对数滚子偏斜时的弹流润滑研究

针对工程上滚子摩擦副偏斜的问题,研究了对数滚子偏斜时的弹流润滑特性。研究表明,偏斜后接触区出现大端和小端,大端处的压力增大而膜厚减小,小端处的压力减小而膜厚增大,并且这一趋势随着偏斜角的增大而趋于明显。偏斜现象总体上将恶化滚子的润滑状态。在同样的偏斜角下,滚子长径比越大,偏斜的影响越显著。适当增大对数滚子的凸度量可减弱偏斜现象的影响,因此,对于易发生偏斜的工况,设计时可适当增大滚子凸度量以补偿偏斜因素的影响。     

Effects of Loading Process and Contact Shape on Point Impact Elastohydrodynamics

The squeeze effect is an important subject in studies of elastohydrodynamic lubrication (EHL). By impact loading, the oil between point contact surfaces is entrapped at the central region or the peripheral region depending on the initial conditions. The effects of the loading process, surface roughness, and ellipticity ratio of contacts on the film thickness and pressure distributions are not fully understood yet. In the current study, those effects are elucidated through numerical analyses by specified initial impact gaps, which produce the central or the peripheral oil entrapments. The loading process, which can produce rather low pressure, has been proposed. Moreover, conditions, under which a microdimple is produced in the central circular bump are clarified.     

A Mixed Flow Model for Lubrication with Emulsions

An oil-in-water emulsion in the inlet zone of a concentrated contact is modeled by treating the oil particles as flattened cylinders surrounded by water. In an independent flow model, the oil and water flows are coupled only through the pressure gradient. However, the model leads to anomalous behavior with regard to the flow of water. To overcome this problem, corrections to the pressure gradients due to interactions between the oil and water were derived. Both models showed that the emulsion became concentrated because the higher viscosity oil was preferentially drawn into the conjunction. The net effect was similar to an inlet starved of oil. The inlet film thickness predicted by the interactive theory was in good agreement with Dow's experimental measurements for an EHL contact.     

Effect of surface roughness on elastohydrodynamic traction: Part 1

The effect of surface roughness on traction performance was experimentally studied using a two‐roller tester. The nature of the contact was investigated using electrical resistance and electrical capacitance methods. Increased shear stress was observed in the viscous region, which could be attributed to a higher average shear rate and to greater viscosity under EHD contact conditions due to pressure fluctuations caused by the surface texture.     

A Study of Tricresyl Phosphate as an Additive for Boundary Lubrication

A method of combining thin-layer chromatography with activation analysis to measure quantitatively the individual impurities in tricresyl phosphate (TCP) is described. The relative amounts and types of impurities found in commercial grades of TCP are discussed. Preparative thin-layer chromatography and iron powder chromatography are applied to produce TCP samples with known concentrations of several impurities. The use of the four-ball wear tester as a method of determining trends in wear values as a function of base stock and additive quality is demonstrated. The relationship of acid phosphate rather than TCP concentration to antiwear properties of compounded lubricants is suggested by transition load studies.     

Elastohydrodynamically lubricated finite line contact with couple stress fluids

The effect of couple stress fluid on the elastohydrodynamically lubricated finite line contact is studied. Modified Reynolds equation is derived from Stokes microcontinuum theory and solved numerically using finite difference method. Owing to the finite contact analysis, the effect of couple stress fluid at the edges of the roller is examined. The study reveals that overall film thickness increases significantly with couple stress parameter. This suggests less wear as there may be a chance of getting direct metal-to-metal contact. The coefficient of friction, which is of greater importance in lubrication, also decreases with increase in the couple-stress parameter. Based on the numerically evaluated results, empirical formulae for central and central minimum film thickness are developed.     

表面波纹度和凹坑对线接触弹流的影响*

由于加工误差和表面损伤等,轴承零件表面会出现不同的表面形貌,表面凹坑和波纹度严重影响线接触表面的润滑性能。采用系统法求解高载和低载下波纹表面和凹坑表面的润滑膜压力和膜厚以及表层Mises应力,发现表面波纹度会使油膜压力出现波动,压力波峰处的压力值会大于光滑接触表面的油膜压力,表面会出现应力集中,高载时波纹度的影响更明显;表面凹坑会使凹坑两侧出现尖锐的压力峰,表面凹坑两侧出现肿块;当凹坑在接触中心时,油膜压力对凹坑深度非常敏感,较小的凹坑深度就会导致油膜崩溃;而出口区的凹坑会使二次压力峰移动到凹坑靠近接触中心的一侧,而且峰值压力远大于正常接触压力,凹坑处有局部高应力和严重的应力集中,高载时较小的凹坑深度会引起相对更明显的压力峰和应力集中。     

等温条件下非牛顿流体的弹流特性分析

为研究弹流润滑的非牛顿效应,对稳态和时变条件下等温点接触牛顿流体与非牛顿流体的弹流特性差异进行分析。假设润滑剂为Ree-Eyring非牛顿流体,研究卷吸速度、滑滚比、最大赫兹接触压力以及特征剪应力对弹流润滑性能的影响,分析时变条件下非牛顿流体的弹流特性,并与牛顿流体进行比较。结果表明,等温、轻载工况下,速度的增加导致牛顿流体产生较为尖锐的第二压力峰,导致非牛顿流体的接触区入口膜厚增加,且滑滚比越大增加越明显;高速、大滑滚比条件下,载荷越轻非牛顿效应越明显;时变条件下,速度波动对牛顿流体和非牛顿流体都产生较大影响,非牛顿流体的第二压力峰在各个瞬时始终小于牛顿流体。因此,等温点接触弹流润滑条件下,动态效应和非牛顿效应不应忽视。     

点接触纯滚动被试轴承球润滑性能研究

润滑工况是滚动接触疲劳寿命的主要影响因素之一,而润滑剂、接触形式等因素都对润滑状态有所影响。采用新研制的三点接触纯滚动轴承球加速疲劳试验机,研究了被试球钢球和陶瓷球在润滑油N32润滑下的润滑性能,并计算了最小油膜厚度及润滑膜参数,分析了润滑状态。结果表明,所用的润滑油N32是合适的,被测试的钢球和陶瓷球工作在弹性流体动力润滑(EHL)状态。分析结果为钢球和陶瓷球的对比滚动接触疲劳性能试验提供了理论基础。     

ELASTOHYDRODYNAMIC LUBRICATION OF LOGARITHMIC PROFILE ROLLER CONTACTS

0 INTRODUCTIONThe profiled roller contacts are widely used inheavy radial load and high rotational speed conditionsfOr overcoming the problems of edge effects caused bytheir finite length and by misal ig nment. E x tensivemathematical analyses['] and computer ..lc.lati...[2Jhave shown that the most favorable effect in respectof edge stress reduction is obtained when thegeneratrix of roller contacts corresPOnds to a certainlogarithmic function. But the theoretical basis of theseodculatbo …