Starvation and Reflow in a Grease-Lubricated Elastohydrodynamic Contact

The lubrication mechanisms of a grease in a rolling-element bearing has been studied through the measurement of film thickness in a rolling point contact. To simulate bearing conditions the contact runs under fully starved conditions; there is no attempt to maintain bulk flow of the grease into the inlet using an external supply. In consequence the film thickness drops off rapidly as the contact progressively starves. After a few minutes rolling (at constant speed) an equilibrium film thickness is attained which has two components: a residual film (h_R) comprised of degraded grease thickener and a hydrodynamic component (h_EHD) due to the liquid phase from the grease. The hydrodynamic contribution represents a balance between lubricant lost from the contact and replenishment from the grease close to the track. The ability of the grease to replenish the rolling track has been inferred from measurements of lubricant reflow around the static contact. These results are discussed in light of current starvation and grease lubrication models.     

润滑点接触粗糙表面滑动摩擦因数的实验研究

利用多功能微摩擦试验机,在轻载荷条件下测量了具有横向纹理圆盘表面的摩擦因数,得到了包括流体润滑、混合润滑和边界润滑完整的Stribeck曲线。考虑了载荷和时间对实验结果的影响,对不同粗糙度表面的Stribeck曲线进行了比较。实验的初步结果表明:增加载荷与实验时间,会获得更加稳定的实验结果;表面越粗糙,从混合润滑向流体润滑转换的临界速度越大;表面越光滑,Stribeck曲线的“谷底”越明显。     

表面凹坑对点接触脂润滑油膜特性的影响

通过数值计算方法,研究了点接触脂润滑摩擦副表面存在凹坑时油膜厚度和油膜压力的分布规律,并与光滑表面条件下的油膜特性进行了对比。研究结果表明:点接触脂润滑摩擦副表面存在凹坑时,在凹坑边缘位置会出现油膜压力峰,而在凹坑中心周围油膜压力值较低;靠近入口处一侧凹坑边缘位置油膜厚度出现"凹陷"现象,润滑脂流经凹坑时油膜厚度则会"跃升";凹坑引起油膜压力和油膜厚度分布的变化会随着凹坑位置的变化而相应的变化;表面凹坑不利于点接触脂润滑摩擦副的润滑。     

The Heat Transfer Coefficient and Lubricated Contact Temperature

This paper is one of a series dealing with the surface temperature conditions in disks and gears. It attempts to apply and extend the theory proposed in an earlier paper which predicted the behavior of the surface temperature of machine elements subjected to repeated frictional contacts. In considering the critical temperature hypothesis proposed by Blok as a criterion for failure by scuffing, it is essential that the operating surface temperature is taken into account in addition to the well known “flash temperature.” There have been many papers referrinq to this “flash temperature,” but little is known of the factors which affect the operating surface temperature, commonly called the bulk temperature. This paper demonstrates that the bulk temperature growth under loaded conditions can be predicted theoretically, and that by observing the behavior of the surface temperature the heat transfer coefficient and friction conditions can be calculated. Finally full details of the thermocouple used by the authors in their tests are given.     

Performance of Lubricated Sliding Contact in Magnetic Field

Results of experimental studies concerning the influence of permanent magnetic field on wear of lubricated sliding contact operating at short stroke and high frequency are presented. It was found that horizontal magnetic is affecting performance of the contact. The jagged delamination regions produced in the presence of a magnetic field can be regarded as easily undergoing oxidisation because oxygen is readily adsorbed there. Magnetic field is likely to intensify the abrasive action by wear particles and mitigate wear of the plate specimen. It is postulated that all these effects are caused by the influence of magnetic field on the electrical charge of the worn surface created on Si3N4 ball.     

点接触齿面取不同坐标系求解过程的研究

本文系统地阐述了点接触齿面啮合理论中求解接触点的完整过程，并导出了在取不同坐标系时求解接触点的同一计算公式。在啮合传动中，根据具体问题选取不同的坐标系，可应用同一计算公式进行啮合分析与计算。     

Wear of Silicon Carbide in Sliding Contact with Lubricated Thin-Film Rigid Disk

Silicon carbide (SiC) is a potential ceramic material for recording heads, yet its tribological performance against lubricated thin-film rigid disks is not fully known. Square pins with a 100 mm radius spherical surface were made from hot pressed SiC, chemical vapor deposited (CVD) SiC, and Al₂O₃TiC, and tested with lubricated thin-film disks. The pin-on-disk tests showed that the region of contact on the spherical surface of the SiC and CVD-SiC pins wears away to form a circular wear plateau with smears in and around the plateau. The wear plateau is formed rapidly in the first 1000 drag revolutions and then very gradually grows in size with further revolutions. Analysis of the smears showed that a large fraction of the smears contained SiO₂ which had been oxidized from SiC due to high temperatures generated at the pin surface in contact with the disk. In contrast, tests with Al₂O₃. TiC pins did not show any formation of a wear plateau on the pins.     

Wear of Aluminum-Alloy Matrix Composites in Lubricated Conformal Contact with Case Hardened Steel

The wear behavior of SiC particle-reinforced aluminum alloy matrix composites as journal bearing materials in conformal contact against case hardened AISI 1016 steel under mixed lubrication conditions using SAE 10W30 oil was investigated. The bearings exhibited weight gain, followed by weight loss and subsequent weight gain as the sliding distance increased. Iron transfer and tribo-chemical reaction product formation were responsible for the observed weight gain. The surfaces of the composites contained transferred iron, layers rich in Fe, S, P and Zn, and hard tribo-deposits of high phosphorus concentration. The hard tribo-deposits were thought to be an important factor in lubrication breakdown and contact failure.     

水润滑橡胶轴承不同结构的摩擦噪声分析

利用ABAQUS软件对水润滑轴承系统进行了噪声分析,利用有限元复特征值分析方法,依据复特征值实部的正负判断轴承系统发生噪声的可能性,如果有实部为正的特征值,则可判断系统有发生噪声的可能性.分别研究了水润滑轴承不同结构,包括水润滑轴承过渡圆弧半径大小、水道槽半径大小、水道槽数量及橡胶厚度对摩擦噪声的影响.研究表明,对于中...     

Mechanism of Crack Growth in Lubricated Rolling/Sliding Contact

In order to explain the mechanism of rolling-contact fatigue crack growth analytically, fracture mechanics are applied to a semicircular surface crack inclined at an angle to the elastic half-space loaded by Hertzian stresses.

It is shown that the surface traction is the controlling factor for lubricant seepage into the crack and for shear mode crack growth rate. It is also clarified that the generation of pits results from tensile mode crack growth mainly due to the oil hydraulic pressure action.     

固体润滑滚子轴承的接触表面应力分析研究

为获得固体润滑滚动轴承滚动体与滚道处的接触应力,通过固体润滑滚子轴承拟动力学分析并考虑涂层的影响,获得了滚子轴承稳定运行过程中滚动体的力载分布。通过建立带涂层接触的平面应变问题的力学模型,将涂层与基底两种材料的特性等效为一种材料来求解滚子与接滚道触应力分布情况,并与轴承的拟动力学分析相结合,获得了滚子轴承中滚动体与固体润滑膜接触表面的接触变形、接触半径与外加载荷之间的关系,讨论了不同涂层的弹性模量以及不同涂层厚度对接触界面应力分布的影响。当涂层弹性模量比基底大时,涂层的存在使得接触半宽减少,最大名义接触应力增加;涂层弹性模量比基底小时,则与之相反。当涂层的厚度<0.01mm时,涂层的存在对固体润滑滚子轴承的接触表面应力分布影响较小;在一定范围内,当涂层的厚度逐渐增大时,涂层对轴承接触表面应力分布的影响增大。     

轴承用球三点接触纯滚动接触疲劳寿命试验机

介绍了一种新型的轴承用球三点接触式纯滚动疲劳寿命试验机。试验机主要包括驱动装置、从动装置和加载装置3部分,附加装置中的热电偶、加速度传感器和计数器分别测量温度、振动和转动圈数。被测试样球仅在同一最大圆截面上受到3次非等间隔但等强度的循环接触载荷作用,并沿此圆周作纯滚动,试样球的最大转速为23 000 r/min,最大赫兹接触应力可达7 GPa。该试验机可用于评定各种材料轴承用球的滚动接触疲劳性能。     

齿轮线接触与点接触理论与有限元分析

由于制造误差、安装误差、支撑条件、齿轮承载变形等因素的影响,齿轮接触情况复杂且难以试验验证。齿轮接触按照初始接触条件通常分为线接触和点接触,承载后均为面接触:前者接触面为矩形,后者为椭圆形。线接触理论利用赫兹接触理论已经成熟,即采用两个圆柱体的线接触方式进行计算;点接触理论计算较为复杂,须考虑接触椭圆和其他非线性因素。用有限元方法分析渐开线及其修形齿轮的接触状态,计算实例表明,没有考虑安装误差的影响,线接触的仿真结果与赫兹接触理论相吻合,且接触状况明显好于点接触;当考虑安装误差的影响,二者接触应力均有上升,但线接触的接触状况明显恶化,接触应力急剧上升57倍以上,而点接触的接触应力上升不到1倍,说明齿轮线接触对安装误差的敏感性远大于齿轮点接触,极易造成齿轮的点蚀破坏。     

Tribological Properties of Greases Based on Biogenic Base Oils and Traditional Thickeners in Sapphire-Steel Contact

Friction and wear tests were performed with a number of greases based on biogenic esters and thickened with two metal soaps and a highly dispersed silica acid gel. The series of experiments was performed on a Nonotribometer in material combination of sapphire ball on steel disks with a range of normal loads from 1 up to 500 mN. Results directly show influences of the bulk grease components on frictional and wear behavior. Comparison of frictional and wear results makes manifest that, while in most combinations of base oil and thickener, the highest influence is found in the thickening agent, some combinations are mainly influenced by the base oil. All frictional results along with wear widths and depths as well as micrographs of the prevailing wear mechanisms are presented and discussed.     

润滑条件下中低碳空冷贝氏体钢的滚动滑动接触疲劳行为

研究了三种高强度或超高强度高韧性空冷贝氏体钢在油润滑条件下的接触疲劳行为。发现引起麻点剥落的疲劳裂纹不仅可在接触表面 ,也可以在距表面一定深度下的亚表面萌生 ,亚表面萌生裂纹的深度比理论计算最大剪切应力所在深度小近一个数量级 ,裂纹萌生由塑性变形和剪应力共同作用产生 ,一端向接触表面扩展 ,到达表面后润滑油被挤压进入裂纹中产生支点效果 ,另一端向最大剪应力深度扩展 ,最后在外力和润滑油支点共同作用下 ,由裂纹包围的金属屑被折断 ,形成疲劳剥落坑。钢的初始硬度或强度在低接触应力下对接触疲劳寿命影响不明显 ,在高接触应力下影响显著 ,初始硬度越高 ,接触疲劳寿命越长。     

点接触弹流润滑供油条件退化的乏油分析

在点接触弹流润滑中,如果不能及时补充新油,则接触区的供油条件会随着润滑次数而退化。分析了供油油膜厚度、中心膜厚、最小膜厚和润滑油膜压力区形成位置与润滑次数的关系。结果表明:润滑开始时,由于供油油膜厚度较大,系统处于充分供油状态;随着润滑次数的增加,有一部分油从两侧泄漏,系统逐渐转到乏油状态,供油油膜厚度、中心膜厚和最小膜厚均逐渐变小,压力区形成位置则逐渐向Hertz接触区靠近;最终供油油膜厚度、中心膜厚和最小膜厚趋于定值,压力区趋于Hertz接触区,从而达到一种稳定乏油状态。     

Slider Wear on Disks Lubricated by Ultra-Thin Perfluoropolyether Lubricants with Different Molecular Weights

In this study, the wear properties of a magnetic head slider on disks lubricated by ultra-thin perfluoropolyether (PFPE) lubricants with different molecular weights were evaluated by the continuous sliding of magnetic head sliders using the slider contact by the dynamic flying height control. Two types of PFPE lubricants (Z-tetraol and D-4OH) with different molecular weights were evaluated. Results show that the slider wear depended on the coverage of the lubricant film; i.e., the lubricant film with sufficient coverage reduced slider wear. The lubricant film with a low molecular weight (low-Mw), including a lubricant material with a Fomblin and Demnum main chain, exhibited better coverage on a diamond-like carbon surface. Sliders with a low-Mw lubricant film showed less wear than those of a high molecular weight (high-Mw), and the depletion of the low-Mw lubricant film was less than that of the high-Mw lubricant film.     

关于相错轴斜齿轮传动两轮齿为点啮合的证明

本文根据斜齿圆柱齿轮齿廓曲面的数学方程，运用微分几何学中的两类基本量，分析了斜齿轮齿廓曲面在一点邻近的形状，从而证明了相错轴斜齿轮传动的两轮齿为点啮合。     

Different Magnetic Models in the Design of Hydrodynamic Journal Bearings Lubricated with Non-Newtonian Ferrofluid

This work is concerned with theoretical study of hydrodynamic journal bearings lubricated with ferrofluids exhibiting non-Newtonian behavior. Based on the momentum and continuity equations for ferrofluid under an applied magnetic field, a modified Reynolds equation has been obtained. Assuming linear behavior for the magnetic material of the ferrofluid, the magnetic force was calculated. The Reynolds equation has been derived to be able to apply to any magnetic field distribution model. Using different magnetic field models, the equation has been solved numerically by the finite-difference technique with appropriate iterative technique and pressure distributions have been obtained. The boundary shape of the load-carrying active regions (positive-pressure regions) and cavitation regions (zero-pressure regions) could be then determined. The solution renders the bearing performance characteristics, namely: load-carrying capacity, attitude angle of the journal center, frictional force at the journal surface, friction coefficient and bearing side leakage. The results indicated that the flow-behavior index has a large effect on the bearing performance. When the bearing operates at high eccentricity ratios, the increase of flow-behavior index gives higher load capacity, lower attitude angle, higher frictional force, lower friction coefficient and higher side leakage. At low eccentricity ratios where the magnetic effects are significant, the effect of the flow-behavior index depends mainly on the magnetic field distribution model used.