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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 two-dimensional O-ring seal nonlinear axisymmetric finite element model are established which is used for swinging hydraulic cylinder. Some factors influencing rubber O-ring sealing performance were taken into account, such as rotating shaft diameter, O-ring seal section diameter. The results indicate that when medium pressure is zero, the two factors influence Von Mises and maximum contact stress of sealing face greatly. Under medium pressure (P=10Mpa), the two factors have a little influence to Von Mises and maximum contact stress.

Tribological testing of moving shaft/sealing pairs in complex environments is at the frontline of research. Machines working in abrasive conditions are subject to different wear effects. It is not only valid on Earth but especially valid for rovers and future robots used in Mars and Moon missions. The aim of our joint research with the European Space Agency is to study the abrasion phenomena of moving machine elements on Mars and the Moon by using artificial soil samples (“simulants”). This review details mainly the available simulant sources and recommend a selection of the most suitable ones for tribological testing. Moreover, the potential mating structural materials subjected to abrasive space applications are reviewed briefly. The tribological tests are exploring the features of the rotary shaft/seal relationship that is subject to dry friction and intense abrasion. By using the simulants, measurements are performed under laboratory conditions with both a sample test and a real shaft/seal connection. Parameters of the selection criteria were defined, and classification of the simulant sources were made. It was found that simulant particle size distribution and chemical substance content are detailed enough only for a limited type of available artificial Moon and Mars soil samples. Four simulants were identified and applied later in the tribological testing. For the shaft materials, based on a detailed case study of polymers, steel, and aluminum alloys, a high-strength aluminum alloy with a hard anodized surface and a stainless steel were selected for further abrasion tests.

A new measurement device is introduced for analysing worn radial shaft seals (RSSs). This device enables unified and reproducible analysis and allows an automated nanoindentation for reliably detecting material changes at the seal edge.

Higher parameters of centrifugal machines are constantly required, such as the pressure of the medium to be sealed and the speed of rotation of the shaft. However, as the parameters increase, it becomes more and more difficult to ensure the effectiveness of sealing. In addition, sealing systems affect the overall safety of equipment operation, especially vibration. In order to harmonize the sealing functions and increase the dynamic rigidity of the rotors of centrifugal machines, a method for modeling complex sealing systems has been developed. Non-contact seals are considered as hydrostatic–dynamic bearings that can effectively dampen rotor oscillations. A general approach to the analysis of non-contact seals as automatic control systems and an algorithm for constructing their dynamic characteristics at the design stage were proposed for the first time. Models of “rotor-gap seal”, impulse seal and “rotor–hydraulic face” systems, and seal-supports of a shaftless pump have been studied to assess the effect of these seal systems on the oscillatory characteristics of the rotor. Analytical dependencies are obtained for calculating the dynamic characteristics and stability limits of seals as hydromechanical systems. The directions for improving the safety of operation of critical pumping equipment due to a targeted increase in the rigidity of non-contact seals are determined, which leads to an increase in the vibration resistance of the rotor and the environ-mental safety of centrifugal machines. The paper proposes a method for designing sealing systems based on the configuration of sealing components in order to achieve harmonization between sealing and vibration reliability, taking into account oscillatory processes due to hydrodynamic sealing characteristics.

The current paper investigates two particular features of a novel rotary split engine. This internal combustion engine incorporates a number of positive advantages in comparison to conventional reciprocating piston engines. As a split engine, it is characterized by a significant difference between the expansion and compression ratios, the former being higher. The processes are decoupled and take place simultaneously, in different chambers and on the different sides of the rotating pistons. Initially, a brief description of the engine’s structure and operating principle is provided. Next, the configuration of the compression chamber and the sealing system are examined. The numerical study is conducted using CFD simulation models, with the relevant assumptions and boundary conditions. Two parameters of the compression chamber were studied, the intake port design (initial and optimized) and the sealing system size (short and long). The best option was found to be the combination of the optimized intake port design with the short seal, in order to keep the compression chamber as close as possible to the engine shaft. A more detailed study of the sealing system included different labyrinth geometries. It was found that the stepped labyrinth achieves the highest sealing efficiency.

Effective gutta-percha/sealer removal is essential for predictable nonsurgical endodontic retreatment, but the effects of key operational parameters on nickel–titanium rotary removal instruments remain insufficiently understood. This study aimed to examine how varying downward loads and rotational speeds affect the removal efficiency and torque/force generation of the HyFlex Remover. Sixty transparent straight resin canals filled with gutta-percha and AH Plus sealer were prepared using the HyFlex Remover at two rotational speeds (400 and 800 rpm) and three downward loads (2, 3, and 4 N; n = 10/group). The removal rate, calculated using micro-computed tomography, as well as removal time, maximum force, maximum torque, and cumulative torque were recorded and evaluated using two-way analysis of variance with Bonferroni correction (α = 0.05). The removal rate was consistently higher at 400 rpm than at 800 rpm (p < 0.001), while removal time and cumulative torque were greater at 400 rpm (p < 0.001). Maximum torque differed only between the 800-2 N and 800-4 N groups (p = 0.006). Maximum force increased with higher loads (p < 0.001), and at 3 N and 4 N, it was lower at 400 rpm than at 800 rpm (3 N: p = 0.039, 4 N: p < 0.001). Overall, lower downward loads reduced torque but prolonged working time, whereas higher rotational speeds shortened both working time and torque but decreased the removal rate.

Water hydraulic technology is a potential application to deep-sea manipulators and their proportional valves. In the ocean, water is a better choice as the working medium than mineral oil because of its environmentally friendly advantages. However, no water hydraulic proportional valve for deep sea exists yet. In this study, a novel water hydraulic rotary proportional valve with a four-way, three-position principle and a plane sealing method for the environment-friendly manipulator is invented. The static and dynamic performance of the proportional valve is studied using a mathematical model and experiments. A valve-control swing cylinder system, which simulates the working state of the manipulator, is also facilitated in a deep-sea simulation device for simulating a depth of 6500 m in the ocean. Results show that the numerical and experimental data match well. The proportional valve can achieve zero leakage, and the dead zone is approximately 10%. The bandwidths are 30 and 6 Hz when the input signal amplitude is 5% and 100% of the valve's full stroke, respectively. The proportional valve can accurately control the swing cylinder on the manipulator's elbow joint with a rotation angle error of ±0.1°. The rotary proportional valve has excellent application to deep-sea manipulators.

Magnetic fluid sealing is a novel sealing technology wherein magnetic fluids play a pivotal role in the sealing process. The yield stress of the magnetic fluid directly affectsits sealing performance and is governed by multiple interdependent factors. Conventional approaches that evaluate the effect of a single parameter while keeping other parameters constant are insufficient to fully characterize the relative contributions of each parameter to the yield stress. In this study, we investigate the preparation factors affecting the yield stress of kerosene-based magnetic fluids and propose a parameter sensitivity analysis method based on orthogonal experimental design to determine the optimal combination of factor levels within the studied range. The sensitivity of key preparation factors affecting the yield stress of kerosene-based magnetic fluids was determined via range and variance analyses of the orthogonal experimental data. The factors, ranked in descending order of sensitivity, were surfactant (C18H34O2) dosage, precipitant (NH3·H2O) dosage, and deionized water (H2O) volume. Moreover, the effects of different levels of the same factor were analyzed using multiple approaches. These findings provide a theoretical foundation for optimizing the preparation of magnetic fluids and enhancing their sealing performance.