Mechanical seal leakage prediction theory and its application

 

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Mechanical seals in industrial production, especially in the petrochemical industry has been widely applied. The basic performance of mechanical seals including face friction characteristics (ie, ability to resist friction and wear) and sealing characteristics (ie, the leakage rate indicators).

Engineering, generally control the leakage rate is not excessive under the premise, as far as possible to improve the interfacial friction characteristics, in order to extend the service life of mechanical seals. Due to many factors, the length of the service life of mechanical seals vary, which makes machinery and equipment using leak-proof mechanical seal there are potentially dangerous. Can not accurately predict the leakage rate and mechanical seal life, and often leads to premature replacement of the seals, or delays in maintenance timing, cause flammable, explosive, a large number of harmful media leak and cause accidents.

The scholars made a lot of theoretical and experimental research on the sealing characteristics of the mechanical seal and friction characteristics, the leakage rate calculation model, which greatly improved the mechanical seal theory and engineering practice plays an important role in guiding.

However, these studies are based on the end surface morphology of the same, constant conditions of friction conditions, established by the mechanical seal leakage model have failed to consider the process of running mechanical seal contact face surface morphology changes (or only consider the initial surface roughness and waviness) on the leakage loss, but does not consider the relationship between leakage losses and time.

In fact, the mechanical seal in different operating conditions or in the entire process under the same conditions, the friction surface morphology and the sealing gap geometry are constantly changing, in order to adopt the traditional method to accurately calculate the mechanical seal leakage rate it is very difficult. This project seeks to introduce the fractal theory, the size-independence of fractal parameters characterize the friction and wear processes, mechanical seal friction surface morphology and its changes, investigate in accordance with the basic theory of mechanical seals, seal face topography, leakage prediction model established, friction and wear accelerated test methods, friction and wear and seal Experimental research and engineering applications of this technology route, study and explore the mechanical seal leakage prediction theory.

In to discuss the size of France, the box dimension method, the power spectrum method, the variation method, the structure function method, the outline of the root mean square method, covariance method and wavelet transform method several fractal dimension calculated on the basis that the structure function The method has higher accuracy than other methods and deterministic. The AF-LI profile measuring instrument, were measured surface profile curve on the seal faces. Mechanical seal surface profile has fractal characteristics of the structure function of the contour curve obtained on the basis of the measured data and the measurement scale double logarithmic relationship can be determined.

Use of the Navier-Stokes equations, the mechanical seal leakage and seal end clearance relationship between the law of the mechanical seal surface morphology and sealing properties and friction characteristics. Studies have shown that the process of running mechanical seal surface morphology and its change have a significant impact on the sealing properties and Friction Characteristics. Pointed out that the correct characterization of seal face topography and its changes, is the key mechanical seal leakage Prediction Technology. Weierstrass-Mandetbrot function, the fractal characteristics of the Seals were analyzed.

Majumdar-Bhushan-based fractal model, the mechanical seal moving contact of the stationary ring simplified to an equivalent rough surface and an ideal rigid smooth surface contact, the gap on the mechanical seal outside diameter at the annular cross-section as the contact surface micro- leak channel cross section, its characterization, leak prediction model based on fractal theory and fractal parameters. The Seals gap with the face morphology changes in the law, as well as mechanical seal leakage rate of the medium pressure, medium viscosity, end than the load, the seal ring material properties, seal face morphology changes and time.

Based on the similarity theory, discusses the mechanical seal friction and wear accelerated test method. Move by mechanical seal stationary ring friction and wear tests on the HDM-2 friction and wear testing machine to obtain a time-related relationship Seals fractal dimension. Early in the friction and wear test, due to the smaller fractal dimension, the surface is rough, face small contact area, contact stress, the wear volume; with the friction process is ongoing, the fractal dimension gradually increases and reaches a maximum value the contact area increases, the contact stress decreases, reducing the amount of wear. A small amount of wear and tear, the fractal dimension slowly become smaller, and for quite some long time in a relatively stable value. When the fractal dimension is reduced to a certain value, because the face is too rough, leading to friction and wear increase quickly lower the fractal dimension of the face.

Self-designed mechanical seal test device, the GY-70 mechanical seal seal performance test. In the early running, the mechanical seal leakage rates. Over running time, the friction face gradually run together, the leakage rate decreases. Thereafter, as the friction process is ongoing, face a long period of time in a more stable state of the friction, the leak rate remained basically unchanged. End load the same case, the leak rate with the media pressure increases. The leak rate tests and theoretical predictions is basically the same trends over time, the test value is less than the theoretical prediction, but in the same order of magnitude.

The results show that the use of the proposed mechanical seal leakage to predict the fractal model can accurately predict either a working time of the mechanical seal leakage rate under certain operating conditions.

Fault tree analysis on the mechanical seal leakage failure cause analysis, pointed out that under normal operating conditions, the seal face topography difference is the main reason for the mechanical seal leakage failure. A petrochemical enterprise in service pumps with mechanical seal leakage rate and life prediction results verify the correctness of the prediction model based on fractal theory of the mechanical seal leakage.

Mechanical seal leakage prediction theory and technique, not only reveals the influence of the mechanical seal running friction surface morphology of the leakage loss, the law of surface morphology and the relationship between the leak rate changes over time, but also to real-time understanding of the mechanical seal leak condition, and make the decision whether to continue to use or repair to ensure the safety and reliability and low cost operation. The results for the mechanical seal design, manufacture, use and maintenance.

 

 

 
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