A heat and vibration based sealing ring life prediction method for junction boxes

Abstract

The application discloses a kind of sealing ring life prediction methods of terminal box based on heat and vibration, after being assembled, several terminal boxes are connected to wire, and wire is placed in the gap groove of first sealing ring and second sealing ring, wire is energized, and the time of energization is different, while terminal box is placed in vibration environment, acceleration sensor is arranged on the inner side of first sealing ring and second sealing ring, for obtaining vibration value, temperature sensor is arranged around the gap groove of first sealing ring and second sealing ring or the temperature at the gap groove is obtained by infrared sensor;The application evaluates the life of first sealing ring and second sealing ring under thermal aging by the frictional heat effect caused by current heat effect and vibration, and fatigue damage also occurs under vibration condition, and the overall life of first sealing ring and second sealing ring is evaluated by combining thermal aging rate and fatigue damage, so that the prediction result is more comprehensive and accurate.

Description

Technical Field

[0001] This invention relates to the field of junction box sealing ring life testing technology, specifically to a method for predicting the life of junction box sealing rings based on heat and vibration. Background Technology

[0002] like Figure 1 The junction box shown has a first sealing ring and a second sealing ring. The first and second sealing rings are provided with notches for placing wires. When the junction box is in use, the heat of the wires will be transferred to the first and second sealing rings. In addition, when the junction box is in a vibrating installation environment, corresponding vibrations will also be generated, causing frictional heat to occur on the contact surface. For the first and second sealing rings, heat will cause them to age, thereby reducing the sealing effect. Therefore, it is necessary to predict their lifespan to guide production. Summary of the Invention

[0003] The purpose of this invention is to provide a method for predicting the lifespan of junction box seals based on heat and vibration, so as to assess the lifespan of seals under working conditions.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for predicting the lifespan of a junction box seal ring based on heat and vibration, wherein the junction box has a first seal ring and a second seal ring, comprising the following steps:

[0006] S100. Connect several assembled junction boxes to wires and place the wires in the notches of the first and second sealing rings. Then, energize the wires for different durations. Simultaneously, place the junction boxes in a vibration environment. Install acceleration sensors on the inner surfaces of the first and second sealing rings to obtain vibration values. Install temperature sensors around the notches of the first and second sealing rings or obtain the temperature at the notches using infrared sensors. Take the average of the temperature values ​​detected by each temperature sensor as the temperature rise T of the first and second sealing rings. The energizing time is consistent with the vibration time.

[0007] S200. Calculate the heat Q1 at the notch based on the magnitude of the current and the energizing time, and calculate the temperature rise ΔT caused by the current based on the heat Q1. Calculate the frictional heat T' generated by the vibration based on the detected temperature rise T and ΔT, where T' = T - ΔT.

[0008] S300. The actual thermal aging rate is calculated using ΔT, T, and T'. The lifespan of the first and second sealing rings is predicted based on the actual thermal aging rate. The formula for calculating the actual thermal aging rate is as follows:

[0009] In the above formula, A is the pre-exponential factor; Ea is the activation energy, the minimum energy threshold required for the material to undergo thermal aging; R' is the ideal gas constant; α is the vibration-thermal synergy factor, and β is the current-thermal synergy factor.

[0010] S400: Calculate fatigue damage based on vibration acceleration, and predict the lifespan of the first and second sealing rings based on fatigue damage and actual thermal aging rate.

[0011] The present invention further provides that the formula for calculating the electrical heat Q1 is as follows: Q1 = I 2 Rt, calculate the temperature rise caused by the current based on the generated heat Q1. The temperature rise calculation method is as follows: Where T a Here, k is the ambient temperature, k is the heat dissipation coefficient, t is the energizing time, m is the mass of the first or second sealing ring, and c is the mass of the second sealing ring. p This refers to the specific heat capacity of the first or second sealing ring.

[0012] In a further embodiment of this invention, the temperature rise calculation caused by vibration is first performed by calculating the heat Q2 generated by the vibration. The calculation method is: Q2 = μFVt, where μ is the coefficient of friction, F is the normal force on the first or second sealing ring, t is the vibration time, and V is the sliding velocity of the first and second sealing rings during vibration; the calculation formula is: V = 2πfA vib Where f is the vibration frequency, A vib Let F be the amplitude, where F = ma, and a is the vibration acceleration. Then its temperature rise... m is the mass of the first or second sealing ring, and c p This refers to the specific heat capacity of the first or second sealing ring.

[0013] The invention further includes calculating the dynamic stress of the first and second sealing rings based on the vibration acceleration, using the formula: Δσ(t)=m·a(t)·SCF; subsequently, the actual number of cycles n under the dynamic stress value Δσ(t) is obtained. i Then fatigue damage was calculated. in Where N i (T) represents the fatigue life of the material under dynamic stress Δσ(t) at the current temperature T; N0 represents the fatigue life at the reference temperature T0; q represents the temperature decay coefficient, which reflects the accelerated decay effect of temperature increase on fatigue life; and SCF represents the stress concentration factor.

[0014] The present invention further provides that the stress concentration factor SCF is measured based on strain gauges.

[0015] The present invention further specifies that the life calculation formula based on fatigue damage and actual thermal aging rate is: L = k theermal ·D mech / (k thremal +D mech );

[0016] The present invention further provides that the pre-exponential factor A and the activation energy Ea are obtained through aging experiments at different temperatures.

[0017] The present invention further provides that, when calibrating the vibration-thermal synergy factor α, the first sealing ring and the second sealing ring are placed at the same temperature and different vibration conditions are applied for calibration.

[0018] The present invention further provides that the formula for calculating the stress concentration factor (SCF) under vibration conditions is as follows:

[0019] SCF=SCF'·k d , where k d is the dynamic amplification factor, with a value ranging from 1.2 to 2.0, and SCF' is the strain gauge measurement value.

[0020] The invention further specifies that k d The value is selected based on the following: the natural frequency f of the first and second sealing rings. n With vibration frequency f vib contrast:

[0021] If f vib <f n k d ≈1.2;

[0022] If f vib ≈f n k d ≈2.0;

[0023] If f vib >f n k d ≈1.5.

[0024] The beneficial effects of the present invention are as follows: The present invention evaluates the life of the first and second sealing rings under thermal aging by using the thermal effect of electric current and the frictional heat effect caused by vibration. Furthermore, fatigue damage will also occur under vibration conditions. By combining the thermal aging rate and fatigue damage, the overall life of the first and second sealing rings is evaluated, making the prediction results more comprehensive and accurate. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0026] Figure 1 This is a schematic diagram of the junction box of the present invention. Figure 1 .

[0027] Figure 2 This is a schematic diagram of the junction box of the present invention. Figure 2 .

[0028] Figure label:

[0029] 10. Top cover; 20. Base; 30. First sealing ring; 40. Second sealing ring; 50. Notch / groove; 60. Cable guide port; Detailed Implementation

[0030] The following will describe in detail the implementation of this application with reference to the accompanying drawings and embodiments, so that the implementation process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0031] The junction box in this invention is as follows Figure 1 As shown, it includes an upper cover 10 and a base 20. One end of the upper cover 10 and the base 20 are hinged, and the other end is fastened to each other in use. The upper cover 10 is provided with a first sealing ring 30, and the base 20 is provided with a second sealing ring 40. The first sealing ring 30 and the second sealing ring 40 are provided with notches and grooves 50, which correspond to forming wire passages 60 on the upper cover 10 and the base 20.

[0032] Based on the above junction box, in actual use, since the first sealing ring and the second sealing ring will be in direct contact during wiring, the heat generated by the current will directly affect the life of the first sealing ring and the second sealing ring. In addition, frictional heat will also be generated when the junction box is in a vibrating environment. Therefore, it is necessary to predict the life of the first sealing ring and the second sealing ring in view of the above situations.

[0033] Based on the aforementioned first and second sealing rings, as Figure 2 As shown, the present invention provides a method for predicting the lifespan of a junction box seal ring based on heat and vibration. The junction box has a first seal ring and a second seal ring. The steps are as follows:

[0034] S100. Connect several assembled junction boxes to wires and place the wires in the notches of the first and second sealing rings. Then, energize the wires for different durations. Simultaneously, place the junction boxes in a vibration environment. Install accelerometers on the inner surfaces of the first and second sealing rings to acquire vibration values. Install temperature sensors or use infrared sensors around the notches of the first and second sealing rings to acquire the temperature at the notches. Take the average of the temperature values ​​detected by each temperature sensor as the temperature rise T of the first and second sealing rings. Since both the first and second sealing rings have six notches, when calculating the temperature rise, for the first sealing ring, the average of the temperatures from the six notches is taken. That is, if the six temperature values ​​are T1, T2, T3, T4, T5, T6, then T = (T1 + T2 + T3 + T4 + T5 + T6) / 6. The calculation of the temperature rise T for the second sealing ring is similar. The energizing time is consistent with the vibration time.

[0035] S200. Calculate the heat Q1 at the notch based on the magnitude of the current and the energizing time, and calculate the temperature rise ΔT caused by the current based on the heat Q1. Calculate the frictional heat T' generated by the vibration based on the detected temperature rise T and ΔT, where T' = T - ΔT.

[0036] S300. The actual thermal aging rate is calculated using ΔT, T, and T'. The lifespan of the first and second sealing rings is predicted based on the actual thermal aging rate. The formula for calculating the actual thermal aging rate is as follows:

[0037] In the above formula, A is the pre-exponential factor; Ea is the activation energy, the minimum energy threshold required for the material to undergo thermal aging reaction; R' is the ideal gas constant; α is the vibration-thermal synergy factor, and β is the current-thermal synergy factor; where T is the ambient temperature of the first and second sealing rings, which is an absolute temperature. Therefore, T' and ΔT need to be converted to absolute temperatures during the calculation.

[0038] S400: Calculate fatigue damage based on vibration acceleration, and predict the lifespan of the first and second sealing rings based on fatigue damage and actual thermal aging rate.

[0039] The pre-exponential factor A and activation energy Ea were obtained through aging experiments at different temperatures.

[0040] The experimental procedure is as follows:

[0041] A certain quantity of the first sealing rings was obtained and placed in constant temperature chambers at different temperatures: 40℃, 60℃, 80℃, 100℃, and 120℃. The time t for the hardness to decrease to 50% was recorded. failThen according to the formula Perform linear fitting and combine t fail The following data were obtained from the experiment: ∝1 / k

[0042]

[0043] According to the formula Convert to Then perform linear fitting, i.e. The intercept is ln(C / A), and the slope is Ea / R'. After fitting, the slope value is 10200K, and the intercept is 5.80. Therefore, Ea = 10200K·8.314J / (mol·K) ≈ 84.8J / mol. C is a proportionality constant, which is taken as 1. Then 1 / A = e 5.80 =330, then A = 1 / 330 hours -1 .

[0044] When calibrating the vibration-thermal synergy factor α, the first and second sealing rings are placed at the same temperature, and different vibration conditions are applied for calibration. The specific methods are as follows:

[0045] Calibration of the vibration-thermal synergy factor α:

[0046] The first and second sealing rings were placed in an environment with a temperature of 100℃, and their lifespans were tested at vibration frequencies of 50Hz, 100Hz, and 150Hz, respectively. The lifespans were calculated based on the failure times of the first and second sealing rings. After obtaining the failure times, the formula was used... Calculate the value of α, k in the above formula thermal Calculated based on failure time.

[0047] The current-thermal synergy factor β was then calibrated using the following method: The junction box was placed in a constant-temperature environment, with no vibration or under the same vibration conditions. Different currents (5A, 10A, and 15A) were then applied for the same duration. A temperature sensor or infrared thermometer was used to measure the temperature rise at the notch, and the failure time t of the sealing ring at different temperature rises was recorded. fail Under vibration-free conditions, the aging formula simplifies to: ΔT), based on the experimental data, linear regression is performed, and the formula is transformed into: by With ΔT as the vertical axis and ΔT as the horizontal axis, the experimental data obtained by fitting the slope β through linear regression are as follows:

[0048]

[0049] Based on the above data, a fitting was performed, and the slope of the fitted data is β = 0.018℃-1.

[0050] Specifically: In this embodiment, the formula for calculating the electrical heat Q1 is as follows: Q1 = I 2 Rt, calculate the temperature rise caused by the current based on the generated heat Q1. The temperature rise calculation method is as follows: Where T a Here, k is the ambient temperature, k is the heat dissipation coefficient, t is the energizing time, m is the mass of the first or second sealing ring, and c is the mass of the second sealing ring. p This refers to the specific heat capacity of the first or second sealing ring.

[0051] In this embodiment, the temperature rise caused by vibration is calculated by first calculating the heat Q2 generated by the vibration. The calculation method is: Q2 = μFVt, where μ is the coefficient of friction, F is the normal force on the first or second sealing ring, t is the vibration time, and V is the sliding velocity of the first and second sealing rings during vibration; the calculation formula is: V = 2πfA vib Where f is the vibration frequency, A vib Let F be the amplitude, where F = ma, and ma is the vibration acceleration. Then its temperature rise... m is the mass of the first or second sealing ring, and c p This refers to the specific heat capacity of the first or second sealing ring.

[0052] The invention further includes calculating the dynamic stress of the first and second sealing rings based on the vibration acceleration, using the formula: Δσ(t)=m·a(t)·SCF; subsequently, the actual number of cycles n under the dynamic stress value Δσ(t) is obtained. i Then fatigue damage was calculated. in Where N i (T) represents the fatigue life of the material at the current temperature T under dynamic stress Δσ(t); N0 represents the fatigue life at the reference temperature T0; q is the temperature attenuation coefficient, reflecting the accelerated attenuation effect of temperature increase on fatigue life; and SCF is the stress concentration factor. The temperature attenuation coefficient q is calibrated as follows:

[0053] Experimental design: Fatigue tests were conducted at temperatures T = 25℃, 50℃, and 75℃, and the number of cycles N corresponding to the dynamic stress Δσ was recorded. i (T);

[0054] For ln(N) i Linear regression was performed using (T))=ln (N0)-q(T-T0), and the results were calibrated experimentally. The experimental data are as follows:

[0055]

[0056] Based on the above data, the fitted result is q = 0.0277℃. -1 The stress concentration factor (SCF) is measured using strain gauges. The lifespan calculation formula based on fatigue damage and actual thermal aging rate is: L = k thermal ·D mech / (k thermal +D mech );

[0057] The formula for calculating the stress concentration factor (SCF) under vibration conditions is as follows:

[0058] SCF=SCF'·k d , where k d is the dynamic amplification factor, with a value ranging from 1.2 to 2.0; SCF' is the strain gauge measurement value; k d The value is selected based on the following: the natural frequency f of the first and second sealing rings. n With vibration frequency f vib contrast:

[0059] If f vib <f n k d ≈1.2;

[0060] If f vib ≈f h k d ≈2.0;

[0061] If f vib >f n k d ≈1.5.

[0062] In this invention, the lifespan of the first and second sealing rings under thermal aging is evaluated by the thermal effect of electric current and the frictional heat effect caused by vibration. Furthermore, fatigue damage also occurs under vibration conditions. By combining the thermal aging rate and fatigue damage, the overall lifespan of the first and second sealing rings is evaluated, making the prediction results more comprehensive and accurate.

[0063] If certain terms are used in the specification and claims to refer to specific components, those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The term "comprising" as used throughout the specification and claims is an open-ended term and should be interpreted as "comprising but not limited to." "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error.

[0064] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes that element.

[0065] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept by means of the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for predicting the lifespan of junction box seals based on heat and vibration, characterized in that, The junction box has a first sealing ring and a second sealing ring, and the steps are as follows: S100. Connect several assembled junction boxes to wires and place the wires in the notches of the first and second sealing rings. Then, energize the wires for different durations. Simultaneously, place the junction boxes in a vibration environment. Install acceleration sensors on the inner surfaces of the first and second sealing rings to obtain vibration values. Install temperature sensors around the notches of the first and second sealing rings or obtain the temperature at the notches using infrared sensors. Take the average of the temperature values ​​detected by each temperature sensor as the temperature rise T of the first and second sealing rings. The energizing time is consistent with the vibration time. S200. Calculate the heat Q1 at the notch based on the magnitude of the current and the energizing time, and calculate the temperature rise ΔT caused by the current based on the heat Q1. Calculate the frictional heat T' generated by the vibration based on the detected temperature rise T and ΔT, where T' = T - ΔT. S300. The actual thermal aging rate is calculated using ΔT, T, and T′. The lifespan of the first and second sealing rings is predicted based on the actual thermal aging rate. The formula for calculating the actual thermal aging rate is as follows: In the above formula, A is the pre-exponential factor; Ea is the activation energy, the minimum energy threshold required for the material to undergo thermal aging; R' is the ideal gas constant; α is the vibration-thermal synergy factor, and β is the current-thermal synergy factor. S400: Calculate fatigue damage based on vibration acceleration, and predict the lifespan of the first and second sealing rings based on fatigue damage and actual thermal aging rate.

2. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 1, characterized in that, The formula for calculating the electrical heat Q1 is as follows: Q1 = I 2 Rt, calculate the temperature rise caused by the current based on the generated heat Q1. The temperature rise calculation method is as follows: Where T a Here, k is the ambient temperature, t is the heat dissipation coefficient, m is the energizing time, and c is the mass of the first or second sealing ring. p This refers to the specific heat capacity of the first or second sealing ring.

3. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 1, characterized in that, In calculating the temperature rise caused by vibration, the heat Q2 generated by the vibration is first calculated using the following method: Q2 = μFVt, where μ is the coefficient of friction, F is the normal force on the first or second sealing ring, t is the vibration time, and V is the sliding velocity of the first and second sealing rings during vibration; the formula is: V = 2πfA vib Where f is the vibration frequency, A vib Let F be the amplitude, where F = ma, and a is the vibration acceleration. Then its temperature rise... m is the mass of the first or second sealing ring, and c p This refers to the specific heat capacity of the first or second sealing ring.

4. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 1, characterized in that, The dynamic stress of the first and second sealing rings is calculated based on the vibration acceleration using the formula: Δσ(t)=m·a(t)·SCF; then, the actual number of cycles n under the dynamic stress value Δσ(t) is obtained. i Then fatigue damage was calculated. in Where N i (T) represents the fatigue life of the material under dynamic stress Δσ(t) at the current temperature T; N0 represents the fatigue life at the reference temperature T0; q represents the temperature decay coefficient, which reflects the accelerated decay effect of temperature increase on fatigue life; and SCF represents the stress concentration factor.

5. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 4, characterized in that, The stress concentration factor (SCF) is measured using strain gauges.

6. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 4, characterized in that, The life calculation formula based on fatigue damage and actual thermal aging rate is: L = k thermal ·D mech / (k thermal +D mech ).

7. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 1, characterized in that, The pre-exponential factor A and activation energy Ea were obtained through aging experiments at different temperatures.

8. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 4, characterized in that, When calibrating the vibration-thermal synergy factor α, the first and second sealing rings are placed at the same temperature and different vibration conditions are applied for calibration.

9. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 5, characterized in that, The formula for calculating the stress concentration factor SCF under vibration conditions is: SCF = SCF'·k d , where k d is the dynamic amplification factor, with a value ranging from 1.2 to 2.0, and SCF' is the strain gauge measurement value.

10. The method for predicting the lifespan of a junction box sealing ring based on heat and vibration according to claim 9, characterized in that, k d The value is selected based on the following: the natural frequency f of the first and second sealing rings. n With vibration frequency f vib contrast: If f vib <f n k d ≈1.2; If f vib ≈f n k d ≈2.0; If f vib >f n k d ≈1.5.

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