Lubrication Science最新文献

In this work, the tribological properties of a novel iron-based self-lubricating composite as the tribopairs of a plunger pump were systematically studied on an end-face tribometer, and the tribological mechanism was also revealed. The results show that the wear mechanism of the composite can be ascribed to adhesive wear when the sliding speed is lower than 1.5 m/s. As the sliding speed increases from 1.5 to 2.0 m/s, the wear type transforms to oxidative wear due to the increase of tribo-oxidation. In addition, the failure criteria of the tribopair composite materials are summarised. When the average coefficient of friction is greater than 0.04, or the wear rate is greater than 9.66 μm³/(N m), the tribopair fails. This offers a valuable reference for industrial application of the tribopairs made from the iron-based self-lubricating composite.

Nowadays, researches on the use of alkali metal salts as friction-reducing and anti-wear oil additives are continuing. In this study, the tribological effects of heavy metal containing MoS₂ and alkali metal salt CaF₂ additives on pure engine oil (20W50) were investigated using block-on-ring tester configured as surface contact geometry. The tests were performed at various contact loads, revolutions, and additive ratios. The crystal structure of the additives and their effects on surface quality and surface roughness analysed by x-ray crystallography, scanning electron microscope and profilometry. Moreover, Energy dispersive spectrometry was used for element detection on worn surfaces. Results indicated that additives of MoS₂ and CaF₂ can reduce the friction, increase the capacity of load-carrying and the wear resistance of surfaces. The additives improved the operation of the base oil in boundary lubrication zone by increasing the tribofilm forming effect. It was observed that the CaF₂ additive exhibited more stable friction behaviour, while the MoS₂ additive has better protective effects against scratches on the block surface.

The oil film lubrication performance of a large hydrostatic turntable operating at the model of constant surface cutting speed is studied. Firstly, the rotary speed equation which is bound by the constant surface cutting speed is established. According to the fluid lubrication theory, the gap flow equation, the oil film temperature rise equation and the double-rectangular-cavity oil pad bearing capacity equation are derived. Further, a prediction model of oil film lubrication performance in the operating mode is established. The change rules of temperature, pressure and other performance indexes of the film with time are obtained by numerical simulation. And, the above laws are verified by design experiments. It is found that the cutting speed, feed rate leaves a significant impact on the law of variations of oil film performance with time. According to the conclusions, it will be beneficial to improve the bearing capacity of the hydrostatic turntable and further improve the machining accuracy by using cutting parameters reasonably to control the speed within a certain range.

The locally oriented roughness is a common feature of surface finished by a machining process, such as the surface of the cylinder liner, and may significantly influence lubrication characteristic. A homogenised transient Reynolds equation for the locally oriented roughness is derived. The Jacobsson–Floberg–Olsson (JFO) boundary conditions was implicitly incorporated into the transient Reynolds equation to ensure the mass flow conservation. On this foundation, a model for the transient lubrication in the cylinder liner-piston ring considering the effects of the surface roughness and cavitation is established. Then, the results of model developed here are compared with those from the stochastic model by Patir and Cheng. and the effect of the direction of roughness on the lubrication properties is analysed. The homogenised transient Reynolds equation and the lubrication model developed here have great potential for understanding and optimising the transient lubrication considering the surface local roughness orientation, cavitation and starved lubrication.

This study analysed and discussed the friction and wear properties, as well as the interface evolution behaviour of polycrystalline diamond compact (PDC) under various base oils, through conducting friction experiments on PDC/Si₃N₄ with different base oils. The friction and lubrication mechanism of PDC under different base oils were examined using scanning electron microscopy (SEM), x-ray energy dispersive spectrometry (EDS), three-dimensional white light interferometry, and Raman spectroscopy. The results of the study demonstrated that PDC exhibited the best friction and wear performance when lubricated with synthetic oil PAO, followed by castor oil. The inferior performance of paraffin oil can be attributed to its low viscosity, resulting in a lower presence of ions capable of passivating the carbon dangling bond. Consequently, paraffin oil displayed inadequate oxidation stability and increased susceptibility to oil film destruction, ultimately leading to suboptimal friction and wear characteristics. Overall, this study provides valuable insights for industrial applications, aiding in the selection of appropriate base oils as cutting fluids for PDC cutting tools and enhancing the friction and wear properties of PDC.

In liquid hydrogen (LH₂) delivery, submersible centrifugal pump is an important device. Its reliability and efficiency rely on the stability of the bearings. In a high-speed range, cavitation occurs due to the hydrodynamic effect induced pressure undulation. Compared with other cryogenic fluids, cavitation in LH₂ is prone to happen due to its special properties. In this paper, a cavitation model considering thermal properties of LH₂ is proposed based on Rayleigh–Plesset equation. Cavitation characteristics are studied in spiral grooved thrust bearing (SGTB) lubricated by LH₂. The effect of cavitation on load capacity and friction torque are investigated. The most severely-eroded location is predicted by the distribution of mass transfer rate. The influence of bearing structure parameters is studied in respect of cavitation, load capacity and friction torque. The analysis of variance (ANOVA) and range analysis results may provide a reference for optimising LH₂ lubricated SGTB.

In this study, the advancing and receding contact angles of three types of pure liquid on four different surfaces have been measured. The contact angles of the droplet have been measured by analysing the captured photo by tilted plate method. Droplet behaviour has been modelled by two experimental equations. Additionally, the data has been modelled by an artificial neural network using genetic algorithm and a hyperbolic tangent activation function. The input parameters are density, molecular weight of pure liquid and solid, viscosity and surface tension of pure liquid, roughness of the solid surface and the two outputs are advancing and receding contact angles of the droplet. Number of 81 data points were used for training, 27 data for validation and 28 data for testing. The topography of {7,7,2} for artificial neural network has been proposed. The resulting RMS errors were 8%, 8% and 7% for training, validation and testing, respectively.

In order to predict the spiral bevel gear churning power loss, based on the Computational Fluid Dynamics (CFD) method, the computational model for the splash lubrication of the spiral bevel gear pair is established and validated by experiments. The churning power loss of spiral bevel gears is obtained and the corresponding flow field distribution in the gearbox with a pair of spiral bevel gears is analysed under a standard operating condition. For the churning power loss of spiral bevel gears, the loss of teeth surface is mainly caused by pressure while the loss of gear side is mainly generated by the viscous force. The effects of the gear rotational speed, oil level, oil temperature and oil shroud on the churning loss are also investigated and analysed. Ultimately, an optimisation method is proposed for the original spiral bevel geared transmission.

It is very crucial to solve the Reynolds equation quickly and accurately using the numerical methods in the research field of fluid lubrication. For the static Reynolds equation of self-acting gas journal bearings, the typical solution algorithm of the finite difference method is put forward and a new solution algorithm of the finite difference method is proposed. Secondly, the Reynolds equation is solved numerically with the same parameters and the pressure distribution of gas bearings is obtained. Finally, the numerical solution from the new solution algorithm can be obtained with less number of iterations and the less computing time under the different computational grids and bearing numbers. Therefore, the new solution algorithm of the finite difference method is superior to the typical solution algorithm of the finite difference method.

In this research, an angular contact ball bearing with two-half inner rings is used as a carrier. Considering the two-phase flow characteristics of oil and air in the bearing, the flow characteristics of lubricating oil inside the bearing with under-race lubrication are studied. Based on the volume of fluid (VOF) method and the standard k–ε turbulent flow model, the characteristics of oil and air two-phase flow inside the ball bearing are analysed. The bearing internal pressure field distribution, streamline distribution, and other flow properties for the different radial working clearances, pocket clearances and guide clearances are determined. The distribution of the lubricating oil in key areas is observed. The oil phase volume fraction of the key lubrication areas, such as the cage pocket surface and the inner and outer ring surfaces is used to evaluate the influence of different structural parameters on the bearing lubrication performance. The lubrication influences of the inner and outer guides of the cage are evaluated, and the internal flow characteristics of the bearing are analysed with different guide clearances. The results show that with the radial working clearance range from 0.100 to 0.145 mm, the pressure in the working contact area of the bearing decreases 26%. The pocket clearance ranges from 0.48 to 0.28 mm, and the pressure in the working contact area of the bearing significant increases from 0.642 to 1.165 MPa. From this perspective, the larger the radial working clearance and pocket clearance are, the more favourable it is for bearing lubrication. For bearings with under-ring lubrication, when the bearing adopts outer guidance, the distribution of lubricating oil in the key areas of the bearing is worse than that for internal guidance. However, the pressure in the working contact area of the bearing slightly increases from 0.642 to 0.759 MPa with the inner guide clearance increasing from 0.4 to 0.8 mm.