Workpiece center surface temperature difference adjusting current heat compensation method based on PID (Proportion Integration Differentiation) control

Abstract

The invention discloses a workpiece core and surface temperature difference adjusting current heat compensation method based on PID control, and belongs to the technical field of workpiece heat treatment. The invention aims to solve the problem of overlarge temperature difference between the surface and the core in the heat treatment process of a large workpiece. Comprising the following steps: on the basis of a one-dimensional unsteady state heat conduction equation, obtaining a heat treatment furnace heating temperature field curve of a to-be-heated workpiece heated from an initial temperature to a set temperature in a heat treatment furnace at the set temperature by adopting a numerical simulation method; meanwhile, a self-resistance heating temperature field curve of the workpiece to be heated under the set current condition is obtained; a comprehensive heating unsteady-state temperature field curve of the workpiece to be heated is obtained under the condition that the set linear heating rate and self-resistance heating are combined; and when the workpiece to be heated is heated under the condition of the set linear heating rate, current is adjusted through PID control based on the comprehensive heating unsteady-state temperature field curve, and self-resistance heating is conducted on the workpiece to be heated. The method is used for reducing the center-surface temperature difference in the workpiece heat treatment process.

Description

Technical Field

[0001] The invention relates to a current heating supplement method for regulating the temperature difference between the center and surface of a workpiece based on PID control, and belongs to the technical field of workpiece heat treatment. Background Art

[0002] During heat treatment, large workpieces, due to their large size and weight, are prone to experiencing significant temperature differences between the workpiece surface and core. This temperature difference can lead to significant thermal stresses within the workpiece, compromising its structural stability and even causing cracks or fissures. Furthermore, uneven temperature distribution can affect the workpiece's structural uniformity, further impacting its mechanical properties.

[0003] Therefore, how to optimize the temperature distribution during the heating process and reduce the temperature difference between the center and the surface becomes a key factor in improving the quality of the workpiece. Summary of the Invention

[0004] Aiming at the problem of excessive temperature difference between the surface and the core of large workpieces during heat treatment, the present invention provides a current heating compensation method for adjusting the temperature difference between the core and the surface of the workpiece based on PID control.

[0005] The present invention provides a method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control, comprising:

[0006] Based on the one-dimensional unsteady-state heat conduction equation, a numerical simulation method is used to obtain a heat treatment furnace heating temperature field curve of a workpiece to be heated from an initial temperature to the set temperature in a heat treatment furnace at a set temperature. A self-resistance heating temperature field curve of the workpiece to be heated under a set current is also obtained. Based on the characteristics of the heat treatment furnace heating temperature field curve and the self-resistance heating temperature field curve, the workpiece to be heated is heated simultaneously under a set linear heating rate in the heat treatment furnace and under a set current for self-resistance heating to obtain a comprehensive heating unsteady-state temperature field curve for the workpiece to be heated.

[0007] While the workpiece to be heated is heated in a heat treatment furnace under a set linear heating rate condition, PID control is used to adjust the current size based on the comprehensive heating non-steady-state temperature field curve, and self-resistance heating is performed on the workpiece to be heated, so that the actual comprehensive heating temperature field curve of the workpiece to be heated tends to be stable, thereby achieving uniform heating of the workpiece to be heated.

[0008] According to the workpiece core-surface temperature difference regulating current heating method based on PID control of the present invention, the PID control adjusts the heating current based on the temperature error between the surface temperature and the core temperature of the workpiece to be heated at the current moment, so that the core temperature tends to the surface temperature, thereby making the actual comprehensive heating temperature field curve of the workpiece to be heated tend to be stable.

[0009] According to the current heating compensation method for adjusting the temperature difference between the center and the surface of the workpiece based on PID control of the present invention, the temperature error is expressed as error:

[0010] error=T(1)-T(2),

[0011] Where T(1) is the surface temperature of the workpiece to be heated, and T(2) is the core temperature of the workpiece to be heated.

[0012] According to the current heating compensation method for adjusting the temperature difference between the center and the surface of the workpiece based on PID control of the present invention, the output current I of the PID control is:

[0013] I=Kp·error+Ki·∫errordt+Kd(error) / dt,

[0014] Where Kp is the proportional gain, Ki is the integral gain, Kd is the differential gain, and t is the time.

[0015] According to the current heat compensation method for adjusting the temperature difference between the center and the surface of the workpiece based on PID control of the present invention, the one-dimensional unsteady-state heat conduction equation is:

[0016]

[0017] Where T(x, t) is the temperature field function related to position x and time t; x is the longitudinal position coordinate of the workpiece to be heated, α is the thermal diffusivity, and Q is the Joule heat generated by current self-resistance heating.

[0018] According to the current heating compensation method for adjusting the temperature difference between the center and the surface of the workpiece based on PID control of the present invention, the calculation method of the Joule heat Q generated by the current self-resistance heating is:

[0019]

[0020] Where R is the resistance of the workpiece to be heated, ρ0 is the resistivity of the workpiece material, L is the length of the workpiece to be heated, and B is the cross-sectional area of the workpiece to be heated.

[0021] According to the current heat compensation method for regulating the temperature difference between the center and the surface of the workpiece based on PID control of the present invention, the one-dimensional unsteady-state heat conduction equation is solved by using the heat transfer difference equation:

[0022]

[0023] In the formula is the temperature field at position x at time t, Q x is the Joule heat generated by the current self-resistance heating at position x;

[0024] The difference equation of the boundary condition of the one-dimensional unsteady heat conduction equation is:

[0025]

[0026] Where Bi is the Bivouac number, is the ambient temperature at time t.

[0027] According to the current heating method for adjusting the temperature difference between the center and the surface of the workpiece based on PID control of the present invention, the method for performing self-resistance heating on the workpiece to be heated is:

[0028] Current heating electrodes are respectively arranged on both end surfaces of the workpiece to be heated, and the two current heating electrodes are connected to a DC power supply to perform self-resistance heating on the workpiece to be heated.

[0029] According to the current heating compensation method for regulating the temperature difference between the center and the surface of a workpiece based on PID control of the present invention, the current heating compensation electrode is a surface contact electrode composed of a plurality of electrode branches connected in parallel.

[0030] According to the PID control-based current heating compensation method for adjusting the temperature difference between the center and the surface of the workpiece, the temperature inside the heat treatment furnace is synchronously adjusted with the heating current to make the temperature error of the workpiece to be heated uniform.

[0031] The present invention has the following beneficial effects: During the heat treatment of large workpieces, the present method combines self-resistance heating with electric current to reduce the temperature difference between the workpiece center and surface. By incorporating PID control to further fine-tune the temperature distribution, the temperature difference between the workpiece center and surface is made more uniform, significantly reducing thermal stress and preventing quality problems such as cracks and deformation caused by excessive temperature differences.

[0032] The results of computer simulation experiments show that the method of the present invention can reduce the temperature difference between the center and the surface of the workpiece to no more than 5°C when the workpiece is heated. By improving the uniformity of temperature distribution, the uniformity of material structure is optimized. It has broad application prospects and is particularly suitable for heat treatment of large workpieces with large size and weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the heating temperature field curve of a heat treatment furnace according to the method of adjusting the current for heating by the temperature difference between the center and the surface of the workpiece based on PID control of the present invention;

[0034] Figure 2 This is a schematic diagram of the temperature field curve of the self-resistance heating method of the workpiece center-surface temperature difference adjustment current heating method based on PID control of the present invention;

[0035] Figure 3 It is a schematic diagram of the comprehensive heating unsteady temperature field curve;

[0036] Figure 4 It is a schematic diagram of the actual comprehensive heating temperature field curve obtained after PID control of the current. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0039] The present invention will be further described below with reference to the accompanying drawings, but is not intended to limit the present invention.

[0040] Combine Figures 1 to 4 As shown, the present invention provides a method for adjusting current heating of a workpiece core-surface temperature difference based on PID control, comprising:

[0041] Based on the one-dimensional unsteady-state heat conduction equation, a numerical simulation method is used to obtain a heat treatment furnace heating temperature field curve of a workpiece to be heated from an initial temperature to the set temperature in a heat treatment furnace at a set temperature. A self-resistance heating temperature field curve of the workpiece to be heated under a set current is also obtained. Based on the characteristics of the heat treatment furnace heating temperature field curve and the self-resistance heating temperature field curve, the workpiece to be heated is heated simultaneously under a set linear heating rate in the heat treatment furnace and under a set current for self-resistance heating to obtain a comprehensive heating unsteady-state temperature field curve for the workpiece to be heated.

[0042] While the workpiece to be heated is heated in a heat treatment furnace under a set linear heating rate condition, PID control is used to adjust the current size based on the comprehensive heating non-steady-state temperature field curve, and self-resistance heating is performed on the workpiece to be heated, so that the actual comprehensive heating temperature field curve of the workpiece to be heated tends to be stable, thereby achieving uniform heating of the workpiece to be heated.

[0043] The temperature difference between the core and the surface of the workpiece can be reduced by current heating. However, in actual applications, due to differences in the size, shape, thermal properties and other characteristics of different workpieces, the temperature difference adjustment process still has certain instabilities. Without precise control of the current intensity and duration, the temperature difference between the surface and the core of the workpiece may still vary greatly, leading to thermal stress problems. This embodiment uses PID control to precisely adjust the current for core heating, and monitors and adjusts the core-surface temperature difference in real time, which can ensure uniform heating and heat treatment quality of the workpiece, and further optimize temperature uniformity and workpiece quality.

[0044] The heat treatment furnace is equipped with a surface temperature control system to monitor the temperature distribution on the workpiece surface in real time and adjust the heating parameters according to the temperature distribution.

[0045] The surface temperature control system includes a surface temperature sensor and a surface heating regulator. The surface temperature sensor, located on the workpiece surface, monitors the surface temperature distribution in real time and transmits this data to the control system. Based on the uniformity of the surface temperature distribution, the control system adjusts the heat treatment furnace's heating parameters, such as heating power and heating time, to optimize the workpiece surface temperature distribution.

[0046] In this embodiment, the PID control adjusts the heating current based on the temperature error between the current surface and core temperatures of the workpiece being heated, aligning the core temperature with the surface temperature, thereby stabilizing the actual integrated heating temperature field curve of the workpiece being heated. PID control adjusts the injection signal based on real-time feedback of the temperature difference signal, ensuring uniform temperature distribution across the workpiece.

[0047] The PID control system can monitor and feedback the temperature difference between the surface and the core of the workpiece in real time through sensors, automatically adjust the current size, and minimize the temperature difference between the core and the surface of the workpiece as much as possible.

[0048] A PID control system includes a temperature acquisition module, a PID controller, and an actuator. The temperature acquisition module uses a temperature sensor to collect real-time temperature signals from the workpiece core and transmits them to the PID controller. Based on the preset target temperature and the actual temperature, the PID controller uses a PID algorithm to calculate a current regulation signal. This signal is then sent to the actuator of the current heating device, which adjusts the current and thus controls the temperature of the workpiece core.

[0049] Denote the temperature error as error:

[0050] error=T(1)-T(2),

[0051] Where T(1) is the surface temperature of the workpiece to be heated, and T(2) is the core temperature of the workpiece to be heated.

[0052] The output current I of PID control is:

[0053] I=Kp·error+Ki·∫errordt+Kd(error) / dt,

[0054] Where Kp is the proportional gain, Ki is the integral gain, and Kd is the differential gain, which respectively affect the controller's response to the error; t is time.

[0055] Furthermore, the one-dimensional unsteady-state heat conduction equation is:

[0056]

[0057] Where T(x, t) is the temperature field function related to position x and time t; x is the longitudinal position coordinate of the workpiece to be heated, α is the thermal diffusivity, and Q is the Joule heat generated by current self-resistance heating.

[0058] The calculation method for the Joule heat Q generated by current self-resistance heating is:

[0059]

[0060] Where R is the resistance of the workpiece to be heated, ρ0 is the resistivity of the workpiece material, L is the length of the workpiece to be heated, and B is the cross-sectional area of the workpiece to be heated.

[0061] The one-dimensional unsteady heat conduction equation is solved using the heat transfer difference equation:

[0062]

[0063] In the formula is the temperature field at position x at time t, Q x is the Joule heat generated by the current self-resistance heating at position x;

[0064] The difference equation of the boundary condition of the one-dimensional unsteady heat conduction equation is:

[0065]

[0066] Where Bi is the Bivouac number, is the ambient temperature at time t.

[0067] Furthermore, the method of self-resistance heating of the workpiece to be heated is:

[0068] Current heating electrodes are respectively arranged on both end surfaces of the workpiece to be heated, and the two current heating electrodes are connected to a DC power supply to perform self-resistance heating on the workpiece to be heated.

[0069] The current heating electrode is used to contact the workpiece and conduct current; the DC power supply is used to provide a stable DC current. The heat treatment furnace is used to provide an external high-temperature heat source, providing a basic heating environment for the workpiece. The DC power supply applies DC current to the workpiece, causing the workpiece to replenish heat in the core through self-resistance heating.

[0070] As an example, the current heating electrode is a surface contact electrode composed of a plurality of electrode branches connected in parallel.

[0071] The temperature inside the heat treatment furnace is adjusted synchronously with the heating current to ensure that the workpiece is heated along with the furnace and the temperature error of the workpiece to be heated is uniform.

[0072] In actual use, the PID control system adjusts the magnitude and duration of the current according to the size, shape, thermal properties and other parameters of the workpiece to achieve the best core-surface temperature difference control effect.

[0073] The specific process of the method of the present invention comprises the following steps:

[0074] (1) Place the workpiece in a heat treatment furnace and apply direct current to start the current heating device.

[0075] (2) Start the PID control system to monitor the temperature of the workpiece core in real time, and use the temperature difference between the core and the surface of the workpiece as a signal to adjust the current through the PID controller so that the temperature of the workpiece core reaches the preset target value.

[0076] (3) At the same time, the surface temperature control system is started to monitor the temperature distribution on the workpiece surface in real time, and the heating parameters of the heat treatment furnace are adjusted according to the uniformity of the temperature distribution.

[0077] (4) Through the coordinated work of the PID control system and the surface temperature control system, the temperature of the core and surface of the workpiece is evenly distributed, achieving the effect of zero temperature difference between the core and the surface. Specific embodiment:

[0079] This embodiment incorporates PID control on the basis of the current heating device. By adjusting the magnitude of the DC current applied during the heat treatment process, it further achieves uniform distribution of the workpiece temperature, thereby further improving the quality and uniformity of the workpiece, and has broad industrial application prospects. The specific implementation steps are as follows:

[0080] 1) Electrode installation: Install the current heating electrode to the designated position of the workpiece to ensure good contact between the electrode and the workpiece and no current leakage occurs.

[0081] 2) Set up a PID control system: Connect the PID control system to a temperature sensor to monitor the temperature difference between the workpiece surface and the core in real time. Based on this real-time temperature difference data, the PID control system automatically adjusts the current density to ensure that the core-surface temperature difference is within the target range.

[0082] 3) Apply DC power and start PID control: Connect the DC power supply to the electrodes and set the initial current density. The PID control system adjusts the current intensity in real time based on the real-time feedback of the temperature difference signal to maintain the stability of the temperature difference. The DC power supply should have good stability to ensure the continuity and accuracy of the current.

[0083] 4) Start heating the heat treatment furnace: Place the workpiece in the heat treatment furnace with both the ambient and workpiece temperatures at 100°C. Set the furnace to heat up linearly, up to 1200°C, ensuring that the workpiece heats up in sync with the furnace temperature. During this stage, the PID control system coordinates with the furnace's heating process, adjusting the current density to gradually reduce the temperature difference between the workpiece surface and core.

[0084] 5) Current Heating and Real-Time PID Control: The DC power supply is activated, and current begins to flow to the workpiece. This current is conducted through the electrodes to the workpiece, generating Joule heat and gradually heating it. The PID control system adjusts the current in real time based on the temperature difference between the workpiece surface and core, ensuring the temperature difference remains within a preset range.

[0085] 6) End of Current Heating: When the workpiece reaches the desired temperature of 1200°C, the PID control system stops regulating the current, shuts off the DC power supply, and disconnects the electrode from the workpiece. At this point, the current heating process ends, and the workpiece's core-surface temperature difference is precisely controlled within the desired range.

[0086] Simulation experiment:

[0087] Based on the one-dimensional unsteady heat conduction equation, the thermophysical parameters of a high-alloy steel were used to perform numerical simulation calculations using MATLAB software. The one-dimensional unsteady heat conduction equation was solved using the heat transfer difference equation and the boundary condition difference equation.

[0088] To control the current I, a PID controller is used to calculate the current error and adjust the current I to make the temperature tend to the target value.

[0089] Figure 1 The figure shows the distribution of the temperature field of the workpiece when it is heated only in the heat treatment furnace. The parameters used are shown in Table 1:

[0090] Table 1

[0091] Parameter name Numerical Workpiece length L / (m) 0.1 <![CDATA[Initial temperature T0 / (°C)]]> 100 <![CDATA[Ambient temperature T ∞ / (°C)]]> 1200 Thermal conductivity k / (W / m·K) 2.5 <![CDATA[Material density ρ / (kg / m 3 )]]> 7900 <![CDATA[Specific heat capacity c p / (J / kg·K)]]> 460 <![CDATA[Convective heat transfer coefficient h / (W / m 2 ·K)]]> 200 <![CDATA[Resistivity ρ0 / (Ω·m)]]> 1e-6

[0092] Figure 2 The temperature field distribution of the workpiece is shown in the case of current heating only. The parameters used are shown in Table 2:

[0093] Table 2

[0094]

[0095]

[0096] Figure 3 The temperature field distribution of the workpiece formed by the current heating method without PID control is simulated. The parameters used are shown in Table 3:

[0097] Table 1

[0098] Parameter name Numerical Workpiece length L / (m) 0.1 <![CDATA[Initial temperature T0 / (°C)]]> 100 <![CDATA[Ambient temperature T ∞ / (°C)]]> 100 Thermal conductivity k / (W / m·K) 2.5 <![CDATA[Material density ρ / (kg / m 3 )]]> 7900 <![CDATA[Specific heat capacity c p / (J / kg·K)]]> 460 <![CDATA[Convective heat transfer coefficient h / (W / m 2 ·K)]]> 200 <![CDATA[Resistivity ρ0 / (Ω·m)]]> 1e-6 Current I / (A) 32

[0099] Figure 3 The ambient temperature in the experiment is set to rise linearly up to 1200°C, simulating the temperature rise of the workpiece along with the furnace.

[0100] Figure 4 The temperature field distribution of the workpiece formed by the current heating method combined with PID control is shown in Table 4.

[0101] Table 4

[0102]

[0103]

[0104] Combine Figures 1 to 4 It can be seen that after using the method proposed by the present invention, the temperature field distribution is as follows Figure 4 As shown, the core-surface temperature difference is controlled within 5°C as a whole.

[0105] The advantages of the method of the present invention are:

[0106] 1) Precise Temperature Differential Control: The PID control system monitors the temperature difference between the workpiece surface and interior in real time and adjusts the current based on real-time feedback, thereby precisely controlling the temperature difference between the workpiece surface and core, further reducing temperature fluctuations and avoiding cracks or deformation caused by excessive temperature differences. This system can more accurately maintain the ideal temperature distribution on the workpiece, improving heat treatment quality.

[0107] 2) Energy-saving and efficient: The PID control system's real-time adjustment function precisely controls the current output, eliminating the energy waste associated with traditional heating methods. By precisely controlling the heat input, the PID control system dynamically adjusts the current based on the actual needs of the workpiece, significantly reducing energy consumption and improving energy efficiency.

[0108] 3) Automation and Intelligence: By introducing a PID control system, the method can achieve automated regulation without manual intervention. The system can adaptively adjust the current based on real-time temperature data, thereby reducing the complexity and error probability of manual operation and achieving higher process accuracy and consistency.

[0109] The above content elaborates on the application of the present invention in numerical simulation and its calculation results. However, it should be emphasized that the content is only the theoretical calculation and simulation analysis of the present invention, which is intended to demonstrate the implementation of the principle of the present invention. The simulation cases in this section are only exemplary and cannot be used as a limitation on the scope of implementation of the present invention. In practical applications, any equivalent changes, improvements or adjustments based on the core ideas and technical features of the present invention or according to actual needs should be regarded as the scope of patent protection of the present invention. Therefore, all corresponding changes, adjustments or optimizations based on the basic principles and technical solutions of the present invention, regardless of whether they involve specific parameters, material selection, configuration methods or other aspects, should be included in the scope of protection of the patent of the present invention.

Claims

1. A method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control, characterized in that include: Based on the one-dimensional unsteady-state heat conduction equation, a numerical simulation method is used to obtain a heat treatment furnace heating temperature field curve of a workpiece to be heated from an initial temperature to the set temperature in a heat treatment furnace at a set temperature. A self-resistance heating temperature field curve of the workpiece to be heated under a set current is also obtained. Based on the characteristics of the heat treatment furnace heating temperature field curve and the self-resistance heating temperature field curve, the workpiece to be heated is heated simultaneously under a set linear heating rate in the heat treatment furnace and under a set current for self-resistance heating to obtain a comprehensive heating unsteady-state temperature field curve for the workpiece to be heated. While the workpiece to be heated is heated in a heat treatment furnace under a set linear heating rate condition, PID control is used to adjust the current size based on the comprehensive heating non-steady-state temperature field curve, and self-resistance heating is performed on the workpiece to be heated, so that the actual comprehensive heating temperature field curve of the workpiece to be heated tends to be stable, thereby achieving uniform heating of the workpiece to be heated.

2. The method for adjusting current heat compensation based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 1 is characterized in that: The PID control adjusts the heating current based on the temperature error between the surface temperature and the core temperature of the workpiece to be heated at the current moment, so that the core temperature tends to the surface temperature, thereby making the actual comprehensive heating temperature field curve of the workpiece to be heated tend to be stable.

3. The method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 2 is characterized in that: Denote the temperature error as error: error=T(1)-T(2), Where T(1) is the surface temperature of the workpiece to be heated, and T(2) is the core temperature of the workpiece to be heated.

4. The method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 3 is characterized in that: The output current I of PID control is: I=Kp·error+Ki·∫errordt+Kd(error) / dt, Where Kp is the proportional gain, Ki is the integral gain, Kd is the differential gain, and t is the time.

5. The method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 4 is characterized in that: The one-dimensional unsteady heat conduction equation is: Where T(x, t) is the temperature field function related to position x and time t; x is the longitudinal position coordinate of the workpiece to be heated, α is the thermal diffusivity, and Q is the Joule heat generated by current self-resistance heating.

6. The method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 5 is characterized in that: The calculation method for the Joule heat Q generated by current self-resistance heating is: Where R is the resistance of the workpiece to be heated, ρ0 is the resistivity of the workpiece material, L is the length of the workpiece to be heated, and B is the cross-sectional area of the workpiece to be heated.

7. The method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 6 is characterized in that: The one-dimensional unsteady heat conduction equation is solved using the heat transfer difference equation: In the formula is the temperature field at position x at time t, Q x is the Joule heat generated by the current self-resistance heating at position x; The difference equation of the boundary condition of the one-dimensional unsteady heat conduction equation is: Where Bi is the Bivouac number, is the ambient temperature at time t.

8. The method for adjusting current heating based on the workpiece core-surface temperature difference based on PID control according to claim 1 is characterized in that: The method of self-resistance heating of the workpiece to be heated is: Current heating electrodes are respectively arranged on both end surfaces of the workpiece to be heated, and the two current heating electrodes are connected to a DC power supply to perform self-resistance heating on the workpiece to be heated.

9. The method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 8, characterized in that: The current heating electrode is a surface contact electrode composed of a plurality of electrode branches connected in parallel.

10. The method for adjusting current heating based on the temperature difference between the center and the surface of a workpiece by PID control according to claim 1, characterized in that: The temperature inside the heat treatment furnace is adjusted synchronously with the heating current to make the temperature error of the workpiece to be heated uniform.

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