Performance of three-lobe pressure-dam bearings

The use of multi-lobe bearings, considered to be more stable than ordinary circular bearings in industry is increasing daily. Studies have shown that performance can be further improved if pressure dams are incorporated into these bearings. Analysis of two-lobe pressure dam bearings has been reported in the literature. The present work was carried out to assess the performance of a three-lobe bearing with pressure dams. The results show that the performance of a three-lobe pressure-dam bearing is far superior to that of an ordinary three-lobe bearing.     

Investigation of sintered bronze bearings under high-speed conditions

An experimental study has been made of sintered bronze bearings under high speed and light load conditions. The temperature rise, friction coefficient, oil loss rate and wear of the bearings were all measured during the tests at a speed of 69 000 r/min with or without oil supplement and under different loads. Contrary to the theory, the results showed that sintered bronze bearings could operate under hydrodynamic conditions for long periods (more than 4000 hours). The effects of different oils on the performance of the bearings were studied for speeds in the range 5000–50 000 r/min and with a load of 2.34 kgf/cm². The results indicated that the correct selection of oil for porous bearings is very important.     

Properties and prospective applications of ultra thin layered rubber-metal laminates for limited travel bearings

Limited and/or oscillating motions represent the most severe operating conditions for conventional bearings, both sliding and antifriction. Thin-layered rubber-metal laminates seem to be ideal substitutes for conventional bearings for oscillating motions. This paper descirbes experimental investigations of the compression and shear properties of flat and spherical laminates. The very high compression stiffness and strength of the laminates are accompanied by low shear stiffness. Strong non-linearity of the hardening type in compression is accompanied by weak non-linearity of the softening type in shear. Substantial non-linearity in compression starts as early as at relative compression 0.001. Applications of thin-layered laminates for compensating couplings, U-joints, gears, vibration isolators and impact cushioning in joints of mechanisms are described. Expressions have been derived for efficiency of couplings and joints equipped with laminates     

Static and Dynamic Characteristics of Four-Lobe Pressure-Dam Bearings

The stability of ordinary journal bearings is found to increase by the use of multi-lobes. Studies have shown that performance can be further improved by incorporation of pressure dams into these bearings. This paper analyses the performance of a four-lobe pressure-dam bearing which is produced by incorporating two pressure dams on the upper two lobes and two relief-tracks on the lower two lobes of an ordinary four-lobe bearing. The results show that the performance of a four-lobe bearing with pressure dams is superior to that of an ordinary four-lobe bearing.     

Self Adapting Mechanical Step Bearings for Variations in Load

As the application of small-scale and precision technologies increases, the need will grow for bearings which are able to provide precision control of their location. Thus, there is a need for new bearing technologies to reduce friction and wear, and provide precision control of bearing motion. This control can be provided by electronically controlled actuators and sensors, but then the system is dependant on the reliability of the electronics. This work uses numerical methods to research the design and behavior of self adapting step bearings. These step bearings are designed to change their surface profiles to achieve an optimal or controlled behavior, without the use electronics or external control. The bearing changes its profile to control the film height of the bearing to a near constant value for different loads. The result is a self adapting step bearing design that may be applied at multiple scales for use in a wide variety of machine components. The numerical simulation shows that the self adapting step bearing is able to autonomously adapt in real time to dynamic loads and maintain a desired film thickness with a relatively small amount of deviation. The self adapting step bearing also exhibits smaller dynamic responses to transient loads in comparison to a conventional static geometry step bearing. A self adapting step bearing using a linear spring instead of a non-linear spring also appears to show similar improvements in performance.     

A new model for combined Couette and Poiseuille flows in the transverse groove of a plane inclined slider bearing

Although extensive research has been performed on the grooving of hydrodynamic bearings, there is much to be done on the flow interactions near to and in axial grooving. This work was initiated when the pressure boundary conditions were unknown for the case of a journal bearing with multiple axial grooves each being fed by an external lubricant source. This work is a forerunner to a more extensive research programme using journal bearings. A new technique has been devised to calculate the pressure profile across and along an axial groove. There is a strong pressure flow along the groove and Couette and pressure flow in the direction of sliding. Good correlation between experimental results and theoretical predictions for a wide range of operating conditions has been achieved.     

涡旋式制冷压缩机止推轴承润滑性能研究的最新进展

在涡旋式制冷压缩机运行过程中,止推轴承动止推盘两端的压力差对轴承的润滑性能有显著的影响;止推轴承本身的结构特点,如键槽的存在,也会影响止推间隙的压力分布以及倾斜角,从而影响止推轴承的润滑性能.对止推轴承动止推盘两端的压力差、止推轴承本身结构等影响因素从理论或试验等方面进行探讨,并对将来涡旋式制冷压缩机止推轴承润滑性能的研究进行展望.     

Stability of the rotor supported in gas journal bearings with a chamber feeding system

This paper describes the results of numerical investigations of the stability problem of the rigid symmetrical rotor supported in two externally pressurized gas journal bearings. The bushes of the bearings are mounted on a system of linear springs and viscous dampers. When the stiffness and damping coefficients of these springs and dampers are chosen correctly, it is possible to avoid the self-excited vibrations of the rotor. Such vibrations, which are caused by the phenomenon of a half-synchronic whirl, are the major obstacle to the widespread application of gas bearings. The results of authors numerical experiments have shown that the elastic support of the bearing bushes can be designed as an additional externally pressurized air ring, surrounding the bush. The set of parameters of such a ring is optimal when the bearing has a chamber feeding system.     

Inlet roughness tribodevices: dynamic coefficients and leakage

The new class of bearings recently described by the author has some interesting properties. These bearings generate pressure by an effective wedge or inlet step formed by the local roughness instead of the standard inlet geometries. This means that the micro- rather than macro-geometry in the inlet zone ensures that the flow into the bearing meets less resistance than it does out of the bearing. The first paper presented a simple model, consisting of flat pads of infinite width sliding over a smooth counterface. The roughnesses were in the form of transverse or longitudinal grooves. Load capacity, friction and coefficient of friction were calculated. In the present paper the model is studied further and the normal stiffness and damping coefficients as well as the flow are calculated and compared with values for similar smooth standard shapes. It is seen that the coefficients of the new class of devices may be considerably higher and the flow lower than for similar conventional bearings when the film thicknesses are small. It is concluded that they should find useful applications in many practical devices when a certain film is needed for lubrication purposes, but when leakage should be kept a minimum. Piston rings, high precision bearings and possibly hard disks may be envisaged.     

水润滑轴承水膜压力无线测试系统研究

为了深入研究水润滑轴承特性,需要了解轴承真实的水膜压力分布,而传统的滑动轴承润滑膜压力测试无法获得轴承全周水膜压力的连续分布,且采用集流环作为信号传输媒介,其成本较高、对输出信号干扰较大。针对以上不足,研究并设计了一种无线测试系统,可测量水润滑轴承全周水膜压力,并实时监测水润滑轴系的运转情况。介绍了测试系统组成,包括无线采集发射与接收装置、传感器与信号调理模块、测试软件及水润滑轴承试验台,最后应用此系统对八沟槽水润滑平面橡胶轴承的水膜压力进行测试,并与仿真结果对比分析。结果表明,该测试系统实用性良好,可用于测试其他材料和结构的水润滑轴承的水膜压力。     

Relating contact conditions to abrasive wear

Damage caused by particles within rolling/sliding contacts can severely reduce the operational life of machinery such as roller bearings, gears and pumps.Abrasive wear of spherical roller thrust bearings has been studied using a stylus apparatus and scanning electron microscopy (SEM). Both a standard bearing and a bearing with rollers coated with metal mixed amorphous carbon (Me-C:H) were studied. The SEM measurements were performed systematically across the contact surfaces so that surfaces with gradually different contact situations could be examined. These measurements were compared to the measured wear depth of the components of the roller bearing. Also, the calculated contact conditions in terms of creep, contact size and surface separation have been related to the observed wear pattern at various locations.To attempt to understand the wear behaviour of the bearing with coated rollers, the coating as well as the material content of the surfaces were examined using both SEM and energy dispersive X-ray spectrometry (EDS). This revealed that the coating did not flake off but rather was scratched off.It is possible to link the abrasive wear behaviour to the contact conditions. It is crucial to understand this relationship when building a simulation model of abrasive wear.     

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     

A method of temperature monitoring in fluid film bearings

In the present paper a method to improve temperature monitoring of fluid film bearings is described. The method is tested in an industrial tilting pad thrust bearing. Test results for steady state and transient operating conditions are reported. Temperatures monitored by a thermocouple through the utilisation of the proposed method are compared to those measured by thermocouples in the pad backing and in the collar. The method is also tested on a PTFE-faced bearing. Test results show that the proposed method improves sensitivity to thermal transients in conventional babbitted bearings and provides adequate means of temperature monitoring in the PTFE-faced bearings.     

Experimental investigations of precision spindles equipped with high stiffness gas journal bearings

The journal high stiffness bearings (HSBs) presented in this paper have been supplemented with special regulation systems that enable us to select optimal bearing characteristics by a slight circumferential turn of the journal bearing bush with respect to its fixed casing. The regulation system allows us to obtain the desired bearing characteristic compensating for the inaccuracy of its element production. Two different regulation systems are presented in this paper. The experimental investigations for static conditions of a single HSB with two above-mentioned regulation systems have been performed. Then, two spindles equipped with journal HSBs have been investigated. Each spindle was supported using two HSBs with the same regulation system. The results of these investigations for different rotational frequencies are reported. The effectiveness of the HSB regulation systems for practical optimization of the spindle characteristic have been shown. These bearings can be applied in precision grinding machines.     

The use of experimental results in solving tribological problems

The use of extreme pressure (EP) additives resulted in increased gear life for the driving unit of a hot roll stand in a steel work. For large diameter sliding bearings operational problems caused by the surface roughness of the journal and bearing linings can be eliminated by using oil of the correct viscosity together with careful filtering.Seizure of the jaw coupling of a steam turbine can be eliminated by an appropriate material combination which is assessed by seizure investigations. Structural changes based on the results of an experimental investigation of sticking have eliminated unreliable operation of a starting device for a steam turbine.     

Relative comparison of stiffness and damping properties of double decker high precision and conventional rolling-element bearings

This paper reports the relative comparison of stiffness and damping properties of Double Decker High Precision Bearing (DDHPB) and conventional rolling-element bearings. It has been determined that under different load and speed conditions, DDHPB and the conventional bearings have identical critical speed, comparable net deflection and stiffness. On the contrary, relative damping of the DDHPB, evaluated by rotating speed component of vibrations, at different operating conditions is approximately three times more than that of the conventional bearing. Excitation tests at different speeds have also indicated better damping characteristics of DDHPB as compared to the conventional bearing. This potential of DDHPB permits its use in typical industrial applications where damping is a significant requirement.     

Thermoelastic behaviour of journal bearings undergoing seizure

Extensive numerical results are presented for the behaviour of journal bearing undergoing seizure. Included in the results is a sensitivity study performed to investigate the influence of various bearing parameters and operating conditions on the onset of seizure. It is demonstrated that high shaft speeds could lead to a very rapid seizure when the bearing is subjected to dry sliding. The significance of housing flexibility, internal cooling, and heat conduction through the contact between the shaft and bearing are discussed in depth.     

Modelling pressure distribution in a rectangular gas bearing using neural networks

Gas ubricated bearings are of tremendous use especially in the biomedical and aerospace industries. For that reason, gas bearings have been the subject of much research for the past decade or so. Experimental as well as theoretical work has been done to calculate the pressure distribution inside the bearing. The models available to predict the pressure are primitive and need to be improved. This paper discusses a new modelling scheme known as artificial neural networks. The pressure distribution and the load-carrying capacity are predicted using feedforward architecture of neurons. The inputs to the networks are a collection of experimental data. This data is used to train the network using the Levenberg-Marquardt optimization technique. The results of the neural network model are compared to a theoretical model and the results are promising. The neural network model outperforms the avallable theoretical model in predicting the pressure as well as the load-carrying capacity.     

The effect of texture shape on the friction coefficient and stiffness of gas-lubricated parallel slider bearings

Surface texturing is used to increase hydrodynamic pressure and reduce friction and wear between gas-lubricated parallel sliding surfaces in a variety of applications. The shape, geometry, and density of the patterned microtexture features (“dimples”) play a key role in the tribological performance of textured slider bearings. In this paper we evaluate the friction coefficient and stiffness of gas-lubricated textured parallel slider bearings as a function of six different texture shapes. The texture geometry and density are optimized in terms of minimum friction coefficient and maximum bearing stiffness for each individual texture shape, and then compared relative to each other. The ellipsoidal shape is found to yield the minimum friction coefficient and the highest bearing stiffness, independent of the operating conditions.     

Improvement of static characteristics of an aerostatic journal bearing using the elastic deformation of an O-ring

A new type of aerostatic journal bearing in which the elastic deformation of an O-ring is used to improve its static characteristics is proposed. The static characteristics of this bearing are determined theoretically by both the finite difference method and the small perturbation method. Effects of parameters on the static characteristics are shown, and the optimum design method for the static characteristics is discussed. Further, theoretical results are compared with experimental results to confirm the validity of theoretical predictions. It is consequently found that the new type of bearing possesses higher static stiffness and greater load capacity than conventional point source bearings with inherently compensated feeding holes.