Inductive heating using a control mode switch-over process

Abstract

An elongated rolled product (2) made of metal is conveyed through a working region (3) of an inductive heating element (1) in a transport direction (x) by means of a transport device (4) such that first a rolled product head (6), then a starting region (7) which adjoins the rolled product head (6), then a central piece (8) which adjoins the starting region (7), then a terminating region (9) which adjoins the central piece (8), and finally a rolled product foot (10) which terminates the terminating region (9) enter the working region (3) and then later exit the working region (3). The working region (3) is the region in which the inductive heating process is carried out. The starting region (7), the central piece (8), and the terminating region (9) are defined in that at a first point in time (t1) at which the rolled product head (6) exits the working region (3), the transition from the starting region (7) to the central piece (8) enters the working region (3) and at a second point in time (t2) at which the rolled product foot (10) enters the working region (3), the transition from the central piece (8) to the terminating region (9) exits the working region (3). Prior to the first point in time (t1) and after the second point in time (t2), the controller (11) operates the inductive heating element (1) according to a voltage control, and between the first and second point in time (t1, t2), the controller operates the inductive heating element according to a power control.

Description

[0001] Description

[0002] Title of the invention

[0003] Inductive heating with switching of the control mode

[0004] field of technology

[0005] The present invention is based on an operating method for an inductive heating device for heating an elongated rolled metal product,

[0006] - wherein the rolling stock is conveyed by means of a transport device of the inductive heating device in a transport direction through an effective area of ​​an inductive heating element of the inductive heating device, in which the inductive heating takes place, so that first a rolling stock head, then a starting area adjoining the rolling stock head, then a middle section adjoining the starting area, then a final section adjoining the middle section and finally a rolling stock foot closing the final area enters the effective area and later exits the effective area again,

[0007] - wherein the initial area, the middle section and the final area are defined by the fact that at a first point in time at which the rolling stock head runs out of the effective area, the transition from the initial area to the middle section runs into the effective area and at a second point in time at which the rolling stock foot runs into the effective area, the transition from the middle section to the final area runs out of the effective area,

[0008] - wherein the control device operates the inductive heating element before the first time according to a first control type, between the first and the second time according to a second control type and from the second time onwards again according to the first control type.

[0009] The term "control type" does not mean - at least within the scope of the present invention - that only the value of the setpoint being controlled changes, i.e., that instead of "3," it is now controlled to "5." Nor does it mean that the controller characteristics change, for example, that a switch is made from proportional control to proportional-integral control. Rather, the term "control type" means that the technological variable for which a setpoint is specified changes.

[0010] The present invention is further based on a control program for a control device of an inductive heating device for heating an elongated rolled metal product,

[0011] - wherein the rolling stock is conveyed by means of a transport device of the inductive heating device in a transport direction through an effective area of ​​an inductive heating element of the inductive heating device, in which the inductive heating takes place, so that first a rolling stock head, then a starting area adjoining the rolling stock head, then a middle section adjoining the starting area, then a final section adjoining the middle section and finally a rolling stock foot closing the final area enters the effective area and later exits the effective area again,

[0012] - wherein the initial area, the middle section and the final area are defined by the fact that at a first point in time at which the rolling stock head runs out of the effective area, the transition from the initial area to the middle section runs into the effective area and at a second point in time at which the rolling stock foot runs into the effective area, the transition from the middle section to the final area runs out of the effective area,

[0013] - where the control program comprises machine code,

[0014] - wherein the processing of the machine code by the control device causes the control device to operate the inductive heating element before the first time and after the second time according to a first control type and to operate it between the first and the second time according to a second control type.

[0015] The present invention further relates to a control device of an inductive heating device for heating an elongated rolled metal stock, wherein the control device is programmed with such a control program, so that the control device, during operation, controls at least one inductive heating element of the inductive heating device

[0016] - before a first time point at which a rolling stock head of the elongated rolling stock runs out of an effective range of the inductive heating element, and after a second time point at which a rolling stock foot of the elongated rolling stock runs into the effective range, operates according to a first control type and

[0017] - operates between the first and second points in time according to a second control mode.

[0018] The present invention further relates to an inductive heating device for heating an elongated rolled metal product,

[0019] - wherein the inductive heating device comprises an inductive heating element with an effective range in which the inductive heating takes place,

[0020] - wherein the inductive heating device comprises a transport device by means of which the rolling stock can be conveyed in a transport direction through the active area, so that first a rolling stock head, then a starting area adjoining the rolling stock head, then a middle section adjoining the starting area, then a final section adjoining the middle section and finally a rolling stock foot closing the final section enters the active area and later exits the active area again,

[0021] - wherein the inductive heating device has such a control device that controls at least the inductive heating element. State of the art

[0022] Such an operating method is known, for example, from US 3 610 861 A. In this operating method, the first control mode is current control, and the second control mode is voltage control.

[0023] From US 4 433 226 A, an operating method for inductively heating an elongated product is known, in which the elongated product is guided through the effective range of an inductive heating element of an inductive heating device and an energization level with which the inductive heating element is operated is set to different values ​​depending on the progress of the transport of the elongated product.

[0024] Summary of the invention

[0025] Induction heating elements are often used in the production of elongated rolled stock. The format of the rolled stock can vary from case to case. It can be flat rolled stock (slab, transfer strip, strip, or heavy plate), rolled stock with a billet cross-section (square or round), or with a bar-shaped cross-section (also square or round). The stage of production progress can also vary from case to case. Heating can take place, for example, between casting and rough rolling, between rough rolling and finish rolling, before pickling, before coating, etc. Depending on the individual case, heating can take place from the ambient temperature or from a significantly higher temperature.

[0026] During inductive heating, the rolling stock in the working area of ​​the inductive heating element is exposed to an alternating magnetic field generated by a current-carrying coil. This generates eddy currents in the rolling stock, which in turn heat the rolling stock. This allows the temperature of the rolling stock or other properties, such as the microstructure or a surface characteristic, to be adjusted as required. The coil can be designed as a longitudinal field module or a transverse field module, as required.

[0027] During inductive heating, the desired target properties should be achieved as precisely as possible.

[0028] The object of the present invention is to create possibilities by means of which precisely this is made possible. This object is achieved by an operating method having the features of claim 1. Advantageous embodiments of the operating method are the subject of dependent claims 2 to 9.

[0029] According to the invention, an operating method of the type mentioned at the outset is designed in that the first control type is a voltage control and the second control type is a power control.

[0030] Before the first time and after the second time, the control is based on a target voltage. Between the first and second time, the control is based on a target power. The technological variable being controlled is therefore a voltage in one case and a power in the other.

[0031] The present invention is based on the realisation that it is indeed possible to set the required power values ​​with which the inductive heating element should be controlled between the first and the second point in time. Before the first point in time (i.e. up to the point in time at which the rolling stock head runs out of the effective range) and after the second point in time (i.e. from the point in time at which the rolling stock root runs into the effective range), such control is not possible or only possible with great difficulty because the inductive heating element can only be inadequately controlled by means of power control without a section of the rolling stock in the effective range, i.e. in idle mode, so to speak. As a result, a different control of the inductive heating element is required before the first point in time and after the second point in time. It is precisely this different control that is implemented by voltage control.

[0032] Preferably, the control device determines a first target power for the inductive heating element based on first actual properties that the centerpiece has before entering the effective range and first target properties that the centerpiece should have at a time after leaving the effective range. The control device operates the inductive heating element between the first and second times such that the actual power of the inductive heating element corresponds as closely as possible to the first target power. The first target power is determined in such a way that the first target properties are achieved as effectively as possible. This ensures that the centerpiece is heated as desired.

[0033] In the simplest case, the first target power is constant along the length of the middle section. However, if the first actual properties and / or the first target properties vary along the length of the middle section, the first target power can also vary accordingly.

[0034] In individual cases, the actual power may be apparent power. However, it is usually the real power of the inductive heating element. The real power can be determined, for example, using the effective values ​​for the voltage and current, taking into account the phase shift between the voltage and current.

[0035] It is preferably provided that the control device

[0036] - a second target power for the inductive heating element is determined using second actual properties which the initial area has before entering the effective range and second target properties which the initial area should have at a time after leaving the effective range,

[0037] - the second target power is determined under the assumption that the initial area is completely within the effective range of the inductive heating element, and

[0038] - a first target voltage is determined based on the second target power and the inductive heating element is operated before the first time in such a way that an actual voltage of the inductive heating element corresponds as closely as possible to the first target voltage.

[0039] This ensures that the initial area is heated up as desired.

[0040] The second actual properties can be identical to the first actual properties. Alternatively, they can be different properties from the first actual properties. The same applies to the relationship between the second target properties and the first target properties.

[0041] Preferably, the second target power is the power at which the second target properties are achieved as well as possible. In this case, it is possible for the control device to determine a provisional target voltage corresponding to the second target power and to determine the first target voltage by multiplying the provisional target voltage by a first adjustment factor. Alternatively, it is possible for the control device to determine a final target power by multiplying the second target power by the first adjustment factor and to determine the first target voltage as the voltage corresponding to the final target power. The first adjustment factor has a value between a predetermined first minimum value and a predetermined first maximum value. The predetermined first minimum value is between 0 and 1, and the predetermined first maximum value is at least 1.

[0042] The procedure explained above also includes the case where the first adjustment factor has exactly the value 1. In this case, the respective multiplication is degenerate into a simple transfer of the corresponding value and both alternatives lead to the same result.

[0043] In general, the first adjustment factor can compensate for a temperature deviation in the initial range that is often given purely in fact, particularly in the case where second actual properties and second target properties are not specified separately for determining the second target power, but the corresponding first properties are used.

[0044] As a rule, the predetermined first minimum value is at least 0.5 and the predetermined first maximum value is at most 1.5. Preferably, the predetermined first minimum value is at least 0.8 and the predetermined first maximum value is at most 1.2.

[0045] Preferably, the control device detects an operating voltage with which the inductive heating element is operated immediately before the second time, determines a second target voltage based on the detected operating voltage, and operates the inductive heating element from the second time onwards in such a way that an actual voltage of the inductive heating element corresponds as closely as possible to the second target voltage. This ensures that the heating of the terminal area occurs as desired.

[0046] The operating voltage is the actual voltage of the inductive heating element immediately before the second time point. The term "operating voltage" was chosen to avoid confusion with the actual voltage at other times.

[0047] Preferably, the control device determines the second target voltage by multiplying the operating voltage by a second adjustment factor, wherein the second adjustment factor has a value between a predetermined second minimum value between 0 and 1 and a predetermined second maximum value of at least 1.

[0048] The second adjustment factor can be used - analogous to the first adjustment factor - to compensate for a temperature deviation in the final area that often actually occurs.

[0049] Analogous to the first adjustment factor, the predetermined second minimum value is generally at least 0.5, and the predetermined second maximum value is at most 1.5. Here, too, the stated values ​​are preferably at least 0.8 and at most 1.2.

[0050] The problem is further solved by a control program having the features of claim 10. Advantageous embodiments of the control program are the subject of dependent claims 11 and 12.

[0051] According to the invention, the processing of the machine code by the control device results in the first control mode being voltage control and the second control mode being power control. The resulting advantages are the same as those of the operating method for the inductive heating device explained above.

[0052] Preferably, the processing of the machine code by the control device causes the control device to operate the inductive heating element according to one of the advantageous embodiments explained above in connection with the operating method for the inductive heating device. The advantages thereby achieved are the same as those explained above for the operating method.

[0053] It is possible for the control device to control only the inductive heating element, but not the transport device. Preferably, however, the processing of the machine code by the control device also causes the control device to control the transport device of the inductive heating device. In this case, the control device operates the transport device such that the rolling stock is conveyed by the transport device in one transport direction through the effective area of ​​the inductive heating element, so that first the rolling stock head, then the initial area, then the middle section, then the final area, and finally the rolling stock root enter the effective area and later exit the effective area again.

[0054] The object is further achieved by a control device having the features of claim 13. According to the invention, the control device is programmed with a control program according to the invention, so that the first control type is a voltage control and the second control type is a power control.

[0055] The object is further achieved by an inductive heating device having the features of claim 14. According to the invention, the control device of the inductive heating device is designed as a control device according to the invention.

[0056] Short description of the drawings

[0057] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of an embodiment, which is explained in more detail in conjunction with the drawings.

[0058] FIG 1 an inductive heating device,

[0059] FIG 2 a flow chart,

[0060] FIG 3 a timing diagram and

[0061] FIGS 4 to 9 flow diagrams. Description of the embodiments

[0062] According to FIG. 1, an inductive heating device comprises an inductive heating element 1. An elongated metal rolling stock 2 is to be inductively heated by means of the inductive heating element 1. The rolling stock 2 is typically made of steel, but can also be made of another metal, for example, aluminum. The inductive heating element 1 can be designed as a longitudinal field module or a transverse field module, as required. It has an effective area 3. The effective area 3 has an effective length L, viewed in a transport direction x. The inductive heating of the rolling stock 2 takes place in the effective area 3, i.e., over the effective length L.

[0063] The inductive heating device further comprises a transport device 4. By means of the transport device 4, the rolled stock 2 is conveyed in a transport direction x through the active area 3. The transport device 4 can, for example, comprise a plurality of transport rollers 5, wherein at least some of the transport rollers 5 are driven. Only a few of the transport rollers 5 are shown in FIG. 1, and only a few of the transport rollers 5 shown are provided with their reference symbols.

[0064] The rolled stock 2 has a rolling stock head 6. In this case, the rolling stock head 6 is the end face of the rolling stock 2 which is at the front as seen in the transport direction x, i.e. with which the rolling stock 2 first enters the active area 3 and first exits the active area 3. The rolling stock head 6 is followed by a starting area 7 of the rolling stock 2. The starting area 7 is ultimately determined by the effective length L of the active area 3. In particular, the length of the starting area 7 corresponds to the effective length L. A middle section 8 of the rolling stock 2 follows the starting area 7. The length of the middle section 8 can be as required. Typically, the middle section 8 is longer - usually considerably longer - than the starting area 7. The middle section 8, in turn, is followed by a closing area 9. The final area 9 is determined – analogously to the initial area 7 – by the effective length L of the effective area 3.In particular, the length of the end region 9 corresponds to the effective length L. At the very end of the rolling stock 2, the rolling stock 2 has a rolling stock foot 10. In this case, the rolling stock foot 10 refers to the end face of the rolling stock 2 that is located at the rear, as seen in the transport direction x, i.e., with which the rolling stock 2 last enters the effective region 3 and last exits the effective region 3.

[0065] The inductive heating device further comprises a control device 11. The control device 11 controls at least the inductive heating element 1. In many cases, the control device 11 also controls the transport device 4. The control device 11 is programmed with a control program 12. The control program 12 comprises machine code 13. The processing of the machine code 13 by the control device 11 causes the control device 11 to operate the inductive heating element 1 and, if appropriate, also the transport device 4 according to an operating method which is explained in more detail below in connection with FIG. 2. According to FIG. 2, the transport of the rolling stock 2 is initially started in a step S1. Step S1 can be executed by the control device 11 as part of the processing of the machine code 13. However, it can also be implemented differently. For this reason, step S1 is only shown in dashed lines in FIG. 2.The transport of the rolling stock 2 is maintained in the further execution of the procedure of FIG 2.

[0066] During the transport of the rolling stock 2, the entire rolling stock 2 gradually passes through the effective range 3. Figure 3 shows various states, which are assumed one after the other, as a function of time t. The various states are shown one above the other in Figure 3 according to their temporal sequence. The earliest state is shown at the top, and the latest state is shown at the bottom. The boundaries of the effective range 3 are indicated in Figure 3 by vertical dashed lines.

[0067] Initially, the rolling stock 2 is still completely in front of the effective area 3. At an initial time tA, the rolling stock head 6 enters the effective area 3, thus reaching the beginning of the effective area 3. Due to further transport, the rolling stock head 6 passes through the effective area 3 and reaches the end of the effective area 3 at a first time t1. At the first time t1, the rolling stock head 6 thus runs out of the effective area 3. Furthermore, at this time - this is how the initial area 7 is defined - the entire initial area 7 and only the initial area 7 are in the effective area 3.

[0068] The rolling stock 2 is now conveyed further through the effective area 3. At a second time t2, the rolling stock root 10 reaches the beginning of the effective area 3. At the second time t2, the rolling stock root 10 thus enters the effective area 3. Furthermore, at this time – this is how the end area 9 is defined – the entire end area 9 and only the end area 9 is located in the effective area 3. The rolling stock 2, however, is conveyed further, so that the rolling stock root 10 also gradually passes through the effective area 3 and exits the effective area 3 at a final time tF. At an even later time – shown at the very bottom of FIG. 3 – the rolling stock 2 is located completely behind the effective area 3.

[0069] During the transport of the rolled stock 2 through the active area 3, the control device 11 initially operates the inductive heating element 1 in a step S2 according to a voltage regulation. The control device 11 therefore determines control signals C for the inductive heating element 1 such that an actual voltage U of the inductive heating element 1 is regulated to a first target voltage U1*. The control device 11 thus initially operates the inductive heating element 1 such that the actual voltage U corresponds as closely as possible to the first target voltage U1*. For example, the control device 11 can determine control signals C for a converter 14 of the inductive heating element 1 such that an actual voltage U regulated to the first target voltage U1* is applied to an induction coil 15 of the inductive heating element 1 via the converter 14.

[0070] The exact time at which execution of step S2 begins is of secondary importance. However, it must be before the initial time tA.

[0071] In a step S3, the control device 11 checks whether the first time t1 has been reached, i.e. whether the rolling stock head 6 is currently running out of the effective area 3. There are various options for checking this fact. For example, the first time t1 can be determined based on conventional path tracking. The first time t1 can also be determined based on the evaluation of the signal from a detector that detects the presence or absence of metal or hot metal. Such detectors (a light barrier or a so-called hot metal detector) are generally known to those skilled in the art. Furthermore, it is possible to evaluate the frequency response of the induction coil 15 and thus determine whether the first time t1 has been reached. Such evaluations are also generally known to those skilled in the art.

[0072] If the first time t1 is not reached, the control device 11 returns to step S2. Step S2 is thus repeatedly executed until the first time t1 is reached.

[0073] Once the first time t1 is reached, the control device 11 proceeds to step S4. In step S4, the control device 11 operates the inductive heating element 1 according to a power control. The control device 11 determines the control signals C for the inductive heating element 1 such that an actual power P of the inductive heating element 1 is controlled to a first target power P1*. An attempt is thus made to adjust the actual power P of the inductive heating element 1 so that it corresponds as closely as possible to the first target power P1*. The control of the inductive heating element 1 with the control signals C is carried out analogously to step S2.

[0074] In a step S5, the control device 11 checks whether the second time t2 has been reached, i.e., whether the rolling stock base 10 is currently entering the effective area 3. The same options are available for checking this fact as for the check in step S3.

[0075] If the second time t2 is not reached, the control device 11 returns to step S4. Step S4 is thus repeatedly executed until the second time t2 is reached.

[0076] If the second time t2 is reached, the control device 11 proceeds to a step S6.

[0077] In step S6, the control device 11 again operates the inductive heating element 1 according to a voltage regulation. The control device 11 thus determines the control signals C for the inductive heating element 1 such that the actual voltage U of the inductive heating element 1 is regulated to a second target voltage U2*. The implementation of step S6 is completely analogous to the implementation of step S2.

[0078] In step S7, the control device 11 checks whether the voltage regulation of step S6 should be terminated. If the voltage regulation should not be terminated yet, the control device 11 returns to step S6. Step S6 is therefore repeatedly executed until the voltage regulation is to be terminated.

[0079] The exact time at which voltage regulation is to end is of secondary importance. However, it must be after the final time tF.

[0080] If the voltage regulation is to be terminated, the control device 11 goes to a step

[0081] 58, where it terminates the voltage regulation.

[0082] Finally, in a step S9, the transport of the rolling stock 2 is terminated. Step S9 can be executed by the control device 11 as part of the processing of the machine code 13. However, it can also be implemented in another way. For this reason, step

[0083] 59 is shown only in dashed lines in FIG. 2. The time interval between the execution of steps S8 and S9 can be determined as needed. It is of secondary importance within the scope of the present invention.

[0084] FIG 4 shows two possible embodiments of the procedure of FIG 2. The two embodiments can be implemented independently of each other.

[0085] Within the scope of one embodiment, first actual properties E1 and first target properties Z1 are known to the control device 11 according to FIG. 4 in a step S11. The first actual properties E1 are properties that the center piece 8 has before entering the effective area 3. Examples of such properties are the cross-section, the temperature, and the chemical composition of the center piece 8. The first target properties Z1 are properties that the center piece 8 should have at a time after leaving the effective area 3, for example, immediately after leaving the effective area 3. Examples of such properties are the temperature and the structure of the center piece 8.

[0086] In a step S12, the control device 11 determines the first target power P1*. The determination is performed using the first actual properties E1 and the first target properties Z1. Steps S11 and S12 are always executed by the control device 11 before the first execution of step S4. Usually, they are even executed before step S2 and often even before step S1.

[0087] The other embodiment consists in a preferred manner of determining the actual power P. This is because the actual power P is preferably an active power of the inductive heating element 1. For example, the control device 11 can record the actual voltage U and the associated actual current I in a step S16. These two values ​​II, I can be effective values. Furthermore, the control device 11 can record a phase shift (p) between the actual voltage U and the actual current I in step S16. Then, the control device 11 can determine the actual power P as active power in a step S17, for example by forming the product of the actual voltage II, the actual current I and the cosine of the phase shift cp.

[0088] The remaining steps shown in FIG 4 have already been explained in connection with FIG 2.

[0089] FIG 5 shows a further possible embodiment of the procedure of FIG 2. This embodiment can be implemented as an alternative or in addition to the embodiments of FIG 4, as required.

[0090] Firstly, in a step S21, second actual properties E2 and second target properties Z2 are known to the control device 11 according to FIG 4. The second actual properties E2 are properties that the initial area 7 has before entering the effective area 3. In principle, these properties can be similar to the first actual properties E1. The second target properties Z2 are properties that the initial area 7 should have at a time after leaving the effective area 3, for example, immediately after leaving the effective area 3. In principle, these properties can be similar to the first target properties Z1.

[0091] In a step S22, the control device 11 determines a second target power P2*. The determination is carried out—analogously to the determination of the first target power P1*—using the second actual properties E2 and the second target properties Z2. It is also assumed that the initial area 7 is located entirely within the effective area 3, i.e., the effective area 3 is completely filled, particularly as seen in the transport direction x.

[0092] In a step S23, the control device 11 determines the first target voltage U1 based on the second target power P2*. Steps S21 to S23 are always executed by the control device 11 before the first execution of step S2. They are usually executed before step S2 and often even before step S1.

[0093] The remaining steps shown in FIG 5 have already been explained in connection with FIG 2.

[0094] The second target power P2* is generally the power at which the second target properties Z2 are achieved as closely as possible. The first target voltage U1* is generally the voltage which corresponds to the second target power P2* when the effective area 3 is completely filled with the rolling stock 2, as viewed in the transport direction x. Nevertheless, a correction may be necessary. This may be the case in particular if the second actual properties E2 and / or the second target properties Z2 are not specified independently, but are implicitly determined by the specification of the first actual properties E1 and / or the first target properties Z1. In this case, it may be necessary to modify step S23 according to FIG. 6 or FIG. 7.

[0095] According to FIG. 6, step S23 is modified in that the control device 11 initially determines a target voltage II* corresponding to the second target power P2*. However, this value does not yet correspond to the first target voltage U1*, but is only provisional. The provisional target voltage II* is then multiplied by a first adjustment factor k1. The first adjustment factor k1 can be specified to the control device 11 externally, for example, by an operator (not shown).

[0096] The first adjustment factor k1 has a value between a predetermined first minimum value between 0 and 1 and a predetermined first maximum value of at least 1. This means that the possible specifications for the first adjustment factor k1 are limited to the value range between the first minimum value and the first maximum value. A specification outside this value range is therefore not possible.

[0097] Usually, the predetermined first minimum value, as shown in FIG. 6, is 0.5 or higher, for example, at least 0.8. Similarly, the predetermined first maximum value is usually 1.5 or lower, for example, at most 1.2.

[0098] The embodiment according to FIG 7 is similar to the embodiment of FIG 6. According to FIG 7, step S23 is modified in that the control device 11 first determines the second target power P2*, but then multiplies the second target power P2* by the first adaptation factor k1. Only this value - hereinafter referred to as the final target power P* - serves as the basis for determining the first target voltage U1. The determined first target voltage U1 is the voltage corresponding to the final target power P*. FIG 8 shows a further possible embodiment of the procedure of FIG 2. This embodiment can be implemented as required as an alternative to or in addition to the embodiments of FIG 4 and / or FIG 5 (including their embodiments).

[0099] According to FIG. 8, the control device 11 detects the respective actual voltage II in a step S31. Step S31 is executed in conjunction with step S4. It can, for example, be part of step S16 of FIG. 4. The actual voltage U detected during the last execution of step S31 is referred to below as the operating voltage and is provided with the reference symbol II'. Step S31 is executed by the control device 11 immediately before or immediately after step S4. The operating voltage II' is thus the voltage with which the inductive heating element 1 is operated immediately before the second time t2.

[0100] Furthermore, the control device 11 determines the second target voltage II* in a step S32 based on the detected operating voltage LT. In the simplest case, the control device 11 adopts the operating voltage II' as the second target voltage U2*. Regardless of the specific procedure, however, the determination takes place immediately before the first execution of step S6.

[0101] The remaining steps shown in FIG 8 have already been explained in connection with FIG 2.

[0102] Analogous to the first target voltage U1*, a correction may be necessary. In this case, step S32 is modified as shown in FIG. 9 such that the control device 11 determines the second target voltage U2* by multiplying the operating voltage U' by a second adjustment factor k2. The above statements regarding the first adjustment factor k1 apply analogously to the second adjustment factor k2.

[0103] The present invention has many advantages. In particular, the rolling stock 2 can be heated more precisely and evenly in the initial region 7 and the final region 9 than is possible in the prior art. This allows the rolling stock 2 to be fed to subsequent processing stations (not shown) with improved quality, allowing more uniform processing there as well. Furthermore, any problems that could arise from uneven heating are avoided. Not only can the present invention be implemented in a newly constructed inductive heating device, but it is also easily possible to convert an existing prior art inductive heating device to the inventive method.

[0104] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

[0105] List of reference symbols

[0106] 1 heating element

[0107] 2 Rolled goods

[0108] 3 Effective range

[0109] 4 Transport device

[0110] 5 transport rollers

[0111] 6 rolling stock head

[0112] 7 Initial area

[0113] 8 middle pieces

[0114] 9 Final area

[0115] 10 Rolled stock foot

[0116] 11 Control device

[0117] 12 Control program

[0118] 13 Machine code

[0119] 14 inverters

[0120] 15 Induction coil

[0121] C Control signals

[0122] E1 , E2 actual properties

[0123] I actual current k1, k2 adjustment factors

[0124] L effective length

[0125] P Actual performance

[0126] P*, P1*, P2* Target performance

[0127] S1 to S32 steps t time tA, t1, t2, tF times

[0128] U actual voltage

[0129] U' operating voltage

[0130] U*. U1*. U2* Target voltages x transport direction

[0131] Z1 , Z2 target properties

[0132] Phase shift

Claims

Claims 1. Operating method for an inductive heating device for heating an elongated rolled product (2) made of metal, - wherein the rolling stock (2) is conveyed by means of a transport device (4) of the inductive heating device in a transport direction (x) through an effective area (3) of an inductive heating element (1) of the inductive heating device, in which the inductive heating takes place, so that first a rolling stock head (6), then a starting area (7) adjoining the rolling stock head (6), then a middle section (8) adjoining the starting area (7), then a final area (9) adjoining the middle section (8) and finally a rolling stock foot (10) closing the final area (9) enters the effective area (3) and later exits the effective area (3), - wherein the initial region (7), the middle section (8) and the final region (9) are defined in that at a first time (t1), at which the rolling stock head (6) runs out of the active region (3), the transition from the initial region (7) to the middle section (8) runs into the active region (3) and at a second time (t2), at which the rolling stock foot (10) runs into the active region (3), the transition from the middle section (8) to the final region (9) runs out of the active region (3), - wherein the control device (11) operates the inductive heating element (1) before the first time (t1) and after the second time (t2) according to a voltage control and between the first and the second time (t1, t2) according to a power control.

2. Operating method according to claim 1, characterized in that the control device (11) determines a first target power (P1*) for the inductive heating element (1) using first actual properties (E1) which the middle piece (8) has before entering the effective area (3) and first target properties (Z1) which the middle piece (8) should have at a time after leaving the effective area (3), and operates the inductive heating element (1) between the first and the second time (t1, t2) in such a way that an actual power (P) of the inductive heating element (1) corresponds as far as possible to the first target power (P1*).

3. Operating method according to claim 2, characterized in that the actual power (P) is an active power of the inductive heating element (1).

4. Operating method according to claim 1, 2 or 3, characterized in that the control device (11) - using second actual properties (E2) which the initial area (7) has before entering the effective area (3) and second target properties (Z2) which the initial area (7) should have at a time after leaving the effective area (3), a second target power (P2*) for the inductive heating element (1) is determined, - the second target power (P2*) is determined under the assumption that the initial area (7) is completely within the effective range (3) of the inductive heating element (1), and - starting from the second target power (P2*), a first target voltage (U1*) is determined and the inductive heating element (1) is operated before the first time (t1) in such a way that an actual voltage (II) of the inductive heating element (1) corresponds as far as possible to the first target voltage (U1*).

5. Operating method according to claim 4, characterized in that - that the second target performance (P2*) is the performance at which the second target properties (Z2) are achieved as well as possible, - that the control device (11) determines a provisional target voltage (II*) corresponding to the second target power (P2*) and determines the first target voltage (U1*) by multiplying the provisional target voltage (II*) by a first adjustment factor (k1) or determines a final target power (P*) by multiplying the second target power (P2*) by the first adjustment factor (k1) and determines the first target voltage (U1*) as the voltage corresponding to the final target power (P*) and - that the first adjustment factor (k1) has a value between a predetermined first minimum value between 0 and 1 and a predetermined first maximum value of at least 1.

6. Operating method according to claim 5, characterized in that the predetermined first minimum value is at least 0.5 and the predetermined first maximum value is a maximum of 1.

5.

7. Operating method according to one of the above claims, characterized in that the control device (11) detects an operating voltage (LT) with which the inductive heating element (1) is operated immediately before the second time (t2), determines a second target voltage (U2*) based on the detected operating voltage (LT) and operates the inductive heating element (1) from the second time (t2) in such a way that an actual voltage (II) of the inductive heating element (1) corresponds as far as possible to the second target voltage (U2*).

8. Operating method according to claim 7, characterized in that that the control device (11) determines the second target voltage (U2*) by multiplying the operating voltage (LT) by a second adjustment factor (k2) and that the second adjustment factor (k2) has a value between a predetermined second minimum value between 0 and 1 and a predetermined second maximum value of at least 1.

9. Operating method according to claim 8, characterized in that the predetermined second minimum value (k2) is at least 0.5 and the predetermined second maximum value is at most 1.

5.

10. Control program for a control device (11) of an inductive heating device for heating an elongated rolled product (2) made of metal, - wherein the rolling stock (2) is conveyed by means of a transport device (4) of the inductive heating device in a transport direction (x) through an effective area (3) of an inductive heating element (1) of the inductive heating device, in which the inductive heating takes place, so that first a rolling stock head (6), then a starting area (7) adjoining the rolling stock head (6), then a middle section (8) adjoining the starting area (7), then a final area (9) adjoining the middle section (8) and finally a rolling stock foot (10) closing the final area (9) enters the effective area (3) and later exits the effective area (3), - wherein the initial region (7), the middle section (8) and the final region (9) are defined in that at a first time (t1), at which the rolling stock head (6) runs out of the active region (3), the transition from the initial region (7) to the middle section (8) runs into the active region (3) and at a second time (t2), at which the rolling stock foot (10) runs into the active region (3), the transition from the middle section (8) to the final region (9) runs out of the active region (3), - wherein the control program comprises machine code (13), - wherein the processing of the machine code (13) by the control device (11) causes the control device (11) to operate the inductive heating element (1) before the first time (t1) and after the second time (t2) according to a voltage control and to operate it between the first and the second time (t1, t2) according to a power control.

11. Control program according to claim 10, characterized in that the processing of the machine code (13) by the control device (11) causes the control device (11) to operate the inductive heating element (1) according to the features of at least one of claims 2 to 9.

12. Control program according to claim 10 or 11, characterized in that the processing of the machine code (13) by the control device (11) causes the control device (11) to also control the transport device (4) of the inductive heating device and to operate the transport device (4) in such a way that the rolling stock (2) is conveyed by means of the transport device (4) in a transport direction (x) through the effective area (3) of the inductive heating element (1), so that first the rolling stock head (6), then the initial area (7), then the middle section (8), then the final area (9) and finally the rolling stock foot (10) runs into the effective area (3) and later runs out of the effective area (3) again.

13. Control device (11) of an inductive heating device for heating an elongated rolled stock (2) made of metal, wherein the control device (11) is programmed with a control program according to claim 10, 11 or 12, so that the control device (11) in operation at least one inductive heating element (1) of the inductive heating device - before a first time at which a rolling stock head (6) of the elongated rolling stock (2) runs out of an effective area (3) of the inductive heating element (1), and after a second time at which a rolling stock foot (10) of the elongated rolling stock (2) runs into the effective area (3), operates according to a voltage control and - operates between the first and the second time (t1, t2) according to a power control.

14. Inductive heating device for heating an elongated rolled product (2) made of metal, - wherein the inductive heating device comprises an inductive heating element (1) with an effective area (3) in which the inductive heating takes place, - wherein the inductive heating device comprises a transport device (4) by means of which the rolling stock (2) can be conveyed in a transport direction (x) through the active area (3), so that first a rolling stock head, then a starting area adjoining the rolling stock head (6), then a middle section (8) adjoining the starting area (7), then a final area (9) adjoining the middle section (8) and finally a rolling stock foot (10) closing the final area (9) enters the active area (3) and later exits the active area (3), - wherein the inductive heating device comprises a control device (11) according to claim 13, which controls at least the inductive heating element (1).

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