INDUCTOR AND DEVICE FOR INDUCTIVE HEATING OF COMPONENTS AND METHOD FOR THIS

Description

[0001] The invention relates to an inductor for inductively heating components, a device comprising such an inductor, and furthermore to a method which serves in particular for operating such a device. State of the art

[0002] Such inductors are typically used for the heat treatment of components, such as shafts or eccentrics, where increased structural strength or increased hardness of the structure is required for wear protection. Such an inductor generates eddy currents via a magnetic field in the component or workpiece, which lead to an increase in the temperature in the component. The component geometry and the skin effect occurring during heating lead to an inhomogeneous temperature distribution, particularly on surface areas of the component, as shown in Fig. 1A using a component shown during the inductive heat treatment phase and in Fig. 1B This is illustrated by a corresponding temporal temperature development. This results in a temperature increase in process zones close to the surface compared to areas further away from the surface, which leads to different structural strengths within the microstructure of a correspondingly heat-treated component.

[0003] From EP 0 771 764 A1 and EP 0 743 289 A1 a device for heating a glass rod is known, wherein the device comprises an induction furnace for drawing optical glass fibers from a preform. revelation Advantages of the invention

[0004] The inductor with the characterizing features of patent claim 1 has the advantage that, with the inductor according to the invention, more homogeneous temperature distributions can be achieved in a component treated with it, and thus components with qualitatively more uniform structural strengths can be achieved or produced. For this purpose, the approximately annular coil has a passage that runs through the coil from its inner circumferential surface to its outer circumferential surface as a recess, allowing electromagnetic radiation to pass from the inside to the outside via the passage and be measured.This makes it possible to measure heat radiation, which escapes from a component held in the interior of the ring-shaped induction coil of the inductor during inductive heat treatment, outside the inductor and to assign a temperature to the measured heat radiation. This temperature provides information about the process development in a process zone close to the surface and thus allows access to the process quality, in contrast to conventional inductors in which this process zone is completely shielded and thus inaccessible from a metrological point of view.

[0005] The passage expediently extends in an approximately radial direction, the passage having an inlet opening on the inner circumferential surface and, at its other end, an outlet opening on the outer circumferential surface, so that reflection losses of the transmitted thermal radiation on the wall of the passage remain at the lowest possible level.

[0006] Preferably, the passage extends approximately in a straight line and also has an approximately circular inner cross-section in order to achieve optimal beam guidance.

[0007] A further development of the invention can consist in the passage extending approximately halfway along the longitudinal axis of the inductor. As a result, the passage extends through an annular section of the inductor approximately midway between a lower and an upper boundary of the inductor, viewed in the axial direction. This provides metrological access to a process zone located within an area of ​​influence of higher field strength compared to the lower and upper boundaries of the inductor, where the field strength naturally drops sharply.

[0008] In a device comprising such an inductor, a pyrometer is arranged relative to the passage such that a lens of the pyrometer faces the exit opening of the passage. The thermal radiation emerging through the passage can then enter the lens of the pyrometer and be imaged onto the pyrometer sensor for detection.

[0009] In order to achieve an optimal photon yield, according to an advantageous embodiment of the invention, the objective of the pyrometer is aligned with its optical axis coaxial to the longitudinal direction of the passage.

[0010] An advantageous and preferred embodiment of the invention can consist in the pyrometer being designed as a two-color pyrometer. In a two-color pyrometer, which is often also referred to as a two-color pyrometer, the incident thermal radiation is measured at two different wavelengths or wavelength ranges, so that knowledge of the emissivity of the measuring object or component generating the thermal radiation is not required to determine the temperature.

[0011] A practical embodiment of the invention provides that a process computing device is in a signal and / or data transmission connection with the pyrometer in order to receive and process measurement signals and / or measurement data transmitted from the pyrometer's output. Furthermore, by having the process computing device in a control connection with a generator for generating electrical power for the inductor, the heat treatment process can be controlled. For this purpose, the process computing device calculates parameters for controlling the inductive heat treatment based on temperature measurement signals and / or temperature measurement data received from the pyrometer.

[0012] A method that is particularly suitable for operating the device comprises the method steps a) activating the inductor, b) detecting thermal radiation coming from a region of the component accommodated in the inductor via the passage of the inductor, wherein a temperature locally assigned to the respective region is determined from the detected thermal radiation, c) comparing the temperature determined for the respective region with a reference value, and d) readjusting process parameters if a deviation between the detected temperature and the reference value is determined during the comparison, wherein the readjustment is carried out in accordance with the determined deviation. A temperature is used as the reference value, which is extracted from a temperature distribution simulation for the component for the region on which the detection according to method step b) is based.The temperature distribution simulation is based on a calculation of an electromagnetic field generated by the inductor, eddy currents induced by the field in the component, a resulting heat energy generated there and a temperature distribution that develops in the component as a result.

[0013] The electrical power supplied to the inductor during its activation and / or the duration of the inductor's activation and / or a feed rate at which the inductor is moved along its longitudinal axis, i.e., relative to a component to be treated, during its activation period are selected as process parameters. The method according to the invention advantageously enables a fairly precise adjustment of the structural state in the component through direct metrological access to the process zone via the passage formed in the inductor. This is because undesirable temperature increases in the process zone can be detected in a timely manner and can be reduced largely and virtually instantly through readjustment.

[0014] It is advisable to take into account the geometry and / or material properties of each component to be treated in the simulation in order to be able to model the component as accurately as possible.

[0015] Further advantageous developments and refinements of the invention result from the measures listed in the subclaims. Short description of the drawings

[0016] Embodiments of the invention are explained in more detail in the following description and in the accompanying drawings. The latter show, in schematic views: Fig. 1A a simulation of a 3D temperature distribution view of a component in an inductive heat treatment phase, Fig. 1B a diagram with a plurality of temperature curves, each of the temperature curves representing the temporal development of the temperature plotted along the ordinate for a respective area of ​​the component and with the Fig. 1A shown 3D temperature distribution view, Fig. 2 a highly schematic perspective view of an approximately ring-shaped coil of an inductor which serves for the inductive heating of a metallic component and has a passage penetrating the coil radially from the inside to the outside, Fig. 3 a perspective view of a part of the device according to the invention with the inductor of Fig. 1 , in the interior of which a component is accommodated, Fig. 4 a block diagram illustrating the device according to the invention, which Fig. 1 illustrated inductor, a generator for electrically controlling the inductor, a pyrometer and a process computing unit connected to the pyrometer in a measurement data transmission connection, and Fig. 5 a flow chart with essential process steps of the method according to the invention for operating the device of Fig. 4 . Embodiments of the invention

[0017] Before using Fig. 2 bis 5 the essential properties of the inductor according to the invention and the device according to the invention together with the treiben The method suitable for the device will be explained first with reference to Fig. 1A und 1B the characteristics of an inductor according to the state of the art are explained.

[0018] Fig. 1A shows a perspective view of a temperature distribution of a rotationally symmetrical component during a typical heat treatment phase, which is calculated by means of a simulation based on a calculation of the electromagnetic field generated by the induction coil of the inductor, which induces eddy currents in the component, and the heat energy generated in the component due to eddy current losses, taking into account the geometry and material properties of the component. In the simulated temperature distribution of the component, different temperature zones are formed, as they manifest themselves, for example, in different areas or locations 31 to 35 on the surface of the component, which partiallycause inhomogeneous temperature distribution in the component; in zones close to the surface of the component, higher temperatures generally prevail due to eddy currents acting predominantly close to the surface, while significantly reduced temperatures prevail inside the component due to the heat conduction taken into account in the simulation. This is shown in . Fig. 1B a diagram with a total of five temperature curves 31' - 35', wherein for the respective temperature curves, the temperature T is shown for different areas or locations 31 - 35 of the component shown in Fig. 2A as a function of the time t plotted along the abscissa. The simulation shows that for the temperature curves 33' to 35', which are assigned to areas of the component close to the surface, after a steep rising edge at the beginning of the heat treatment, there is a significant temperature increase with a temperature peak ≥ 1100 °C at a time t ≈ 2 s (on the time axis) compared to the temperature curve 31' of an area 31 relatively far from the surface.

[0019] Fig. 2 shows, in a highly schematic perspective view, an inductor, designated as a whole by 10, which is used for the inductive heating of metallic components. The inductor 10 has a coil 10', which, due to an outer peripheral surface 11 and an inner peripheral surface 12 arranged concentrically thereto with respect to a longitudinal central axis 10" of the coil 10', is annular or hollow-cylindrical in shape in order to accommodate and inductively heat a rotationally symmetrical component within its inner peripheral surface 11.In order to be able to measure the temperature prevailing on the surface of the component accommodated in the coil 10' during the inductive heating phase, a passage 13 is formed in the coil 10', which passes through the coil 10' in a radial direction from the inside to the outside so that thermal radiation emitted by the component from the interior of the coil 10' can pass to the outside, where a pyrometer arranged near an outlet opening 13' of the passage 13 can detect the incoming radiation in order to determine a temperature. The passage 13, which extends straight in the radial direction, thus has an outlet opening 13' on the outer circumferential surface 11 and, at its other end, an inlet opening 13" on the inner circumferential surface 12 opposite the outlet opening 13'.

[0020] From a manufacturing point of view, in order to form the passage 13 during winding of the coil, for example, a hollow cylindrical tube is attached or arranged to a support body at the beginning of the winding process and, if necessary, removed again at the end of the winding process.

[0021] Fig. 3 shows a perspective view of part of the device 100 according to the invention for inductively heating a component 14, which is rotatably received about its axis of symmetry in the interior of the inductor 10. For this purpose, the component 14 is mounted on a rotatable holding device 20 and rotates about its axis of symmetry or longitudinal center axis during the heat treatment, so that the most homogeneous temperature distribution possible is achieved in the component 14. During the activation period of the inductor 10, which is connected via the electrical connections 15', 15" to a Fig. 3 A correspondingly aligned pyrometer (not shown) can be connected to the inductor 10 via the passage 13. Fig. 3 shown) detect the heat radiation which is radiated from the area directly adjacent to the passage 13 and radially facing the surface of the component 14, and from this determine the temperature prevailing there.

[0022] Fig. 4 shows, in a highly schematic view, the device 100 according to the invention, which essentially comprises the inductor 10 according to the invention, a generator 15 for generating the high-frequency electrical power for the inductor 10, which can be fed to the coil 10' of the inductor 10 via electrical connecting lines 15', 15", a pyrometer 16 for detecting thermal radiation 17, which is emitted by a component 14 received from the interior of the coil 10' of the inductor 10 and reaches the outside via the passage 13 of the inductor 10, and a process computing unit 18, which is connected to an output of the pyrometer 16 via a signal and data transmission line 19 in order to receive and process temperature measurement data from the pyrometer. The pyrometer 16 is arranged or aligned in the vicinity of the inductor 10 in such a way that it can be seen with its objective orits entrance lens 16' is aligned with the longitudinal direction of the passage 13, wherein the objective lens 16' of the pyrometer 16 and the exit opening 13' of the inductor 10 face each other. The measuring axis of the pyrometer, formed by the objective lens 16' and the sensor (not shown), runs coaxially to the longitudinal direction of the passage 13. As a result, the objective lens 16' of the pyrometer 16 can image the thermal radiation 17 arriving from the exit opening 13' onto the sensor, which detects the radiation and converts it into electrical signals. In the preferred embodiment, the pyrometer is designed as a two-color pyrometer, so that the emissivity of the measurement object or component is irrelevant for temperature determination. Since the component is held in place during the inductive heat treatment by means of the rotatable holding device 20 (. Fig. 3 ), the pyrometer 16 can thermally scan the area of ​​the component passing the inlet opening 13" of the passage 13 during the rotation via the detected thermal radiation 17.

[0023] Fig. 5shows a flowchart with the essential method steps of the method used to operate the device 100. In a first method step 210, the inductor 10 is activated by supplying the electrical power generated by the generator 15 to the inductor 10 via the electrical connecting lines 15', 15". Subsequently, in a method step 220, the thermal radiation 17 emitted by the component 14 via the passage 13 is detected and evaluated by the pyrometer 16 within a predetermined time interval Δt, i.e., on the basis of the Stefan-Boltzmann law, a respective temperature is assigned to the area on the surface of the component adjacent to the inlet opening of the passage 13 - viewed in the radial direction - at the time of a measurement, and converted into temperature measurement data.

[0024] According to a subsequent method step 230, the temperature measurement data determined by the pyrometer 16 are transmitted to the process computing unit 18, whereupon the transmitted temperature measurement data are processed there in an immediately subsequent method step 240.

[0025] In a further method step 250, the temperature determined by the pyrometer for an area on the surface of the component at the time of a respective measurement is compared in the process computing unit 18 with a temperature from a simulated temperature distribution of the component, wherein the temperature extracted from the simulated temperature distribution is assigned to the same area on the surface on which the respective measurement is based.

[0026] In a subsequent test step 260, it is determined whether the comparison results in a deviation ΔT between the temperature determined on the basis of the detected thermal radiation and the temperature extracted from the simulated temperature profile. In the negative case, i.e. if there is practically no deviation, the process returns to step 220, so that the pyrometer detects radiation for a next time interval and determines temperature measurement data from this. In the positive case, i.e. if a deviation ΔT is present, the process is readjusted in a subsequent method step 270 on the basis of the determined temperature deviation ΔT, for example by adjusting the electrical power of the generator and / or the treatment duration and / or the feed rate of the inductor as a function of the deviation ΔT within a control loop.Following the readjustment, a return to step 220 occurs in a method step 280 until the predetermined heat treatment duration is reached.

[0027] Advantageously, in the method according to the invention, the electromagnetic radiation 17 detected by the pyrometer 16 via the passage 13 and the temperature determined therefrom provide information about the heat process development as a measured variable.

[0028] In summary, the method 200 according to the invention comprises the method steps a) activating 210 the inductor 10, b) detecting electromagnetic radiation coming via the passage 13 of the inductor 10 from a region of the component 14 accommodated in the inductor, wherein a temperature locally assigned to the respective region is determined from the detected radiation, c) comparing 220 the temperature determined for the respective region with a reference value, wherein the reference value is a temperature extracted from a temperature distribution simulation for the component for the region which is the basis for the detection according to method step b), wherein the temperature distribution simulation is based on a calculation of an electromagnetic field generated by the inductor 10, the eddy currents induced in the component by the field,the resulting heat energy generated there and the temperature distribution formed by heat conduction in the component, and d) the readjustment 280 of process parameters if a deviation ΔT between the recorded temperature and the reference value is determined during the comparison, wherein the readjustment is carried out in accordance with the determined deviation ΔT.

[0029] Physically based simulation methods are used to model the temperature distribution in the component. These are based on finite element simulation of electromagnetic-thermal field equations. Data-based machine learning methods such as support vector machines or nearest neighbor approaches are used to classify the temperature fields.

Claims

1. Inductor (10) for inductively heating metallic components with at least one coil, wherein the coil is approximately annular and has a passage (13) which passes through the coil from its inner circumferential surface to its outer circumferential surface in the form of a cutout to allow radiation to pass from the inside to the outside through the passage (13), characterized in that the component is receivable in an interior of the inductor (10) so as to be rotatable about its axis of symmetry or longitudinal central axis, wherein the component (14) is mounted on a rotatably designed holding device (20) and rotates during the heat treatment about its axis of symmetry or longitudinal central axis to achieve the most homogeneous temperature distribution possible in the component (14).

2. Inductor according to Claim 1, characterized in that the passage (13) extends in the approximately radial direction.

3. Inductor according to Claim 1 or 2, characterized in that the passage (13) has an entry opening (13') at the inner circumferential surface and at its other end an exit opening (13") at the outer circumferential surface.

4. Inductor according to any of Claims 1 to 3, characterized in that the passage (13) extends approximately in a straight line.

5. Inductor according to any of Claims 1 to 4, characterized in that the passage (13) has an approximately circular inner cross section.

6. Inductor according to any of Claims 1, characterized in that the passage (13) extends at approximately half the height with respect to a direction of extent of the longitudinal axis of the inductor (10).

7. Apparatus comprising an inductor according to any of the preceding claims, wherein a pyrometer (16) is arranged with respect to the passage (13) in such a way that an objective (16') of the pyrometer (16) is facing the exit opening (13') of the passage (13).

8. Apparatus according to Claim 7, characterized in that the objective (16') of the pyrometer (16) is aligned with its optical axis coaxially to the direction of longitudinal extent of the passage (13).

9. Apparatus according to Claim 7 or 8, characterized in that the pyrometer (16) is in the form of a quotient pyrometer.

10. Apparatus according to any of Claims 7 to 9, characterized in that a process computing device (18) is connected to the pyrometer (16) for signal and / or data transmission to receive measurement signals and / or measurement data transmitted by the pyrometer (16) on the output side and to process them.

11. Apparatus according to Claim 10, characterized in that the process computing device (18) is connected in a control connection to a generator for generating electrical power for the inductor (10).

12. Apparatus according to Claim 10 or 11, characterized in that the process computing device (18) calculates parameters for controlling the inductive heat treatment based on temperature measurement signals and / or temperature measurement data received from the pyrometer (16).

13. Method, in particular, for operating the apparatus according to any of Claims 7 to 12, having the following method steps: a) activating (210) the inductor (10), b) detecting (220) electromagnetic radiation coming from a region of the component (14) received in the inductor via the passage (13) of the inductor (10), wherein a temperature locally assigned to the respective region is ascertained from the detected radiation, c) comparing (240) in each case the temperature ascertained for the respective region with a reference value, and d) readjusting (280) process parameters when a deviation between the detected temperature and the reference value is ascertained during the comparison, wherein the readjustment is carried out according to the ascertained deviation, wherein the component (14) is mounted on a rotatably designed holding device (20) and rotates during the heat treatment about its axis of symmetry or longitudinal central axis to achieve the most homogeneous temperature distribution possible in the component (14).

14. Method according to Claim 13, characterized in that a temperature which is extracted from a temperature distribution simulation for the component for that region on which the detection (220) according to method step b) is appropriately based is used as the reference value.

15. Method according to Claim 14, characterized in that the temperature distribution simulation is carried out on the basis of a calculation of an electromagnetic field generated by the inductor (10), of eddy currents induced by the field in the component, of a heat energy generated there as a result, and of a temperature distribution which occurs as a result in the component.

16. Method according to any of Claims 13 to 15, characterized in that the process parameters selected is / are the electrical power supplied to the inductor (10) during its activation and / or the duration of the activation of the inductor (10) and / or a feed rate at which the inductor (10) is moved along its longitudinal axis (10") during its activation duration.

17. Method according to any of Claims 14 to 16, characterized in that the geometry and / or material properties of a component to be treated in each case are taken into account in the simulation.