Method and apparatus for thermal relaxation test of a spring

Abstract

The present application belongs to the technical field of gas turbine, and particularly relates to a spring thermal relaxation test method and device, the thermal relaxation test method comprising 1) measuring and recording the initial height of the spring; 2) after compressing the spring to a compressed state, placing the spring into a heating device; 3) measuring and recording the remaining free height of the spring after heating; 4) repeating steps 2) and 3) to obtain multiple sets of spring remaining free height; 5) collecting test data and fitting the spring thermal relaxation data curve, fitting the data according to the exponential decay equation, y0 being the expected remaining free height of the spring after the full service period; 6) if y0 of step 5) is greater than or equal to the minimum required value of the spring design, the spring meets the requirement of thermal relaxation resistance; otherwise, it does not meet the requirement. The test method is suitable for a high temperature range, simple in test method, low in cost and high in test efficiency.

Description

Technical Field

[0001] This invention belongs to the field of gas turbine technology, specifically relating to a method and apparatus for testing the thermal relaxation of springs. Background Technology

[0002] Gas turbines utilize a large number of high-temperature compression springs. During unit operation, the average operating temperature of some springs exceeds 450℃, with the highest operating temperature approaching 500℃ under extreme conditions. Springs bear loads during service, and some are subjected to centrifugal forces from themselves and adjacent components, resulting in a fully compressed state. Under such extreme conditions for extended periods, even springs made of high-temperature alloys will experience significant thermal relaxation, meaning their effective length shortens. Excessive spring relaxation can lead to various accidents. For example, if a spring installed at the root slot pin hole of the compressor blade fails, it will lose its restraining function on the blade, causing axial movement under external forces, leading to rubbing between moving and stationary parts, and in severe cases, even blade detachment. To avoid such accidents, a series of technical requirements have been proposed for springs operating under these extreme conditions, with thermal relaxation resistance being the most critical.

[0003] Currently, among common technical standards, only JB / T 6655—2013, "Technical Conditions for Heat-Resistant Cylindrical Helical Compression Springs," provides a brief general test method for the thermal relaxation resistance of high-temperature compression springs, but it lacks specific test equipment and evaluation requirements. In practice, repeatedly installing and disassembling springs for heating and testing using conventional methods is inefficient and introduces significant human error when measuring smaller springs. Furthermore, thermal relaxation resistance testing devices that combine testing and heating components require heating the sensor in an electric furnace, which can damage precision instruments and introduce errors. Additionally, a single sensor can only measure a single spring, making manufacturing too costly and impractical. Therefore, a spring heating test device that is both accurate and practically feasible is needed to accurately evaluate the thermal relaxation resistance of high-temperature compression springs used in gas turbines.

[0004] The prior art CN105300673A discloses a reliability determination method based on spring stress relaxation test data. The specific steps are: 1) installation and test preparation of the test equipment; 2) determining the test temperature, carrying out stress relaxation tests of compression springs at different temperatures, collecting the load-bearing capacity at different test times and plotting stress relaxation curves; 3) plotting the load-bearing capacity and test time collected in step 2) with the spring load loss rate as the vertical axis and the logarithm of the corresponding test time as the horizontal axis, respectively plotting the semi-logarithmic curves of the spring load loss rate versus time at each test temperature; thereby obtaining the stress relaxation equation of the spring sample at the actual working temperature, and calculating the load loss rate and remaining load at the end of the life of the spring sample at the actual working temperature; 4) obtaining the reliability of the spring sample (8) at the end of its life. This prior art effectively solves the problems of large dispersion of compression spring reliability assessment data, long test time, and poor accuracy of the assessment data source. However, this prior art targets a small temperature range, requires a pressure sensor for each spring, has high cost, involves many parameters, has a relatively complex test method, and has relatively low test efficiency. Summary of the Invention

[0005] To address the aforementioned technical problems—namely, the need for testing in areas with low temperature ranges, complex testing methods, high costs, and low testing efficiency—the present invention provides the following technical solution:

[0006] A method for thermal relaxation testing of a spring, the method comprising a positioning post, a test plate, and a flat washer, wherein the spring is inserted through the positioning post, the bottom end of the spring contacts the test plate below the positioning post, and the top end of the spring is covered by the flat washer; the method includes the following steps.

[0007] 1) Measure and record the initial height of the spring;

[0008] 2) After compressing the spring to a compressed state, place it into the heating device;

[0009] 3) Measure and record the remaining free height of the spring after heating;

[0010] 4) Repeat steps 2) and 3) to obtain multiple sets of remaining free heights of the springs. In step 3), the heating time is as follows: measure once every 6 hours within 24 hours, and measure once every 24 hours after 24 hours.

[0011] 5) Summarize the experimental data and fit the spring thermal relaxation data curve, based on the exponential decay equation. The data is fitted, where y is the remaining free height of the spring in step 3), y0 is the expected remaining free height of the spring after the full service cycle, x is the cumulative heating time, and A1 and t1 are the fitting parameters to be determined.

[0012] 6) Determine the thermal relaxation resistance of spring 1. If y0 in step 5) is greater than or equal to the minimum design requirement of the spring, then the spring meets the thermal relaxation resistance requirement; otherwise, it does not.

[0013] Furthermore, the heating temperature in step 3) is 400°C, 450°C, or 490°C.

[0014] Furthermore, the cumulative heating time is at least 120 hours.

[0015] Furthermore, the height from the bottom of the spring to the upper surface of the flat washer is measured, and the initial height of the spring or the remaining free height of the spring is calculated based on the thickness of the flat washer.

[0016] The present invention also provides a thermal relaxation testing device for springs, used to implement the above-mentioned thermal relaxation testing method. The testing component further includes a top plate, a limiting sleeve, and a limiting post. The bottom of the testing plate is provided with several testing holes and adjustment through holes. The limiting post is disposed in the adjustment through holes. The limiting sleeve passes through the limiting post. The top plate passes through the limiting post and the positioning post, and the top plate is disposed above the testing plate.

[0017] Furthermore, the height of the limiting sleeve is the sum of the height of the spring and the thickness of the flat washer.

[0018] Furthermore, it also includes a detection component, which includes an X-axis slide, a Y-axis slide, a laser displacement measuring instrument, and a bracket. The Y-axis slide is positioned above the X-axis slide, and the laser displacement measuring instrument is positioned on the top of the bracket.

[0019] Furthermore, the laser displacement measuring instrument includes an RS-CMOS image sensor.

[0020] Furthermore, the X-axis slide and the Y-axis slide have the same structure, both including a base, sliders, linear guides, ball screws, support seats, and servo motors. The two linear guides are set on two opposite long sides of the base, and two sliders are set on each of the two linear guides. A ball screw parallel to the linear guides is set in the middle of the base, and three support seats are set on the ball screw. A servo motor is set at one end of the ball screw.

[0021] Furthermore, it also includes a heating device for heating the test component.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The experimental method of this invention is based on the exponential decay equation. The data is fitted to determine the spring's resistance to thermal relaxation. y is the spring's remaining free height, y0 is the expected remaining free height of the spring after the entire service cycle, x is the test time, and A1 and t1 are fitting parameters to be determined. The spring's resistance to thermal relaxation is then determined based on the y0 value. This method involves few parameters, has a wide applicable temperature range, is simple in testing, low in cost, and highly efficient. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the thermal relaxation test apparatus of the present invention;

[0025] Figure 2 This is a schematic diagram of the test plate for the present invention;

[0026] Figure 3 This is a test component in an installed state according to the present invention;

[0027] Figure 4 This is a test component in another installation state of the present invention;

[0028] Figure 5 This is the detection component of the present invention;

[0029] Figure 6 This invention refers to the X-axis slide or the Y-axis slide.

[0030] Figure 7 This is a flowchart of the test method of the present invention;

[0031] Figure 8 A graph showing the test results of the spring's remaining free height versus cumulative heating time, based on the thermal relaxation test data of the spring used at the root slot of the compressor blade of a gas turbine.

[0032] Figure 9 This is a schematic simulation diagram of the structure between the spring and the plate under the first load step of large deformation based on a three-dimensional finite element model;

[0033] Figure 10 This is a schematic simulation diagram of the structure between the spring and the plate under the second load step under large deformation based on a three-dimensional finite element model;

[0034] Figure 11 The graph shows the relationship between the reaction force F between the spring and the plate and time t.

[0035] Reference numerals in the attached diagram: 1-Spring; 2-Positioning pin; 3-Test plate; 31-Test hole; 32-Fixing hole; 33-Adjusting through hole; 4-Y-axis slide; 5-X-axis slide; 41-Base; 42-Support seat; 43-Slider; 44-Linear guide rail; 45-Servo motor; 46-Ball screw; 6-Laser displacement measuring instrument; 7-Bracket; 8-Flat washer; 9-Limit sleeve; 10-Nut; 11-Limiting pin; 12-Top plate. Detailed Implementation

[0036] The technical solution of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0037] It should be noted that the terms "center", "upper", "lower", "horizontal", "left", "right", "front", "rear", "lateral", "longitudinal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0038] like Figures 1 to 4 As shown, the present invention provides a thermal relaxation device for a spring, including a test component and a detection component. The test component is used to feed the spring into a heating device for high-temperature testing, and the detection component is used to measure the height of the spring 1. In this embodiment, the heating device is an electric heating furnace. The test component includes a test plate 3, a top plate 12, a limiting sleeve 9, a positioning post 2, a flat washer 8, a limiting post 11, and a nut 10, etc. The test plate 3 and the top plate 12 have the same structure. In this embodiment, the test plate 3 is 10mm thick, and the test plate 3 has several test holes 31, 12 fixing holes 32, and 4 adjustment through holes 33. Positioning pin 2 is installed in test hole 31. In this embodiment, positioning pin 2 is a bolt, and test hole 31 is a threaded hole. Spring 1 passes through positioning pin 2, and the bottom end of spring 1 contacts test plate 3 below positioning pin 2. Flat washer 8 covers the upper end of spring 1. The outer diameter of flat washer 8 is larger than the outer diameter of spring 1. Flat washer 8 can improve the accuracy of spring 1 measurement. Limiting pin 11 is installed in adjustment through hole 33. In this embodiment, limiting pin 11 is a stud. Limiting sleeve 9 is installed in limiting pin 11. The height of limiting sleeve 9 is the sum of the height of spring 1 and the height of flat washer 8. When spring 1 needs to be compressed, top plate 12 passes through positioning pin 2 and limiting pin. The inner surface of top plate 12 contacts flat washer 8. Nut 10 is used to tighten both ends of limiting pin 11. Therefore, test plate 3 is the fixing device of spring 1. The compression of spring 1 is adjusted by the cooperation of limiting pin 11 and limiting sleeve 9. The test plate 3, top plate 12, flat washer 8, and limiting sleeve 9 are all made of stainless steel, and their upper and lower surfaces are precision ground to ensure small shape tolerances and high dimensional accuracy, thus guaranteeing that multiple springs 1 have a consistent compression amount after being compressed. In addition, the parts included in the test components are easy to process and can be modified at any time according to actual needs. Multiple springs 1 can be installed on the test plate at one time for testing, which significantly improves the testing efficiency.

[0039] like Figure 1 , Figure 5 and Figure 6 As shown, the detection component includes an X-axis slide 5, a Y-axis slide 4, a bracket 7, and a laser displacement measuring instrument 6. The Y-axis slide 4 is positioned above the X-axis slide 5. The laser displacement measuring instrument 6 is mounted on the top of the bracket 7. The laser displacement measuring instrument 6 is used to measure the height of the spring 1 and uploads the measured data to the host computer for storage and recording. The laser displacement measuring instrument 6 adopts RS-CMOS image sensor technology, and the measurement error can be controlled within 0.1μm. The sampling period is 200μs, ensuring high-speed and high-precision measurement of the height of the spring 1 with high measurement efficiency.

[0040] The X-axis slide 5 and the Y-axis slide 4 have the same structure, both including a base 41, sliders 43, linear guides 44, ball screws 46, support seats 42, and servo motors 45. The two linear guides 44 are set on the two opposite long sides of the base 41, and two sliders 43 are respectively set on the two linear guides 44. The ball screw 46 parallel to the linear guides 44 is set in the middle of the base 41, and three support seats 42 are set on the ball screw 46. The servo motor 45 is set at one end of the ball screw 46. The base 41 of the Y-axis slide 4 is mounted on the support seat 42 of the X-axis slide 5.

[0041] When it is necessary to measure the height of spring 1, the test component containing spring 1 is fixed to the support base 42 and four sliders 43 of the Y-axis slide 4 of the testing component through the fixing hole 32. The ball screw 46 is controlled by the servo motor 45 of the Y-axis slide 4, which in turn moves the test plate along the linear guide rail 44 of the Y-axis slide 4. The ball screw of the X-axis slide 5 is controlled by the servo motor of the X-axis slide 5, which in turn moves the Y-axis slide 4 along the linear guide rail of the X-axis slide. The positioning accuracy of the X-axis slide 5 and the Y-axis slide 4 can reach 0.05mm, which meets the requirement of accurately positioning the position of spring 1. Due to the use of the double-layer structure slide of X-axis slide 5 and Y-axis slide 4, the precise control of the movement of the test plate containing spring 1 by the servo motor and ball screw, and the precise measurement of the height of each spring 1 by the laser displacement measuring instrument 6, the error caused by human factors is greatly reduced. Furthermore, since the test component and the detection component are detachable, when heating is required, only the test component with the spring needs to be sent into the heating device, without having to send the detection component into the heating device together. This avoids damage to the detection component and errors in the measurement results caused by long-term high-temperature thermal relaxation testing, making it highly feasible.

[0042] This invention also provides a method for testing the thermal relaxation of a spring, using the aforementioned thermal relaxation testing apparatus, and the procedure is as follows: Figure 7 As shown,

[0043] Step 1: Measure and record the initial height of spring 1;

[0044] Specifically, the test plate of the test component containing multiple springs 1 is fixed to the Y-axis slide 4 of the detection component. The initial height of the spring 1 is measured using a laser displacement measuring instrument 6. The specific measurement process is as follows: First, the servo motor is controlled to reset the X-axis slide 5 and the Y-axis slide 4. At this time, the spot of the laser displacement measuring instrument 6 is located on the test plate 3 in front of the first spring 1 in the first column. Then, the servo motor is controlled to drive the X-axis slide 5 to rotate. This rotational motion is converted into linear motion to move the Y-axis slide 4, so that the spot of the laser displacement measuring instrument 6 sweeps across all the springs 1 in the X-axis direction of this column. After restoring the initial position of this stroke, the Y-axis slide 4 is moved so that the spot of the laser displacement measuring instrument 6 is located on the test plate 3 in front of the first spring 1 in the second column. The servo motor is controlled to move the X-axis slide 5, so that the spot of the laser displacement measuring instrument 6 sweeps across all the springs 1 in the X-direction of this column. This cycle is repeated until all the springs 1 are swept. The data from the laser displacement measuring instrument 6 is stored and recorded by the host computer. The measured height data is the height from the bottom of the spring to the upper surface of the flat washer. Therefore, the height of the spring is the height obtained by subtracting the thickness of the flat washer 8 from the data measured by the laser displacement measuring instrument 6.

[0045] Step 2: After compressing the spring to a compressed state, place it into the heating device;

[0046] Specifically, after measuring and recording the height of all springs 1, the test plate 3 is removed from the Y-axis slide 4, the top plate 12 is installed above the springs, all springs 1 are compressed to the compressed state (i.e. all springs 1 are fully compressed, with the spring wires touching each other), and the test component with the compressed springs 1 is sent into the electric heating furnace for heating. In this embodiment, the heating temperature is 400℃, 450℃ or 490℃.

[0047] Step 3: Measure and record the remaining free height of the spring after heating;

[0048] Specifically, after removing the heated test component and allowing it to cool completely, the top plate 12 is removed, and the test plate 3 is fixed to the Y-axis slide 4. The remaining free height of the spring 1 is measured using a laser displacement measuring instrument 6. The measurement process is the same as that for measuring the initial height of the spring 1, and the data is uploaded to the host computer for storage and recording.

[0049] Step 4: Repeat steps 2 and 3 to obtain multiple sets of remaining free heights of the springs. In step 3, the heating time is as follows: measure once every 6 hours within 24 hours, and measure once every 24 hours after 24 hours.

[0050] Specifically, the temperature of the electric heating furnace is set to 400℃, 450℃ or 490℃. The test component with spring 1 is sent into the electric heating furnace for heating. Within 24 hours, spring 1 is taken out and its remaining free height is measured every 6 hours of heating. After 24 hours, spring 1 is taken out and its remaining free height is measured every 24 hours of heating. Multiple sets of spring remaining free heights are obtained and uploaded to the host computer for storage and recording. In this embodiment, the thermal relaxation test data of a specific batch of springs 1 are shown in Table 1.

[0051] The aforementioned heating interval was adopted because, after conducting multiple tests on the spring involved in this invention, and comparing the test results with actual engineering application results, it was found that the free height change of spring 1 was most significant in the first 24 hours under extreme conditions. The free height change of spring 1 in the first 24 hours accounted for more than 30% of the free height change of this type of spring 1 over its entire service life (approximately 20,000 hours). In addition, excessively frequent measurements would affect the accuracy and operability of the test spring. After repeated attempts, it was determined that measurements should be taken once every 6 hours of heating in the first 24 hours after the start of the test, and once every 24 hours of heating thereafter. This can reduce the impact of the measurement itself on the accuracy of the spring. Furthermore, through multiple tests, it was found that for this type of spring operating under extreme conditions, after a cumulative heating test duration of 72 hours, the average free height change reached more than 75% of the entire service life; after a cumulative heating test duration of 96 hours, the average free height change reached more than 85% of the entire service life; and after a cumulative heating test duration of 120 hours, the average free height change reached 95% of the entire service life. Therefore, to ensure the accuracy of the experiment, the experiment should be paused only after the total duration reaches 120 hours.

[0052] Table 1 is a summary table of the thermal relaxation test results for a batch of springs.

[0053]

[0054]

[0055]

[0056] Step 5: Summarize the experimental data and fit the spring thermal relaxation data curve, based on the exponential decay equation. The data is fitted, where y is the remaining free height of the spring in step 3), y0 is the expected remaining free height of the spring after the full service cycle, x is the cumulative heating time, and A1 and t1 are the fitting parameters to be determined.

[0057] This experiment uses the exponential decay equation to fit the curve. Specifically, the height data of the spring at different temperatures obtained in steps 1, 3 and 4 are summarized to obtain the spring thermal relaxation data curve, where the X-axis is the cumulative heating time of the spring and the Y-axis is the remaining free height of the spring.

[0058] Step 6: Determine the thermal relaxation resistance of spring 1. If y0 in step 5) is greater than or equal to the minimum design requirement of the spring, i.e. the minimum height required to ensure the spring maintains normal operation, then the spring meets the thermal relaxation resistance requirement; otherwise, it does not.

[0059] The springs used at the root slots of the compressor rotor blades in a certain type of gas turbine were under compression throughout their entire service life. Some springs operated at 400℃, and a few at 450℃. During a major overhaul of the gas turbine, all springs of this type were removed and replaced. Testing revealed that springs with an average initial height of 17.8mm had an average remaining free height of approximately 16.80mm (400℃) and 15.70mm (450℃) after completing their service life. Now, due to gas turbine upgrades, the operating temperature at the compressor rotor blade root has increased to a maximum of 490℃. To ensure safety, thermal relaxation tests were conducted on the springs used under these extreme operating conditions at 400℃, 450℃, and 490℃. Figure 8 Table 2 shows the test results curves of the remaining free height of the spring versus the cumulative heating time for the corresponding type of spring in the thermal relaxation test data. The fitted equation and predicted values ​​for the corresponding type of spring in the thermal relaxation test are also presented in Table 2. The fitted equation is the exponential decay equation. y0 represents the expected remaining free height of the spring after the entire service life, x represents the cumulative heating time, and A1 and t1 are the fitting parameters to be determined. The fitting results show that after the test time reaches 120h, the remaining free heights of this type of spring are 16.31mm (400℃), 15.40mm (450℃), and 13.74mm (490℃), respectively. The fitting results of the expected remaining free height y0 of the spring after the entire service life are 16.30mm (400℃), 15.22mm (450℃), and 13.45mm (490℃), respectively. Table 3 shows the fitting equation and predicted value of the spring of the compressor blade root groove under extreme high temperature conditions during thermal relaxation test. A comparison table of the average remaining free height of springs after the actual service cycle is presented. The coefficients of determination for the three fitted curves are 0.9668 (400℃), 0.97854 (450℃), and 0.98271 (490℃), all higher than 0.95. Furthermore, the fitting results of y0 at the 400℃ and 450℃ test temperatures are less than or equal to the measured values ​​of this type of spring removed during the overhaul, indicating a basic consistency. This demonstrates that the exponential decay function effectively describes the relationship between the spring's free height and time during thermal relaxation. At the 490℃ test temperature, the final fitting result of y0 is 13.45mm. It can be concluded that the predicted free height of this type of spring will decrease to a maximum of 13.45mm after completing its full service cycle under 490℃ conditions. Based on the designers' assessment, this batch of springs is ultimately judged to meet the requirements for thermal relaxation resistance.

[0060] Table 2 shows the fitting equation and predicted values ​​of the spring at the root groove of the compressor blade under extreme high-temperature conditions during thermal relaxation testing.

[0061]

[0062]

[0063] Table 3 shows the fitting equation and predicted values ​​of the springs at the root grooves of the compressor blades under extreme high-temperature conditions during thermal relaxation testing, as well as the average remaining free height data of the springs after the entire service life.

[0064]

[0065] Regarding the exponential decay equation used in this invention As a fitting equation, this invention provides a method for solving the relationship between spring force and time based on finite element simulation, thereby verifying the use of the exponential decay equation. A method for simulating the correctness of spring strength includes the following steps:

[0066] S1. Establish a three-dimensional finite element model of the spring;

[0067] A three-dimensional finite element model of the spring was created using the solid186 element. The solid186 element is a high-order three-dimensional 20-node solid structural element with the ability to support plasticity, hyperelasticity, creep, large deformation, and large strain. The solid186 element was directly meshed into a tetrahedral mesh, resulting in 23,520 elements.

[0068] S2, Spring material properties assigned to the three-dimensional finite element model of the spring;

[0069] This includes defining the constant parameters of the spring model and assigning a creep constitutive model. Specific constant parameters include density, elastic modulus, and Poisson's ratio. A special creep constitutive model needs to be assigned, as creep is divided into three stages: initial creep, steady-state creep, and accelerated creep. The creep constitutive model assigned to the spring is steady-state creep, which can be characterized as follows: In the formula ε cr Where σ is the creep strain rate, T is the temperature, C1, C2, and C3 are material parameters, and e is the natural index.

[0070] S3. The three-dimensional finite element model of the spring is subjected to a load under large deformation;

[0071] To facilitate calculation, a flat plate is built at the bottom of the three-dimensional finite element model of the spring. Contact settings are created between the flat plate and the spring, and the bottom of the flat plate is fixed with constraints.

[0072] When solving for spring creep, enable large deformation and apply boundary conditions in two load steps. In the first load step, apply vertical displacement to the spring for 1 second. In the second load step, apply a temperature of 400℃, enable the creep option, maintain vertical displacement, and set the time to 720000s (200 hours).

[0073] like Figure 9 As shown, a downward force of 2 mm is applied to the spring in the first load step for 1 second; Figure 10 As shown, the spring is deformed after applying a 2mm downward force to the spring in the first load step for 1 second, and then applying the second load step.

[0074] S4. Extract the reaction force of the spring every 5000 seconds, fit the curve of reaction force versus time, and obtain the determination coefficient and initial value of the exponential decay function.

[0075] Extract the reaction force F between the spring and the top surface of the plate.

[0076] The formula for spring force is F = kx, where F is the spring force, k represents the spring constant, and x represents the degree of spring deformation.

[0077] When a spring operates in a high-temperature environment, it undergoes creep, resulting in permanent deformation strain ε. p The total strain ε of the spring remains constant, resulting in a decrease in the elastic strain ε of the spring. e =(ε-ε p The decrease in ε leads to a decrease in the spring force, F = k(ε - ε) p *L, where L is the spring length, the simulation results of the reaction force F between the spring and the plate versus time t are shown in Table 4. The relationship between the reaction force F and time t was fitted using Matlab software. The curve of the reaction force F versus time t is shown in... Figure 11 As shown.

[0078] Table 4 shows the simulation data of the reaction force F between the spring and the plate versus time t.

[0079]

[0080]

[0081] Using the exponential decay function F = 3.34685 + 0.4562e -t / 167866When fitting the curve, the coefficient of determination was 0.9989, indicating that the simulated values ​​of the reaction force and duration of the spring creep model perfectly match the characteristic distribution of the exponential decay function. The reaction force F on the plate is related to the spring compression, the spring free height, and the spring stiffness, specifically, the reaction force F = (spring free height - spring compression) × spring stiffness. The spring compression and spring stiffness remain constant in the same experiment, meaning the reaction force F is directly proportional to the spring free height. Therefore, it is reasonable to use the exponential decay function to describe and fit the subsequent data on the spring free height and experimental duration.

[0082] The above technical features constitute the preferred embodiment of the present invention, which has strong adaptability and optimal implementation effect. Non-essential technical features can be added or removed according to actual needs to meet the needs of different situations.

[0083] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for testing the thermal relaxation of a spring, the testing method involving a testing component comprising a positioning column, a testing plate and a flat washer, the spring being threaded in the positioning column, the bottom end of the spring being in contact with the testing plate below the positioning column, the upper end of the spring being covered by the flat washer; characterized in that: Includes the following steps, 1) Measure and record the initial height of the spring; 2) After compressing the spring to its compressed state, place it into the heating device; 3) Measure and record the remaining free height of the spring after heating; 4) Repeat steps 2) and 3) to obtain multiple sets of remaining free heights of the springs. In step 3), the heating time is as follows: measure once every 6 hours within 24 hours, and measure once every 24 hours after 24 hours. 5) Summarize the experimental data and fit the spring thermal relaxation data curve, based on the exponential decay equation. The data is fitted, where y is the remaining free height of the spring in step 3), y0 is the expected remaining free height of the spring after the full service cycle, x is the cumulative heating time, and A1 and t1 are the fitting parameters to be determined. 6) Determine the spring's resistance to thermal relaxation. If y0 in step 5) is greater than or equal to the minimum design requirement for the spring, then the spring meets the requirements for resistance to thermal relaxation; otherwise, it does not.

2. The thermal relaxation test method according to claim 1, characterized in that: The heating temperature in step 3) is 400 degrees Celsius, 450 degrees Celsius, or 490 degrees Celsius.

3. The thermal relaxation test method according to claim 1, characterized in that: The total heating time is at least 120 hours.

4. The thermal relaxation test method according to claim 1, characterized in that: Measure the height from the bottom of the spring to the upper surface of the flat washer, and calculate the initial height or remaining free height of the spring based on the thickness of the flat washer.

5. The thermal relaxation test method according to claim 1, characterized in that: The test component also includes a top plate, a limiting sleeve, and a limiting post. An adjustment through hole is opened at the bottom of the test plate, the limiting post is set in the adjustment through hole, the limiting sleeve passes through the limiting post, the top plate passes through the limiting post and the positioning post, and the top plate is set above the test plate.

6. The thermal relaxation test method according to claim 5, characterized in that: The height of the limiting sleeve is the sum of the height of the spring and the thickness of the flat washer.

7. The thermal relaxation test method according to claim 5, characterized in that: It also includes a detection component, which includes an X-axis slide, a Y-axis slide, a laser displacement measuring instrument, and a bracket. The Y-axis slide is positioned above the X-axis slide, and the laser displacement measuring instrument is positioned on the top of the bracket.

8. The thermal relaxation test method according to claim 7, characterized in that: The laser displacement measuring instrument includes an RS-CMOS image sensor.

9. The thermal relaxation test method according to claim 7, characterized in that: The X-axis slide and the Y-axis slide have the same structure, both including a base, sliders, linear guides, ball screws, support seats, and servo motors. The two linear guides are set on the two opposite long sides of the base, and two sliders are set on each of the two linear guides. A ball screw parallel to the linear guides is set in the middle of the base, and three support seats are set on the ball screw. A servo motor is set at one end of the ball screw.

10. The thermal relaxation test method according to claim 5, characterized in that: It also includes a heating device for heating the test components.

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