WO2021176486A1

WO2021176486A1 - Induction heating method and apparatus

Info

Publication number: WO2021176486A1
Application number: PCT/IT2021/050049
Authority: WO
Inventors: Alessandro Tonelli
Original assignee: Teknel S.R.L.
Priority date: 2020-03-05
Filing date: 2021-03-05
Publication date: 2021-09-10
Also published as: EP4115707A1; IT202000004723A1

Abstract

Embodiments concern an induction heating method and apparatus. The induction heating method provides to power an inductor connected to, or provided on, a heating head of an induction heating device by means of an alternating electric current so as to generate an alternating electromagnetic field. The method also provides to position a metal element to be heated in the alternating electromagnetic field generated by the inductor and to heat the metal element by Joule effect by inducing parasitic currents in it. The induction heating apparatus comprises a heating device provided with a heating head suitable to be positioned, during use, in the proximity of, or in contact with, a metal element to be heated. The heating head comprises, or is connected to, a coil, or inductor, formed by a plurality of spirals to be passed through by an electric current and to generate an electromagnetic field suitable to generate parasitic currents in the metal element located in proximity, so as to heat it. The apparatus also comprises a generator that can be connected to an electric power supply network and is suitable to supply an alternating current with desired intensity and frequency to the inductor.

Description

“INDUCTION HEATING METHOD AND APPARATUS”

FIELD OF THE INVENTION

Embodiments described here concern an induction heating method and apparatus. The heating apparatus of the type discussed can be used, for example, in the industrial, manufacturing or mechanical field, where it is required to heat a metal element by electromagnetic induction.

In particular, the heating apparatus according to the invention can be used to weld, unsolder, straighten, deform, heat or harden metal elements.

BACKGROUND OF THE INVENTION

Different types of heating devices are known, suitable to heat metal elements, including electromagnetic induction heating devices, resistive heating device or by burning a fuel and generating flames.

Thanks to their functional and structural characteristics, these electromagnetic induction heating devices are normally preferred over resistive heating devices or devices using flames.

Known induction heating devices are normally provided with a power supply unit which is configured to generate an alternating electric current at a frequency comprised between 10 kHz and 50 kHz.

The alternating electric current is used to generate an alternating magnetic field in a heating mean of the device, which induces parasitic currents in the metal element located in proximity or in contact with the device.

The parasitic currents generate in the metal element a rise in temperature due to the Joule effect, functionally dependent on the power actually transmitted from the power supply unit to the heating mean.

One of the main problems related to known induction heating devices is that it is difficult to provide a control, or simply a reliable detection, of the temperature of the metal element during heating.

One of the known solutions to provide a temperature detection consists in applying temperature sensors in contact with the metal element to be heated.

The main disadvantage of this solution is that the temperature signal detected by the sensor can be distorted by the electromagnetic field and/or by the heat reached in the areas to be heated which, in some cases, can be such as to damage the sensor itself, compromising its correct functioning.

Furthermore, a measurement carried out using a sensor which is in contact with the surface of the element provides information relating to the contact area of the sensor, and possibly to the immediately adjacent areas.

Another known solution provides to detect the temperature of the heated metal element by means of infrared measurement systems.

This solution is particularly inconvenient due to the fact that establishing a stable line of sight between the infrared sensor and the metal element is particularly complicated, if not impossible in practice.

Another disadvantage is that, if the area of interest of the temperature measurement is in a surface of the heated element that is difficult to reach, or if it is inside the element itself, the temperature information, detected by means of the known solutions as above, can be distorted by the thickness and/or the geometry of the element.

In fact, the heat, which is very intense near the magnetic field, propagates according to the characteristics of the metal, so thicknesses of 6-7 mm generally have considerable temperature differences on both sides.

In this case, with regard to the type of metal, and the thickness of the element to be heated, it may happen that on the surface opposite that on which the temperature is being detected, the metal may reach melting point before the required temperature is reached on the detection side.

In particular, in known solutions it is almost impossible to correctly detect the temperature below the inductor. Contact-type detection systems, in fact, cannot be inserted below the inductor and would in any case be strongly conditioned by the powerful magnetic fields in order to obtain a reliable measurement. Even optical detection systems are not able to take readings below the inductor, and moreover, they entail a delay in the detection, so that, in the time that passes between the movement of the inductor and the temperature reading, the value of the latter is by now much lower than the maximum peak reached, and the measurement carried out is therefore not correct.

There is therefore a need to perfect an induction heating method and apparatus which can overcome at least one of the disadvantages of the state of the art.

In particular, one purpose of the present invention is to provide an induction heating method and apparatus capable of providing a temperature measurement that is not distorted by the magnetic field and/or by the heat present in the measurement zone.

Another purpose is to provide a method and an apparatus to detect and regulate the temperature of a metal element heated by means of an induction heating device, which are effective and economical.

Another purpose of the present invention is to provide a method and an apparatus which allow to detect and regulate the temperature of a metal element, heated by means of an induction heating device, in areas located inside it or on its surfaces which are unlikely to lend themselves to a temperature measurement.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION The present invention is set forth and characterized in the independent claims. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

In accordance with the above purposes, an induction heating method and apparatus are provided which overcome the limits of the state of the art and eliminate the defects present therein.

An induction heating apparatus of the type in question comprises a heating device provided with a heating head suitable to be positioned, during use, in the proximity of, or in contact with, a metal element to be heated. The heating head can comprise, or be connected to, a coil, or inductor, formed by a plurality of spirals configured to be passed through by an electric current and generate an electromagnetic field.

The heating device also comprises electrical energy supply means that can be connected to an electric power supply network and are suitable to supply the inductor with an alternating current with desired intensity and frequency. The alternating electromagnetic field generated by the inductor is in turn suitable to generate parasitic currents in a metal element located in the proximity, so as to obtain a heating of the metal element due to the Joule effect.

In the case of ferromagnetic materials, moreover, it is possible to obtain a heating of the metal material also due to hysteresis phenomena.

According to some embodiments, the heating apparatus comprises at least one detection device configured to detect the values of at least one electrical quantity correlated to the electrical energy supplied by the generator to the inductor.

According to preferred embodiments, the detection device comprises a current intensity sensor and a phase sensor.

According to other embodiments, a plurality of detection devices can be provided, disposed along the electrical circuit between the generator and the induction head, for example associated with the generator, the amplification unit, or other circuit components.

The heating apparatus can also comprise a processing unit connected to the at least one detection device and to the induction heating device.

The processing unit can be configured to receive the values detected by the detection device, and process them in order to compare them with reference values, and identify whether the Curie temperature has been reached in the metal element heated by means of the induction heating device.

The receiving and processing of the data are preferably carried out in real time, so as to be able to promptly intervene on the heating device as soon as it is detected that the Curie temperature has been reached, and prevent the metal element from overheating in an unwanted manner.

In particular, the processing unit monitors the trend of the intensity and phase values of the electric current in the inductor, in order to identify when a variation occurs in them, correlated to a variation in the magnetic properties of ne metal element, and to recognize when the metal element reaches its Curie temperature.

According to some embodiments, the processing unit is configured to control, either directly or by means of a control and command unit, the functioning of the heating device, as a function of the estimated temperature and a set temperature value to be obtained.

According to some embodiments, the apparatus is configured to implement a heating method according to the present invention, as will be described below.

In accordance with some embodiments, a method for the induction heating of a metal element is provided, which provides to:

- power an inductor connected to, or provided on, a heating head of an induction heating device by means of an alternating electric current so as to generate an alternating electromagnetic field;

- position a metal element to be heated in the electromagnetic field generated by the inductor and heat the metal element by Joule effect by inducing parasitic currents in it;

- detect at least one value of at least one electrical quantity correlated to the electrical energy supplied by the inductor;

- process the actual values detected by the detection device and compare them with reference values in order to determine possible deviations from the reference values in order to identify possible changes in at least one electrical quantity correlated to a variation in the magnetic properties of the heated metal element;

- estimate the temperature of the metal element on the basis of the comparison between the values detected and the reference values. In some embodiments, the at least a value of at least one electrical quantity correlated to the electrical energy supplied by the inductor can be selected from the values of current intensity, voltage, frequency and phase of the alternating electric current circulating in the inductor.

Advantageously, in this way the measurement is not distorted by the electromagnetic field or by the heat generated in the heated metal element, even if it depends on the temperature of the metal element being worked, and varies clearly when the Curie temperature is reached.

The measurement therefore exploits the Curie effect, whereby some magnetic and/or electromagnetic properties of metal materials change after a certain temperature, named Curie temperature, has been exceeded.

In particular, materials that normally exhibit ferromagnetic properties, exhibit paramagnetic properties above the corresponding Curie temperature.

It is also known that every material subjected to the Curie effect has its own characteristic Curie temperature. For example, the Curie temperature for iron Fe is 770°C, and the Curie temperature for nickel Ni is 347°C.

In addition, it is known that in the case of an electromagnetic field applied to a metal element, the values correlated to the electric current that generates this electromagnetic field vary as the metal element passes from the ferromagnetic state to the paramagnetic state, and vice versa.

These values can include, for example, the current intensity, voltage, frequency and phase of the electric current that generates the electromagnetic field in the proximity of the metal element in question.

According to some embodiments, the reference values are values of current intensity, voltage, frequency and phase of the alternating electric current that passes through the inductor previously detected and recorded.

In the embodiments as above, the comparison can consist in detecting possible variations in the last recorded values with respect to the values previously recorded of current intensity, voltage, frequency and phase of the alternating electric current that passes through the inductor.

According to other embodiments, the reference values are predefined values, for example based on tables and graphs and processed by means of a mathematical algorithm implemented in the processing unit.

In the embodiments as above, the comparison can comprise verifying whether or not the values detected fall within a range around the respective reference value. Or the comparison can comprise verifying whether the values detected are greater or lesser than the associated reference value, and possibly quantifying the deviation. According to some embodiments, the method also comprises setting a target temperature to be reached during the heating of the metal element.

In other embodiments, the method also comprises controlling the power supplied to the inductor in order to interrupt, or not, the heating of the metal element on fne basis of the result of the comparison.

In the embodiments as above, the interruption of the heating can take place immediately, the moment in which a significant variation is detected in the values detected with respect to the reference values.

According to possible variants, the interruption of the heating can take place after a predetermined period of time from the moment in which the significant variation is detected in the values detected with respect to the reference values.

In some embodiments, the period of time after which the interruption of the heating occurs is correlated to the target temperature set.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a schematic representation of an embodiment of an apparatus that implements the method according to the present invention.

It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS We will now refer in detail to the possible embodiments of the invention, of which one or more examples are shown in the attached drawing. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, one or more characteristics shown or described insomuch as they are part of one embodiment can be varied or adopted on, or in association with, other embodiments to produce another embodiment. It is understood that the present invention shall include all such modifications and variants.

Before describing these embodiments, we must also clarify that the present description is not limited in its application to details of the construction and disposition of the components as described in the following description using the attached drawings. The present description can provide other embodiments and can be obtained or executed in various other ways. We must also clarify that the phraseology and terminology used here is for the purposes of description only, and cannot be considered as limitative. Fig. 1 shows, by way of example, a heating apparatus 10 according to some embodiments described here, configured to heat a metal element 20 by means of electromagnetic induction. By metal elements 20 we mean, by way of example, elements of any shape and section whatsoever, produced with one or more metals or their alloys, or also an element comprising a conductive material that is capable of admitting electric currents.

According to some embodiments, the metal elements 20 of the type in question can consist of, or comprise, one or more metals having ferromagnetic properties. The apparatus 10 comprises an induction heating device 11 comprising a heating head 12 provided with, or connected to, a coil, or inductor 13, having a plurality of spirals suitable to be passed through by an alternating electric current and configured to generate an alternating magnetic field.

The apparatus 10 can also comprise power supply means suitable to supply electrical energy to the inductor 13.

The apparatus 10 can comprise, in particular, a power supply unit 14 which can be connected, during use, to an electric power supply network 15 which supplies an electric current and voltage, and is configured to transform the mains electric current and voltage into supply current and voltage having desired intensity and frequency values.

The apparatus 10 can also comprise a generator 16, connected downstream of the power supply unit and configured to generate high frequency alternating current waves.

In some embodiments, the generator 16 can comprise one or more inverter devices, or current inverters.

According to some embodiments, an amplification unit 17 can also be provided, disposed and connected between the generator 16 and the inductor 13, and configured to amplify the alternating electric current at exit from the generator 16 so as to supply a desired current and voltage in the inductor 13 which are suitable to generate an electromagnetic field with characteristics suitable for working the metal element 20.

In fact, it is known that in order to suitably heat metal elements 20 made of different metals, or having different thicknesses, it is necessary to use alternating currents with different frequencies.

According to some embodiments, the alternating electric current supplied to the inductor 13 can have values comprised between a few hundred amperes and a few thousand amperes, as a function of the applications of the heating device 11.

A transformer can also be present, comprising a primary circuit connected to the power supply network 15 and a secondary circuit connected to the inductor 13 and suitable to supply the latter with an electric current with the desired characteristics of intensity and frequency.

By way of example, the alternating current flowing in the inductor 13 can have a frequency comprised between 0.1 and 1000 kHz, or even higher, as a function of the applications of the heating device 11.

The apparatus 10 also comprises at least one detection device 18 configured to detect the values of at least one electrical quantity correlated to the electrical energy supplied to the inductor 13.

According to some embodiments, the detection device 18 is associated with the inductor 13.

According to some embodiments, the detection device 18 comprises one or more sensors configured to detect at least one quantity between the current intensity, frequency, phase and voltage of the alternating current circulating in the inductor 13.

According to some embodiments, the detection device 18 comprises one or more sensors configured to detect the current intensity and/or the phase of the alternating electric current circulating in the inductor 13.

The induction heating apparatus 10 can also comprise a processing unit 19 connected to the at least one detection device 18 and to the induction heating device 11.

The processing unit 19 can be configured to receive the values detected by the detection device 18, and process them in order to estimate a current temperature of the metal element 20 in the heating phase.

The processing unit 19 can be configured to command, either directly or by means of a control and command unit 21, the functioning of the heating device 11, as a function of the estimated temperature and a set temperature value to be obtained.

In particular, the processing unit 19 is configured to monitor, in real time, the trend of the intensity and phase values of the electric current in the inductor 13, in order to identify when a variation occurs in them, correlated to a variation of the magnetic properties of the metal element 20, and therefore recognize when the metal element 20 has reached its Curie temperature.

According to other embodiments, additional sensor devices 22, 23, 24 can be provided, associated with one or more of either the power supply unit 14, the generator 16 or the amplification unit 17 and configured to detect respective values of the electrical quantity measured, in order to monitor its trend. According to some embodiments, the additional sensor devices 22, 23, 24 are configured to detect at least one quantity between the current intensity, frequency, phase and voltage of the electric current circulating in the circuit with which they are associated.

According to some embodiments, the additional sensor devices 22, 23, 24 are configured to detect at least the current intensity and/or the phase of the electric current circulating in the circuit with which they are associated.

According to some embodiments, the detection device 18 and the additional sensor devices 22, 23, 24 are connected in feedback with the processing unit 19 and possibly with the control and command unit 21.

According to some embodiments, the processing unit 19 and the control and command unit 21 can be implemented on a single card, or be manufactured as distinct elements connected to each other.

In some embodiments, the processing unit 19 can be configured to communicate with the control and command unit 21.

In particular, the processing unit 19 can communicate the outcome of the comparison to the control and command unit 21, that is, whether the values detected have or have not changed with respect to the reference values, and possibly the extent of the deviation.

In some embodiments, the control and command unit 21 can therefore estimate the temperature of the metal element 20 by associating the possible deduced alteration of the magnetic and/or electromagnetic properties of the metal element 20, once the Curie temperature has been reached in the rnetal element 20.

In some embodiments, the control and command unit 21 can be configured to communicate with the power supply unit 14, the generator 16 and the amplification unit 17 in order to regulate their functioning as a function of the values detected by the detection device 18 and/or by the additional sensor devices 22, 23, 24.

According to some embodiments, a method to heat a metal element 20 according to the invention provides to:

- power an inductor 13 connected to, or provided on, the heating head 12 of the induction heating device 11 by means of an alternating electric current so as to generate an alternating electromagnetic field; - position a metal element 20 to be heated in the electromagnetic field generated by the inductor 13 and heat the metal element 20 by Joule effect by inducing parasitic currents generated in it by the alternating electromagnetic field;

- detect at least a value of at least one electrical quantity correlated to the electrical energy supplied by the inductor 13;

- process the actual values detected by the detection device and compare them with reference values, in order to determine possible deviations from these reference values in order to identify possible deviations of the at least one electrical quantity, correlated to a variation in the magnetic properties of the metal element 20 and dependent on the temperature of this metal element 20;

- estimate the temperature of the metal element 20 on the basis of the comparison between the values detected and the reference values.

In particular, if, from the comparison, significant deviations are detected between the values detected and the reference values, it is possible to deduce whether some magnetic and/or electromagnetic properties of the metal element 20 have been altered and therefore estimate the temperature of the metal element 20. Specifically, in this way, it is possible to deduce whether the metal element 20 has passed from a ferromagnetic behavior to a paramagnetic behavior due to the Curie temperature typical of the material with which it is made being reached in the metal element 20.

In some embodiments, estimating the temperature therefore consists in associating the possible, deduced, alteration of the magnetic or electromagnetic properties of the metal element 20, once the Curie temperature has been reached in the metal element 20 itself.

The electrical quantities considered vary greatly depending on the electromagnetic coupling that is generated between the inductor 13 and the metal of the metal element 20. By way of example, once the Curie temperature has been reached, there can be detected a value of the electric current absorbed by the inductor 13 lower than the value of the electric current detected at lower temperatures. For example, the electric current can drop by as much as an additional 30%.

In some embodiments, the at least a value of at least one electrical quantity correlated to the electrical energy can be chosen among the values of current intensity, voltage, frequency and phase of the alternating electric current which generates the alternating electromagnetic field, that is, which passes through the inductor 13. In some embodiments, the reference values can be predefined and preset values, and the comparison consists in verifying whether or not the values detected fall within a range around the respective fixed reference value, or verifying whether the values detected are greater or lesser than the associated reference value. In other embodiments, fhe reference values can be the values of current intensity, voltage, frequency and phase of the alternating electric current which passes through the inductor 13 previously recorded, and the comparison consists in detecting any significant variations between the previously detected values and those just detected. According to some embodiments, it can be provided to detect at least the intensity and phase of the electric current circulating in the inductor 13 and transmit them in feedback to the processing unit 19.

In one possible variant, the method can comprise setting a target temperature, that is, the temperature to which the metal element 20 is to be heated. By “setting a target temperature” we mean that a user can directly set the value of the target temperature, for example by means of a user interface provided on the apparatus 10 and connected to one of either the processing unit 19, or selecting, by the user, a working/treatment to which the metal element 20 is to be subjected. A predefined target temperature can be associated with the working/treatment.

Setting a target temperature can also provide to define what the specific material of the metal element 20 to be heated is, with a respective value of the Curie temperature depending on the type of material.

Below is a table that lists, by way of example, some materials with their respective Curie temperatures.

In further embodiments the method can also comprise controlling the power fed to the heating head 12.

In particular, controlling the power can provide to deactivate the amplification unit 17, in order to interrupt the heating of the metal element 20 by Joule effect, or possibly adjust its functioning in order to reduce the power supplied, based on the result of the comparison as above.

In some embodiments, the method can provide that the interruption of the heating occurs immediately the moment in which a significant deviation is detected of the values detected with respect to the reference values. According to some embodiments, since in normal functioning, before the Curie temperature is reached, the values of the electrical quantity considered, for example the electric current in the inductor 13, are very stable, it can be provided to identify this temperature value when an even minimal deviation occurs with respect to the reference values, for example smaller than 5-10%. In other embodiments, the method can provide that the interruption occurs after a predetermined period of time from the moment in which the significant deviation is detected of the values detected with respect to the reference values.

In some embodiments, the predetermined period of time after which the interruption of the heating occurs is correlated to the target temperature previously set.

In fact, once a reference temperature is known, that is, the temperature at which the metal element 20 finds itself, estimated on the basis of the variations of the electrical quantities correlated to the Curie temperature being reached, it is possible to determine for how much time the metal element 20 has to remain subjected to the alternating electromagnetic field, in order to heat up until it reaches the determined target temperature. For example, the processing unit 19 can sample and record the values of the electrical quantity detected, or the estimated temperature values, and define a growth curve of the temperature of the metal element 20 in the heating phase. On the basis of the actual values detected and the growth curve, the processing unit can also calculate the necessary time remaining for the target temperature to be reached and command the heating device 11 accordingly.

According to some embodiments, the processing unit 19 can also calculate, or measure, how long the heating has lasted, from ambient conditions until it is determined that the Curie temperature has been reached, and then determine a temperature gradient on the basis of which to predict the time required to reach the target temperature. By way of example, the gradient can be determined proportionally; in the event that it takes 8 sec to reach 800°C, it can be provided to keep the device 10 on for 1 sec if the target temperature is 900°C, or 2 sec if the target temperature is 1,000°C.

It is clear that modifications and/or additions of parts or steps may be made to the induction heating method and apparatus 10 as described heretofore, without departing from the field and scope of the present invention as defined by the claims.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of induction heating method and connected apparatus 10, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby .

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

Claims

1. Method to heat a metal element (20) by means of electromagnetic induction, comprising:

- powering an inductor (13) connected to, or provided on, a heating head (12) of an induction heating device (11) by means of an alternating electric current so as to generate an alternating electromagnetic field;

- positioning a metal element (20) to be heated in the alternating electromagnetic field generated by said inductor (13) and heating said metal element (20) by Joule effect by inducing parasitic currents in it, characterized in that said method also provides to:

- detect at least a value of at least one electrical quantity correlated to the electrical energy supplied to said inductor (13);

- process the actual values detected and compare them with reference values to determine possible deviations from said reference values in order to identify possible changes in the at least one electrical quantity correlated to a variation in the magnetic properties of said heated metal element (20);

- estimate the temperature of said metal element (20) on the basis of the comparison between the values detected and the reference values;

- regulate the functioning of said heating device (11) as a function of said estimated temperature.

2. Method as in claim 1, characterized in that it provides to detect one or more of either the current intensity, voltage, frequency and phase of the alternating electric current that passes through the inductor (13).

3. Heating method as in claim 1 or 2, characterized in that said reference values are values of said at least one electrical quantity detected which were previously detected and recorded and in that the comparison consists in detecting possible variations in the last recorded values of said at least one electrical quantity with respect to the values previously recorded.

4. Heating method as in any claim hereinbefore, characterized in that the reference values are predefined values of said at least one electrical quantity, processed by means of a mathematical algorithm implemented in a processing unit (19) and in that the comparison can comprise verifying whether or not the values detected fall within a range around the respective reference value, or the comparison can comprise verifying whether the values detected are greater or lesser than the associated reference value, and possibly quantifying the deviation.

5. Heating method as in any claim hereinbefore, characterized in that it comprises:

- setting a target temperature to be reached during the heating of said metal element (20);

- comparing said estimated temperature with said target temperature and as a function of the outcome of the comparison determining whether to interrupt the supply of electric current to the inductor (13) or maintain it for a predetermined period of time, from the moment in which a significant variation is detected in the values detected with respect to said reference values, suitable for reaching said target temperature.

6. Heating method as in claim 5, characterized in that it provides to calculate the duration of said period of time on the basis of the actual values detected, of a growth curve of the temperature of said metal element (20) defined on the basis of values previously detected, or the time elapsed between the start of the power supply to the inductor (13) and the identification of the variation in the electrical quantity, and the difference between said estimated temperature and said target temperature.

7. Induction heating apparatus comprising:

- a heating device (11) provided with a heating head (12) suitable to be positioned, during use, in the proximity of, or in contact with, a metal element (20) to be heated, wherein said heating head (12) comprises, or is connected to, a coil, or inductor (13), formed by a plurality of spirals configured to be passed through by an electric current and to generate an electromagnetic field suitable to generate parasitic currents in said metal element (20);

- power supply means (14, 16, 17) connectable to an electric power supply network (15) and suitable to supply an alternating current with desired intensity and frequency to said inductor (13); characterized in that it comprises at least one detection device (18) configured to detect the values of at least one electrical quantity correlated to the electrical energy supplied by said generator to said inductor (13) and a processing unit (19) connected to said at least one detection device (18) and to said heating device (11) and configured to receive the values detected by said at least one detection device (18), and compare them with reference values in order to determine possible deviations from said reference values correlated to a variation in the magnetic properties of said heated metal element (20), estimate a current temperature of said heated metal element (20), correlated to said variation in the magnetic properties, and regulate the functioning of said heating device (11) as a function of said estimated temperature.

8. Induction heating apparatus as in claim 7, characterized in that it comprises additional sensor devices (22, 23, 24) associated with one or more of said power supply means (14, 16, 17) and said heating head (12) and in that said sensor devices (22, 23, 24) are configured to detect at least one electrical quantity between current intensity, phase, voltage and frequency of the alternating electric current circulating in the circuit with which they are associated and supply the values detected to said processing unit (19).

9. Induction heating apparatus as in claim 7 or 8, characterized in that said processing unit (19) is configured to monitor in real time the trend of the values detected of said at least one electrical quantity in said inductor (13) and identify when a variation in them occurs, correlated to a variation in the magnetic properties of said metal element (20) and recognize when said metal element (20) reaches its Curie temperature.

10. Induction heating apparatus as in any claim from 7 to 9, characterized in that said processing unit (19) is configured to command directly, or through a control and command unit (21), the functioning of said heating device (11), as a function of the estimated temperature and of a set target temperature value to be obtained.