A method for monitoring the condition of an induction furnace based on electrical parameters

Abstract

This invention discloses a method for monitoring the condition of an induction furnace based on electrical parameters, comprising the following steps: establishing an equivalent electric furnace load model based on the structure of the induction furnace to determine the implicit functional relationship between the liquid level and current within the induction furnace; collecting current data at each moment during the melting process of the induction furnace and comparing it with the current data at each moment of the equivalent induction furnace model; judging the melting state within the induction furnace based on the melting process of the induction furnace; and issuing an anomaly warning based on the melting state. Therefore, the method of this invention can simultaneously achieve continuous online monitoring of the liquid level within the furnace and real-time identification and warning of charge bridging phenomena. This provides accurate and real-time liquid level data support for adaptive adjustment of heating power during the melting process, and can also identify bridging faults in advance and avoid safety risks such as dry burning and power mismatch, ensuring the stable and smooth operation of the melting process.

Description

Technical Field

[0001] This invention relates to the field of casting technology, and in particular to a method for monitoring the condition of an induction furnace based on electrical parameters. Background Technology

[0002] With its advantages of fast heating speed, high thermal efficiency, and precise composition control, the medium-frequency coreless induction furnace has become the core equipment in modern foundry workshops and special steel smelting. Since the refractory material in the furnace lining experiences different thermal shocks at different liquid levels, the height of the molten metal level in the furnace is a key state parameter that determines the quality of the smelting process and the safety of equipment operation.

[0003] If the liquid level cannot be accurately monitored, operators will find it difficult to identify the phenomenon of bridging of the furnace charge, i.e., the lower part is melted and hollowed out while the upper solid charge is stuck. If the liquid level is misjudged as high and heating continues, it will cause extreme overheating of the molten iron at the bottom, which can easily lead to major safety accidents such as furnace penetration, leakage, and explosion.

[0004] Traditional methods address this by using servo motors to drive the test electrodes up and down, and then using the detection of current flow or arc changes to determine the liquid level position through contact monitoring. However, these methods are costly to maintain and cannot achieve continuous acquisition of liquid level data. In particular, they do not consider the actual situation of solid-liquid coexistence. During the solid-liquid coexistence stage of the furnace charge, the monitor cannot effectively penetrate the liquid surface inside the furnace due to interference from the upper solid metal layer, resulting in insufficient monitoring accuracy. This makes it difficult to meet the actual needs of industrial production and to obtain information about the state during the smelting process. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for monitoring the furnace condition of an induction furnace based on electrical parameters.

[0006] A method for monitoring the furnace condition of an induction furnace based on electrical parameters according to an embodiment of the present invention includes: An equivalent electric furnace load model is established based on the structure of the induction furnace to determine the implicit functional relationship between the liquid level and the current in the induction furnace. The current data at each moment during the induction furnace melting process is collected and compared with the current data at each moment of the equivalent induction furnace model. The melting state inside the induction furnace is judged in combination with the melting process of the induction furnace, and an abnormal warning is issued based on the melting state.

[0007] The impedance calculations for each part include: calculating the resistance and reactance of the inductor, solid charge, and liquid charge, as well as the leakage impedance and excitation impedance; before calculating the impedance, the current penetration depth is calculated based on the power supply frequency, charge resistivity, and relative permeability, and the cylindrical charge coefficient is introduced to affect the calculation of charge reactance and resistance.

[0008] It should be noted that the coefficient of cylindrical furnace charge is only related to the ratio of the furnace charge diameter to the current penetration depth.

[0009] Furthermore, in this step, the solid furnace charge with gaps inside the induction furnace is regarded as a solid solid cylinder with increased resistivity and decreased relative permeability, and the liquid furnace charge inside the furnace is regarded as a solid liquid cylinder.

[0010] Therefore, it is necessary to calculate the impedance of solid and liquid furnace charge independently, connect the impedance of liquid furnace charge in parallel with the impedance of solid furnace charge, and then connect it in series with the leakage impedance and the inductor impedance. The series connection is then connected in parallel with the excitation impedance, and the total impedance after parallel connection is connected in series with the inductor resistance, thereby completing the impedance matching of the equivalent electric furnace load model.

[0011] The total impedance on the charge side is transferred to the inductor side, and the total system impedance from the inverter's perspective is obtained by combining the inductor turns correction. The implicit functional relationship between current I and liquid level height H is then derived.

[0012] When judging the melting state in the induction furnace, if the current data collected at a certain moment deviates from the current data of the equivalent induction furnace model at that moment, and the difference in current data continues to be greater than the preset fluctuation threshold, and the resistivity and relative permeability of the lower liquid furnace charge calculated by the equivalent induction furnace model remain stable within this range, but the fluctuation of the impedance of the upper solid furnace charge is within the preset tolerance range, it is determined that furnace charge bridging has occurred. At this time, it is necessary to open the furnace cover and manually change the state of the solid furnace charge.

[0013] The underlying mechanism is as follows: When bridging occurs within the furnace, the rise of the liquid level in the bottom molten pool stagnates, causing the equivalent resistivity and relative permeability of the liquid charge within the inductor's coverage area to remain stable. Simultaneously, due to the suspension of the upper solid charge due to bridging, the effective coverage area of ​​the upper inductor coil lacks charge filling, preventing the formation of continuous and effective electromagnetic coupling in this section. Its equivalent impedance varies within a certain range, causing the downward trend of the system's total equivalent impedance, as perceived from the inverter's perspective, to stall. With the inverter's secondary output voltage remaining constant, the measured current in the circuit fluctuates only within a limited range, resulting in a current plateau period that contradicts the pattern observed under normal smelting conditions.

[0014] Specifically, taking a 3-ton medium-frequency induction melting furnace as an example, during the entire melting process, the inductor has capacitor compensation, and its coil voltage will quickly reach the threshold of 2800V. Therefore, when monitoring the melting status, the voltage is taken as a constant value.

[0015] Whether bridging occurs: Bridging may occur throughout the smelting process. During the smelting process, if the current fluctuates within a certain threshold range (e.g., 100A) for a long time when it is between 5500A and 6500A, it is determined that bridging has occurred.

[0016] Whether the furnace lining is eroded: The current state when the furnace charge is completely melted is used as the basis. For example, in a newly built induction furnace, when the furnace charge is completely melted, the current value is only about 7000A. However, after a long period of melting, the furnace lining is gradually eroded. When the furnace charge is completely melted, the current value will increase. When it reaches about 7400A, it is determined that the furnace lining can no longer be used and the furnace needs to be rebuilt.

[0017] Is melting complete? In actual process, when the melting process is nearing its end and the current value exceeds 6800A, there is a relatively long plateau period. At this time, it is determined that the melting is complete and the cover can be opened for subsequent operations. There is no need to keep the cover open to observe the melting process.

[0018] Beneficial effects: This invention establishes a mapping relationship between liquid level and current within the smelting furnace by constructing an equivalent induction furnace model, enabling continuous online monitoring of the smelting state within the furnace. Based on the mapping law between the furnace charge liquid level and current, and according to the current characteristics, it can achieve real-time identification of charge bridging phenomena and provide a reference for the furnace lining repair cycle. Furthermore, it eliminates the need for frequent opening of the furnace lid to observe the smelting process, thereby avoiding the operation of probing the smelting furnace liquid level while monitoring the smelting process, significantly improving the safety and stability of the smelting process.

[0019] Furthermore, this method does not require modification of the existing smelting furnace system. It can directly reuse the electrical operating parameters of the existing smelting furnace inverter for feature mapping, eliminating the need for expensive physical contact sensors and resulting in extremely low monitoring costs. Attached Figure Description

[0020] Figure 1 This is a circuit diagram of the equivalent induction furnace model in the embodiment; Figure 2 This is a diagram showing the continuous mapping relationship between the theoretical liquid level height H and the current I in the embodiment; Figure 3 This is a curve fitting the field measured data in the embodiment; Figure 4 This is a schematic diagram comparing the effects of heat retention and non-heat retention on the smelting process in the examples; Figure 5 This is a schematic diagram comparing the bridging state with the normal smelting process in the embodiment. Detailed Implementation

[0021] The technical solutions of the embodiments disclosed in this application will be clearly and completely described below with reference to the accompanying drawings. The descriptions of the embodiments are merely illustrative and exemplary, and are not intended to limit the scope of this disclosure or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort should fall within the scope of protection of this disclosure. Furthermore, techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification.

[0022] Combined with appendix Figures 1 to 5 The technical solution is described in detail below. According to an embodiment of the present invention, a method for monitoring the condition of an induction furnace based on electrical parameters includes the following steps: In this embodiment, taking a 3-ton medium-frequency induction melting furnace as an example, the inductor has capacitor compensation during the entire melting process, and its coil voltage will quickly reach the threshold of 2800V. Therefore, when monitoring the melting status, the voltage is taken as a constant value.

[0023] In addition, the inner diameter of the sensor, the inner diameter of the furnace opening, and the resistivity of the sensor copper tube are given based on actual measured values.

[0024] Sensor operating frequency The inner diameter of the sensor The inter-turn insulation coefficient of the sensor is taken as The reactance correction factor is taken as Sensor height The resistivity of the copper tube in the sensor is taken as The relative permeability of the copper tube of the sensor is taken as Number of turns of the sensor coil .

[0025] Inner diameter of the furnace opening of the smelting furnace The resistivity of the liquid furnace charge is taken as The relative magnetic permeability of the liquid furnace charge is taken as The resistivity of solid furnace charge is taken as The relative magnetic permeability of the solid furnace charge is taken as Secondary voltage .

[0026] The resistivity and relative permeability of solid furnace charge in this model refer to the average equivalent values.

[0027] The specific steps for constructing an equivalent electric furnace load model are as follows: 1. Calculate the resistance and reactance of a single-turn inductor; Since the sensor has a hollow structure and the current flows through the surface of the hollow metal tube, it is necessary to calculate the depth of current penetration.

[0028] Current penetration depth in metal : ; in, -Resistivity - The operating frequency of the sensor -Relative permeability; Single-turn system inductor copper tube resistor : ; in, - Sensor inner diameter, - The operating frequency of the sensor - Insulation fill factor between inductors (take 0.8 to 0.92). - The depth to which the current penetrates the copper tube. - Height of the inductor heating coil; Inductor reactance of a single-turn system : ; 2. Calculate the resistance of the charge inside the induction furnace. With reactance The design basis for the parallel connection of solid and liquid furnace charge impedances is as follows: the liquid and solid furnace charge are spatially layered, but wrapped together in the same induction coil, sharing the main magnetic flux change, and each forming a closed eddy current loop on the horizontal level without interfering with each other. The induced electromotive forces are from the same source and equal. The impedances of the liquid and solid furnace charge change continuously during the heating process.

[0029] Cylindrical furnace charge coefficient : ; ; in, -Inner diameter of the smelting furnace - Depth of electric current penetration in a metal; By introducing a cylindrical charge coefficient, the true magnetic field energy storage under the short coil structure is accurately reflected, which significantly improves the accuracy of equivalent impedance and continuous liquid level monitoring.

[0030] Single-turn system in-furnace liquid metal charge resistance : ; in, - Relative magnetic permeability of liquid furnace charge - Height of liquid charge inside the furnace - Liquid charge coefficient - The sensor's operating frequency, with a value of 300; Single-turn system in-furnace liquid metal charge reactance : ; in, --Liquid furnace charge coefficient - The operating frequency of the sensor - Relative magnetic permeability of liquid furnace charge -Inner diameter of the smelting furnace - Height of liquid charge inside the furnace; Single-turn system in-furnace solid charge resistance : ; in, - Relative magnetic permeability of solid furnace charge - Height of the inductor heating coil; - Solid charge coefficient, - The operating frequency of the sensor -Inner diameter of the smelting furnace - Height of liquid charge inside the furnace; Single-turn system in-furnace solid charge reactance : ; in, --Solid charge coefficient - Relative magnetic permeability of solid furnace charge - Height of the inductor heating coil - The operating frequency of the sensor -Inner diameter of the smelting furnace - Height of liquid charge inside the furnace.

[0031] Parallel resistance of liquid and solid furnace charge : ; Parallel reactor of liquid and solid furnace charge : ; The method of independently calculating the impedance of solid and liquid furnace materials solves the problem of insufficient calculation accuracy in the solid-liquid coexistence stage of traditional methods.

[0032] Since the furnace body separates the inductor from the charge, it is necessary to calculate the gap reactance of the single-turn system. In this context, solid furnace charge with gaps inside the furnace is considered as a solid solid cylinder with increased resistivity and decreased relative permeability; liquid furnace charge inside the furnace is considered as a solid liquid cylinder.

[0033] The gap reactance is the impedance generated by the gap between the induction coil and the furnace charge, while the excitation impedance is the external magnetic circuit reactance that exchanges reactive components between the power supply and the magnetic field. The gap reactance is connected in series with the load impedance, the excitation impedance is connected in parallel with the load impedance, and the inductor reactance is routed to the load branch.

[0034] Single-turn system gap reactance

[0035] ; in, - Sensor inner diameter, - The operating frequency of the sensor -Inner diameter of the smelting furnace - Height of the inductor heating coil; External magnetic circuit reactance of single-turn system

[0036] ; in, -- Reactance correction factor, - Sensor inner diameter, - The operating frequency of the sensor - Height of the inductor heating coil; 4. Coefficients for calculating furnace charge parameters to the inductor side

[0037] ; in, For the inductor reactance of a single-turn system, External magnetic circuit reactance of a single-turn system Single-turn system gap reactance, Parallel reactors of liquid and solid furnace charge Parallel resistance of liquid and solid furnace charge; Total resistance after accounting for the sensor side : ; Total reactance after accounting for the sensor side : ; Total impedance of a single-turn system : ; Total impedance referred to the sensor side

[0038] ; in, --Number of turns in the sensor coil; Current in the sensor

[0039] ; Through the above formula calculation and derivation, the implicit functional relationship between current I and liquid level height H can be obtained.

[0040] It should be noted that the metal charge in the furnace is a single-turn short-circuit coil, i.e., the secondary side of the transformer; the induction coil connected to the inverter is a high-voltage multi-turn coil, i.e., the primary side of the transformer. According to the transformer principle, the voltage on the primary side is directly proportional to the voltage on the secondary side, and the current is inversely proportional. Therefore, the final impedance must be multiplied by the square of the number of turns.

[0041] Furthermore, based on the implicit functional relationship between current I and liquid level height H, we can obtain the following: Figure 2 The diagram shows the continuous mapping relationship between the liquid level height H and the current I.

[0042] Specifically, under normal melting conditions, the current I exhibits a nonlinear trend of "fast at first and slow later" as the liquid level height H rises. This characteristic trend is extracted as the core state feature for subsequent reinforcement learning to judge the furnace condition and identify the bridging of the furnace charge.

[0043] Because induction melting involves complex solid-liquid phase transitions, the relationship between liquid level and melting time is not a simple linear one. Therefore, this verification employs dimensionless processing, utilizing the commonality that liquid level and heating time continuously and strictly monotonically increase in the macroscopic physical process, to uniformly map liquid level and heating time to the common dimension of "melting progress".

[0044] like Figure 3 As shown, when the theoretically derived curves and the field measured data are compared in the same way as the smelting process, both show a consistent nonlinear upward trend in the whole, which fully verifies the accuracy of the equivalent electromagnetic impedance model of the present invention.

[0045] Meanwhile, it can be observed that the measured curve is slightly lower than the theoretical value in the middle and front section and is accompanied by local step-like fluctuations. This is not a calculation error, but a true reflection of the complex engineering reality of the industrial site: discontinuous data acquisition on site and electromagnetic coupling fluctuations caused by uneven collapse of solid furnace material.

[0046] Furthermore, considering that in actual production, after a furnace smelting is completed, the molten charge inside is usually not completely emptied, but rather a portion of the initial melt is retained. Therefore, if... Figure 4 The furnaces that retained molten broth in actual production, as shown, had significantly higher initial current reference values ​​than those that did not retain molten broth, and the heating cycle for a single furnace smelting was greatly shortened.

[0047] In addition, such as Figure 5As shown, in order to solve the safety hazard that solid charge bridging can easily cause overheating of the liquid charge at the bottom, leading to leakage through the furnace, this embodiment detects that charge bridging has occurred when the measured current curve shows a plateau period with a fluctuation range less than a preset threshold.

[0048] At this point, the residual heat from the molten, high-temperature liquid metal at the bottom is conducted upwards, softening the solid furnace charge above and causing the bridging structure to collapse. Simultaneously, to prevent leakage through the furnace, a power reduction command is issued after bridging, thereby reducing the sensor's output power and curbing the continued abnormal heating of the liquid furnace charge at the bottom.

[0049] Once the measured current breaks through the plateau period and shows an upward trend, it is determined that the bridging structure has successfully collapsed, and full power supply can then be restored. In this way, the method achieves a safe closed-loop control to prevent furnace leakage without altering the existing hardware topology.

[0050] In some embodiments of this application, under the same charge level conditions, the furnace lining thickness directly affects the electromagnetic coupling strength between the induction coil and the metal charge inside the furnace. The thicker the furnace lining, the larger the magnetic circuit gap between the coil and the charge, the weaker the electromagnetic coupling, and the correspondingly lower the equivalent load impedance. As a result, with a constant system power supply voltage, the loop current value increases accordingly.

[0051] Therefore, based on the above electromagnetic coupling law, the effective inner diameter of the furnace opening and the actual equivalent thickness of the furnace lining can be calculated by inverting the correspondence between liquid level and current, providing a quantitative reference for judging the degree of furnace lining erosion, determining the furnace construction cycle and maintenance nodes.

[0052] Among them, during the long-term service life of the induction furnace, its furnace body diameter The effective inner diameter gradually increases due to erosion by high-temperature liquid furnace charge, and is also affected by complex physicochemical processes such as slag adhesion and subsequent high-temperature slag formation, which can cause changes in the inner diameter.

[0053] Given that the deformation of the furnace body between adjacent furnaces is negligible, a short-term comparison strategy between adjacent furnaces is adopted. The "current-level" time series curve of normal furnaces with no bridging and smooth melting after the new furnace lining is constructed is extracted and configured as the prior reference mapping curve of the current furnace, that is, used as a new equivalent load model.

[0054] During the current furnace operation, specific nodes are measured and compared with the baseline mapping curve. At these specific nodes, the actual effective furnace inlet diameter is calculated and updated online. This adaptive correction mechanism automatically filters out systematic errors in the equivalent load model caused by slag adhesion and erosion, and the calculated effective inner diameter of the furnace opening also provides a reference for the furnace construction cycle. Thus, based on the continuous mapping relationship, an adaptive tuning mechanism for equivalent parameters based on the temporal characteristics of adjacent furnace runs is constructed.

[0055] Therefore, the method of the present invention can simultaneously realize continuous online monitoring of the liquid level in the furnace and real-time identification and early warning of the bridging phenomenon of the furnace charge. It can provide accurate and real-time liquid level data support for the adaptive adjustment of heating power in the smelting process, and can identify bridging faults in advance and avoid safety risks such as dry burning and power mismatch, thus ensuring the stable and smooth operation of the smelting process.

[0056] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0057] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0058] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for monitoring the condition of an induction furnace based on electrical parameters, characterized in that, Includes the following steps: S1. Establish an equivalent electric furnace load model based on the structure of the induction furnace to determine the implicit functional relationship between the liquid level and the current in the induction furnace. S2. Collect the current data at each moment during the induction furnace melting process, compare it with the current data at each moment of the equivalent induction furnace model, and determine the melting state in the induction furnace in combination with the melting process of the induction furnace. Perform process operation or abnormal warning based on the melting state.

2. The method for monitoring the furnace condition of an induction furnace based on electrical parameters according to claim 1, characterized in that, The method for constructing the equivalent electric furnace load model includes the following steps: Based on the sensor's operating frequency Calculation of current penetration depth based on furnace charge resistivity and relative permeability The resistance of a single-turn inductor can be calculated. and reactance ; The resistance of the furnace charge inside the induction furnace is calculated based on the liquid level height, the relative magnetic permeability of the charge, and the charge coefficient. With reactance ; Calculate the gap reactance based on the structural parameters of the induction furnace. and magnetic circuit reactance ; Based on the obtained resistance of the single-turn inductor and reactance The resistance of the furnace charge inside the induction furnace With reactance and the gap reactance and the magnetic circuit reactance Obtain the total impedance under a single-turn inductor ; Combined with the number of sensor turns and the total impedance under the single-turn inductor The implicit functional relationship between the liquid level H and the current I in the induction furnace is obtained.

3. The method for monitoring the furnace condition of an induction furnace based on electrical parameters according to claim 2, characterized in that, The resistance of the charge inside the induction furnace Including liquid furnace charge resistance and solid furnace charge resistance The liquid furnace charge resistance and the resistance of the solid furnace charge The resistance of the charge inside the induction furnace is obtained by parallel connection. The reactance of the charge inside the induction furnace Including liquid charge reactance and solid furnace charge reactance The reactance of the liquid furnace charge and the reactance of the solid furnace charge The reactance of the furnace charge inside the induction furnace is obtained by parallel connection. .

4. The method for monitoring the furnace condition of an induction furnace based on electrical parameters according to claim 1, characterized in that, The melting state inside the induction furnace includes the melting completed state. When it is at the end of the melting process, the difference between the collected current data and the current data of the equivalent induction furnace model is within a preset threshold range, and the collected current data is in a stable stage, then the induction furnace is considered to be in the melting completed state. At this time, the furnace cover is opened to perform the pouring operation.

5. The method for monitoring the furnace condition of an induction furnace based on electrical parameters according to claim 1, characterized in that, The melting state inside the induction furnace includes the charge bridging state. When the collected current data fluctuates within a limited amplitude range within a certain time interval and deviates from the current data of the equivalent induction furnace model within that time interval, and the difference in current data continues to exceed the preset fluctuation threshold range, the induction furnace is considered to be in the charge bridging state. At this time, it is necessary to reduce the sensor power or open the furnace cover to manually change the state of the solid charge.

6. The method for monitoring the furnace condition of an induction furnace based on electrical parameters according to claim 1, characterized in that, The melting state inside the induction furnace includes the lining erosion state. The current value of the preset limit thickness of the induction furnace lining is a safety threshold. If the current data collected at a certain moment is close to the safety threshold, it is considered that the induction furnace is in the state of charge bridging. At this time, the lining needs to be repaired and the furnace needs to be rebuilt.

7. The method for monitoring the furnace condition of an induction furnace based on electrical parameters according to claim 1, characterized in that, The data collected from the Nth heat, which is in a smooth melting state without bridging, is used to calculate the inner diameter of the current effective induction furnace opening. The inner diameter of the induction furnace opening is then corrected to the equivalent electric furnace load model, and the corrected equivalent electric furnace load model is configured as the equivalent load model for the N+1th heat.

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