Wear properties of DLC-coated steel rollers running with highly contaminated lubrication

The presence of hard contaminants in lubrication can lead to the premature failure of rolling bearings. To reduce the negative effect of such contaminants, hard carbon-based coatings (diamond-like carbon; DLC) can be applied to the surfaces of steel bearings. DLC coatings generate a low friction and a high sliding wear resistance to enhance the tribological properties and improve the durability of running components. This work explores the merits of DLC coatings for use in very demanding applications, such as in highly contaminated environments. The wear properties of DLC-coated bearing rollers were evaluated by comparing them with uncoated rollers. The degree of wear found on the coated rollers was serious, especially under relatively high contaminant concentrations. The three-body abrasive wear produced a relatively coarse scoring of the coating surface, which caused the corresponding disc to suffer more damage than the disc running against an uncoated roller under the same operating conditions. The results indicate that supposedly wear-protective coatings cause even more damage to running surfaces once they have been broken up by hard contaminants, and highlight the importance of keeping the bearing coating intact. In practise, it is important to eliminate contaminants from the lubricant of rolling bearings, in particular for bearings with a DLC anti-wear coating.     

Influence of different surface modification technologies on friction of conformal tribopair in mixed and boundary lubrication regimes

Moving machine assemblies are generally designed to operate in full film lubrication regime to ensure high efficiency and durability of components. However, it is not always possible to ensure this owing to changes in operating conditions such as load, speed, and temperature. The overall frictional losses in machines are dependent on the operating lubrication regimes (boundary, mixed or full-film). The present work is thus aimed at investigating the role of different surface modification technologies on friction of a sliding bearing/roller tribopair both in boundary and mixed lubrication regimes. A special test rig comprising of two bearings was built for the experimental studies. Tribological tests were conducted in a wide speed range to enable studies in boundary and mixed lubrication regimes. The influence of application of different surface modification technologies on both the sliding bearing and the roller surfaces on friction has been studied. The rollers used in these studies were provided with five different coatings (hard DLCs and a soft self-lubricating coating). Additionally, two uncoated rollers having different surface roughness were also studied. Uncoated bearings were used in all tribopairs except two. These two bearings were coated with DLC and phosphate coatings respectively and uncoated rollers were the mating counterparts. Friction measurements were made on the new as well as the previously run-in surfaces. It was found that the rollers with self-lubricating coating resulted in lowest boundary friction closely followed by the rollers with the hardest DLC coatings. The DLC coating applied on to the bearing showed lower boundary friction after running-in. Mixed friction has been found to be mainly dependent on the surface topography characteristics of both the original and the run-in surfaces of bearings and rollers. The harder DLC coatings and the phosphated bearing showed the lowest mixed friction due to an efficient running-in of the bearing surface.     

Filtration and coating effects on self-generated particle wear in boundary lubricated roller bearings

A specially designed test system involving boundary lubricated roller bearings was used to study wear at low particle concentration levels. A separate oil system circulated the oil through the test bearings. The effects of self-generated contaminants from the system were studied. Even at very low concentration levels, self-generated contaminants can cause significant wear. The concentration of self-generated particles was very high during the running-in period. It is therefore important that the filtration be very efficient during this period. The experimental results show that filtration during run-in for 1 h with a 3 μm filter can reduce both the mass loss and the number of self-generated particles by a factor of 10. Furthermore, the results also show that while the bearings with standard rollers can have significant wear, those with coated rollers are at the same time almost unaffected by wear. Also, the number of particles generated in the contact was significantly less when using coated rollers. There were twice as many self-generated particles when using a standard bearing as those compared with a coated bearing.     

The lubrication of roller bearings subjected to couples

Roller bearings are generally designed to carry mainly radial loads with additional bearings employed to carry any axial loads. Occasionally, limited space prevents the use of these additional bearings, so that the roller bearing itself must carry the axial load. This must be taken by flanges on both the inner and outer races. The effect on the rollers themselves is to modify the load distribution on their generator contact surfaces because the rollers are now subjected to a couple in addition to the radial load. A similar effect is produced if two flanged (or unflanged) roller bearings support a loaded shaft. As its ends are nominally direction fixed, the rollers must be subjected to terminal couples, thus causing a modification to the load distribution at the contact surfaces. The effect of such forces on the footprint shape and on the bearing lubrication is investigated.     

An Approach to Evaluate the Abrasive Land Wear of High-Speed Bearings

State-of-the-art bearing materials, such as Pyrowear 675(P675) have been developed to meet the requirements of the next generation of gas turbine engines. P675 bearings have exhibited higher land wear compared to conventional M50 bearings under contaminated test conditions. Surface modification techniques can be applied to enhance the wear resistance of bearing land surfaces. A coating has been developed to minimize abrasive wear of land surfaces. A new procedure using a 40 mm bearing test rig has been developed to effectively evaluate land wear under simulated contaminated condition. Test conditions including contamination concentration, test duration, test temperature and lubricant flow rate were optimized to obtain measureable wear on the land surfaces in a reasonable test time. Results obtained using M50 Nil, P675 and M50 bearings are presented to illustrate the viability of the test procedure.     

Investigation on Wear Resistance and Fatigue Damage of Laser Cladding Coating on Wheel and Rail Materials under the Oil Lubrication Condition

The aim of this study is to investigate the wear resistance and fatigue spalling damage of wheel and rail materials with and without laser cladding coating under oil lubrication using a rolling–sliding machine. It illustrates that the laser cladding Co-based alloy coating improves the wear resistance of wheel and rail rollers. Serious spalling is dominant for untreated wheel and rail rollers. The wheel or rail roller undergoing laser cladding treatment takes on slight abrasive wear and visible ploughing. Furthermore, there are no cracks on the contact surface and subsurface. The laser cladding Co-based alloy coating exhibits outstanding resistance to wear and fatigue spalling damage due to its microstructure in the coating under oil lubrication.     

Particle Generation by Solid-Lubricated Bearings and Ball Screws in Vacuum Environments©

Rolling bearings used for transporting wafers and liquid crystals in the film-forming process of semiconductor and LC panel manufacturing are required to minimize the particles (originating from both lubricant and bearing material) they generate while in operation. The research reported in this paper focuses on the particle generation under different rotational conditions of ball bearings and ball screws coated with various solid lubricants and operating in a vacuum environment. The results of the tests indicated that a specially composed and applied polytetrafluoroethylene (PTFE) coating was superior in minimizing particle generation by ball bearings and ball screws. Observation of the bearing interior surfaces indicated that particle generation is primarily caused by wear of cage-pocket surfaces, while sudden and large increases in wear are the result of the balls making direct surface-to-surface contact with the raceways and cages due to erosion of the solid lubricant coatings.     

航空发动机主轴轴承失效模式分析

航空发动机圆柱滚子主轴承常常因为工作条件恶劣,发生失效。采用光学显微镜、扫描电镜、能谱仪、X射线光电子能谱等对服役后的圆柱滚子轴承进行失效分析。结果表明:根据失效机制与微观形貌对失效模式,可以将圆柱滚子轴承的失效模式分为8种不同的失效模式,包括划伤和擦伤、打滑蹭伤、压坑凹坑、疲劳剥落、振纹、受热变色、内圈烧伤、保持架镀银层磨损。对打滑蹭伤、烧伤和保持架镀银层磨损等失效模式的轴承进行分析,结果表明:在打滑蹭伤的轴承表面发现O元素,表明打滑蹭伤过程中发生了氧化磨损;在烧伤轴承表面发现了Fe的氧化物FeO和Fe₂O₃,表明轴承在烧伤时温度较高,润滑油膜被破坏,滚子和内圈互相接触发生剧烈磨损;保持架表面银层脱落,部分磨损区域露出铜表面,表明保持架在服役过程中发生了摩擦磨损。     

Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than that of an all-steel rolling element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives of the deep-groove, angular-contact, and cylindrical roller hybrid bearings with races made of post-1960 bearing steel increased by factors of 3.7, 3.2, and 5.5, respectively, from those calculated using the Lundberg-Palmgren equations. An all-steel bearing under the same load will have a longer life than the equivalent hybrid bearing under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than all-steel bearings by 58% for deep-groove bearings, 41% for angular contact bearings, and 28% for cylindrical roller bearings.     

考虑滚子位置变化的圆柱滚子轴承非线性刚度特性分析

以圆柱滚子轴承为研究对象,考虑轴承运转过程中滚子周向位置分布的周期性变化,对经典圆柱滚子轴承载荷分布理论进行改进,并对由此引起的轴承刚度时变特性进行分析,同时研究圆柱滚子轴承平均刚度及平均接触滚子数随径向力的非线性变化规律。为了对改进理论算法进行验证,采用有限元接触分析方法对圆柱滚子轴承刚度及滚子接触状态进行分析。研究结果表明,改进理论算法和有限元接触法均能准确预测轴承瞬时刚度的时变特性及平均刚度随径向力的非线性变化特性,同时证明轴承平均接触滚子数的改变是轴承刚度变化的根源。基于改进理论算法进而分析轴承初始径向游隙、径向力、滚子设计数量等关键参数对圆柱滚子轴承性能的定量影响规律。     

Effect of Roller Geometry on Roller Bearing Load–Life Relation

Cylindrical roller bearings typically employ roller profile modification to equalize the load distribution, minimize the stress concentration at roller ends, and allow for a small amount of misalignment. The 1947 Lundberg-Palmgren analysis reported an inverse fourth-power relation between load and life for roller bearings with line contact. In 1952, Lundberg and Palmgren changed their load–life exponent to 10/3 for roller bearings, assuming mixed line and point contacts. The effect of the roller–crown profile was reanalyzed in this article to determine the actual load–life relation for modified roller profiles. For uncrowned rollers (line contact), the load–life exponent is p = 4, in agreement with the 1947 Lundberg-Palmgren value, but crowning reduces the value of the exponent, p. The lives of modern roller bearings made from vacuum-processed steels significantly exceed those predicted by the Lundberg-Palmgren theory. The Zaretsky rolling-element bearing life model of 1996 produces a load–life exponent of p = 5 for flat rollers, which is more consistent with test data. For the Zaretsky model with fully crowned rollers, p = 4.3. For an aerospace profile and chamfered rollers, p = 4.6. Using the 1952 Lundberg-Palmgren value p = 10/3, the value incorporated in ANSI/ABMA and ISO bearing standards, can create significant life calculation errors for roller bearings.     

A Noise Analysis of Cylindrical Roller Bearings Operating Under Zero External Load

The purpose of this article is to numerically investigate one source of acoustic noise in roller bearings, that which results from the motion of the rollers in the bearing under zero external load. For the sake of simplification, it was assumed that the cylindrical roller bearings are infinitely long. Furthermore, the effects of the following on the noise of the bearing were also examined: the radial clearance of the bearing, the viscosity of the lubricant, and the number of rollers. The results of the study show that the fundamental frequency of the noise components of the cylindrical roller bearing corresponds to the multiplication of the number of rollers and the whirling frequency of the roller center. The acoustical frequency spectra of the cylindrical roller bearing are pure tone spectra, containing the fundamental frequency of the roller bearing and its superharmonics. The factors that decrease the sound pressure level of a cylindrical roller bearing include low lubricant viscosity, high radial clearance, and a reduced number of rollers. The results and discussions of the present article could aid in the design of low-noise cylindrical roller bearings.     

Evaluation of Hot Pressed Silicon Nitride as a Rolling Bearing Material

A series of tests has been conducted to evaluate the suitability of silicon nitride as a bearing material for rolling contact applications. The ability of silicon nitride to be lubricated by some conventional lubricants was found to be satisfactory. This was determined by wettability studies, lubricant film thickness and traction coefficient measurements on the optical EHD rig and friction coefficient measurements by the pin-on-disk method. The abrasive wear coefficient, measured on a lopping machine using 600 grit SiC abrasive, was found to be high compared to other ceramics. It was also dependent on the composition of the silicon nitride. Comparative rolling contact fatigue tests on steel and silicon nitride flat washers were conducted using steel rollers and balls. A high wear rate leading to grooving in the rolling track on silicon nitride was observed. The spalling resistance of silicon nitride was found to be higher than that of steel under the test conditions used. Surface interactions in the Si₃N₄-M50 steel contacts, detrimental to the life of the steel rolling elements, were recognized. Attempts were made to reduce the severity of these interactions and prolong the life of bearings containing ceramic elements.     

双列调心凹面滚子轴承接触载荷分析

在考虑滚子与套圈、滚子与保持架以及保持架与引导套圈作用力的条件下,建立双列调心凹面滚子轴承动力学模型.以某双列调心凹面滚子轴承为研究对象,与静力学分析模型滚子最大接触载荷计算结果对比,验证了模型的正确性.并分析了工况条件(轴向载荷、径向载荷、倾覆力矩、转速)和结构参数(滚子数量、滚子长度、径向游隙)对滚子最大接触载荷的...     

A study on the sound of roller bearings operating under radial load

The purpose of the paper is to numerically investigate the sound characteristics of roller bearings operating under radial load. For the sake of simplifying the analysis, it was assumed that the roller bearings are infinitely long, a noise source due to pressure fluctuation of oil film is taken as a line noise source, and acoustic energy losses in the bearing are neglected. To obtain sound characteristics of the bearing, the rolling contact load and the sound pressure level distributions were calculated for various operating conditions, and the results were compared with each other. How much the bearing noise can be affected by the design parameters, such as radial clearance of the bearing, viscosity of lubricant, and the number of rollers was also investigated. The results and discussions of the present paper could aid in the design of low-noise roller bearings and to solve the noise problems related to such bearings.     

横向交变载荷作用下三种涂层螺栓的防松性能

选用二硫化钼涂层和碳化钨涂层对45钢螺栓进行表面处理,通过横向振动试验研究横向交变载荷作用下螺栓连接结构的松动行为,并与常用的电镀锌涂层螺栓进行对比分析,讨论3种涂层螺栓的防松性能。利用扫描电子显微镜和电子能谱仪分析试验后螺纹表面损伤形貌及化学成分,揭示螺纹表面的磨损机制。试验结果表明：二硫化钼涂层螺栓螺纹表面的主要磨损机制为疲劳磨损、磨粒磨损和氧化磨损,碳化钨涂层和电镀锌涂层螺栓螺纹表面的主要磨损机制为疲劳磨损和磨粒磨损;相同预紧力或等效应力条件下,二硫化钼涂层螺栓因其界面摩擦因数低,防松性能较差,碳化钨涂层螺栓因其表面耐磨性能优异,防松性能最好;相同预紧力矩条件下,二硫化钼涂层螺栓因预紧力高,防松性能最好,碳化钨涂层螺栓次之,电镀锌涂层螺栓最差。     

基于ANSYS的四列圆柱滚子轴承接触应力和刚度分析

对四列圆柱滚子轴承的接触应力、变形以及径向刚度进行了研究.建立了四列圆柱滚子轴承的有限元三维模型,基于ANSYS和Hertz接触理论,阐述了建模过程中的关键步骤,结合短应力线轧机的应用实例,计算了轴承滚子、内圈的接触应力与变形分布,直观表达了交错排列滚子之间的应力分布情况,计算结果和Hertz理论值相比较,具有较好的一致性.通过计算不同载荷下的轴承变形（轴承内孔轴线的相对位移）,获得了轴承刚度随径向载荷变化的规律.     

Ensuring the reliability of liquid-friction bearings for rolling mills

Means of ensuring the reliability of liquid-friction bearings are considered on the basis of spectral analysis of discrepancies in the shape and mutual position of the contact surfaces and supporting pins of rollers. The amplitude and phase spectra of the discrepancies in shape and mutual position of the basic bearing surfaces within the roller assembly are shown to influence the oscillatory motion of the common axis and the reliability of the components.     

Microtribology

Contacts in microsystems are under very light loads, and contact elements are made of hard materials. However, contact surfaces are not always atomically smooth but have relatively high peaks of asperity. Silicon is hard but has poor anti‐wear properties. Good hard coatings thus become necessary for low wear. Liquid lubricants or adsorbed water generate meniscus forces and stiction. Therefore, a new lubrication method is required for coated surfaces. The present understanding of mechanisms of stiction and the generation of pull‐off force and high friction is reviewed for such contact conditions. New hard coating materials and a new concept of N2 lubrication that exhibit promising friction and wear behaviour are introduced. Copyright © 2006 John Wiley & Sons, Ltd.     

Tribological performance of a DLC coating in combination with water-based lubricants

The tribological behaviour in water-based environments has been studied for a tungsten carbide-doped DLC coating (WC/C) deposited by physical vapour deposition (PVD) on bearing steel. Several tribological test equipments have been used to characterise the wear rate, coefficient of friction and resistance to seizure of the coated system, in comparison with uncoated bearing steel surfaces. It was observed that the wear was decreased and the coefficient of friction reduced in pin-on-disc measurements for poor lubricants. Further, the resistance to seizure in the four-ball method was improved by a factor of approximately three. Results from Reichert measurements showed a decreased wear rate and also a very pronounced running-in behaviour of the coating for some water-based lubricants. It has been shown that the performance of tribological systems with water-based lubricants can be significantly improved with this type of DLC coating.