A kind of pull rivet nut air-tightness detection device and detection method

Abstract

The application discloses a kind of pull rivet nut air-tight detection device and detection method;The present application receives and amplifies the low-energy, wide-frequency excitation output by vibration table, and converts into narrow-frequency, high-energy force transmission to the measured nut joint part, using the cross-sectional size of the stepped reducing taper frequency conversion plate to realize the focusing of vibration energy and the guiding distribution of harmonic mode, so that high-frequency vibration is compressed layer by layer in the transmission process and forms an energy concentration area at the end, thereby effectively improving the resonance excitation efficiency of the micro pull rivet nut joint part, and then triggering the natural frequency response of the micro pull rivet nut;At the same time, according to the difference between the volume expansion effect caused by creep and the real leakage signal, false positives or false negatives are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pull nut air tightness detection, and particularly relates to a pull nut air tightness detection device and a detection method. BACKGROUND

[0002] With the continuous pursuit of modern industry for product precision, miniaturization and integration, the micro connecting parts represented by pull nuts are increasingly widely used in high-tech fields such as automobiles, electronics, aerospace, etc. These micro components usually bear the key functions of connection, fixation or sealing, and their performance, especially air tightness, is directly related to the reliability, safety and service life of the whole machine. In the actual application environment, these components are often affected by various dynamic loads, especially high-frequency vibrations.

[0003] Therefore, rigorous and accurate detection of the air tightness of the micro pull nut under simulated vibration conditions has become an indispensable important link in the product quality control process. Effective air tightness detection not only can timely find potential manufacturing defects, but also can predict the failure risk of the product under complex working conditions, thereby providing solid protection for improving the overall performance of the product and reducing the maintenance cost in the later period. SUMMARY

[0004] The present application overcomes the shortcomings of the prior art and provides a pull nut air tightness detection device and a detection method.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a pull nut air tightness detection device, comprising: an air tightness detection mechanism, a vibration excitation mechanism, and a frequency conversion mechanism.

[0006] The air tightness detection mechanism comprises: an air tightness detection cavity, a sealing plate arranged in the middle of the air tightness detection cavity, and the air tightness detection cavity is divided into a first cavity and a second cavity; wherein a through hole for mounting a pull nut is formed on the sealing plate.

[0007] The air tightness detection mechanism further comprises: an adjustment unit and a detection unit.

[0008] The adjustment unit adjusts the pressure of the second cavity in real time according to the creep pressure-time curve of the first cavity to suppress the creep of the first cavity.

[0009] The creep pressure-time curve setting comprises: loading the pressure steps of the first cavity, keeping the pressure in the second cavity constant at each step loading stage, and collecting the pressure change signal of the first cavity in real time within each step duration to obtain the creep pressure-time curve of the first cavity under the constant pressure.

[0010] The detection unit is used for detecting the air inlet and outlet amount and pressure change of the first cavity and the second cavity in real time.

[0011] The vibration excitation mechanism is used for generating mechanical vibration with preset frequency and amplitude.

[0012] The frequency conversion mechanism is arranged between the vibration excitation mechanism and the air tightness detection cavity, is installed at the vibration table position of the vibration excitation mechanism, is used for receiving and amplifying the vibration excitation output by the vibration excitation mechanism, and is used for converting the vibration excitation into dynamic excitation acting on the air tightness detection cavity.

[0013] In a preferred embodiment of the present application, the first cavity is provided with an air inlet, and the second cavity is provided with an air outlet.

[0014] In a preferred embodiment of the present application, the air inlet and the air outlet are both provided with a gas flow sensor, and the first cavity and the second cavity are both provided with a pressure sensor.

[0015] In a preferred embodiment of the present application, the vibration excitation mechanism comprises an electromagnetic vibration table or a hydraulic vibration table, and the vibration excitation frequency range of the vibration table covers 10 Hz to 5000 Hz.

[0016] The table surface of the vibration table is provided with a mounting interface, which is used for fixing the frequency conversion mechanism through bolt connection.

[0017] In a preferred embodiment of the present application, the frequency conversion mechanism comprises a plurality of tapered frequency conversion plates and a plurality of frequency conversion parts.

[0018] The plurality of tapered frequency conversion plates are symmetrically arranged, and the plurality of tapered frequency conversion plates are fixedly connected to the air tightness detection cavity near one end.

[0019] The plurality of frequency conversion parts are installed on the corresponding tapered frequency conversion plates and move towards or away from each other.

[0020] The frequency conversion part comprises a moving sleeve, a damping block symmetrically installed in the inner cavity of the moving sleeve, and an adjusting rod penetrating through the damping block and the moving sleeve.

[0021] The adjusting rod is symmetrically provided with threads, and the screw lines of the symmetrically arranged threads are opposite in direction.

[0022] The symmetrically arranged damping blocks are respectively sleeved on the threads opposite in screw line direction and are threadedly connected with the adjusting rod.

[0023] The adjusting rod is rotationally connected with the moving sleeve.

[0024] In a preferred embodiment of the present application, the tapered frequency conversion plate is arranged in a stepped diameter reduction structure close to the airtight detection cavity.

[0025] An airtight detection method for a pull nut, comprising the following steps:

[0026] Step S1, a low-energy vibration excitation signal is applied to the pull nut joint of the airtight detection cavity, and the vibration excitation signal acting on the pull nut joint is received and amplified, wherein there is a sealing plate in the airtight detection cavity, which divides the airtight detection cavity into a first cavity and a second cavity, and the pull nut is installed on the sealing plate;

[0027] Step S2, based on the creep pressure-time curve of the first cavity, the limiting differential pressure between the first cavity and the second cavity for inhibiting creep is calculated, and the pressure in the second cavity is controlled according to the limiting differential pressure, thereby forming a differential pressure double cavity;

[0028] Step S3, the pressure change in the differential pressure double cavity is monitored in real time, and the air intake of the first cavity and the second cavity is adjusted according to the creep pressure-time curve, so that the double cavity is always in a differential pressure state, and the creep of the first cavity is inhibited;

[0029] Step S4, whether there is a leakage phenomenon at the position of the pull nut joint is judged by correlating the air intake of the first cavity and the second cavity.

[0030] In a preferred embodiment of the present application, in the step S2, the following sub-steps are included:

[0031] Step S21, a first cavity loading pressure step sequence is set, and the pressure in the second cavity is kept constant at each step loading stage, and the pressure change signal of the first cavity is collected in real time within each step duration;

[0032] Step S22, the pressure change signal of the constant pressure in the first cavity within each time period is recorded, and the creep pressure-time curve of the first cavity under the constant pressure is obtained;

[0033] Step S23, the difference between the pressure of each time period and the initial pressure of the first cavity is the limiting differential pressure;

[0034] Step S24, according to the limiting differential pressure of the current time period, the pressure in the second cavity within the previous time period is increased in real time to inhibit the creep of the first cavity.

[0035] In a preferred embodiment of the present application, according to the limiting differential pressure of the current time period, the pressure in the second cavity within the previous time period is increased, i.e. the air intake of the second cavity is increased, so that the double cavity is always in a differential pressure state, and the creep of the first cavity is inhibited.

[0036] In a preferred embodiment of the present application, in the step S4, the air intake of the second cavity in the current time period is increased in real time according to the limit differential pressure obtained from the creep pressure-time curve, the creep of the first cavity is inhibited, and whether the position of the rivet nut assembly has a leakage phenomenon is judged based on the pressure change of the first cavity.

[0037] If the pressure of the first cavity is always maintained in the specified range, the position of the rivet nut assembly does not have a leakage phenomenon; otherwise, the position of the rivet nut assembly has a leakage phenomenon.

[0038] The present application solves the defects in the background art and has the following beneficial effects:

[0039] (1) The present application provides a rivet nut air tightness detection device, which can receive and amplify the low-energy, wide-frequency excitation output by the vibration table through the setting of the stepped reducing taper frequency conversion plate and the adjustable damping component, and convert it into narrow-frequency, high-energy force to be transmitted to the measured nut joint part. The stepped reducing taper frequency conversion plate realizes the focusing of vibration energy and the guided distribution of harmonic mode by gradually reducing the cross-sectional size, compresses the high-frequency vibration layer by layer in the transmission process, and forms an energy concentration area at the end, thereby effectively improving the resonance excitation efficiency of the micro rivet nut joint part, triggering the natural frequency response of the micro rivet nut, significantly amplifying the local strain and stress concentration, solving the technical bottleneck that small mass high-frequency parts are difficult to be effectively driven, realizing high-precision energy coupling under lower excitation power, and enabling the device to maintain stable resonance amplification performance when dealing with test pieces of different sizes and different natural frequencies, thereby simulating the high-frequency fatigue stress environment of the nut under real working conditions, and making the detection result highly consistent with the actual failure mode.

[0040] (2) The present application provides a rivet nut air tightness detection method, which introduces multi-stage step constant pressure loading during the detection process, maintains constant pressure at each step stage, and records the change of the pressure of the first cavity with time, constructs a creep pressure-time curve, captures the slow volume expansion and pressure decay process of the shell under continuous constant pressure stress in a time sequence manner, and then forms a curve index reflecting the creep rate, which is used as a creep criterion. According to the change of the curve slope, the creep condition of the first cavity in this time period is determined, which can accurately identify the difference between the volume expansion effect caused by creep and the real leakage signal, and avoid misjudgment or omission.

[0041] (3) The application provides a pull rivet nut air tightness detection method, the minimum differential pressure value capable of inhibiting the creep of the first cavity is determined through a creep pressure-time curve, and the value is taken as the limit differential pressure of the double-cavity pressure control, the minimum differential pressure value can be dynamically adjusted according to the creep of the first cavity, the creep of the first cavity is inhibited, and then the internal pressure change caused by the creep of the first cavity is avoided, the misjudgment between the volume expansion effect caused by the creep and the real leakage signal is avoided, and the accuracy of the pull rivet nut air tightness detection is further improved.

[0042] (4) The application provides a pull rivet nut air tightness detection method, the pressure in the second cavity is adjusted in real time according to the dynamic limit differential pressure, the first cavity and the second cavity always maintain differential pressure under the premise of inhibiting the creep of the first cavity, the gas flow deviation and pressure fluctuation caused by leakage can be amplified, the lag problem that a signal can be shown only after a long time pressure drop accumulation in the traditional detection is avoided, the response speed of the leakage signal is improved, the detection rate is changed from chronic pressure drop observation to rapid differential pressure response, and the detection period is greatly shortened. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor;

[0044] Figure 1 is a front view structural diagram of the preferred embodiment of the application;

[0045] Figure 2 is a top view structural diagram of the preferred embodiment of the application;

[0046] Figure 3 is a frequency modulation part structural diagram of the preferred embodiment of the application;

[0047] Figure 4 is an air tightness detection cavity internal structure diagram of the preferred embodiment of the application;

[0048] In the figure: 1, air tightness detection cavity; 2, sealing plate; 3, first cavity; 4, second cavity; 5, pull rivet nut; 6, vibration excitation mechanism; 7, air inlet; 8, air outlet; 9, conical frequency conversion plate; 10, moving sleeve; 11, damping block; 12, adjusting rod. DETAILED DESCRIPTION

[0049] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described, obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the protection scope of the present application.

[0050] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other manners different from those described herein, therefore, the protection scope of the present application is not limited to the specific embodiments disclosed below.

[0051] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the protection scope of the present application. In addition, the terms "first", "second" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified and limited, the term "a plurality of" means two or more.

[0052] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connecting", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the communication between the two elements inside. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0053] In order to simulate the dynamic stress in the real use environment, the measured part is often placed on a vibration table, and a vibration excitation with a preset frequency and amplitude is applied to evaluate the sealing stability under dynamic conditions. However, the general vibration table commonly used in the prior art has a frequency range usually designed below 2000Hz or 5000Hz to meet various test requirements. Although these vibration tables can provide a certain frequency range, it is difficult to simultaneously output sufficient energy at such a high frequency to drive the micro components to resonate, which faces a severe technical bottleneck.

[0054] Applicants found that, for micro pull nut air tightness detection, due to its extremely small mass and relatively high material stiffness, it often has very high natural frequency. To make these micro components effectively simulate the high-frequency resonance stress in the real environment under vibration conditions, the key is to drive them to the vicinity of their natural frequency, so as to excite the resonance effect. In the resonance state, even if the external excitation energy is relatively small, it can also produce significant strain and stress concentration inside the component, thereby effectively revealing potential sealing defects.

[0055] As shown in Figure 1 and Figure 4 , a pull nut air tightness detection device, comprising: an air tightness detection mechanism, a vibration excitation mechanism, a frequency conversion mechanism;

[0056] The air tightness detection mechanism comprises: an air tightness detection cavity 1, a sealing plate 2 arranged in the middle of the air tightness detection cavity 1, and the air tightness detection cavity 1 is divided into a first cavity 3 and a second cavity 4; wherein the sealing plate 2 is provided with a through hole for installing a pull nut 5;

[0057] By dividing the air tightness detection cavity 1 into the first cavity 3 and the second cavity 4, a pressure difference can be generated between the two cavities, so as to amplify the gas flow deviation and pressure fluctuation caused by leakage, avoid the lag problem that the signal must be accumulated for a long time in the traditional detection, improve the response speed of the leakage signal, and change the detection rate from chronic pressure drop observation to fast differential pressure response, thereby greatly shortening the detection period.

[0058] The air tightness detection mechanism further comprises: an adjusting unit and a detection unit;

[0059] The adjusting unit adjusts the pressure of the second cavity in real time according to the creep pressure-time curve of the first cavity, so as to suppress the creep of the first cavity;

[0060] The creep pressure-time curve setting comprises: loading a pressure intensity step sequence in the first cavity, keeping the pressure in the second cavity constant at each step loading stage, and collecting the pressure change signal of the first cavity in real time within each step duration, to obtain the creep pressure-time curve of the first cavity under the constant pressure;

[0061] The detection unit is used to detect the gas inlet and outlet amount and the pressure change of the first cavity and the second cavity in real time.

[0062] Specifically, the pressure in the second cavity 4 is first set constant, the pressure of the first cavity 3 is selected, the change of the pressure in the first cavity 3 in a detection time range is detected, and the detection time range is divided into several time periods to obtain the pressure change difference value of the first cavity 3 in each time period and the total difference value between the pressure of the first cavity 3 after the creep is completed and the initial pressure; wherein the total difference value between the pressure of the first cavity 3 during the creep process and the initial pressure is the limit differential pressure;

[0063] By analogy, different pressures of the first cavity 3 are selected for testing, and different constant pressures of the second cavity 4 are selected for testing, and the test results are counted to obtain the creep pressure-time curve.

[0064] In the actual detection process, the total difference value between the pressure of the first cavity 3 in the subsequent time period during the creep process and the initial pressure is obtained according to the creep pressure-time curve, and the pressure in the second cavity 4 is increased by this difference value to inhibit the creep of the first cavity 3;

[0065] The minimum differential pressure value capable of inhibiting the creep of the first cavity 3 is determined through the creep pressure-time curve, and the value is taken as the limit differential pressure of the double-cavity pressure control. The minimum differential pressure value can be dynamically adjusted according to the creep of the first cavity 3 to inhibit the creep of the first cavity 3, thereby avoiding the misjudgment between the volume expansion effect caused by the creep of the first cavity 3 and the real leakage signal due to the change of the internal pressure of the first cavity 3, and further improving the accuracy of the air tightness detection of the pull nut 5.

[0066] The vibration excitation mechanism 6 is used to generate mechanical vibration of a preset frequency and amplitude;

[0067] The vibration excitation mechanism 6 mainly undertakes the task of generating mechanical vibration of a preset frequency and amplitude. Specifically, the vibration excitation mechanism 6 includes an electromagnetic vibration table or a hydraulic vibration table, and the excitation frequency range of the vibration table covers 10 Hz to 5000 Hz.

[0068] The table surface of the vibration table is provided with a mounting interface for fixing the frequency conversion mechanism by bolt connection.

[0069] For example, an electromagnetic vibration table with a maximum excitation force of 2000 N, a maximum peak acceleration of 100 g gravity acceleration, and a speed of 980 m / s 2 The effective excitation frequency range of the vibration table covers 10 Hz-5000 Hz, and the frequency and amplitude of the output vibration can be accurately controlled, with a frequency control accuracy of ±0.1 Hz and an amplitude control accuracy of ±0.5%;

[0070] The table surface of the vibration table is made of high-strength aluminum alloy or magnesium alloy material and is precisely machined and roughened to ensure rigid and stable connection with the frequency conversion mechanism.

[0071] Considering that it is difficult for the vibration table to provide sufficient energy to drive the micro pull nut 5 to resonance, a frequency conversion mechanism is arranged to amplify the frequency of the vibration table vibration, wherein the frequency conversion mechanism is arranged between the vibration excitation mechanism 6 and the airtight detection cavity 1, is installed at the vibration table position of the vibration excitation mechanism 6, is used to receive and amplify the vibration excitation output by the vibration excitation mechanism 6, and converts the vibration excitation into dynamic excitation acting on the airtight detection cavity 1.

[0072] As shown in Figure 3 , the frequency conversion mechanism comprises: a plurality of tapered frequency conversion plates 9, and a plurality of frequency conversion parts;

[0073] The plurality of tapered frequency conversion plates 9 are symmetrically arranged, and the plurality of tapered frequency conversion plates 9 are fixedly connected to the airtight detection cavity 1 near one end;

[0074] The plurality of frequency conversion parts are installed on the corresponding tapered frequency conversion plates 9 and move towards or away from each other;

[0075] The tapered frequency conversion plates 9 are arranged in pairs or multiple pairs of symmetry, are rigidly connected to the airtight detection cavity 1 near one end, and are responsible for guiding the broadband and low-energy excitation of the vibration table into the plates to form a controllable modal amplification path.

[0076] The frequency conversion part comprises: a moving sleeve 10, a damping block 11 symmetrically installed in the inner cavity of the moving sleeve 10, and an adjusting rod 12 penetrating through the damping block 11 and the moving sleeve 10;

[0077] The adjusting rod 12 is symmetrically provided with threads, and the symmetrically arranged threads have opposite screw line directions;

[0078] The symmetrically arranged damping blocks 11 are respectively sleeved on the threads with opposite screw line directions and are threadedly connected with the adjusting rod 12;

[0079] The adjusting rod 12 is rotationally connected with the moving sleeve 10.

[0080] The frequency conversion part is fixed to the vibration table by bolts, and a plurality of threaded holes are arranged on the vibration table to facilitate the movement of the frequency conversion part on the tapered frequency conversion plate 9, thereby adjusting the amplified frequency of the tapered frequency conversion plate 9.

[0081] By controlling the approach or distance of the frequency conversion part to the tapered frequency conversion plate 9, dynamic adjustment of the frequency can be realized, mainly because the movement of the frequency conversion part changes the stress distribution and coupling stiffness on the tapered frequency conversion plate 9, so that the natural frequency of the system shifts;

[0082] When the frequency conversion part approaches, the forced constraint of the tapered plate is enhanced, the equivalent stiffness of the plate body is increased, and the natural frequency is shifted to the high frequency direction; when the frequency conversion part moves away, the constraint is weakened, the plate body returns to the free vibration characteristics, and the natural frequency is reduced.

[0083] The frequency modulation mechanism has real-time adaptive capability, can quickly match the optimal excitation frequency according to the size, material and defect characteristics of different measured parts, thereby improving the robustness and accuracy of detection, and reducing the dependence on external electric control devices.

[0084] It should be noted that when the frequency modulation part moves on the tapered frequency conversion plate 9, the bolts fixing the frequency modulation part and the vibration table are loosened, the adjusting rod 12 is rotated, the damping blocks 11 are driven away from each other, the frequency modulation part is moved to the designated position, and the frequency modulation part is fixed on the vibration table. The adjusting rod 12 is driven again, the symmetrically arranged damping blocks 11 are driven to approach each other and contact the tapered frequency conversion plate 9; the frequency modulation of the tapered frequency conversion plate 9 is completed.

[0085] As shown in Figure 2 In the present application, the tapered frequency conversion plate 9 is arranged in a stepped reducing diameter structure close to the airtight detection cavity 1.

[0086] The tapered frequency conversion plate 9 with stepped reducing diameter realizes the focusing of vibration energy and the guided distribution of resonance mode by gradually reducing the cross-sectional size, so that the high-frequency vibration is compressed layer by layer in the transmission process and forms an energy concentration area at the end, thereby effectively improving the resonance excitation efficiency of the micro pull nut 5 joint part, and triggering the natural frequency response of the micro pull nut 5, significantly amplifying the local strain and stress concentration;

[0087] Further solve the technical bottleneck that small mass high frequency parts are difficult to be effectively driven, realize high precision energy coupling under lower excitation power, so that the device can still maintain stable resonance amplification performance when dealing with test pieces of different sizes and different natural frequencies, and further simulate the high-frequency fatigue stress environment of the nut under real working conditions, so that the detection result is highly consistent with the actual failure mode.

[0088] In the present application, the first cavity 3 is provided with an air inlet 7, and the second cavity 4 is provided with an air outlet 8.

[0089] In the present application, gas flow sensors are arranged at the positions of the air inlet 7 and the air outlet 8, and pressure sensors are arranged in the first cavity 3 and the second cavity 4.

[0090] A pull nut airtight detection method, comprising the following steps:

[0091] Step S1, a low-energy vibration excitation signal is applied to the pull nut 5 joint part of the airtight detection cavity 1, and the vibration excitation signal is received and amplified to act on the pull nut 5 joint part, wherein the airtight detection cavity 1 is divided into a first cavity 3 and a second cavity 4 by a sealing plate 2, and the pull nut 5 is installed on the sealing plate 2;

[0092] The low-energy vibration excitation signal is applied at the pull nut 5 joint of the airtight detection cavity 1, and the signal is amplified and focused by the frequency conversion mechanism, so that it effectively acts on the nut part to be detected.

[0093] The core is to utilize the low-energy, wide-band vibration table output, and through the impedance matching and frequency conversion of the tapered frequency conversion board 9 and the frequency conversion part, the excitation energy is effectively amplified and concentrated near the inherent frequency at the nut joint part.

[0094] Because the micro pull nut 5 has small mass and high stiffness, the inherent frequency is often high, and if only relying on the direct loading of the general vibration table, the energy is difficult to be effectively coupled, and the resonance effect cannot be triggered; and through the signal application and conversion of the present step, the nut joint area can realize significant strain response and stress concentration under low power condition.

[0095] The high-frequency resonance stress that the nut may encounter in actual working conditions can be fully simulated in the early detection stage, so that potential sealing defects are exposed in advance due to stress amplification. Compared with the existing simple pressurization or single-cavity vibration method, the excitation method of the present application avoids energy attenuation and frequency mismatch in the transmission process, and significantly improves the coupling efficiency between the excitation and the measured part.

[0096] Further effect is that the method not only improves the detection sensitivity of micro leakage, but also ensures that the detection result is closer to the failure mode of the nut in the real application environment, thereby improving the reliability and accuracy of the airtightness detection, and laying a solid dynamic stress loading foundation for subsequent differential pressure maintenance and leakage judgment.

[0097] Step S2, based on the creep pressure-time curve of the first cavity 3, and the limit differential pressure of the first cavity 3 and the second cavity 4 is calculated, the pressure in the second cavity 4 is controlled according to the limit differential pressure, and then the differential pressure double cavity is formed;

[0098] In step S2, the following sub-steps are included:

[0099] Step S21, set the first cavity 3 loading pressure step sequence, and keep the pressure in the second cavity 4 constant in each step loading stage, and in each step duration, real-time acquisition of the pressure change signal of the first cavity 3;

[0100] Step S22, record the pressure change signal of the first cavity 3 under constant pressure in each time period, and obtain the creep pressure-time curve of the first cavity 3 under the constant pressure;

[0101] Step S23, the difference between the pressure of each time period and the initial pressure of the first cavity 3 is the limit differential pressure;

[0102] Step S24, according to the limit differential pressure of the current time period, the pressure in the second cavity 4 in the previous time period is increased in real time, and the creep of the first cavity 3 is inhibited.

[0103] Wherein, the creep pressure refers to the creep phenomenon of the cavity within the specified detection time threshold under constant pressure;

[0104] The limit differential pressure is the difference between the creep pressure of the first cavity 3 and the pressure of the second cavity 4.

[0105] In step S2, considering that the cavity may have a creep phenomenon after being filled with high-pressure gas, resulting in an increase in the volume of the cavity and a decrease in the pressure in the cavity, and the part of the pressure that is reduced is easy to be defined as the leakage of the rivet nut 5, because in order to accurately detect the air tightness of the rivet nut 5, the creep phenomenon of the cavity needs to be considered.

[0106] Specifically, the relationship between the creep pressure of the first cavity 3 and the time, and the pressure of the second cavity 4 needs to be obtained, for example:

[0107] First, the pressure in the second cavity 4 is set to be constant, the pressure of the first cavity 3 is selected, the change of the pressure in the first cavity 3 within the detection time range is detected, and the detection time range is divided into several time periods, the difference of the pressure change in the first cavity 3 in each time period is obtained, and the total difference between the pressure after the creep of the first cavity 3 is completed and the initial pressure; wherein, the total difference between the pressure during the creep of the first cavity 3 and the initial pressure is the limit differential pressure;

[0108] By analogy, different pressures of the first cavity 3 are selected for testing, and different constant pressures of the second cavity 4 are selected for testing, and the statistics are obtained, which can obtain the creep pressure-time curve.

[0109] During the detection process, multi-stage step constant pressure loading is introduced, and the pressure of the first cavity 3 is recorded at each step stage, and the creep pressure-time curve is constructed, the slow volume expansion and pressure decay process of the shell under continuous constant pressure stress are captured in time sequence, and then the curve index reflecting the creep rate is formed, and the curve is used as the creep criterion, the creep of the first cavity 3 in this time period is determined according to the change of the slope of the curve, and the difference between the volume expansion effect caused by the creep and the real leakage signal can be accurately identified, and false judgment or omission is avoided.

[0110] In the actual detection process, the total difference between the pressure in the first cavity 3 during the creep process in the next time period and the initial pressure is obtained according to the creep pressure-time curve, and the pressure in the second cavity 4 in this time period is increased by this difference, so as to inhibit the creep of the first cavity 3.

[0111] The minimum differential pressure value capable of inhibiting the creep of the first cavity 3 is determined through the creep pressure-time curve, and this value is taken as the limit differential pressure of the dual-cavity pressure control. The minimum differential pressure value can be dynamically adjusted according to the creep of the first cavity 3 to inhibit the creep of the first cavity 3, thereby avoiding the internal pressure change of the first cavity 3 due to the creep, avoiding the misjudgment between the volume expansion effect caused by the creep and the real leakage signal, and further improving the accuracy of the air tightness detection of the pull nut 5.

[0112] In summary, by proposing the creep pressure-time curve of the first cavity 3, the limit differential pressure capable of inhibiting the creep between the first cavity 3 and the second cavity 4 is calculated, and the limit differential pressure is taken as the control reference of the second cavity 4, thereby forming a differential pressure dual-cavity.

[0113] First, the response of the first cavity 3 under different constant pressure loading conditions is monitored step by step to establish a creep-time curve to reveal the slow deformation law of the material under constant pressure stress. In this process, the system can distinguish the pressure drop rate caused by volume expansion and distinguish it from the leakage signal.

[0114] If the single-cavity pressure drop monitoring is directly relied on, the slow pressure decay caused by material creep will mask or even fake the leakage phenomenon, seriously affecting the detection reliability. By introducing the limit differential pressure threshold, when the pressure difference maintained by the second cavity 4 is greater than the limit differential pressure, the creep deformation in the first cavity 3 will be effectively inhibited, and the pressure change will only reflect the real leakage channel effect.

[0115] Based on the limit differential pressure compensation of the second cavity 4 pressure, the creep of the first cavity 3 is inhibited, the detection baseline is more stable, false signals caused by material compliance or temperature rise are avoided, and the accuracy of leakage judgment is improved.

[0116] Compared with the simple constant pressure method or single-cavity method in the prior art, the present scheme realizes active compensation through dual-cavity differential pressure and limit differential pressure control, and solves the technical bottleneck that the traditional detection method cannot eliminate the influence of material creep on air tightness detection.

[0117] Step S3, real-time monitoring of the pressure change in the differential pressure dual-cavity, and adjusting the air inlet amount of the first cavity 3 and the second cavity 4 according to the creep pressure-time curve to control the dual-cavity to be always in a differential pressure state and inhibit the creep of the first cavity 3.

[0118] According to the limit differential pressure of the current time period, the pressure in the second cavity 4 in the previous time period is increased, that is, the air inlet amount of the second cavity 4 is increased, and the dual-cavity is always controlled to be in a differential pressure state to inhibit the creep of the first cavity 3.

[0119] By collecting the pressure data of the first cavity 3 and the second cavity 4 in real time, and combining the creep pressure-time curve obtained in step S2, a dynamic differential pressure control mechanism is formed. When the pressure of the first cavity 3 is found to slowly decrease due to the creep effect, the system immediately restores the set differential pressure by adjusting the air inlet and outlet amounts according to the threshold value of the limit differential pressure.

[0120] In essence, the slow interference caused by creep is regarded as a dynamic disturbance, and its influence is eliminated through real-time compensation of the air inlet and outlet paths, ensuring that the first cavity 3 is always in a stable stress state during the entire detection process, thereby avoiding false signal interference caused by creep.

[0121] Compared with the existing single pressurization detection method, the present scheme no longer relies on the accumulation of pressure drop for a long time, but maintains a stable differential pressure through rapid compensation, thereby improving the stability and repeatability of the detection results.

[0122] Step S4, by correlating the air inlet amounts of the first cavity 3 and the second cavity 4, it is determined whether there is a leakage phenomenon at the position of the pull nut 5 joint.

[0123] In step S4, according to the limit differential pressure obtained from the creep pressure-time curve, the air inlet amount of the second cavity 4 in the current time period is increased in real time to suppress the creep of the first cavity 3, and based on the pressure change of the first cavity 3, it is determined whether there is a leakage phenomenon at the position of the pull nut 5 joint.

[0124] If the pressure of the first cavity 3 is always maintained within the specified range, then there is no leakage phenomenon at the position of the pull nut 5 joint; otherwise, there is a leakage phenomenon at the position of the pull nut 5 joint.

[0125] The air inlet amounts and air outlet amounts of the first cavity 3 and the second cavity 4 during the differential pressure maintenance process are compared and analyzed as key parameters. Under stable differential pressure, if the air inlet amount of the first cavity 3 and the air outlet amount of the second cavity 4 remain balanced for a long time, it indicates that the overall cavity is well sealed.

[0126] If there is a need to input gas into the first cavity 3, it indicates that there is a real leakage path, achieving high sensitivity in identifying leakage phenomena, and especially distinguishing between the slow pressure drop caused by creep and the gas loss caused by leakage, thereby improving the accuracy of detection.

[0127] The above is based on the ideal embodiment of the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A device for detecting the airtightness of rivet nuts, characterized in that, The utility model relates to a kind of air-tightness detection devices, comprising: Air-tightness detection mechanism, vibration excitation mechanism, frequency conversion mechanism; The air-tightness detection mechanism comprises: air-tightness detection cavity, sealing plate arranged in the middle of the air-tightness detection cavity, the air-tightness detection cavity is divided into first cavity and second cavity by the sealing plate;Wherein, the sealing plate is provided with through hole for installing pull-rivet nut; The air-tightness detection mechanism further comprises: adjusting unit, detection unit; The adjusting unit adjusts the pressure of the second cavity in real time according to the creep pressure-time curve of the first cavity to inhibit the creep of the first cavity; Wherein, the creep pressure-time curve setting comprises: loading the first cavity with a sequence of pressure steps, and keeping the pressure in the second cavity constant during each step loading phase, and collecting the pressure change signal of the first cavity in real time during the time period of each step to obtain the creep pressure-time curve of the first cavity under the constant pressure; The detection unit is used to detect the gas inlet and outlet volume and pressure change of the first cavity and the second cavity in real time; The vibration excitation mechanism is used to generate mechanical vibration with a predetermined frequency and amplitude; The frequency conversion mechanism is arranged between the vibration excitation mechanism and the air-tightness detection cavity, installed at the vibration table position of the vibration excitation mechanism, used to receive and amplify the vibration excitation output by the vibration excitation mechanism, and convert the vibration excitation into dynamic excitation acting on the air-tightness detection cavity.

2. The device for detecting the air tightness of a pull-rivet nut according to claim 1, characterized in that: The first cavity is provided with an air inlet, and the second cavity is provided with an air outlet.

3. The device for detecting the air tightness of a pull-rivet nut according to claim 2, characterized in that: Gas flow sensors are arranged at the positions of the air inlet and the air outlet, and pressure sensors are arranged in the first cavity and the second cavity.

4. The device for detecting the air tightness of a pull-rivet nut according to claim 1, characterized in that: The vibration excitation mechanism comprises an electromagnetic vibration table or a hydraulic vibration table, and the vibration frequency range of the vibration table covers 10 Hz to 5000 Hz. The table surface of the vibration table is provided with a mounting interface for fixing the frequency conversion mechanism by bolt connection.

5. The device for detecting the air tightness of a pull-rivet nut according to claim 1, characterized in that: The frequency conversion mechanism comprises a plurality of conical frequency conversion plates and a plurality of frequency conversion parts. The plurality of conical frequency conversion plates are symmetrically arranged, and the plurality of conical frequency conversion plates are fixedly connected to the air-tightness detection cavity near one end. The plurality of frequency conversion parts are installed on the corresponding conical frequency conversion plates and move towards or away from each other. The frequency conversion part comprises a moving sleeve, a damping block symmetrically installed in the inner cavity of the moving sleeve, and an adjusting rod penetrating through the damping block and the moving sleeve. The adjusting rod is symmetrically provided with threads, and the screw lines of the symmetrically arranged threads are opposite in direction. The symmetrically arranged damping blocks are respectively sleeved on the threads with opposite screw line directions and are threadedly connected with the adjusting rod. The adjusting rod is rotationally connected with the moving sleeve.

6. The device for detecting the air tightness of a pull-rivet nut according to claim 5, characterized in that: The conical frequency conversion plate is arranged in a stepped diameter-reducing structure near the air-tightness detection cavity.

7. A method for detecting the air tightness of a pull nut based on the pull nut air tightness detection device according to any one of claims 1-6, characterized in that, The utility model relates to a kind of air-tightness detection devices, comprising: Step S1, apply low-energy vibration excitation signal to the pull-rivet nut joint of the air-tightness detection cavity, receive and amplify the vibration excitation signal acting on the pull-rivet nut joint, wherein there is a sealing plate in the air-tightness detection cavity, which divides the air-tightness detection cavity into first cavity and second cavity, and the pull-rivet nut is installed on the sealing plate. Step S2, based on the first cavity creep pressure-time curve, and the limit differential pressure between the first cavity and the second cavity is calculated, the pressure in the second cavity is controlled according to the limit differential pressure, and the differential pressure double cavity is formed; Step S3, real-time monitoring of the pressure change in the differential pressure double cavity, and according to the creep pressure-time curve, the air intake of the first cavity and the second cavity is adjusted, the double cavity is always in differential pressure state, and the creep of the first cavity is inhibited; Step S4, by correlating the air intake of the first cavity and the second cavity, it is judged whether there is a leakage phenomenon in the position of the pull nut assembly.

8. The method of claim 7, wherein: In the step S2, the following sub-steps are included: Step S21, set the first cavity loading pressure step sequence, and keep the pressure in the second cavity constant in each step loading stage, and collect the pressure change signal of the first cavity in real time in each time period; Step S22, record the pressure change signal of the constant pressure in the first cavity in each time period, and obtain the creep pressure-time curve of the first cavity under the constant pressure; Step S23, according to the difference between the pressure of each time period and the initial pressure of the first cavity, the limit differential pressure is obtained; Step S24, according to the limit differential pressure of the current time period, the pressure in the second cavity in the previous time period is increased in real time, and the creep of the first cavity is inhibited.

9. The method of claim 8, wherein: According to the limit differential pressure of the current time period, the pressure in the second cavity in the previous time period is increased, that is, the air intake of the second cavity is increased, the double cavity is always in differential pressure state, and the creep of the first cavity is inhibited.

10. The method of claim 7, wherein: In the step S4, according to the limit differential pressure obtained from the creep pressure-time curve, the air intake of the second cavity in the current time period is increased in real time to inhibit the creep of the first cavity, and based on the pressure change of the first cavity, it is judged whether there is a leakage phenomenon in the position of the pull nut assembly; If the pressure of the first cavity is always maintained in the specified range, there is no leakage phenomenon in the position of the pull nut assembly; On the contrary, there is a leakage phenomenon in the position of the pull nut assembly.

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