A resistance heating control device and method for a thermal tightening bolt

Abstract

The present invention belongs to the field of machinery, and particularly relates to a resistance heating control device and method for thermal tightening bolts. At present, domestic power plants mainly use resistance heaters to heat bolts. Due to problems such as unclear control standards and long heating times during the heating and fastening and disassembly processes, it leads to screw thread deformation, steam leakage at the split surface, and even bolt failure, thus delaying the maintenance period. This device includes a DC electrical cabinet, a resistance heating rod, a temperature monitoring and feedback device, an elongation measurement device, an intelligent control center, and a bolt fastening device; the DC electrical cabinet is connected to the resistance heating rod through a cable, and the resistance heating rod is inserted into the thermal tightening bolt. The present invention can effectively shorten the heating time and reduce the bolt failure rate.

Description

Technical Field

[0001] The present invention belongs to the field of machinery, and particularly relates to a resistance heating control device and method for thermal tightening bolts. Background Art

[0002] In power plants, steam turbine cylinders are generally fastened using large high-strength bolts with through holes drilled in the center for easy heating with heating rods. Currently, domestic power plants mainly use resistance heaters to heat the bolts. However, due to unclear control standards and long heating times during the heating and fastening and removal processes, problems such as screw thread deformation, steam leakage at the split surface, and even bolt failure may occur, delaying the maintenance schedule.

[0003] To avoid problems during the resistance heating of thermal tightening bolts, it is necessary to determine the maximum temperature, maximum temperature difference, and maximum temperature rise rate during the heating process for bolts of different materials, specifications, and models, ensuring that the maximum allowable temperature and maximum stress of the bolts are not exceeded, which can effectively shorten the heating time and reduce the bolt failure rate. Summary of the Invention

[0004] 1. Objective:

[0005] Invent a resistance heating intelligent control device for thermal tightening bolts of steam turbines. Using this device to heat the thermal tightening bolts of the cylinder can effectively shorten the heating time, improve the disassembly and assembly efficiency, and reduce the bolt failure rate.

[0006] 2. Technical Solution:

[0007] A resistance heating control device for thermal tightening bolts includes a DC electrical cabinet, a resistance heating rod, a temperature monitoring and feedback device, an elongation measurement device, an intelligent control center, and a bolt fastening device; the DC electrical cabinet is connected to the resistance heating rod through a cable, and the resistance heating rod is inserted into the thermal tightening bolt.

[0008] The bolt fastening device includes a nut, a thermal tightening bolt, a convex washer, and a concave washer; the nut is fixedly connected to the upper surface of the steam turbine cylinder flange, and an adsorption type temperature measurement probe is arranged on the surface of the nut; the concave washer and the convex washer are closely fitted to form a set of washers.

[0009] The steam turbine cylinder flange includes a lower flange and an upper flange; the middle position of the upper surface of the upper flange is recessed, and the washer is located in the recess.

[0010] The nut and the thermal tightening bolt are threadedly connected; washers are spaced between the nut and the upper flange.

[0011] The elongation measurement device is connected to the intelligent control center.

[0012] The adsorption type temperature measurement probe is connected to a thermometer, and the thermometer is also connected to the intelligent control center.

[0013] A method for controlling the resistance heating of a thermal tightening bolt, comprising Step 1: collecting the parameters of the thermal tightening bolt and setting the electric power input curve; Step 2: assembling the device and establishing conditions; Step 3: monitoring the change in heating temperature; Step 4: monitoring the elongation for disassembly and assembly. The Step 3: monitoring the change in heating temperature specifically includes: inserting a resistance heating rod into the central hole of the thermal tightening bolt, and setting the effective heating section at the plain rod of the thermal tightening bolt; using an adsorption type temperature measurement probe to track and record the temperature of the thermal tightening bolt, and starting the heating operation after the detection device is normal; during the heating of the bolt, constantly monitoring the change in the nut wall temperature, adjusting the input power according to the change situation, and if it is found that the nut temperature exceeds 100 °C, the heating should be stopped.

[0014] The Step 1: collecting the parameters of the thermal tightening bolt and setting the electric power input curve specifically includes: collecting the specification models and material information of the thermal tightening bolt and nut, determining the maximum allowable heating temperature, yield strength, maximum allowable stress, and maximum allowable temperature change rate of the bolt, and the highest allowable temperature parameter of the internal thread of the nut; customizing the optimal heating tool according to the bolt diameter, effective length, and heating hole diameter structure information, and the control parameters include the heating rod length, diameter, and installation position; after determining the above data, calculating the curve of the electric power input changing with time, and inputting it into the intelligent control center.

[0015] The Step 2: assembling the device and establishing conditions specifically includes: setting up a bolt resistance heating workbench, and determining that the surrounding environment meets the usage requirements of the heater: the surrounding medium temperature is not higher than 50 °C and not lower than -10 °C; the relative air humidity is not greater than 95%; the space does not contain chemical corrosive and explosive gases; there is no vibration and bump, and the installation slope does not exceed 5 degrees; before the DC electrical cabinet is powered on, the shell should be reliably grounded, and the voltage should be adjusted to the "0" position.

[0016] The Step 4: monitoring the elongation for disassembly and assembly specifically includes: before thermal tightening, using a marker pen to record the tightening angle position of the nut 5, lubricating the threaded part and the bearing surface of the nut with an anti-seize compound, and cleaning the bottom of the central hole with compressed air; using a bolt elongation measurement device to measure the change in the bolt elongation in real time and feedback it to the intelligent control center, tightening the nut when the bolt elongation reaches the required elongation, and checking whether the nut reaches the tightening angle. If the required elongation is not reached after heating for 60 minutes, the heating should be stopped; during thermal loosening, when the bolt elongation measurement device shows that the elongation starts to change, disassemble the nut.

[0017] 3. Effects:

[0018] 1) Ensure the safe operation of the resistance heating process of the thermal tightening bolt

[0019] Adopting the DC heating method, with an output voltage of 0 - 130V and a stable waveform, it can reduce the peak voltage borne by the electric heater during the heating process by nearly 10% compared to using AC heating, greatly extending the service life of the electric heater and making the operation safer.

[0020] At the same time, for each type of bolt, technical analysis and simulation calculations were carried out using the system software, and after multiple heating tests in the laboratory, fine-tuning and correction were made to the monitoring and adjustment parameters during implementation, ensuring that the bolt can still maintain an available state after being reheated 100 times.

[0021] 2) Intelligent and automatic adjustment control

[0022] During the heating process of the bolt, numerical values such as the surface of the nut, the inner and outer walls of the bolt, the cylinder flange, the working environment temperature, and the bolt elongation can be monitored in real time and analyzed and regulated intelligently, avoiding operation and monitoring deviations, accelerating the disassembly and assembly speed, and reducing the bolt defect rate. For each type of bolt, the intelligent control center has preset the curve of the relationship between the input electric power and time. The electric power can be automatically adjusted and controlled based on the monitored temperature and elongation data, realizing intelligent and automatic adjustment.

[0023] 3) Effectively shorten the bolt disassembly and assembly time, reduce the bolt failure rate, and improve economic benefits.

[0024] It can effectively shorten the heating time, improve the disassembly and assembly efficiency, and at the same time avoid defects such as bolt jamming, deformation, and material property change, effectively ensuring the fastening requirements of the middle split surface of the steam turbine cylinder body. Description of the drawings

[0025] Figure 1 Schematic diagram of the resistance heating device for the thermal tightening bolt of the steam turbine

[0026] Figure 2 Thermal tightening bolt heating and temperature and elongation measurement

[0027] Figure 3 Flow chart

[0028] In the figure: 1. Power supply, 2. DC electrical cabinet, 3. Intelligent control center, 4. Resistance heating rod, 5. Nut, 6. Elongation measurement device, 7. Adsorption type temperature measurement probe, 8. Steam turbine cylinder flange, 9. Thermometer, 10. Lower flange, 11. Upper flange, 12. Convex washer, 13. Concave washer, 14. Thermal tightening bolt. Detailed implementation manners

[0029] Such as Figure 1 And Figure 2As shown, the intelligent control device for resistance heating of thermal tightening bolts of steam turbines mainly includes a power-adjustable DC electrical cabinet 2, resistance heating rods 4, a temperature monitoring and feedback device, an elongation measurement device 6, and an intelligent control center 3:

[0030] 1) Power-adjustable DC electrical cabinet 2: The device is connected to three-phase alternating current (380V, 50HZ). After passing through the rectifier bridge inside the frequency converter, it becomes direct current. The output voltage is 0 - 130V (continuously adjustable in the main circuit), with a stable waveform. This can make the peak voltage borne by the electric heater during the heating process nearly 10% lower than that when using alternating current for heating, greatly extending the service life of the electric heater. The output voltage is adjustable and the voltage control is precise, effectively increasing the service life of the electric heater and improving work efficiency. The load form of this electrical cabinet is twelve-way output, with a power of 10KW for each way and a total power of 120KW.

[0031] 2) Resistance heating rods 4: Through a finite element analysis model, the resistance heating rods 4 are optimized for bolts of different materials, specifications, and fastening methods to determine the parameters of the resistance heating rods 4 with the best heating effect, including the diameter, length, installation position, etc. of the resistance heating rods 4. Also, the heating conditions of the thermal tightening bolts 14 are analyzed and studied to determine the installation range of the heating rods and their effects on the temperature, stress, and elongation of the thermal tightening bolts 14.

[0032] 3) Temperature monitoring and feedback device: An adsorption type temperature measurement probe is installed on the surface of the nut 5 and connected to a thermometer to continuously monitor the temperature and its changes on the surface of the nut 5. The data measured by the thermometer 9 is promptly uploaded to the intelligent control center 3. The intelligent control center 3 analyzes the maximum temperature, maximum temperature difference, maximum temperature rise rate of the thermal tightening bolts 14 and the thread temperature at the nut 5 based on the heating rod power and the recorded temperature, and adjusts the heating power in real-time.

[0033] 4) Bolt elongation measurement device 6: An elongation measurement device 6 is installed on the nut 5 to measure the bolt elongation and feedback it to the intelligent control center 3.

[0034] 5) Intelligent Control Center 3: Equipped with a professional computer, including intelligent computing and analysis software, which contains the characteristic parameters of the bolts to be heated (including bolt material, morphology, maximum allowable heating temperature, maximum allowable temperature difference, maximum allowable temperature change rate, maximum allowable temperature of the internal thread of the nut, heating power output and process control curve, measured and predicted heating time, etc.). This software can read and calculate the temperature at the selected point of the bolt during the heating process, and will deduce information such as the temperature of the internal thread of the nut 5, the maximum temperature inside the thermal tightening bolt 14, the maximum temperature difference and its change trend, and the preset allowable threshold values. When the difference between the actual monitored temperature distribution and the preset temperature distribution is within 10%, heat according to the preset value until the required elongation of the thermal tightening bolt 14 is reached; when the difference between the actual monitored temperature distribution and the preset temperature distribution is more than 10%, then adjust the output power appropriately to achieve heating according to the expected power curve. When the temperature monitoring parameters exceed the standard (i.e., exceed the maximum allowable heating temperature, maximum allowable temperature difference, maximum allowable temperature change rate, maximum allowable temperature of the internal thread of the nut 5, etc.), the system issues an alarm and stops heating. The heating process is as follows.

[0035] In the Intelligent Control Center 3, there is also a relationship model curve established through theoretical calculation and experimental verification for each type of bolt between temperature change, elongation change and power output change. The Intelligent Control Center can automatically adjust the power output according to the measured temperature and elongation change. After the heating is completed, the power change and temperature change data of this heating are detailedly recorded in seconds, and at the same time, they are stored and applied to the next bolt of the same specification.

[0036] The advancement of the present invention lies in

[0037] 1) The software analysis method of the Intelligent Control Center 3 is based on the finite element analysis model of the bolt thermal-stress coupling field. Taking the maximum heating temperature, maximum temperature difference, maximum temperature rise rate and the temperature of the thread at the nut as limiting conditions for bolts of different materials, specifications, fastening methods and the material of the resistance heating rod 4, the optimal heating power curve is determined through simulation calculation.

[0038] 2) For bolts of different materials, specifications, and fastening methods, parameters such as the diameter of the heating rod, the effective heating length, and the installation position are optimized and analyzed, and the parameters of the resistance heating rod 4 with the best heating effect are determined, which can achieve the optimal heating power output.

[0039] 3) Temperature induction probes are installed on the surface of the nut 5, the inner and outer walls of the stud, and the cylinder flange, and the temperature recorder reads and displays the data. The data measured by the temperature recorder are all input into the Intelligent Control Center 3. The analysis software in the Intelligent Control Center 3 calculates the limiting parameters such as the temperature of the thread at the nut 5, the maximum temperature inside the thermal tightening bolt 14 and the maximum temperature difference value, as well as the change trend, and compares them with the preset threshold values to realize the intelligent adjustment and control of the input power.

[0040] 4) A device for measuring elongation is installed on the upper end face of the nut 5 to measure the change in the elongation of the thermal tightening bolt 14 in real time, and transmit the data to the intelligent control center 3 for comparison with the preset value and the elongation curve to avoid excessive elongation.

[0041] The specific implementation steps are as follows:

[0042] 1. Before implementation, set the electric power input curve according to different thermal tightening bolts

[0043] Before heating, collect information such as the specifications, models, and materials of the thermal tightening bolt 14 and the nut 5 to determine the maximum allowable heating temperature, yield strength, maximum allowable stress, maximum allowable temperature change rate of the bolt 14, and the maximum allowable temperature parameter of the internal thread of the nut 5. At the same time, according to the structural information such as the diameter, effective length, and heating hole diameter of the bolt 14, customize the optimal heating tool (control parameters include the length, diameter, and installation position of the heating rod). After determining the above data, calculate the curve of the electric power input changing with time and input it into the intelligent control center 3.

[0044] 2. Assemble the device and establish conditions before implementation

[0045] As shown in the appendix Figure 1 Build a bolt resistance heating workbench to ensure that the surrounding environment meets the requirements for using the heater: 1. The temperature of the surrounding medium is not higher than 50°C and not lower than -10°C; 2. The relative air humidity is not greater than 95%; 3. The space does not contain chemical corrosive and explosive gases; 4. There is no vibration or bump, and the installation slope does not exceed 5 degrees; 5. Before the control cabinet 2 is powered on, the shell should be reliably grounded and the voltage should be adjusted to the "0" position.

[0046] 3. Monitor the temperature change during the heating process

[0047] As shown in the appendix Figure 2 The bolt fastening device consists of a nut 5, a thermal tightening bolt 14, a convex washer 12, and a concave washer 13, which is used to fasten the upper and lower flanges 8. The resistance heating rod 4 is inserted into the central hole of the thermal tightening bolt 14, and the effective heating section is set at the smooth rod of the thermal tightening bolt to avoid overheating the internal thread of the nut.

[0048] An adsorption type temperature measurement probe 7 is installed at the nut 5 and connected to the thermometer 9 to track and record the temperature of the thermal tightening bolt 14; start the heating work after the detection device is normal. During the heating of the bolt 14, continuously monitor the change in the wall temperature of the nut 5, adjust the input power according to the change situation, and stop heating if it is found that the temperature of the nut 5 exceeds 100°C.

[0049] 4. Monitor the change in elongation and perform disassembly and assembly work during the heating process

[0050] Before thermal tightening, use a marker pen to record the tightening angle position of the nut 5, lubricate the threaded part and the bearing surface of the nut 5 with an anti-seize compound, and clean the bottom of the central hole with compressed air. Use the bolt 14 elongation measuring device 6 to measure the change in the elongation of the bolt 14 in real time and feed it back to the intelligent control center 3. When the elongation of the bolt 14 reaches the required elongation, tighten the nut 5, and check whether the nut 5 reaches the tightening angle. If the required elongation is not reached after heating for 60 minutes, stop heating. During thermal loosening, when the elongation measuring device of the bolt 14 shows that the elongation begins to change, the nut 5 can be disassembled.

Claims

1. A method for controlling the resistance heating of a thermal tightening bolt, characterized in that: It includes Step 1: Collecting the parameters of the thermal tightening bolt (14) and setting the electric power input curve; Step 2: Assembling the device and establishing conditions; Step 3: Monitoring the change of heating temperature; Step 4: Monitoring the elongation for disassembly and assembly. The specific content of Step 3: Monitoring the change of heating temperature includes: Inserting the resistance heating rod (4) into the central hole of the thermal tightening bolt (14), and setting the effective heating section at the smooth rod of the thermal tightening bolt; The adsorption type temperature measurement probe (7) tracks and records the temperature of the thermal tightening bolt (14), and starts the heating operation after the detection device is normal; During the heating of the thermal tightening bolt (14), constantly monitor the wall temperature change of the nut (5), adjust the input power according to the change situation, and if it is found that the temperature of the nut (5) exceeds 100 °C, stop heating. The specific content of Step 4: Monitoring the elongation for disassembly and assembly includes: Before thermal tightening, record the tightening angle position of the nut (5) with a marker pen, lubricate the thread part and the bearing surface of the nut (5) with anti-seize compound, and clean the bottom of the central hole with compressed air; Use the elongation measurement device (6) of the thermal tightening bolt (14) to measure the elongation change of the thermal tightening bolt (14) in real time and feedback it to the intelligent control center (3). When the elongation of the thermal tightening bolt (14) reaches the required elongation, tighten the nut (5), and check whether the nut (5) reaches the tightening angle. If the required elongation is not reached after heating for 60 minutes, stop heating; During thermal loosening, when the elongation measurement device of the thermal tightening bolt (14) shows that the elongation starts to change, disassemble the nut (5).

2. The method for controlling the electrical resistance heating of a thermal tightening bolt according to claim 1, characterized in that: The specific content of Step 1: Collecting the parameters of the thermal tightening bolt (14) and setting the electric power input curve includes: Collecting the specification models and material information of the thermal tightening bolt (14) and the nut (5), determining the maximum allowable heating temperature, yield strength, maximum allowable stress, and maximum allowable temperature change rate of the thermal tightening bolt (14), and the highest allowable temperature parameter of the internal thread of the nut (5); According to the diameter, effective length, and heating hole diameter structure information of the thermal tightening bolt (14), customize the optimal heating tool, and the control parameters include the length, diameter, and installation position of the heating rod; After determining the above data, calculate the electric power input curve changing with time and input it into the intelligent control center (3).

3. A method for controlling the electrical resistance heating of a thermal tightening bolt according to claim 1, characterized in that: The specific content of Step 2: Assembling the device and establishing conditions includes: Building a bolt resistance heating workbench, and determining that the surrounding environment meets the requirements for the use of the heater: the surrounding medium temperature is not higher than 50 °C and not lower than -10 °C; the relative air humidity is not greater than 95%; the space does not contain chemically corrosive and explosive gases; there is no vibration or bump, and the installation slope does not exceed 5 degrees; Before the DC electrical cabinet (2) is powered on, the shell should be reliably grounded, and the voltage should be adjusted to the "0" position.

4. A thermal tightening bolt resistance heating control device, characterized in that: Based on the thermal tightening bolt resistance heating control method described in any one of claims 1 - 3, it includes a DC electrical cabinet (2), a resistance heating rod (4), a temperature monitoring and feedback device, an elongation measurement device (6), an intelligent control center (3), and a bolt fastening device; The DC electrical cabinet (2) is connected to the resistance heating rod (4) through a cable, and the resistance heating rod (4) is inserted into the thermal tightening bolt (14).

5. The thermal tightening bolt resistance heating control device according to claim 4, characterized in that: The described bolt fastening device includes a nut (5), a thermal tightening bolt (14), a convex washer (12) and a concave washer (13); the nut (5) is fixedly connected to the upper surface of the steam turbine cylinder flange (8), and an adsorption type temperature measurement probe (7) is arranged on the surface of the nut (5); the convex washer (12) and the concave washer (13) are closely fitted to form a set of washers.

6. The thermal tightening bolt resistance heating control device according to claim 5, characterized in that: The described steam turbine cylinder flange (8) includes a lower flange (10) and an upper flange (11); the middle position of the upper surface of the upper flange (11) is recessed, and the washer is located in the recess.

7. A resistance heating control device for a thermal tightening bolt according to claim 6, characterized in that: The nut (5) and the thermal tightening bolt (14) are threadedly connected; there is a washer spaced between the nut (5) and the upper flange (11).

8. A resistance heating control device for a thermal tightening bolt according to claim 4, characterized in that: The elongation measurement device (6) is connected to the intelligent control center (3).

9. A resistance heating control device for a thermal tightening bolt according to claim 5, characterized in that: The adsorption type temperature measurement probe (7) is connected to the temperature measuring instrument (9), and the temperature measuring instrument (9) is also connected to the intelligent control center (3).

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