Junction box sealing ring service life prediction method based on heat and vibration

Abstract

The invention relates to a junction box sealing ring service life prediction method based on heat and vibration, which comprises the following steps: connecting a plurality of assembled junction boxes to a wire, placing the wire in a notch groove of a first sealing ring and a second sealing ring, electrifying the wire at different times, and simultaneously placing the junction boxes in a vibration environment to predict the service life of the junction boxes. Acceleration sensors are arranged on the inner side faces of the first sealing ring and the second sealing ring and used for obtaining vibration numerical values, and temperature sensors are arranged around the notch grooves of the first sealing ring and the second sealing ring or the temperature of the notch grooves is obtained through infrared sensors; according to the invention, the service lives of the first sealing ring and the second sealing ring under thermal aging are evaluated through the current thermal effect and the friction thermal effect brought by vibration, and fatigue damage also occurs under the vibration condition, so that the overall service lives of the first sealing ring and the second sealing ring are evaluated by combining the thermal aging rate and the fatigue damage; and the prediction result is more comprehensive and accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of junction box sealing ring life detection, and in particular to a junction box sealing ring life prediction method based on heat and vibration. Background Art

[0002] like Figure 1 A junction box is shown, which has a first sealing ring and a second sealing ring. The first sealing ring and the second sealing ring 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 sealing ring and the second sealing ring. In addition, when the junction box is in a vibrating installation environment, corresponding vibrations will also be generated, causing frictional heat on the contact surface. For the first sealing ring and the second sealing ring, the heat will cause them to age, thereby reducing the sealing effect. Therefore, it is very necessary to predict their lifespan to guide production. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for predicting the life of a junction box sealing ring based on heat and vibration, so as to evaluate the life of the sealing ring under a working environment.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A method for predicting the life of a junction box sealing ring based on heat and vibration, wherein the junction box has a first sealing ring and a second sealing ring, the method comprises 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 energization times. Simultaneously, place the junction boxes in a vibration environment. Acceleration sensors are provided on the inner sides of the first and second sealing rings to obtain vibration values. Temperature sensors are provided around the notches of the first and second sealing rings or infrared sensors are used to obtain the temperature at the notches. The temperature values detected by the temperature sensors are averaged to obtain the temperature rise T of the first and second sealing rings. The energization time is consistent with the vibration time.

[0007] S200, calculating the electric heat amount Q1 at the notch according to the current and the power-on time, and calculating the temperature rise ΔT caused by the current based on the electric heat amount Q1, and calculating the friction heat T' generated by the vibration based on the detected temperature rise T and ΔT, where T'=T-ΔT;

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

[0009] In the above formula, A is the pre-exponential factor; Ea-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;

[0010] S400 , calculating fatigue damage according to vibration acceleration, and predicting the lifespan of the first sealing ring and the second sealing ring according to the fatigue damage and actual thermal aging rate.

[0011] The present invention further provides that the calculation formula of the electric heat Q1 is as follows Q1=I 2 Rt, calculates the temperature rise caused by the current based on the heat generated by Q1. The temperature rise is calculated as follows: Where T a is the ambient temperature, k is the heat dissipation coefficient, t is the power-on time, m is the mass of the first sealing ring or the second sealing ring, c p is the specific heat capacity of the first sealing ring or the second sealing ring.

[0012] The present invention further provides that, in the calculation of the temperature rise caused by vibration, the heat Q2 generated by the vibration is first calculated, and the calculation method is: Q2 = μFVt, where μ is the friction coefficient, F is the normal force exerted on the first sealing ring or the second sealing ring, t is the vibration time, and V is the sliding speed of the first sealing ring and the second sealing ring during vibration; the calculation formula is: V = 2πfA vib , where f is the vibration frequency, A vib is the amplitude, where F=ma, where a is the vibration acceleration, then the temperature rise m is the mass of the first sealing ring or the second sealing ring, c p is the specific heat capacity of the first sealing ring or the second sealing ring.

[0013] The present invention further provides that the dynamic stress of the first sealing ring and the second sealing ring is calculated according to the vibration acceleration, and the formula is: Δσ(t) = m·a(t)·SCF; then the actual number of cycles n under the dynamic stress value Δσ(t) is obtained. i , and then calculate the fatigue damage in where N i (T) is the fatigue life of the material under dynamic stress Δσ(t) at the current temperature T; N0 is the fatigue life at the reference temperature T0, q is the temperature attenuation coefficient, which reflects the accelerated attenuation effect of temperature increase on fatigue life, and SCF is the stress concentration factor.

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

[0015] The present invention further provides that the life calculation formula based on fatigue damage and actual thermal aging rate is: L = ktheermal ·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 calculation formula of the stress concentration factor SCF under vibration conditions is:

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

[0020] The present invention further arranges that k d The value of is selected according to the following: the natural frequency f of the first sealing ring and the second sealing ring n and 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] Beneficial effects of the present invention: In the present invention, the service life of the first sealing ring and the second sealing ring under thermal aging is evaluated by the thermal effect of electric current and the frictional thermal effect caused by vibration, and fatigue damage will also occur under vibration conditions. By combining the thermal aging rate and fatigue damage to evaluate the overall service life of the first sealing ring and the second sealing ring, the prediction results are more comprehensive and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1The structure of the junction box of the present invention is shown as follows Figure 1 .

[0027] Figure 2 The structure of the junction box of the present invention is shown as follows Figure 2 .

[0028] Reference numerals:

[0029] 10. Upper cover; 20. Base; 30. First sealing ring; 40. Second sealing ring; 50. Notch; 60. Wire opening; DETAILED DESCRIPTION

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

[0031] The junction box of the present invention is as follows Figure 1 As shown, it includes a top cover 10 and a base 20. One end of the top cover 10 and the base 20 are hinged, and the other end is interlocked when in use. A first sealing ring 30 is disposed within the top cover 10, and a second sealing ring 40 is disposed within the base 20. The first and second sealing rings 30 and 40 are each provided with a notch 50. The notch 50 forms a corresponding wire opening 60 on the top cover 10 and the base 20.

[0032] Based on the above-mentioned junction box, during 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, friction will also occur when the junction box is in a vibrating environment to generate frictional heat. Therefore, it is necessary to predict the life of the first sealing ring and the second sealing ring based on the above situation.

[0033] Based on the above first sealing ring and second sealing ring, as Figure 2 As shown, the present invention provides a method for predicting the life of a junction box sealing ring based on heat and vibration, wherein the junction box has a first sealing ring and a second sealing ring, and the steps are as follows:

[0034] S100. Connect several assembled junction boxes to wires, and place the wires in the notches of the first sealing ring and the second sealing ring. Then, energize the wires with different energization times. At the same time, place the junction box in a vibration environment. Set acceleration sensors on the inner sides of the first sealing ring and the second sealing ring to obtain vibration values. Set temperature sensors around the notches of the first sealing ring and the second sealing ring or use infrared sensors to obtain 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 sealing ring and the second sealing ring. There are 6 notches on each of the first sealing ring and the second sealing ring. Therefore, when calculating the temperature rise of the first sealing ring and the second sealing ring, for the first sealing ring, the temperatures of the temperature sensors at the 6 notches are obtained and then averaged. That is, if the 6 temperature values are T1, T2, T3, T4, T5, and T6, then T = (T1+T2+T3+T4+T5+T6) / 6. The calculation of the temperature rise T of the second sealing ring is similar. The energization time is consistent with the vibration time.

[0035] S200, calculating the electric heat amount Q1 at the notch according to the current and the power-on time, and calculating the temperature rise ΔT caused by the current based on the electric heat amount Q1, and calculating the friction heat T' generated by the vibration based on the detected temperature rise T and ΔT, where T'=T-ΔT;

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

[0037] In the above formula, A is the pre-exponential factor; Ea is the activation energy, which is 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; T is the ambient temperature of the first and second sealing rings, which is an absolute temperature. Therefore, when calculating, T' and ΔT also need to be converted into absolute temperature.

[0038] S400 , calculating fatigue damage according to vibration acceleration, and predicting the lifespan of the first sealing ring and the second sealing ring according to the fatigue damage and actual thermal aging rate.

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

[0040] The experimental process is as follows:

[0041] Obtain a certain amount of the first sealing ring and place it in a constant temperature box at different temperatures: 40℃, 60℃, 80℃, 100℃, 120℃, and record the time t when the hardness drops to 50%. fail , then according to the formula Perform linear fitting and combine t fail ∝1 / k and the data obtained in this experiment are as follows:

[0042]

[0043] According to the formula Convert to Then perform linear fitting, that is The intercept is ln(C / A), the slope is Ea / R', the slope value obtained after fitting is 10200K, the intercept is 5.80, and thus Ea=10200K·8.314J / (mol·K)≈84.8J / mol, C is the proportionality constant, which is 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 calibrated under different vibration conditions. The specific methods are as follows:

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

[0046] Place the first and second sealing rings in an environment with a temperature of 100°C and test the sealing ring life at vibration frequencies of 50Hz, 100Hz, and 150Hz respectively; the above life is calculated based on the failure time of the first and second sealing rings. After obtaining the failure time, use the formula Calculate the value of α, k in the above formula thermal Calculated by failure time.

[0047] The current-heat synergy factor β is then calibrated as follows: the junction box is placed in a constant temperature environment, without vibration or under the same vibration conditions, and then different currents are passed through it, specifically set to 5A, 10A, and 15A. The power-on time is kept the same, and the temperature rise at the notch is measured using a temperature sensor or infrared thermometer. Similarly, the failure time t of the sealing ring under different temperature rises is recorded. fail , under vibration-free conditions, the aging formula is simplified to: ΔT), perform linear regression based on experimental data and transform the formula into: by The vertical axis is ΔT, the horizontal axis is ΔT, and the slope β is fitted by linear regression. The experimental data obtained are as follows:

[0048]

[0049] The fitting was performed based on the above data, and the slope after fitting was β = 0.018°C-1.

[0050] Specifically: In this embodiment, the calculation formula of the electric heat Q1 is as follows: Q1 = I 2 Rt, calculates the temperature rise caused by the current based on the heat generated by Q1. The temperature rise is calculated as follows: Where T a is the ambient temperature, k is the heat dissipation coefficient, t is the power-on time, m is the mass of the first sealing ring or the second sealing ring, c p is the specific heat capacity of the first sealing ring or the second sealing ring.

[0051] In addition, in the present embodiment, in the calculation of the temperature rise caused by vibration, the heat Q2 generated by the vibration is first calculated, and the calculation method is: Q2 = μFVt, where μ is the friction coefficient, F is the normal force exerted on the first sealing ring or the second sealing ring, t is the vibration time, and V is the sliding speed of the first sealing ring and the second sealing ring during vibration; the calculation formula is: V = 2πfA vib , where f is the vibration frequency, A vib is the amplitude, where F=ma, where ma is the vibration acceleration, then the temperature rise m is the mass of the first sealing ring or the second sealing ring, c p is the specific heat capacity of the first sealing ring or the second sealing ring.

[0052] The present invention further provides that the dynamic stress of the first sealing ring and the second sealing ring is calculated according to the vibration acceleration, and the formula is: Δσ(t) = m·a(t)·SCF; then the actual number of cycles n under the dynamic stress value Δσ(t) is obtained. i , and then calculate the fatigue damage in where N i (T) is the fatigue life of the material under dynamic stress Δσ(t) at the current temperature T; N0 is the fatigue life at the reference temperature T0, q is the temperature attenuation coefficient, which reflects 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°C, 50°C, and 75°C, and the number of cycles N corresponding to the dynamic stress Δσ was recorded. i (T);

[0054] For ln(N i (T))=ln (N0)-q(T-T0) for linear regression, and calibration is also performed through experiments. The experimental data are as follows:

[0055]

[0056] According to the above data fitting, we can get q = 0.0277 °C -1 The stress concentration factor SCF is measured by strain gauge. The life calculation formula based on fatigue damage and actual thermal aging rate is: L = k thermal ·D mech / (k thermal +D mech );

[0057] The calculation formula of stress concentration factor SCF under vibration conditions is:

[0058] SCF=SCF'·k d , where k d is the dynamic amplification factor, which is 1.2-2.0, SCF' is the strain gauge measurement value; k d The value of is selected according to the following: the natural frequency f of the first sealing ring and the second sealing ring n and 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 the present invention, the life of the first and second sealing rings under thermal aging is evaluated by the thermal effect of current and the frictional thermal effect caused by vibration. Fatigue damage will also occur under vibration conditions. By combining the thermal aging rate and fatigue damage to evaluate the overall life of the first and second sealing rings, the prediction results are more comprehensive and accurate.

[0063] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of the components as the criteria for distinction. For example, "including" mentioned throughout the specification and claims is an open term and should be interpreted as "including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve technical problems within a certain error range and basically achieve technical effects.

[0064] It should be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or system comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or system. In the absence of further limitations, an element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the product or system comprising the element.

[0065] The foregoing description shows and describes several preferred embodiments of the present invention. However, as previously mentioned, 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. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the present invention through the above teachings or through technology or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A method for predicting the life of a junction box sealing ring 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 energization times. Simultaneously, place the junction boxes in a vibration environment. Acceleration sensors are provided on the inner sides of the first and second sealing rings to obtain vibration values. Temperature sensors are provided around the notches of the first and second sealing rings or infrared sensors are used to obtain the temperature at the notches. The temperature values detected by the temperature sensors are averaged to obtain the temperature rise T of the first and second sealing rings. The energization time is consistent with the vibration time. S200, calculating the electric heat amount Q1 at the notch according to the current and the power-on time, and calculating the temperature rise ΔT caused by the current based on the electric heat amount Q1, and calculating the friction heat T' generated by the vibration based on the detected temperature rise T and ΔT, where T'=T-ΔT; S300, calculating the actual thermal aging rate using ΔT, T, and T′. The lifespan of the first sealing ring and the second sealing ring is predicted based on the actual thermal aging rate. The calculation formula for the actual thermal aging rate is as follows: In the above formula, A is the pre-exponential factor; Ea-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; S400 , calculating fatigue damage according to vibration acceleration, and predicting the lifespan of the first sealing ring and the second sealing ring according to the fatigue damage and actual thermal aging rate.

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

3. The method for predicting the life of a junction box sealing ring based on heat and vibration according to claim 1, characterized in that: In the calculation of temperature rise caused by vibration, the heat Q2 generated by vibration is calculated first. The calculation method is: Q2 = μFVt, where μ is the friction coefficient, F is the normal force on the first sealing ring or the second sealing ring, t is the vibration time, and V is the sliding speed of the first sealing ring and the second sealing ring during vibration. The calculation formula is: V = 2πfA vib , where f is the vibration frequency, A vib is the amplitude, where F=ma, where a is the vibration acceleration, then the temperature rise m is the mass of the first sealing ring or the second sealing ring, c p is the specific heat capacity of the first sealing ring or the second sealing ring.

4. The method for predicting the life 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. The formula is: Δσ(t) = m·a(t)·SCF. Then, the actual number of cycles n under the dynamic stress value Δσ(t) is obtained. i , and then calculate the fatigue damage in where N i (T) is the fatigue life of the material under dynamic stress Δσ(t) at the current temperature T; N0 is the fatigue life at the reference temperature T0, q is the temperature attenuation coefficient, which reflects the accelerated attenuation effect of temperature increase on fatigue life, and SCF is the stress concentration factor.

5. The method for predicting the life 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 a strain gauge.

6. The method for predicting the life 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 life 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 life 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 sealing ring and the second sealing ring are placed at the same temperature and calibrated under different vibration conditions.

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

10. The method for predicting the life of a junction box sealing ring based on heat and vibration according to claim 9, characterized in that: k d The value of is selected according to the following: the natural frequency f of the first sealing ring and the second sealing ring n and 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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