An analytical model to investigate skidding in rolling element bearings during acceleration

Skidding, which occurs in rolling element bearings during shaft rotational acceleration, causes wear and incipient failure. This paper presents an analytical model to investigate skidding during rolling element bearing acceleration, taking account of the contact force and friction force between the rolling elements and the races and the cage, gravity, and the centrifugal force of the rolling elements. The Hertzian contact theory is applied to calculate the non-linear contact force. The Coulomb friction law is used to calculate the friction force. All forces above are included in force equilibrium equations to derive the non-linear governing equations of the bearing during acceleration, and are solved using a fourth-order Runge-Kutta algorithm with fixed time step. The proposed model is verified by comparison to other published results and with experimental results. The proposed model can be used to investigate skidding in rolling element bearings during acceleration and the transient motion behavior of rolling elements, and it will lay the theoretical foundations for eliminating skidding in rolling element bearings.     

Cage Speed of Hydrodynamic Rolling Hybrid Bearings

Hydrodynamic bearings are subjected to wear during starts and stops due to the absence of sufficient film pressure to effect complete separation of the sliding surfaces. In an earlier publication, our group reported the development of a new hydrodynamic rolling hybrid bearing (HRHB) to overcome the wear problem in hydrodynamic bearings. In the configuration, the transition of operation modes between the rolling bearing supporting state and the hydrodynamic bearing supporting state was realized by the clearance of the rolling bearing. Here we report on the development of a method to identify the operation modes for HRHBs based on monitoring the cage speed of the rolling bearing. The variation of cage speed with the shaft speed is measured. The effects of external load and starting time on the cage speed are also investigated experimentally. The results show that variation in the cage speed reflects changes in the load on the rolling bearing, as well as the operation modes of the HRHBs. With increases in the shaft speed, the variation in the cage speed presents three stages: the increasing stage, the decreasing stage, and the stationary stage. In the first two stages, the HRHB works at the rolling bearing supporting state while in stationary stage, the HRHB works at the hydrodynamic bearing supporting state. In additions to its property of no wear sufferance during starts and stops, compared to hydrodynamic bearings there is little risk of catastrophic failure with HRHBs during any interruption to the lubricant supply and compared to rolling bearings there is no fatigue failure. Therefore this hybrid design is useful at very high speeds.     

水泵轴连轴承的常见失效形式与改进

水泵轴连轴承失效形式主要为:心轴断裂,心轴滚动表面、外圈沟(滚)道表面、滚动体表面的磨损和疲劳剥落及密封失效。针对其主要失效形式,对轴承的内部几何形状及保持架和密封结构进行了改进。     

On the wear and failure of high speed roller bearings

A laboratory bearing test rig was constructed to study wear and failure mechanisms in high speed roller bearings under different conditions of loading and lubrication. The design of the rig permitted three bearings to be tested simultaneously. A test run of 720 h duration was performed during which wear of the bearings was monitored using ferrography and atomic absorption oil analysis. Wear debris particles collected from the bearings by ferrography were studied with scanning electron microscopy using energy-dispersive X-ray analysis. The results of ferrography were correlated with the metallographic observations made on the worn bearings.It was found that for lightly loaded high speed roller bearings rolling contact fatigue including surface pitting is not a significant wear or failure mechanism. However, misalignment due to shaft deflection above a critical point cannot be tolerated. Wear of high speed engine bearings can successfully be monitored by ferrography but, as the wear condition accelerates, frequent oil sample collections are beneficial.     

起重机用滚动轴承有限元分析及故障检测

针对起重机用滚动轴承故障率高且难以检测的问题,首先采用Ansys软件对起重机用滚动轴承进行基于实际接触状态的有限元分析,然后采用基于小波包能量法和Hilbert变换方法对滚动轴承进行信号处理、分析以及故障检测。结果表明:滚动轴承的滚动体与内外圈接触部位存在较大应力集中,最易在此处首先发生破坏;根据轴承故障特征频率与内圈、外圈、滚动体三种故障类型所对应的频谱特征和能量谱相比较,可有效判断轴承故障类型。研究所采用的检测方法可为起重机用滚动轴承的故障预防和检测提供一定理论依据和指导作用。     

滚动轴承保持器磨损对轴承失效的影响

针对滚动轴承运行特点,采用XRF技术调查和分析铜、铁及尼龙为主体材料的保持器在脂润滑条件下的磨损,研究保持器磨损与轴承滚动体磨损之间的相关性及对轴承磨损失效过程的影响,并对不同材料保持器所产生的磨损颗粒对轴承及润滑脂的影响进行初步分析和探讨。统计数据分析结果表明,不同结构或材料构成的保持器在脂润滑轴承运转过程中始终存在着一定程度的磨损,且与轴承滚动体的磨损在磨损相对数量上显著相关;高聚物尼龙保持器所形成的磨损颗粒的影响,更多地反映为保持器材料中硬质填料的机械作用,而钢制保持器因其磨损颗粒具有金属活性和催化性,磨损颗粒同时还加速润滑脂的化学氧化过程及对脂稠化剂网状结构的破坏。     

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。     

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.     

滚动轴承打滑蹭伤试验研究

基于高速滚动轴承试验机对滚动轴承打滑蹭伤展开试验研究,获得不同工况参数下滚动轴承打滑蹭伤的临界转速;研究滚动轴承在打滑蹭伤临界转速下不同运行时间对滚动轴承磨损程度的影响,以及滚动轴承打滑蹭伤后,继续以更高转速运行对滚动轴承磨损程度的影响。结果表明:滚动轴承发生打滑蹭伤瞬间伴随着摩擦扭矩、温度及振动加速度的同步突增,且其在润滑不充分及轻载工况下出现打滑蹭伤时的临界转速更低;滚动轴承在打滑蹭伤临界转速下运转时间越长,磨损越严重,这可能是由于打滑蹭伤破坏滚动轴承表面光洁度,使摩擦因数增大从而导致磨损速度加快;滚动轴承打滑蹭伤后,继续以更高转速运转时易出现二次淬火烧伤,大大降低轴承使用寿命。     

主动电磁轴承失效后转子坠落在备用轴承过程中的非线性动力学

用有限元法建立了任意个由滚动轴承组成的固定间隙备用轴承-主动电磁轴承-多盘多质量转子系统在主动电磁轴承失效前后的动力学方程,以一个多盘转子系统为例分析了主动电磁轴承失效后转子坠落在备用轴承过程中的瞬态非线性动力学特性,讨论了柔性备用轴承的支撑刚度、支撑阻尼和间隙对转子在坠落过程中动力特性的影响。结果表明采用具有较大阻尼柔性结构的备用轴承能够显著地改善转子坠落在备用轴承上的瞬态动力特性,抑制转子在坠落过程中可能出现具有较大振动和冲击力的全间隙区的涡动运动,减小转子坠落对备用轴承寿命和可靠性的影响。柔性结构备用轴承的支撑阻尼越大,支撑刚度越小,间隙越大,转子坠落后出现全间隙区涡动运动的可能性越小。     

Study of solid contamination in ball bearings through vibration and wear analyses

In rolling bearings, contamination of lubricant oil by solid particles is one of the main reasons for early bearing failure. In order to deal with this problem, it is fundamental not only the use of reliable techniques concerning detection of solid contamination but also the investigation of the effects of certain contaminant characteristics on bearing performance. Nowadays, non-invasive techniques, such as vibration measurements, are being increasingly used for on-time monitoring of machinery performance. In this context, the present work investigates the effect of lubricant contamination by solid particles on the dynamical behavior of rolling bearings, in order to determine the trends in the amounts of vibration affected by contamination in the oil and by the bearing wear itself. Experimental tests were performed with radial ball bearings lubricated by oil bath. Quartz powder in three concentration levels and different particle sizes was used to contaminate the oil. Vibration signals were analyzed in terms of the root mean square (rms) values. The results show that changes in the rms values of vibration in the high-frequency band, from 600 to 10,000 Hz, were associated to the changes in oil lubrication in the bearing contacts, caused by oil contamination and wear damage on the bearing surfaces.     

滚动轴承动力特性测试方法

轴承的动力特性对转子－轴承系统的动力特性有重要的影响。但至今，滚动轴承的动力特性仍缺乏系统的资料，在许多情况下，将滚动轴承简化为无阻尼的定常弹性元件。本文分析了滚动轴承动力特性的主要影响因素，介绍了滚动轴承动力特性的两种测试方法，并以某航空轴承为例作了具体测试，取得了比较一致的结果。本文提出的方法可作为建立滚动轴承动力特性数据库的基本手段。     

Effect of fluid film wave bearings on attenuation of gear mesh noise and vibration

The attenuation of the gear mesh noise/vibration by fluid film wave bearings relative to rolling element bearings was experimentally investigated. Tests were performed on a gearbox that can accommodate both rolling element bearings and wave bearings. It was found that at specific speeds and torques, the wave bearings could significantly reduce the noise/vibration compared to rolling element bearings. Because the gear noise is accompanied by noise from other sources, a method was developed to extract from the original signal only the mesh harmonic components.The wave bearing dynamic coefficients were also predicted. It was found that adjusting the wave bearing parameters could considerably increase the capacity of the wave bearings to attenuate the gear mesh noise and vibration.     

Wear mechanisms of statically loaded hydrodynamic bearings by contaminant abrasive particles

Wear mechanisms in hydrodynamic bearings by contaminant abrasive particles in the oil were investigated. This type of wear is one of the main factors responsible for failure of hydrodynamic bearings especially when operating in dusty environments. A test bearing system was developed to study this type of wear under carefully controlled conditions. Experiments were conducted with two shaft materials and three liner materials, giving a total of six material combinations. The circumferential liner wear distribution and the relative magnitude of shaft and liner wear were found to depend mainly on the shaft-to-liner hardness ratio. A smaller hardness ratio resulted in relatively more liner wear and less shaft wear. A model is proposed to account for this behaviour whereby the action of the abrasive particle is considered to consist of both cutting and rolling motions.     

基于双谱分析的滚动轴承故障模式识别

当滚动轴承发生故障时,其产生的振动信号一般是包含较强噪声的非高斯和非线性信号。本文对高阶统计量方法用于滚动轴承故障特征提取进行了研究,提出了基于双谱估计的滚动轴承故障诊断方法。利用这种方法可以同时获得包含滚动轴承故障信号幅值和相位信息的双谱特征图谱。研究表明,双谱图谱可以有效地监测滚动轴承工作状态的模式,因而可以快速地识别滚动轴承不同的故障特征。     

Investigations of Bearing Failures Associated with White Etching Areas (WEAs) in Wind Turbine Gearboxes

A critical problem for wind turbine gearboxes is failure of rolling element bearings where axial cracks form on the inner rings. Metallurgical analyses show that the failure mode is associated with microstructural alterations manifested by white etching areas (WEAs) and white etching cracks (WECs). This article presents field experience from operating wind turbines that compares performance of through-hardened and carburized materials. It shows that through-hardened bearings develop WEA/WECs and fail with axial cracks, whereas carburized bearings do not. In another comparison of two rotor bearings with different carburized metallurgies, one bearing developed WEA/WECs and failed by macropitting, whereas the other bearing did not develop WEAs or WECs and did not fail. The field experience shows that a carburized bearing that has a core with low carbon content, high nickel content, greater compressive residual stresses, and a higher amount of retained austenite provides higher fracture resistance and makes carburized bearings more durable than through-hardened bearings in the wind turbine environment.     

基于小波包近似熵和SVM的圆柱滚子轴承诊断

为了解决特种车辆变速箱圆柱滚子轴承由于振动信号的非线性、非平稳特征较为微弱,提取的特征量数值不明显且现实中难以获得大量含丰富特征的典型故障样本而难以对其进行准确诊断的问题,应用小波包近似熵和支持向量机对特种车辆变速箱圆柱滚子轴承进行诊断。首先,在自行搭建的模拟实验台上采集某型特种车辆变速箱圆柱滚子轴承正常、外圈磨损、滚动体故障、点蚀和压痕4种典型状态的振动信号;然后,分别提取4种典型状态振动信号的小波包近似熵值作为支持向量机的输入,根据支持向量机的输出结果来确定圆柱滚子轴承是否发生故障和故障类型。结果表明,该方法能有效对某型特种车辆变速箱圆柱滚子轴承的典型状态进行诊断,为其他相似变速箱圆柱滚子轴承的故障诊断提供一种参考途径,具有一定的工程实用价值。     

Rolling element bearings absolute life prediction using modal analysis

In this paper, the authors introduce an experimental procedure for predicting the fatigue life of each individual rolling element bearing separately using vibration modal analysis. The experimental procedure was developed based on a statistical analysis. A statistical analysis was performed to find an empirical model that correlates the dynamic load capacity of rolling bearings to their dynamic characteristics (Natural frequencies and damping). These dynamic characteristics are obtained from the frequency response function of each individual bearing that results from vibration modal analysis. A modified formula to the already known Lundberg-Palmgren life formula is proposed for rolling element bearings. Given the modified formula, one can predict the fatigue life of each individual rolling element bearing based on its dynamic characteristics. The paper compares the results from the modified formula with those from Lundberg-Palmgren formula. The modified formula provides an accurate prediction for the fatigue life of each individual bearing based on its dynamic characteristics. The experimental validation of the modified formula is considered for future work. Therefore, it can be used in various applications of rolling element bearings in machinery systems.     

Journal Design Considerations for Turbomachine Shafts Supported on Foil Air Bearings

Foil air bearings can offer substantial improvements over traditional rolling element bearings in many applications and are attractive as a replacement to enable the development of advanced oil-free turbomachinery. In the course of rigorous testing of foil journal bearings at NASA Glenn Research Center, shaft failure was repeatedly encountered at high ambient temperature and rotational speed, with moderate radial load. The cause of failure is determined to be excessive non-uniform shaft growth, which increases localized viscous heating in the gas film and eventually leads to a high-speed rub and destruction of the bearing and journal. Centrifugal loading of imbalance correction weights and axial temperature gradients within the journal due to the hydrodynamic nature of the foil bearings, determined by experiment and finite element analysis, are shown to be responsible for the non-uniform growth. Qualitative journal design guidance is given to aid in failure prevention.     

机电液一体化磨损试验机的研制

滚动轴承磨损试验机的精度、性能特点对有效开展滚动轴承试验,准确进行轴承质量评估等有着重要的现实意义.针对目前多数的滚动轴承磨损试验机功能单一、试验参数调整范围较小、控制精度低的情况,从机电液一体化的角度出发,采用机电液一体化技术设计,以Labview为平台研制了滚动轴承磨损试验机并开发测控软件,实现了对滚动轴承磨损试验机的转速、压力的闭环智能精确控制和实时参数显示,为滚动轴承磨损试验的高效开展提供了基础.