Water-lubricated Rubber Research Articles

Magnetic-controlled friction behavior of a water-lubricated magnetorheological rubber bearing under boundary lubrication

To solve the issue of the non-adjustable friction coefficient of water-lubricated bearings in operation, a water-lubricated rubber bearing is designed based on magnetorheological (MR) rubbers in this study. The experimental platform measured the friction coefficients with different magnetic fields and low speed. The friction coefficient of the MR rubber bearing peaks in boundary lubrication. The friction coefficient of the bearings is controlled by the magnetic field, resulting in a reduction of the friction coefficient up to 36%. The theoretical analysis combines the magnetic-dipole model and the theory of friction trinomials. It revealed that the magnetic-controlled modulus of elasticity and loss factor of MR rubber bearings affect the friction coefficient, with the modulus of elasticity factor dominating.

Theoretical and In Situ High Speed Measurement Study on Friction-Induced Vibration in Water Lubricated Rubber Bearing-Shaft System

A water-lubricated rubber stern bearing causes frictional vibration and noise under extreme conditions, severely threatening the survivability and concealment performance of underwater vehicles. To investigate the mechanism of friction-induced vibration and noise, a four-degree-of-freedom nonlinear dynamic model that included bearing support vibration, frictional bearing vibration and torsional shaft vibration was proposed. The velocity-dependent Stribeck friction model described the dynamic friction characteristics between the rubber bearing and stern shaft. Nonlinear system stability was examined using the Lyapunov indirect method and the transient dynamic responses determined by the Runge-Kutta method. Meanwhile, a high-speed in situ measurement experimental study was adopted to explore the mechanism of frictional and torsional vibrations in a water-lubricated bearing-shaft system. Results showed that nonlinear friction excitation was the fatal cause of friction-induced vibration in bearing-shaft system. Under different friction excitations, the coupling vibrations formed between the bearing and bearing support were different, resulting in two main modes of friction-induced vibration: “Chatter” and “Squeal.” The frictional vibration of the bearing and torsional vibration of the stern shaft were tightly coupled. These trends and results might provide a theoretical basis for further research on frictional vibration and wear control in water-lubricated rubber bearing-shaft systems.

Analytical expressions of friction-induced self-excited vibration amplitudes of the marine rubber bearing-shaft system

By the analytical method, this paper investigates the mode-coupling friction-induced instability and the resulting stick-slip self-excited vibration of the marine stern water-lubricated rubber bearing-shaft system. The 2-DOF simplified theoretical model is reasonably developed to characterize stern water-lubricated rubber bearing-shaft system. The complex eigenvalue analysis is conducted to analyze the instability behaviors of the model. Results show the normal force and nonlinear stiffness often deteriorate the stability of the model. Subsequently, two types of analytical expressions for stick-slip vibration amplitude of the model are by the Krylov-Bogoliubbov-Mitropolsky method, which match well with the results from numerical integration. Then, parameter discussion about the influences of friction coefficient, damping, normal force and nonlinear contact stiffness on self-excited vibration amplitudes are performed. The results indicate that the bearing-shaft system can keep the steady-state static equilibrium or the oscillations with small amplitude if the proper parameter values of the variables are chosen, which will benefits controlling the friction-induced vibration of the water-lubricated rubber bearing-shaft system. The novelty of this work is to give analytical expressions for stick-slip self-excited vibration amplitude of the simplified model.

Research on the Vibration Behavior of Ring–Block Friction Pair Made of Materials of Water-Lubricated Rubber Bearing under Special Operating Conditions

A water-lubricated rubber bearing (WLRB) is prone to generate frictional vibration noise under special operating conditions, which seriously affects the acoustic stealth performance of warships and threatens their navigation safety. Meanwhile, the main factor affecting the frictional vibration behavior of a WLRB is the materials of the friction pair. Therefore, this work selects a friction pair composed of a copper ring and a rubber block as the research object and studies the frictional vibration behavior of the ring–block friction pair under low-speed and starting conditions. The real friction coefficient curve is used to establish a transient dynamic finite element analysis model for the ring–block friction pair. The effects of the load, friction coefficient, and Young’s modulus on the frictional vibration behavior under special operating conditions are studied. The analysis’s results show that the frequency of the medium-high frequency friction-induced vibration disappears under low-speed operating conditions when the friction coefficient is below 0.1. During the startup process, even if the friction coefficient is very low, the medium-high frequency friction-induced vibration still exists. The research results provide ideas for future theoretical research and guidance suggestions for engineering practice.

Tribological modification of hydrogenated nitrile rubber nanocomposites for water-lubricated bearing of ship stern shaft

A water-lubricated rubber bearing (WLRB) of ship stern shaft often operates under harsh conditions, which requires a higher tribological performance for bearing materials. Uniformly dispersed nano-fillers can significantly improve the various properties of rubber materials, but nano-fillers are prone to agglomerate in the process of operation, which affects the modification effect. In this paper, a solution blending masterbatch method was used to prepare hydrogenated nitrile rubber (HNBR) nanocomposites and the modification effects of ultra-high molecular weight polyethylene (UHMWPE), nano graphite (NG) powder, nano molybdenum disulfide (NM) and graphite fluoride (GF) on HNBR basic formulation were studied. The results show that the tribological modification of HNBR by UHMWPE is better under low-speed conditions, while the tribological modification of HNBR by GF is better under high-speed conditions. Therefore, in practical engineering application, the reasonable nano fillers are selected for tribological modification according to the operating conditions of water lubricated rubber bearings. It should be pointed out that in order to cover all working conditions, multi nano filler synergistic tribological modification technology is an important technical way to obtain the best comprehensive performance results.

Coupling analysis of turbulent and mixed lubrication of water-lubricated rubber bearings

Water lubricated rubber bearings (WLRBs) are widely used in steam turbines, submarines and other large equipment. Due to the low viscosity of water, water-lubricated bearings are usually in a turbulent and mixed lubrication state at operation. Therefore, a turbulent mixed lubrication model of WLRBs was established by developing an extended average Reynolds equation and includes turbulent, and its rationality was verified by experiments. The results reveal the effect mechanism of turbulence on mixed lubrication under different load, rotational speed, axial misalignment and radius clearance. The contact pressure of WLRBs presents chaotic distribution after considering turbulence. The results also give an optimal axial misalignment and radius clearance that can maximize the turbulent force. The numerical simulation can provide some guidance for the theoretical analysis of WLRBs.

Lubrication Characteristics of Water-Lubricated Rubber Bearings Based on an Improved Algorithm of the Mass Conservation Boundary Condition

Abstract Water-lubricated rubber bearings (WLRBs) are widely used in the propulsion systems of ships and military crafts. Based on the mass conservation boundary condition, the elastohydrodynamic lubrication model of WLRBs is established after considering the elastic deformation of the rubber liner and solved by the finite difference method. An improved algorithm is proposed to track the mass conservation boundary. For the first time, the algorithm allocates independent finite difference grids for the film pressure and fluid fraction to overcome the instability issues and to ensure the flow conservation of each grid cell. The accuracy and stability of the algorithm are verified by the experimental data in the literature, comparison of film pressures calculated by two different finite difference schemes, and flowrate calculations of two different bearings. The lubrication characteristics under the mass conversation boundary condition are compared with classical boundary conditions. The results indicate that the film pressure distribution, velocity distribution, and size and shape of the cavitation zone vary greatly under different boundary conditions in the clearance divergence region. The bearing capacity, attitude angle, and friction force under the mass conservation boundary condition are the largest; those under the double Reynolds boundary condition are smaller; and those under the Reynolds boundary condition are the smallest.

Analysis of mixed lubrication performance of water-lubricated rubber tilting pad journal bearing

Water-lubricated rubber bearing (WLRB) often operate in mixed lubrication. Friction and wear are their common failure modes. In present study, the tilting-pad structure is employed to improve the conventional WLRB. A mixed lubrication model of water-lubricated rubber tilting-pad journal bearing (WLRTPJB) is developed to reveal the mixed elastohydrodynamic (Mixed-EHD) performance. The influence of structure and operating parameters on the tribological properties and pad swing characteristics are studied. The results show a lower contact load of a WLRTPJB, especially under heavy load conditions. The studies also give the optimum pivot offset and preload factor that can minimize the contact pressure. Moreover, the equilibrium tilting-pad angle is sensitive to changes in design and operating parameters. This study would provide certain guiding significance for design optimization of WLRB.

The Influence of Surface Texture on Tribological Characteristics of Water-lubricated Rubber Bearing

To study the effect of surface texture on the tribological characteristics of ship’s water-lubricated rubber bearings, the surface texture modification technology is applied to the friction surface of the lining, and the tribological characteristics of the surface texture are studied. The tribological characteristics of the flow field, such as velocity change, water film pressure distribution, and the influence of water film thickness on the surface texture flow field were discussed by simulation analysis. The results show that the average velocity is decreased on the texture surface, and the water film pressure obtained by the inclined cylinder pitted surface texture is the least.

Effect of different turbulent lubrication models on the lubrication characteristics of water-lubricated rubber bearings at a high Reynolds number

To study the lubrication characteristics of water-lubricated rubber bearings under high-Reynolds-number operating conditions, four different turbulent lubrication mathematical models are used. With these models, adopting the finite difference method, initially, the distributions of the Reynolds number, water film thickness, lining deformation, and film pressure are analyzed. Second, for the same models, the variation in the Reynolds number with the eccentricity is investigated. Third, the bearing capacity and maximum film pressure variation with the eccentricity, rotating speed, and clearance ratio for the four turbulent lubrication models are examined. The results show that the lining deformation and maximum film pressure of the above models are larger than those of laminar lubrication models, and according to the importance of descending orders, they are as follows: Aokihiro-Harada Masahiro turbulence model, Ng–Pan model, Constantinescu model, and Hirs model; the type of the lubrication model has a little effect on the Reynolds number. The bearing capacity and film pressure calculated by the turbulent lubrication models are much higher than those by the laminar lubrication model, and the laminar flow assumption is no longer applicable to the actual operating conditions of the water-lubricated rubber bearings at a high Reynolds number. Concurrently, the Aokihiro-Harada Masahiro turbulent lubrication theory is more accurate than the other three lubrication models. With the increase in the eccentricity and rotational speed, the bearing capacity and maximum film pressure increase non-linearly and approximately linearly, respectively. By contrast, with the increase in the clearance ratio, the bearing capacity exhibits a non-linear decrease, whereas the pressure increases approximately linearly.

Mechanical and Tribological Properties of Nitrile Rubber Reinforced by Nano-SiO2: Molecular Dynamics Simulation

This paper investigated the mechanism of enhancing the mechanical and tribological properties of nitrile rubber (NBR) via the addition of nano-SiO2 on the molecular scale. Molecular dynamics (MD) simulations were performed on molecular structure models of pure NBR, NBR/SiO2, and three-layer friction pairs. The results showed that the hydrogen bonds and interfacial interaction between nano-SiO2 and NBR molecular chains decreased the fractional free volume of NBR nanocomposites and increased the shear modulus of NBR by 25% compared with that of pure NBR. During the friction process, nano-SiO2 decreased the radius of gyration of NBR molecular chains and effectively lowered the peak atomic velocity, the peak temperature, and the peak friction stress at the interface between NBR and copper atoms. The average friction stress on NBR/SiO2 was 34% lower than that on NBR, which meant the tribological properties of NBR were significantly improved by nano-SiO2. The mechanism of nano-SiO2-reinforcing NBR on a molecular scale can lay a theoretical foundation for the design of water-lubricated rubber bearings.

Stick-slip vibration in water-lubricated bearing-shaft system simulated in persistent homology-based machine learning model

Stick-slip vibration images of water-lubricated rubber stern bearing are collected by using machine vision technology. Then these images are analyzed by the methods of persistent homology-based machine learning (PHML). During this analysis, the corresponding barcode is obtained by calculating the homology of the simplicial complex of the vibration images, and the topological characteristics of the vibration images are obtained based on the barcode images, then the support vector machine (SVM) learning is used to study the topological features, and finally the classification and identification of the stick-slip vibration of water-lubricated rubber stern tube bearing are completed. The results have shown that the length of the longest 1D Betti number is closely related to vibration value. Based on these data, it is possible to use the warning beep effectively, create an intelligent description of the beep process, and provide a new idea for simulating stick-slip vibration in the stern bearing.

Numerical study on the dynamic characteristics of water-lubricated rubber bearing under asperity contact

PurposeIn this study, the dynamic characteristics of the water-lubricated rubber bearing considering asperity contact are numerically studied, including water-film stiffness and damping coefficients and plastic-elastic contact stiffness coefficient.Design/methodology/approachThe Kogut-Etsion elastic-plastic contact model is applied to calculate the contact stiffness coefficient at the bearing-bush interface and the perturbed method is used to calculate the stiffness and damping coefficients of water-film. In addition, the rubber deformation is determined by the finite element method (FEM) during the simulation. Parametric studies are conducted to assess the effects of the radial clearance, rubber thickness and elastic modulus on the dynamic characteristic of water-lubricated rubber bearing.FindingsNumerical results indicate that stiffness and damping coefficients of water film and the contact stiffness of asperity are increased with the decreasing of the radial clearance and the dynamic coefficients are less sensitive to the rubber thickness compared with the elastic modulus of rubber. Furthermore, due to the existed groove, a sudden change of the water film direct stiffness and damping coefficients is observed when the eccentricity ratio ranges from 0.6 to 1.0.Originality/valueIt is expected this study can provide more information to establish a dynamic equation of water-lubricated rubber bearings exposed to mixed lubrication conditions.

Effects of sediment size and type on the tribological properties of NBR in water

Nitrile Butadiene Rubber (NBR) is widely used in ship water-lubricated stern tube bearings. Sediments in the water would cause a serious effect on friction and wear properties of the water-lubricated bearings. In this study, the tribological performance of water-lubricated rubber bearings under different sediment particle sizes and sand types were analyzed. Two sediment sand types are involved in the research, (i) SiO2 particles with sizes of 0–25 μm, 48–60 μm, 75–90 μm and 150–200 μm, respectively; (ii) Sediment particles collected from the Yangtze River with sizes of 48–60 μm, 75–90 μm and 120–150 μm, respectively. The friction coefficients and wear volumes as well as surface morphology were measured. It was found that NBR worn by SiO2 particles was worse than that by the sediment within a certain particle size range. On the other hand, the particle sizes exhibited significant effects on the tribological properties. As the particle size increased, the largest wear volume of NBR occurred at particle size of 75–90 μm, While the friction coefficient grew firstly and then fell down, and reached its maximum at particle size of 48–60 μm. Additionally, the friction coefficient demonstrated a negative correlation with sliding speed regardless of the sediment type and particle size. The particle sizes were prevented from flowing into the friction pair as applied load increased. In conclusion, this research offers a great insight for designing water-lubricated bearings.

A Fluid–Solid–Heat Coupling Analysis for Water-Lubricated Rubber Stern Bearing Considering the Deflection of Propeller Shaft

The novelty of the present study is that it investigates the effect of propeller shaft deflection, caused by the propeller self-weight and interfacial mixed forces, on the fluid–solid–heat (FSH) coupling performance of water lubricated rubber stern bearing (WLRSB). In the FSH coupling model, the generalized average Reynolds equation and the Kogut–Etsion asperity contact model are used to determine the hydrodynamic and the elastic–plastic contact behaviors of WLRSB. In the thermal analysis, the journal, water film, and rubber bushing are considered as an integrated system (JWR system) using the Euler method. To prove the correctness of the developed model, the predicted results are verified by comparisons with the experimental results given in the literature. In addition, to assess the effect of the force-driven deflection during FSH simulation, comparisons of the FSH predictions between the aligned journal case and the deflected journal case are carried out. The results indicate that, especially under a heavy load condition, the deflection of the stern shaft should be incorporated into the lubrication gap between the journal–rubber interface during the analysis of FSH performance of the JWR system.

Experimental study on the lubrication characteristics of water-lubricated rubber bearings at high rotating speeds

A test rig is designed to study the lubrication characteristics of water-lubricated rubber bearings. The film pressure signal quality is improved by installing signal conditioners inside the hollow shaft. Four triaxial force sensors are adopted to measure the bearing load in two directions simultaneously. The experimental results show that the film pressure drops rapidly downstream of the minimum clearance. The water film can bear a certain negative pressure without cavitation. As the rotating speed increases, the valley value of the film pressure decreases, and the peak value increases. The increase of water supply pressure improves the hydrostatic pressure, thereby, the film pressure rises over the whole circumference. Different from the laminar flow, the bearing load increases faster as the rotating speed increases, indicating a turbulent flow at high rotating speeds.

The Friction-Induced Vibration of Water-Lubricated Rubber Bearings during the Shutdown Process.

The vibration noise generated by water-lubricated rubber bearings (WLRBs) seriously reduces the concealment of a ship’s navigation. The purpose of this study was to obtain the relationships between friction-induced vibration and the friction coefficient, specific pressure, temperature, and stiffness of the bearing support during the shutdown process of WLRBs. Using transient dynamic analysis (Abaqus/Standard), the shutdown process of the bearing system was simulated by setting a friction coefficient curve, and with the fast Fourier transform (FFT), the data in the time domain were then converted to the frequency domain. In addition, an orthogonal table was applied to select the best level for each factor. The results show that proportionally increasing the friction coefficient and specific pressure caused higher vibrations, and the effect of the specific pressure on vibration is more prominent than that of the friction coefficient. Higher temperatures led to an increase in the peak frequency of noise (squeal) and the virtual value of acceleration. Increasing the stiffness of the bearing support decreased the higher-frequency squeal but dramatically increased the lower-frequency chatter. The results of the study are of guiding significance for the improvement of research methods and the optimization of the materials and structures of WLRBs.

Tribological behaviors of the water-lubricated rubber bearings under different lubricated conditions

Purpose This study aims to evaluate the tribological behavior of water-lubricated rubber bearings sliding against stainless steel under different lubricate conditions. Design/methodology/approach The water-lubricated rubber bearings under various normal loads and sliding speeds were carried out on the ring-block friction test, and the wear morphology is test conducted by using scanning electron microscope. Findings The results indicate that the surface of water-lubricated rubber bearings has a more alternative friction coefficient and wear rate under seawater than other lubricate conditions. The seawater not only acts as a lubricating medium but also brings microstructure while corroding the rubber interface, thereby further enhancing the lubricating effect and storing abrasive debris. Originality/value In this paper, tribological properties of the water-lubricated rubber bearing on ring-block friction test has been investigated. Water-lubricated rubber bearing was carried out on various lubricate conditions, and the friction coefficient, wear rate and worn surface were analyzed. Also, the effects of sliding speeds were investigated. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2020-0204/

Water-Lubricated Stern Bearing Rubber Layer Construction and Material Parameters: Effects on Frictional Vibration Based on Computer Vision

The frictional vibration generated in water-lubricated rubber bearings operating under low speed, heavy load, startup and shutdown conditions can severely degrade the reliability and the sheltered performance of underwater vehicles. The rubber layer of the ship stern tube water-lubricated rubber bearings is easily elastically deformed under certain loads, which affects the damping performance of the bearing system. To explore the effects of thickness, hardness, and concavo-convexity on the damping property of water-lubricated rubber stern bearings, frictional force, vibration, noise, and displacement and deformation of the contact area were studied using a test rig with a transparent glass cylinder. An orthogonal L9(3)4 test design was applied accordingly to determine the optimum construction and material parameters of the rubber layer. Orthogonal test results indicate that among rubber layer hardness, thickness, and test block concavo-convexity, the former is most significant in terms of the frictional vibration, followed by the thickness and, finally, the radius of the surface. When the hardness is 65 A, the thickness is 12 mm, and the plate type is concave, the frictional vibration performance of the rubber layer is optimal. More important, based on the static deformation and the dynamic displacement of the rubber, the causes of the frictional vibration and the influence of different materials and structural parameters on frictional vibration were visually analyzed. The overall trends and the mechanism discussed in this research may be considered as a guideline for the design, optimization, and manufacture of water-lubricated bearings.

Theoretical and experimental analysis of a water-lubricated rubber journal bearing with a large aspect ratio

Purpose The hydrodynamic characteristics of liquid film for bearings, especially water-lubricated bearings with a large length-to-diameter ratio, affect the dynamics behavior of rotor bearing systems. The purpose of this study is to carry out theoretical analysis and experiments to determine the hydrodynamic characteristics of water-lubricated journal bearings. Design/methodology/approach The finite difference method is adopted for the simulation of the characteristics of water-lubricated bearings. The comparison results between water-lubricated bearings with and without grooves, as well as with and without the consideration of the effects of rubber deformation, are presented. The test bearings, test bench, and monitoring system, especially the force exciter for the bearing experiment, are presented. Dynamic coefficient identification verification experiments were performed in different working situations. The obtained results include the calibration of magnetic force, two kinds of excitation, vibration data of the rotor system and dynamic coefficients. Findings The theoretical results demonstrate that the hydrodynamic effect was obvious when the speed was increased and that the water film had improved capability at a working speed of 1800 rpm. The identification results reveal the lubrication situation of the test bearing under low-speed and high-load conditions. Moreover, it was found that the liquid film was not continuous at low speeds. Originality/value The theoretical results can lead to the enhancement of the design level of water-lubricated rubber journal bearings with a large aspect ratio. The experimental results can lead to the improvement of the dynamic behavior design of rotor systems supported using water-lubricated bearings with a large length-to-diameter ratio.