Static characteristics of a new hydrodynamic–rolling hybrid bearing

An analytic model is developed to predict static characteristics of a new hydrodynamic–rolling hybrid bearing (HRHB). Experiments are carried out to measure the equilibrium positions, the load sharing, and the rotational speeds of the rolling bearing cage. The results show that the working states of HRHB are divided into two distinct phases by a transition speed at which the hydrodynamics and contact models are decoupled. The cage speeds can be used to determine transition speed. The theoretical results agree with the experimental results, and it can be employed to design the bearing parameters according to the expected performance.     

Hybrid journal bearings with particular reference to hole-entry configurations

There is a spectrum of pressure-fed journal bearings ranging from the purely hydrostatic bearing characteristics, ie zero speed operation, to the purely hydrodynamic bearing characteristics which depend completely on speed. Between these two extremes, hybrid bearing characteristics rely on mixed modes of external pressurisation and speed-dependent pressurisation. Large high speed hydrodynamic bearings require the lubricant to be pumped under pressure for temperature control. It is therefore attractive to use this external source of pressure to enhance the start-up performance by reducing wear and improving stability. Hybrid bearings offer the possibility of improving on both the zero-speed characteristics of hydrostatic bearings and on the whole range of speed characteristics of hydrodynamic bearings. It is concluded that hole-entry bearings may be particularly effective when compared with other bearing configurations for good load support and low energy consumption, when used in any of the four modes of operation including: zero-speed hydrostatic mode; high-speed hydrodynamic mode; zero and high-speed hybrid mode; and jacking mode where areas are pressurised for start-up. A modification to the procedure for solving the Reynolds equation is introduced to cope with cavitated regions. The technique presented for solving the bearing pressures and cavitation boundaries is efficient and has relevance to any type of liquid film bearing     

Hydrostatic air foil bearings: Analytical and experimental investigation

Air foil bearings have been used in various micro-turbomachinery applications. One of the critical technical challenges in extending the operating envelope of the air foil bearing to larger systems than current applications is the issue of coating wear on the top foil and rotor during starts/stops.This paper reports the design, construction, and testing of the first hydrostatic air foil bearing (HAFB). The HAFB showed higher load capacity with much less air consumption than the hydrodynamic counterpart, which is a noticeable advantage of HAFB in efficiency and cooling capacity. In addition, start torque was very small and comparable to the friction torque of steady-state hydrodynamic operation. The small start torque clearly indicates that the HAFB can help to eliminate the wear problem that has been a chronic failure mode in heavily loaded air foil bearings.A simple analytical model for prediction of top foil deflection and sagging effects under hybrid (both hydrostatic and hydrodynamic) mode was developed. The new top foil deflection model showed very good agreement with published experimental data. The top-foil deflection model and associated bump dynamics were integrated into time-domain orbit simulations to predict imbalance responses of a rigid rotor supported by HAFBs.     

A feed back control system for plain bearings using film thickness measurement

A method for on-line monitoring and control of hydrodynamic journal bearings using film thickness measurement is proposed such that an adequate film thickness is maintained at all times. Such systems are considered to be useful in industrial applications, particularly in large installations such as power plants, rolling mills etc. The method uses the journal speed as the controlling parameter purely for demonstration purposes. Other alternatives such as use of an external lubrication pump to provide hybrid type of bearing operation may be envisaged. An analysis of the control system to predict the stability and steady state error is also included. The initial experimental results show that the proposed system works well.     

转速波动工况滚动轴承打滑动力学特性分析

滚动轴承实际运转过程中经常存在的转速波动现象,对滚动轴承的运行状态产生重要影响。基于Hertz接触理论和变形-位移相容条件建立滚动体与套圈的相互作用模型,采用非线性弹簧模拟滚动体与保持架间的相互作用,建立了转速波动工况下滚动轴承打滑动力学模型。通过与实验测试结果的对比,验证了所提出的动力学模型的正确性,并在此基础上分析了转速波动对滚动轴承打滑的影响及不同转速波动幅值、频率下滚动轴承的打滑特性。结果表明:轴承转速波动会造成保持架转速出现波动,导致轴承出现打滑,且滑动主要出现在滚动体与内圈之间;转速波动幅值对轴承打滑影响较大而频率影响较小。     

An experimental investigation into the friction and wear characteristics of unlubricated roller bearings

Lubricated rolling element bearings usually fail by fatigue. In the case of unlubricated rolling element bearings failure is due to wear of the rolling elements and cage. As the amount of wear increases so the friction torque of the bearing increases until catastrophic failure occurs and the bearing seizes.     

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。     

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。     

Hydro-Roll: A Novel Bearing Design with Superior Thermal Characteristics

A novel journal bearing design, called hydro-roll, which combines a hydrodynamic journal bearing with a rolling-element bearing in series, is presented. The hydro-roll principally operates as a rolling-element bearing at low speeds and as a hydrodynamic bearing at high speed. When properly designed, the hydro-roll can offer superior performance over the conventional hydrodynamic bearing in terms of both wear and thermal characteristics. The hydro-roll prevents the severe wear which occurs during the start-up of hydrodynamic journal bearings since it operates as a rolling-element bearing whenever the sliding friction is too high. This characteristic has the important advantage of reducing the risk of catastrophic failure by bearing seizure.

At a steady high speed, the hydro-roll operates as a hydrodynamic journal bearing while the sleeve together with the inner race of the rolling-element bearing turn at a low speed. This study focuses on the thermal analysis of a journal bearing with a rotating sleeve in comparison to an identical stationary sleeve. The results indicate that the sleeve rotation reduces the risk of bearing failure due to local overheating of the sleeve. The minimum sleeve speed required for this effect is evaluated.     

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。     

Performance of worn non-recessed hole-entry hybrid journal bearings

Non-recessed journal bearings have been successfully used in various engineering applications because of their good performance over a wide range of speed and load, besides their relative simplicity in manufacturing. Due to many starts and stops in its lifespan, the bearing bush wears progressively on account of rubbing, which affects bearing performance. The present work is an attempt to analytically study the performance of a worn non-recessed (hole-entry) capillary-compensated hybrid journal-bearing system. FEM has been used to solve the Reynolds equation, governing the flow of lubricant in the bearing clearance space along with the restrictor flow equation using suitable iterative technique. A study is conducted for two configurations, i.e., symmetrical and asymmetrical hole-entry journal-bearing system. The simulated results of bearing characteristics parameters in terms of maximum fluid-film pressure, minimum fluid-film thickness, flow rate, frictional torque, rotor dynamic coefficients, stability threshold speed and whirl frequency ratio, etc. have been presented for the wide range of various values of load and speed. The results indicate that the wear affects the bearing performance considerably; therefore, a due consideration of wear defect should be given for an accurate prediction of the bearing performance over a number of cycles. The computed results further indicate that the influence of wear defect on journal bearing performance may be minimized if a designer selects a suitable bearing configuration.     

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。     

Thermohydrodynamic analysis of a worn plain journal bearing

Hydrodynamic journal bearings are widely used in industry because of their simplicity, efficiency and low cost. They support rotating shafts over a number of years and are often subjected to many stops and starts. During these transient periods, friction is high and the bushes become progressively worn, thus inducing certain disabilities. This paper seeks to present the thermohydrodynamic performance of a worn plain journal bearing. The study deals with a 100 mm diameter bearing, submitted to a static load varying from 5000 to 30,000 N with a rotational speed varying from 1000 to 10,000 rpm. The defects caused by wear are centered on the load line and range from 10% to 50% of the bearing radial clearance. Our main focus was on hydrodynamic pressure, temperature distributions at the film/bush interface, oil flow rate, power losses and film thickness. Defects caused by wear of up to 20% have little influence on bearing performance whereas above this value (30 to 50%) they can display an interesting advantage: a significant fall in temperatures, due to the tendency of the bearing to go into the footprint created by the wear. Thus, the worn bearing presents not only some disadvantages but also advantages, such as lower temperature, since in certain cases of significant defects due to wear the geometry approaches that of a lobe bearing.     

Parametric study of solid-lubricant composites as ball-bearing cages

The performance of two polymer-based materials (polyimide/MoS₂ and ptfe/ glass fibre/MoS₂) as self-lubricating cages for ball bearings has been comprehensively evaluated. The two composites emerged as the most promising for operating at elevated temperatures during screening tests in a thrust-bearing geometry and were then tested in four sizes of 440C stainless steel single-row radial ball bearings at a range of loads, speeds and temperatures.Two regimes of operation were observed: the first with essentially zero steel wear when the lubricant transfer film is complete and bearing life is dictated by cage wear; the second with finite steel wear when the transfer film is only partially effective and bearing life is dictated by increase in internal clearance. The ball/raceway stress at which steel wear starts to occur is very low (< 1.2 × 10³ MN m^?2) compared to the stress implied by the catalogue load capacity of the bearings. The ball/raceway stress also has an important effect on both steel wear rate and cage wear rate.Overall, the ptfe-based composite gave lower steel and cage wear than did the polyimide-based composite, but the latter could be operated at higher temperatures (up to 360° C) and at slow speeds it gave a higher load capacity before the onset of steel wear.Using the wear results as a basis, a Bearing Performance Guide has been produced which provides a convenient means of approximately predicting the bearing life over a wide range of operating conditions     

高速角接触球轴承中的冲击滑动研究

高速角接触球轴承中,球与保持架的碰撞会导致球与滚道的冲击滑动,从而引起滚道划伤和轴承早期失效。为探究球与保持架的冲击碰撞导致的瞬时滑动,以某高速角接触球轴承为研究对象,通过对联合载荷下角接触球轴承的动力学仿真,分析了变速工况及保持架结构参数对球与保持架的冲击碰撞、球与滚道的冲击滑动以及零件磨损率的影响。结果发现,加减速及恒定转速下,球与保持架的运动呈现周期性变化;由于球进入和离开径向载荷区域时公转角速度的变化,球与保持架碰撞并导致球相对内、外圈滚道发生冲击滑动;为适应球公转角速度的变化,适当增大兜孔间隙,可以减小球与保持架兜孔碰撞力的大小和频率,从而减小球与滚道的冲击滑动以及保持架的磨损率。     

Assessment of polymer composites for hydrodynamic journal‐bearing applications

Polymer composites are used as facing materials in hydrodynamic bearings for their low friction and ‘compliant’ properties, which play an important role during machinery operation. In journal bearings, this low friction property can be of significant importance during start and stop cycles when insufficient oil is available to fully separate the surfaces in relative motion. Current work is aimed at determining a suitable material for use in hydrodynamic journal bearings for applications in hydroelectric power plants. This study investigates friction and wear encountered during the transition from the stationary state to operational speed (acceleration) during initial start‐up. This is examined for virgin poly‐tetra‐fluoro‐ethylene (PTFE) together with a series of commercially available PTFE‐based composites and a babbitt material in boundary/mixed lubrication conditions. Tests are performed using standard laboratory block‐on‐ring test apparatus with a VG32 mineral oil. Copyright © 2009 John Wiley & Sons, Ltd.     

Some Mechanical Considerations in the Design of Large Thrust Bearings

The modern thrust bearing is a very important part of the waterwheel generator, for it must support the weight of the rotating parts of the turbine and generator and the hydraulic thrust load. With the continuous increase in size of hydroelectric generating units, machines now are built with thrust loads well above 1000 tons and requiring bearings ten feet in diameter or larger. Continuous trouble-free operation for periods of twenty years or more are desired for the bearings of large hydroelectric units.

Except during the starting period, the pivoted pad thrust bearing operates according to the well-known hydrodynamic theory of lubrication which permits the predetermination of its performance with reasonable accuracy. Alternating slipping between the thrust bearing runner and the supporting structure can result in excessive wear which destroy the accuracy of the bearing surfaces. Such wear can cause undesirable vibrations or damage to the bearing surface which prevents the formation of an adequate oil film. As a result of laboratory tests and experience in the field, it is now possible to make large thrust bearings with a supporting structure which will permit them to operate continuously for long periods of time with practically no wear or loss of adequacy.     

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.     

考虑不同加速工况的滑动轴承的启停性能分析*

滑动轴承的摩擦磨损主要发生在启停阶段。为了研究启停工况下的滑动轴承的摩擦学性能,建立一种面向径向滑动轴承的混合润滑数值分析模型。采用质量守恒边界条件的雷诺方程求解流体压力,采用Greenwood和Tripp接触模型预测固体表面接触,而通过Johnson载荷分配概念将润滑模型和接触模型联系起来,从而实现对滑动轴承在启停工况下从混合润滑过渡到动压润滑的摩擦学行为分析。利用该模型,研究轴承系统在启停阶段从边界润滑、混合润滑到动压润滑演化过程中的摩擦学性能;以径向滑动轴承系统为例,结合不同的轴承转速变化函数,分析轴承加速对轴承启停性能的影响;同时研究工作工况、润滑油温度、轴承的结构参数对轴承启停性能的影响。结果表明：轴承启动加速度在合理范围内越大越好,能使轴承更快进入动压润滑;较高的转速、较低的润滑油温度和较大的径向轴承间隙能使轴承拥有更好的启停性能。     

Analysis of Capacitive Effect and Life Estimation of Hydrodynamic Journal Bearings on Repeated Starts and Stops of a Machine Operating Under the Influence of Shaft Voltages

A theoretical analysis has been carried out to study the capacitive effect and life estimation of hydrodynamic journal bearings on repeated starts and stops of a machine operating under the influence of shaft voltages. The analysis gives the time required for the charge accumulation and increase of charge with time on the liner surface of a journal bearing based on bearing capacitance, resistance of film thickness, and the shaft voltage. Also, it investigates the effect of gradual leakage of the accumulated charges with time as the shaft voltage falls when the power supply to the machine is switched off. This paper gives an approach to determine the ratio of the number of shaft revolutions required for charge accumulation and gradual discharge of the accumulated charges on the liner surface of a bearing depending on bearing-to-shaft voltage. Also, the number of repeated starts and stops before initiation of craters on the liner surface of a hydrodynamic journal bearing is established to restrict deterioration and damage of the liner. The diagnosis has the potential to study the transient effect of the shaft voltages on a journal bearing during the start and stop cycle of a machine.