Method for improving sealing performance of profound hypothermia gasket of propellant pipeline system

Abstract

The invention provides a method for improving the sealing performance of a profound hypothermia gasket of a propellant pipeline system. The method comprises the following steps: firstly, analyzing and solving macroscopic contact pressure distribution of contact interface mechanics by virtue of a finite element simulation method; then, by means of the real rough surface morphology and in combination with contact pressure distribution, the microscopic contact morphology is calculated, and then the average height of a leakage channel is solved; a leakage rate quantitative calculation model is constructed by adopting a grid model in consideration of medium flow characteristics, and finally the leakage rate serving as a sealing performance evaluation standard is obtained. According to the technical scheme, the sealing problem of the deep hypothermia connecting pipe system is effectively solved, the performance is improved, the design is optimized, and the cost is reduced.

Description

Technical Field

[0001] The invention provides a method for improving the sealing performance of a cryogenic gasket of a propellant pipeline system, and belongs to the technical field of sealing. Background Art

[0002] In modern spacecraft and rocket propulsion systems, the sealing of propellant pipe joints is particularly critical under extreme cryogenic conditions. Propellant pipe joints usually use cryogenic fluid media such as liquid hydrogen and liquid oxygen. As the temperature changes rapidly, the sealing interface will produce microscopic contact deformation due to the frequent alternation between deep low temperature and normal temperature, resulting in seal failure. In addition, in a deep cryogenic environment, the physical properties and contact behavior of the sealing material change significantly compared to normal temperature. Existing sealing technology cannot effectively maintain sealing performance under these extreme conditions.

[0003] Seal leakage not only affects the operating efficiency of the system, but may also lead to serious safety hazards. Therefore, researching and developing an efficient sealing structure and a method to predict sealing performance are of great significance to improving the reliability and safety of the propulsion system.

[0004] The existing technology mainly uses a combination of simulation and experiment in the study of gasket sealing. Among them, the literature uses the finite element method to deeply study the sealing performance of metal gaskets under different loading conditions, providing an important theoretical basis for understanding the mechanical behavior and sealing mechanism of gaskets. The literature conducts numerical simulation on the leakage rate of non-metallic gaskets, further enriching the research content of gasket sealing performance. In addition, the literature innovatively considers the influence of temperature on gasket materials in finite element simulation, and conducts a detailed study on the contact pressure changes on the gasket surface, revealing the important role of temperature on gasket sealing performance.

[0005] The technical solutions of these existing technologies mainly focus on the study of gasket sealing performance under conventional working conditions, and through simulation and experimental methods, they deeply explore the influence of factors such as gasket materials, loading conditions and temperature on sealing performance.

[0006] Although the existing technology has made significant progress in the study of gasket sealing performance, there are still some obvious shortcomings. First, the existing gasket sealing research is mainly based on conventional working conditions, and the research on the changes in material properties under deep low temperatures is not in-depth enough. Under deep low temperature extreme conditions, the physical properties and microscopic contact behavior of the sealing material will change significantly, and the existing technology does not fully consider the impact of these factors on the sealing performance.

[0007] Secondly, the theory of cryogenic gasket sealing is still imperfect. Although there are many models that can be used to calculate the leakage rate, such as the parallel plate model, the triangular groove leakage model, the spiral groove contact channel model, the porous medium model and the single hub leakage model, the applicability and accuracy of these models under cryogenic conditions still need to be verified. In particular, the parallel plate model, the triangular groove leakage model and the spiral groove contact channel model have their own limitations, such as only considering the leakage in a specific direction or the large amount of calculation and long time consumption.

[0008] Finally, although the grid leakage model is a model based on the grid method, which can more comprehensively consider the influence of the cross-sectional height and leakage direction of the leakage channel, its application in the study of the sealing performance of cryogenic gaskets is still in its infancy and needs further improvement and optimization. Therefore, the existing technology still has a lot of room for development and challenges in the study of the sealing performance of cryogenic gaskets.

[0009] In summary, although the existing technology provides important theoretical basis and experimental data for the study of gasket sealing performance, the research under deep low temperature conditions is still not in-depth and complete enough, and further exploration and innovation are needed. Summary of the invention

[0010] The present invention aims to solve the sealing leakage problem of the joint connection of the propellant pipeline system of the launch vehicle under normal and extreme service conditions, especially in a deep cryogenic environment. In the prior art, the gasket sealing structure is prone to reduce the sealing reliability and increase the leakage rate under deep cryogenic conditions due to factors such as changes in material properties, changes in the surface microscopic sealing mechanism, and pressure fluctuations. Specifically, the prior art has the following disadvantages:

[0011] 1. Changes in material properties: In a deep low temperature environment, the physical properties and microscopic contact behavior of the gasket material change significantly, resulting in a decrease in sealing performance.

[0012] 2. Imperfect micro-sealing mechanism: Existing research does not have a deep understanding of the contact deformation of the sealing surface micro-morphology under deep low temperatures and the formation mechanism of leakage channels.

[0013] 3. Inaccurate leakage rate calculation model: The traditional leakage rate calculation model fails to fully consider the influence of the leakage channel cross-sectional height and leakage direction, resulting in a large deviation between the calculation results and the actual situation.

[0014] In view of the above shortcomings, the present invention proposes a method for predicting the sealing performance of the joint connection of a cryogenic pipe system, aiming to improve the reliability and stability of the sealing structure and reduce the leakage rate.

[0015] The present invention, the specific technical scheme is as follows:

[0016] The present invention analyzes and solves the macroscopic contact pressure distribution of contact interface mechanics through finite element simulation method, combines the real rough surface morphology, calculates the microscopic contact morphology, and then solves the average height of the leakage channel. Considering the flow characteristics of the medium, a grid model is used to construct a quantitative calculation model for the leakage rate, and finally the leakage rate as a standard for judging the sealing performance is obtained.

[0017] The technical solution includes the following steps in detail:

[0018] S1. Contact interface mechanical analysis:

[0019] Construct a local 2D axisymmetric geometry model including joints, nozzles and gaskets;

[0020] Finite element simulation was performed using ABAQUS software, taking into account the effects of deep low temperatures on the structure and gasket material performance;

[0021] Set reasonable grid precision to ensure the accuracy of calculation results;

[0022] Analyze the pressure distribution on the contact interface and obtain macroscopic contact pressure data.

[0023] S2. Rough morphology treatment of sealing surface:

[0024] Use three-dimensional white light interferometry to obtain microscopic morphological data of the joint end face, gasket end face and side face;

[0025] Perform singular point filtering on the surface topography coordinate data and reshape it into a two-dimensional digital topography matrix;

[0026] MATLAB and other tools are used to construct the microscopic rough digital morphology of the gasket surface for subsequent mechanical solutions.

[0027] S3. Grid leakage model construction:

[0028] The surface morphology of the sealing surface under contact pressure is constructed using the fast Fourier transform (FFT) algorithm;

[0029] The cross section of the leakage channel is divided into multiple grids, and different numbers of grids are considered to reflect the cross-sectional height of the leakage channel;

[0030] According to the height matrix of the surface gap, it is determined whether the gap space runs through the inner and outer boundaries of the sealing surface leakage direction, and a microscopic leakage channel is established;

[0031] Combined with fluid mechanics analysis, the analytical expression of leakage rate under different flow states is derived to achieve quantitative calculation of leakage rate.

[0032] S4. Experimental verification:

[0033] Design and build a gasket sealing performance simulation tooling test bench to conduct leakage rate tests;

[0034] The stress-strain curves of gasket materials at different temperatures are obtained using a low-temperature mechanical properties test platform and input into the material database for finite element simulation analysis;

[0035] Conduct gasket sealing performance experiments under different temperatures, medium pressures and torque loads, and record the experimental data;

[0036] The simulation results are compared with the experimental results to verify the accuracy of the model and numerical solution established in the theoretical simulation analysis.

[0037] Combined with the technical solution, the beneficial effects brought by the present invention are briefly described as follows:

[0038] 1. Improved sealing performance: The grid leakage model is used to accurately calculate the leakage rate with small errors, which significantly improves the sealing performance of the joint connection of the cryogenic pipe system.

[0039] 2. Design optimization: Finite element simulation is combined with real rough surface morphology to help optimize the design of sealing structure and reduce leakage risks.

[0040] 3. Enhanced stability: Comprehensively consider the influence of multiple parameters to ensure that the sealing structure is stable and reliable under extreme working conditions.

[0041] 4. Cost reduction and efficiency improvement: Accurate calculation and verification reduce design iterations, reduce costs, and improve R&D efficiency.

[0042] In summary, the technical solution of the present invention effectively solves the sealing problem of the cryogenic take-over system, improves performance, optimizes design, and reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of the gasket sealing structure of an embodiment;

[0044] Figure 2 It is a schematic diagram of the sealing principle of an embodiment;

[0045] Figure 3 A schematic diagram of a local two-dimensional axisymmetric geometric model of an embodiment;

[0046] Figure 4 A schematic diagram of one-dimensional flow of fluid in a parallel plate channel of an embodiment;

[0047] Figure 5 A schematic diagram of a low-temperature mechanical properties testing platform of an embodiment;

[0048] Figure 6 It is a comparison curve between the leakage rate simulation value and the experimental value of the embodiment. DETAILED DESCRIPTION

[0049] The specific technical solution of the present invention is described in conjunction with the accompanying drawings.

[0050] The gasket sealing structure of this embodiment is as follows Figure 1 As shown in the figure, the gasket seal is a static seal. On a microscopic scale, there are tiny protrusions and depressions on the sealing surface. Therefore, under the action of load, the actual contact occurs on the discrete micro-protrusions of the nominal contact area, such as Figure 2 The sealing mechanism is the total sealing force synthesized by the sealing force generated by the system pressure and the initial sealing force. When the force increases to a level sufficient to cause plastic deformation of the surface, the tiny protrusions on the sealing surface are filled, thereby blocking the leakage channel. The essence is to control the material exchange between the sealing space and the internal and external environments to ensure the normal operation of the system.

[0051] The structure of a liquid rocket propellant pipeline joint is taken as the research object. The gasket is located between the joint and the nozzle. The gasket clamping method is adopted, that is, the gasket is clamped by tightening the outer nut to achieve sealing. Considering the symmetry of the gasket sealing structure, the local two-dimensional axisymmetric geometric model of the structure is constructed using ABAQUS software, such as Figure 3 The joint and the nozzle are made of 304 stainless steel, the gasket material is polyimide (PI) gasket, and the mechanical parameters of the gasket material are obtained through the material low-temperature mechanical properties test platform.

[0052] Assume that the microchannel is Figure 4 In the infinitely wide parallel plate model shown in the figure, the xoy plane is the cross-section at the center of the leakage channel. At this time, the height dimension of the leakage channel is the distance h between the plates. The viscous flow gas flows one-dimensionally in the x direction at a rate v in the xoy plane, and the arrow represents the direction of fluid movement.

[0053] Figure 5 This is a schematic diagram of the low-temperature mechanical properties test platform, which can be used to perform uniaxial compression tests on materials, with the test temperatures set to 293, 173, 77 and 20 K. Compression tests were performed in accordance with the relevant standards and requirements of GB / T1041-92 "Plastic Compression Properties Test Method".

[0054] like Figure 6, under the medium pressure of 1MPa, when applying a load of 1000N, the relative order of magnitude difference between the experimental leakage rate and the simulated leakage rate is 0.176; when applying a load of 1200N, the relative order of magnitude difference is 0.146; when applying a load of 1400N, the relative order of magnitude difference is 0.095; when applying a load of 1600N, the relative order of magnitude difference is 0.328; when applying a load of 1800N, the relative order of magnitude difference is 0.303. The difference between the simulation results and the experimental test results is within one order of magnitude, and the agreement is high, indicating that the numerical calculation method of the leakage rate can effectively realize the quantitative analysis of the true leakage rate of the gasket seal. The leakage rate exceeds one order of magnitude when the load changes from 1000 to 1200N and 1400 to 1600N. This is because under low loads, due to processing defects on the surface of the PI gasket and the surface of the pressing block, there are a large number of leakage channels between the two surfaces. As the load increases, the rough peaks of the contact surface are further compressed, and part of the leakage channels are blocked, resulting in a decrease in the leakage rate.

[0055] The present invention realizes comprehensive consideration of the cross-sectional height and leakage direction of the leakage channel by constructing a grid leakage model, thereby improving the accuracy and reliability of leakage rate calculation.

[0056] The present invention solves the macroscopic contact pressure distribution and microscopic contact morphology of contact interface mechanics by finite element simulation method, and verifies the accuracy of the simulation results by experiments, thereby ensuring the reliability and effectiveness of the entire technical solution.

[0057] The gasket of the present invention is made of special materials and has excellent low temperature resistance and elastic recovery ability; the shape and size of the gasket are accurately calculated to ensure uniform contact pressure distribution at the joint connection, thereby improving the sealing effect.

[0058] The present invention constructs a grid leakage model for quantitatively calculating the leakage rate. The model takes into account the cross-sectional height and leakage direction of the leakage channel and can more accurately evaluate the sealing performance.

[0059] The present invention adopts a reusable and easy-to-operate simulation tool test equipment to verify the sealing performance of the sealing gasket; the test equipment includes a joint pipe system, a clamping device, a pressure control system and a leakage detection system. Among them, the joint pipe system simulates the actual cryogenic pipe system; the clamping device is used to fix the joint and the gasket; the pressure control system is used to adjust the medium pressure; the leakage detection system is used to detect the leakage rate.

[0060] There are possible alternatives to the above technical solutions:

[0061] (1) Replacement of some structures and devices

[0062] Gasket material replacement: Although polyimide (PI) gaskets are used in the original article, other materials with similar mechanical properties and low-temperature stability, such as some special rubbers or polymer composite materials, can also be used as alternative materials. These materials can also maintain good elasticity and sealing properties at low temperatures.

[0063] Alternative sealing structures: In addition to the step gasket sealing structure mentioned in the original text, other types of sealing structures can also be considered, such as O-ring seals, metal bellows seals, etc. These sealing structures may have better adaptability and sealing effects under different working conditions.

[0064] Alternative test platform: In the leak rate test experiment, in addition to using the helium mass spectrometer leak detector, you can also consider using other high-precision leak detection equipment, such as mass spectrometer-mass spectrometer or laser leak detector, etc. These devices may have better performance in detection sensitivity and accuracy.

[0065] (2) Replacement of method steps

[0066] Alternatives to finite element simulation methods: Although ABAQUS software was used in the original article for finite element simulation analysis, other simulation software with similar functions, such as ANSYS, MSC.Nastran, etc., can also be used to solve the macroscopic contact pressure distribution and microscopic contact morphology of contact interface mechanics.

[0067] Alternatives to leakage rate calculation models: In addition to the grid leakage model, other leakage rate calculation models can also be considered, such as the parallel plate model, triangular groove leakage model, etc. These models may have better applicability and accuracy under different working conditions.

[0068] Alternative experimental methods: In the material mechanical properties test and sealing surface roughness morphology test, in addition to using the test methods and equipment in the original text, you can also consider using other test techniques and equipment, such as electron scanning microscope (SEM), atomic force microscope (AFM), etc., to obtain more accurate material properties and surface morphology data.

[0069] In addition to the design ideas in this embodiment, other perspectives may be considered to achieve the same purpose of the invention, such as by improving the structural design of the joint and the nozzle, optimizing the clamping method of the gasket, etc. These alternatives may require more innovation and attempts during the design process.

Claims

1. A method for improving the sealing performance of cryogenic gaskets in a propellant pipeline system, characterized in that: Firstly, the finite element simulation method is used to analyze and solve the macroscopic contact pressure distribution of the contact interface mechanics. Then, the microscopic contact morphology is calculated using the real rough surface morphology combined with the contact pressure distribution, and the average height of the leakage channel is solved. Considering the flow characteristics of the medium, a grid model is used to construct a quantitative calculation model for the leakage rate, and finally the leakage rate is obtained as the standard for judging the sealing performance.

2. The method for improving the sealing performance of cryogenic gaskets in a propellant pipeline system according to claim 1, characterized in that: The following steps are involved: S1. Contact interface mechanical analysis: Construct a local 2D axisymmetric geometry model including joints, nozzles and gaskets; Finite element simulation was performed using ABAQUS software, taking into account the effects of deep low temperatures on the structure and gasket material performance; Set reasonable grid precision to ensure the accuracy of calculation results; Analyze the pressure distribution on the contact interface and obtain macroscopic contact pressure data; S2. Rough morphology treatment of sealing surface: Use three-dimensional white light interferometry to obtain microscopic morphological data of the joint end face, gasket end face and side face; Perform singular point filtering on the surface topography coordinate data and reshape it into a two-dimensional digital topography matrix; Use MATLAB and other tools to construct the microscopic rough digital topography of the gasket surface for subsequent mechanical solutions; S3. Grid leakage model construction: The surface morphology of the sealing surface under contact pressure is constructed using the fast Fourier transform algorithm; The cross section of the leakage channel is divided into multiple grids, and different numbers of grids are considered to reflect the cross-sectional height of the leakage channel; According to the height matrix of the surface gap, it is determined whether the gap space runs through the inner and outer boundaries of the sealing surface leakage direction, and a microscopic leakage channel is established; Combined with fluid mechanics analysis, the analytical expression of leakage rate under different flow states is derived to achieve quantitative calculation of leakage rate; S4. Experimental verification: Design and build a gasket sealing performance simulation tooling test bench to conduct leakage rate tests; The stress-strain curves of gasket materials at different temperatures are obtained using a low-temperature mechanical properties test platform and input into the material database for finite element simulation analysis; Conduct gasket sealing performance experiments under different temperatures, medium pressures and torque loads, and record the experimental data; The simulation results are compared with the experimental results to verify the accuracy of the model and numerical solution established in the theoretical simulation analysis.

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