (22). The magnetic field generated by the transmission coil generates an induced voltage or electromotive force onto the coils (1 9) of the detection system configured as reception coils. The induced voltage or electromotive force is affected by the presence of the spatial distribution of electrical conductivity in the measuring field (22), which in turn is affected by the presence in the measuring field (22) both of metal in the molten state (5) and of metal materials not yet molten (36). Since for all metals electrical conductivity is a function of temperature and, in particular, it decreases monotonously until reaching the molten condition of the metal, the detection system (3), by measuring the electrical conductivity of the material contained inside the furnace (1 ), is able to provide information or a measure of the melting state of the material contained inside the furnace (1 ), thus being able to indicate the presence or non-presence of metal materials not yet molten (36) or being able to provide information about a quantity ratio of metal in the molten state (5) versus metal materials not yet molten (36).

As previously explained, it will be possible to provide solutions of the detection system (3) and of the related detection method in which each of the coils (1 9) of the detection system is alternatively used as a transmission coil and as a reception coil, or solutions in which a first series of coils (1 9) of the detection system is exclusively intended to be used as a series of transmission coils and a second series of coils (1 9) of the detection system is exclusively intended to be used as a series of reception coils.

Considering the first case, which is the most complex, the second case, too, will be readily clear to a person skilled in the art. The transmission coil is periodically changed so as to cover the whole number of available coils (1 9) of the detection system. For each transmission, phases and amplitudes of the electrical signal picked up by the coils (1 9) of the detection system, in this phase configured as reception coils, are recorded. The complete data set so obtained is indicated by the term "scan". For example, in order to periodically change the transmission coil among the available coils ( 1 9) of the detection system and to correspondingly use the remaining coils (1 9) of the detection system as reception coils, it is possible to use a multiplexer device (43).

The processing system (26) can, for example, comprise acquisition and digital conversion systems of the electrical signals picked up by the coils (1 9) of the detection system. Based on the scans made, it is then possible to proceed in different ways, either simultaneously or alternatively:

- calculating an overall percentage value indicating a quantity ratio of metal in the molten state (5) versus metal materials not yet molten (36) of the material inside the furnace

O );

- obtaining a two-dimensional or three-dimensional map of the measured conductivity of the material contained inside the furnace (1 ).

The first way allows obtaining an immediate evaluation value of the melting condition that can be easily used for managing the previously explained actions to be undertaken.

The second way allows obtaining a visual representation of the situation inside the furnace (1 ) from which it is possible not only to have a general picture of the melting condition, but also to find out any problems, such as the presence of large-sized metal materials not yet molten (36). In this case, too, it will be possible to provide suitable actions to be undertaken, which have been previously explained. For example, if it is found out that large-sized metal materials not yet molten (36), which are harder to be molten, are still present, it will be possible to direct the burners towards the zone indicated by the map or it will be possible to perform localized carbon or oxygen injections, or it will be possible to intervene on the power of the electrodes if the system is used in an electric arc furnace.

Preferably, the distribution of the coils (1 9) of the detection system is planar with an arrangement on a plane following the lower profile of the wall of the furnace (1 ) in such a way that the coils (1 9) of the detection system are arranged on the deposition surface according to a configuration such as to have an approximately constant distance between the detection system (3) and the furnace (1 ) in correspondence of the measuring area corresponding to the deposition surface of the coils (1 9) of the detection system.

For the processing of the scan of the signals made by means of the coils (1 9) of the detection system, for example, it will be possible to resort to a processing process in which

- a direct model is created based on the electromagnetic model y=F(s) of the detection system (3) also comprising the effect due to the presence of the furnace (1 ) and optionally of the stirrer (2), if present. In order to create this model one can use Maxwell's equations for the electromagnetic field, as it is known to a person skilled in the art. In particular“s” represents the electrical conductivity or the spatial distribution of electrical conductivity, which is the final physical quantity that one wishes to obtain for detecting the melting state of the metal materials (5, 36) inside a melting furnace (1 ). In particular“y” represents the measure actually obtained from the detection system (3), that is to say, for example, amplitude and phase values of the signal induced onto the coils (1 9, 1 9’, 1 9”, 1 9n) of the detection system. In particular “F” represents the functional, that is to say, the created electromagnetic model, which links to each other “s”, i. e. electrical conductivity or spatial distribution of electrical conductivity, and“y”, i. e. the measure actually obtained from the detection system (3). For example, for the creation of the electromagnetic model it will be possible to use finite element methods (FEM) known to a person skilled in the art;

- the inverse function s=F ^A (-1 )(y) is identified, i. e. the inverse function that allows obtaining the electrical conductivity or the spatial distribution of electrical conductivity starting from the measures actually obtained from the detection system (3), such as the amplitude and phase values of the signal induced onto the coils (1 9, 1 9', 1 9", 1 9n) of the detection system. Since the variations in electrical conductivity between solid metal and molten metal are very limited, such as lower than 1 0%, it is possible to linearize the functional F without introducing excessive errors and to obtain a simplification of the calculation operations. One will thus obtain a relation dy = J ds, in which“J” represents the sensitivity or Jacobian matrix of the electromagnetic model identified by the functional F. The sensitivity or Jacobian matrix J can be calculated beforehand solving the direct model. The variables ds and dy represent the variations in electrical conductivity and the variations in the measures acquired by means of the coils (1 9, 1 9', 1 9", 1 9n) of the detection system, respectively. In order to calculate the sensitivity or Jacobian matrix J, it is necessary to solve the magnetic induction field B distribution inside the measuring area of the detection system (3) namely in the volume in front of the coils (1 9, 1 9', 1 9", 1 9n) of the detection system (3), by means of, for example, the above-mentioned FEM techniques. Once the sensitivity or Jacobian matrix J has been calculated, the problem can be inverted by calculating ds=J ^A (-l )(dy).

This method allows obtaining a map of electrical conductivity in real time, since the calculation of ds=J ^A (-l )(dy) can be performed in times compatible with the melting process.

In practice, the method provides the following phases:

• the direct model is created, consisting of the electromagnetic model of the coils (1 9, 1 9', 1 9", 1 9n) of the detection system and comprising the metals surrounding the coils (1 9, 1 9', 1 9", 1 9n) of the detection system, using for example Maxwell's equations for the electromagnetic field and a FEM modeler;

• in the direct model one also takes into account a predefined quantity of metal in the molten state (5) or a predefined quantity of metal materials not yet molten (36) or a predefined quantity given by a set of metal in the molten state (5) and metal materials not yet molten (36) inside the furnace (1 ), used as a reference parameter for the contents of the furnace (1 );

• one calculates the magnetic field generated by each coil (1 9, 1 9', 1 9", 1 9n) of the detection system in a spatial grid that in a first approximation coincides with the volume of the reference measuring field (22) consisting of the volume occupied by metal in the molten state (5) or a predefined quantity of metal materials not yet molten (36) or a predefined quantity given by a set of metal in the molten state (5) and metal materials not yet molten (36) inside the furnace (Ί );

• the Jacobian matrix Jij is created, whose terms are the scalar product Bi x Bj where the indexes i, j are melt flow indexes along the series of coils (1 9, 1 9', 1 9", 1 9n) of the detection system for the total number of coils of the detection system (3);

• given the measures dy, i. e. the variations in the measures acquired by means of the coils (1 9, 1 9', 1 9", 1 9n) of the detection system, ds=J ^A (-1 )(dy) is calculated;

• the approximate solution is s = sO + ds, where sO represents the conductivities of the predefined quantity of metal in the molten state (5) or a predefined quantity of metal materials not yet molten (36) or a predefined quantity given by a set of metal in the molten state (5) and metal materials not yet molten (36) inside the furnace (1 ), used as a reference quantity. However, the value of sO is a constant value, which is simply taken into account, as will be evident to a person skilled in the art and which, for practical purposes, can be ignored.

At the end of the processing of the signals one obtains a tomographic spatial map of the electrical conductivity distribution from which it is possible to distinguish the different melting states of the material contained inside the furnace (1 ) thus identifying the presence of metal materials not yet molten (36) in the metal in the molten state (5) inside the furnace (1 ). In fact, for all metals, electrical conductivity is a function of temperature and in particular it decreases monotonously up to the liquid state. The use of the described detection system (3) in combination with two-dimensional or three- dimensional methods for calculating the electrical conductivity distribution allows obtaining the electrical conductivity distribution of the material contained inside the furnace (1 ) in a given moment as a function of the thermal state of the metal. The so defined detection system (3) can be considered as a tomograph realizing the system and method for measuring the melting condition of the metal materials inside the melting furnace (1 ) and such detection system or method (3) can be used in combination with a stirrer (2) for stirring the metal in the molten state (5) inside the furnace (1 ) realizing the system and method for measuring and stirring the metal materials inside the melting furnace (1 ).

With reference to the installation of the detection system (3) on the furnace (1 ), it is necessary to consider that the electromagnetic field generated by the transmission coils (1 9) of the detection system must penetrate the stainless steel shell constituting the wall (7) of the furnace (1 ), cross the layer of refractory material (8) and penetrate the metal that is just behind. For this reason, sinusoidal signals of radio-frequency transmission are not suitable for the purpose and, therefore, the signal generator (23) is a low-frequency signal generator, in particular a low-frequency signal generator intended to generate a sinusoidal signal having a frequency between 0.1 Hz and 5.0 Hz. The transmission sinusoidal signals, with which the transmission coils (1 9) of the detection system are supplied, are sinusoidal signals having a frequency between 0.1 Hz and 5.0 Hz, preferably in the order of 0.5 Hz-1 .5 Hz.

It will also be possible to provide sequences of measuring phases in which the frequency of the transmission signal sent to the transmission coils (1 9) of the detection system (3) is modified from one phase to the following one in such a way as to make evaluations about conductivity by operating with electromagnetic fields having different penetration depths, allowing to obtain a higher measurement precision.

In the particular case in which the detection system (3) operates on a furnace (1 ) that is not provided with an electromagnetic stirrer (2), the measurement by means of the detection system (3) can be performed continuously during the melting process.

In the particular case in which the detection system (3) operates on a furnace (1 ) that is provided with an electromagnetic stirrer (2), the measurement by means of the detection system (3) can be performed continuously during the initial melting process when the stirrer (2) is in an off condition. Following the detection by the detection system (3) of a melting condition sufficient to allow the activation of the stirrer. (2), since the detection system (3) and the stirrer (2) operate at frequencies that are close to each other, there may be problems of interference with the measurement by the very intense electromagnetic fields generated by the stirrer (2). In this case the integrated measuring and electromagnetic stirring system and method can provide alternating phases, in which measuring phases by means of the detection system (3) enabled and the stirrer (2) off are alternated with stirring phases with the detection system (3) disabled and the stirrer (2) on. One can provide predefined measuring intervals alternated with longer periods of operation of the stirrer (2). In this way it is possible to measure the evolution of the electrical conductivity distribution over time. The electrical conductivity distribution will have a time trend that will reflect the melting state of the material contained inside the furnace (1 ). According to the measurements carried out after the first start of the stirrer (2), the detection system can provide measures of conductivity of the molten material or of the material being molten that will be useful for the control unit (1 2), for example, to control an increase in the intensity of the electromagnetic stirring field produced by the stirrer (2), for example, by increasing the intensity of the current of the stirrer (2).

As previously explained, the detection system (3) can provide a two-dimensional or three-dimensional image of the electrical conductivity volume, which at all times will be compared with an objective value. The stirrer (2) will be activated only upon reaching this threshold. At predefined intervals, the electromagnetic stirrer will thus be deactivated to enable measurement without interferences and, afterwards, will be re-activated to check the progress of melting until all the parameters of the process, including the parameter of the melting state of the materials, will be within the expected values in order to perform the casting of the material out of the furnace (1 ) for its subsequent use in the production lines downstream of the furnace.

There can also be an additional phase of identification of a starting or activation condition of the stirrer (2) after reaching a melting condition of the set of metal in the molten state (5) and metal materials not yet molten (36) inside the furnace (1 ), for example by calculating an average conductivity value, <ds>, to be compared with a predefined threshold value for starting the stirrer (2). By average value one means an average value in the measuring volume.

To conclude, the present invention relates (Fig. 1 , Fig. 2, Fig. 3, Fig. 4, Fig. 7, Fig. 8, Fig. 9, Fig. 1 0, Fig. 1 3) to a detection system (3) of a melting state of metal materials (5, 36) for detecting the melting state of the metal materials (5, 36) inside a melting furnace (1 ). The metal materials generally consist of a set of metal in the molten state (5) and metal materials not yet molten (36). The detection system (3) comprises at least one series of coils (1 9, 1 9', 1 9") in which each of the coils (1 9, 1 9', 1 9") consists of one or more windings closed in a loop configuration on a winding plane (45) of the coil. The series of coils (1 9, 1 9', 1 9") comprises (Fig. 1 1 , Fig. 1 2, Fig. 1 3) at least one first coil (1 9') of the detection system configured as a transmission coil and at least one second coil (1 9") of the detection system configured as a reception coil, the first coil (1 9') being connected to a transmission system (24) configured to amplify a transmission sinusoidal signal generated by a signal generator (23). The transmission system (24) is configured to supply to the at least one first coil (1 9') the amplified transmission sinusoidal signal for the generation of a measuring field (22) for the interaction with the metal materials inside the furnace (1 ). The at least one second coil (1 9") is configured to receive a generated reception signal as resulting from eddy currents induced by the measuring field (22) on the metal materials inside the furnace ( 1 ). The at least one second coil (1 9") is connected to a reception system (25) configured to convert the reception signal into reception data and to send the reception data to a control unit (1 2). The detection system (3) is applied in correspondence of the bottom wall (7) of the melting furnace in such a way that the electromagnetic field generated by the at least one first coil (1 9') is a field penetrating the wall (7) of the furnace (1 ) and crossing the layer of refractory material (8) for the penetration of the metal materials inside the furnace (1 ) and for contact-less measurement, the series of coils (1 9, 1 9', 1 9") being arranged (Fig. 1 4, Fig. 1 5, Fig. 1 6, Fig. 1 7, Fig. 1 8) on a deposition surface (44), wherein the deposition surface is arranged according to a planar or essentially planar or arched configuration or a configuration made up of reciprocally slightly inclined deposition planes, wherein the winding plane (45) of the coils is parallel to the deposition surface (44) of the coils (1 9, 1 9', 1 9"), the coils (1 9, 1 9', 1 9") being arranged after one another on the deposition surface (44) forming at least one measuring zone hit by the measuring field (22) that is arranged parallel to the deposition surface (44) of the coils (1 9, 1 9', 1 9") and orthogonally spaced apart from the deposition surface (44). The transmission coil and the at least one reception coil are not facing each other on opposite sides of the metal materials inside the furnace (1 ), but are arranged on the same deposition surface (44) facing the metal materials inside the furnace (1 ) and the deposition surface (44) is arranged externally below the furnace (1 ) in such a way that the measuring field (22) is in a zone essentially parallel to the deposition surface (44) and inside the furnace (1 ), due to the fact that the generated electromagnetic field crosses the wall (7) of the furnace (1 ) and the layer of refractory material (8) of the furnace (1 ). The control unit (1 2) comprises first calculation means for calculating electrical conductivity or resistivity values of the metal materials inside the furnace (1 ) as a function of or starting from the reception data and the control unit (1 2) comprises second calculation means for determining the melting condition of the metal materials inside the furnace (1 ) as a function of or starting from the electrical conductivity or resistivity values of the metal materials (5, 36) inside the furnace.

The deposition surface (44) can be made up of deposition planes arranged after one another, wherein each plane is inclined with respect to the following one by an angle between 1 60° and 1 80° or can be an arched surface such as an arched surface in which the ratio between the bending radius and the length of the arc constituting the deposition surface (44) is between 1 .5 and 2.1 or, in general, an arched surface that follows the bottom of the furnace (1 ) in correspondence of which it is installed, i. e. having a bending corresponding to the bending of the lower part of the furnace (1 ).

In an embodiment (Fig. 1 1 , Fig. 1 2, Fig. 1 3) the detection system (3) of the melting condition of metal materials inside a melting furnace (1 ) comprises a multiplexer device (43), which is configured for the connection of the transmission system (24) of a sinusoidal signal alternatively to a different coil selected from the coils of the series of coils (1 9, 1 9', 1 9") in such a way as to change the transmission coil among the coils of the series of coils (1 9, 1 9', 1 9") for the generation of the measuring field (22) in different measuring zones. The multiplexer device (43) can be configured for the sequential switching of the connection of the transmission system (24) between adjacent coils of the series of coils (1 9, 1 9', 1 9") and correspondingly for the sequential switching of the connection of the reception system (25) among coils of the series of coils (1 9, 1 9', 1 9") with the exclusion of the transmission coil. The detection system (3) can be configured according to configurations in which:

- the control unit (1 2) comprises processing means for calculating an overall percentage value indicating a quantity ratio of metal in the molten state (5) versus metal materials not yet molten (36) of the material inside the furnace (1 );

- the detection system (3) is a tomographic detection system (3) in which the control unit (1 2) comprises processing means for processing the electrical conductivity or resistivity values of the metal materials inside the furnace (1 ), wherein the processing means for processing the electrical conductivity or resistivity values are intended to output a two-dimensional or three-dimensional map of the measured conductivity of the material contained inside the furnace (1 ) and consisting of the set of metal in the molten state (5) and metal materials not yet molten (36).

The present invention also relates to a detection and stirring system (20) comprising a detection system (3) for detecting a melting state of metal materials inside a melting furnace (1 ) and an electromagnetic stirrer (2) for the electromagnetic stirring of the metal materials inside the furnace (1 ), wherein the electromagnetic stirrer (2) comprises at least one respective series of coils (1 8) of the stirrer in which each of the coils (1 8) of the stirrer consists of one or more windings closed in a loop configuration on a respective winding surface, wherein the detection system (3) comprises at least one series of coils (1 9, 1 9', 1 9"), the series of coils (1 9, 1 9', 1 9") comprising at least one first coil (1 9') configured as a transmission coil and at least one second coil (1 9") configured as a reception coil, the first coil (1 9') being connected to a transmission system (24) of a sinusoidal signal for driving at least one first coil (1 9') for the generation of a measuring field (22) for the interaction with the metal materials inside the furnace (1 ), the at least one second coil (1 9") being configured to receive a generated reception signal as resulting from eddy currents induced by the measuring field (22) on the metal materials inside the furnace (1 ), the at least one second coil (1 9") being connected to a reception system (25) for sending reception data of the reception signal to a control unit (1 2), wherein the detection system (3) is a detection system (3) of the melting condition of metal materials inside a melting furnace (1 ) as previously described and the control unit comprises control means for controlling the electromagnetic stirrer (2) for the electromagnetic stirring of the metal materials inside the furnace (1 ).

Furthermore the present invention relates to a detection method of a melting condition of metal materials for detecting the melting state of the metal materials inside a melting furnace (1 ), wherein the method provides the following phases:

a) positioning of an electromagnetic detection system (3) in the vicinity of a measuring zone for the generation of a measuring field (22) on the metal materials inside the furnace (1 ), wherein the detection system (3) comprises at least one series of coils (1 9, 1 9', 1 9") in which each of the coils (1 9, 1 9', 1 9") consists of one or more windings closed in a loop configuration on a winding plane (45), the series of coils (1 9, 1 9', 1 9") comprising at least one first coil (1 9') configured as a transmission coil and at least one second coil (1 9") configured as a reception coil;

b) generation of the measuring field (22) for the interaction with the metal materials inside the furnace (1 ), the generation of the measuring field (22) occurring by driving the at least one first coil (1 9') with a sinusoidal signal;

c) reception, by the at least one second coil (1 9"), of a generated reception signal as resulting from eddy currents induced by the measuring field (22) on the metal materials inside the furnace (1 );

d) conversion of the reception signal into reception data; e) sending of the reception data to a control unit (1 2)

The phase of generation of the measuring field (22) is a phase of generation of an electromagnetic field in a measuring zone that is subject to the measuring field (22) and that is arranged parallel to a deposition surface (44) of the series of coils (1 9, 1 9', 1 9") on which both the at least one transmission coil and the at least one reception coil are arranged, the phase of generation of the measuring field (22) comprising a phase of penetration of the measuring field (22) up to the measuring zone subject to the measuring field (22) which is orthogonally spaced from the deposition surface (44) in such a way that the measuring field (22) penetrates up to the metal materials inside the melting furnace (1 ), the phase of reception being a phase of reception of the generated reception signal as resulting from eddy currents induced by the measuring field (22) on the metal materials inside the furnace ( 1 ), which occurs by means of the reception coil that is arranged on the same deposition surface (44) as the transmission coil in which the winding plane (45) is parallel to the deposition surface (44), the coils (1 9, 1 9', 1 9") being arranged after one another on the deposition surface (44).

The method further comprises:

i) a first calculation phase by the control unit (1 2) wherein the first calculation phase is a calculation phase for calculating electrical conductivity or resistivity values of the metal materials inside the furnace (1 ) starting from the reception data;

ii) a second calculation phase by the control unit (1 2) wherein the second calculation phase is a phase of determination of the melting condition of the metal materials inside the furnace (1 ) starting from the electrical conductivity or resistivity values of the metal materials inside the furnace (1 ).

The detection method can comprise a switching phase by means of a multiplexer device (43), the switching phase being a switching phase in which the transmission system (24) of the sinusoidal signal is alternatively connected to a different coil selected from the coils of the series of coils (1 9, 1 9', 1 9") in such a way as to change the transmission coil among the coils of the series of coils (1 9, 1 9', 1 9") for the generation of the measuring field (22) in different measuring zones. Furthermore, in an embodiment, the detection method can have a switching phase that is a phase of sequential switching of the connection of the transmission system (24) between adjacent coils of the series of coils (Ί 9, 1 9', 1 9") and correspondingly for the sequential switching of the connection of the reception system (25) among coils of the series of coils (1 9, 1 9', 1 9") with the exclusion of the transmission coil.

In the embodiment in which the detection system (3) comprises (Fig. 1 8) two series of coils (1 9, 1 9', 1 9") of the detection system, the switching phase can comprise a subphase of switching between the two series of coils (1 9, 1 9', 1 9") of the detection system arranged on two parallel rows of coils (1 9) of the detection system.

The phase of determination of the melting condition of the metal materials inside the furnace (1 ) can be a phase of calculation of an overall percentage value indicating a quantity ratio of metal in the molten state (5) versus metal materials not yet molten (36) of the material inside the furnace (1 ).

The calculation phase of electrical conductivity or resistivity values of the metal materials inside the furnace (1 ) can be carried out by means of a tomographic calculation method in which there is a processing phase of the electrical conductivity or resistivity values of the metal materials inside the furnace (1 ) in such a way as to output a two-dimensional or three-dimensional map of the measured conductivity or resistivity of the material contained inside the furnace (1 ) and consisting of the set of metal in the molten state (5) and metal materials not yet molten (36). The tomographic calculation method can comprise the following phases:

- calculation of a direct model based on an electromagnetic model y=F(s) of the detection system (3) in which “s” represents the electrical conductivity or the spatial distribution of electrical conductivity, “y” represents a measure actually obtained from the detection system (3), “F” represents a functional that links to each other the electrical conductivity or spatial distribution of electrical conductivity and the measure actually obtained from the detection system (3); - identification of an inverse function s=F ^A (-1 )(y) for obtaining the electrical conductivity or the spatial distribution of electrical conductivity starting from the measures actually obtained from the detection system (3);

- calculation of the two-dimensional or three-dimensional map of the measured conductivity or resistivity of the material contained inside the furnace (1 ) by means of the inverse function F ^A (-1 ) and of the measures actually obtained y from the detection system (3).

The phase of identification of the inverse function s=F ^A (-1 )(y), for obtaining the electrical conductivity or the spatial distribution of electrical conductivity starting from the measures actually obtained from the detection system (3), can occur by means of a phase of linearization of the functional F obtaining a relation dy = J ds, in which “J” represents a sensitivity or Jacobian matrix of the electromagnetic model identified by the functional F, ds and dy being variations in electrical conductivity and variations in the measures acquired by the coils (1 9, 1 9’, 1 9”, 1 9n) of the detection system, respectively. It is also possible to have a calculation phase of the sensitivity or Jacobian matrix J by means of a finite elements modelling technique.

Furthermore, the present invention relates to a detection method for detecting a melting condition of metal materials inside a melting furnace (1 ) and for the electromagnetic stirring of the metal materials inside the melting furnace (1 ), wherein the method comprises a phase of starting of an electromagnetic stirrer (2) for the electromagnetic stirring of the metal materials inside the melting furnace (1 ), the phase of starting of the electromagnetic stirrer (2) occurring after:

- at least one initial detection phase of the melting condition of metal materials inside the furnace (1 ) obtaining a detected condition of the melting condition of metal materials inside the furnace (1 ), and

- at least one comparison phase with positive result between a desired minimum condition of the melting condition of metal materials inside the melting furnace (1 ) and the detected condition of the melting condition of metal materials inside the furnace (1 ) The at least one initial detection phase of the melting condition of metal materials inside the furnace (1 ) occurs by means of the detection method of a melting condition of metal materials as previously described.

Furthermore, the detection method for detecting a melting condition of metal materials inside a melting furnace (1 ) and for the electromagnetic stirring of the metal materials inside the melting furnace (1 ), after the phase of starting of an electromagnetic stirrer (2) for the electromagnetic stirring of the metal materials inside the melting furnace (1 ), comprises switching phases between:

- phases of stopping of the electromagnetic stirrer (2) in which further following phases of additional detection of the melting condition of metal materials inside the furnace (1 ) are carried out obtaining following detected melting conditions of metal materials inside the furnace (1 ), and

- phases of re-starting of the electromagnetic stirrer (2);

the switching phases between the phases of stopping of the stirrer (2) and additional detection and the phases of re-starting of the stirrer (2) being repeated until obtaining a final desired condition of the melting condition or composition of the metal materials inside the furnace (1 ).

The detection method for detecting a melting condition of metal materials inside a melting furnace (1 ) and for electromagnetic stirring can also comprise calculation phases of power and frequency for starting the stirrer (2) for the application of new power and frequency values for starting the stirrer (2) in said phases of re-starting of the electromagnetic stirrer (2).

The present invention also relates to a melting furnace (1 ) for melting metal materials that comprises a detection system (3) of the melting condition of metal materials inside a melting furnace (1 ) as previously described.

The present invention also relates to a melting furnace (1 ) for melting metal materials that comprises an electromagnetic stirrer (2) for the electromagnetic stirring of the metal materials inside the furnace (1 ), wherein the furnace comprises a detection and stirring system (20) as previously described.

The description of the present invention has been made with reference to the enclosed figures in a preferred embodiment, but it is evident that many possible changes, modifications and variations will be immediately clear to those skilled in the art in the light of the foregoing description. Thus, it should be understood that the invention is not limited to the foregoing description, but embraces all such changes, modifications and variations in accordance with the appended claims.

Nomenclature used

With reference to the identification numbers reported in the enclosed figures, the following nomenclature has been used:

1 . Furnace

2. Stirrer

3. Detection system

4. Electrodes

5. Metal in the molten state

6. Direction of movement

7. Wall

8. Refractory material

9. Force field

1 0. Tapping hole

1 1 . Cooling station

1 2. Control unit

1 3. Junction box

1 4. Fluid direction

Ί 5. Fluid control system

1 6. Casing of the stirrer

1 7. Casing of the detection system

1 8. R, S, T. Coil of the stirrer 1 9. Coil of the detection system

1 9'. First coil of the detection system 1 9". Second coil of the detection system 1 9n. n coil of the detection system

20. Detection and stirring system

21 . Fluid circuit ducts

22. Measuring field

23. Signal generator

24. Transmission system

25. Reception system

26. Processing system

27. Measuring device

28. Closing element

29. Capsule

30. Fluid circuit coupling

31 . First electrical connection

32. Second electrical connection

33. Third electrical connection

34. Base

35. Longitudinal axis of the stirrer

36. Metal material not yet molten

37. Further measuring signals

38. Sensor

39. Communication interface

40. Control signal

41 . Cover element

42. Longitudinal axis of the detection system

43. Multiplexer device 44. Deposition surface

45. Winding plane S. Space

D. Distance