Preventive maintenance system

Abstract

A preventive maintenance system according to an embodiment of the present invention comprises: an induction heating device having an inductor including a coil that heats a material to be heated by electromagnetic induction of a high-frequency current from an inverter; a voltage detector that detects and outputs a voltage of the coil; a current detector that detects and outputs a current of the coil; and a control device that calculates an impedance of a circuit including the coil on the basis of the detected voltage and current. The control device calculates the impedance on the basis of the voltage and current detected before the material to be heated reaches the coil or after the material to be heated is discharged from the coil, and stores the calculated impedance in association with each time when the voltage and the current used to calculate the impedance are detected.

Description

Preventive Maintenance System

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a preventive maintenance system for an induction heating device.

[0002] In the hot rolling line, the rolled material is heated in a heating furnace to a temperature at which it can be rolled, and then roughly rolled in a roughing mill to form a rough rolled bar. The formed rough rolled bar is then finish rolled in a finishing mill to the desired plate thickness and plate width to produce a product.

[0003] Generally, in a hot rolling line, when the temperature of the steel material drops, the load on the rolling mill increases. Therefore, an induction heating device may be installed to increase the temperature of the rolled material, soak it in heat, and reduce the load. The rolled material that is heated by the induction heating device is called the heated material.

[0004] Known induction heating devices include edge heaters, which are designed to heat both edge portions of the material to be heated, bar heaters, which are designed to heat the entire width of the material to be heated, and uniform temperature heaters, which are designed to heat the center portion of the material to be heated in the width direction.

[0005] Steel manufacturing facilities are operated for long periods of time and are required to produce high-quality products over such long periods. The induction heating equipment installed on the line also needs to continue operating for long periods of time. If the induction heating equipment suddenly stops operating due to aging or deterioration, it will be necessary to stop operation for an extended period of time in order to investigate the cause and take measures, which may have an impact on the operation of the line.

[0006] Therefore, from the viewpoint of preventing the operation of an induction heating device from being stopped, proposals have been made regarding preventive maintenance of the induction heating device, and for example, a technique disclosed in Patent Document 1 is known. In the technique disclosed in Patent Document 1, the deterioration state of any location inside the induction heating device is detected using a temperature sensor having an optical fiber.

[0007] The technology disclosed in Patent Document 1 allows for the monitoring of the deterioration of the inductor over time by installing a temperature sensor between the heating coil and heat-resistant plate that constitute the inductor. However, maintenance of the induction heating device must be performed while the line is stopped, and the temperature sensor is exposed to high temperatures until the maintenance period. This can lead to the deterioration of the temperature sensor itself, or in severe cases, the temperature sensor may burn out.

[0008] JP 2012-163459 A

[0009] Maintenance of induction heating equipment can require a large number of inspection items, and depending on the inspection content, it can take a long time. For this reason, it is necessary to consider the maintenance content in advance and implement preventive maintenance that is carried out in a planned manner. There is a growing need to establish methods for implementing preventive maintenance that accurately grasp the deterioration status of induction heating equipment and perform efficient maintenance inspections that focus on maintenance inspection points.

[0010] The embodiments of the present invention have been made to solve the above-mentioned problems, and have an object to provide a preventive maintenance system that can accurately grasp the deterioration state of an induction heating device.

[0011] A preventive maintenance system according to an embodiment of the present invention includes an induction heating device having an inductor including a coil that heats a material to be heated by electromagnetic induction by passing a high-frequency current supplied from an inverter through the induction heating device, a voltage detector that detects and outputs a voltage applied to the coil, a current detector that detects and outputs a current flowing through the coil, and a control device that calculates an impedance of a circuit including the coil based on the voltage detected by the voltage detector and the current detected by the current detector. The control device calculates the impedance based on the voltage and current detected before the material to be heated reaches the coil or after the material to be heated is discharged from the coil, and stores the calculated impedance in association with the date and time when the voltage and current used to calculate the impedance were detected.

[0012] According to an embodiment of the present invention, a preventive maintenance system is provided that can accurately grasp the deterioration state of an induction heating device.

[0013] 1 is a schematic block diagram illustrating a preventive maintenance system according to an embodiment; FIG. 2 is a schematic equivalent circuit diagram of a heating coil of an inductor; FIG. 3 is a schematic diagram illustrating an inductor; FIG. 4 is a schematic diagram illustrating a cooling system of an inductor that is part of the preventive maintenance system according to an embodiment;

[0014] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. Note that in this specification and each drawing, elements similar to those previously described with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions will be omitted as appropriate.

[0015] 1 is a schematic block diagram illustrating a preventive maintenance system according to an embodiment. As shown in FIG. 1, the preventive maintenance system 100 according to the embodiment includes a bar heater 1, a measurement transformer 5, a measurement current transformer 6, a capacitor 9, and a control device 10.

[0016] Bar heater 1 has inductor 2. As will be described in detail with reference to Figures 3 and 4, inductor 2 has heating coil 13 made of a wound conductor, and inverter 18 is electrically connected to heating coil 13. Heating coil 13 generates a magnetic field due to high-frequency current output from inverter 18, and the magnetic field generated by heating coil 13 generates a high-frequency induced current in material 15 by electromagnetic coupling with material 15 to be heated. Material 15 is heated by this induced current.

[0017] The capacitor 9 is connected in parallel to the heating coil 13 of the inductor 2. The capacitor 9 forms a parallel resonant circuit together with the heating coil 13, and also adjusts the power factor to the heating coil 13.

[0018] The measuring transformer 5 is provided to detect the voltage across the heating coil 13 of the inductor 2. The measuring transformer 5 detects the voltage across the heating coil 13 at a predetermined cycle and outputs the detected voltage data to the control device 10.

[0019] The measuring current transformer 6 is provided to detect the current flowing in the parallel circuit of the heating coil 13 and the capacitor 9. The measuring current transformer 6 detects the current flowing in the parallel circuit of the heating coil 13 and the capacitor 9 at a predetermined cycle and outputs the detected current data to the control device 10. The cycle of current detection matches the cycle of voltage detection.

[0020] The control device 10 is connected to the outputs of the measurement transformer 5 and the measurement current transformer 6. The control device 10 sequentially calculates the impedance of the parallel circuit based on data on the voltage across the heating coil 13 output by the measurement transformer 5 and data on the current flowing through the parallel circuit of the heating coil 13 and the capacitor 9. The control device 10 stores data on the impedance of the parallel circuit calculated when no material to be heated is present in the inductor 2.

[0021] Figure 2 is a schematic equivalent circuit diagram of the heating coil of the inductor 2. As shown in Figure 2, the heating coil 13 of the inductor 2 can be represented by a series circuit of inductances L1 to L3 and resistances R1 to R3. The series circuit of inductances L1 to L3 and resistances R1 to R3 is connected in parallel with a capacitor 9. An inverter 18 is connected to both ends of the parallel circuit of the heating coil 13 and capacitor 9.

[0022] The inductance L1 and the resistance R1 each have an inductance value and a DC resistance value required to function as the heating coil 13. The inductance value of the inductance L1 is approximately equal to the self-inductance value of the heating coil 13, and the DC resistance value of the resistance R1 is approximately equal to the DC resistance value of the conductor of the heating coil 13.

[0023] Inductance L2 and resistance R2 represent the impedance generated by electromagnetic coupling between heating coil 13 and material 15 to be heated when material 15 to be heated is present inside inductor 2. The inductance value of inductance L2 and the DC resistance value of resistance R2 are determined depending on the material to be heated. When material 15 to be heated is not present inside inductor 2, the inductance value of inductance L2 and the DC resistance value of resistance R2 approximate zero and can be ignored.

[0024] Inductance L3 and resistance R3 represent the impedance generated by electromagnetic induction between the heating coil 13 and scale and other metal-containing compounds (hereinafter referred to as scale, etc.) that have peeled off from the material to be heated 15, etc. Since scale, etc., accumulates over time inside the inductor 2, the inductance value of inductance L3 and the DC resistance value of resistance R3 are determined by the accumulation area and accumulation thickness of scale, etc., regardless of whether material to be heated 15 is present inside the inductor 2. The larger the accumulation area of ​​scale, etc., and the thicker the accumulation thickness, the larger the inductance value of inductance L3.

[0025] Fig. 3 is a schematic diagram illustrating an inductor. As shown in Fig. 3, in the inductor 2 of the bar heater 1, the material to be heated 15 is transported through an opening of the inductor 2. A heat-resistant plate 16 is provided within the opening of the inductor 2. The heat-resistant plate 16 is provided to protect the inductor 2 from radiant heat from the material to be heated 15. A shield cover 17 is provided around the inductor 2. The shield cover 17 is provided to reduce the impact of electromagnetic waves radiated from the inductor 2 on the surrounding area.

[0026] In a hot rolling line, descaling equipment such as a descaler is installed to remove scale and the like formed on the surface of the rolled material before and after rolling. Even when a descaler or the like is installed, some scale and the like may remain attached to the heated material 15 when the material is fed into the bar heater 1. When the induction heating device is operated for a long period of time, scale and the like remaining on the heated material 15 fed into the bar heater 1 may peel off inside the inductor 2 due to vibrations during transportation, and adhere to and accumulate inside the inductor 2.

[0027] From the perspective of the induction heating device, the scale and other materials that have adhered to and accumulated inside the inductor 2 are equivalent to an inductive load consisting of an inductance L3 and a resistance R3, as shown in Figure 2. Therefore, when the amount of accumulated scale and other materials increases, the induction heating device will input power to the accumulated scale and other materials along with the material to be heated 15. In order to eliminate insufficient heating of the material to be heated 15, it will be necessary to input more power than usual, which may accelerate the deterioration of electrical components such as the inductor 2 and capacitor 9, as well as insulating materials. Furthermore, if the input power is maintained, there is a concern that the material to be heated 15 will not be heated sufficiently, increasing the load on the subsequent finishing mill.

[0028] Therefore, the preventive maintenance system 100 according to the embodiment calculates the impedance of the circuit including the heating coil 13 as data representing information on the adhesion and accumulation status of scale, etc. More specifically, the preventive maintenance system 100 calculates the impedance of the parallel circuit between the heating coil 13 and the capacitor 9 when no heated material 15 is present in the inductor 2. This makes it possible to store the impedance data of the parallel circuit as time-series data, excluding the influence of the inductance L2 and the resistance R2, which are determined according to the heated material. The stored time-series data of the impedance of the parallel circuit can be output as information for preventive maintenance.

[0029] When bar heater output command information 12 is active, power is supplied to a parallel circuit consisting of heating coil 13 and capacitor 9, and when bar heater output command information 12 is inactive, power supply to the parallel circuit is stopped. For example, in a specific example of introducing an induction heating device into a hot rolling line, bar heater output command information 12 becomes active a predetermined time before material to be heated 15 enters inductor 2. Furthermore, bar heater output command information 12 becomes inactive a predetermined time after material to be heated 15 passes through inductor 2 and is discharged from inductor 2.

[0030] The control device 10 can calculate the impedance of the parallel circuit using the voltage data and current data of the parallel circuit acquired during a period in which the bar heater output command information 12 is active, a predetermined time before the time when the material to be heated 15 enters the inductor 2. Furthermore, the control device 10 may calculate the impedance of the parallel circuit after the material to be heated 15 is discharged from the inductor 2, using the voltage data and current data of the parallel circuit acquired during a period in which the bar heater output command information 12 is active.

[0031] When there is no material to be heated 15 in the inductor 2 and the bar heater output command information 12 is active, the impedance Z of the parallel circuit of the heating coil 13 and the capacitor 9 can be calculated according to the following equation (1).

[0032] Z=ZL / (1+jω·ZL·C) (1) Here, ZL is the sum of the impedance of the heating coil and the impedance due to the scale, and is expressed by the following equation (2): ZL=R1+R3+jω·(L1+L3) (2)

[0033] The control device 10 calculates the impedance Z in equation (1) and stores, for example, the real part and the imaginary part of the impedance Z. The control device 10 may also calculate and store the magnitude |Z| and the phase angle of the impedance Z.

[0034] The control device 10 stores the values ​​of the real and imaginary parts of the impedance Z as time-series data in association with the date and time at which the voltage data detected by the measurement transformer 5 and the current data detected by the measurement current transformer 6 were acquired. Because the voltage and current data are measured synchronously at a predetermined cycle, the time-series data regarding the impedance calculated by the control device 10 is data synchronized with the time at which the voltage and current data were acquired.

[0035] Time-series data of the impedance Z of the circuit including the heating coil 13 when the bar heater output command information 12 is active and the material to be heated 15 is not present in the inductor 2 can be output to a monitor connected to the control device 10 by, for example, an operator operating the preventive maintenance system 100. For example, the control device 10 has a threshold value for the impedance Z. The threshold value can be set based on experiments, performance data, or the like. For example, the operator can check the time-series data and the threshold value displayed on the monitor 11, and if the data of the impedance Z reaches the threshold value, plan to perform equipment maintenance work on the inductor 2 on the day of the next regular equipment inspection.

[0036] The control device 10 may have a plurality of threshold levels. When the calculated and stored data of the impedance Z reaches a higher threshold level among the plurality of threshold levels, the control device 10 may warn to set an emergency equipment maintenance activity for the next line shutdown period. By setting in this manner, it is possible to warn when more immediate measures are required, and to prevent line shutdowns due to unforeseen circumstances in advance.

[0037] In the above-described specific example, the impedance Z of the parallel circuit of the heating coil 13 and the capacitor 9 is calculated, stored, and output to grasp the accumulation status of scale and the like on the inductor 2. As shown in FIG. 1 , if a coil current measuring current transformer 7 can be provided to detect the current flowing through the heating coil 13, the impedance can be calculated using the current in the heating coil 13 and the voltage across the heating coil 13. Time-series data of the real and imaginary parts of this impedance may be used for maintenance activities. While the above-described specific example describes sequentially acquiring data on the voltage of the parallel circuit consisting of the heating coil 13 and the capacitor 9 and data on the current flowing through the parallel circuit, this is not limited to this. For example, data on the voltage and current of the parallel circuit may be acquired during a period when the bar heater output command information 12 is active and no material to be heated 15 is present in the inductor 2, and data acquisition may be suspended during other periods.

[0038] The preventive maintenance system 100 according to the embodiment can grasp the accumulation status of scale and the like based on the change in impedance of the heating coil 13, and can also calculate the amount of heat dissipated by the cooling system of the heating coil 13 and use the calculated amount of heat dissipated in preventive maintenance activities. The amount of heat dissipated is the amount of heat generated when the cooling system cools the heating coil 13, which is the target for cooling.

[0039] 1 , in the preventive maintenance system 100 according to the embodiment, the bar heater 1 has temperature sensors 3 and 8 and a flow rate sensor 4. The outputs of the temperature sensors 3 and 8 are connected to the control device 10. The output of the flow rate sensor 4 is connected to the control device 10.

[0040] Temperature sensors 3 and 8 are provided to measure the temperature of the cooling water for the inductor 2. Temperature sensor 8 detects the temperature of the cooling water before cooling the inductor 2 and outputs the detected data to the control device 10. Temperature sensor 3 detects the temperature of the cooling water after cooling the inductor 2 and outputs the detected data to the control device 10.

[0041] The flow rate sensor 4 is provided to detect the flow rate of the cooling water for the inductor 2. The flow rate sensor 4 detects, for example, the flow rate of the cooling water after cooling the inductor 2, and outputs the detected data to the control device 10.

[0042] The control device 10 stores the data on the temperature of the cooling water before and after cooling and the data on the flow rate of the cooling water as time-series data, in association with the date and time when these data were acquired.

[0043] The configuration and operation of the preventive maintenance system 100 according to the embodiment will be described in more detail. In the preventive maintenance system 100 according to the embodiment, the cooling water piping of the inductor 2 also serves as the heating coil 13. FIG. 4 is a schematic diagram illustrating an example of an inductor. As shown in FIG. 4, the inductor 2 has the heating coil 13 and a mold 14. The mold 14 covers the periphery of the wound heating coil 13. The mold 14 is provided to insulate the heating coil 13. The mold 14 is also provided to improve the heat dissipation of the heating coil 13 and to protect the heating coil 13 from the intrusion of scale, water, and the like.

[0044] Due to the skin effect of high-frequency current, most of the current flowing through heating coil 13 flows near the surface of the conductor that makes up heating coil 13. Even if a bulk conductor is used for heating coil 13, almost no current flows near the center of the conductor. For this reason, in bar heater 1, a hollow tubular conductor is wound and used for heating coil 13, as shown in Figure 4.

[0045] Since the heating coil 13 is made of a hollow tubular conductor, the heating coil 13 itself can be used as piping for the cooling system by connecting a cooling system to the heating coil 13. Note that using a hollow tubular conductor for the heating coil 13 also has the advantage of making the heating coil 13 lighter.

[0046] Fig. 5 is a schematic diagram illustrating an inductor cooling system that is part of a preventive maintenance system according to an embodiment. In Fig. 5, to avoid complexity in the illustration, a heating coil 13 formed of a hollow tubular body is indicated by a thick line. In reality, the thick line represents a pipe through which cooling water can flow. Pure water is used as the cooling water used to cool the inductor 2, so that insulation can be maintained even in the event of a water leak.

[0047] As shown in Fig. 5, electromotive terminals 20a, 20b are connected to both ends of the heating coil 13 of the inductor 2, and the inductor 2 is electrically connected to the inverter 18 via the electromotive terminals 20a, 20b. As shown in Fig. 3, the material to be heated 15 is transported through the opening, so the heating coil 13 is wound around the material to be heated 15 passing through the opening.

[0048] 5, a water inlet and a water outlet for cooling water flowing through the heating coil 13 are provided for each turn of the heating coil 13, and hose nipples 21 are provided at each of the water inlet and the water outlet, and the water inlet and the water outlet are fluidly connected to the cooling pipes. Hose nipples are also provided at both ends of the heating coil 13, and are fluidly connected to the cooling pipes.

[0049] Main pipes 22 and 23 are arranged as cooling pipes in the cooling system of the inductor 2. In the specific example of Fig. 5, the main pipe 22 is a pipe through which cooling water pumped up from a cooling tank by a pump (not shown) flows, and the main pipe 23 is a pipe that flows through the heating coil 13 to cool the heating coil 13 and returns the cooling water to the cooling tank.

[0050] Main pipe 22 is provided with n governing pipes 22-1 to 22-n. Main pipe 23 is provided with n governing pipes 23-1 to 23-n. In the specific example of FIG. 5 , heating coil 13 is wound n times. More specifically, governing pipes 22-1 to 22-n are fluidly connected to heating coil 13 in the order in which they are wound around heating coil 13. Governing pipes 23-1 to 23-n are fluidly connected to heating coil 13 in the order in which they are wound around heating coil 13.

[0051] More specifically, the first winding coil is fluidly connected to a governing pipe 22-1 so that cooling water can enter from one side of the winding coil, and is fluidly connected to a governing pipe 23-1 so that cooling water can be discharged from the other side. The cooling water flowing through this portion is at a flow rate CW １ Water enters the heating coil 13 at a flow rate CW １ The water is discharged at a flow rate of CW １ and flow rate CW １ ' is equal to the flow rate CW １ The cooling water flows into the heating coil 13 from the control pipe 22-1 and is discharged from the control pipe 23-1. Similarly, the cooling water flowing into the n-th winding coil is at a flow rate CW ｎ Water enters the heating coil 13 at a flow rate CW ｎ The water is discharged from the heating coil 13 at a flow rate CW ｎ and flow rate CW ｎ ' is equal to the flow rate CW ｎ The cooling water flows into the heating coil 13 through the control pipe 22-n and is discharged through the control pipe 23-n.

[0052] The flow rate sensors 4-1 to 4-n detect the flow rate CW １ '~CW ｎ '(=Flow rate CW １ ~CW ｎ ) and outputs the detected data to the control device 10.

[0053] Heat dissipation amount P of the i-th winding coil ｌｏｓｓ i is calculated by the following equation (3).

[0054] P ｌｏｓｓ i = (T ｏｕｔ i-T ｉｎ ) CW ｉ (3) where i is an integer from 1 to n. ｏｕｔ i is the temperature of the cooling water flowing through the governing pipe 23-i detected by the temperature sensor 3-i, T ｉｎ represents the temperature of the cooling water before cooling detected by the temperature sensor 8.

[0055] Cooling water temperature before cooling T ｉｎ is detected by the temperature sensor 8. The temperature T of the cooling water after cooling ｏｕｔ 1 to T ｏｕｔThe flow rate CW of the cooling water is detected by the temperature sensors 3-1 to 3-n. １ ~CW ｎ are detected by the flow rate sensors 4-1 to 4-n, respectively.

[0056] The control device 10 detects the temperature T ｉｎ , T ｏｕｔ 1 to T ｏｕｔ n and flow rate CW １ ~CW ｎ By applying each data to equation (3), the amount of heat dissipation P ｌｏｓｓ 1 to P ｌｏｓｓ The control device 10 calculates the temperature T ｉｎ , T ｏｕｔ 1 to T ｏｕｔ n and flow rate CW １ ~CW ｎ The amount of heat loss P for each area on the date and time of detection ｌｏｓｓ 1-P ｌｏｓｓ n data are stored in association with each other.

[0057] It is preferable that the temperature sensors 3-1 to 3-n and 8 and the flow rate sensors 4-1 to 4-n detect physical quantities when the material to be heated 15 is not present within the inductor 2. When the bar heater output command information 12 is inactive, the material to be heated 15 is not present within the inductor 2, and temperature and flow rate data can be acquired without being affected by radiant heat from the material to be heated 15. The temperature and flow rate data may also be acquired in synchronization with the voltage and current data of the parallel circuit between the heating coil 13 and the capacitor 9. This simplifies the configuration of the programs and other components involved in acquiring and calculating each piece of data.

[0058] As in this specific example, the control device 10 calculates the heat dissipation amount for each region corresponding to the position of the wound coil, stores and outputs time-series data of the calculated heat dissipation amount, thereby making it possible to output the number of regions of the heating coil 13 in which the heat dissipation amount of the wound coil is increasing. The operator of the preventive maintenance system 100 can calculate the heat dissipation amount P for each wound coil of the heating coil 13 wound n times. ｌｏｓｓBy observing the time series data for i (i = an integer from 1 to n) and recognizing in which area of ​​the heating coil 13 the amount of heat generation is increasing, it is possible to estimate in which area scale and the like is adhering and accumulating.

[0059] The control device 10 may output data on the heat dissipation amounts of the first to nth regions to the monitor 11 via software that graphically displays the heating coil 13. In such a case, the heating coil 13 may be displayed graphically, and the estimated positions of high-temperature areas and areas where scale or the like has adhered may be displayed on the displayed graphic data of the heating coil.

[0060] The effects of the preventive maintenance system 100 according to the embodiment will be described. The preventive maintenance system 100 according to the embodiment detects the current flowing through the inductor 2 constituting the bar heater 1 and the voltage applied across it, and can calculate, store, and output time-series data on the impedance associated with the inductor 2. The impedance associated with the inductor 2 fluctuates over time due to the adhesion and accumulation of scale and the like, so by observing the time-series data on the impedance, it is possible to indirectly recognize the state of adhesion and accumulation of scale and the like.

[0061] The impedance associated with the inductor 2 differs depending on whether or not a material to be heated 15 is present within the inductor 2. Therefore, in the preventive maintenance system 100 according to this embodiment, the control device 10 acquires voltage and current data for calculating the impedance associated with the inductor 2 when the material to be heated 15 is not present within the inductor 2. The control device 10 can determine whether the material to be heated 15 is present within the inductor 2 by monitoring the tracking signal of the material to be heated 15 or by monitoring the output of a sensor installed near the bar heater 1. Furthermore, since the power supply to the inductor 2 is controlled by the bar heater output command information 12, the impedance of the inductor 2 can be calculated using voltage and current data acquired during a period when the bar heater output command information 12 is active and the material to be heated 15 is not present within the inductor 2. In this manner, impedance data that fluctuates over time due to factors such as a scale can be accurately calculated regardless of the material to be heated 15.

[0062] The detection means for acquiring voltage and current data for calculating the impedance associated with the inductor 2 can utilize existing devices such as a measuring transformer 5 and a measuring current transformer 6, and can be easily introduced into existing bar heaters 1.

[0063] Furthermore, in the preventive maintenance system 100 according to the embodiment, the bar heater 1 can acquire data on the temperature and flow rate of the cooling water in the cooling system for cooling the inductor 2 and calculate the amount of heat dissipated by the cooling water.

[0064] The heating coil 13 constituting the inductor 2 is formed by winding a hollow tubular conductor. Cooling water can be circulated through the conductor of the heating coil 13, thereby achieving a highly efficient cooling effect.

[0065] The heating coil 13 is divided into regions, and the temperature and flow rate of the cooling water before and after cooling are detected for each region. Based on the detected temperature difference and flow rate, the amount of heat dissipated by the cooling water for each region of the heating coil 13 can be calculated. The amount of heat dissipated can be stored and output as time-series data by correlating it with the date and time when the temperature and flow rate data was acquired. By outputting the time-series data of the amount of heat dissipated for each region of the heating coil 13, the operator of the preventive maintenance system 100 can know the trend of changes in the amount of heat dissipated for each region of the heating coil 13.

[0066] Due to the change over time in the amount of heat dissipated from each region of the heating coil 13, it is expected that areas where the temperature of the heating coil 13 rises locally more will have more accumulation of scale and the like than other areas, and this can be used as a reference when planning maintenance.

[0067] During operation of the induction heating device, the host computer may transmit the power value required for heating to the control device 10 as a command value based on attribute information of the heated material 15. The attribute information of the heated material 15 may include, for example, the thickness, width, and transport speed of the material. In this case, the difference between the temperature rise value resulting from the power command value and the calculated heat dissipation amount is considered to be the radiant heat of the heated material. The control device 10 calculates the radiant heat, stores it as time-series data, and outputs it to determine the deterioration of the components of the inductor 2 due to radiant heat, which can be used as a reference for developing a maintenance plan. Deterioration of components due to radiant heat includes, for example, deformation of the shield cover 17. Furthermore, if a change is observed in the time-series data of radiant heat, it may be possible that a gap has appeared in the heat-resistant plate 16, making it effective to include an inspection of the heat-resistant plate 16 in the maintenance plan.

[0068] In the above-described specific example, a bar heater has been described as the induction heating device. However, the above-described matters are not limited to bar heaters and can be applied to induction heating devices for use in steel production lines, such as edge heaters and soaking heaters.

[0069] In this way, a preventive maintenance system that can accurately grasp the deterioration state of the induction heating device is realized.

[0070] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

[0071] 1...bar heater, 2...inductor, 3, 3-1 to 3-n, 8...temperature sensor, 4, 4-1 to 4-n...flow rate sensor, 5...measurement transformer, 6...measurement current transformer, 7...current transformer for measuring coil current, 9...capacitor, 10...control device, 11...monitor, 12...bar heater output command information, 13...heating coil, 14...mold, 15...material to be heated, 16...heat-resistant plate, 17...shield cover, 18...inverter, 20a, 20b...electrical terminal, 21...hose nipple, 22, 23...main pipe, 22-1 to 22-n, 23-1 to 23-n...control pipe, 100...preventive maintenance system

Claims

1. A preventive maintenance system comprising: an induction heating device having an inductor including a coil that heats a material to be heated by electromagnetic induction by passing high-frequency current supplied from an inverter through it; a voltage detector that detects and outputs the voltage applied to the coil; a current detector that detects and outputs the current flowing through the coil; and a control device that calculates the impedance of a circuit including the coil based on the voltage detected by the voltage detector and the current detected by the current detector, wherein the control device calculates the impedance based on the voltage and current detected before the material to be heated reaches the coil or after the material to be heated is discharged from the coil, and associates the calculated impedance with the date and time when the voltage and current used to calculate the impedance were detected and stored.

2. The preventive maintenance system of claim 1, wherein the coil is formed by winding a hollow tubular conductor and is cooled by cooling water circulating through the conductor, and in the inductor, the cooling water circulates through the conductor which is divided into a plurality of regions, and the inductor has: a first temperature sensor that detects the temperature of the cooling water before cooling; a plurality of second temperature sensors provided in the plurality of regions that detect the temperatures of the cooling water in the plurality of regions, respectively; and a plurality of flow rate sensors provided in the plurality of regions that detect the flow rates of the cooling water in the plurality of regions, and the control device calculates and stores a plurality of amounts of heat dissipation in the plurality of regions based on data on the temperature of the cooling water before cooling detected by the first temperature sensor, data on the temperatures of the cooling water in the plurality of regions detected by the plurality of second temperature sensors, and data on the flow rates of the cooling water in the plurality of regions detected by the plurality of flow rate sensors.

3. A preventive maintenance system as claimed in claim 1 or 2, wherein the induction heating device is either a bar heater type, an edge heater type or a uniform heating heater type.