A Limiting Solution for the Dependence of Film Thickness on Velocity in EHL Contacts with Very Thin Films

In recent years there have been substantial improvements in the capabilities of numerical modeling of elastohydrodynamic lubricant (EHL) films and it is now possible to analyze a very wide range of conditions rather than needing to rely on extrapolation using classical film thickness regression equations such as those of Dowson and Higginson. However, a new controversy has arisen concerning the film thickness-velocity dependence in EHL contacts at very low speeds and high loads, with some predictions showing a film thickness much less than that predicted by the classical equations. The present article applies the well-established limiting analysis, first presented by Grubin-Ertel, to the inlet of the EHL contact. It is shown that when the load is high and the speed is low (and the pressure gradient is very high in the inlet) an accurate resolution of the inlet pressure rise is critical for the determination of the film thickness. Discretization errors of this type might be responsible for discrepancies between the classical equations and some recently published numerical predictions.     

Experimental Study of Central and Minimum Elastohydrodynamic Film Thickness by Colorimetric Interferometry Technique

Recently developed colorimetric interferometry technique was used for the study of both minimum and central film thicknesses for a wide range of operating parameters. Over 300 film thickness maps were obtained for the combination of four values of the materials parameter G, five values of the load parameter W and many values of the speed parameter U. The use of a spacer layer extended the range of film thickness measurement down to 5 nm. An excellent agreement was found between experimental values and data obtained from numerical solution presented by Venner and ten Napel, especially for thin lubrication films. An increase in a speed exponent with increasing material parameter G was observed for both central and minimum film thicknesses. The minimum film thickness and, thereby, the ratio between central and minimum film thickness was confirmed to be of a stronger dependence on material and load dimensionless parameters than Hamrock and Dowson equations predict.     

轧钢机动压轴承油膜补偿与临界轧速分析

采用有限元方法求解雷诺方程,对形成动压润滑的临界轧制速度以及影响板厚轧制精度的油膜厚度进行计算机数值模拟以评价不同轧制工况下油膜轴承的承载能力性特性参数。计算得出的不同轧速下厚预报值以及临界轧速一实际数据吻合。     

塑膜厚度在线检测系统的设计及应用

介绍了采用非接触式电容传感器、电涡流传感器组合系统获取检测信号，利用基于LabVIEW软件平台的计算机实现对塑料薄膜进行在线检测的工作原理，并对该检测系统的硬件设计、软件设计进行了详细地探讨。最后，给出了测试结果，证明了系统的可靠性与可行性。     

涂层厚度对金刚石薄膜附着强度的影响

应用扫描电镜和断续车削实验法研究了涂层厚度对金刚石薄膜涂层刀具附着强度的影响。以Ｗ和ＷＣ—１．５％Ｃｏ硬质合金为基体的金刚石薄膜涂层刀具在涂层厚度不超过１０μｍ时可获得较高的附着强度。     

薄膜式锰铜传感器——一种新型的超高压力传感器

文中综述了动态高压锰铜传感器最近十多年来的研究现状,着重介绍了一类新型的锰铜传感器———薄膜式锰铜传感器的研发进展。该类传感器的研制旨在提高传感器高压测试极限和缩短响应时间。目前已进行了直到80GPa以下的初步标定,响应时间最快达32ns     

The Effects of Roughness on Piston Ring Lubrication—Part II: The Relationship between Cylinder Wall Surface Topography and Oil Film Thickness

In this investigation, a theoretical piston ring/cylinder wall model has been utilized to study the dependence of the oil film thickness on surface roughness shape and amplitude, as well as on engine operating conditions. For a given roughness, a plateau honed cylinder wall surface was found to produce a thinner oil film. It has also been shown that the small crosshatch angle used when honing the cylinder wall produces surfaces that enhance hydrodynamic action.     

精密电容式动态在线薄膜测厚仪的研制

介绍一种以８０３１单片机为核心,采用电容传感器对薄膜厚度进行动态在线测量的高精度高分辨率仪器。仪器采用反馈运算方法,使用驱动电缆技术,克服了电容传感器输出的非线性,并提高了仪器整机的抗干扰能力。测量结果在单片机系统的控制下,实时进行数显,同时将被测过程量的变化情况通过ＴＶ板变成视频信号送入视频显示器,直观反映出测量结果的变化趋势。     

薄膜式锰铜传感器--一种新型的超高压力传感器

文中综述了动态高压锰铜传感器最近十多年来的研究现状,着重介绍了一类新型的锰铜传感器－薄膜式锰铜传感器的研发进展。该类传感器的研制旨在提高传感器高压测试极限和缩短响应时间。目前已进行了直到８０ＧＰａ以下的初步标定,响应时间最快３２ｎｓ。     

对角修形窄斜齿轮的弹流数值计算和膜厚测试

本文从弹流角度分析了修形前后线载荷分布及最大压力沿接触线的变化规律。本文应用Ｎｅｗｔｏｎ－Ｒａｐｈｓｏｎ方法与Ｎｅｗｔｏｎ下山法相组合的方法，在假定刚体中心膜厚相等的前提下，首先求出了修前斜齿轮某一时刻全接触线上的弹流润滑解，进而求解出修形后斜齿轮某时刻全部接触线各点的载荷分配，压力分布和油膜形状，在文献的基础上，研制了一套微机数据采和处理系统，测量了斜齿轮的中心油膜厚度，测量结果与计量结果基本一     

Effects of Ethanol Contamination on Friction and Elastohydrodynamic Film Thickness of Engine Oils

The use of ethanol as engine fuel has increased for environmental reasons, both in flex-fuel engines and as increasing amounts of ethanol blended with gasoline in conventional engines. This article describes an investigation into the effects of ethanol contamination of lubricants during engine use with ethanol fuel. To facilitate this, a new technique was developed to measure small amounts of ethanol in lubricants. Elastohydrodynamic film thickness measurements and Stribeck curves were obtained for Group I base and formulated oils containing small added amounts of ethanol. The effect of the water present in hydrated ethanol was evaluated by carrying out tests using both hydrated and anhydrous ethanol. Measurements were also carried out using a Group II base oil with added ethanol. These measurements showed that in the low entrainment speed region, where the elastohydrodynamic film is very thin so that boundary lubrication prevails, the addition of ethanol produced a boundary film, which was not present for the base oils. By contrast, the addition of ethanol to formulated oil reduced film thickness in all lubrication regimes. The friction tests showed friction reduction due to addition of ethanol to the base oil, in particular at low speeds. For the formulated oil, ethanol reduced friction at high speeds, which was associated with a reduction in the viscosity of the lubricant, but at low speeds, ethanol reduced the formation of a boundary layer, increasing friction. The presence of water in hydrated ethanol did not significantly change the film thickness and friction when compared with anhydrous ethanol.     

Experimental Investigation of Elastohydrodynamic (EHD) Film Thickness Behavior at High Speeds

At very high speeds, elastohydrodynamic (EHD) films may be considerably thinner than is predicted by classical isothermal regression equations such as that due to Dowson and Hamrock. This may arise because of viscous dissipation, shear thinning, frictional heating or starvation.

In this article, the contact between a steel ball and a glass disc over an entrainment speed ranging from 0.05 m s^?1 to 20 m s^?1 was studied. Two sets of tests were performed. In the preliminary testing, the disc was driven at speeds of up to 20 m s^?1 and the ball was driven by tractive rolling against the disc, its speed being determined using a magnetic method. After all possible explanations for the reduction in film thickness at high speeds were considered, it was shown that the results, which fall well below classical predictions, are consistent with inlet shear heating at the observed sliding speeds.

Another set of tests was then performed, with both disc and ball driven separately, so that the accuracy of the shear heating theory for different types of oils and at different sliding conditions could be assessed. It was found that the thermal correction factor predicts the trend of film thickness behavior well for the oils tested and is particularly accurate at certain slide–roll ratios (depending on the type of oil). Experimental data were also used to obtain improved coefficients for the correction factor for different types of oil to achieve better prediction of film thickness at high speed throughout the whole range of slide–roll ratios.