RU2779350C1 - Heating apparatus for induction heating of a flat steel strip in a hot rolling mill - Google Patents

Abstract

FIELD: rolling.

SUBSTANCE: group of inventions relates to the field of rolling production and can be used for induction heating of a flat steel strip in a hot rolling mill. Heating apparatus is located between two groups of rolling stands of a hot rolling mill, and the flat steel strip is passed through the heating apparatus in the transport direction; wherein the heating apparatus includes several transverse field modules located one after the other along the strip transport direction, several longitudinal field modules located one after the other along the strip transport direction, a first current source for powering at least one transverse field module, and a second current source for powering at least one longitudinal field module, wherein each of said current sources has its own frequency converter, an electrically connected capacitor battery and a frequency input enabling setting of the nominal frequency. Also proposed are methods for induction heating of a flat steel strip using the above heating apparatus.

EFFECT: increase in the uniformity of heating of the strip in width and thickness.

15 cl, 10 dwg

Description

The invention relates to a heating device and a method for inductively heating a flat steel strip in a hot rolling mill, wherein the heating device is located between two groups of rolling stands of the hot rolling mill, and the flat steel strip passes through the heating device in the conveying direction at a certain speed. In principle, however, this heating device could also be located in front of a group of rolling stands (eg a roughing group of rolling stands) or between two stands of a group of rolling stands (eg a finishing group of stands).

Flat steel strip (abbreviated steel strip, rolling or steel strip) is usually transported in a hot rolling mill on a roller table from the first group of rolling stands (also roughing group of rolling stands or English roughing mill ) to the second group of rolling stands (also finishing group of rolling stands or English finishing mill ). In this case, the flat steel strip moves at a certain speed in the direction of transport, which corresponds to the longitudinal direction of the flat steel strip. Due to the contact of the hot flat steel strip with air, the flat steel strip is covered with scale. In order to prevent dross rolling, the dross is removed from the flat steel strip prior to rough and/or finish rolling, whereby the temperature is lowered. In order to compensate for the heat loss of the flat steel strip due to descaling and transport between two sets of rolling stands, and to allow the flat steel strip to finish rolling in the last stand of the finishing group of rolling stands in a certain temperature range (for example, in the austenitic region), the flat steel strip is heated with any, in particular inductive, heating device, which is located between two groups of rolling stands.

When heating a flat steel strip in a hot rolling mill with an inductive heating device, the operating point of the heating device must be taken into account. With prior art inductive heating devices, this means that the heating device is either adapted to heat thin steel strips, for example 6 mm to 15 mm thick, or the heating device is adapted to heat thick steel strips, for example greater than 15 mm thick. By adapting each of the operating points to the prevailing operating conditions, the heating device in each thickness range can meet the requirements for efficiency and the desired temperature profile, i.e. temperature distribution over the width and preferably the thickness of the steel strip. This results in that in the first case, thick steel strips, eg > 18 mm thick, are not heated properly, and in the second case, thin steel strips, eg, < 12 mm thick, cannot be heated properly. By "improperly" is meant that the efficiency and/or temperature profile of the heating device is poor or unacceptable.

The reason for this problem is that different thickness ranges of steel strips require different heating concepts, for example, that a heating device creates a magnetic field in the steel strip across or along the conveying direction of the steel strip having a certain operating frequency, and this magnetic field corresponds to a certain thickness range.

Since the concept of heating and the operating frequency (i.e., the frequency of the alternating voltage at which the heating device is operated or operated) of an inductive heating device is largely determined by its structure, the flexibility to cover a large range of thicknesses in prior art heating devices is either unattainable or available only to a very limited extent. In addition, the operating frequency of the prior art induction heating cannot be changed. Changes to the operating frequency are only possible after a lengthy reset of the heating device.

In order to be able to produce many different end products in a hot rolling mill, such as a cast-rolling combined plant, in particular an Arvedi ESP plant, a CSP plant or a QSP-DUE plant, it is desirable to be able to heat the steel strip in an energy efficient and homogeneous manner with respect to temperature profile. wide range of thicknesses.

The object of the invention is to provide an improved heating device and an improved method for inductively heating a flat steel strip which moves in the conveying direction between two sets of rolling stands of a rolling mill, in particular a combined casting and rolling plant, at a certain speed. In particular, the temperature profile of the steel strip should be more homogeneous than known heating devices in the width direction, eg 900 to 2100 mm, and in the thickness direction, eg 6 to 65 mm.

The problem according to the invention is solved by using a heating device with the characteristics of claim 1 of the claims. Preferred embodiments of the invention are the subject of the dependent claims.

The heating device according to the invention for inductively heating a flat steel strip in a hot rolling mill, the heating device being located between two sets of rolling stands of the hot rolling mill, and the flat steel strip passing through the heating device in the conveying direction at a certain speed, comprises:

- several, in particular 6-12, particularly preferably 8-10, located one behind the other along the direction of transport of the flat steel strip of transverse field modules;

a plurality, in particular 2 to 8, arranged one behind the other along the transport direction of the flat steel strip of longitudinal field modules, which are located along the transport direction before or after the transverse field modules, and

- a first current source for supplying at least one transverse field module with a first alternating voltage and a second current source for supplying at least one longitudinal field module with a second alternating voltage, this first and second current source each having its own frequency converter and an electrically connected capacitor bank having several capacitors connected in parallel.

The transverse field module comprises at least one coil, preferably one coil above the steel strip and one coil below the steel strip, which coil or coils, respectively, generate a magnetic field transverse to the transport direction, specifically in the thickness direction, and at the same time perpendicular to top and bottom side of the flat steel strip, and thus the steel strip can be inductively heated. The transverse field module is intended in particular for heating a thin steel strip.

The longitudinal field module includes one or more coils which generate a magnetic field in the longitudinal direction, specifically in the transport direction, and at the same time parallel to the top and bottom side of the flat steel strip, and thus the steel strip can be inductively heated. The longitudinal field module is intended, in particular, for heating a thick steel strip.

By combining several modules of the transverse field and the longitudinal field, both thin and thick steel strips can be inductively heated with a high efficiency and a homogeneous temperature profile in the width direction of the steel strip.

In accordance with the invention, the heating device includes a first current source for supplying at least one transverse field module with a first alternating voltage and a second current source for supplying at least one longitudinal field module with a second alternating voltage, and these current sources each have their own frequency converter and an electrically connected capacitor bank having a plurality of capacitors connected in parallel.

Since the first alternating voltage is generally different in frequency, voltage amplitude, current strength and power from the second alternating voltage, according to the invention, it is provided that the first current source supplies at least one transverse field module with the first alternating voltage, and the second current source at least one longitudinal field module with a second alternating voltage. The first and second AC voltages are each optimized for optimal operation of said at least one transverse field and longitudinal field module.

The inductances of the coil or, respectively, the coils of one or more modules of the transverse field form the first electrical circuit with the capacities of the capacitor bank of the first current source. In a similar way, the inductances of the coil or, respectively, the coils of one or more longitudinal field modules form a second electrical circuit with the capacities of the capacitor bank of the second current source.

Preferably, the first and/or second current source or, respectively, the frequency converter of each current source includes a frequency input for setting a rated frequency, the frequency of the alternating voltage generated in each case following this rated frequency. In particular, the frequency may change during the heating process.

In the first case, the current source or, respectively, the frequency converter is not controlled by the load or, respectively, controlled from the outside, the frequency converter, or, respectively, not controlled by the load, or, respectively, controlled from the outside. Specifically, this means that the operating frequency of the alternating voltage is not obtained due to the inductances and capacitances present in the electrical circuit, but the operating frequency can be set separately, for example, via a frequency input.

In the second case, the current source or frequency converter is a load-controlled frequency converter or a load-controlled current source, whereby the operating frequency of the AC voltage can be changed by changing, for example, connecting or disconnecting capacitors, a capacitor bank and/or changing eg connecting or disconnecting the coils of the longitudinal field or transverse field modules. A load-controlled frequency converter always creates an alternating voltage depending on the inductances and capacitances present in the electrical circuit (also called an oscillating LC circuit). A separate setting of the operating frequency of the alternating voltage is not possible.

Accordingly, there are two possibilities for changing the operating frequency of the AC voltage:

1) The frequency converter is a load-controlled frequency converter or is operated as a load-controlled frequency converter. In this case, the frequency converter creates an alternating voltage, the frequency of which is obtained from the inductances and capacitances available in the oscillating LC circuit. Thus, the operating frequency of the alternating voltage can be changed by changing the inductance of the coil or coils present in the electrical circuit and/or the capacitance of the capacitor banks present in the electrical circuit. In any of the simple embodiments, the capacitors of the capacitor bank or coil can be connected or disconnected. Due to the connection or disconnection, a phased change in the operating frequency is carried out.

2) The frequency converter is not a load-controlled frequency converter, or therefore not operated as a load-controlled frequency converter. In this case, the frequency converter creates an alternating voltage, regardless of the inductances and capacitances present in the oscillating LC circuit. In this case, the operating frequency of the alternating voltage is directly set by the frequency converter. Any change in the inductance of the coil or, respectively, the coils and/or the capacitance of the capacitor banks, in general, is not necessary. Changing the operating frequency can be done continuously or in stages.

The frequency input can be, for example, an analog or digital input, or just a simple switch to change the capacitance of a capacitor bank.

For example, the frequency can be adjusted depending on the thickness of the flat steel strip or other parameters; the adjustment can be carried out in particular in a controlled or regulated manner. The thickness of the flat steel strip can either be measured or obtained from the pass program of the preceding set of rolling stands. By means of the frequency, the heating of the steel strip can be influenced in a targeted manner, with higher frequencies rather heating only areas close to the surface, while lower frequencies cause a relatively uniform heating of all thickness areas.

The transverse field modules according to the invention are operated with an alternating voltage having a frequency of 200 to 1500 Hz. And the longitudinal field modules are operated with alternating voltage, however, from 3000 to 8000 Hz, in the case of particularly thin strips even up to 40 kHz.

In one of the embodiments, the frequency of the alternating voltage during operation of the heating device or, respectively, during the heating process may change, for example, switch. Alternatively, the frequency can be switched without tuning during plant downtime, i. e. before or after the heating process.

The frequency input is usually connected to the control system of the hot rolling mill plant or a control or regulation device.

Preferably, the first and/or second current source of at least one transverse field module or one longitudinal field module includes a current input for setting a nominal current, and the current of the generated AC voltage follows this nominal current. This current can be either the current generated by the frequency converter or the current that flows through the coil or respectively the coils of the transverse field or longitudinal field module. The current input is usually an analog (eg 4-20 mA) or digital input. The change in current is most often continuous or pseudo-continuous, for example, following a 6-(64 steps), 8-(256 steps) or 10-bit signal, using a current control element, such as a current regulator.

Preferably, if the first and/or second current source, in particular a frequency converter, of at least one transverse field module or one longitudinal field module includes a voltage input for setting the nominal voltage amplitude, while the voltage amplitude of the generated alternating voltage follows this nominal amplitude voltage. The voltage input can, in turn, be an analog (for example, the so-called 4-20 mA) or a digital input.

In addition, it is preferable if the first and/or second current source, in particular the frequency converter of at least one transverse field module or one longitudinal field module, includes a power input for setting the rated power, while the heating power of the generated alternating voltage follows this rated power. The power input can, in turn, be an analog (eg, so-called 4-20 mA) or digital input.

Preferably, the heating device includes a moveable actuator for changing the width position of at least one coil of the transverse field module in the direction of the width of the flat steel strip. It is particularly advantageous if the first sliding actuator can move at least one coil on the upper side of the steel strip and the second sliding actuator can move at least one coil on the lower side of the steel strip. Due to this, the transverse field module can evenly heat different widths of the steel strip, and excessive heating of the edge regions is prevented.

Preferably, at least one transverse field module has a width input for setting a nominal width position, and the width position of the coil of the transverse field module in the width direction follows this nominal width position. The conversion of the nominal width position into the width position is carried out, for example, using a position controller.

Preferably, the heating device has at least one lifting actuator for changing the height position of at least one transverse field module coil in the height direction. It is particularly advantageous if the first lifting actuator can raise or lower, respectively, relative to the flat steel strip, at least one coil on the upper side of the steel strip, and the second lifting actuator can raise at least one coil on the lower side of the steel strip. Thanks to this, a constant so-called. a coupling gap between the coil or coils and the flat steel strip even with different thicknesses, so that the efficiency of the heating device is increased. In addition, the coil or the coils can be removed from the steel strip in the event of a malfunction in the hot rolling mill, thereby improving the possibility of maintenance.

Preferably, at least one transverse field module includes a height input for setting a nominal height position, and the height position of the transverse field module coil in the thickness direction follows this nominal height position. The conversion of the nominal height position to the height position is carried out, for example, using a position controller.

The movable or lifting actuators can be, for example, hydraulic, pneumatic or electromagnetic actuators.

The width or height input can in turn be an analog input (eg 4-20 mA) or a digital input.

Preferably, the heating device includes a control or regulation device, which control or regulation device includes at least one output, preferably several outputs, from the group

- frequency output for setting the nominal frequency of the first alternating voltage;

- current output for setting the nominal current of the first alternating voltage;

- voltage output for setting the rated voltage of the first alternating voltage;

- power output for setting the rated power of the first alternating voltage;

and the control or regulation device further includes

- width output for setting the nominal width position in the direction of the coil width of the transverse field module and/or

- height output for setting the nominal position in height in the direction of the coil thickness of the transverse field module;

in this case, at least one output from the group rated current, rated frequency, rated voltage and rated power, as well as additionally the nominal position in width and / or nominal position in height, are adjusted depending on at least one parameter of the flat steel strip from the group thickness, width, speed, temperature before entering the heating device and temperature after leaving the heating device.

The aforementioned control or regulation device is optimized for the operation of transverse field modules.

Preferably, the heating device includes a control or regulation device, which control or regulation device includes at least one output from the group

- frequency output for setting the nominal frequency of the second alternating voltage;

- current output for setting the nominal current of the second alternating voltage;

- voltage output for setting the nominal voltage of the second alternating voltage;

- power output for setting the rated power of the second alternating voltage;

while at least one output from the group rated current, rated frequency, rated voltage and rated power are adjusted depending on at least one parameter of a flat steel strip from the group thickness, width, speed, temperature before entering the heating device and temperature after exit from the heater.

Said control or regulation device is optimized for the operation of the longitudinal field modules.

It is, of course, possible for the control or regulation device to consist of several modules or assemblies, for example a first node for setting the rated frequency and/or rated current and a second node for setting the width position and/or height position at least one coil. In this case, both nodes are adjusted depending on at least one parameter of the flat steel strip from the group thickness, width, speed, temperature before entering the heating device and temperature after leaving the heating device. The control or regulation device can activate one or more transverse field modules. In addition, it is possible for the control or regulation device to adjust the current strength and, if necessary, the current strength of one or more longitudinal field modules depending on at least one of the above-mentioned parameters.

By means of control or regulation devices, the heating device can optimally heat steel strips of different thicknesses, widths, speeds and temperatures in terms of efficiency and temperature profile in an optimum manner.

The technical problem is also solved using the method according to claim 12 of the claims. Preferred embodiments of the invention are the subject of the dependent claims.

, при этом L_Ges указывает общую индуктивную нагрузку, а C_Ges общую емкостную нагрузку в электрической цепи.According to claim 12, a flat steel strip is inductively heated by a heating device according to the invention, wherein the heating device is located between two sets of rolling stands of a hot rolling mill, and the flat steel strip passes through the heating device in the conveying direction at a certain speed. In this case, the flat steel strip is heated by a plurality of transverse field modules located one behind the other along the conveying direction and by means of several longitudinal field modules arranged one behind the other along the conveying direction of the flat steel strip, wherein the longitudinal field modules in the conveying direction are located before and/or after the transverse field modules. According to the invention, the current source for supplying at least one transverse field module or at least one longitudinal field module has a frequency converter, which is operated as a load-controlled frequency converter, wherein the frequency f of the generated alternating voltage

, with L _Ges indicating the total inductive load and C _Ges the total capacitive load in the electrical circuit.

, при этом L_Ges указывает общую индуктивную нагрузку, а C_Ges общую емкостную нагрузку в электрической цепи.Alternatively, the flat steel strip according to claim 13 is inductively heated by the heating device according to the invention, the heating device being located between two sets of rolling stands of the hot rolling mill and the flat steel strip passing through the heating device in the transport direction at a certain speed. In this case, the flat steel strip is heated by a plurality of transverse field modules located one behind the other along the conveying direction and by means of several longitudinal field modules arranged one behind the other along the conveying direction of the flat steel strip, wherein the longitudinal field modules in the conveying direction are located before and/or after the transverse field modules. According to the invention, the current source for supplying at least one transverse field module or at least one longitudinal field module has a frequency converter, which is operated as an externally controlled frequency converter, with the frequency f of the generated alternating voltage

, with L _Ges indicating the total inductive load and C _Ges the total capacitive load in the electrical circuit.

According to any of the preferred embodiments, the flat steel strip during charging and discharge from the heating device is heated at a controlled voltage or, respectively, regulated voltage, so that the voltage follows the rated voltage, and during pseudo-continuous operation of the heating device is heated at a controlled power or, respectively, adjustable power, so that the heating power follows the rated power.

In one embodiment, at least one transverse field module is operated with an alternating voltage having a certain frequency, this frequency changing during a rolling campaign or between two rolling campaigns. The frequency is preferably adjusted depending on the thickness of the flat steel strip. Of course, other parameters may be involved in frequency tuning.

In one embodiment, the frequency during operation of the heating device, i. e. during the rolling campaign, switches or changes in a variable way. Alternatively, the frequency may also be changed before or after the heating process, i.e. between two rolling campaigns.

According to any of the embodiments, at least one transverse field module or, respectively, at least one longitudinal field module is operated with an alternating voltage having a certain current, and this current is adjusted depending on at least one parameter of a flat steel strip from groups thickness, speed, temperature before entering the heating device and temperature after leaving the heating device.

According to another embodiment, using a sliding actuator to move at least one coil of the transverse field module in the width direction, the width position of the coil is adjusted depending on the width and/or temperature profile of the flat steel strip. The temperature profile of the flat steel strip can be measured by measuring the temperature at several positions in the width direction of the steel strip, either before entering the heating device or before entering a subsequent set of rolling stands. In particular, the temperature profile can be measured, for example, before descaling, or preferably also after descaling.

According to another embodiment, by means of a lifting actuator for moving at least one coil of the transverse field module in the thickness direction, the height position s _H of the coil is adjusted depending on the thickness of the flat steel strip. Thanks to this, the so-called. the gap between the workpiece and the coil at different thicknesses of the workpiece can be adjusted and, for example, kept constant.

The embodiments described combine different inductive heating concepts, for example transverse field modules and longitudinal field modules with different, in particular switchable or variably adjustable operating frequencies, so that a wide range of thicknesses of the flat steel strip to be heated can be covered. The power distribution along the heating device and the operating frequencies of the individual transverse field modules and longitudinal field modules can be selected by adjusting the current strength according to the actual thickness of the flat steel strip. This means, for example, that for certain thicknesses the heating is carried out exclusively or predominantly by means of the longitudinal field modules, while by means of the transverse field modules it is only maintained at certain frequencies. For other flat steel strip thicknesses, this may be the other way around.

Different frequencies or sets of frequencies can be selected. Enabling or varying frequencies to optimize heating efficiency and temperature profile can be done either online or offline. The power distribution along the heating device can also be selected to optimize the heating efficiency and temperature profile. Different power distributions and different operating frequencies along the heating device can be chosen to influence the material properties of the final product obtained from the flat steel strip to be heated.

By combining different heating concepts with switchable or variable operating frequencies, the product range of a rolling mill can be significantly extended. By using different switching patterns (more or less power for transverse field modules and longitudinal field modules) at a certain operating frequency, the heating efficiency can be markedly improved and the temperature distribution across the thickness of the flat steel strip can be influenced. In this case, energy savings of up to 50% are possible.

The width of the flat steel strip may be, for example, from 900 mm to 2100 mm, the thickness, for example, from 6 mm to 65 mm, in particular from 8 mm to 45 mm. The mass flow through the heating device may be, for example, from 200 t/h to 500 t/h. The described heating device can adapt to changes in the thickness of the flat steel strip and the mass flow. Thanks to the optimized heating of the beginning and end of the flat steel strip, a high performance is obtained in continuous operation, as well as in intermittent or semi-endless operation. By means of the device or method described, a homogeneous heating of a flat steel strip in the width and thickness directions is achievable. Particularly short heating device lengths can be achieved with high power density and reduced heat loss, even at low mass flow.

Due to the reduced number of inductive modules and low mechanical complexity, costs can be reduced.

The arrangement of the transverse field modules and the longitudinal field modules according to the invention in groups instead of one at a time makes it easier to control the entire heating device.

Each type of inductive module or group of modules, such as transverse field modules, longitudinal field modules or modules having different frequencies, has a characteristic heating behavior so that different temperature profiles are created in each case. For regulation, it is easier if the first group of modules creates a certain temperature profile, for example, by means of longitudinal field modules that raise the temperature evenly across the width of the flat steel strip, and then by means of a second group of modules, for example, transverse field modules, the created temperature profile is changed and optimized according to requirements. Other sequences may alternatively be used. Eg. The temperature profile can first be pre-adjusted with the transverse field modules and then the temperature homogenization can be achieved with the longitudinal field modules.

Transverse field inductors can normally be operated at lower frequencies, because due to the specific formation of magnetic fields, heat can be better transferred into the material. The usual operating ranges are about 200 Hz-1500 Hz.

When only transverse field modules are used, the efficiency increases greatly when thinning the strips (from approx. 60% at 18 mm to approx. 80% at 8 mm). The thinnest strips have an almost homogeneous temperature distribution across the width of the strip with small temperature deviations at the edges. As the strip thickness increases, the temperature deviations at the edges also increase and, starting at approx. from 14 mm - 15 mm, take higher values. Starting from 20 mm - 25 mm, this leads to overheating of the edges, which can negatively affect the quality of the product. The heating of the strip reaches the core as low operating frequencies can be applied. Due to the low operating frequencies, a simpler voltage supply design is possible.

For longitudinal field inductors, the heat transfer and efficiency decrease sharply when the strips are thinned. And this is eliminated by increasing the frequency. If, for example, a frequency range of 3000 Hz to 8000 Hz is sufficient for thicknesses greater than 15 mm, then for thicknesses of thin strips approx. up to 10 mm to ensure efficient operation, frequencies from 10 kHz to 15 kHz are preferred.

If the strip thickness continues to decrease, frequencies up to 40 kHz can also be reached.

With the exclusive use of longitudinal field modules, when the strips are thinned, the efficiency decreases (from approx. 70% at 18 mm to approx. 40% at 8 mm). That is, for the same output, a larger furnace and higher capital costs would be required. For all strip thicknesses, an almost homogeneous temperature distribution always takes place. Therefore, the inlet temperature profile rises “only” evenly. In this case, the cold edges at the inlet remain cooler even after heating.

If a larger range of thicknesses is to be covered, then a combination of induction modules can also be used, which are matched and designed each for a constant operating frequency.

Alternatively, in this case, induction modules can also be used, which, depending on the current production parameters, can be switched to the desired optimum operating frequency or varied accordingly.

The present invention allows, with a combination of stacked longitudinal field modules and transverse field modules for all types of ESP plants, to configure an optimized heating device having a high efficiency and an optimized temperature profile.

As an example, the following types of heating devices for ESP production plants should be mentioned here:

- intermediate strip thickness from 6 mm to 17 mm: approx. 80-90% of the produced intermediate strip has a thickness of 6 to 12 mm, the rest of the production has a thickness of 12 mm to 17 mm. In this case, the heating device may include, for example, 8-10 transverse field modules. Optionally, two more longitudinal field modules can be used to optimize the temperature profile.

- intermediate strip thickness from 6 mm to 20 mm: the entire thickness range is used in production. In this case, the heating device may include, for example, 8-10 transverse field modules and two to four longitudinal field modules. This results in a good efficiency of the transverse field modules in the case of thin strips and a homogeneous temperature profile due to uniform heating by the longitudinal field modules.

- intermediate strip thickness from 6 mm or 8 mm to 45 mm or 50 mm: in this case, the heating device may include, for example, 8-10 transverse field modules and 6-8 longitudinal field modules. In the case of a thick intermediate strip, the energy is transmitted mostly by means of the longitudinal field modules. This is preferred in the case of thick strips. The transverse field modules mainly serve to heat the corner regions and the core of the intermediate strip and thereby homogenize the temperature profile in the direction of the width and thickness of the intermediate strip. In the case of a thin intermediate strip, the energy is transmitted mostly by means of transverse field modules. This is preferred in the case of thin strips. The longitudinal field modules are either disabled or only transmit a small amount of power to the intermediate band.

The intermediate strip is a flat steel strip or strip which has been rolled in the first set of rolling stands (roughing stand group) of the hot rolling mill but has not yet been finally rolled in the second set of stands (finishing stand group).

The above described features, features and advantages of this invention, as well as how they are achieved, become clearer and clearer in the context of the following description of exemplary embodiments, which are explained in more detail with reference to the drawings. This shows:

1 is a schematic plan view of a first non-inventive embodiment of a heating device for heating a flat steel strip;

2 is a schematic plan view of a second non-inventive embodiment of a heating device for heating a flat steel strip;

Fig. 3 is a schematic plan view of a first embodiment according to the invention of a heating device for heating a flat steel strip;

4 is a schematic plan view of a second embodiment of the invention for heating a flat steel strip;

Fig. 5a: schematic representation of a transverse field module for heating a flat steel strip;

Fig. 5b: schematic representation of the supply of current and magnetic field of the transverse field module for heating a flat steel strip;

6a: schematic representation of a longitudinal field module for heating a flat steel strip;

fig.6b: schematic representation of the supply of current and magnetic field of the longitudinal field module for heating a flat steel strip;

7a is a front view of a third embodiment of the heating device according to the invention;

fig.7b: top view of the heating device of fig.7a;

fig.7c: partially dissected image along the line A-A from fig.7b;

fig.8a: a schematic representation of the first control or regulation device for the heating device of fig.7a-fig.7c;

fig.8b: schematic representation of the second control or regulation device for the heating device of fig.7a-fig.7c;

Fig. 9 is a schematic plan view of yet another heating device according to the invention for heating a flat steel strip;

10a...c: in each case a schematic representation of a power source for a heating device according to the invention for heating a flat steel strip.

Corresponding parts in all figures are provided with the same reference symbols.

Figure 1 shows a schematic view of a first embodiment of a heating device 1 not proposed by the invention for inductively heating a flat steel strip 2. The flat steel strip leaves a roughing group of stands, not shown, is heated by the heating device 1 and, after heating, enters a not shown finishing group rolling stands. Optionally, scale can still be removed from the heated flat steel strip 2 before entering the finishing group of stands. The heating device 1 includes eight transverse field modules 3. The transverse field module 3 includes one inductor each above and below the flat steel strip 2, which generate a magnetic field transverse to the transport direction R, specifically in the thickness direction and at the same time perpendicular to the top and bottom side of the flat steel strip 2, and thus inductively heat her. In the embodiment shown, eight transverse field modules 3 arranged one behind the other are provided. However, more or less transverse field modules 3 can also be provided. The transverse field modules 3 are operated with an alternating voltage of the first frequency f1. This heating device 1 is intended, for example, for heating flat steel strips with a thickness of 6 mm to 17 mm. The flat steel strip 2 can have different widths b1, b2. To prevent overheating of the edge areas of the flat steel strip 2, the inductors of the transverse field modules 3 can each move with their own actuating element relative to the edge, for example, the upper inductor located above the strip relative to the edge shown above, and the lower inductor located under the strip relative to the edge shown below.

FIG. 2 shows a schematic view of a second non-inventive embodiment of a heating device 1 for inductively heating a flat steel strip 2, in particular for heating between two sets of rolling stands in a hot rolling mill. The heating device 1 includes ten transverse field modules 3. The transverse field module 3 in turn includes one inductor each above and below the flat steel strip 2, which generate a magnetic field transverse to the transport direction R, specifically in the thickness direction, and thus heat it inductively. In the embodiment shown, ten transverse field modules 3 arranged one behind the other are provided. However, more or fewer transverse field modules 3 can also be provided. The transverse field modules 3 are operated with an alternating voltage having a switchable frequency, this frequency being either f1 or f2, where f2 is greater than f1. This heating device 1 is intended, for example, for heating flat steel strips with thicknesses from 6 mm to 15 mm, however with the additional possibility of setting the temperature profile.

FIG. 3 shows a schematic view of a first embodiment according to the invention of a heating device 1 for inductively heating a flat steel strip 2, in particular between two sets of rolling stands of a hot rolling mill. The heating device 1 includes a number of transverse field modules 3 and longitudinal field modules 4 located one behind the other. The transverse field module 3 includes one or more inductors which generate a magnetic field across the transport direction R, specifically in the thickness direction of the flat steel strip 2, and thus inductively heat it. In the embodiment shown, eight transverse field modules 3 arranged one behind the other are provided. However, more or less transverse field modules 3 can also be provided. The longitudinal field module 4 includes one or more inductors which generate a magnetic field in the longitudinal direction, specifically in the transport direction R and at the same time parallel to the upper and lower side of the flat steel strip 2, and thus heat it inductively. However, more or fewer longitudinal field modules 4 can also be provided. In the embodiment shown, four longitudinal field modules 4 arranged one behind the other are provided. The transverse field modules 3 are operated with an alternating voltage of the first frequency f1. This heating device 1 is intended, for example, for heating flat steel strips with a thickness of 6 mm to 20 mm.

Fig. 4 shows a schematic view of a second embodiment of the invention of a heating device 1 for inductively heating a flat steel strip 2, in particular for heating between two sets of rolling stands of a hot rolling mill. The heating device 1 includes a number of transverse field modules 3 and longitudinal field modules 4 located one behind the other. The transverse field module 3 includes one or more inductors which generate a magnetic field across the transport direction R, specifically in the thickness direction of the flat steel strip 2, and thus inductively heat it. In the embodiment shown, eight transverse field modules 3 arranged one behind the other are provided. However, more or less transverse field modules 3 can also be provided. The longitudinal field module 4 includes one or more inductors which generate a magnetic field in the longitudinal direction, specifically in the transport direction R and at the same time parallel to the upper and lower side of the flat steel strip 2, and thus heat it inductively. In the embodiment shown, eight longitudinal field modules 4 arranged one behind the other are provided. However, more or fewer longitudinal field modules 4 can also be provided. The transverse field modules 3 are operated with an alternating voltage having a switchable frequency, this frequency being either f1 or f2, where f2 is greater than f1. The longitudinal field modules 4 are operated either at a frequency of f3 or f4, with f3 > f2 and f4 > f2. This heating device 1 is intended, for example, for heating flat steel strips with a thickness of 6 mm to 65 mm.

Fig. 5a schematically shows a transverse field module 3 having two coils which are located above and below a flat steel strip 2. When current is applied to the coils 5 of the transverse field module 3, a magnetic field M is generated transverse to the transport direction R in the thickness direction of the strip 2. B As a result, the flat steel strip 2 having a thickness d and a width b1 is heated. Eddy currents W are formed on the upper and lower side of strip 2.

5b shows the supply of current I (currents entering the drawing plane are shown with a cross, currents leaving the drawing plane with a dot) to the coils 5 and the magnetic flux lines of the magnetic field M for another module 3 of the transverse field.

FIG. 6a schematically shows a longitudinal field module 4 having a coil 5 which surrounds the flat steel strips y 2 across the transport direction R. When current is applied to the coil 5 of the longitudinal field module 4, a magnetic field M is generated in the transport direction R parallel to the top and bottom sides of the strip 2. As a result, the flat steel strip 2 having a thickness d and a width b1 is heated. Eddy currents W are formed parallel to the upper and lower side of strip 2.

6b shows the supply of current I (currents entering the drawing plane are shown with a cross, currents leaving the drawing plane with a dot) to the coil 5 and the magnetic flux lines of the magnetic field M for the longitudinal field module 4.

Figures 7a and 7b show an elevation and a plan view of a heating device according to the invention in a hot rolling mill. After the flat steel strip 1 has been rolled in the last stand 9 of the roughing group of stands, the roll 2 is transported along a roller table not shown in detail to the first stand 10 of the finishing group of stands and is inductively heated by means of a heating device 1. This heating device includes in six modules 3 of the transverse field, having one coil 5 above and below the roll 2, as well as two modules 4 of the longitudinal field, which are located behind the modules 3 of the transverse field. The width b, the thickness d, the speed v and the temperature profile T _{1 of} the roll 2 after the last stand 9 of the roughing group of rolling stands are measured with suitable measuring instruments and entered into the control or regulation device 8 (see FIG. 8a). After passing through the heating device 1 from the roll 2, the scale is removed by means of two descaling devices 12 at high pressure, for example 150-400 bar. Before and after the descaling, a pair of pull rollers 13 are provided to prevent the pressurized water from escaping from the descaling area. Either before or preferably after the descaling, the roll temperature profile T ₂ is measured with the pyrometer 11 and also entered into the control or regulation device 8 . Optionally, a pyrometer 11, shown in dashed lines, can be placed in front of the descaling devices, which measures the temperature profile of the roll 2 before descaling. The coils 5 of the transverse field modules 3 are each housed in their own coil cart 19 (see also FIG. 7c). The bobbins 19 together with the bobbins 5 above and below the roll 2 can be moved by means of a movable actuator 6 in the direction of the width of the roll. In this way, the width position of s _B can be adjusted, i. e. the distance between the side edge of the roll 2 and the end of the coil 5. In addition, the position s _H along the height of the coils 5 can change and, at the same time, the distance between the upper coil 5 and the upper side of the roll, as well as the lower coil 5 and the lower side of the roll 2. Change in height carried out with the help of several lifting actuators 7 (see also fig.7c). The current source 14 of one or more transverse field modules 3 is located in the air-conditioned and clean room 20 of electrical equipment. Fig. 7c is a schematic sectional view across the transport direction R along the line AA of Fig. 7b, including a frequency converter 16 for generating an alternating voltage having a certain frequency f and a certain current I, a capacitor bank 17 having a plurality of capacitors connected in parallel, and flexible cables 15, here coaxial cables, for connecting the capacitor bank 17 to the mobile coils 5 on the trolley 19 for the coil. The connection between the frequency converter 16 located in the cabinet 16a and the capacitor bank 17 is carried out by means of current buses 18. In the event that a parasitic electric arc occurs in the area of the current source 14, the excess pressure in the room 20 of the electrical equipment is discharged outside through the shaft having an explosion-proof valve 21. This ensures that there is no any harmful gases or vapors entering the hot rolling mill. As shown schematically in FIG. 7b, the current source 14 has a frequency input for setting the nominal frequency f _Nom. , current input for setting the nominal force I _Nom. current, width input for nominal position setting s _B-Nom. in width and height input for setting the nominal position s _H-Nom. in height. Through these inputs, one or more transverse field modules 3 can be adapted to the current production conditions in terms of frequency f and AC voltage I, as well as in width position s _B and height position s _H. On fig.7b for the sake of clarity shows only one single source 14 current. Of course, all transverse field modules 3 are connected to current sources 14, whereby one current source 14 can feed one or more transverse field modules 3. The current source of the longitudinal field modules 4 has not been shown.

Figures 8a and 8b show in each case a diagram of a control or regulation device 8 into which the current data of the production process, such as width b, thickness d, roll speed v, as well as temperature profiles T ₁ of roll 2 before entering the heating chamber, are permanently entered. device 1 and after leaving the heating device 1. In accordance with Fig.8a, the control or regulation device 8 calculates from these input values the rated frequency f _Nom. and nominal force I _Nom. current for current sources 14, as well as the nominal position s _B-Nom. in width and nominal position s _H-Nom. in height for trolleys 19 coils of transverse field modules. In accordance with figb device 8 control or regulation calculates from these input values the rated voltage U _Nom. and rated power P _Nom. heating for current sources 14 of longitudinal field modules. These nominal values are connected via the respective outputs of the control or regulation device 8 by signal technology to the inputs of the current source or, respectively, the inputs on the transverse field modules. The control or regulation device 8 can be, for example, a PLC (Programmable Logic Controller) or a process computer. It is also possible for the functionality of the control or regulation device 8 to be taken over by the control of the rolling mill.

Figure 9 schematically shows a top view of the heating device according to the invention, having four transverse field modules 3 and four longitudinal fields, as well as current sources 14 intended for them, 14b.

; в отключенном состоянии частота f получается по

. Кроме того, преобразователем частоты может задаваться амплитуда U напряжения или номинальная мощность P нагрева.10a schematically shows a first variant of the current source 14a, 14b. The frequency converter 16 is a load-controlled frequency converter that adjusts the frequency f of the generated AC voltage depending on the load, specifically the capacitive load of the capacitor bank 17 and the inductive load of the coils 5. The first capacitor shown on the left, having a capacitance C, can be connected or disconnected by means of a switch , which turns on depending on the frequency input 22. In the connected state, the frequency f is obtained from

; in the off state, the frequency f is obtained from

. In addition, the voltage amplitude U or the rated heating power P can be set by the frequency converter.

; в отключенном состоянии частота f получается по

. Преобразователем частоты может снова задаваться амплитуда U напряжения или номинальная мощность P нагрева.10b schematically shows the second version of the current source 14a, 14b. The frequency converter 16 is identical to the frequency converter of FIG. 10a. However, the capacitors of the capacitor bank 17 cannot be turned on. But either one or two coils 5 can be energized. In one case, the frequency f is obtained from

; in the off state, the frequency f is obtained from

. The frequency converter can again set the voltage amplitude U or the rated heating power P.

Of course, both inductances and capacitances in an electrical circuit can be connected or, respectively, disconnected.

. В противоположность этому, действительная частота f переменного напряжения может отличаться от f₀, потому что f задается непосредственно в преобразователе 16 частоты частотным входом 22. При эксплуатации управляемого извне преобразователя частоты следует принимать во внимание, что источник тока должен вводить в преобразователь частоты не только мощность нагрева, но и реактивную мощность.Finally, FIG. 10c shows a third variant of a current source 14a, 14b having a frequency converter 16 that is not controlled by the load or, respectively, controlled from the outside. The load is 2C for capacitor bank 17 and L for coil 5. In the case of a load-controlled frequency converter, the frequency f of the AC voltage would be obtained by

. In contrast, the actual frequency f of the AC voltage may differ from f ₀ because f is set directly in the frequency converter 16 by the frequency input 22. When operating an externally controlled frequency converter, it should be taken into account that the current source must not only supply power to the frequency converter. heating, but also reactive power.

In the description of Fig.10a...cf ₀ denotes the resonant frequency of the so-called. oscillatory LC circuit.

The electrical circuits shown in Figs. 10a…10c are schematic and do not take into account the magnetic coupling of the coil or, respectively, the coils 5 with the flat steel strip 2.

LIST OF REFERENCES

1 heating device

2 Flat steel strip, rolling

3 Transverse field module

4 Longitudinal field module

5 Coil

6 Movable actuator

7 Lifting element

8 Control or regulation device

9 Stand of roughing group of stands

10 Stand of the finishing group of stands

11 Thermometer or pyrometer respectively

12 Scale remover

13 Pull roller

14, 14a, 14b Current source

15 Flexible cable

16 Frequency converter

16a Frequency converter cabinet

17 Capacitor bank

18 Current bar

19 Reel trolley

20 Electrical room

21 Explosion-proof valve

22 Frequency input

23 Switch

b, b1, b2 Flat steel strip width

C Capacity

d Thickness of flat steel strip

f, f1, f2, f3, f4 Frequency, actual frequency

f ₀ Resonant frequency of the oscillating LC circuit

f _Nom. Rated frequency

M Flux

I Current, current, actual current

I _Nom. Rated current

L Inductance

P Power

R Direction of transport

s _B Coil width position, actual pos. in width

s _B-Nom. Nominal position across coil width

s _H Coil height position, actual pos. height

s _H-Nom. Nominal coil height position

T ₁ , T ₂ temperature or, respectively, temperature profile

U Voltage

v Flat steel strip speed

W Eddy current

Claims (36)

1. Heating device (1) for inductively heating a flat steel strip (2) in a hot rolling mill, wherein the heating device (1) is located between two groups of rolling stands of the hot rolling mill, and the flat steel strip (2) passes through the heating device (1 ) in the direction (R) of transportation at a certain speed, while the heating device (1) includes: - several modules (3) of the transverse field located one behind the other along the direction (R) of transport of the flat steel strip (2), a plurality of longitudinal field modules (4) arranged one behind the other along the transport direction (R) of the flat steel strip, which are arranged along the transport direction (R) before or after the transverse field modules (3), and - the first current source (14a) for supplying at least one transverse field module (3) with the first alternating voltage and the second current source (14b) for supplying at least one longitudinal field module (4) with the second alternating voltage, and these sources (14a , 14b) current have each its own frequency converter (16) and an electrically connected capacitor bank (17) having several capacitors connected in parallel, while the first and/or second current source (14a, 14b) includes a frequency input that provides a setting rated frequency (f _nom. ) and the frequency (f) of the generated AC voltage follows this rated frequency (f _nom. ). 2. Heating device (1) according to claim 1, in which the first and/or second current source (14a, 14b) includes a current input for setting the nominal strength (I _Nom. ) of the current, and the current strength of the generated alternating voltage follows this rated strength (I _Nom. ) current. 3. The heating device (1) according to claim 1 or 2, in which the first and/or second current source (14a, 14b) includes a voltage input for setting the rated voltage (U _Nom. ), and the amplitude (U) of the voltage generated AC voltage follows this rated voltage (U _Nom. ). 4. Heating device (1) according to any one of paragraphs. 1-3, in which the first and/or second current source (14a, 14b) includes a power input for setting the rated power (P _Nom. ), and the heating power of the generated AC voltage follows this rated power (P _Nom. ). 5. Heating device (1) according to any one of paragraphs. 1-4, which contains a movable actuating element (6) for changing the position (s _B ) across the width of at least one coil (5) of the transverse field module (3). 6. The heating device (1) according to claim 5, in which the transverse field module (3) has a width input for setting the nominal position (s _B-Nom. ) in width, and the position (s _B ) in width of the coil (5) of the module (3) The transverse margin in the width direction follows this nominal position (s _B-Nom. ) in width. 7. Heating device (1) according to any one of paragraphs. 1-6, which contains a lifting actuating element (7) for changing the height position (s _H ) of at least one coil (5) of the transverse field module (3). 8. The heating device (1) according to claim 7, in which the transverse field module (3) includes a height input for setting a nominal position (s _H-Nom. ) in height, and a position (s _H ) in height of the coil of the transverse module field in thickness direction follows this nominal position (s _H-Nom. ) in height. 9. Heating device (1) according to any one of paragraphs. 1-8, which contains a control or regulation device (8), and this control or regulation device (8) includes at least one output from the group: - frequency output for setting the rated frequency (f _Nom. ) of the first AC voltage, - current output for setting the nominal strength (I _Nom. ) of the current of the first alternating voltage, - voltage output for setting the rated voltage (U _Nom. ) of the first alternating voltage, - power output for setting the rated power (P _Nom. ) of the first AC voltage, - width output for setting the nominal position (s _B-Nom. ) in width in the width direction of the coil (5) of the transverse field module (3) and/or - height output for setting the nominal position (s _H-Nom. ) in height in the direction of the thickness of the coil (5) of the transverse field module (3), at least one output from the group: rated current (I _Nom. ), rated frequency (f _Nom. ), rated voltage (U _Nom. ) and rated power (P _Nom. ), as well as additionally rated position (s _B-Nom. ) in width and/or nominal position (s _H-No. ) in height, made with adjustment depending on at least one parameter of a flat steel strip (2) from the group: thickness (d), width (b ), speed (v), temperature (T ₁ ) before entering the heating device (1) and temperature (T ₂ ) after leaving the heating device (1). 10. Heating device (1) according to any one of paragraphs. 1-9, which contains a control or regulation device (8), and this control or regulation device (8) includes at least one output from the group: - frequency output for setting the rated frequency (f _Nom. ) of the second alternating voltage, - current output for setting the nominal strength (I _Nom. ) of the current of the second alternating voltage, - voltage output for setting the rated voltage (U _Nom. ) of the second alternating voltage, - power output for setting the rated power (P _Nom. ) of the second alternating voltage, at least one output from the group: rated current (I _Nom. ), rated frequency (f _Nom. ), rated voltage (U _Nom. ) and rated power (P _Nom. ) is configured depending on at least at least one parameter of a flat steel strip (2) from the group: thickness (d), width (b), speed (v), temperature (T ₁ ) before entering the heating device (1) and temperature (T ₂ ) after leaving the heating devices (1). 11. The method of inductively heating a flat steel strip (2) in a hot rolling mill, including the use of a heating device (1) according to any one of paragraphs. 1-10, wherein the heating device (1) is located between two sets of rolling stands of the hot rolling mill, and the flat steel strip (2) passes through the heating device (1) in the conveying direction (R) at a certain speed, and the following steps: - heating the flat steel strip (2) by means of several transverse field modules (3) arranged one behind the other along the transport direction (R), and - heating a flat steel strip (2) with a plurality of longitudinal field modules (4) arranged one behind the other along the transport direction (R), which are arranged along the transport direction (R) before and/or after the transverse field modules (3), wherein the current source (14) for supplying at least one module (3) of the transverse field or at least one module (4) of the longitudinal field has a frequency converter (16) that operates as a load-controlled frequency converter, while the frequency f of the generated AC voltage

where L _Ges is the total inductive load and C _Ges is the total capacitive load in the electrical circuit. 12. The method of inductively heating a flat steel strip (2) in a hot rolling mill, including the use of a heating device (1) according to any one of paragraphs. 1-10, this heating device (1) is located between two sets of rolling stands of the hot rolling mill, and the flat steel strip (2) passes through the heating device (1) in the conveying direction (R) at a certain speed, and the following steps: - heating a flat steel strip (2) with the help of several transverse field modules (3) arranged one behind the other along the transport direction (R) and - heating a flat steel strip (2) with a plurality of longitudinal field modules (4) arranged one behind the other along the transport direction (R), which are arranged along the transport direction (R) before and/or after the transverse field modules (3), wherein the current source (14) for supplying at least one module (3) of the transverse field or at least one module (4) of the longitudinal field has a frequency converter (16) that operates as an externally controlled frequency converter, while the frequency f of the generated AC voltage

where L _Ges is the total inductive load and C _Ges is the total capacitive load in the electrical circuit. 13. The method according to claim 11 or 12, wherein the transverse field module (3) is supplied with an alternating voltage having a frequency (f, f1, f2) and this frequency (f, f1, f2) is changed during the rolling process or between two rolling processes. 14. The method according to claim 13, wherein the frequency (f, f1, f2) is adjusted depending on the thickness (d) of the flat steel strip (2). 15. The method according to any one of paragraphs. 11-14, in which the module (3) of the transverse field is fed with a current, the strength (I) of which is adjusted depending on at least one parameter of a flat steel strip (2) from the group: thickness (d), speed (v), temperature before the inlet to the heating device (T ₁ ) and the temperature after leaving the heating device (T ₂ ).

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