Bearing Oil Film Research Articles

Generation mechanism and anti-friction effect evaluation of continuous micro-groove texture machined by ball-end milling process

Abstract The tool path in ball-end milling process is flexible and controllable considering the structure characteristics and moving way of the cutter. This paper aims to reveal the generation method of continuous surface micro-groove texture by using ball-end milling process and evaluate the corresponding anti-friction performance by combining simulation and friction experiments. Results indicate that continuous micro-grooved surface texture can be obtained by combining small feed per tooth and large radial cutting depth. Radial depth of cut and tool radius affect aspect ratio of micro-groove. The bearing capacity of the oil film shows an increasing and then decreasing trend with the increase of radial depth of cut and orientation angle. Radial depth of cut increased from 0.1 mm to 0.3 mm, resulting in a maximum 4.87% increase in the bearing capacity of oil film because of the enhanced wedge effect. However, further increase in radial depth of cut leads to increased vortex, weakening the wedge effect. The oil film bearing capacity is reduced so that the friction coefficient increases by a maximum of 510%. Moreover, as the orientation angle increases from 10° to 20°, the bearing capacity of the oil film increases by 22.7%. The minimum friction coefficient currently is 0.0215. However, when the micro-groove orientation angle is further increased, the countercurrent effect is enhanced and the dynamic pressure effect is weakened, which finally leads to a decrease in the bearing capacity of the oil film. The friction coefficient has increased by 30.2% maximum. This study is of great significance which provides a new method for guiding the friction reduction on the die surface.

Analysis of oil film flow characteristics and lubrication performance of thrust bearing of 1000MW Hydraulic Turbine Unit

Abstract Hydro-generator unit is the core component of the hydropower station, and the stability of the shaft system directly determines the safety of the hydropower station. Thrust bearing is the only component to bear axial load, and working performance directly affects the stable operation and efficiency of the unit. In this study, a full 3D model of the shaft system of a 1000 MW hydro-generator unit is established, and the oil flow of thrust bearing oil film and oil in the oil tank considering the spray system and the overall model is analysed by means of the thermo-hydrodynamic method. The results show that the load increases with increasing inclination angle. Within certain limits, the pressure and temperature of the oil film increase with increasing inclination. And there are many vortices in the tank. Although the spray system reduces the oil churn, the lubricating oil flow between pads is chaotic. The loss is mainly caused by the chaotic flow between pads. Analyzing the effects of oil film thermal effects on bearing loads, lubricant flow, and bearing surface temperatures of tilting pads provides valuable insights for bearing design and maintenance guidance.

Nonlinear Dynamic Analysis and Forecasting of Symmetric Aerostatic Cavities Bearing Systems

Symmetric Aerostatic Cavities Bearing (SACB) systems have attracted increasing attention in the field of high-precision machinery, particularly rotational mechanisms applied at ultra-high speeds. In an air bearing system, the air bearing serves as the main support, and the load-carrying capacity is not as high as that of oil film bearings. However, the aero-spindle can operate at considerably high rotational speeds with relatively lower heat generated from rotation compared with that of oil film bearings. In addition, the operating environment of air bearings does not easily cause the rotor to deform. Hence, through adequate design, air pressure systems exhibit a certain level of stability. In general, the pressure distribution function of air bearings exhibits strong nonlinearity when there are changes in the rotor mass or rotational speed, or when the bearing system is inadequately designed. These issues may lead to instabilities in the rotor, such as unpredictable nonperiodic movements, rotor collisions, or even chaotic movements under certain parameters. In this study, rotor oscillation was analyzed using the maximum Lyapunov exponent to identify whether chaotic behavior occurred. Machine learning methods were then used to establish models and predict the rotor behavior. Especially, random forest and extreme gradient boosting were combined to develop a new model and confirm whether this model offered higher prediction performance and more accurate results in predicting tendencies with considerable changes compared with other models. The results can be effectively used to predict the SACB system and prevent nonlinear behavior from occurring.

Simulation study on the performance of gap oil film lubrication under extreme working conditions of micro‐textured hydrostatic support

AbstractBased on the theory of fluid mechanics, the lubrication performance of micro‐textured hydrostatic bearings is derived. Under extreme operating conditions, the lubrication performance of clearance oil film without micro‐texture and with rectangular and triangular micro‐textures added to the oil sealing edge is simulated, and the experimental verification of the lubrication performance of the double rectangular cavity without micro‐texture is conducted. The results show that regardless of whether micro‐texture is added or not, the oil film pressure is distributed in a stepped shape, and the highest temperature of the oil film occurs at the intersection of the oil sealing edges on the outside of the double rectangular cavity. When the maximum depth of triangular micro‐texture is 1.5 mm and the dimension of a segment is 1 mm, triangular micro‐texture with an obtuse angle of 103° has the best comprehensive lubrication performance, but its oil film bearing capacity still does not exceed that of rectangular micro‐texture.

Generation method and antifriction performance evaluation of discrete micro-pit surface texture based on high speed ball-end milling process

Benefiting from the structural characteristics of the ball-end milling cutter and the tool motion characteristics during the cutting process, the high speed ball-end milling process can be directly used to manufacture discrete surface micro-pits texture with different sizes and distributions. The influencing mechanism of the interval and distribution of the micro-pit texture on the antifriction performance was investigated by combining Fluent fluid simulation and reciprocating sliding friction test under oil immersion lubrication condition. Results show that the textured surface with micro-pit features shows obvious antifriction ability. The friction coefficient of textured surface was reduced by 61.5 % compared with that of polished specimens. The interval can influence the oil film bearing capacity and then the antifriction ability. The most significant friction reduction effect was achieved when the micro-pit interval was 900 μm. Additionally, the friction coefficient can be further reduced by optimizing the distribution of the micro-pits. The friction coefficient decreased to 0.121 for the orientation angle 70° condition.

Investigation on the Dynamic Pressure Effect of Clearance Oil Film at a Stepped Hydrostatic Thrust Bearing Working in Heavy Loading Duty

The dynamic pressure effect of the clearance oil film of stepped hydrostatic thrust bearing is studied by taking the double rectangular cavity oil cushion as an example. According to the hydrodynamics theory, the dynamic pressure of lubricating oil film in different clearance height regions is theoretically deduced and calculated. The dynamic pressure effect of the clearance oil film in the stepped hydrostatic thrust bearing is studied through the combination of theoretical calculation, simulation, and experimental verification. It is found that the experimental value of the dynamic pressure is between the theoretical value and the simulated value, which is basically not affected by the load. In the speed range of 0 r/min–200 r/min, compared with the viscosity of lubricating oil, the speed is the main factor affecting the dynamic pressure of the oil film of the stepped hydrostatic thrust bearing. The dynamic pressure value of the clearance oil film increases in a stepped fashion along the radial direction of the double rectangular cavity oil cushion. The dynamic pressure value has an obvious upward trend at the junction of the circumferential right oil cavity and the sealing edge and then decreases to 0 after reaching the peak value.

Tilting Pad Journal Bearing Computational Fluid Dynamic Parametric Modeling for New Energy Transition Challenges

Abstract The necessity of increasing the efficiency and reducing the carbon foot-print of machines is pushing centrifugal compressor bearings design to higher and higher peripheral speed and lower oil consumptions especially in the new energy transition fields, resulting in an increase in the bearing temperatures. Therefore, the bearing thermal management starts to play a major role in extending the machine operability and reducing the maintenance frequency. A full three-dimensional (3D) parametric conjugate heat transfer computational fluid dynamic (CFD) model for tilting pad journal bearings (TPJBs) is introduced in this paper to address the temperature aspects of oil-film bearings. The parametric geometry of the model and the automatic mesh update, allow the equilibrium position search to be obtained without adopting any dynamic mesh algorithms. The tilting pad and rotating shaft equilibrium position are automatically calculated with a Newton–Raphson algorithm. The static performance of the TPJB is investigated for different journal diameters, bearing clearance, and operating conditions. The numerical results obtained are compared with experimental data from compressor mechanical running tests to demonstrate the reliability of the model presented. The 3D distributions of the oil pressure, velocity, and temperature given by the CFD model, can be locally optimized to face the new energy transition challenges.

Experimental study on hydro- thermal behavior of journal bearing oil film profile in a slow speed diesel engine

Utilizing universal journal bearing test rig, the performance of a heavy-loaded main journal bearing has been investigated based on tracing operational behavior of oil film temperature and pressure profiles. Test trials were conducted observing the loading program of slow speed diesel engine. Examining the effect of different oil grades, it turned out that oil grade of higher viscosity index enhances journal bearing performance and maintains oil film temperature profile stability at both maximum speeds and heavy loads. Further, medium viscosity grade oil reduces fuel consumption and costs from power production for all operational conditions. Regarding the impact of heavy loads on shaft power performance with medium viscosity oil grade, the differences between optimal and heavy loads get lower as the shaft speed increases. Those were 22 %, 9.7 % and 2.1 % corresponding to the shaft speeds of 43 rpm, 90 rpm and 104 rpm respectively. Additionally, the lower the value of the maximum oil film pressure Pmax difference between optimal and heavy load, the higher the ability of the lubricant to promote performance and provide enhanced operating condition stability. Yet, at part load operating conditions entailing running journal shaft at slow speeds during ship maneuverability, it cannot be considered as the best selection due to the heavy loads often applied in such critical operating conditions. Finally, the test-trial based experimental outcomes can provide useful guidance regarding the proper selection of a lubricant for enhanced performance, cost saving and prolonged journal bearing working life.

Thermal characteristics and distribution rule of lubrication film of full ceramic ball bearing under different service condition

PurposeThe study aims to the distribution rule of lubricating oil film of full ceramic ball bearing and improve its performance and life.Design/methodology/approachThe paper established an analysis model based on the fluid–solid conjugate heat transfer theory for full ceramic ball bearings. The distribution of flow, temperature and pressure field of bearings under variable working conditions is analyzed. Meanwhile, the mathematical model of elastohydrodynamic lubrication (EHL) of full ceramic ball bearings is established. The numerical analysis is used to study the influence of variable working conditions on the lubricant film thickness and pressure distribution of bearings. The temperature rise test of full ceramic ball bearing under oil lubrication was carried out to verify the correctness of simulation results.FindingsAs the speed increased, the oil volume fraction in full ceramic ball bearing decreased and the surface pressure of rolling element increased. The temperature rise of full ceramic ball bearings increases with increasing speed and load. The lubricant film thickness of full ceramic ball bearing is positively correlated with speed and negatively correlated with load. The pressure of lubricating film is positively correlated with speed and load. The test shows that the higher inner ring speed and radial load, the higher the steady-state temperature rise of full ceramic ball bearing. The test results are in high agreement with simulation results.Originality/valueBased on the fluid–solid conjugate heat transfer theory and combined with Reynolds equation, lubricating oil film thickness formula, viscosity temperature and viscosity pressure formula. The thermal analysis model and EHL mathematical model of ceramic ball bearings are established. The flow field, temperature field and pressure field distribution of the full ceramic ball bearing are determined. And the thickness and pressure distribution of lubricating oil film in the contact area of full ceramic ball bearing were determined.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2023-0126/

Study on Hydrodynamic Lubrication and Friction Reduction Performance of Cylindrical Rolls With Tesla Valve Texture

Friction and wear seriously affect the efficiency and life of a machine device. The dynamic pressure lubrication and friction properties of the surface are improved by surface texture technology, which plays an extremely important role in reducing friction and wear. In order to maximize the hydrodynamic lubrication and friction reduction performance of surface texture, a Tesla valve surface texture is proposed in this article. The oil film bearing capacity and wall friction of Tesla valve texture are examined through computational fluid dynamics fluid simulation. Cylindrical rolls with Tesla valve texture are prepared by using laser processing technology, and comparative friction wear tests are conducted. The results show that the lubrication performance of Tesla valve texture is four times higher than without this texture. The friction coefficient and wear loss of the cylindrical rolls with Tesla valve texture are, respectively, 39.7% and 66.7% lower than those of the cylindrical rolls without texture. Tesla valve texture effectively improves the dynamic pressure lubrication and friction in the cylindrical rolls.

A review on recent advancements in an automotive turbocharger rotor system supported on the ball bearings, oil film and oil-free bearings

A review on recent advancements in an automotive turbocharger rotor system supported on the ball bearings, oil film and oil-free bearings

A method for the estimation of oil film parameters in an asymmetric rotor-bearing system

PurposeAsymmetric rotating machinery supported by oil film bearings is relatively common in practical applications. The purpose of this study is to propose a method for estimating the oil film parameters of the bearings in an asymmetric rotor-bearing system.Design/methodology/approachThe proposed method requires the finite element model and translational displacement responses at the center of mass and bearings locations to form a regression equation to estimate the unknown parameters. Due to the transverse stiffness of the asymmetric rotor is not symmetrical, the analysis and parameter estimation procedures are performed in a rotating coordinate. Numerical simulations were carried out to illustrate the vibration characteristics of the asymmetric rotor system. The proposed method is applied to the simulated responses to estimate the assumed oil film parameters. The influence of the estimated parameter deviations on the rotor dynamic characteristics is discussed.FindingsThe vibration characteristics of asymmetric rotors are different from those of symmetrical rotors. The bearing parameters estimated by the proposed method are close to the assumed values, within a maximum error of 9%. The deviations of the estimated parameters have little effect on the vibration characteristic of the rotor system.Originality/valueThe proposed method does not require changing the rotational speed or applying additional excitation force to the rotor, which is suitable for the field test.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2023-0111/

Vibration characteristics of turbocharger rotor system considering internal thread texture parameters of semi-floating ring bearing

The internal thread texture causes changes in the dynamic characteristics of the oil film of the semi-floating ring bearing, which affects the amplitude of vibration and operating life of the turbocharger rotor system. Based on the fluid lubrication theory, the oil film governing equation of a semi-floating ring bearing with surface texture parameters is derived. The effects of the texture depth, position, and number of turns of the internal thread on the dynamic characteristics of the bearing oil film, such as the maximum pressure, load-carrying capacity and stiffness damping, are analyzed. Taking a type of turbocharger as an example, a hydrodynamic model is established to analyze the oil film lubrication in the semi-floating ring bearings, and the dynamic characteristic of the oil film is analyzed by computational fluid dynamics method. The results show that the maximum pressure, bearing capacity, and stiffness damping coefficient of oil film increase firstly and then decrease with the increase of texture depth and the number of thread turns in the range of journal rotation speed from 1000 to 20,0000 r/min. Compared with the non-texture bearings, the dynamic characteristics coefficients of the oil film such as bearing capacity and stiffness damping increase the most, when the depth of texture is 0.006 mm and the number of thread turns is 9. Secondly, the dynamic characteristic coefficient of oil film is improved when the texture is distributed in the middle than on both sides. The thread texture with appropriate parameters can suppress the rotor system vibration amplitude. The conclusion can provide a reference for the design of textual parameters of semi-floating ring bearings.

Research on Load-Sharing Technology of Toroidal Planetary Worm Based on Sliding Oil Film Supporting Roller

In the manufacturing and assembly of a toroidal drive mechanism, errors have a great influence on the load sharing of the mechanism. In order to improve the load-sharing characteristics of the mechanism, a floating oil film structure system is designed to support the planetary gear and to compensate for inaccuracies in the manufacturing and assembly of the mechanism parts in this paper. The elasticity and hydrodynamic effect of the floating oil film allow the planetary gear to achieve its own small floatation and produce a certain axial displacement, which compensates for the influence of error and achieves load sharing. To examine the effect of the floating oil film structure, the floating oil film bearing is simulated by FLUENT, the characteristics of the floating oil film are analyzed, and the stiffness and damping coefficients of the floating oil film are calculated. In ADAMS, the method of equivalent replacement of the floating oil film with spring damping is adopted to conduct a dynamic analysis on the toroidal drive mechanism with the floating oil film load-sharing structure, and the results show that the system with a floating oil film structure can effectively compensate the influence of errors and improve the uniform load performance.

Calculation and Lubrication Characteristics of Cylindrical Roller Bearing Oil Film with Consideration of Thermal Effects

Aiming at the problem of how the thermal characteristics of cylindrical roller bearings affect the lubrication characteristics of bearings under actual working conditions, the influence of parameters such as speed and load on the lubrication characteristics of cylindrical roller bearings under thermal effects is analyzed. The numerical calculation method combining the quasi-static model of cylindrical roller bearing and the thermal elastohydrodynamic lubrication model is adopted. The effects of rotational speed, load and thermal effect on the lubrication performance of the bearing and the lubrication state under certain oil supply conditions were analyzed via numerical model calculation. The oil film thickness was measured via an immersion ultrasonic method to verify the correctness of the model. The results show that the larger the bearing speed, the larger the central film thickness and the minimum film thickness. At the same time, the thermal effect on the film thickness is more obvious; the greater the load, the greater the maximum oil film pressure. The film thickness gradient in the inlet region is greatly reduced, but the thermal effect has no obvious effect on the overall film thickness. In addition, there is a critical value of effective lubrication film thickness for each set of operating parameters. When the actual film thickness is equal to the critical value, the bearing lubrication state is at its best; the numerical simulation results are compared with the experimental values. Under the calculation conditions, the maximum error at the measuring point is within 10%, which meets the error requirements and provides a theoretical basis for revealing the bearing lubrication mechanism.

The Effects of Interval Uncertainties on Dynamic Characteristics of a Rotor System Supported by Oil-Film Bearings

Rotating systems equipped with oil-film bearings are critical and common in many industrial machines. There are various non-random uncertainties in such fluid-lubricated dynamic systems. It is important to quantify the effects of uncertainties without adequate statistical information on the dynamics of rotor-bearing systems. In this paper, a rotor system with oil-film bearings at both ends is investigated considering many interval uncertainties. The rotating system is modeled in a deterministic sense. The Chebyshev interval method is used to track the propagation of different uncertainties. Deviations in the steady state responses, time history, and shaft orbits are calculated and comparatively discussed. Influence patterns of different interval parameters and dispersions in various dynamics are presented in detail. It is found that there can be global and local impacts as well as cumulative effects caused by multi-source uncertainties. The findings of the present study could be helpful for a more insightful dynamic analysis of rotor-bearing systems as well as their optimal design and maintenance.

Oil Cavitation Morphology Analysis of Textured Cylindrical Rotating Friction Pair on Circular-Disk End Faces

Cavitation is a destructive hydraulic phenomenon; it causes damage to small hydraulic machinery and large water-conservancy projects, and cavitation and cavitation corrosion problems are long-standing problems for hydraulic machinery experts. Micro-textures are often machined onto the end face near the indirect contact point to increase the oil film bearing capacity and reduce the transfer torque in hydraulic machinery, but the pressure disturbance caused by the texture dimple and boundary can induce cavitation. To delay or eliminate cavitation on the textured surface of equipment such as mechanical seals and dynamic bearings, the cavitation effect of a cylindrical texture on a rotating frictional pair was investigated from theoretical, imitational, and experimental perspectives. Low pressure is extremely important for inducing cavitation; once cavitation conditions are met, a full bubble can be formed in about 0.015 s. Cavitation mainly occurs at the outer radius of the rotating end face, i.e., in the high-speed region. There is a mutual mass transfer between gas and liquid phases when cavitation occurs, but the generation of cavitation bubbles is faster than its collapse, thus causing an increasing cavitation region.

Analytical Research on the Bearing Characteristics of Oil Film Supplied with Constant Oil Flow Hydrostatic Turntables under Fixed Eccentric Load Condition

This study was initiated in view of the phenomenon that hydrostatic turntable rails are prone to scrape damage when the liquid hydrostatic turntable is running under fixed partial load. The existing bias-load hydrostatic turntable oil film bearing characteristics are mainly calculated by using the calculus integration method and CFD fluid simulation method. The calculating formula obtained by the calculus integration method is complex and inefficient. The CFD fluid simulation calculation method requires 3D modeling and meshing of the oil film, which is a tedious and time-consuming process and may not yield convergent calculation results due to improper meshing methods or boundary condition settings. In order to solve the shortage of the above calculation methods, this paper simplifies and equates the uneven thickness of the oil film of each sealing edge of the oil pad of the bias-loaded hydrostatic rotary table to the equivalent uniform thickness of the oil film, and based on this idea, the analytical calculation formula of the oil film bearing capacity, bending moment and stiffness under constant bias-load conditions of the constant-flow liquid hydrostatic rotary table is derived. In this paper, Fluent software was used to numerically simulate the oil film under this working condition, and a hydrostatic turntable test bench was established to conduct an experimental study on the biased load hydrostatic turntable; the experimental data and simulation results were compared with the results obtained from this simplified method of calculating the oil film loading characteristics. The results show that the error of oil film bearing capacity is less than 6% and the error of overturning moment is less than 7%, which has verified the validity of the calculation method. The simplified analytical calculation method proposed in this paper is used to study the influence of tilt displacement rate, lubricant flow rate and turntable speed on the basic performance parameters of oil film, which provides a theoretical basis for the study of oil film load-bearing characteristics under constant bias-load conditions of the constant-flow liquid hydrostatic turntable.

Tribological properties and lubrication state transitions of textured CSS-42L bushing filled with Sn-Ag-Cu-Ti3C2 of oil-film bearing

To improve the antifriction and vibration reduction performances of oil-film bearings in hydroelectric generating set, textured CSS-42L surfaces filled with Sn-Ag-Cu-Ti3C2 (TSs-SACT) were prepared, and the friction and vibration experiments under oil lubrication were carried out. The results showed that TSs-SACT with texture pitch of 600 μm and MXene of 5 wt.% (TSs-SACT(5%)-600) had the best antifriction, which reduced the fluctuation amplitudes of frictional forces and suppressed the friction-induced vibrations. The wear morphologies were improved by the synergistic effects of oil, grooves and Sn-Ag-Cu-Ti3C2, and TSs-SACT(5%)-600 with uniform profiles had the excellent wear resistance. The complexity of surface profiles could be characterized by fractal dimension, which can be enhanced by Sn-Ag-Cu-Ti3C2. TSs-SACT(5%)-600 with complex profiles keeps good antifriction during lubrication state transitions, which effectively improves the operation reliability of oil-film bearing in hydroelectric generating set.

Research on cavitation effect of microtextured array

In this paper, the surface texture parameters and distribution patterns are studied by numerical simulation and experiment. First, a three-dimensional micro-textured CFD fluid lubrication model with cavitation effect is established, and different texture arrays are designed to study the influence of different distribution modes on bearing capacity, friction coefficient and pressure distribution of the oil film. Then, the simulation results are further analyzed and verified by the visualized plane slider experimental platform, and the formation rules of cavitation bubbles in the micro-textured array, as well as the influences of the surface shape and different distribution modes of the micro-textured array on the cavitation bubbles are discussed. The results show that the existence of cavitation is one of the main reasons for the microtexture to increase the bearing capacity of the oil film, which cannot be ignored in the simulation study. The texture array with single symmetric orientation is the best to improve the oil film bearing capacity, and the bearing performance is the best when the texture inclination angle is 26.6°.The friction coefficient of the asymmetrically oriented textured array is 29.4% lower than that of the non-textured sample.The results in the experiment are consistent with the simulation.