Determination of stability boundaries of shaft movement in a conical bearing with porous surface layer

A method to determine the stability boundaries of shaft movement in a conical slider bearing in the presence of a porous layer on its working surface is developed. Evaluation of the effect of taper angle and porous layer permeability on the dependences determining the stability boundaries of the bearing operation is presented.     

Dynamic characteristics of the rotor in a magnetically suspended control moment gyroscope with active magnetic bearing and passive magnetic bearing

For a magnetically suspended control moment gyroscope, stiffness and damping of magnetic bearing will influence modal frequency of a rotor. In this paper the relationship between modal frequency and stiffness and damping has been investigated. The mathematic calculation model of axial passive magnetic bearing (PMB) stiffness is developed. And PID control based on internal model control is introduced into control of radial active magnetic bearing (AMB), considering the radial coupling of axial PMB, a mathematic calculation model of stiffness and damping of radial AMB is established. According to modal analysis, the relationship between modal frequency and modal shapes is achieved. Radial vibration frequency is mainly influenced by stiffness of radial AMB; however, when stiffness increases, radial vibration will disappear and a high frequency bending modal will appear. Stiffness of axial PMB mainly affects the axial vibration mode, which will turn into high-order bending modal. Axial PMB causes bigger influence on torsion modal of the rotor.     

Generating surface of a tool for shaping the internal surface of the shaft in a low-pressure turbine

Continuous shaping of the internal surfaces of a shaft in a low-pressure turbine by a single contacting working roller is considered, on the basis of semifree strip grinding with constant radial force, in the absence of a servo system. Formulas for semifree grinding that permit the determination of the basic parameters corresponding to the product specifications are established.     

Cavitation erosion of a flat surface near a rotating shaft

To clarify the phenomenon of cavitation erosion in the sliding bearings of internal combustion engines, an apparatus was prepared and tests were conducted on cavitation in the oil between the cylindrical face of a rotating shaft and the tip of a horn attached to an ultrasonic oscillator. This apparatus produces an oil flow and a plus-minus oil pressure between a shaft and a horn tip to simulate erosion and its distribution on bearing surfaces.From patterns of cavitation erosion on the tip of a horn made of an Al-Sn alloy and the pressure distribution on the wedge oil film, it was determined that the region where cavitation bubbles occur and the region where erosion occurs owing to the collapse of the bubbles do not necessarily coincide.Cavitation erosion was found to occur in both the plus and the minus oil film pressure regions and erosion due to bubble collapse occurs in the regions where pressure increases in the direction of oil flow.The test results allow the postulation of the mechanism and the reasons for the occurrence of cavitation erosion on actual sliding bearing surfaces.     

Integral characteristics of a porous gas axial bearing

A flat axial bearing with pressurized gas supply through an annular flow valve made from anisotropic porous material is considered. The differential equation for the pressure in the lubricant layer adjacent to the porous wall is numerically solved using the Runge-Kutta method, with two boundary conditions taken into account. One of these, which is integral, has remained out of sight in the porous support analysis until recently. An algorithm for calculating the lifting force and rigidity of support as well as mass rate of gas flow through this support is presented. The optimization of support is performed, and conclusions are drawn as to its influence on different factors.     

Experimental studies on the effects of bearing supply gas pressure on the response of a permanent magnet disk-type motor rotor

Vibrations, particularly low-frequency vibrations caused by self-excited gas films, significantly affect the safety and economy of turbomachinery, which becomes dangerous at high rotational speeds. This experimental study focuses on the dynamic characteristics of a Permanent magnet (PM) disk-type motor rotor supported by gas aerostatic bearings. Nonlinear dynamic behavior, including double low frequency and gas film half whirling, was analyzed in the experiments. The dynamic features of double low frequency and gas whirling are described in the paper. The most important finding is that the sum of the whirling ratios of low frequencies 1 and 2 is always 1.00. The occurrence mechanism requires further study. The effects of bearing supply gas pressure on the dynamic response characteristics of the multi-disk PM rotor are implemented to improve rotor stability.     

Simulation of combined wearing of the shaft and bush in a heavily loaded sliding bearing

The problem of simultaneous wear of an elastic cylinder and a cylindrical notch surface in an elastic space is discussed (in the planar formulation). The contact problem formulation omits the limitation of the contact area. The contact is solved in steps; the linear wear and contact parameters of the shaft and bush are solved at each step in time. The Multopp-Kalandia method is applied to the solution of the contact problem. The constructed model is used to investigate the evolution of contact pressure and form changes of the shaft and bush in the process of wear.     

Contactless surface-temperature measurement for the rotating shaft of an unlubricated bearing

A contactless method of determining the surface temperature of a shaft in frictional heating is proposed. The measurement error is no more than 2.6%.     

Study of the flaking-off phenomenon on a jet Engine's shaft bearing using the thin layer activation technique

The Thin Layer Activation technique has been applied in order to study the flake-off phenomenon on a jet engine's shaft bearing. The external track of the bearing has been activated following the reaction ⁵⁶Fe(p,n)⁵⁶Co, over a depth of 80 μm. In spite of a very low activation level, the first signs of flaking-off were detected 30 min before any significant increase in the vibration level appeared. At that point, the mass of particles leaving the track was measured on line, with a precision of 0.2 mg.     

某燃气轮机轴承钢球缺陷分析

某燃气轮机工作25 000h后,在首翻期修理时,发现主齿轮箱内一球轴承钢球表面存在缺陷,但并未影响系统正常工作。通过能谱分析,结合国内外常见球轴承钢球加工过程分析,找到了故障钢球缺陷产生的原因。     

超精密气浮定位平台动力学特性分析

设计了一种超精密气浮定位平台,并运用Ansys对导轨和滑台分别作了有限元模态分析,校核了其动态刚度。在此基础上,分析了导轨的厚度对导轨刚度的影响以及滑台顶板厚度对滑台刚度的影响,为结构的优化设计提供了参考依据。分析结果显示,定位平台的刚度满足设计要求。     

Hydrodynamics of a radial bearing with electrically conducting gas lubricant

The proposed method permits self-similar hydrodynamic calculation of a radial bearing with electrically conducting gas lubricant. The method takes account of the magnetic field.     

淬火凸轮轴表面硬度检测工装的设计

以凸轮轴的轴心和凸轮的回程面定位设计凸轮淬火后表面硬度检测工装,改进了以前工装使用过程中存在的检测面窄、凸轮转动等缺点,同时使凸轮硬度检测工装的操作更简单,人为影响更少,误差经计算几乎可以忽略.     

轴承端面缺陷自动检测研究

针对微小轴承端面字符与缺陷两者的灰度值相差无几,对缺陷的直接检测造成干扰,提出了基于缺陷周围高亮度特征的检测方法通过对图像的迭代法阈值分割,定义检测目标的像素数作为缺陷识别的主要依据.结合PLC控制系统,开发的缺陷自动检测程序系统,可实现不合格轴承的在线分拣处理.实验结果表明,系统检测误检率不超过1‰,满足了高精度、高效率检测轴承端面缺陷的要求.     

轴承端面缺陷自动检测研究

针对微小轴承端面字符与缺陷两者的灰度值相差无几,对缺陷的直接检测造成干扰,提出了基于缺陷周围高亮度特征的检测方法;通过对图像的迭代法阈值分割,定义检测目标的像素数作为缺陷识别的主要依据.结合PLC控制系统,开发的缺陷自动检测程序系统,可实现不合格轴承的在线分拣处理.实验结果表明,系统检测误检率不超过1‰,满足了高精度、高效率检测轴承端面缺陷的要求.     

Computational results of a dynamic simulation of the conforming shell gas journal bearing

A time-dependent mathematical model for the conforming shell gas journal bearing is presented. A computational simulation of the mathematical model is used to investigate the dynamic behaviour and steady state characteristics of the bearing. The onset of dynamic instabilities, violation of the minimum film thickness criteria and component separations are found to be the three factors which form upper and lower bounds on the range of acceptable loads.     

Experimental studies of pressure distributions in finite slider bearing with single continuous surface profiles on the pads

There are indications in the literature that surface profiling/texturing can have significant and positive influence on the load carrying capacity of hydrodynamic pad thrust bearings. Moreover, due to cost and resource conservation considerations, lubricating oils are being used for much longer period of service than in the past. This causes lubricant to be subjected to higher levels of contamination in spite of good filtrations. In turn, hydrodynamic bearings generally operate in the presence of tiny contaminant particulate. Thus, performance study of hydrodynamic thrust bearing with pads’ surface profiling and contaminated oil are vital. Presently, one finds dearth of experimental research in this area. Therefore, the objective of this paper is to compare the experimental results of pressure distributions in slider bearing with various single continuous surface profiles of pads (cycloidal, catenoidal, polynomial, and plane) using clean and contaminated lubricating oils. Pressure results presented in this paper can provide a platform for validation of theoretical models based on contamination in lubricating oil.     

透平膨胀机气体静压轴承的修复

介绍了PLN-6/4-0.25型透平膨胀机气体静压轴承在生产运行中常见的故障,在作业现场采取了合理的修复措施和切实可行的修复方法,消除了故障的根源,大大减少了停机次数,保证了生产正常运行。     

Vibration of a hydrostatic gas bearing due to supply pressure oscillations

The vibration of a statically loaded, inherently compensated hydrostatic journal bearing due to oscillating supply pressure is investigated. Both angular and radial vibration modes are analyzed. The time-dependent Reynolds equation governing the pressure distribution between the oscillating journal and the sleeve is solved numerically together with the journal equation of motion to obtain the response characteristics of the bearing. The Reynolds equation and the equation of motion are simplified by applying regular perturbation theory for small displacements. The results presented include Bode plots of bearing oscillation gain and phase for a particular bearing configuration for various combinations of parameters over a range of frequencies, including the resonant frequency. The results are compared with the results of an earlier study involving the response of a similar bearing to oscillating exhaust pressure.     

Investigation of nonlinear numerical mathematical model of a multiple shaft gas turbine unit

The development of numerical mathematical model to calculate both the static and dynamic characteristics of a multi-shaft gas turbine consisting of a single combustion chamber, including advanced cycle components such as intercooler and regenerator is presented in this paper. The numerical mathematical model is based on the simplified assumptions that quasi-static characteristic of turbo-machine and injector is used, total pressure loss and heat transfer relation for static calculation neglecting fuel transport time delay can be employed. The supercharger power has a cubical relation to its rotating velocity. The accuracy of each calculation is confirmed by monitoring mass and energy balances with comparative calculations for different time steps of integration. The features of the studied gas turbine scheme are the starting device with compressed air volumes and injector’s supercharging the air directly ahead of the combustion chamber.