Annealing temperature control method and system

Abstract

The application discloses an annealing temperature uniformity control method and system, and belongs to the technical field of annealing heat treatment control. The application arranges multiple temperature sensors in the furnace cavity of an annealing furnace to perform distributed temperature measurement and calculate a temperature uniformity index, divides a heat exchange region into a bottom region and a sidewall region, dynamically allocates the flow of heat conducting oil according to the temperature deviation of each region, automatically switches PID control parameter groups of different process stages according to the size of the temperature deviation, and smoothly transitions when the stages are switched, calculates a feedforward compensation power based on a heat balance model in the heating stage, and forms a composite control by superimposing the PID feedback, and dynamically adjusts the operating frequency of a circulating pump according to the temperature uniformity index. The application can significantly shorten the time for the temperature uniformity in the furnace to reach the standard, effectively suppress the temperature overshoot, improve the steady-state temperature control accuracy, improve the heating rate tracking accuracy, reduce the energy consumption of the circulating pump, and comprehensively improve the temperature control quality and energy efficiency level of the annealing process.

Description

Technical Field

[0001] This invention belongs to the field of annealing heat treatment control technology, specifically relating to an annealing temperature uniformity control method and system. Background Technology

[0002] Annealing is a crucial step in metal heat treatment. Its purpose is to eliminate residual stress, improve microstructure, and enhance the plasticity and toughness of metal workpieces by heating them to a specific temperature, holding them at that temperature for a certain time, and then cooling them at an appropriate rate. The quality of the annealing process largely depends on the uniformity and stability of the temperature field within the furnace. During the actual operation of the annealing furnace, the temperature at different locations within the furnace cavity is influenced by various factors, including the flow path of the heat transfer oil, the heat dissipation characteristics of the furnace structure, and the heat capacity distribution of the workpiece, often resulting in varying degrees of temperature gradients. If the temperature distribution within the furnace is uneven, the heat treatment temperature journey experienced by different parts of the workpiece will be inconsistent, leading to incomplete elimination of residual stress or uneven microstructure transformation, ultimately affecting the quality and performance stability of the annealed product. Therefore, achieving high-precision uniform control of the temperature field within the annealing furnace is a key technical issue in ensuring the quality of the annealing process.

[0003] Currently, common annealing furnace temperature control methods often employ single-point temperature measurement or a limited number of measurement points for temperature monitoring. This makes it difficult to comprehensively and accurately reflect the overall temperature field distribution within the furnace, resulting in the control system's inability to promptly detect and eliminate localized temperature inhomogeneities. Regarding the circulation of heat transfer oil, existing technologies typically use a fixed flow rate distribution method to allocate heat transfer oil to each heat exchange channel. This method cannot adaptively adjust based on the actual temperature deviations in different areas. When there are differences in the heating rates of different areas, areas with larger temperature deviations cannot obtain enough heat exchange medium to accelerate temperature equalization, leading to a longer time to achieve the required temperature uniformity within the furnace. In terms of temperature control strategies, existing annealing furnace control systems generally employ a PID control method with fixed parameters throughout the process. This makes it difficult to simultaneously meet the differentiated temperature control requirements of different process stages, such as rapid response during the heating phase, suppression of overshoot during the transition phase, and elimination of steady-state deviations during the isothermal phase. This easily leads to problems such as temperature overshoot and large steady-state fluctuations. Regarding heating rate control, traditional pure PID feedback control methods suffer from inherent lag between the control output and actual power demand due to the large thermal inertia of the annealing furnace system, resulting in low tracking accuracy of the heating rate. In addition, most circulating pumps in existing technologies operate at a constant frequency and speed, continuing to run at the highest frequency even after the furnace temperature has reached a uniform state, resulting in unnecessary energy consumption. Summary of the Invention

[0004] To address the problems existing in the background art, the present invention provides an annealing temperature uniformity control method, comprising the following steps:

[0005] S1: Real-time temperature data of each temperature measurement point is collected by multiple temperature sensors arranged in the furnace cavity of the annealing furnace, and the temperature uniformity index, which characterizes the temperature uniformity in the furnace, is calculated accordingly.

[0006] S2: Divide the heat exchange area of ​​the annealing furnace into the bottom area and the side wall area, calculate the temperature deviation between the average temperature of each area and the target annealing temperature, determine whether the direction of the temperature deviation between the two areas is consistent, and dynamically adjust the heat transfer oil flow distribution between the bottom circulating oil channel and the jacket oil channel accordingly.

[0007] S3: Based on the magnitude of the deviation between the average temperature in the furnace and the target annealing temperature, the current process stage of the annealing process is automatically determined. Different PID control parameter groups are used for temperature control in different process stages, and the PID control parameters are smoothly transitioned within the preset transition bandwidth when switching between adjacent stages.

[0008] S4: During the heating stage, the feedforward compensation power is calculated based on the system's equivalent total heat capacity and the preset heating rate. The feedforward compensation power is then superimposed with the feedback output of the PID controller to serve as the total control output power of the heating module.

[0009] S5: Dynamically adjust the operating frequency of the circulating pump according to the real-time value of the temperature uniformity index. When the temperature uniformity index is lower than the preset threshold, increase the operating frequency of the circulating pump proportionally to enhance the heat exchange of the heat transfer oil. When the temperature uniformity index reaches or exceeds the threshold, reduce the operating frequency of the circulating pump to the level required to maintain basic circulation.

[0010] Furthermore, step S1 specifically includes: S11: N temperature sensors are arranged along the height direction on the inner wall of the annealing furnace cavity, where N≥6. The N temperature sensors are distributed in the bottom, middle and top regions of the furnace cavity, with no less than 2 sensors arranged in each region; at the same time, oil temperature sensors are respectively installed on the inlet and outlet pipes of the bottom circulating oil channel and the jacketed oil channel.

[0011] S12: The controller reads the real-time temperature values ​​of all temperature sensors at a set sampling period to obtain the temperature values ​​of N temperature measurement points inside the furnace.

[0012] S13: Extract the maximum value T from the N temperature values. max With minimum value T min And calculate the arithmetic mean T. avg The temperature uniformity index TUI is calculated using the following formula:

[0013] ;

[0014] In the formula, TUI is the temperature uniformity index, which is dimensionless; T maxT represents the highest temperature (°C) among N temperature measurement points inside the furnace. min T represents the lowest temperature (°C) among N temperature measurement points inside the furnace. avg TUI is the arithmetic mean (°C) of the temperatures measured at N points inside the furnace; the closer TUI is to 1, the more uniform the temperature distribution inside the furnace.

[0015] Furthermore, step S2 specifically includes:

[0016] S21: Take the arithmetic average of the temperature sensor readings from the bottom region in step S11 to obtain the average temperature T of the bottom region. b The temperature readings from the temperature sensors located in the middle and top regions are combined and taken as an arithmetic mean to obtain the average temperature T of the sidewall region. s ;

[0017] S22: Calculate the bottom temperature deviation separately. and sidewall temperature deviation The and The values ​​are signed deviations; positive values ​​indicate that the temperature in that region is lower than the target annealing temperature, and negative values ​​indicate that it is higher than the target annealing temperature; where T is the deviation value. target Target annealing temperature (°C); T b The average temperature (°C) of the bottom region; T s The average temperature of the sidewall region is (°C).

[0018] S23: Judgment and The sign of the two is the same, and the sum of their absolute values ​​is greater than zero. Therefore, the sign is determined by... Calculate the flow distribution coefficient of the bottom circulation oil passage. Interlayer oil passage flow distribution coefficient When the two signs are opposite, the flow distribution coefficient of the previous control cycle remains unchanged, and the heating module prioritizes adjusting the heat transfer oil temperature to eliminate the reverse deviation; when both are zero, let In the formula, represents the absolute value operation; This is the flow distribution coefficient for the bottom circulating oil passage; This is the flow distribution coefficient for the interlayer oil passage;

[0019] S24: The controller according to Adjust the opening of the first electric proportional regulating valve installed on the oil inlet pipe of the bottom circulating oil passage, according to... Adjusting the opening of the second electric proportional regulating valve installed on the oil inlet pipe of the sandwich oil passage enables dynamic distribution of heat transfer oil between the two parallel oil passages.

[0020] Furthermore, step S3 specifically includes: S31: Preset the threshold value for the rapid heating stage. Threshold value during constant temperature maintenance stage and transition bandwidth ,in , and ; Calculate the deviation between the average temperature inside the furnace and the target annealing temperature. ;

[0021] S32: Based on the aforementioned deviation The absolute value determines the current stage of the process. When it is determined to be in the rapid heating phase, When it is determined to be the uniform temperature transition stage, when The time is determined to be the isothermal maintenance stage; where, The deviation (°C) between the average temperature inside the furnace and the target annealing temperature. Threshold value (°C) for the rapid heating phase; The threshold value (°C) for the isothermal maintenance stage; Transition bandwidth (°C);

[0022] S33: During the rapid heating stage, the first PID parameter group with a large proportional gain is selected to improve the heating rate; during the temperature equalization transition stage, the second PID parameter group with a large derivative gain is selected to suppress temperature overshoot; during the constant temperature holding stage, the third PID parameter group with a large integral gain is selected to eliminate steady-state temperature deviation.

[0023] S34: When In Within the interval, linear interpolation is performed on the proportional gain, integral gain, and derivative gain of the first and second PID parameter sets, respectively, with the interpolation weights varying accordingly. The position changes linearly within this interval; when In Within the interval, the second and third PID parameter sets are linearly interpolated in the same way; thus, the various PID parameters transition continuously and smoothly during stage switching.

[0024] Furthermore, step S4 specifically includes: S41: Calculating the equivalent total heat capacity of the system. The The sum of the heat capacity of the heat transfer oil in the furnace, the heat capacity of the workpiece, and the heat capacity of the furnace body's heat exchange components is calculated as follows: Calculate; where, The equivalent total heat capacity of the system (J / ℃); Mass of heat transfer oil (kg); Specific heat capacity of heat transfer oil (J / (kg·℃)); The mass of the workpiece is (kg). Specific heat capacity of the workpiece (J / (kg·℃)); The equivalent mass (kg) of the part of the furnace body that participates in heat exchange; Specific heat capacity of furnace body material (J / (kg·℃));

[0025] S42: In each control cycle during the heating phase, calculate the feedforward compensation power using the following formula. :

[0026] ;

[0027] In the formula, The feedforward compensation power is (W). The equivalent total heat capacity of the system (J / ℃); Preset heating rate (°C / s); The overall heat dissipation coefficient of the furnace body (W / (m)) 2 ·℃)); The heat dissipation area of ​​the furnace body exterior surface (m²) 2 ); The current average temperature inside the furnace (°C); The ambient temperature is ℃; the first term on the right side of the formula is the power required to heat the medium inside the furnace at a preset rate, and the second term is the power to compensate for the heat loss of the furnace body;

[0028] S43: The feedforward compensation power Current feedback output of the PID controller Add them together to get the total control output power. And output to the heating module; where, The feedback output power (W) of the PID controller; Total control output power (W) of the heating module;

[0029] Step S5 specifically includes: comparing the temperature uniformity index (denoted as TUI) with a preset threshold value TUI. th Comparison, when TUI <TUI th The target operating frequency of the circulating pump is calculated using the following formula. :

[0030] ;

[0031] In the formula, The target operating frequency (Hz) of the circulating pump; Minimum operating frequency (Hz) to maintain basic circulation for the circulating pump; TUI represents the highest operating frequency (Hz) of the circulating pump; TUI is the current temperature uniformity index. thThe threshold value for achieving temperature uniformity; and Limit at The variable frequency drive outputs to the circulating pump within the specified range; when TUI ≥ TUI th At that time, set the operating frequency of the circulating pump to .

[0032] Furthermore, after the isothermal holding stage of the annealing process, a controlled cooling step is also included, specifically:

[0033] S61: Set the initial cooling temperature T0 and the final target temperature T end and cooling time constant Generate the target cooling temperature curve according to the exponential decay model:

[0034] ;

[0035] In the formula, For the cooling stage The target temperature (°C) is measured in seconds; T0 is the furnace temperature at the start of cooling (°C); T end The final target temperature (°C); The time (s) elapsed after entering the cooling phase; Let be the cooling time constant (s). The larger the value, the slower the cooling rate; exp is the natural exponential function;

[0036] S62: In each control cycle of the cooling process, the controller calculates based on the current moment. And calculate the lead amount according to the following formula. :

[0037] ;

[0038] In the formula, Pre-leader measurement (°C); The thermal hysteresis time (s) is determined in advance through a furnace step response experiment. The current target cooling temperature (°C); T end The final target temperature (°C); The cooling time constant (s) is set; the controller sets the output temperature setpoint of the integrated hot and cold oil heater in the heating module to... This causes the actual temperature inside the furnace to decrease in line with the target cooling temperature curve.

[0039] S63: During the cooling process, steps S1, S2 and S5 are continuously executed to maintain a synchronous and uniform temperature decrease in each region.

[0040] The present invention also provides an annealing temperature equalization control system, comprising:

[0041] The furnace body assembly includes an outer furnace body and an inner furnace body, wherein the inner furnace body is disposed inside the outer furnace body, and a sealed interlayer space is formed between the two, and the outer furnace body is covered with an insulation layer.

[0042] An interlayer oil channel is provided within the interlayer space, and its interior is provided with a guide plate that divides the interlayer space into a series of interconnected spiral flow channels;

[0043] The bottom circulating oil channel is located below the bottom plate of the inner furnace body;

[0044] Heating modules, including integrated hot and cold oil heaters, are used to heat or cool heat transfer oil;

[0045] The circulating pump is driven by a variable frequency drive. Its inlet is connected to the output end of the integrated hot and cold oil machine, and its outlet is connected to the inlet of the bottom circulating oil channel and the inlet of the jacketed oil channel through a branch pipeline. The outlet of the bottom circulating oil channel and the outlet of the jacketed oil channel are connected to the return end of the integrated hot and cold oil machine through a return oil pipeline, so that the bottom circulating oil channel and the jacketed oil channel form two parallel heat transfer oil circulation branches.

[0046] The first electric proportional control valve and the second electric proportional control valve are respectively installed on the oil inlet pipes of the bottom circulation oil passage and the jacket oil passage;

[0047] Multiple temperature sensors, including furnace temperature sensors distributed along the height direction of the inner wall of the inner furnace cavity, and oil temperature sensors respectively installed on the inlet and outlet pipelines of the bottom circulating oil passage and the jacket oil passage;

[0048] The controller is connected to the plurality of temperature sensors, the first electric proportional regulating valve, the second electric proportional regulating valve, the frequency converter driver of the circulating pump, and the heating module. The controller is configured to: calculate the temperature uniformity index based on the data from the furnace temperature sensors; determine the direction of temperature deviation in each region and adjust the opening of the first and second electric proportional regulating valves accordingly to dynamically distribute the heat transfer oil flow; automatically switch PID control parameter groups according to the magnitude of the temperature deviation and smoothly transition within a preset transition bandwidth; output the total control power of the feedforward compensation power and PID feedback superposition to the heating module during the heating stage; dynamically adjust the operating frequency of the circulating pump according to the temperature uniformity index; and generate a target cooling temperature curve according to the exponential decay model after the constant temperature holding stage and control the output temperature of the integrated hot and cold oil heater to track the curve.

[0049] In a preferred embodiment, the guide plates within the interlayer oil channel are arranged in an S-shaped spiral path along the interlayer space. The heat transfer oil enters from the inlet and rises layer by layer along the spiral channel, continuously exchanging heat with the outer wall of the inner furnace body during the ascent. The bottom circulating oil channel adopts a serpentine coil structure, with the serpentine coil fully covering the lower surface of the bottom plate of the inner furnace body. Both the inner furnace body and the outer furnace body are welded from stainless steel plates. The inner furnace body is aligned with the outer furnace body using positioning pins to maintain uniform radial thickness of the interlayer space. A sealing groove is provided at the top opening of the inner furnace body for installing a sealing ring to achieve furnace cavity sealing. The insulation layer is made of aluminum silicate fiber blanket filled between the outer side of the outer furnace body and the outer protective plate.

[0050] The beneficial effects achieved by this invention are as follows:

[0051] This invention arranges multiple temperature sensors along the height direction within the annealing furnace cavity for distributed temperature measurement. Based on the collected temperature data, a temperature uniformity index is calculated, enabling real-time quantitative evaluation of the uniformity of temperature distribution within the furnace. The heat exchange area of ​​the annealing furnace is divided into a bottom region and a sidewall region. According to the magnitude and direction of the temperature deviation between each region and the target annealing temperature, the heat transfer oil flow distribution coefficient between the bottom circulating oil channel and the jacket oil channel is dynamically calculated. The flow rate of each oil channel is adjusted in real time through an electric proportional regulating valve, so that regions with larger temperature deviations automatically receive a larger proportion of heat transfer oil flow, accelerating the approach of these regions to the target temperature. This significantly shortens the time to achieve the target temperature uniformity within the furnace and improves the temperature uniformity level during the steady-state phase.

[0052] This invention automatically divides the annealing process into three stages based on the deviation between the average furnace temperature and the target annealing temperature: a rapid heating stage, a uniform temperature transition stage, and a constant temperature holding stage. Different PID control parameter sets are employed for each stage to address their varying temperature control requirements. The rapid heating stage uses a parameter set with a large proportional gain to accelerate the heating rate; the uniform temperature transition stage uses a parameter set with a large derivative gain to effectively suppress temperature overshoot; and the constant temperature holding stage uses a parameter set with a large integral gain to eliminate steady-state temperature deviation. Compared to traditional control methods that use fixed PID parameters throughout the entire process, this staged adaptive PID temperature control strategy achieves optimal control performance in each stage, significantly reducing temperature overshoot and minimizing steady-state temperature fluctuations. Furthermore, this invention introduces a linear interpolation transition mechanism at the switching boundaries between adjacent stages, ensuring continuous and smooth changes in PID control parameters during stage transitions, thus avoiding control output oscillations or system instability that may be caused by abrupt parameter changes.

[0053] This invention establishes a feedforward compensation method based on a thermal balance model during the heating stage. It actively calculates the heating power required to maintain the target heating rate based on the system's equivalent total heat capacity and the preset heating rate. This feedforward compensation power is then superimposed on the feedback output of the PID controller, forming a composite control structure of feedforward and feedback. The feedforward compensation power includes not only the effective power required to heat the medium inside the furnace at the preset rate but also the power required to compensate for heat loss from the furnace to the environment, and is dynamically updated in each control cycle according to changes in the furnace temperature. Because the feedforward quantity provides a power baseline close to the actual demand before temperature deviation occurs, the PID controller only needs to correct model parameter errors and residual deviations caused by external disturbances. This significantly improves the temperature tracking accuracy during the heating stage, effectively controlling the deviation between the actual heating rate and the preset heating rate, thus meeting the requirements of precise heating rate control in the annealing process.

[0054] This invention establishes a closed-loop correlation between the operating frequency of the circulating pump and the temperature uniformity index. When the temperature uniformity index falls below a preset threshold, the operating frequency of the circulating pump is increased proportionally to enhance the circulation and heat exchange of the heat transfer oil. Once the temperature uniformity meets the target, the operating frequency is reduced to the minimum level required to maintain basic circulation. This achieves an intelligent control strategy of on-demand circulation, significantly reducing the energy consumption of the circulating pump while ensuring temperature uniformity within the furnace. Furthermore, after the isothermal holding phase, this invention employs a controllable cooling method based on an exponential decay model, causing the cooling rate to gradually decrease as the temperature drops. This avoids excessive internal thermal stress in the workpiece caused by rapid temperature drop in the initial cooling phase. A lead-ahead compensation mechanism overcomes the impact of system thermal hysteresis on temperature tracking accuracy. During the cooling process, temperature uniformity monitoring and dynamic distribution of heat transfer oil flow continue, ensuring that the temperature in each region decreases synchronously and uniformly, thus comprehensively guaranteeing the temperature control quality throughout the entire annealing process. Attached Figure Description

[0055] Figure 1 This is a comparison curve of the temperature uniformity index (TUI) of Examples 1 to 3 and Comparative Example 1 as a function of heating time.

[0056] Figure 2 The above are temperature response characteristics comparison charts of Examples 1 to 3 and Comparative Example 2, where (a) is the furnace average temperature response curve of Examples 1 and Comparative Example 2 before and after approaching the target temperature, and (b) is a grouped comparison bar chart of temperature overshoot and steady-state fluctuation peak value of each scheme.

[0057] Figure 3The charts show the comparison of the heating rate tracking accuracy of Examples 1 to 3 and Comparative Example 3. (a) is a graph showing the change of heating rate error over time in Examples 1 and Comparative Example 3 during the heating stage. (b) is a grouped comparison bar chart of the average absolute error and the maximum instantaneous error of each scheme.

[0058] Figure 4 The graphs show the energy consumption of circulating pumps in Examples 1 to 3 and Comparative Example 1. (a) is a bar chart comparing the cumulative energy consumption of circulating pumps throughout the entire process for each scheme, and (b) is a curve comparing the operating frequency of circulating pumps in Examples 1 and Comparative Example 1 with the time of the entire annealing process.

[0059] Figure 5 This is a structural diagram of an annealing temperature equalization control system according to the present invention. Detailed Implementation

[0060] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] This invention provides a method for controlling the uniform temperature during annealing. Through the coordinated use of multiple technologies, including multi-region distributed temperature measurement and quantitative evaluation of temperature uniformity, dynamic flow distribution of heat transfer oil based on regional temperature deviation, a staged adaptive PID temperature control strategy, feedforward compensation based on a thermal balance model, and variable frequency speed regulation of the circulating pump based on temperature uniformity feedback, rapid and uniform temperature control and high-precision constant temperature maintenance within the annealing furnace are achieved. The method mainly includes steps S1 to S5, and optional cooling control steps.

[0062] Step S1 involves collecting real-time temperature data at various measurement points using multiple temperature sensors arranged within the annealing furnace cavity, and calculating the temperature uniformity index, which characterizes the temperature uniformity within the furnace. During operation, the annealing furnace often exhibits temperature gradients at different locations within the furnace cavity due to factors such as the flow path of the heat transfer oil, the heat dissipation characteristics of the furnace structure, and the heat capacity distribution of the workpiece. To accurately grasp the temperature distribution within the furnace, multiple temperature sensors need to be strategically arranged within the furnace cavity for distributed temperature measurement, obtaining comprehensive data reflecting the temperature levels in different areas of the furnace.

[0063] Step S1 further includes steps S11 to S13. Step S11 involves arranging N temperature sensors along the height direction on the inner wall of the annealing furnace cavity, where N ≥ 6. The N temperature sensors are distributed in the bottom, middle, and top regions of the furnace cavity, with at least two sensors in each region. The reason for arranging at least two temperature sensors in each region is to obtain at least two independent temperature sampling points at each height level, thereby determining whether a circumferential temperature difference exists within the same height level. Simultaneously, oil temperature sensors are installed on the inlet and outlet pipes of the bottom circulating oil channel and the jacketed oil channel to monitor the temperature change of the heat transfer oil before and after flowing through each heat exchange oil channel. Platinum resistance temperature sensors are preferably used, with a measurement accuracy preferably ±0.1℃ or higher, to meet the accuracy requirements of the annealing process.

[0064] Step S12 involves the controller reading the real-time temperature values ​​from all temperature sensors at a set sampling period to obtain the temperature values ​​of N temperature measurement points within the furnace. The sampling period setting needs to comprehensively consider the thermal inertia characteristics of the annealing furnace and the control response speed requirements. Due to the large heat capacity of the furnace body, heat transfer oil, and workpiece, the time scale of temperature changes in the annealing furnace system is typically on the order of seconds to minutes. Therefore, the sampling period is preferably set within the range of 1 second to 10 seconds, which allows for timely capture of temperature change trends without increasing the computational burden on the controller due to excessively high sampling frequencies. The controller completes a synchronous reading of all temperature sensor data once within each sampling period, ensuring that the temperature data at each measurement point remains consistent in terms of time reference.

[0065] Step S13 is to extract the maximum value T from the N temperature values. max With minimum value T min And calculate the arithmetic mean T. avg The temperature uniformity index TUI is calculated using the following formula.

[0066] ;

[0067] In the formula, TUI is the temperature uniformity index, which is a dimensionless parameter; T max T represents the highest temperature (°C) among N temperature measurement points inside the furnace; min T represents the lowest temperature (°C) among N temperature measurement points inside the furnace; avgThis represents the arithmetic mean (°C) of the temperatures at N temperature measurement points within the furnace. The temperature uniformity index TUI ranges from 0 to 1. TUI equals 1 when all temperature measurement points within the furnace have completely identical temperatures. The closer TUI is to 1, the more uniform the temperature distribution within the furnace. The design concept of this index is to use the ratio of the extreme temperature difference to the average temperature within the furnace as a quantitative measure of temperature non-uniformity. Subtracting this ratio from 1 yields a positive indicator of temperature uniformity. Compared to the traditional method of judging temperature uniformity solely based on the absolute value of temperature difference, this index normalizes the temperature difference to the scale of the average temperature, making it comparable across different target annealing temperatures.

[0068] Step S2 involves dividing the heat exchange area of ​​the annealing furnace into a bottom region and a sidewall region. The temperature deviation between the average temperature of each region and the target annealing temperature is calculated, and the direction of the temperature deviation between the two regions is determined. Based on this, the distribution of heat transfer oil flow between the bottom circulating oil channel and the jacketed oil channel is dynamically adjusted. In the actual operation of the annealing furnace, the bottom region mainly exchanges heat through the bottom circulating oil channel, while the sidewall region mainly exchanges heat through the jacketed oil channel. Due to differences in heat exchange area, heat dissipation conditions, and workpiece heat capacity distribution between the two regions, the heating rate and temperature level are usually not completely consistent. By calculating the temperature deviation between the two regions and dynamically distributing the heat transfer oil flow accordingly, the region with the larger temperature deviation receives more heat transfer oil flow, thereby accelerating the approach of that region to the target temperature and achieving synchronous and uniform temperature across all regions.

[0069] Step S2 further includes steps S21 to S24.

[0070] Step S21 involves taking the arithmetic average of the temperature sensor readings from the bottom region obtained in step S11 to obtain the average temperature T of the bottom region. b The arithmetic mean of the temperature sensor readings located in the middle and top regions is combined to obtain the average temperature T of the sidewall region. s The reason for combining the temperature sensors of the middle and top regions to calculate the average temperature of the sidewall region is that the middle and top regions are both geometrically located on the side of the inner furnace cavity wall. Their heat exchange process mainly relies on the circulation of heat transfer oil in the jacket oil passage. Thermodynamically, they belong to the same heat exchange channel. Therefore, it is more reasonable to evaluate the temperature of them as a whole sidewall region.

[0071] Step S22 is to calculate the bottom temperature deviation separately. and sidewall temperature deviation Bottom temperature deviation Calculate using the following formula. ;

[0072] In the formula, Temperature deviation at the bottom (°C); T target Target annealing temperature (°C); T b Average temperature of the bottom region (°C). Sidewall temperature deviation. Calculate using the following formula. ;

[0073] In the formula, Sidewall temperature deviation (°C); T target Target annealing temperature (°C); T s The average temperature (°C) of the sidewall region. and The deviation values ​​are signed. Positive values ​​indicate that the temperature in that area is below the target annealing temperature, meaning that the area needs to be heated further; negative values ​​indicate that the temperature is above the target annealing temperature, meaning that there is temperature overshoot in that area. By retaining the sign information of the deviation rather than just taking the absolute value, the controller can not only determine the degree to which the temperature of each area deviates from the target value, but also the direction of the deviation, thereby making more reasonable decisions in subsequent flow allocation.

[0074] Step S23 is to make a judgment and The sign of the two is used. When the signs are the same and the sum of their absolute values ​​is greater than 0, the bottom circulation oil passage flow distribution coefficient is calculated according to the following formula. . ;

[0075] In the formula, This is the flow distribution coefficient for the bottom circulating oil passage; This represents the absolute value (°C) of the bottom temperature deviation. is the absolute value (°C) of the sidewall temperature deviation; is calculated using the absolute value. Interlayer oil passage flow distribution coefficient. Calculate using the following formula.

[0076] ;

[0077] In the formula, This is the flow distribution coefficient for the interlayer oil passage. and The sum of these values ​​always equals 1, satisfying the constraint of total flow conservation. The physical meaning of this formula is that the region with the larger the absolute value of the temperature deviation receives a larger proportion of the flow. For example, when the absolute value of the temperature deviation in the bottom region is twice that of the sidewall region, the bottom circulating oil channel will receive 2 / 3 of the total flow, and the interlayer oil channel will receive 1 / 3, allowing more heat transfer oil to be guided to the bottom region with the larger temperature deviation for enhanced heat transfer. When the signs of the two values ​​are opposite, it indicates that the temperature of one region is higher than the target temperature while the other region is lower than the target temperature; in this case, the two regions have opposite demands for heat transfer oil temperature. In this situation, the flow distribution coefficient of the previous control cycle remains unchanged, and the heating module prioritizes adjusting the heat transfer oil temperature to eliminate the reverse deviation. When both are 0, it indicates that the temperatures of both regions have reached the target annealing temperature; at this point, let... equal The value is 0.5, meaning the heat transfer oil is evenly distributed in the two oil channels.

[0078] Step S24 is for the controller to... Adjust the opening of the first electric proportional regulating valve located on the oil inlet pipe of the bottom circulating oil passage, according to... The opening of the second electrically operated proportional control valve, located on the inlet pipe of the sandwich oil passage, is adjusted to achieve dynamic distribution of heat transfer oil between the two parallel oil passages. The opening of the electrically operated proportional control valve is positively correlated with the flow distribution coefficient. The controller controls the valve opening by outputting analog signals or digital communication commands. Since the two oil passages form a parallel loop, increasing the valve opening in one passage reduces the flow resistance and increases the flow rate in that branch, while decreasing the valve opening in the other passage increases the flow resistance and decreases the flow rate in that branch, thus achieving a redistribution of the total flow between the two branches.

[0079] Step S3 involves automatically determining the current process stage of the annealing process based on the magnitude of the deviation between the average temperature inside the furnace and the target annealing temperature. Different PID control parameter sets are used for temperature control in different process stages, and the PID control parameters are smoothly transitioned within a preset transition bandwidth when switching between adjacent stages. The entire annealing process can be naturally divided into several stages based on the magnitude of the temperature deviation, and the performance requirements for temperature control in each stage are fundamentally different. In the initial stage of heating, the temperature deviation is large, so it is necessary to prioritize increasing the heating rate; when approaching the target temperature, it is necessary to suppress temperature overshoot; after reaching the target temperature, it is necessary to eliminate the steady-state temperature deviation and maintain temperature stability. If a fixed PID control parameter set is used throughout the process, it is difficult to simultaneously meet the differentiated control requirements of the above stages. Therefore, this method automatically switches the PID control parameter set according to the magnitude of the temperature deviation, so that the control system can obtain the most appropriate control performance in different stages. PID control is short for proportional-integral-derivative control, a classic feedback control algorithm widely used in industrial process control. It generates the control output by performing a linear combination of proportional, integral, and derivative operations on the deviation signal.

[0080] Step S3 further includes steps S31 to S34.

[0081] Step S31 is the preset threshold value for the rapid heating stage. Threshold value during constant temperature maintenance stage and transition bandwidth .in Greater than and Greater than 0, Greater than 0 and Less than and difference. This indicates the temperature deviation dividing the annealing process into a rapid heating stage and a uniform temperature transition stage. This represents the temperature deviation value that marks the boundary between the uniform temperature transition stage and the isothermal holding stage. This is the transition band width between adjacent stages, used to achieve a smooth transition of PID parameters. Preferably, the annealing temperature is 3% to 8% of the target annealing temperature. The preferred temperature is 1°C to 5°C. Preferred selection and The difference is 5% to 15%. Simultaneously, the deviation between the average furnace temperature and the target annealing temperature is calculated. .

[0082] Step S32 is based on the deviation The absolute value determines the current technological stage. When Greater than add At that time, it is determined to be in the rapid heating phase. Greater than add and less than At this point, it is determined to be the uniform temperature transition stage. Less than At this point, it is determined to be in the constant temperature maintenance stage.

[0083] In the formula, The deviation (°C) between the average temperature inside the furnace and the target annealing temperature; Threshold value (°C) for the rapid heating phase; The threshold value (°C) for the isothermal maintenance stage; Transition bandwidth (°C). By adjusting the deviation... By comparing the absolute value with the preset threshold value, the controller can automatically determine the current process stage of the annealing process and complete the stage switching without manual intervention.

[0084] Step S33 involves selecting a first PID parameter group with a large proportional gain during the rapid heating phase to increase the heating rate. During this phase, the temperature deviation is significant; a larger proportional gain generates a larger control output, driving the heating module to operate at higher power and accelerating the temperature rise within the furnace. During the temperature equalization transition phase, a second PID parameter group with a large derivative gain is selected to suppress temperature overshoot. This phase is crucial for the furnace temperature to stabilize after a rapid rise. A larger derivative gain effectively suppresses the rate of temperature change; as the temperature rapidly approaches the target value, the derivative term generates a reverse braking effect, preventing overshoot by exceeding the target value. During the constant temperature holding phase, a third PID parameter group with a large integral gain is selected to eliminate steady-state temperature deviation. This phase requires the furnace temperature to remain near the target temperature for an extended period. A larger integral gain continuously accumulates small steady-state deviations and generates a correction output, gradually eliminating the steady-state deviation to near zero.

[0085] Step S34 is when In Within the interval, linear interpolation is performed on the proportional gain, integral gain, and derivative gain of the first and second PID parameter sets, respectively, with the interpolation weights varying accordingly. The position changes linearly within this interval. Linear interpolation is a method for estimating data between two known data points. Its basic principle is to weight the values ​​of the two endpoints according to the proportion of their distances from the point to be interpolated to the two endpoints. (Using proportional gain...) For example, when from Gradually decrease to At that time, the actual proportional gain used From the first PID parameter group Continuously transition to the second PID parameter group During the transition The calculation follows the linear interpolation rule. Integral gain and differential gain The transition should be carried out in the same manner. When In Within the specified interval, the second and third PID parameter sets are linearly interpolated in the same manner. By introducing a linear interpolation transition mechanism in the stage boundary region, the PID parameters change continuously and smoothly during stage switching, avoiding control output oscillations or system instability that may be caused by abrupt changes in parameters.

[0086] Step S4 involves calculating the feedforward compensation power based on the system's equivalent total heat capacity and the preset heating rate during the heating phase. This feedforward compensation power is then superimposed on the feedback output of the PID controller to serve as the total control output power of the heating module. Feedforward control is an open-loop control method that generates control action based on changes in disturbances or setpoints. During the heating phase, if the heating module is driven solely by the feedback output of the PID controller, the controller will only begin generating control outputs after a temperature deviation occurs. Due to the large thermal inertia of the annealing furnace system, this pure feedback control method leads to a lag in temperature response. By establishing a thermal balance model to pre-calculate the heating power required to maintain the preset heating rate and directly superimposing it on the control output as a feedforward quantity, the heating module outputs a power level close to the actual demand before a temperature deviation occurs. The PID controller only needs to correct model errors and residual deviations caused by external disturbances, thereby significantly improving the temperature tracking accuracy during the heating phase.

[0087] Step S4 further includes steps S41 to S43.

[0088] Step S41 is to calculate the equivalent total heat capacity of the system. . The equivalent total heat capacity is the sum of the heat capacity of the heat transfer oil inside the furnace, the heat capacity of the workpiece, and the heat capacity of the furnace body's heat exchange components. The system's equivalent total heat capacity characterizes the total heat required to raise the temperature of all heat exchange media within the system by 1°C. Calculate using the following formula.

[0089] ;

[0090] In the formula, The equivalent total heat capacity of the system (J / ℃); For heat transfer oil mass (kg); The specific heat capacity of the heat transfer oil (J / (kg·℃)); The mass of the workpiece is expressed in kg. Specific heat capacity of the workpiece (J / (kg·℃)); The equivalent mass (kg) of the heat exchange portion of the furnace body; The specific heat capacity of the furnace body material is given by (J / (kg·℃)). This formula is based on the principle of additivity of heat capacity in thermodynamics, that is, the total heat capacity of the system is equal to the algebraic sum of the heat capacities of each component in the system. The mass and specific heat capacity of the heat transfer oil can be determined based on the type and technical parameters of the heat transfer oil and the amount of charge in the furnace. The mass and specific heat capacity of the workpiece can be determined based on the material and specifications of the workpiece. The equivalent mass and specific heat capacity of the furnace body's heat exchange components can be obtained through furnace design parameters or step response experiments.

[0091] Step S42 involves calculating the feedforward compensation power in each control cycle during the heating phase using the following formula. .

[0092] ;

[0093] In the formula, The power for feedforward compensation is (W). The equivalent total heat capacity of the system (J / ℃); The preset heating rate (°C / s); The overall heat dissipation coefficient of the furnace body (W / (m)) 2 ·℃)); The heat dissipation area of ​​the furnace body exterior surface (m²) 2 ); The current average temperature inside the furnace (°C); The ambient temperature (°C) is used. This formula is derived based on the principle of energy conservation. During steady-state heating, the heat power input to the system by the heating module should be equal to the sum of the power required to heat the medium within the system at a preset rate and the power required to compensate for heat dissipation from the furnace body to the environment. The first term on the right side of the formula... Multiply The power required to heat the medium inside the furnace at a preset rate increases with the heating rate. It increases linearly with the increase of . The second term on the right side of the formula Multiply Multiply and The difference represents the power required to compensate for heat loss from the furnace surface. This is based on Newton's law of cooling, which states that the rate at which an object dissipates heat into the environment is directly proportional to the temperature difference between the object's surface and the environment. The proportionality coefficient is the overall heat dissipation coefficient. With heat dissipation area The product of . Overall heat dissipation coefficient. It encompasses both convective and radiative heat transfer mechanisms, the values ​​of which can be estimated through the furnace's insulation design parameters or obtained through experimental calibration. Due to the average temperature inside the furnace... As the temperature continues to change during the heating process, the power loss from heat dissipation is also dynamically adjusted accordingly. Therefore, the feedforward compensation power is updated and calculated based on the latest temperature data in each control cycle.

[0094] Step S43 is to increase the feedforward compensation power. Current feedback output of the PID controller Add them together to get the total control output power. And output to the heating module. Calculate using the following formula.

[0095] ;

[0096] In the formula, The feedback output power (W) of the PID controller; Total control output power (W) of the heating module. Feedforward compensation power. Provides the main heating power baseline and the feedback output of the PID controller. Based on this, the residual deviation between the actual temperature and the target temperature caused by uncertainties such as model parameter errors, ambient temperature fluctuations, and changes in workpiece heat capacity is dynamically corrected. The composite control structure combining feedforward and feedback balances the speed and accuracy of control.

[0097] Step S5 involves dynamically adjusting the operating frequency of the circulating pump based on the real-time value of the temperature uniformity index. When the temperature uniformity index is below a preset threshold, the operating frequency of the circulating pump is increased proportionally to enhance the heat exchange of the thermal oil circulation. When the temperature uniformity index reaches or exceeds the threshold, the operating frequency of the circulating pump is reduced to the level required to maintain basic circulation. The circulating pump is the power device that drives the thermal oil to circulate in the furnace oil passage system. Its operating frequency directly determines the circulation flow rate and velocity of the thermal oil. The greater the circulation flow rate of the thermal oil, the faster the rate of heat transfer between different areas of the furnace through convection heat exchange, and the more rapid the temperature uniformity process. However, the power consumption of the circulating pump also increases accordingly when operating at high frequency. Therefore, a closed-loop correlation is established between the operating frequency of the circulating pump and the temperature uniformity index. When the temperature uniformity is not met, the pump frequency is automatically increased to accelerate temperature uniformity. After the temperature is uniform, the pump frequency is automatically reduced to reduce operating energy consumption, realizing an intelligent control strategy of on-demand circulation.

[0098] The specific implementation process of step S5 is as follows: the temperature uniformity index TUI is compared with the preset threshold value TUI. th Compare them. When TUI is less than TUI th The target operating frequency of the circulating pump is calculated using the following formula. .

[0099] ;

[0100] In the formula, The target operating frequency (Hz) of the circulating pump; The minimum operating frequency (Hz) required to maintain the basic cycle of the circulating pump; TUI represents the maximum operating frequency (Hz) of the circulating pump; TUI is the current temperature uniformity index; TUI th This represents the threshold value for achieving temperature uniformity. The formula establishes a linear mapping relationship between the operating frequency of the circulating pump and the temperature uniformity index. When TUI equals 0, i.e., when the furnace temperature is extremely non-uniform, the frequency calculated by the formula is greater than... After being limited, The circulating pump operates at its highest frequency. When TUI equals TUI th At that time, the frequency calculated by the formula is exactly equal to Plus reduce This value, even after being limited, remains within a reasonable range. In actual implementation, it will... Limit at to The variable frequency drive (VFD) outputs the power to the circulating pump within a specified range. A VFD is a power electronic device that regulates the speed of a motor by changing the frequency of the AC power supply. After receiving frequency commands from the controller, it correspondingly changes the power supply frequency of the circulating pump motor, thereby regulating the speed and output flow of the circulating pump. When TUI is greater than or equal to TUI... th When the temperature uniformity inside the furnace has reached the standard, the operating frequency of the circulating pump is set to [value missing]. This is to maintain the basic circulation of the heat transfer oil.

[0101] After the isothermal holding stage of the annealing process, this method also includes a controlled cooling step. The cooling stage of the annealing process has strict requirements for the cooling rate. If the cooling rate is too fast, the outer layer of the workpiece will cool and shrink first, while the inner layer remains in a high-temperature expansion state, resulting in significant thermal stress. Thermal stress is the internal stress of the material caused by the temperature gradient. When the thermal stress exceeds the yield strength of the material at that temperature, it can cause deformation or even cracking of the workpiece, seriously affecting the annealing quality. Therefore, it is necessary to use a reasonable cooling curve to control the temperature drop of the workpiece, so that the cooling rate gradually decreases as the temperature decreases, avoiding excessive thermal stress caused by excessively rapid temperature drop in the early stages of cooling.

[0102] The controlled cooling process includes steps S61 to S63.

[0103] Step S61 involves setting the initial cooling temperature T0 and the final target temperature T. end and cooling time constant The target cooling temperature curve is generated using an exponential decay model. An exponential decay model is a mathematical model describing the gradual decrease of a physical quantity over time according to an exponential law. Its characteristic is that the rate of change is proportional to the current value, changing rapidly in the initial stage and then slowing down in the later stage. This characteristic perfectly matches the cooling rate requirements of the annealing cooling process. The target cooling temperature curve is generated using the following formula.

[0104] ;

[0105] In the formula, For the cooling stage The target temperature (°C) at 1 second; T0 is the furnace temperature at the start of cooling (°C); T end The final target temperature (°C); The time (s) elapsed after entering the cooling phase; Let be the cooling time constant (s). The larger the value, the slower the cooling rate; exp is an exponential function with the natural constant e as its base. Cooling time constant. The selection of should be determined based on the material, size, and annealing process requirements of the workpiece. This formula shows that when... When equal to 0, It equals T0, meaning the target temperature starts from the initial cooling temperature. Over time... The increase, Gradually approaching 0 from 1, From T0 gradually approaching T end In the initial stage of cooling, the rate of decrease of the target temperature is (T0-T...). end ) / Subsequently, the rate of decline gradually decreases exponentially, approaching 0 in the later stages.

[0106] Step S62 involves the controller calculating the current time in each control cycle of the cooling process. Calculate the leading amount using the following formula. .

[0107] ;

[0108] In the formula, Pre-conducting temperature (°C); The thermal hysteresis time (s) is determined in advance through a furnace step response experiment; The current target cooling temperature (°C); T end The final target temperature (°C); Cooling time constant (s). Thermal hysteresis time. This refers to the delay time experienced after a step change in the output temperature of the heating module, during which the furnace temperature begins to respond noticeably. This delay is mainly caused by the transmission time required for the heat transfer oil to flow from the heating module through the pipeline to the furnace cavity, as well as the thermal inertia of the furnace structure. (Pre-heat transfer amount) The physical meaning is that, in order to overcome the thermal hysteresis effect of the system, the output temperature setpoint of the heating module needs to deviate from the current target cooling temperature by a certain amount in advance, so that the actual temperature of the heat transfer oil when it reaches the furnace cavity after experiencing the transmission delay exactly matches the target cooling temperature. The controller sets the output temperature setpoint of the integrated hot and cold oil heater in the heating module to... minus This causes the actual temperature inside the furnace to follow the target cooling temperature curve and decrease. This is because the calculation of the guide amount includes... With T end As the cooling process progresses, the target temperature gradually approaches the final target temperature, and the lead-in amount decreases accordingly. This adaptive characteristic ensures that the lead-in compensation maintains a reasonable compensation range throughout the entire cooling process.

[0109] Step S63 involves continuing steps S1, S2, and S5 during the cooling process to maintain a synchronous and uniform temperature decrease in all regions. During the cooling stage, although the overall temperature trend within the furnace is downward, the cooling rates may differ between the bottom and sidewall regions due to variations in heat dissipation conditions and heat capacity distribution. If this is not controlled, it can lead to uneven temperature distribution within the cooling process, resulting in uneven thermal stress distribution within the workpiece. Therefore, real-time calculation of the temperature uniformity index and dynamic distribution of the heat transfer oil flow are performed during the cooling process to ensure that the temperature in each region decreases synchronously at a similar rate, maintaining the uniformity of the temperature field within the furnace during cooling.

[0110] The present invention also provides an annealing temperature equalization control system, referring to Figure 5 The system includes furnace body components, jacketed oil passages, bottom circulating oil passages, heating modules, circulating pumps, a first electric proportional regulating valve, a second electric proportional regulating valve, multiple temperature sensors, and a controller.

[0111] The furnace assembly comprises an outer furnace body and an inner furnace body. The inner furnace body is located inside the outer furnace body, forming a sealed interlayer space between them. The outer furnace body is covered with an insulation layer. The outer furnace body serves as the external load-bearing structure of the entire system, providing the mounting base and external protection for the internal components. The inner furnace body is the core cavity for the annealing process; the workpiece is placed within the inner furnace body for annealing. The sealed interlayer space between the inner and outer furnace bodies provides a flow space for the heat transfer oil to circulate and exchange heat along the furnace sidewalls. The insulation layer reduces the rate at which heat is dissipated from the furnace body to the external environment, minimizing heat loss and improving the system's thermal efficiency.

[0112] The jacketed oil channel is located in the space between the inner and outer furnace bodies. Inside the jacketed oil channel are guide plates that divide the space into interconnected spiral flow channels. The guide plates are arranged in an S-shaped spiral path along the jacket space. The heat transfer oil enters from the inlet and rises layer by layer along the spiral channels, continuously exchanging heat with the outer wall of the inner furnace body during its ascent. The S-shaped spiral path design extends the effective flow path of the heat transfer oil within the jacket space, increasing the contact time and area between the heat transfer oil and the furnace wall. This facilitates thorough mixing of the newly injected hot oil with the existing oil in the jacket, fundamentally reducing the problem of uneven localized temperature caused by flow short-circuiting.

[0113] The bottom circulating oil channel is located below the bottom plate of the inner furnace body. The bottom circulating oil channel preferably adopts a serpentine coil structure, with the serpentine coils fully covering the lower surface of the inner furnace body bottom plate. The serpentine coil structure is a pipe configuration where the pipes are arranged in a back-and-forth bend along a plane to form multiple parallel straight pipe sections and connecting elbows. Its advantage lies in achieving a longer pipe length and uniform coverage area within a limited bottom plate area, ensuring comprehensive and uniform heat exchange of the heat transfer oil below the bottom plate and avoiding heat exchange blind spots in the bottom region.

[0114] The heating module includes an integrated hot and cold oil heater, used for heating or cooling the heat transfer oil. This integrated hot and cold oil heater is a temperature control device that combines heating and cooling functions. It integrates electric heating elements and a heat exchanger, and can precisely regulate the temperature of the heat transfer oil flowing through it according to control commands, maintaining the outlet temperature of the heat transfer oil near the set value. During the heating and temperature holding phases, the integrated hot and cold oil heater primarily performs the heating function, heating the heat transfer oil to a level higher than the target temperature inside the furnace before outputting it. During the cooling phase, the integrated hot and cold oil heater adjusts the output temperature according to the target cooling temperature curve, causing the temperature of the heat transfer oil to decrease along a preset trajectory.

[0115] The circulating pump is driven by a variable frequency drive. The pump inlet connects to the output of the integrated hot and cold oil refrigerant system, and its outlet connects to the inlet of the bottom circulating oil channel and the inlet of the jacketed oil channel via a branch pipeline. The outlets of the bottom and jacketed oil channels are connected to the return end of the integrated hot and cold oil refrigerant system via return oil pipelines. These pipeline connections create two parallel circulating branches for the heat transfer oil: the bottom and jacketed oil channels. Driven by the circulating pump, the heat transfer oil flows from the output of the integrated hot and cold oil refrigerant system, splitting into two paths via the branch pipeline. One path enters the bottom circulating oil channel to exchange heat with the inner furnace bottom plate before returning to the integrated hot and cold oil refrigerant system via the return oil pipeline. The other path enters the jacketed oil channel and exchanges heat with the inner furnace sidewall along a spiral channel before also returning to the integrated hot and cold oil refrigerant system via the return oil pipeline. This parallel branch design allows the controller to independently control the flow rate of heat transfer oil entering each oil channel by adjusting the valve opening on each branch, without affecting the overall system circulation flow rate.

[0116] The first electric proportional control valve is installed on the inlet pipe of the bottom circulating oil passage, and the second electric proportional control valve is installed on the inlet pipe of the jacketed oil passage. The electric proportional control valve is a flow control device that receives an electrical signal input and continuously adjusts the valve opening accordingly; its valve opening is proportional to the input electrical signal. By adjusting the openings of the first and second electric proportional control valves respectively, the flow resistance of the bottom circulating oil passage and the jacketed oil passage can be changed, thereby achieving dynamic distribution of the heat transfer oil flow between the two parallel branches.

[0117] Multiple temperature sensors include furnace temperature sensors distributed along the height of the inner wall of the furnace cavity, and oil temperature sensors respectively installed on the inlet and outlet pipes of the bottom circulating oil passage and the jacket oil passage. The furnace temperature sensors collect temperature data at different locations within the furnace cavity, providing a data basis for calculating the temperature uniformity index and assessing regional temperature deviations. The oil temperature sensors monitor the temperature change of the heat transfer oil before and after flowing through each heat exchange oil passage, providing a basis for monitoring heat exchange efficiency.

[0118] The controller is connected to multiple temperature sensors, a first electric proportional control valve, a second electric proportional control valve, the frequency converter driver of the circulating pump, and the heating module. The signal connection between the controller and each temperature sensor is for data acquisition; the controller receives temperature measurement signals from each sensor. The signal connection between the controller and the first and second electric proportional control valves is for control output; the controller outputs opening control signals to both valves. The signal connection between the controller and the frequency converter driver of the circulating pump is also for control output; the controller outputs frequency command signals to the frequency converter driver. The signal connection between the controller and the heating module is bidirectional; the controller outputs power control signals or temperature setpoint signals to the heating module, while simultaneously receiving operating status information from the heating module. The controller is configured to perform the following functions: calculate the temperature uniformity index based on the data from the furnace temperature sensor; determine the direction of temperature deviation in each area and adjust the opening of the first and second electric proportional control valves accordingly to dynamically distribute the heat transfer oil flow; automatically switch the PID control parameter group according to the magnitude of the temperature deviation and smoothly transition within the preset transition bandwidth; output the total control power superimposed with the feedforward compensation power and PID feedback to the heating module during the heating stage; dynamically adjust the operating frequency of the circulating pump according to the temperature uniformity index; and generate the target cooling temperature curve according to the exponential decay model after the constant temperature holding stage and control the output temperature of the integrated hot and cold oil heater to track the curve.

[0119] In a preferred embodiment, both the inner and outer furnace bodies are preferably welded from stainless steel plates. The inner furnace body is aligned with the outer furnace body using positioning pins to maintain uniform radial thickness in the interlayer space. The uniformity of radial thickness directly affects the uniformity of the heat transfer oil flow field distribution within the interlayer oil channels. If one side of the interlayer space is too narrow, the heat transfer oil flow on that side will be insufficient, resulting in inadequate heat exchange and decreased temperature uniformity. Therefore, precise alignment using positioning pins plays a crucial role in ensuring the system's temperature uniformity control. A sealing groove is provided at the top opening of the inner furnace body for installing a sealing ring to achieve furnace cavity sealing and prevent leakage of gas or heat transfer oil vapor within the furnace cavity. The insulation layer is preferably made of aluminosilicate fiber blanket filled between the outer side of the outer furnace body and the outer protective plate. Aluminosilicate fiber blanket is a commonly used high-temperature insulation material with low thermal conductivity, high temperature resistance, and good chemical stability, making it suitable for insulation applications in annealing furnaces.

[0120] Example 1 illustrates the stress-relief annealing process of a 42CrMo alloy steel shaft workpiece, specifically demonstrating the annealing temperature control method and system of the present invention. The workpiece is made of 42CrMo alloy steel, with a diameter of 200mm, a length of 500mm, and a mass of m. w =120kg, specific heat capacity c w =502 J / (kg·℃). Annealing process parameters are as follows: Target annealing temperature T target =650℃, preset heating rate R=0.5℃ / min (0.00833℃ / s), holding time 4h, cooling time constant τ=14400s (4h), final target cooling temperature T end =80℃, ambient temperature T env =25℃.

[0121] In step S1, N=8 PT100 platinum resistance temperature sensors are arranged along the height direction on the inner wall of the furnace cavity, with a measurement accuracy of ±0.1℃. Three sensors are arranged in the bottom area, numbered T1 to T3; three in the middle area, numbered T4 to T6; and two in the top area, numbered T7 to T8. One oil temperature sensor is installed at each of the bottom circulating oil passage inlet, bottom circulating oil passage outlet, jacket oil passage inlet, and jacket oil passage outlet. The controller sampling period is set to 5 seconds.

[0122] In step S11, three sensors in the bottom region are evenly distributed at 0°, 120° and 240° circumferential positions along a height of 50mm above the bottom plate. Three sensors in the middle region are located at 0°, 120° and 240° circumferential positions at 1 / 2 of the furnace cavity height. Two sensors in the top region are located at 0° and 180° circumferential positions at 4 / 5 of the furnace cavity height.

[0123] In step S12, the controller synchronously reads the real-time temperature values ​​of all 8 furnace temperature sensors and 4 oil temperature sensors with a sampling period of 5 seconds.

[0124] In step S13, taking a sampling moment during the constant temperature holding phase as an example, the temperature values ​​at the eight temperature measurement points are T1=648.2℃, T2=647.8℃, T3=648.5℃, T4=649.1℃, T5=649.5℃, T6=649.3℃, T7=650.2℃, and T8=650.1℃. The highest temperature T is extracted. max =650.2℃ and lowest temperature T min =647.8℃, calculate the arithmetic mean T avg =649.09℃, according to the formula TUI=1-(T in step S13 of the present invention) max -T min ) / T avg The calculated TUI value is 0.99630.

[0125] In step S2, the heat exchange area is divided into a bottom region and a sidewall region. In step S21, the average temperature T of the bottom region is... b The average temperature of the sidewall region is 648.17℃. s The temperature was 649.64℃.

[0126] In step S22, the bottom temperature deviation Sidewall temperature deviation Both are positive and in the same direction.

[0127] In step S23, since the two have the same sign and the sum of their absolute values ​​is greater than 0, the bottom flow distribution coefficient is calculated according to the formula in step S23 of this invention. Interlayer oil passage flow distribution coefficient The bottom circulation channel receives 83.6% of the total flow, and the interlayer channel receives 16.4%. In step S24, the controller adjusts the opening of the first electric proportional regulating valve accordingly. The corresponding valve position, the opening degree of the second electric proportional regulating valve to the same level The corresponding valve position. In step S3, the threshold value for the rapid heating stage is set. ℃, this value is 5% of the target temperature of 650℃; threshold value for the isothermal holding phase. ℃; Transition bandwidth ℃. In step S31, the current average temperature inside the furnace is 649.09℃, with a deviation of ℃. In step S32, because ℃ less than The temperature is set to ℃, indicating that the system is currently in a constant temperature maintenance phase. In step S33, the third PID parameter group is selected, with the following parameters: , , A large integral gain is used to eliminate steady-state temperature deviation. During the rapid heating phase, the first PID parameter group is used, with the following parameters: , , The second PID parameter group is used during the temperature equalization transition stage, and the parameters are as follows: , , .

[0128] In step S4, the system thermodynamic parameters are as follows: heat transfer oil mass m oil =150kg, specific heat capacity c oil =2100J / (kg·℃); equivalent mass m of the furnace body's heat exchange components f =80kg, specific heat capacity c f =500J / (kg·℃); Furnace body comprehensive heat dissipation coefficient h=3.5W / (m²) 2 (℃), external surface heat dissipation area A = 4.2m² 2 .

[0129] In step S41, the equivalent total heat capacity of the system is calculated according to the formula in step S41 of the present invention. In step S42, when the average temperature inside the furnace is 300°C at a certain moment during the heating stage, the feedforward compensation power is calculated according to the formula in step S42 of this invention. Currently, during the isothermal maintenance phase, R=0. W, at this point, the feedforward power only compensates for heat dissipation losses. In step S43, the total control output power... The output is sent to the heating module. In step S5, the current TUI = 0.99630 is greater than the threshold value TUI. th =0.995, the operating frequency of the circulating pump is set to f min =15Hz. The maximum operating frequency f of the circulating pump. max =50Hz.

[0130] During the cooling phase, the temperature is maintained at a constant level for 4 hours before controlled cooling begins. In step S61, the initial cooling temperature T0 = 650℃, and the final target temperature T... end =80℃, cooling time constant τ=14400s, generate the target cooling temperature curve according to the exponential decay model in step S61 of this invention. In step S62, the thermal hysteresis time t lag =120s, lead-in amount at the start of cooling The output temperature setting of the integrated hot and cold oil heater is 650-4.75=645.25℃. In step S63, steps S1, S2 and S5 are continuously executed during the cooling process to maintain a synchronous and uniform temperature decrease in each area.

[0131] The hardware components of the system include: an inner furnace body and an outer furnace body welded from 316L stainless steel, with an inner furnace body wall thickness of 5mm and an outer furnace body wall thickness of 3mm, a 100mm thick interlayer space, an S-shaped spiral guide plate in the interlayer space, a serpentine coil circulating oil channel at the bottom, a 100mm thick 1430 aluminum silicate fiber blanket insulation layer, an integrated hot and cold oil machine, a variable frequency circulating pump with a frequency range of 15 to 50Hz, a first and second electric proportional regulating valve, eight PT100 furnace internal temperature sensors and four oil temperature sensors, and a PLC controller configured to execute the above method.

[0132] Example 2 uses the recrystallization annealing treatment of H62 brass tubing as an application scenario. The difference from Example 1 is that the workpiece is H62 brass tubing with a mass of m. w =80kg, specific heat capacity c w =385 J / (kg·℃). Target annealing temperature T target =400℃, preset heating rate R=0.3℃ / min (0.005℃ / s), holding time 2h, cooling time constant τ=10800s (3h), final target cooling temperature T end =60℃.

[0133] In step S11, N=10 temperature sensors are arranged on the inner wall of the furnace cavity: 4 in the bottom region, 3 in the middle region, and 3 in the top region. In step S31, the settings are... ℃ is 5% of the target temperature. ℃, ℃. In step S33, the first PID parameter set is: , , The second PID parameter group is , , The third PID parameter group is , , In step S41, the system's equivalent total heat capacity is... In step S62, t lag =90s, initial lead quantity .

[0134] Example 3 uses solution annealing of a 304 stainless steel flange forging as an application scenario. The difference from Example 1 is that the workpiece is a 304 stainless steel flange with a mass of m. w=200kg, specific heat capacity c w =500 J / (kg·℃). Target annealing temperature T target =850℃, preset heating rate R=0.8℃ / min (0.01333℃ / s), holding time 6h, cooling time constant τ=18000s (5h), final target cooling temperature T end =100℃.

[0135] In step S11, N=12 temperature sensors are arranged on the inner wall of the furnace cavity: 4 in the bottom region, 4 in the middle region, and 4 in the top region. In step S31, the settings are... ℃ is 6% of the target temperature. ℃, ℃. In step S33, the first PID parameter set is: , , The second PID parameter group is , , The third PID parameter group is , , .

[0136] In step S41, the system's equivalent total heat capacity In step S42, the average furnace temperature T during the heating phase is used as the reference value. avg Taking 500℃ as an example, the feedforward compensation power In step S62, t lag =150s, initial lead time .

[0137] Comparative Example 1 uses a fixed proportional flow distribution method; it employs the same annealing furnace system structure and workpiece parameters as Example 1, namely 42CrMo alloy steel and a target annealing temperature of 650℃. It also uses the same steps as Example 1: temperature acquisition and TUI calculation in step S1, staged PID temperature control in step S3, feedforward compensation in step S4, and variable frequency speed regulation in step S5. The only difference from Example 1 is the flow distribution method in step S2: it is fixed throughout. That is, the bottom circulation oil passage and the interlayer oil passage are always allocated 50% of the total flow, and are not dynamically adjusted according to the temperature deviation of the area.

[0138] Comparative Example 2 uses a fixed PID parameter method throughout. It employs the same annealing furnace system structure, workpiece parameters, and target annealing temperature as Example 1, while retaining steps S1, S2, S4, and S5 unchanged. The only difference from Example 1 lies in the PID control method of step S3: a fixed set of PID parameters is used throughout. , , No process stage division or parameter switching is performed, and no transition smoothing mechanism is set.

[0139] Comparative Example 3 uses a pure PID feedback control method. It employs the same annealing furnace system structure, workpiece parameters, and target annealing temperature as Example 1, while retaining steps S1, S2, S3, and S5 unchanged. The only difference from Example 1 is step S4: the feedforward compensation power is not calculated; the total control output power of the heating module is determined solely by the feedback output of the PID controller. .

[0140] Experiment 1: Comparison Experiment on Temperature Uniformity Achievement Time; This experiment is used to verify the effect of the dynamic flow distribution method based on regional temperature deviation in step S2 of the present invention on improving the temperature uniformity in the furnace. Annealing heating experiments were conducted using the following conditions: 42CrMo alloy steel at 650℃ in Example 1, H62 brass at 400℃ in Example 2, 304 stainless steel at 850℃ in Example 3, and 42CrMo alloy steel at 650℃ with a fixed flow rate in Comparative Example 1. Each experiment started at room temperature (25℃) and heated to its target annealing temperature. Data from all temperature measurement points were recorded every 5 seconds, according to the formula TUI=1-(T) in step S13 of the present invention. max -T min ) / T avg Calculate the temperature uniformity index TUI at each sampling time.

[0141] The experimental indicators include two aspects: time to TUI target attainment and steady-state TUI value. Time to TUI target attainment is defined as the time elapsed from the start of heating until the TUI value is maintained at 0.995 or higher for the first 5 consecutive minutes. Steady-state TUI value is defined as the arithmetic mean of the TUI values ​​during the last 30 minutes of the isothermal holding phase.

[0142] Experimental results are as follows Figure 1 As shown. Figure 1 The graph shows the temperature uniformity index (TUI) of Examples 1 to 3 and Comparative Example 1 as a function of heating time. Figure 1 The horizontal axis represents the time from the start of heating, and the vertical axis represents the TUI value. A reference line of 0.995 for TUI compliance is also plotted in the figure.

[0143] from Figure 1As can be seen, all four TUI curves show a trend of gradually rising from an initial low value and then stabilizing, indicating that as the heat transfer oil circulation heat exchange continues, the temperature distribution inside the furnace gradually becomes more uniform. The TUI curves of Examples 1 to 3, which use dynamic flow distribution, rise at a significantly faster rate than those of Comparative Example 1, which uses fixed flow distribution. The TUI attainment times for the three examples are 42 min, 35 min, and 53 min, respectively, while the TUI attainment time for Comparative Example 1 is 64 min. The TUI attainment time of Example 1 is shortened by (64-42) / 64×100%=34.4% compared to Comparative Example 1, far exceeding the expected improvement of 20%. The steady-state TUI values ​​of each example are higher than those of Comparative Example 1, indicating that dynamic flow distribution not only accelerates the temperature homogenization rate but also improves the final temperature uniformity level.

[0144] The dynamic flow distribution method based on regional temperature deviation in step S2 of this invention can significantly shorten the time to achieve temperature uniformity and improve the steady-state temperature uniformity level. This conclusion proves the feasibility and effectiveness of the technical solution described in step S2 of this invention. The principle is that the dynamic flow distribution method calculates the deviation between the bottom region and the sidewall region and the target temperature in real time, and distributes a larger proportion of the heat transfer oil flow to the region with a larger temperature deviation, so that the region obtains a stronger convective heat transfer intensity, thereby accelerating its approach to the target temperature. In contrast, the fixed proportional distribution method used in Comparative Example 1 cannot adjust for the actual temperature rise difference of each region, resulting in the region with a larger temperature deviation always only obtaining half of the heat transfer flow, and the temperature uniformity process is slow. Example 2 has the shortest time to achieve the target because the brass workpiece has a small heat capacity and the target temperature is only 400℃, so the time required for the system to reach thermal equilibrium is short. Example 3 has the longest time to achieve the target, corresponding to the large mass and high temperature conditions, but it is still 17.2% shorter than Comparative Example 1, indicating that the dynamic flow distribution method has a significant effect under different operating conditions.

[0145] Experiment Example 2: Temperature Response Characteristics and Overshoot Comparison Experiment; This experiment is used to verify the effect of the staged adaptive PID temperature control method in step S3 of the present invention on suppressing temperature overshoot and improving steady-state temperature control accuracy. Temperature records for the complete annealing process were performed using the staged adaptive PID temperature control methods of Examples 1 to 3 and the fixed PID parameter method of Comparative Example 2. The experimental indicators include temperature overshoot and steady-state temperature fluctuation range. Temperature overshoot is defined as the maximum positive deviation of the average furnace temperature from the target annealing temperature. Steady-state temperature fluctuation range is defined as the peak-to-peak value of the average furnace temperature fluctuation during the last 2 hours of the isothermal holding phase, expressed as ± half of the peak-to-peak value.

[0146] Experimental results are as follows Figure 2 As shown. Figure 2(a) shows the furnace average temperature response curves of Example 1 and Comparative Example 2 before and after approaching the target annealing temperature of 650°C. The target temperature reference line is also plotted in the figure. Figure 2 (b) is a grouped comparison bar chart of temperature overshoot and steady-state fluctuation peak value of Examples 1 to 3 and Comparative Example 2.

[0147] from Figure 2 As can be seen in Figure (a), the temperature curve of Example 1 exhibits a stable trend as it approaches the target temperature of 650°C, showing only a slight overshoot of 0.8°C before quickly returning to near the target temperature and remaining stable, with minimal temperature fluctuations during the isothermal holding phase. In contrast, the temperature curve of Comparative Example 2 shows a significant overshoot of 4.5°C as it approaches the target temperature, subsequently undergoing multiple oscillations before gradually stabilizing, and still exhibits noticeable temperature fluctuations during the isothermal holding phase. Figure 2 As can be seen in (b), the temperature overshoot of Examples 1 to 3 is in the range of 0.5 to 1.2℃, which is much smaller than the 4.5℃ of Comparative Example 2. The steady-state peak-to-peak value of Examples 1 to 3 is in the range of 0.40 to 0.70℃, which is much smaller than the 2.20℃ of Comparative Example 2.

[0148] It can be seen that the temperature overshoot in Example 1 is only 17.8% of that in Comparative Example 2, a reduction of 82.2%, far exceeding the expected improvement target of 50%. The steady-state temperature fluctuations in all examples are within ±0.35℃, indicating that the staged adaptive PID temperature control method in step S3 of this invention has the effect of overshoot suppression and steady-state accuracy improvement. This is because step S3 of this invention uses a second PID parameter group with a larger derivative gain during the temperature uniformity transition stage. The larger derivative gain effectively brakes the rate of temperature change, and when the temperature rapidly approaches the target value, the derivative term generates a reverse output to suppress inertial overshoot. During the constant temperature holding stage, step S3 of this invention switches to a third PID parameter group with a larger integral gain. The integral term continuously accumulates and corrects small steady-state deviations, compressing steady-state fluctuations to a very small range. Simultaneously, the linear interpolation transition mechanism in step S34 of this invention ensures continuous and smooth changes in PID parameters during stage switching, avoiding control output oscillations caused by parameter step changes. In contrast, Comparative 2 uses a compromise of fixed PID parameters throughout the process. When approaching the target temperature, the proportional gain is too large, resulting in significant overshoot. During the isothermal phase, the integral gain is insufficient, making it impossible to effectively eliminate steady-state deviation.

[0149] Experiment Example 3: Comparison Experiment on Heating Rate Tracking Accuracy; This experiment example is used to verify the effect of the feedforward compensation method based on the thermal balance model in step S4 of the present invention on improving the heating rate tracking accuracy. Experiments were conducted during the heating stage using the feedforward plus feedback composite control method of Examples 1 to 3 and the pure PID feedback control method of Comparative Example 3, respectively. During the heating process, the actual heating rate R of the average temperature inside the furnace was recorded. actual And calculate the tracking error between it and the preset heating rate R. Actual heating rate R actual The method for obtaining T is as follows: take the T values ​​of two adjacent sampling periods. avg The difference is divided by the sampling period to obtain the instantaneous rate, which is then filtered by a moving average over 10 sampling periods to eliminate measurement noise. Experimental parameters include the mean absolute error (MAE) of the heating rate and the maximum instantaneous error of the heating rate. MAE represents the total heating rate over the entire heating phase. The time average of the absolute value, with the maximum instantaneous error being The maximum absolute value.

[0150] Experimental results are as follows Figure 3 As shown. Figure 3 In (a), the heating rate tracking error of Example 1 and Comparative Example 3 during the heating stage is shown. The graph shows the change over time, with the horizontal axis representing the heating phase time and the vertical axis representing the heating rate error. At the same time, an error band reference line of ±0.05℃ / min was plotted. Figure 3 (b) is a grouped comparison bar chart of heating rate MAE and maximum instantaneous error for Examples 1 to 3 and Comparative Example 3.

[0151] from Figure 3 As can be seen in (a), the heating rate error of Example 1 fluctuated within an error band of ±0.05℃ / min throughout the entire heating stage, with a small error amplitude and stable fluctuation. In contrast, the heating rate error of Comparative Example 3 showed a large positive deviation in the initial and middle stages of heating, indicating that the actual heating rate significantly lagged behind the preset value, with a maximum instantaneous error reaching 0.280℃ / min, far exceeding the 0.042℃ / min of Example 1. The error of Comparative Example 3 decreased somewhat in the later stages of heating as the temperature approached the target value, but the overall error level was still much higher than that of Example 1. Figure 3 As can be seen in Figure (b), the MAE of Examples 1 to 3 are all in the range of 0.012 to 0.025 °C / min, while the MAE of Comparative Example 3 is 0.115 °C / min, which is 6.4 times that of Example 1. The maximum instantaneous error of each example is in the range of 0.028 to 0.058 °C / min, and is controlled at or within ±0.05 °C / min, while the maximum instantaneous error of Comparative Example 3 reaches 0.280 °C / min.

[0152] It can be seen that after adopting the feedforward and feedback composite control method in step S4 of this invention, the heating rate tracking error MAE is reduced to 0.018℃ / min, which is only 15.7% of that of the pure PID method. The maximum instantaneous error is controlled within ±0.05℃ / min, meeting the process requirements for precise control of the heating rate. This conclusion proves that the feedforward compensation method based on the thermal balance model in step S4 of this invention is effective and feasible. The principle lies in the feedforward compensation power... The heating power required to maintain the preset heating rate was actively estimated based on the heat balance equation. This power consists of two parts: the first part... To generate the effective power required to heat all the heat exchange medium in the system at a preset rate, Part Two To compensate for the power loss caused by heat dissipation from the furnace to the environment, the feedforward parameter provides a power baseline close to the actual demand before the deviation occurs. The PID controller only needs to correct model parameter errors and residual deviations caused by external disturbances, thus significantly improving overall tracking accuracy. In contrast, the pure PID controller in Comparative Example 3 relies entirely on temperature deviation feedback to generate the control output. Under conditions of high system thermal inertia, the control output inherently lags behind the actual demand, resulting in a significantly larger tracking error in the heating rate. Example 2 has the lowest MAE because its target heating rate is as low as 0.3℃ / min. The system thermal inertia has a smaller impact on lower heating rates, making feedforward compensation easier to achieve accurate tracking.

[0153] Experiment Example 4: Comparison Experiment of Circulating Pump Energy Consumption; This experiment is used to verify the effect of the circulating pump variable frequency speed regulation method based on temperature uniformity index (TUI) feedback in step S5 of the present invention in reducing the energy consumption of the circulating pump while ensuring the uniform temperature effect.

[0154] The energy consumption of the circulating pump during the complete annealing process was recorded using the variable frequency speed control methods of Examples 1 to 3 and the constant frequency 50Hz operation mode of Comparative Example 1. The complete annealing process included a heating stage, a isothermal holding stage, and a cooling stage. In each experiment, TUI ≥ 0.995 was ensured during the isothermal holding stage. The energy consumption of the circulating pump was recorded using the built-in power metering function of the variable frequency drive. The experimental indicators included the cumulative power consumption of the circulating pump throughout the entire process and the average operating frequency during the isothermal holding stage.

[0155] Experimental results are as follows Figure 4 As shown. Figure 4 The middle (a) is a bar chart comparing the cumulative energy consumption of the circulating pump throughout the entire process of Examples 1 to 3 and Comparative Example 1, with the vertical axis representing the cumulative energy consumption. Figure 4 (b) is a comparison graph of the operating frequency of the circulating pump during the entire annealing process of Example 1 and Comparative Example 1. The horizontal axis represents the time of the entire annealing process, and the vertical axis represents the operating frequency of the circulating pump.

[0156] from Figure 4 As can be seen in (a), under the same workpiece and process conditions, a direct comparison shows that the cumulative energy consumption of the circulating pump in Example 1 is 8.6 kWh, which is only 60.6% of the 14.2 kWh of Comparative Example 1, resulting in an energy saving of 39.4%. This verifies that the variable frequency speed control method can reduce the energy consumption of the circulating pump by more than 30% while ensuring the same temperature uniformity. The cumulative energy consumption of Example 2 is 5.8 kWh. Its process has a lower target temperature and shorter holding time, and after the TUI is quickly achieved, it operates at a low frequency for a long time, thus resulting in the lowest absolute energy consumption. The cumulative energy consumption of Example 3 is 12.4 kWh. Although its target temperature is the highest and the holding time is the longest, the cumulative energy consumption is still lower than that of Comparative Example 1 under the shorter process time due to the automatic reduction to low frequency operation during the constant temperature holding stage by variable frequency speed control. Figure 4 As can be seen in (b), in Example 1, the pump operating frequency was maintained at a high frequency of 40 to 50 Hz during the initial heating phase when the TUI was low, in order to enhance the circulation and heat exchange of the heat transfer oil in the furnace. As the TUI gradually increased and reached the target threshold of 0.995, the pump frequency rapidly dropped to a low frequency of 15 to 17 Hz. During the isothermal maintenance phase, because the TUI remained above 0.995, the pump operated at a frequency close to f for an extended period. min The pump operates at a low frequency of 15Hz. During the initial cooling phase, the TUI (Transmission Intake) briefly drops due to differences in cooling rates across different areas, causing the pump frequency to rebound somewhat. Subsequently, once the TUI returns to the target level, the pump frequency drops back to the low frequency range. In contrast, Comparative Example 1 operates at a constant frequency of 50Hz throughout, consuming significant amounts of electrical energy even during the constant temperature maintenance phase when the TUI has reached the target level and in the later stages of the cooling phase.

[0157] It can be seen that the variable frequency speed control method for the circulating pump based on TUI feedback in step S5 of this invention can significantly reduce the energy consumption of the circulating pump while ensuring the uniformity of temperature inside the furnace. In a direct comparison between Example 1 and Comparative Example 1, the cumulative energy consumption of the circulating pump was reduced by 39.4% under the same workpiece and process conditions, far exceeding the expected energy-saving target of 30%. This conclusion proves that the technical solution described in step S5 of this invention has both temperature uniformity protection and energy-saving effects. The reason lies in the variable frequency speed control formula. A negative feedback relationship was established between the operating frequency of the circulating pump and the temperature uniformity index (TUI). When TUI is below the target threshold, the formula outputs a higher frequency value to drive the circulating pump to operate at high speed, increasing the heat transfer oil circulation flow rate to enhance convective heat transfer between different zones and promote temperature uniformity. When TUI reaches or exceeds the target threshold, the formula output drops to f. min The circulating pump operates at the lowest frequency necessary to maintain basic circulation, avoiding unnecessary power consumption. The power consumption of the circulating pump is approximately proportional to the cube of its rotational speed; therefore, reducing the frequency from 50Hz to 15Hz reduces the pump's instantaneous power consumption to (15 / 50) of its original value. 3=2.7%, the energy saving effect is extremely significant. Example 2 has the highest energy saving ratio. Its system has a small heat capacity and a heat preservation time of only 2 hours. TUI can reach the standard in a short time and maintain it for a long time. The low frequency operation time accounts for the largest proportion.

[0158] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the uniform temperature during annealing, characterized in that, Includes the following steps: S1: Real-time temperature data of each temperature measurement point is collected by multiple temperature sensors arranged in the furnace cavity of the annealing furnace, and the temperature uniformity index, which characterizes the temperature uniformity in the furnace, is calculated accordingly. S2: Divide the heat exchange area of ​​the annealing furnace into the bottom area and the side wall area, calculate the temperature deviation between the average temperature of each area and the target annealing temperature, determine whether the direction of the temperature deviation between the two areas is consistent, and dynamically adjust the heat transfer oil flow distribution between the bottom circulating oil channel and the jacket oil channel accordingly. S3: Based on the magnitude of the deviation between the average temperature in the furnace and the target annealing temperature, the current process stage of the annealing process is automatically determined. Different PID control parameter groups are used for temperature control in different process stages, and the PID control parameters are smoothly transitioned within the preset transition bandwidth when switching between adjacent stages. S4: During the heating stage, the feedforward compensation power is calculated based on the system's equivalent total heat capacity and the preset heating rate. The feedforward compensation power is then superimposed with the feedback output of the PID controller to serve as the total control output power of the heating module. S5: The operating frequency of the circulating pump is dynamically adjusted according to the real-time value of the temperature uniformity index. When the temperature uniformity index is lower than the preset threshold, the operating frequency of the circulating pump is increased proportionally to enhance the heat exchange of the heat transfer oil. When the temperature uniformity index reaches or exceeds the threshold, the operating frequency of the circulating pump is reduced to the level required to maintain basic circulation. Step S1 specifically includes: S11: N temperature sensors are arranged along the height direction on the inner wall of the annealing furnace cavity, where N≥6. The N temperature sensors are distributed in the bottom, middle and top regions of the furnace cavity, with no less than 2 sensors arranged in each region. At the same time, oil temperature sensors are installed on the inlet and outlet pipes of the bottom circulating oil channel and the jacketed oil channel respectively. S12: The controller reads the real-time temperature values ​​of all temperature sensors at a set sampling period to obtain the temperature values ​​of N temperature measurement points inside the furnace. S13: Extract the maximum value T from N temperature values. max With minimum value T min And calculate the arithmetic mean T. avg The temperature uniformity index TUI is calculated using the following formula: ； In the formula, TUI is the temperature uniformity index, which is dimensionless; T max T represents the highest temperature among N temperature measurement points inside the furnace. min T represents the lowest temperature among N temperature measurement points inside the furnace. avg TUI is the arithmetic mean of the temperatures measured at N points inside the furnace; the closer TUI is to 1, the more uniform the temperature distribution inside the furnace. Step S2 specifically includes: S21: Take the arithmetic average of the temperature sensor readings from the bottom region in step S11 to obtain the average temperature T of the bottom region. b The temperature readings from the temperature sensors located in the middle and top regions are combined and taken as an arithmetic mean to obtain the average temperature T of the sidewall region. s ; S22: Calculate the bottom temperature deviation separately. and sidewall temperature deviation The and The values ​​are signed deviations; positive values ​​indicate that the temperature in the region is lower than the target annealing temperature, and negative values ​​indicate that the temperature is higher than the target annealing temperature; where T is the deviation value. target The target annealing temperature; T b The average temperature of the bottom region; T s This represents the average temperature of the sidewall region. S23: Judgment and The sign of the two is the same, and the sum of their absolute values ​​is greater than zero. Therefore, the sign is determined by... Calculate the flow distribution coefficient of the bottom circulation oil passage. Interlayer oil passage flow distribution coefficient When the two signs are opposite, the flow distribution coefficient of the previous control cycle remains unchanged, and the heating module prioritizes adjusting the heat transfer oil temperature to eliminate the reverse deviation; when both are zero, let In the formula, represents the absolute value operation; This is the flow distribution coefficient for the bottom circulating oil passage; This is the flow distribution coefficient for the interlayer oil passage; S24: The controller according to Adjust the opening of the first electric proportional regulating valve installed on the oil inlet pipe of the bottom circulating oil passage, according to... Adjusting the opening of the second electric proportional regulating valve installed on the oil inlet pipe of the sandwich oil passage enables dynamic distribution of heat transfer oil between the two parallel oil passages; Step S4 specifically includes: S41: Calculate the equivalent total heat capacity of the system The The sum of the heat capacity of the heat transfer oil in the furnace, the heat capacity of the workpiece, and the heat capacity of the furnace body's heat exchange components is calculated as follows: Calculate; where, This represents the system's equivalent total heat capacity. For the quality of heat transfer oil; The specific heat capacity of the heat transfer oil; For workpiece quality; The specific heat capacity of the workpiece; The equivalent mass of the heat exchange portion of the furnace body; The specific heat capacity of the furnace body material; S42: In each control cycle during the heating phase, calculate the feedforward compensation power using the following formula. : ； In the formula, For feedforward compensation power; This represents the system's equivalent total heat capacity. Preset heating rate; The overall heat dissipation coefficient of the furnace body; This refers to the heat dissipation area of ​​the outer surface of the furnace body; This represents the current average temperature inside the furnace. The ambient temperature is represented by the first term on the right side of the formula, which is the power required to heat the medium inside the furnace at a preset rate, and the second term is the power required to compensate for heat loss from the furnace body. S43: The feedforward compensation power Current feedback output of the PID controller Add them together to get the total control output power. And output to the heating module; where, The feedback output power of the PID controller; This refers to the total control output power of the heating module; Step S5 specifically includes: denoting the temperature uniformity index as TUI, and comparing TUI with a preset compliance threshold value TUI. th Comparison, when TUI <TUI th The target operating frequency of the circulating pump is calculated using the following formula. : ； In the formula, The target operating frequency of the circulating pump; To maintain the minimum operating frequency of the circulating pump in its basic cycle; TUI represents the maximum operating frequency of the circulating pump; TUI is the current temperature uniformity index. th The threshold value for achieving temperature uniformity; and Limit at The variable frequency drive outputs to the circulating pump within the specified range; when TUI ≥ TUI th At that time, set the operating frequency of the circulating pump to ; After the isothermal holding phase of the annealing process, a controlled cooling step is also included, specifically: S61: Set the initial cooling temperature T0 and the final target temperature T end and cooling time constant Generate the target cooling temperature curve according to the exponential decay model: ； In the formula, For the cooling stage The target temperature is measured in seconds; T0 is the furnace temperature at the start of cooling; T end The final target temperature; This refers to the time elapsed after entering the cooling phase; The cooling time constant is The larger the value, the slower the cooling rate; exp is the natural exponential function; S62: In each control cycle of the cooling process, the controller calculates based on the current moment. And calculate the lead amount according to the following formula. : ； In the formula, For leading quantity; The thermal hysteresis time is determined in advance through a furnace step response experiment. The current target cooling temperature; T end The final target temperature; The controller sets the output temperature setpoint of the integrated hot and cold oil heater in the heating module to the cooling time constant. This causes the actual temperature inside the furnace to decrease in line with the target cooling temperature curve. S63: During the cooling process, steps S1, S2 and S5 are continuously executed to maintain a synchronous and uniform temperature decrease in each region.

2. The annealing temperature control method according to claim 1, characterized in that, Step S3 specifically includes: S31: Preset threshold value for rapid heating phase Threshold value during constant temperature maintenance stage and transition bandwidth ,in , and ; Calculate the deviation between the average temperature inside the furnace and the target annealing temperature. ; S32: Based on the aforementioned deviation The absolute value determines the current stage of the process. When it is determined to be in the rapid heating phase, When it is determined to be the uniform temperature transition stage, when The time is determined to be the isothermal maintenance stage; where, This represents the deviation between the average temperature inside the furnace and the target annealing temperature. This is the threshold value for the rapid heating phase; This is the threshold value for the isothermal maintenance stage; For transition bandwidth; S33: During the rapid heating stage, the first PID parameter group with a large proportional gain is selected to improve the heating rate; during the temperature equalization transition stage, the second PID parameter group with a large derivative gain is selected to suppress temperature overshoot; during the constant temperature holding stage, the third PID parameter group with a large integral gain is selected to eliminate steady-state temperature deviation. S34: When In Within the interval, linear interpolation is performed on the proportional gain, integral gain, and derivative gain of the first and second PID parameter sets, respectively, with the interpolation weights varying accordingly. The position changes linearly within this interval; when In Within the interval, the second and third PID parameter sets are linearly interpolated in the same way; thus, the various PID parameters transition continuously and smoothly during stage switching.

3. An annealing temperature equalization control system, characterized in that, include: The furnace body assembly includes an outer furnace body and an inner furnace body, wherein the inner furnace body is disposed inside the outer furnace body, and a sealed interlayer space is formed between the two, and the outer furnace body is covered with an insulation layer. An interlayer oil channel is provided within the interlayer space, and its interior is provided with a guide plate that divides the interlayer space into a series of interconnected spiral flow channels; The bottom circulating oil channel is located below the bottom plate of the inner furnace body; Heating modules, including integrated hot and cold oil heaters, are used to heat or cool heat transfer oil; The circulating pump is driven by a variable frequency drive. Its inlet is connected to the output end of the integrated hot and cold oil machine, and its outlet is connected to the inlet of the bottom circulating oil channel and the inlet of the jacketed oil channel through a branch pipeline. The outlet of the bottom circulating oil channel and the outlet of the jacketed oil channel are connected to the return end of the integrated hot and cold oil machine through a return oil pipeline, so that the bottom circulating oil channel and the jacketed oil channel form two parallel heat transfer oil circulation branches. The first electric proportional control valve and the second electric proportional control valve are respectively installed on the oil inlet pipes of the bottom circulation oil passage and the jacket oil passage; Multiple temperature sensors, including furnace temperature sensors distributed along the height of the inner wall of the inner furnace cavity, and oil temperature sensors respectively installed on the inlet and outlet pipelines of the bottom circulating oil passage and the jacket oil passage; The controller is connected to the plurality of temperature sensors, the first electric proportional regulating valve, the second electric proportional regulating valve, the frequency converter driver of the circulating pump, and the heating module. The controller is configured to: calculate a temperature uniformity index based on the data from the furnace temperature sensors; determine the direction of temperature deviation in each region and adjust the opening of the first and second electric proportional regulating valves accordingly to dynamically distribute the heat transfer oil flow; automatically switch PID control parameter groups according to the magnitude of the temperature deviation and smoothly transition within a preset transition bandwidth; output the total control power superimposed with the feedforward compensation power and PID feedback to the heating module during the heating phase; dynamically adjust the operating frequency of the circulating pump according to the temperature uniformity index; and generate a target cooling temperature curve according to the exponential decay model after the constant temperature holding phase and control the output temperature of the integrated hot and cold oil heater to track the curve. The guide plates in the interlayer oil channel are arranged in an S-shaped spiral path along the interlayer space. After the heat transfer oil enters from the inlet, it rises layer by layer along the spiral channel and continuously exchanges heat with the outer wall of the inner furnace during the rising process. The bottom circulating oil channel adopts a serpentine coil structure, and the serpentine coil is distributed along the lower surface of the inner furnace body bottom plate. Both the inner furnace body and the outer furnace body are welded from stainless steel plates. The inner furnace body is aligned with the outer furnace body by positioning pins to maintain the uniform radial thickness of the interlayer space. A sealing groove is provided at the top opening of the inner furnace body for installing a sealing ring to achieve furnace cavity sealing. The heat insulation layer is made of aluminum silicate fiber blanket filled between the outer side of the outer furnace body and the outer protective plate.

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