Raceway Of Bearing Research Articles

Computational model for calculation of static capacity and lifetime of large slewing bearing's raceway

A computational model for determination of static capacity and fatigue lifetime of large slewing bearings is presented. In the proposed model, contact load distribution along the bearing raceways is calculated on the basis of the static equilibrium between contact loads acting on the raceways, and external loads acting on the bearing. On the basis of the maximum contact force and some typical and experimentally determined material parameters, the static capacity of a bearing is calculated and a comparison of different approaches for a calculation of the fatigue lifetime of a bearing is presented. The following calculation methods are compared: ISO standardised calculation approach, a stress-life approach and a strain-life approach. The presented vector based calculation approach for a calculation of the contact load distribution seems to be an appropriate approach for a fast evaluation of the influence of the bearing clearance and the deformation of bearing rings on the contact load distribution. The comparison of fatigue lifetimes calculated with different calculation methods shows that the choice of method for the calculation of an equivalent mean stress significantly effects the calculated lifetimes. Furthermore, the comparison of lifetimes also shows that, by assuming that ISO standardised calculation approach gives relevant results and provided that material parameters are properly defined, the stress-life approach is, to some degree, a proper method for calculation of the rolling bearing fatigue lifetime.

Modelling the Contact between the Rolling Elements and the Raceways of Bulky Slewing Bearings

In slewing bearings, a great number of contact pairs are present on the contact surfaces between the rolling elements and raceways of the bearing. Computations to determine the load of the individual rolling elements, taking into account the flexibility of the bearing ring, are most often carried out using the finite element method. Construction of a FEM full model of the bearing, taking into account the shape of the rolling elements and the determination of the contact problem for every rolling element, leads to a singularity of stiffness matrix, which in turn makes the problem impossible to solve. In FEM models the rolling elements are replaced by one-dimensional finite elements (linear elements) to simplify the computation procedure and to obtain an optimal time for computations. The methods of modelling the rolling elements in the slewing bearing, in which balls have been replaced by truss elements with a material non-linear characteristic located between the raceway centres of the curvatures in their axial section, are presented in the paper.

The Finishing of Rolling Bearing Raceway by Electrochemical Mechanical Finishing (ECMF) Technology

This paper studies the technology of Electrochemical Mechanical Finishing (ECMF) on rolling bearing raceway. The principle of the technology is introduced, and the finishing results are presented. The results show that the surface roughness, supporting length rate, profile roundness, waveness and wave velocity are all improved greatly. Also, the main affecting factors such as the inter-electrode gap, electrochemical process and mechanical process are discussed in this paper. The bearings finished by ECMF have better service performance and life.

The Evaluation of the Micro-Tracks and Micro-Dimples on the Tribological Characteristics of Thrust Ball Bearings

One of the primary remedies for tribological problems is surface modification. The reduction of the friction between the ball and the raceway of bearings is a very important goal of the development of bearing technology. A low friction has a positive effect in terms of the extension of the fatigue life, avoidance of a temperature rise, and prevention of premature failure of bearings. Therefore, this research sought to investigate the effects of micro-tracks and micro-dimples on the tribological characteristics at the contact point between the ball and the raceway of thrust ball bearings (TBBs). The ultrasonic nanocrystal surface modification (UNSM) technology was applied using different intervals (feed rates) to the TBB raceway surface to create micro-tracks and micro-dimples. The friction coefficient after UNSM at 50 microm intervals showed marked sensitivity and a significant reduction of 30%. In this study, the results showed that more micro-dimples yield a lower friction coefficient.

Novel Method for Improving Surface Performance of Rolling Bearing Raceway

The thin film can improve the surface performance of rolling bearings to reduce friction, vibration and noise and to increase the operating life of rolling bearings. This paper proposes a novel method for improving the surface performance of rolling bearings. This method is characterized by adding nanoparticles to the superfinishing liquid to form the nanofilm on the surface of the raceway by means of the special superfinishing technique. The experimental investigation proves that using this method, the fatigue life of the rolling bearing is obviously higher than that of the normal bearing. Surface topography photos of the Scanning Electron Microscope show that the thin film still exists after the fatigue test in 300 hours. Because of low cost, this method can be widely used in the production of rolling bearings.

Ultrasonic Measurement of Rolling Bearing Lubrication Using Piezoelectric Thin Films

This paper describes the measurement of lubricant-film thickness in a rolling element bearing using a piezoelectric thin film transducer to excite and receive ultrasonic signals. High frequency (200 MHz) ultrasound is generated using a piezoelectric aluminum nitride film deposited in the form of a very thin layer onto the outer bearing raceway. This creates a transducer and electrode combination of total thickness of less than 10 μm. In this way the bearing is instrumented with minimal disruption to the housing geometry and the oil-film can be measured noninvasively. The high frequency transducer generates a fine columnar beam of ultrasound that has dimensions less than the typical lubricated contact ellipse. The reflection coefficient from the lubricant-layer is then measured from within the lubricated contact and the oil-film thickness extracted via a quasistatic spring model. The results are described on a deep groove 6016 ball bearing supporting an 80 mm shaft under normal operating conditions. Good agreement is shown over a range of loads and speeds with lubricant-film thickness extracted from elastohydrodynamic lubrication theory.

Frequency Response Analysis for Rolling-Bearing Damage Diagnosis

This paper deals with a new diagnosis method for detecting bearing faults (BFs) based on frequency response analysis. For non-rigid multi-mass systems with dominant mechanical resonance frequencies, the frequency response has to be calculated during the commissioning of the plant for reasons of safety and controlling. This task can be achieved by measuring two control variables of the drive which are both affected by BFs. This paper proposes that the measurement of the frequency response is a suitable strategy for detecting incipient BFs. In doing so, a two-channel analysis method for bearing damage diagnosis without additional sensors is developed. Deviations from the frequency response of the healthy state serve as indicators for a present BF. As the measurement of the two signals can be carried out during normal operation of the plant, online BF diagnosis is achieved. For the investigated two-inertia system, single-point bearing defects on the inner and outer raceways of rolling bearings and generalized roughness faults are within the scope of this paper.

Experimental Study of the Smoothing Effect of a Ceramic Rolling Element on a Bearing Raceway in Contaminated Lubrication

The effects of steel and ceramic rolling elements on protrusions from the raceway of a bearing were experimentally investigated. Such protrusions, which are normally caused by solid contaminants in the lubricating oil, create stress concentrations and lead to a reduction in the rolling contact fatigue life of the bearing. To compare the over-rolling effects of steel and ceramic rollers, experiments with steel discs with artificial dents on the surfaces were performed using a modified twin-disc machine. The results show that ceramic rollers can reduce the height of the protruded edge of an artificial dent more than steel rollers, which means that they are more effective in smoothing a damaged surface. The stresses at the contact were calculated by finite element analysis based on the deformed profile of the dented surface. The reduction in the stress level due to the smoothing effect of ceramic rollers is greater than that of steel rollers. According to the Lundberg–Palmgren bearing fatigue model, that smoothing ensures a significantly longer rolling contact fatigue life for a bearing. To put the idea into practice, a rolling ball bearing with two of its nine steel balls replaced with silicon nitride balls (referred to as a “partial hybrid bearing”) was run, together with a full steel bearing of the same model, on a bearing tester in a highly contaminated lubrication condition. The results show that the partial hybrid bearing suffers from less damage in terms of wear. The post-experiment examination of the damaged surface of the bearing raceway found that the surface of the partial hybrid bearing was smoother than that of the full steel bearing. This reveals the smoothing effect of the rolling ceramic element on the contaminant-damaged bearing surface.

Failure analysis of the deep groove ball bearings of an electric motor

The deep groove ball bearings of an electric motor, driving an oil-injected compressor, were periodically monitored for vibrations. The ball bearings were replaced when before the expected lifetime of the bearing the measured vibration exceeded the tolerated level. The bearing on the axle side of the motor was the locating bearing while the ball bearing of the fan side (where the fan of the electric motor was placed) was mounted as a (spring-loaded) floating bearing. The outer rings of the fan side bearing showed signs of fretting wear. The outer ring of both bearings was ground through to disassemble the bearings. Visual inspection, optical microscopy and scanning electron microscopy of the raceways indicated that the bearings were subjected to an axial load in the range of the permissible axial load, but for each bearing in a different direction. The placement of the wear marks on the raceways of both bearings indicated an axial loading from the inside towards the outside of the electric motor. Also the wear marks on the raceways of both ball bearings showed the typical washboard pattern of the passage of electric current >0.5 A, although the rotor was already equipped with a grounding brush on the non-drive side. While replacing the deep groove ball bearing by a cylindrical roller bearing can easily prevent the fretting wear on the fan side bearing, the origin of the bearing currents merits further investigation.

Electrolytic In-Process Dressing (ELID) and Super-Precision Grinding for the Ring Raceway of Ball Bearings

Electrolytic In-Process Dressing (ELID) and Super-Precision Grinding for the Ring Raceway of Ball Bearings

Stress Analysis on Bearing Raceway by Barkhausen Noise

SNFA has decided to develop the Barkhausen Noise technique in order to determine the state of stresses and the microstructural changes in the contact zones of the bearing raceways and rolling elements. Based on its know-how, its practical experience on site of the X-ray diffraction method and the non-destructive techniques (Micrography, Fluorescent Penetrant Inspection, Magnetic Particle Inspection, Nital Etch and Eddy Current), SNFA is today in a position to officially state the efficiency of the Barkhausen Noise technique to estimate the state of stresses in the bearings. A specifically developed software allows us to estimate the residual stress profiles on the following bearing contact zones: raceways after grinding, raceways after prestressing and raceways after operation on an engine.

Fatigue Life Reduction of Roller Bearings Due to Debris Denting: Part II - Experimental Validation

Life tests have been conducted for tapered roller bearings. Bearing race ways are pre-dented with particles of various types and sizes. Life reductions due to surface indentation are calculated by a stress-based life model using the measured raceway topography. The predictions are compared and validated with testing results. The study concludes that bearing life reduction is primarily determined by the slopes and area densities of surface indentations. Life reduction factor decreases as dent slope and area-density increase. The hardness and fracture toughness of the denting particles have a noticeable effect on bearing life reduction. Ductile particles cause more severe life reduction than the brittle particles. Surface failures associated with small dents are superficial and often appear in forms of “micro-pitting” and “micro-peeling.” Large dents generated by ductile particles cause severe damage to bearing raceways and are more likely to induce surface pits and spalls. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999

Rolling contact fatigue testing of PM high speed steels (HSS): J A Whitehead, et al. (Powdrex Ltd, tonbridge, Kent, UK), Int. J. Powder Metallurgy, Vol 26, No 4, 1990, 345–349

The large diameter bearings (diameter >400 mm) are of great importance in complex engineering mechanisms such as Aircraft gas turbines, Rolling Mills and Nuclear Reactor etc, in which varying load and critical environmental conditions leads to the failure of such bearings. Majorly spalling failure occurs due to contact mechanism. The contact mechanism of ball and raceway of bearing behaves highly non-linear and it reduces the service life of component considerably. This paper presents to determine the contact stress of large diameter ball bearings using analytical and numerical methods. In analytical method the contact stress is found out using the Hertzian Elliptical Contact Theory. The calculation procedure consists of calculation of the maximum contact pressure on the rolling element, which is done by the in-house developed program, and detailed finite element analysis of the contact between the ball and the raceway. The finite element analysis also performed to predict contact pressure in ball and raceway. Comparison of the results is made at the end.

Research and Testing

Equipment, Programmes, Techniques and Projects. In many applications the rollers or balls together with the raceways of roller bearings are subject to high repetitive stresses and as a result may, after many million stress cycles, fail due to metal fatigue. Much attention has been given by the International Standards Organization (I.S.O.) to determining the fatigue life of ball and roller bearings and whilst it is not possible to expect that any one bearing will fail at its calculated life, it is possible to predict that a certain percentage of a group of identical bearings tested under identical load and operating conditions will exceed the calculated life. Furthermore, it has been established that the average life of all the bearings in a group so tested will exceed the calculated life by a considerable margin.