内燃机机油压力低故障原因分析

机油压力是影响润滑效果的关键指标,机油压力低会导致摩擦副之间油膜不理想,使之产生半干摩擦甚至干摩擦,从而造成运转部件摩擦副的磨损,降低使用寿命,甚至拉伤、咬合毁坏的严重后果。在日常运行中,内燃机中机油压力低报警系统亮“红灯”而自动停机的故障较为突出,为了保证内燃机正常工作,就必须维持机油压力在合理的指标内,排除造成机油压力低的原因。

Effect of Ni-coated MoS2 on microstructure and tribological properties of(Cu−10Sn)-based composites

The(Cu−10Sn)−Ni−MoS2 composites,prepared by powder metallurgy,were studied for the effects of Ni-coated MoS2 on the microstructure,mechanical properties and lubricating properties.The mechanism of effects of Ni and MoS2 on the properties of composites was analyzed through a comparative experiment by adding Ni and MoS2 separately.The results show that the nickel wrapping around the MoS2 particles decreases the reaction rate of MoS2 with the copper matrix,and greatly improves the bonding of the matrix.The composites with 12 wt.%Ni-coated MoS2(C12)show the optimum performance including the mechanical properties and tribological behaviors.Under oil lubrication conditions,the friction coefficient is 0.0075 with a pressure of 8 MPa and a linear velocity of 0.25 m/s.The average dry friction coefficient,sliding against 40Cr steel disc,is measured to be 0.1769 when the linear velocity and pressure are 0.25 m/s and 4 MPa,respectively.

Predictions of friction and flash temperature in marine gears based on a 3D line contact mixed lubrication model considering measured surface roughness

Wear and scuffing failures often occur in marine transmission gears due to high friction and flash temperature at the interface between the meshing-teeth.In this paper,a numerical solution procedure was developed for the predictions of transient friction and flash temperature in the marine timing gears during one meshing circle based on the 3D line contact mixed lubrication simulation,which had been verified by comparing the flash temperature with those from Blok’s theory.The effect of machined surface roughness on the mixed lubrication characteristics is studied.The obtained results for several typical gear pairs indicate that gear pair 4-6 exhibits the largest friction and the highest interfacial temperature increase due to severe rough surface asperity contacts,while the polished gear surfaces yield the smallest friction and the lowest interfacial temperature.In addition,the influences of the operating conditions and the gear design parameters on the friction-temperature behaviors are discussed.It is observed that the conditions of heavy load and low rotational velocity usually lead to significantly increased friction and temperature.In the meantime,by optimizing the gear design parameters,such as the modulus and the pressure angle,the performance of interfacial friction and temperature can be significantly improved.

Friction coefficient and microhardness of anodized aluminum alloys under different elaboration conditions

The effects of anodizing conditions （electrolyte, current density and temperature） on the friction coefficient and Vickers mierohardness of anodic oxide layers formed on A1 5754 and A1 1050A substrates were investigated. The studied properties were examined using DELTALAB HVS-1000 Vickers mierohardness tester and rotating pin on disc tribometer. It was established that the highest microhardness （〉HV 400） and the lowest friction coefficient （〈0.4） were obtained with the oxalic acid addition of 10 g/L at high current density of 3 A/dm2 and low temperature of 5 ~C. The presence of oxidized Mg through the anodic oxide layer formed on A1 5754 was examined using glow-discharge optical emission spectroscopy （GDOES）. The MgO was found to act negatively on the mechanical property of the layer. Finally, the scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, and atomic force microscopy （AFM） were used to characterize the anodic layer before and after friction tests. It is found that the wear mechanism is related to many aspects of the initial morphology, chemical composition of the layer （C, S and Mg）, porosity and internal stress.

Effect of applied load on transition behavior of wear mechanism in Cu-15Ni-8Sn alloy under oil lubrication

Tribological behavior of Cu-15Ni-8Sn(mass fraction, %) alloy against GCr15 ring under various loads was investigated on a ring-on-block tester in oil lubrication. The results showed that the wear rate increased slowly from 1.7×10^(-7) to 9.8× 10^(-7) mm^3/mm under the load lower than 300 N, and then increased dramatically to the climax of 216×10^(-7) mm^3/mm under the load over 300 N, which indicated the transition of wear mechanism with the increase of applied load. The wear mechanism mainly was plastic deformation and abrasive wear under the load less than 300 N. As the applied load was more than 300 N, the wear mechanism of Cu-15Ni-8Sn alloy primarily was delamination wear. Besides, the transition can also be confirmed from the different morphologies of worn surface, subsurface and wear debris. It is distinctly indicated that the appearance of flaky debris at the applied load over 300 N may be a critical point for the change of wear mechanism.

Competitive Adsorption of Anticorrosion and Antiwear Additives

Simulated adsorptive experiments using the axletree and lubricating oil containing anticorrosion additive were conducted,and the UV absorbance of the lubricating oil before and after the adsorptive experiments was measured.Through the UV spectral measurements the difference in UV absorbance of the lubricating oil before and after the adsorptive experiments was identified,the adsorbed quantity of anticorrosion additive in the interfacial film between lubricating oil and bearing was calculated using the Lambert-Bell principle to verify the adsorption of corrosion inhibitor on the surface of friction pairs.Adsorption experiments on lubricating oil containing both antiwear and anticorrosion additives were carried out and the UV absorbance of lubricating oil samples before and after the experiments was measured to determine the difference in the UV absorbance among lubricating oil samples with the same mass fraction of anticorrosion additive and different mass fractions of antiwear additive.By measuring the ultraviolet spectral absorbance of lubricating oil samples and calculating the adsorbed quantity of anticorrosion additive in the interfacial film it was possible to determine the influence of antiwear additive on the quantity of adsorbed anticorrosion additive on the surface of friction pairs and verify the competitive adsorption relationship between the antiwear additive and the anticorrosion additive.

Skin friction reduction characteristics of variable ovoid non-smooth surfaces

The use of bionic non-smooth surfaces is a popular approach for saving energy because of their drag reduction property. Conventional non-smooth structures include riblets and dimples. Inspired by sand dunes, a novel variable ovoid non-smooth structure is proposed in this study. The body of the variable ovoid dimple was designed based on three size parameters, the radius, semimajor, and depth, and a 3D model was created based on UG software. The constructed variable dimples were placed in a rectangular array on the bottom of a square tube model. Following ANSYS meshing, the grid model was imported into FLUENT, where the flow characteristics were calculated. Results of skin friction reduction were achieved and the effect of the design parameters on different variable ovoid dimples was obtained by orthogonal testing. Various aspects of the skin friction reduction mechanism were discussed including the distribution of velocity vectors, variation in boundary layer thickness, and pressure distribution.

Influence of groove surface texture on temperature rise under dry sliding friction

Parallel groove surface textures with different area densities were fabricated on ASTM 1045 steel. Friction tests were con- ducted under dry sliding condition. Temperature rise, friction coefficient and wear of both the textured and untextured speci- mens were studied. An embedded K-type thermocouple beneath the friction surfaces was employed to measure frictional tem- perature rise. The results indicated that the temperature rise of the textured specimen was obviously reduced compared with that of the untextured specimen, although the difference between the friction coefficients was not significan.. The specimen with high texture density exhibited a small temperature rise. The difference in temperature rise between the specimens with different texture densities can be primarily attributed to differences in heat dissipation and energy allocation between the tri- bo-pairs caused by the textured structure. The energy consumed by wear and plastic deformation was small in ~：omparison with the total energy input by friction, thus, the influence of these factors on temperature rise can be considered to be~ negligible.