Head-surface zero-temperature-difference heating method for workpiece

Abstract

The invention discloses a workpiece core-surface zero-temperature-difference heating method, and belongs to the technical field of large 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 with a 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; heating a workpiece to be heated under the condition of a set linear heating rate of a heat treatment furnace and under the condition of a set current of self-resistance heating to obtain a comprehensive heating unsteady-state temperature field curve; and based on the comprehensive heating unsteady state temperature field curve, current is adjusted, self-resistance heating is conducted on the to-be-heated workpiece, the actual comprehensive heating temperature field curve of the to-be-heated workpiece tends to be stable, and uniform heating of the to-be-heated workpiece is achieved. The method is used for heat treatment of large castings and forgings.

Description

Technical Field

[0001] The invention relates to a method for heating a workpiece with a zero temperature difference between the center and the surface, and belongs to the technical field of heat treatment of large workpieces. 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 a large workpiece during heat treatment, the present invention provides a method for heating the workpiece with zero temperature difference between the core and the surface.

[0005] A method for heating a workpiece with zero temperature difference between the center and the surface of the workpiece according to the present invention comprises:

[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, the current is adjusted based on the comprehensive heating non-steady-state temperature field curve, and the workpiece to be heated is self-resistance 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 center-surface zero temperature difference heating method of the present invention, the one-dimensional unsteady-state heat conduction equation is:

[0009]

[0010] 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, t is time, α is the thermal diffusivity, and Q is the Joule heat generated by current self-resistance heating.

[0011] According to the zero temperature difference heating method for the workpiece center and surface of the present invention, the calculation method of the Joule heat Q generated by the current self-resistance heating is:

[0012]

[0013] Where I is the current, 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.

[0014] According to the workpiece center-surface zero temperature difference heating method of the present invention, the one-dimensional unsteady-state heat conduction equation is solved by using the heat transfer difference equation:

[0015]

[0016] 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;

[0017] The difference equation of the boundary condition of the one-dimensional unsteady heat conduction equation is:

[0018]

[0019] Where Bi is the Bivouac number, is the ambient temperature at time t.

[0020] According to the workpiece center-surface zero temperature difference heating method of the present invention, the method of performing self-resistance heating on the workpiece to be heated is:

[0021] 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.

[0022] According to the method for heating the workpiece center-surface with zero temperature difference of the present invention, the current heating electrode is a surface contact electrode composed of a plurality of electrode branches connected in parallel.

[0023] According to the workpiece center-surface zero temperature difference heating method of the present invention, the workpiece to be heated includes a shaft.

[0024] According to the workpiece center-surface zero temperature difference heating method of the present invention, when the workpiece to be heated is actually heated, the initial temperature of the heat treatment furnace is equal to the initial temperature of the workpiece to be heated.

[0025] According to the method for heating a workpiece with zero temperature difference between the center and the surface of the workpiece of the present invention, when the workpiece to be heated is actually heated, the current regulating device is used to adjust the current magnitude.

[0026] The present invention has the following beneficial effects: The method of the present invention is used to perform dual heating of large workpieces using a combination of electric current heating and a heat treatment furnace. During the heat treatment of large castings and forgings, a uniform temperature distribution is achieved by applying direct current to the workpiece for supplemental heating, thereby achieving a near-zero temperature gradient. The method of the present invention utilizes a heat treatment furnace in conjunction with self-resistance heating to directly supplement heat in the core of the workpiece via electric current, thereby reducing the temperature difference between the workpiece core and surface, optimizing temperature distribution, achieving a near-zero temperature gradient, and reducing the generation of thermal stress.

[0027] Computer simulation experiments have verified that the temperature difference between the center and surface of a heated workpiece can be reduced to within 30°C. This method improves the uniformity of temperature distribution, thereby optimizing microstructure uniformity and enhancing workpiece quality. It has broad application prospects and is particularly suitable for heat treatment of large and heavy castings and forgings.

[0028] The method of the present invention can optimize the temperature distribution of the workpiece and significantly improve the structural uniformity of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the temperature field curve of the heat treatment furnace according to the method of heating the workpiece with zero temperature difference between the center and the surface of the workpiece according to the present invention;

[0030] Figure 2 Schematic diagram of the temperature field curve of the self-resistance heating method of the workpiece center-surface zero temperature difference heating according to the present invention;

[0031] Figure 3 It is a schematic diagram of the non-steady-state temperature field curve of comprehensive heating. DETAILED DESCRIPTION

[0032] 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.

[0033] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0034] The present invention will be further described below with reference to the accompanying drawings, but is not intended to limit the present invention.

[0035] Combine Figures 1 to 3 As shown, the present invention provides a method for heating a workpiece with zero temperature difference between the center and the surface, comprising:

[0036] 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.

[0037] While the workpiece to be heated is heated in a heat treatment furnace under a set linear heating rate condition, the current is adjusted based on the comprehensive heating non-steady-state temperature field curve, and the workpiece to be heated is self-resistance 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.

[0038] The heat treatment furnace provides an external high-temperature heat source for large workpieces.

[0039] Furthermore, the one-dimensional unsteady-state heat conduction equation is:

[0040]

[0041] 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, t is time, α is the thermal diffusivity, which can be treated as a constant term, and Q is the Joule heat generated by current self-resistance heating.

[0042] Resistance heating utilizes the Joule heating effect of electric current to convert electrical energy into thermal energy to heat the workpiece. The heated object generates heat due to the Joule heating effect, resulting in high thermal efficiency. Assuming the thermal conductivity of the shaft is constant, the Joule heat Q generated by current self-resistance heating is calculated as follows:

[0043]

[0044] Where I is the current, 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.

[0045] By analyzing the heat transfer efficiency and temperature uniformity based on the numerical simulation results, the heating rate of the heat treatment furnace and the current density of the electrode can be adjusted to ensure that the temperature field distribution of the workpiece is uniform.

[0046] The one-dimensional unsteady heat conduction equation is solved using the heat transfer difference equation:

[0047]

[0048] 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;

[0049] The difference equation of the boundary condition of the one-dimensional unsteady heat conduction equation is:

[0050]

[0051] Where Bi is the Biot number, is the ambient temperature at time t.

[0052] During the workpiece heat treatment process, the thermophysical parameters of the workpiece are first determined, and the heating process is optimized and improved based on these parameters. By controlling the heating rate and temperature distribution during the workpiece heat treatment process, it is ensured that heat is evenly and efficiently transferred to all parts of the workpiece.

[0053] The heating current is adjusted according to the results of numerical simulation, and parameters that can make the temperature field distribution tend to be stable are selected to ensure the uniformity of the temperature field distribution.

[0054] The method of self-resistance heating of the workpiece to be heated is:

[0055] 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.

[0056] As an example, the workpiece to be heated is a shaft-like part, and the corresponding current heating electrode is a surface contact electrode composed of multiple electrode branches connected in parallel.

[0057] The current heating electrode contacts the workpiece through a conductive contact surface and conducts current. A DC power supply is used to provide a stable DC current. During use, the current heating electrode is installed at a designated location on the workpiece to ensure good contact and no leakage. The power supply is connected to the electrode, and its initial voltage and current are set. The power supply should have good stability to ensure stable current output. An appropriate current intensity is selected based on the size and requirements of the workpiece. This selection can be determined using numerical simulation methods. During the heat treatment furnace heating process, the heat treatment furnace is heated according to the workpiece heating process, allowing the workpiece to heat up with the furnace. During current heating: The electrode power supply is activated to energize the electrode. Current is conducted through the electrode to the workpiece, directly heating it. The current intensity and application time can be adjusted as needed. A higher current can be set initially to rapidly heat the workpiece surface. As the desired temperature is approached, the current should be gradually reduced to avoid overheating. When the workpiece reaches the desired temperature, the current heating process ends. At this point, the electrode power supply is turned off, and the electrode is disconnected from the workpiece.

[0058] For example, the workpiece to be heated includes a shaft with a diameter of one meter; the self-resistance heating allows the current density of the shaft to range from 200A / ㎡ to 350A / ㎡, specifically adjusted for the type, size, and shape of large castings and forgings.

[0059] In this embodiment, the initial temperature in the heat treatment furnace is equal to the initial temperature of the workpiece to be heated, and the temperature is increased synchronously with the workpiece.

[0060] When the workpiece to be heated is actually heated, a current regulating device is used to adjust the current magnitude and duration.

[0061] This embodiment uses the current heating electrode to supplement the heat to the core of the casting, thereby reducing the temperature difference between the core and the surface of the casting and reducing the internal stress.

[0062] The method of the present invention solves the problems of uneven heat treatment structure and large thermal stress caused by the large temperature difference between the surface and the core of large castings and forgings. By applying electric current to the workpiece to supplement heat, the temperature distribution of the workpiece during the heat treatment process is optimized, which can prevent the occurrence of deformation, cracking and other phenomena of the workpiece caused by the large temperature difference.

[0063] Examples:

[0064] 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.

[0065] 2) Power connection: Connect the power supply to the electrodes and set the current intensity to 50 A. The power supply should have good stability to ensure that the current output does not fluctuate.

[0066] 3) Start heating the heat treatment furnace: Place the workpiece in the heat treatment furnace, the ambient temperature in the furnace and the workpiece temperature are both 100°C, set the heat treatment furnace to heat up linearly, up to 1200°C, and make the workpiece heat up synchronously with the furnace.

[0067] 4) Current heating: Start the power supply and start energizing the electrodes. The current is conducted through the electrodes to the workpiece, generating Joule heat and gradually heating the workpiece.

[0068] 5) End of current heating: When the workpiece reaches the predetermined temperature of 1200°C, the current heating process ends. At this time, the DC power supply is turned off and the connection between the electrode and the workpiece is disconnected.

[0069] Simulation experiment:

[0070] Numerical simulation is performed using the thermophysical parameters of a high alloy steel.

[0071] The calculation is performed based on the heat transfer differential equation and the boundary condition differential equation. Figure 1The workpiece shown is heated only in a heat treatment furnace, and its temperature field distribution is shown in Table 1:

[0072] Table 1

[0073]

[0074]

[0075] 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:

[0076] Table 2

[0077] 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) 50

[0078] Figure 3 The temperature field distribution of the workpiece formed by the current heating method provided in this embodiment is simulated, and the parameters used are shown in Table 3:

[0079] Table 3

[0080]

[0081]

[0082] 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.

[0083] Depend on Figure 1 It can be seen that using only a heat treatment furnace for heating will result in a large temperature difference between the core and the surface, with the core temperature being low and the surface temperature being high, which is not conducive to the structural adjustment of the workpiece during the heat treatment process, and will generate thermal stress that causes the workpiece to crack. Figure 2 Medium current heating makes the core temperature of the workpiece high and the surface temperature low. After using the method proposed by the present invention, the temperature distribution is as follows Figure 3 As shown, the temperature difference between the core and the surface is controlled within 30℃.

[0084] The advantages of the present invention are:

[0085] 1) Minimize temperature difference: Current heating can effectively improve the temperature distribution on the surface and inside of the workpiece, reduce the temperature difference between the surface and the core of the workpiece, and avoid cracks or deformation caused by thermal stress.

[0086] 2) Reduce energy consumption: Compared with traditional heating methods, electric current heating has higher thermal efficiency and can effectively reduce energy waste.

[0087] 3) Improve production efficiency: Current heating can heat the workpiece in a shorter time, shorten the heat treatment time and improve production efficiency.

[0088] The above content elaborates on the application and calculation results of the present invention in numerical simulation. However, it should be noted 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 part cannot be used as a limitation on the scope of implementation of the present invention. The scope of implementation of the present invention is not limited to the specific numerical values ​​or configurations of the above calculation and simulation results. In practical applications, any equal changes, improvements or adjustments based on actual needs to the present invention should be deemed to be within the scope of patent protection of the present invention. Therefore, any corresponding changes, adjustments or optimizations based on the core ideas and technical features of the present invention, whether in specific parameters, material selection, configuration mode or other aspects, should be deemed to fall within the scope of coverage of the patent of the present invention.

Claims

1. A method for heating a workpiece with zero temperature difference between the center and the surface, 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, the current is adjusted based on the comprehensive heating non-steady-state temperature field curve, and the workpiece to be heated is self-resistance 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 heating a workpiece with zero temperature difference between the center and the surface according to claim 1, 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, t is time, α is the thermal diffusivity, and Q is the Joule heat generated by current self-resistance heating.

3. The method for heating a workpiece with zero temperature difference between the center and the surface according to claim 2, characterized in that: The calculation method for the Joule heat Q generated by current self-resistance heating is: Where I is the current, 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.

4. The method for heating a workpiece with zero temperature difference between the center and the surface according to claim 3, 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 Biot number, is the ambient temperature at time t.

5. The method for heating a workpiece with zero temperature difference between the center and the surface according to claim 1, 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.

6. The method for heating a workpiece with zero temperature difference between the center and the surface according to claim 5, characterized in that: The current heating electrode is a surface contact electrode composed of a plurality of electrode branches connected in parallel.

7. The method for heating a workpiece with zero temperature difference between the center and the surface according to claim 1, characterized in that: The workpiece to be heated includes a shaft.

8. The method for heating a workpiece with zero temperature difference between the center and the surface according to claim 1, characterized in that: When the workpiece to be heated is actually heated, the initial temperature of the heat treatment furnace is equal to the initial temperature of the workpiece to be heated.

9. The method for heating a workpiece with zero temperature difference between the center and the surface according to claim 1, characterized in that: When the workpiece to be heated is actually heated, the current is adjusted by a current regulating device.

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