Observed Effects of Vibrationally Induced Fretting on Bearing–Shaft Systems in Flywheel Energy Storage Systems

Mechanical bearings in a flywheel energy storage system (FESS) may experience unique wear patterns due to the vacuum condition that such systems operate under. The FESS discussed herein uses an aluminum flywheel rotor hub with an integrated shaft and full silicon nitride ceramic bearings. The bearings experienced fretting wear, as is common to many bearing–shaft systems, which eroded the naturally forming oxide layer on the surface of the shaft which was not replaced due to the lack of oxygen. This exposed the soft aluminum surface below creating the opportunity for material transfer between the surfaces and cold welding between components to occur. The existence of fretting and material transfer is demonstrated, and the opportunity for cold welding between components is discussed. The effects of these processes on system components are described. Recommendations to avoid or mitigate fretting and adhesion damage to the system are made for the studied FESS in particular, and, more generally, similar systems operating in vacuum conditions.     

Investigation of tribological properties of boronized Fe-based SAE 1020 and TS-DDK 40 journal bearings at high loads

In practice, ferrous based materials are not used because they show similar properties to shaft material and are known to cause adhesive wear in journal bearings. With boronizing process, adhesive wear can significantly be decreased. In this study, boronizing has been applied to some ferrous based (SAE 1020, TS-DDK 40) journal bearings. Wear experiments were done on SAE 1050 steel shaft as counter abrader with 100 N loads, and 1500 rpm for 5 h by using a radial journal bearing test rig. Boronizing treatment increased wear resistance of SAE 1020, TS-DDK 40 about 10–25, and 5–7 times respectively.     

Friction coefficient estimation in shaft/bush interference using finite element model updating

Reliable finite element modeling has a great degree of importance for studies related to the mechanical design in industry. Finite element modeling is often associated with some uncertainties. Model updating is a tool which can be used to overcoming these uncertainties. This method uses experimental data of the structural components to modify the initial FE model. A typical use of model updating is for interference joint of a shaft and bush. In the modeling of the interference joint for known materials, an approximate value is assumed for friction coefficient of contact areas. Based on intuition, engineering judgments or previous tests, it is difficult to accurately estimate this coefficient. In this paper, model updating is used to estimate and update the friction coefficient in the contact surface of interference shaft and bush joints. Suitable experiments were conducted and the initial finite element model was modified based on the experimental extraction strength of interference fit joints. Finally, typical values of stress fields were extracted from the new model with an updated value of the friction coefficient.     

Analysis of lubricity and cavitation problem of oil and refrigerant mixture for hermetic compressors

The study is based on the results of experimental and theoretical research, the aim of which was to reveal the potential for the decrease of friction losses in the refrigerator's compressors. Lower viscosity oils as well as decreasing crankshaft diameters should lower the said losses. However, these measures can cause an adverse effect, if hydrodynamic lubrication regime transforms into boundary one, and the bearing eccentricity ratio reaches unity. The main objective of the study is to explain why the almost ideal surfaces of shaft and bush do wear when the carrying capacity of lubricating film theoretically exceeds real loads at eccentricity ratio 0.9 or even less. This disagreement, which also is presented in the study, can be explained by cavitation only partially. This study makes an assumption that the boundary value, i.e. oil film height, at which cavitation is starting, depends on a minimum height of the lubricating oil film, i.e. minimum clearance between shaft and bush.     

Failure analysis and finite element simulation of key components of PDM

As one of the most commonly used downhole drilling tools, PDM (Positive Displacement Motor) is widely used in drilling and workover. Drilling practice shows that PDM is frequently scraped for the failure of key components. The coupled thermo-mechanical finite element model of rubber linings, finite element models of thrust bearing and universal shaft petals were established respectively, and the failure reasons were discussed by simulation. It was found that there are oval holes caused by thermal failure in general rubber lining, while no oval holes in the uniform wall thickness rubber lining. Rubber layer peeling and broken appear on the surfaces of rubber linings under the load of drilling fluid and rotor. Thrust bearings experienced serious wear, corrosion and rupture in the terrible downhole environment. The universal shaft petals appear fracture in the root, and wear on contact surfaces under torque and axial load. The results obtained in the paper show that the analyzing model and evaluation methods are quite reasonable and can be generally applied, which have great significance on the enhancement of structural design and repair for PDM in the future industry.     

Dry self-lubricating composites

Chopped strand carbon fibers, glass fibers and their hybrids were used to reinforce an epoxy matrix to which additives of PTFE, graphite and molybdenum disulfide were used for producing a dry self-lubricating material. Their tribology properties were studied using testing machines of thrust and journal radial. Also, the PV value, friction coefficient, wear rate and the contact surface temperatures were determined. The compression strength of the bush ring and the impact strength of material were evaluated. The surfaces of wear were investigated. The mode of fracture mechanism is proposed according to the specimens morphology. The relationship between friction coefficient and loading correlated well with the Myoshis equation in the case of a backing material. This study provided an optimal approach of making dry wear bearings by glass fibers backing at low friction coefficient.     

球磨机滑动主轴承重要参数的选取

讨论了球磨机主轴承宽径比L／D,中空轴轴颈的轴肩与轴瓦两侧面预留间隙值,轴瓦与中空轴轴颈间的配合侧隙,轴瓦与中空轴轴颈的配合接触角以及轴瓦与瓦座的配合接触面对球磨机滑动丰轴承承载能力和轴瓦磨损、发热的影响,并对它们的选取进行分析。     

冻融条件下公路桥梁板式氯丁橡胶支座抗剪试验

公路桥梁橡胶支座比建筑橡胶支座更容易受到气候的影响,为了研究公路桥梁板式氯丁橡胶支座在受到气候影响时的各项抗剪性能指标变化情况,采用标准冻融试验箱模拟低温气候变化,对氯丁橡胶支座进行冻融循环处理25、50、75、100次,并对其进行抗剪试验,采用与标准试件进行对比分析的方法,研究冻融循环对氯丁橡胶支座的抗剪承载力、抗剪强度、水平等效刚度、抗剪弹性模量的影响。结果表明,氯丁橡胶支座在冻融循环处理条件下比标准试件更易发生破坏,且钢板外露、裂缝等破坏现象更严重。氯丁橡胶支座的抗剪承载力、抗剪强度、水平等效刚度、抗剪弹性模量都随冻融程度的加深而降低。采用最小二乘法对其抗剪强度和抗剪弹性模量变化进行分析并给出衰减曲线和衰减函数,抗剪强度和抗剪弹性模量的变化趋势基本符合幂函数规律。     

Failure Investigation of a Locomotive Turbocharger Main Shaft and Bearing Sleeve

A failure investigation was conducted on a locomotive turbocharger main shaft and a bearing sleeve which had been assembled with the main shaft. The fracture of the main shaft took place at a sharp edged groove between two journals with different cross-sectional areas. The dominant failure mechanism of the main shaft was low-cycle and rotation-bending fatigue. Wear failure occurred on the bearing sleeve through a mixed mode of abrasive and adhesive wear. Detailed metallurgical analysis indicated that the bearing sleeve and the journal surface assembled with the sleeve had been subjected to abnormally high temperatures which led to increased friction between the bearing sleeve and the bearing bush, the sleeve, and the journal surface. In addition, the abnormally high temperature softened the induction-hardening case on the journal surface and decreased the fatigue strength. Fatigue crack initiation occurred at the root fillet of the groove because of the stress concentration in that area.     

Failure analysis of a high-speed pinion shaft

The failure of a high-speed pinion shaft from a marine diesel engine was investigated. The shaft, which had been in service for more than 30 years, failed shortly after a service operation in which the bearings were replaced. Examination of the shaft revealed cyclic fatigue as the failure mechanism, with a substantial distribution of nonmetallic inclusions near the fracture initiation site. Fracture mechanics analysis indicated that the inclusions would be unlikely to have served as failure initiation sites if only stresses acting on the shaft were induced by normal service loads. Further examination of the bearing elements revealed an abnormal wear pattern, consistent with the application of elevated bending loads to the shaft after bearing replacement. The root cause of failure was determined to be an increase in service stresses after bearing replacement along with the presence of significant nonmetallic inclusions in the pinion shaft.     

基于离心力和陀螺力矩效应的“主轴-轴承”系统动力学特性研究

研究“主轴-轴承”系统在高转速场中受离心力和陀螺力矩影响的动力学特性对于提高主轴系统运行稳定性有重要的作用。在扩展Harris滚动轴承非线性分析模型、建立滚动轴承耦合刚度矩阵的基础上,建立了一种综合考虑主轴离心力效应和陀螺力矩效应的“主轴-轴承”系统动力学数字模型,并借助锤击模态实验验证了其准确性;分析论述了主轴离心力效应、主轴陀螺力矩效应及滚动轴承运行刚度对“主轴-轴承”系统在高转速场中的动力学特性的影响规律。通过模型分析计算表明：当轴承处于超轻预紧（EL）工况时,主轴的高速效应比轴承运行刚度对“主轴-轴承”系统动力学特性的影响更大,尤以主轴陀螺力矩效应的影响最为突出。     

Numerical study on the lubrication oil distribution in a refrigeration rotary compressor

For a rolling piston rotary compressor, oil supply into various lubrication elements has been analytically studied. The lubrication system, consisting of centrifugal shaft pump, radial oil feeding holes, bearings with grooves and some other sliding surfaces has been modeled by employing equivalent electric circuit network. A computer simulation program has been developed to solve the network model of the lubrication system. Its numerical solutions include total oil flow rate into the shaft inlet, oil flow rates in the main and sub journal bearings and in the eccentric bearing, and oil leakages through roller end clearances into suction and compression chambers. Validation of the numerical simulation has been made by the measurement of the total oil flow rate into the shaft. With the aid of computer simulation, parametric studies have also been carried to investigate the effects of the bearing groove shape and groove inclination angle on the bearing oil flow rates.     

计入应力偶效应和空化效应的滑动轴承热流体动力润滑数值研究

基于应力偶理论和Elrod空化算法建立了滑动轴承热流体动力润滑数学模型，数值求解了应力偶流体的Reynolds方程、油膜能量方程及轴瓦热传导方程，考察了应力偶效应对滑动轴承热流体动力润滑性能产生的影响。结果表明：应力偶流体明显地提高了油膜压力，降低了轴承摩擦系数，同时也使端泄流量和轴承的温度场有所改变。     

Investigation of tribological and mechanical properties of metal bearings

Copper, aluminum and tin-lead based alloys are widely used as journal bearing materials in tribological applications. Bronze and brass are widely used as journal bearing materials for copper based alloys. Zamacs find applications as journal bearing materials for zinc based alloys, while duralumines are chosen as journal bearing materials for aluminum based alloys. In addition, white metals are widely used as journal bearing materials for tin-lead based alloys. These alloys ensure properties expected from journal bearings. In this study, tribological and mechanical properties of these journal bearings manufactured by metals were investigated. SAE 1050 steel shaft was used as counter abrader. Experiments were carried out in every 30 min for a total of 150 min by using radial journal bearing wear test rig.     

Analytical and CFD modeling of the fluid flow in an eccentric-tube centrifugal oil pump for hermetic compressors

A model is presented for calculating the volume flow rate in an eccentric-tube centrifugal oil pump for reciprocating compressors. The oil pump assembly consists of a pick-up tube with an inclined inlet that is mounted off-center with the crankshaft symmetry axis. The pick-up tube is connected to the shaft channel, a helical groove machined on the crankshaft that facilitates the supply of lubricant to the bearings. The analytical models for the pick-up tube and shaft channel were developed independently and were coupled via a numerical procedure to determine the steady-state volume flow rate in the assembly. The steady-state results were verified against a CFD model, which was also used to evaluate the fluid flow in the oil pump assembly during a start-up transient. A parametric analysis was conducted to quantify the influence of some oil pump geometric parameters, such as the pick-up tube diameter and the shaft eccentricity.     

Dynamics of a Rotor in Film Lubrication Bearings

A dynamic model of a rotor system with hydrodynamic plain bearings in which account has been taken of the actually existing phenomenon of the circular anisotropy of the rigidity of hydrodynamic plain bearings has been proposed. The operation of the rotor system has been modeled with the use of uniformity distributed sequences and the region of states of the system representing a set of instantaneous positions of the center of the end rotor surface by which the accuracy of its rotation is evaluated has been obtained.     

无拆卸轴承刚度测试方法的研究

轴承刚度对轴系振动有重要影响,研究无拆卸轴承刚度测试方法有利于快速可靠地了解轴系的振动特性。通过机架安装隔振器、泵进出口安装波纹管、电机与泵转子间采用电磁联轴器等结构措施;构建了离心泵转子-滚动轴承的试验台架。以光电传感器安装位置为转轴相位参考,通过转轴振动位移峰值识别出轴承截面轴系等效偏心质量的相位。通过附加质量于等效偏心质量相位产生激振力,并运用Lab VIEW构建的虚拟仪器测量附加质量前、后振动位移峰值变化量,从而得出轴承刚度。最后通过台架实际配置与转子模型进行了验证。结果表明,轴承刚度无拆卸测试方法有效可行,设计的试验台架可实现附加配重的安装,并能够有效地予以验证;所构建的虚拟仪器也能够准确计算得出转轴偏心质量相位与轴承支撑刚度。     

Influence of the structure of babbitt on the stress-strain state in the zone of friction contact

The methods of mathematical simulation are used to study the process of contact friction interaction for homogeneous lead and heterogeneous intact or run-in B16 babbitt. It is shown that the hard and soft structural components of the run-in babbitt strongly decrease the size of the zones of plastic deformation in the material, improve its wear resistance, and promote the increase in the operating reliability and service life of plain bearings. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 27–30, November–December, 2007.     

Elastic multiple-mass model for rotordynamic analysis of flexible electrical rotors

The paper presents an elastic multiple-mass model for rotordynamic analysis of flexible electrical rotors supported in sleeve bearings, considering mechanical unbalances and electromagnetic forces. This model has been especially developed for flexible electrical rotors, which operate near below or near above the first critical bending speed of the rotor. Using this simplified model, a static rotor active part eccentricity can be simulated and the orbital movement of the rotor can be calculated. Additionally, the influence of different balancing concepts??elastic balancing versus rigid balancing??on the shaft vibrations is analyzed. To verify the model, a finite element analysis was performed, which indicates a satisfactory match. On the one hand, the aim of the paper is to derive an elastic multiple-mass model for rotordynamic analysis of flexible electrical rotors for special boundary conditions. On the other hand, the aim is to show the mathematical coherences??based on a simplified model??between the rotordynamics, the oil film characteristics of the sleeve bearings, the elasticity of the rotor structure, the electromagnetics and the balancing concept.