Dry Lubricated Bearings for Operation in a Vacuum

Ball bearings incorporating two different types of dry self-lubricating retainer materials were successfully operated in a vacuum over the pressure range of 1 × 10^?7 to 2 × 10^?8 (mm of H) torr for prolonged periods of time. A 20 mm bore ball bearing of AISI M-10 tool steel with a filled plastic retainer was operated over a range of temperatures from 100 F to 160 F and similar bearings with filled metal retainers were operated over a temperature range of ?300 F to 450 F, at radial loads up to 75 pounds. Other ball bearings using both types of self-lubricating retainer materials were operated in electric motors in the vacuum environment.

In selecting the dry self-lubricating materials for the ball bearing tests, plastics powders and composite materials were screened in an inert atmosphere to determine wear and friction characteristics. Each of the materials that exhibited desirable lubricating properties was then subjected to a vacuum at elevated temperatures to determine the rate of outgassing. These materials were then satisfactorily used as the dry self-lubricating retainers in the 20 mm bearings which operated in the vacuum environment.     

SNAP 8 Reactor Bearing Development

The SNAP 8 reactor bearings are designed to provide low-friction self-lubrication at 1150 F while in the environment of a nuclear reactor operating in space. A four-phase program is described that has successfully developed these low-speed, oscillating bearings. Phase One was the study and screen testing of static adhesion of bearing materials. Phase Two was the study and screen testing of bearing materials in sliding couple. Phase Three was the application of the bearing materials into bearing designs where prototypes were fabricated and tested. And Phase Four was the optimizing and testing of the final designs for reactor ground test in “poor” vacuum (10^?5 torr), and simulated space—ultrahigh clean vacuum (10^?9 torr). Results of shock and vibration tests are also presented.     

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.     

真空逸气对复合材料尺寸稳定性的影响

为验证聚合物基体在真空环境产生的逸气效应对复合材料尺寸稳定性的影响,对环氧树脂和氰酸脂两种基体的碳纤维复合材料的真空逸气性能进行了试验研究。首先从理论上分析了膨胀系数与逸气系数之间的关系,获得了二者尺寸稳定性存在差异的理论依据。然后设计了能够精确测量尺寸和质量变化的试验组件,按照卫星环境试验条件对多组试验组件进行了3轮真空试验,精确测量了试验前后试验组件的尺寸和质量。试验结果表明:环氧树脂基体和氰酸脂基体的复合材料质损率(TML)分别为0.033%~0.06%和0.014%~0.029%;环氧树脂基体和氰酸脂基体的复合材料尺寸变化量分别为2~8μm和1~3μm。另外,环氧树脂基试件的质量变化约为氰酸脂基的2倍,说明两种材料在真空环境下的尺寸稳定性有差异。     

空间相机扫描机构固体润滑轴承组件的寿命试验

开展了固体润滑轴承组件的真空加速寿命试验,以验证固体润滑轴承组件的设计是否满足在轨寿命要求。研究了MoS2基薄膜固体润滑轴承组件在小角度摆动情况下的寿命。试验采用4对轴承模拟在轨±6°连续往复摆动,通过检测轴承组件工作时的摩擦力矩、电机电流和轴承温升判断轴承运行状态。结果显示,寿命试验运行正常,累计摩擦次数为6.2×10~7次。寿命试验后对轴承进行了尺寸精度和旋转精度复测,然后对轴承组件进行了解剖分析。复测结果显示,轴承尺寸精度和旋转精度与试验前一致,轴承润滑状态良好。试验结果验证了固体润滑轴承组件寿命满足在轨任务要求,为其它空间相机小角度摆动的扫描机构固体润滑轴承组件的长寿命设计提供了依据。     

Wear-resistant coatings for bearing applications

A report is given of the preparation and testing of ball bearings for operation under extreme conditions. The rings and balls were coated with hard materials such as TiC, TiN or Ti(C,N) using the chemical vapour deposition process. Such coated bearing elements have been used with success in ball bearings for nuclear reactors, namely in a helium atmosphere at 300 °C and in space applications in a vacuum of 10^?9 Torr.     

Evaluation Tests of Industrial Vacuum Bearings for Space Use

The tribological performance of industrial vacuum bearings for space use was experimentally evaluated. The bearings selected for investigation were an 8 mm bore deep‐groove ball bearing lubricated with a sputtered MoS₂ film and one lubricated with an ion‐plated Ag film, commercially available from three Japanese bearing manufacturers. Based on survey results of tribological requirements for existing satellite mechanisms, four types of bearing tests were defined and conducted: a vacuum test at room temperature, an atmosphere resistance test, a thermal vacuum test, and a vibration test. In addition to these tests, the variation in the tribological performance of the industrial bearings was also investigated. The results of more than 80 tests demonstrated that the industrial vacuum bearings had sufficient lubrication lives with low frictional torque and the data were reasonably repeatable, indicating a potential for space use.     

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.     

Evaluation of Ion-Sputtered Molybdenum Disulfide Bearings for Spacecraft Gimbals

High-density, sputtered molybdenum disulfide films (MoS₂) were investigated as lubricants for the next generation of spacecraft gimbal bearings where low torque signatures and long life are required. Low friction in a vacuum environment, virtually no out-gassing, insensitivity to low temperature, and radiation resistance of these lubricant films are valued in such applications. One hundred and twenty five thousand hours of accumulated bearing lest time were obtained on 24 pairs of flight-quality bearings ion-sputtered with three types of advanced MoS₂ films. Life tests were conducted in a vacuum over a simulated duty cycle for a space pay bad gimbal. Optimum retainer and ball material composition were investigated. Comparisons were made with test bearings lubricated with liquid space lubricants.

Self-lubricating PTFE retainers were required for long life, i.e., > 40 million gimbal cycles. Bearings with polyimide retainers, silicon nitride ceramic balls, or steel balls sputtered with MoS₂ film suffered early torque failure, irrespective of the type of race-sputtered MoS₂ film. Failure generally resulted from excess film or retainer debris deposited in the ball track which tended to jam the bearing. Both grease lubricated and the better MoS₂ film lubricated bearings produced long lives, although the torque with liquid lubricants was lower and less irregular.     

Materials in Rolling Element Bearings for Normal and Elevated (450°F) Temperature

The effect of vacuum melting has been under investigation by the author's company for several years. Fatigue testing has been conducted on races and balls in full-sized bearings, so that the results can be interpreted directly into bearing performance.

Studies have been made of both induction and consumable electrode vacuum melted steel. Material inspection has shown a more consistently high level of cleanliness in consumable electrode vacuum steel than that melted by induction.

Improvement in life of bearings made of vacuum melted steels does not appear to be commensurate with the improvement in cleanliness. This is regarded as confirming evidence to a long-held view that cleanliness is not the only factor involved in the fatigue property of steel. Fatigue studies have been made of both 52100 and high temperature steels. Bearing ratings range from 17% less than the AFBMA basic load rating to 23% greater than this rating for vacuum melted 52100 steel. In a test of vacuum melted tool steel (M–1), the bearing load rating was 22% greater than the basic load rating for 52100 steel.

There is no indication that vacuum melting has served to reduce the number of early failures more proportionately. Where there has been a change in life, the curve of bearing lives has been displaced, but retains the same general shape.     

基于修正L-P模型的轮毂轴承载荷分布与弯曲疲劳寿命分析

以第三代轮毂轴承为研究对象,推导了弯矩作用下滚动体与内滚道、外滚道的接触变形与接触载荷,提出了更为准确的接触载荷分布计算模型,分析了不同工况下轮毂轴承内部接触载荷和接触角的周向分布规律。在轮毂轴承内部载荷分布的一次修正基础上,考虑不同位置角的滚道材料和滚动体的接触疲劳,利用乘积定律进行统计处理,得到了第三代轮毂轴承疲劳寿命的修正L-P模型。结合ISO281—2007寿命修正计算方法,针对润滑现象进行二次修正,得到了经过润滑修正的第三代轮毂轴承疲劳寿命模型。利用旋转弯曲疲劳试验机进行了轴承的弯曲疲劳试验,试验结果显示,该疲劳寿命模型计算得到的理论值与试验值的误差在10%以内,验证了模型的正确性。     

A Method to Calculate Frictional Effects in Oil-Lubricated Ball Bearings

Friction and heat generation in oil-lubricated ball bearings is mainly the result of sliding in the ball-raceway contacts and agitation of the lubricant in the free space between the balls, cage. and bearing rings. Endurance of a ball bearing is highly dependent on the thicknesses of the oil films which serve to separate the balls from the raceways in a well-lubricated bearing. The film thicknesses, in turn, are dependent upon the lubricant's viscous properties. These are functions of bearing temperatures and are determined by the balance between the rates of frictional heat generation and heat dissipation. Therefore, in the design of a ball bearing application such as the high speed rotor and low speed rotor support bearings in an aircraft gas turbine, it is important to be able to predict the bearing frictional heat generation rates with reasonable accuracy. This paper presents a method to perform the required calculations considering hearing loading and speeds, realistic lubricant rheological properties, and a relatively simple heat transfer system between the hearing rings, halls. And lubricant. The results of the analysis are shown to compare favorably with experimental data.     

Influence of lubricants on the performance of journal bearings – a review

ABSTRACT

The lubricant properties have a significant influence on the static and dynamic performance characteristics of journal bearing such as load-carrying capability, minimum fluid film thickness, maximum pressure, lubricant flow rate, damping coefficients, stiffness coefficients, etc. The present document reviews the behaviour of various lubricants such as power-law lubricants, couple stress lubricants, micropolar lubricants, ionic liquid lubricants and space lubricants. The influence of these lubricants on the performance of hydrostatic, hydrodynamic and hybrid journal bearings is discussed. An effort is made to develop the understanding to choose the suitable lubricant for journal bearings for different journal bearing configurations. Journal bearings operated with non-Newtonian lubricants have shown better performance compared to Newtonian lubricants. Ionic liquid lubricants have shown high potential in vacuum applications and extreme temperature environment such as in bearings of spacecraft moving mechanical assemblies.     

An Overview of Bearing Candidates for the Next Generation of Reusable Liquid Rocket Turbopumps

There is a consensus in the aerospace field that the development of reusable liquid rockets can effectively reduce the launch expense. The pursuit of a long service life and reutilization highly depends on the bearing components. However, the rolling element bearings(REBs) used in the existing rocket turbopumps present obvious and increasing limitations due to their mechanical contacting mode. For REBs, high rotational speed and long service life are two performance indexes that mutually restrict each other. To go beyond the DN value(the product of the bearing bore and rotational speed) limit of REBs, the major space powers have conducted substantial explorations on the use of new types of bearings to replace the REB. This review discusses, first, the crucial role of bearings in rocket turbopumps and the related structural improvements of REBs. Then, with the prospect of application to the next generation of reusable liquid rocket turbopumps, the bearing candidates investigated by major space powers are summarized comprehensively. These promising alternatives to REBs include fluid-film, foil, and magnetic bearings, together with the novel superconducting compound bearings recently proposed by our team. Our more than ten years of relevant research on fluid-film and magnetic bearings are also introduced. This review is meaningful for the development of long-life and highly reliable bearings to be used in future reusable rocket turbopumps.     

Laboratory Experience with Long-Term Bearing Lubrication

This paper presents the results of laboratory testing of several types of size-204 ball bearings. Three of these bearings had lubricant compact ball separators; three other types of conventional bearings were operated without applied lubrication in the form of oils, greases, or dry powders. Bearing performance was judged from friction and wear life results.

Bearings with lubricant compact separators have operated for periods as long as 38,000 hours without failure in a vacuum environment of less than 3 × 10^?6 torr. The test conditions included 1,790-r pm rotational speeds, no applied heat, and a nominal axial load of seven pounds. Based on rate of weight loss, predictions were made on the expected wear lives of the bearings.

Conventional bearings, using three different ball separator designs, were subjected to the same test conditions (in vacuum) as the lubricant compact separator bearings, as well as to similar conditions in an air environment. Average wear lives are reported for the three types of bearings operating in air and for two of these operating in vacuum. The third type of bearing continues to operate in vacuum and a life prediction is made based upon the wear rate of another specimen.     

主动静压气体润滑支承的研究进展

主动静压气体润滑支承可提高其承载力、动刚度和抗扰动能力,成为近期流体润滑学术界的研究热点问题。综述真空预载、电磁预载和压电主动控制的静压气体润滑支承研究现状,分析压电主动控制的静压气体润滑支承的研究进展以及存在的问题,指出主动固有节流器、主动控制节流器或气膜形状可控节流器相结合的主动气体润滑支承,是静压气体润滑支承研究的重点和未来主要发展方向。     

氮化硅陶瓷滚子轴承的加速寿命试验和断油润滑试验

本文介绍了一次组合陶瓷轴承的加速寿命试验和断油润滑试验,试验轴承是用于某航空发动机主轴前支承的短圆柱滚子轴承,滚动体由氮化硅陶瓷材料制成,套圈和保持架仍采用原钢轴承的套和保持架,试验设备为航空轴承专用试验台,试验表明,试验陶瓷轴承在高速条件下工作寿命和短期油润滑能力均好于同型号钢轴承。     

The Performance of a Hybrid Ceramic Ball Bearing Under High Speed Conditions with the Under-Race Lubrication Method

Large bore (150 mm) hybrid ceramic ball bearings and all-M50 steel bearings were tested with under-race lubrication to compare the heat generation and the temperature rise at speeds up to 2.25 million DN. Furthermore, oil shut-off tests were carried out with both bearings over 2.25 million DN.

The experimental results of the heat generation for both bearings were nearly the same at an axial load of 19.6 kN. at 34.3 kN, the heat generation of the hybrid bearing was lower than that of the M50 steel bearing at low speed. The heat generation of both bearings gradually approached each other with increasing speed and became nearly equal at a speed of 15,000 rpm. The survivability of the hybrid bearing in the oil shut-off test was superior to that of the M50 bearing. These experimental results were explained by the calculation results using a computer analysis software which simulates the kinematics and the performance of ball bearings.     

Experimental Study and Numerical Simulation of the Large-Scale Testing of Polymeric Composite Journal Bearings: Two-Dimensional Modeling and Validation

The self-lubricating properties of some polymeric materials make them very valuable in bearing applications, where the lubrication is difficult or impossible. Composite bearings combine the self-lubricating properties of polymeric materials with better mechanical and thermal properties of the fibers. At present, there are few studies about these bearings and their design is mainly based on manufacturers’ experiences. This study includes an experimental and numerical study of the large-scale testing of fiber-reinforced polymeric composite bearings. In the first part of this article, a new tribological test setup for large composite bearings is demonstrated. Besides, a two-dimensional finite-element model is developed in order to study the stress distribution in the composite bearing and kinematics of the test setup. A mixed Lagrangian–Eulerian formulation is used to simulate the rotation of the shaft and the contact between the composite bearing and the shaft. Simulation results correspond closely to the experimental data, and provide careful investigation of the stress distribution in the bearing. In the second part of this article, three-dimensional quasi-static and two-dimensional dynamic models are studied.     

Liquid Metal Bearing Performance in Laminar and Turbulent Regimes

The design and development of a high speed journal bearing test rig is described. Test results are presented for water and high temperature liquid potassium lubricated journal bearings.

The test program included investigations of bearing torque, lubricant flow rate and stability limits for bearings operating in the laminar regime, through the transition to turbulent flow and in the turbulent flow regime. Torque vs. speed curves were obtained over a range of loads and bearing-journal clearance ratios. The test results are compared with predicted laminar bearing performance. Good correlation with theory was obtained in the laminar regime as indicated by plots of friction parameter vs. Reynolds number at zero load. The transition from laminar flow occurred at higher speeds than predicted by Taylor's criterion under all conditions of load. Recorded bearing torques in the nonlaminar regimes were four to forty times as great as predicted by laminar theory. The results of the materials compatibility study which supplemented the bearing study are summarized.