In the metallurgical industry, hydraulic automatic gauge control (HAGC) is a core mechanism for thickness control of plates used in the rolling process. The stability of the HAGC system’s kernel position closed-loop is key to ensuring a process with high precision, speed and reliability. However, the closed-loop position control system is typically nonlinear, and its stability is affected by several factors, making it difficult to analyze instability in the system. This paper describes in detail the functioning of the position closed-loop system. A mathematical model of each component was established using theoretical analysis. An incremental transfer model of the position closed-loop system was also derived by studying the connections between each component. In addition, based on the derived information transfer relationship, a transfer block diagram of disturbance quantity of the system was established. Furthermore, the Popov frequency criterion method was introduced to ascertain its absolute stability. The results indicate that the absolute stability conditions of the position closed-loop system are derived in two situations: when spool displacement is positive or negative. This study lays a theoretical foundation for research on the instability mechanism of an HAGC system.

In this work, the lubrication mechanism and friction-wear characteristics of the friction pair between carbon-fiber-reinforced polyether ether ketone (CF/PPEK) and 316L stainless steel with a micro-hemispherical pit textured surface at different sliding speeds under seawater lubrication were studied through numerical simulation and experimental investigation. The study results indicate that the seawater moves following the sliding direction of the upper specimen, forms a vortex ring flow in the hemispherical pit of the bottom specimen, uses the convergent gap to generate a hydrodynamic effect, produces the bearing capacity, and realizes fluid lubrication. The hemispherical pit diminishes the abrasive wear during the friction process by storing the wear debris, and the main wear forms of the hemispherical-pit surface friction pair are oxidative wear and adhesive wear. The friction coefficient of the hemispherical-pit surface friction pair is 0.018–0.027, the specimen contact temperature is 40.2–55.1 °C, and it is always in the hydrodynamic lubrication state in a rotation speed ranging from 1000 r/min to 1750 r/min. As the sliding speed increases, the specimen contact temperature climbs, and the oxidation reaction gradually becomes full. Oxidative wear and adhesive wear alternately play a dominant role in the friction, and the wear rate first decreases and then increases sharply.

Wear is one of the main failure causes of hydraulic seals. Wear will lead to degradation in the mechanical properties and sealing properties of seals. Compared with hydraulic seals with one-way rotational motion, the hydraulic reciprocating rotary seals work in more complex operating conditions, so their wear mechanism becomes more complicated. Aimed at exploring the friction and wear law of hydraulic reciprocating rotary seals and the property evolution law during the wear process, this paper set up an experimental system to simulate the working conditions of the hydraulic reciprocating rotary seals. The friction characteristics were obtained under different working pressures and different motion parameters. The wear characteristics were obtained under rated working conditions. The surface morphology was observed by SEM and the wear mechanism was analyzed.

As a new type of suspension bearing, Magnetic-Liquid Double Suspension Bearing (MLDSB) is mainly supported by electromagnetic suspension and supplemented by hydrostatic supporting. Its bearing capacity and stiffness can be greatly improved. Because of the small liquid film thickness (it is smaller 10 times than air gap), the eccentricity, crack, bending of the rotor, and the assembly error, it is easy to cause a clearance-rubbing fault between the rotor and stator. The coating can be worn and peeled, the operating stability can be reduced, and then it is one of the key problems of restricting the development and application of MLDSB. Therefore, the clearance-rubbing dynamic equation of 2-DOF system of MLDSB is established and converted into Taylor Series form and the nonlinear components are retained. Dimensionless treatment is carried out by dimensional normalization method. Finally, the rotor displacement response under different rotor eccentricity ratio and rotating speeds is numerically simulated. The studies show that the trajectory of the rotor is periodic elliptic without clearance-rubbing phenomenon when the eccentricity ratio is less than 0.2, while the rotor is greatly affected by the rotation speed and a variety of motions, such as single-period, quasi-period, double-period and chaos, are presented when greater than 0.3. Within the largest range of rotating speed and eccentricity ratio, the rotor presents the single-period trajectory, and then the number of Poincare mapping point is 1, without a clearance-rubbing fault. When the rotational speed is in the scope of (9, 13) krpm and the eccentricity ratio is in the scope of (0.27, 0.4), the number of Poincare mapping point is more than one, the maximum dimensionless rubbing force is −5.7, and then clearance-rubbing fault occurs. The research can provide a theoretical basis for the safe and stable operation of MLDSB.

Durning the design process of hydrostatic rotary worktable, the processing and assembly tolerance, (the offset of worktable and the gap of the oil film’s thickness) is ignored. But it will cause that the real bearing of oil pocket deviates from the initial design value, and then the performance of rotary worktable will be reduced significantly. Up to now, no effort is found toward the research of influence of the processing and assembly tolerance on the performance of the rotary worktable. So the hydrostatic oil film is assumed as the elastomer in this paper, and then the bearing capacity of the oil pocket is studied with and without the mass offset of the worktable by taking an expression between the bearing capacity and the oil film’s thickness of the oil pocket as the deform compatibility equation. The influence of the processing tolerance of the oil sealing belt’s gap on the bearing capacity of the oil pocket is analyzed. In the light of the liquid hydrostatic worktable of Gantry Moving Milling Center using on the scene, the oil pocket’s pressure of the worktable is tested using Rotary Worktable Test System under the circumstance of the mass offset of the worktable and the gap tolerance of the oil sealing belt, and then the equivalent offset of worktable, the average pressure of the oil pocket and the actual thickness of the oil film are analyzed respectively. The test results show that the bearing capacity component of the oil pocket caused by G is consistent, and the component caused by M is relative to the position of the oil pocket. When the oil sealing belt’s gap is larger than the theoretical value, the bearing capacity of the oil pocket is smaller than the others; whereas the bearing capacity of the oil pocket is larger than the others. The maximum and minimum equivalent offsets are 0.256 4 mm and 0.047 5 mm, respectively, and the average oil pocket pressure varies from 0.345 MPa to 0.460 MPa, the maximum and minimum value of the actual oil film thickness are 109.976 μm (No. 7 oil pocket) and 93.467 μm (No. 10 oil pocket), respectively. The research results can be used to detect the offset of the worktable and the actual thickness of the oil film under processing and assembly tolerance, and provides a basis way for detecting the processing and assembly tolerance of rotary worktable signing reasonably of Gantry Moving Milling Center.

The multi-random-effects gamma process has a better characterization effect for degraded data with individual differences. In this paper, a reliability evaluation method for gamma stochastic processes with multiple random effects is studied. The mathematical model of multiple random effects gamma process was established. The model parameters estimation method was established based on the Bayesian approach. The prior distribution acquisition method was discussed, and the parameters of the multiple randomeffects gamma process were estimated by the MCMC-Gibbs method. The correctness of the model and method was verified by numerical simulation, the influence of algorithm parameters on the algorithm solving process was studied. In the fourth part, the reliability of aviation hydraulic rotary joints was studied by using multiple random effects gamma processes.