DLC solid lubricant coatings on ball bearings for space applications

The environment of space offers special challenges for the lubrication of components in sliding and rolling mechanisms. Hydrogenated diamond-like carbon (DLC) films are being studied as solid lubricant coatings to simultaneously fulfil specifications regarding wear resistance and low friction behaviour under ambient atmosphere and in vacuum.In this paper, the tribological behaviour of highly hydrogenated DLC coatings (50 at% hydrogen) is assessed. Coating composition was optimised on flat AISI 52100 steel substrates based on ball-on-disc tribotest results in air, vacuum and dry nitrogen environments. The developed DLC coatings can be tailored to yield ultra-low friction values in vacuum (μ=0.008). The average friction coefficient range obtained in humid air, dry nitrogen and vacuum for the range of applied loads were, respectively, 0.22 to 0.27, 0.02 to 0.03, and 0.007 to 0.013.New in this work is that optimised DLC coatings were applied to ball bearings for space applications. The torque and life tests of coated pairs of angular contact bearings in air revealed that relatively high bearing torques are generated which increase with time, but the amount of coating wear generated during in-air operation appears relatively light. In vacuum, low torques are generated after a prolonged running-in period. Low-torque life exceeds that observed for MoS₂ by a factor of about two. It is concluded that, in contrast to MoS₂ coated bearings, DLC-coated bearings for space applications might therefore be capable of undergoing in-air ground testing without too much disruption of the subsequent in-space performance.     

Reduction of NRRO in ball bearings for HDD spindle motors

In this paper, it is theoretically and experimentally analyzed that the non-repetitive run-out (NRRO) of a ball bearing is caused by geometrical errors of the inner and outer races and the balls, and the number of balls.

The results are summarized as follows:

(1) As for the geometrical errors of the inner and outer races, it is possible to reduce the NRRO to be less than 1 nm by choosing 12 or 18 number of balls, even if the inner and outer races have a harmonic undulation of less than the 11th order.

(2) The NRRO of a ball bearing with 12 balls is very small even if the geometrical errors of ball bearing parts are large. It was confirmed that 12 was an optimal number of balls for ball bearings used for HDD spindle motors.

     

HIPSN陶瓷轴承在高速电主轴中的应用

陶瓷轴承逐步在电主轴制造中得到应用.通过试验研究,对比分析不同类型磨用电主轴的振动、温升特性,为陶瓷球轴承的实际应用提供一定的技术依据.     

Experimental diagnostics of ball bearings using statistical and spectral methods

Vibration measurements and signal analysis is widely used for condition monitoring of ball bearings as their vibration signature reveals important information about the defect development within them. Time domain analysis of vibration signature such as peak-to-peak amplitude, root mean square, Crest factor and kurtosis indicates defects in ball bearings. However, these measures do not specify the position and/or nature of the defects. Each defect produces characteristic vibrations in ball bearings. Hence, examining the vibration spectrum may deliver information on the type of defects. In this paper a test rig is designed and a pair of brand new commercial ball bearings is installed. The bearings run throughout their lifespan under constant speed and loading conditions. Vibration signatures produced are recorded and statistical measures are calculated during the test. When anomalies are detected in the statistical measures, vibration spectra are obtained and examined to determine where the defect is on the running surfaces. At the end of the test, the ball bearings are disassembled in order to take microscopic photos of the defects.     

基于弹流知识的球轴承设计

基于点接触弹流知识与赤兹接触理论,对球轴承设计参数沟道半径系数和滚动体直径与节圆直径的比进行了分析,结果表明,沟道半径系数对微型轴承其取值范围较大;对小的沟道半径系数,滚动体直径与节圆直径的比的大小对形成油膜的能力影响较小,并且最大接触压力随沟道半径系数的变化大,而随滚动体直径与节圆直径的比的变化不大。     

Solid-lubricated ball bearings for use in a vacuum — state-of-the-art

The tribological responses of solid-lubricated ball bearings for vacuum use are described with reference to their friction torque, wear life, performance at high temperatures and high loads, effects of bearing materials other than steel, outgassing, dust generation and cost reduction, based (in part) on the materials offered by Japanese bearing manufacturers. In view of their outgassing and dust-generation characteristics, solid lubricants applied so far are not satisfactory. A new generation of fluorinated-polymer-lubricated bearings provides low contamination properties and can be used in air as well as in vacuum.     

Design effects on the fretting wear behaviour of ball bearings

A change in design of a ball bearing is described based on the results of numerical and experimental analysis to reduce fretting wear. Increasing the radii of curvature of the inner and outer races by a small amount reduces the product of the relative slip δ and the tangential traction τ at the contact region, both of which are caused by Heathcote slip. This results in the consequent reduction in fretting wear because there is a good correlation between the amount of fretting wear and τδ. This prediction is confirmed experimentally by increasing the groove radius of the inner race from 4.02 to 4.21 mm for a ball of radius 3.97 mm.     

Effect of lubricant viscosity grade on mechanical vibration of roller bearings

This work aims to characterize vibration behavior of roller bearings as a function of lubricant viscosity. Experimental tests were performed in NU205 roller bearings, lubricated with mineral oil of three different viscosity grades (ISO 10, 32 and 68). The mechanical vibration was determined through the processing and analysis of bearing radial vibration data, obtained from each of the lubrication conditions, during 2 h of test run for temperature stabilization and under several bearing shaft speeds. The applied radial load was 10% of the bearing nominal load. Through root mean square (RMS) analysis of the vibration signals, it was possible to identify specific frequency bands modulated by the change in lubricant viscosity, which was related to change in oil film thickness.     

Effect of carbide fraction and matrix microstructure on the wear of cast iron balls tested in a laboratory ball mill

The effect of carbide volume fraction from 13 to 41% on the wear resistance of high chromium cast irons was evaluated by means of ball mill testing. Martensitic, pearlitic and austenitic matrices were evaluated.

The 50-mm diameter balls were tested simultaneously in a 40 cm diameter ball mill. Hematite, phosphate rock and quartz sand were wet ground. The tests were conducted for 200 h.

Quartz sand caused the highest wear rates, ranging from 6.5 to 8.6 μm/h for the martensitic balls, while the wear rates observed for the phosphate rock ranged from 1.4 to 2.9 μm/h.

Increasing the carbide volume fraction resulted in decreased wear rates for the softer abrasives. The almost complete protection of the matrix by carbides in eutectic microstructures caused the eutectic alloy to present the best performance against hematite or phosphate rock. The opposite effect was observed for the quartz sand. The quartz abrasive rapidly wears out the matrix, continuously exposing and breaking carbide branches. A martensitic steel presented the best performance against the quartz abrasive.

With phosphate rock, the wear rate of 30% carbide cast irons increased from 1.46 to 2.84 and to 6.39 μm/h as the matrix changed, respectively, from martensitic to austenitic and to pearlitic. Wear profiles of worn balls showed that non-martensitic balls presented deep subsurface carbide cracking, due to matrix deformation. Similar behavior was observed in the tests with the other abrasives.

In pin-on-disc tests, austenitic samples performed better than the martensitic ones. This result shows that pin tests in the presence of retained austenite can be misleading.     

利用弹性支承改善滚动轴承的振动特性

本文研究了弹性支承滚动轴承系统的非线性振动问题，着重分析了利用弹性支承改善滚动轴承振动特性的原理和方法。首先建立了弹性支承滚动轴承的力学模型；然后，根据这一模型对系统进行了振动计算；通过对所得到的最大振幅及轴承动压力的分析，得出了弹性支承可以减小滚动轴承非线性振动的结论；最后，对弹性支承的一个应用实例作了简要说明。     

Model updating of rotors supported on ball bearings and its application in response prediction and balancing

This work attempts experimental studies in finite element model updating of an actual rotor system mounted on ball bearings by using Inverse Eigen Sensitivity Method (IESM). The IESM is applied on state space representation of equations of motion and is used to identify bearing stiffness, damping and shaft material damping parameters. Non-proportional viscous damping model is used to model the bearing and shaft material damping. The experimental identification of viscous coefficient of shaft material damping was not found in the available literature and this work attempts the same as well. The updated model is validated for its accuracy by comparing the predicted frequency response with that obtained from the experiments. Finally, it is shown that the updated finite element model of the rotor system can be efficiently used to predict the unbalance in the rotor.     

角接触球轴承装配工序的技术质量分析

角接触球轴承装配时,只需径向游隙合格。通过加热外圈等方法,可方便地将钢球、保持架与内、外圈装配在一起。轴承装配前要重点控制锁口尺寸的大小,既要防止组装困难,又要防止轴承散套。一般锁口尺寸通过磨加工来保证。     

The Influence of location of balls and ball diameter difference in rolling bearings on the nonrepetitive runout (NRRO) of retainer revolution

The nonrepetitive runout (NRRO) value of retainer revolution is caused mainly by the diameter differences of balls mounted in a bearing. Additionally, when more than one ball has diameter difference, the NRRO value of retainer revolution is believed to vary with the location of balls. In this study, the authors theoretically analyzed the NRRO value of retainer revolution considering the diameter differences and location of balls mounted in a bearing. Consequently, it is clarified that the mean value of the retainer revolution component calculated in all locations of balls decreased with increasing number of balls in a rolling bearing.     

Dynamic modelling of wear evolution in rolling bearings

Condition monitoring tools aim to monitor the deterioration process i.e. wear evolution of defects. The wear evolution is quite complex process due to the involvement of several wear and stress concentration mechanisms. Therefore, the purpose of this paper is to provide a dynamic model of wear evolution that considers the topographical and tribological changes over the lifetime. The model suggests the use of multiple force diagrams to simulate the dynamic impact and utilises several models of contact mechanics to estimate the transition points between the wear evolution stages. The simulated results of the developed evolution model are in principal agreement with the experimental results.     

Condition monitoring of steam turbine-generator through contamination analysis of used lubricating oil

The objective of this paper is to present a systematic analysis of wear particles contained in used lubricant of steam turbine-generator of a thermal power station. The turbogenerator was condition-monitored over a period of two years through wear debris and particulate contamination analysis of the oil. Various sophisticated techniques such as automatic particle counter, ferrography, inductively coupled plasma atomic emission spectrometry (ICPAES), scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDAX) have been employed to extract the relevant information about the health of the machine. Eventually, a correlation of different techniques of wear debris monitoring on the basis of current investigation ascertains the significance of the collective approach of various techniques to avoid catastrophic breakdowns and expensive component replacements.     

深沟球轴承浪形保持架投料工艺探讨

通过对深沟球轴承浪形保持架投料工艺的探讨,认识和熟悉浪形保持架的投料计算方法,提高材料使用率,减低生产成本。     

Effects of grain size on the wear of recycled AZ91 Mg

Magnesium alloy AZ91 chips have been recycled using mechanical milling to yield samples with fine grain sizes. Together with cast samples of the same alloy, the wear behavior of these materials was studied through pin-on-disc sliding, with speeds varying from 1 to , under a normal load of 10 N. Despite the differences in grain size (0.6–) and mechanical properties, the various specimens did not differ significantly in their wear performance. Scanning electron microscopy observed abrasive wear to be dominant under low-speed sliding, and a transition to the formation of a protective mechanically mixed layer (MML) as sliding speed increased.     

磁粉减振器的开发研究

运用磁粉离合器与滚珠丝杠的工作原理,设计了磁粉减振器,通过模拟振动试验,提出一种新型减振方式。     

Measurement of wear in radial journal bearings

In this article, the measurement of wear in radial journal bearings is discussed, where a distinction is made between stationary and non-stationary contact conditions. Starting with Holm/Archard's wear law, equations are derived for the calculation of the specific wear rate k of the bearing material as a function of the wear depth d, measured after an experiment or a period of use in practice. It is also possible to calculate a value for the maximum allowable apparent pressure p_a at given values of k, required lifetime and maximum allowable wear depth d, or a value of d at a given value of p_a. In order to facilitate the use of the equations mentioned above, non-dimensional diagrams are presented. Two examples are given to explain the use of these diagrams.     

A modification of the Jones–Harris method for deep-groove ball bearings

This study presents a modification of the Jones–Harris method (JHM) for the determination of deflection in deep-groove ball bearings. The finite element method (FEM) and curve fitting have been utilized to modify the load–deflection relationships of Hertz contact formulas in JHM. Several cases of deep-groove bearings are simulated to determine contact deflection. Results obtained from the modified JHM (MJHM) are more accurate than the JHM results demonstrated by the comparison between FEM and experimental results.