Compression Heating and Cooling in Elastohydrodynamic Contacts

In this study, the infrared temperature mapping technique, originally developed by Sanborn and Winer (Trans ASME J Tribol 93:262–271, 1971) and extended by Spikes et al. (Tribol Lett 17(3):593–605, 2004), has been made more sensitive and used to study the temperature rise of elastohydrodynamic contacts in pure rolling. Under such conditions lubricant shear heating within the contact is considered negligible and this allows temperature changes due to lubricant compression to be investigated. Pure rolling surface temperature distributions have been obtained for contacts lubricated with a range of lubricants, included a group I, and group II mineral oil, a polyalphaolefin (group IV), the traction fluid Santotrac 50 and 5P4E, a five-ring polyphenyl-ether. Resulting maps show the temperature rise in the contact increases in the inlet due to compression heating and then decreases and in most cases becomes negative in the exit region due to the effect of decompression. Temperature changes increase with entrainment speed but in the current tests are always very small, and less than 1 °C. Contact temperature rises from compression were compared to those from sliding contacts (where a slide-roll ratio of 0.5 was applied). Here the contribution to the contact temperature from compression is shown to decrease dramatically with entrainment speed. The lubricant 5P4E is found to behave differently from other lubricants tested in that it showed a peak in temperature at the outlet. This effect becomes more pronounced with increasing speed, and has tentatively been attributed to a phase change in the exit region. Using moving heat source theory, the measured temperature distributions have been converted to maps showing rate of heat input into each surface and the latter compared with theory. Qualitative agreement between theory and experiment is found, and a more accurate theoretical comparison is the subject of ongoing study.     

滚动轴承新理论与新设计

本文对滚动轴承传统计算方法与新计算方法计算的轴承寿命进行了对比分析。结果表明，滚动轴承材料和工作条件（润滑和污染等）对其寿命有重要影响，证明材料的精化、合理的润滑和密封设计的重要性。     

Traction of Lubricated Rolling Contacts between Thin-Film Coatings and Steel

Tribological thin-film coatings can enhance the performance of mechanical components such as bearings and gears. Although a lubricant is present in most applications, the interactions of the lubricant with the coated surfaces are not always well understood. In the present study, Stribeck curves (i.e., traction coefficient vs. dimensionless film thickness λ) were generated for lubricated rolling contact between coated and uncoated surfaces. Chromium nitride, tungsten carbide–reinforced amorphous hydrocarbon, and silicon-incorporated diamond-like carbon coatings were evaluated. Compositions, hydrogen concentrations, Raman spectra, and surface energies are reported for the films. A ball-on-flat test configuration was used in 5%, 50%, and 100% slide-to-roll conditions. The test lubricant was a polyalphaolefin containing rust and oxidation inhibitor additives only. Differences in traction performance were observed for different coating types. Traction coefficients decreased at high λ with increased hydrocarbon content in the coating. Coating micro-texture and composition were believed to influence traction as λ became small.     

The Influence of W-DLC and CrxN Thin Film Coatings on Impact Damage between Bearing Materials

In this work, the effect of hard tribological coatings was studied in terms of mitigating impact damage between tungsten carbide spherical elements and two different types of steel substrates. The coatings included a hard, highly elastic Tungsten-incorporated diamond-like carbon (W-DLC) coating at two different thicknesses and a harder, less elastic Cr_xN coating. Impacts were created using a drop-test rig described herein and characterized in three ways: a measure of the coefficient of restitution during impact, investigation of the impact site using an optical interferometer, and fixed ion beam cross sections of select impacts for observation of subsurface damage within the coating and substrate. It was found that hard coatings on softer substrates such as 440C steel were able to mitigate surface damage up to a certain impact speed, depending on the coating, but were unable to influence the coefficient of restitution. On harder substrates like 52100 alloy steel, the coatings were found to increase the coefficient of restitution, indicating a reduction in energy loss due to plastic deformation, and to reduce damage at each tested speed. These effects and their potential influence on bearing performance are discussed in regard to impact mechanics, surface metrology, and the material properties of the coating and substrate acquired by nanoindentation.     

A New Form of Rolling Contact Damage in Grease-Lubricated,Deep-Groove Ball Bearings

A new form of rolling contact damage was discovered in the fatigue tests of series 6206 deep groove ball bearings under pure radial load with grease lubrication. The appearance of the damage reveals a few cracks at right angles to the rolling direction of the ball, along with the formation of a dent about 20 μ m deep in the raceway surface. This is found to occur only on the stationary outer ring raceway and the ball surface and is distributed widely within the load zone. Furthermore, under the raceway surface several cracks propagating into the substrate at an angle of about 60-80 degrees relative to the raceway surface are observed not only under the damage site but also in other nearby locations. Only the cracks at the damage position open up to the surface. The grease used for the test contained a lithium complex thickener with mineral oil as the base oil with a kinematic viscosity of 141 mm²/s at 40°C. On the test bearings two pure radial load levels of 9.14 and 12.13 kN were applied. In order to prevent the occurrence of seizure at each load, the speed of the inner ring of the test bearing was maintained at 1800-2500 min^{? 1} and 600-800 min^{? 1}, respectively, to keep the outer ring circumference temperature below 65°C. It is suggested that the damage is caused by metal-to-metal contacts due to lubricant starvation under grease lubrication and to a decrease in oil film thickness due to local increases in temperature.     

Investigating the Effect of Surface Finish on Mixed EHL in Rolling and Rolling-Sliding Contacts

Surface finish may significantly affect the lubrication performance of a tribological interface through the influence of topography on micro/nanoscale fluid flows around localized contacts at surface asperities. This paper aims to study the mixed lubrication performance of a group of engineered surfaces, including turned, isotropically finished, ground, and dimpled surfaces, under different operation conditions by means of a deterministic mixed elastohydrodynamic lubrication (EHL) model. The honed surface was used to mate with other surfaces. The results indicate that a longitudinal contact ellipse favors longitudinally oriented mating surface roughness and that a transverse contact ellipse, as well as a line contact, prefers a transversely orientated mating surface roughness for lubrication enhancement.     

安钢1780热连轧油膜轴承密封防护措施的改造及应用

随着油膜轴承在冶金、重型机械行业的广泛应用,对油膜轴承密封的研究日益深入。油膜轴承的密封状态直接关系到油膜的形成、轴承的运行、润滑油的防漏、污染的控制等方面。安钢1780热连轧油膜轴承密封防护措施经过改造应用,效果良好,对于油膜轴承密封的安装、维护、使用具有一定的指导意义。     

AR模型和SVM在机床滚动轴承故障诊断中的应用

将自回归模型(AR)和支持向量机(SVM)应用到机床滚动轴承的故障诊断中,根据滚动轴承的振动信号建立自回归模型,以自回归参数和残差的方差作为特征向量,然后建立基于支持向量机的多故障分类器,进而判断滚动轴承的故障类型.通过实例分析和与神经网络方法对比,表明该方法能有效地判别机床滚动轴承的故障类型.     

Three-Dimensional Simulation of Rolling Contact Fatigue Crack Growth in UIC60 Rails

In this article, a UIC60 rail with accurate geometry is studied by employing the finite element method. For this purpose, a three-dimensional elastic-plastic finite element model is conducted using model. In addition, the stress distribution of wheel-rail operation is acquired, and its effects on fatigue life are specified by damage mechanic methods. In the finite element model, the displacements and stress intensity factors (SIFs) are computed on the crack near the leading edge to calculate crack propagation trajectories and crack growth rate. The modified Paris model is used to estimate fatigue crack growth rates.     

有利于提高硬态切削滚动轴承疲劳寿命的残余应力临界条件

超精硬态切削在滚动轴承表面形成的残余压应力 ,经工作应力衰减后才成为影响滚动接触疲劳寿命的应力状态。基于此 ,本文在考虑特定滚动轴承使用条件的基础上 ,推导出滚动轴承采用超精硬态切削加工工艺时 ,已加工表面的残余应力需要满足的两个临界条件 ,即在接触区的每一离散点的残余应力必须与工作应力符号相同 ,且随时间变化残余应力的幅值应小于或等于工作应力幅值的两倍时 ,才有利于提高滚动轴承的使用寿命。该结论澄清了长久以来文献中所提出的残余压应力总是有利于提高工件疲劳寿命的这个似是而非的概念。     

机车滚动轴承再生选配法及专业化集中修观点

针对机车滚动轴承使用寿命浪费的问题,结合目前机务部门检修的普遍情况,提出了机车滚动轴承再生选配法及专业化集中修观点。     

In Situ Quantification of Oil Film Formation and Breakdown in EHD Contacts

Abstract

A measurement method using electrical impedance has been developed for simultaneous quantifications of the thickness (h) and breakdown ratio (α) of oil films in elastohydrodynamic (EHD) contacts. First, based on simplified geometrical and electrical models of EHD contacts, theoretical expressions of h and α were derived as explicit functions of the measured electrical impedance by using the Lambert function. Then, to verify the proposed measurement principle, oil film thickness measurements were conducted by using the electrical method together with the optical interferometry method in a ball-on-disc-type apparatus, which utilized the lubricated contact between a steel ball and a glass disc with a transparent conductive layer (i.e., an indium tin oxide layer). As a result, it was confirmed that the measured h-values obtained by the electrical method agreed well with those obtained by the optical method, under various test conditions with changing the entrainment speed, slide-to-roll ratio, normal load, and viscosity. Besides, it was also confirmed that the measured α-values obtained by the electrical method showed consistent correlations with the film parameter and the friction coefficient. It is hoped that the developed electrical method will be applied to practical metal-to-metal contacts (e.g., the contacts in practical ball bearings) to understand invisible behaviors of oil films in EHD contacts.     

用损伤变量D2计算活塞杆裂纹扩展阶段的剩余强度与剩余寿命

提出了弹塑性材料在疲劳载荷作用下,在裂纹扩展阶段,用损伤变量D2作为本阶段强度与寿命的计算参量,提出了这个过程描述多晶材料弹塑性行为的新方程,并以压缩机活塞杆为实例,计算了螺纹连接部位裂尖的剩余强度与剩余寿命。     

Particle Entrapment in Rolling Element Bearings: The Effect of Ellipticity,Nature of Materials,and Sliding

This study on particle entrapment within elastohydrodynamic contacts reports experimental tests mimicking rolling element bearing contacts using a twin-disc machine with a contaminated lubricant as well as numerical simulations. The ball bearing contacts might be nonideally circular, composed of a hybrid couple of contact materials, and operated under rolling–sliding conditions. This study focused on the relative importance of each of these configurations to the mechanisms responsible for particle entrapment. It was found experimentally and confirmed numerically that the contact ellipticity is of primary importance to entrapment probability. Tests mixing two-by-two pure rolling and non-zero slide-to-roll ratios (SRRs) and different materials and contact configurations revealed combined mechanisms leading to entrapment and surface damage.