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Magnetic fluids are the suspensions composed of magnetic nanoparticles, surfactants, and non-magnetic carrier liquids. Magnetic fluids are widely used in various fields, especially in sealing, because of their excellent features, including rapid magnetic response, flexible flow ability, tunable magneto-viscous effect, and reliable self-repairing capability. Here, we provide an in-depth, comprehensive insight into the theoretical analyses and diverse applications of magnetic fluids in sealing from three categories: static sealing, rotary sealing, and reciprocating sealing. We summarize the magnetic fluid sealing mechanisms and the development of magnetic fluid seals from 1960s to the present, particularly focusing on the recent progress of magnetic fluid seals. Although magnetic fluid sealing technology has been commercialized and industrialized, many difficulties still exist in its applications. At the end of the review, the present challenges and future prospects in the progress of magnetic fluid seals are also outlined.

The long-term stability and durability of seals are critical for various instruments and types of equipment. For static sealing, an important sealing state, there are currently two representative sealing methods, namely, pre-compressing static sealing and adhesive static sealing. In this paper, the characteristics and shortcomings of these sealing methods are summarized. At present, some static sealing requirements are urgent and difficult. For example, the deterioration of the sealing performance is an important factor which limits the service life of proton exchange membrane fuel cells and redox flow batteries. Therefore, a new method of static sealing whose sealing materials are rubber elastomers is proposed, named alterable static sealing. Then, its sealing processes are proposed. Furthermore, the actual contact area ratio r is used as the standard for sealability. Based on the mathematical model of pre-compressing static sealing, the influence of interface bonding was considered, and the mathematical model of alterable static sealing was established. Moreover, the compensatory effect of alterable static sealing on the static sealing capacity of rubber elastomers was proved.

A proper criterion to guide how to determine the cross-section diameter of non-standard large-sized O-rings used in deep-ocean pressure chambers (DOPCs) is absent. To design a large-sized O-ring only by scale-up could be a lack of persuasiveness, and it will probably cause the increase of cost. This paper gives a detailed study on the static sealing performance of O-rings by finite element analysis (FEA). The results show that the influence of the inside diameter of O-rings can be ignored, and the O-rings with a large cross-section diameter may not be applicable to the high-pressure DOPCs, but it can allow a larger sealing clearance to be used in the low-pressure DOPCs. The reference values of safe sealing pressure with different cross-section diameters and different sealing clearances are ascertained. An improved criterion to guide how to determine the cross-section diameter of non-standard large-sized O-rings used in DOPCs is proposed. The results obtained in this paper can provide a more convincing guideline for the O-ring sealing design not only in DOPCs but also in the similar pressure vessels.

This paper focuses the flanged static sealing structure of shell-tube heat exchange header, builds an static sealing model based on FEM(Finite Element Method),studies the effect of bolt preload and working medium load on the gasket actual contact stress. The results indicate that: an approximately linear relationship exists among the gasket contact stress, bolt preload and working medium load. When the pressure is gradually increasing, the flat end-plate's outward convex deformation results in the decreasing gasket stress in the center and even leakage. After locating the above leakage reason, the flange gasket structure is improved, and the bolt distribution and bolt preload is adjusted accordingly. The problem of leakage has been solved, approves that the calculating method of gasket sealing is an effective approach.

Chapter 4 treats body sound leakage, static sealing, and dynamic sealing, and describes the mechanisms, analysis, measurement and application of sound absorption and sound insulation on the vehicle body.

The sealing properties of the O-ring of the hydraulic cylinder plunger rod under a high-pressure environment are related to a variety of factors. In this paper, we first establish a simulation model based on an O-ring reciprocating shaft seal under a high pressure-environment through finite element software and study the influence of the compression rate, static pressure, and reciprocating speed of the plunger rod on the sealing performance of O-ring through the simulation model, and then analyze the maximum stress of O-ring during installation, hydrostatic loading and reciprocating motion with the variation of structural parameters. The results indicate that the compression rate of the installation process has a significant effect on the sealing performance of the enhanced O-ring. In the hydrostatic loading process, the equivalent stress of the O-ring is increased with the increase of the compression rate, when the static pressure is low and decreases, and when the static pressure is high, and the equivalent stress shows an increasing trend and the same increase; in the reciprocating motion process, when the static pressure is low, the equivalent stress and contact stress of the O-ring does not change significantly with the compression rate, and when the static pressure is high, there is an obvious phenomenon of abrupt change. The frictional stress of the reciprocating motion is increasing, then decreases, and then increases with the change in static pressure.

Based on the requirements for asphalt pavement crack repair materials, five representative materials were selected for testing: type-A crack sealant, type-B crack sealant, 70# hot asphalt, SBS-modified asphalt, and ambient-temperature water-based crack filler. A series of material performance and pavement performance experiments were conducted on these materials. Additionally, numerical models were developed based on actual asphalt pavement crack repair structural conditions. Under the ambient temperatures of 0 °C, 20 °C, and 50 °C, considering two types of loads, namely static load and dynamic load, the shear stress, tensile stress, and compressive stress of the crack-repair structure were analyzed in detail. The stress state of the repaired structure was specifically examined under the most unfavorable load conditions. These analyses were validated by comparing with laboratory-measured stress data, providing important references for the application of asphalt pavement repair materials. The conclusion of the research indicates that the B-type grouting adhesive, as a special material for crack repair, has obvious advantages in shear and tensile strength, and its overall performance is the best. It is suitable for expressways, first-class roads, and urban expressways. Asphalt materials for heating construction have obvious economic advantages compared with special materials and are suitable for low-grade asphalt pavement with relatively small pressure and small traffic volume on highways, branch roads, and secondary roads. Normal-temperature construction is suitable for temporary repair under adverse conditions such as cracks and dampness after rain.

Understanding the tribological behavior of elastomers in dry conditions is essential for sealing applications, as dry contact may occur even in lubricated conditions due to local dewetting. In recent decades, Persson and co-authors have developed a comprehensive theory for rubber contact mechanics and dry friction. In this work, their model is implemented and extended, particularly by including static friction based on the bond population model by Juvekar and coworkers. Validation experiments are performed using a tribometer over a wide range of materials, temperatures and speeds. It is shown that the friction model presented in this work can predict the static and dynamic dry friction of various commercial rubber materials with different base polymers (FKM, EPDM and NBR) with an average accuracy of 10%. The model is then used to study the relevance of different elastomer friction contributions under various operating conditions and for different roughness of the counter surface. The present model will help in the development of novel optimized sealing solutions and provide a foundation for future modeling of lubricated elastomer friction.

The adhesive force between two contact surfaces often leads to an increase in the friction force of the rubber seal O-ring after a certain dwell time, forming dwell time effects and affecting the reliability of sealing. The dwell time effect may result in substantial instability with respect to the frictional behavior of rubber O-rings, which needs to be carefully taken into account in the design of rubber seals. Therefore, in this paper, the dwell time effect of the friction force was studied experimentally for intermittent reciprocating rubber seal O-rings coupled with stainless steel 316L and a sealing air medium. The friction force of three kinds of rubber materials, including fluorine rubber (FPM), silicone rubber (SI), and nitrile rubber (NBR), was measured under different dwell times, compression ratios, and seal pressure. The results showed that there was a rolling frictional force, and the second peak value of the frictional force caused by the O-ring’s rolling under shear action and after the maximum static frictional force was observed at the starting stage of reciprocating motion. For FPM O-rings, the rolling friction force was much greater than the maximum static frictional force at about four times the value of the compression ratio at 9% and seal pressure at 0; moreover, the force was much greater at greater compression ratios. The dwell time effect was significant in the friction forces of rubber O-rings. The friction force increases with an increase in dwell time. The increase in maximum static friction force exceeded 50% after 5 dwell days. The increase in seal pressure led to the disappearance of the rolling friction feature and the rapid increase in friction during the starting stage. Under gas seal pressure conditions, the dwell time effect still led to a significant increase in friction force. The obtained results might provide guidance for the material selection of sealing designs.

The microwave load water-cooling system was operated in a vacuum cold black environment, and the pressure difference between the inside and outside of the water pipe could reach 0.3 to 0.4 MPa. To ensure the tightness of the water pipe, a conical seal structure was selected, the macro-static model and micro-boundary element contact model were established for the two forms with and without the Viton seal. The macro model simulation was performed by the finite element method to obtain the stress distribution inside the conical structure under different preload stress, the relationship between the contact pressure of the conical sealing interface and the contact area of the O-ring sealing interface as a function of preload stress; the method was used to calculate the micro-contact model, and the critical contact pressure and contact area to achieve the sealing requirements were obtained respectively without Viton seal and with Viton seal. As a result, a conical seal structure with a Viton seal was finally chosen for application. After verification, the structure meets the requirements for the use of microwave load water-cooling systems during the vacuum thermal test.