Rolling-element bearings in China: From ancient times to the 20th century

The development of rolling-element bearings in China has spanned a long period. Based on several typical and important cases, the present article reconstructs the history of rolling-element bearings in China by dividing it into four stages according to the various characteristics of the bearings. The first stage represents the origin of rolling bearings in China, which remains controversial because of several suspected races and cages that were likely the components of bearings more than a millennium ago. At the second stage, a type of simple roller bearing was used for astronomical instruments not later than the 13th century based on clear philological and physical evidence. A similar bearing was also applied to an abridged armillary in the 17th century. Another type of spherical thrust bearings with rolling elements, which is a key component of a traditional Chinese windmill, could support a rotating shaft that moves rotationally and at an angle. At the third stage, the Chinese began studying and using the so-called Europeanstyle bearing since the 17th century. Moreover, over the last 100 years, the modern rolling bearing industry was gradually established in China, particularly because of the technology transfer from the Soviet Union in the 1950s. At the fourth stage, the Chinese government initiated the relatively rapid development of bearing technology. The government launched the “bearing movement” from the 1950s to the 1960s to establish the modern bearing industry and to promote rolling bearings as replacement for traditional sliding bearings. Furthermore, a number of large professional factories and institutions in China have continually introduced advanced technology and equipment. At present, these companies and institutions play a significant role in the international bearing industry.     

Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than that of an all-steel rolling element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives of the deep-groove, angular-contact, and cylindrical roller hybrid bearings with races made of post-1960 bearing steel increased by factors of 3.7, 3.2, and 5.5, respectively, from those calculated using the Lundberg-Palmgren equations. An all-steel bearing under the same load will have a longer life than the equivalent hybrid bearing under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than all-steel bearings by 58% for deep-groove bearings, 41% for angular contact bearings, and 28% for cylindrical roller bearings.     

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.     

Detection of Damage in Assembled Rolling Element Bearings

A nondestructive method, capable of detecting localized surface damage, such as small spalls, nicks, dents and scratches, on the balls (rollers) and races of assembled rolling-element bearings, is discussed. The method utilizes the “almost periodical” character of vibration peaks produced by rotating a damaged bearing at constant speed. These “almost periodical” peaks are compared to the random vibration peaks, generated by the undamaged portions of the rolling surfaces of the bearing. Instrumentation to accomplish this comparison is described. It includes a vibration test spindle with pickup and amplifier, electronic gating circuitry serving as frequency and phase discriminator, and electronic counters to count “almost periodic” and random vibration peaks. Different methods of interpreting the counts and evaluating the degree of bearing damage are discussed.     

Defect diagnostics of roller bearing using instantaneous frequency normalization under fluctuant rotating speed

We investigated the feasibility of utilizing the normalized characteristic frequencies for diagnosing the defective roller bearings in case of fluctuant rotating speeds. The time-frequency distributions of the envelope signals of the vibration data were constructed through the Empirical mode decomposition (EMD) as well as the instantaneous frequency calculation. The bearing defect-related frequencies were then normalized with respect to the instantaneous rotation frequency of the shaft so that the factor of the rotating speed fluctuation was removed; thus the characteristic frequencies of bearing malfunctions could be observed in terms of constant values. The magnitude distributions of the marginal envelope spectra at the corresponding normalized bearing defect-related frequencies were extracted as the feature vectors. The Support vector machine (SVM) was used to classify the extracted feature vectors of different bearing fault classes. A test rig of roller bearing system was performed to illustrate the different bearing faults, including different levels of inner race defect, outer race defect and roller defect. The analysis results demonstrate the capability and effectiveness of the proposed approach for accurately identifying the bearing defects in case of fluctuant rotating speed.     

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.     

Dynamic behaviour of externally pressurized gas journal bearings with multiple supply holes

A theoretical analysis of the dynamic behaviour of externally pressurized journal bearings using a compressible lubricant is made. Two aspects, (i) “squeeze-film” due to harmonic vibration of a stationary journal and (ii) steady-whirl instability of an unloaded rotating journal were studied. The bearing configuration considered had double plane admission feed holes at quarter station. The effect of recess volume at the downstream of the orifices was considered. The dynamic load and moment were determined for various frequencies, recess volumes and bearing design dimensions. Stability charts of whirl are given for various journal speeds, feed and bearing design parameters.     

The use of acoustic emission information to distinguish between dry and lubricated rolling element bearings in low-speed rotating machines

Bearings are known as the vital parts of machines, and their condition is often critical to the success of an operation or process. Presence of a film of lubricant such as grease between the bearing surfaces minimizes the friction and surface wear. Contaminated grease or lack of lubricant may lead to an ineffective bearing performance or malfunction of the machinery parts. Therefore, in order to avoid unexpected breakdowns, reliable and robust bearing condition monitoring techniques are demanded. According to previous studies, acoustic emission (AE) signals contain valuable information that can be used for bearing condition monitoring and fault detection. The main objective of this study is to evaluate the effectiveness of AE signal parameters to distinguish between lubricated and dry bearings under similar operating conditions. To this end, a low-speed rotating test rig is manufactured and used. Eight levels of rotational speeds and four levels of radial loads were applied to the test rig shaft end, which is connected to the testing bearing. In each test, seven time domain AE parameters were computed. The statistical tools were also used to present the dominant experimental variables on AE signal parameters. According to experimental results, it was found that four AE parameters can be used to distinguish between dry and lubricated bearings.     

A comparison of some condition monitoring techniques for the detection of defect in induction motor ball bearings

Rolling element bearings are critical components in induction motors and monitoring their condition is important to avoid failures. Several condition monitoring techniques for the bearings are available. Out of these stator current monitoring is a relatively new technique. Vibration, stator current, acoustic emission and shock pulse methods (SPMs) for the detection of a defect in the outer race of induction motor ball bearing have been compared. The measurements were performed at different loads. The defect in the bearing could be detected by all the methods. Acoustic emission monitoring proved to be the best method followed by SPM when the increase in the levels of the measured parameters were compared with respect to those of healthy bearings.     

Experimental diagnostics of ball bearings using statistical and spectral methods

Vibration measurements and signal analysis is widely used for condition monitoring of ball bearings as their vibration signature reveals important information about the defect development within them. Time domain analysis of vibration signature such as peak-to-peak amplitude, root mean square, Crest factor and kurtosis indicates defects in ball bearings. However, these measures do not specify the position and/or nature of the defects. Each defect produces characteristic vibrations in ball bearings. Hence, examining the vibration spectrum may deliver information on the type of defects. In this paper a test rig is designed and a pair of brand new commercial ball bearings is installed. The bearings run throughout their lifespan under constant speed and loading conditions. Vibration signatures produced are recorded and statistical measures are calculated during the test. When anomalies are detected in the statistical measures, vibration spectra are obtained and examined to determine where the defect is on the running surfaces. At the end of the test, the ball bearings are disassembled in order to take microscopic photos of the defects.     

Defect detection in deep groove ball bearing in presence of external vibration using envelope analysis and Duffing oscillator

This paper deals with detection of local defects existing on races of deep groove ball bearing in the presence of external vibrations using envelope analysis and Duffing oscillator. Experiments have been carried out using a test rig for capturing the vibration signals of test bearing. The external vibration has been imparted to the housing of the test bearing through electromechanical shaker. In envelope analysis the centre frequency has been selected using the spectral kurtosis for the filters length of 32 and 64 for different bandwidths. Through this study, it has been revisited and confirmed that the defect detection in envelope analysis mainly depends on the selection of centre frequency and bandwidth. The spectra of selected centre frequency with several bandwidths have been studied and compared for identification of defective frequency. The system defined by the Duffing equation entered into the periodical state from the chaotic state at the critical value of disturbing periodic force in the presence of defective bearing signal. The state change has been identified using the phase plane trajectories and Lyapunov exponents of Duffing equation. It is worth to mention here that envelope spectrum reveals the information about the defect frequencies and their harmonics. However, the Duffing oscillator only confirms the presence of defect frequencies by indicating closed phase plane trajectories and negative Lyapunov exponents. Authors believe that for speedy assessment about the presence of defects on races of rolling element bearings, the use of Duffing oscillator may be preferred.     

Vibration analysis of rolling element bearings with various defects under the action of an unbalanced force

In this paper, a method based on the finite element vibration analysis is presented for defect detection in rolling element bearings with single or multiple defects on different components of the bearing structure using the time and frequency domain parameters. A dynamic loading model is proposed in order to create the nodal excitation functions used in the finite element vibration analysis as external loading. A computer code written in Visual Basic programming language with a graphical user interface is developed to create the nodal excitations for different cases including the outer ring, inner ring or rolling element defects. Forced vibration analysis of a bearing structure is performed using the commercial finite element package I-DEAS under the action of an unbalanced force transferred to the structure via a ball bearing. Time and frequency domain parameters such as rms, crest factor, kurtosis and band energy ratio for the frequency spectrum of the enveloped signals are used to analyse the effect of the defect location and the number of defects on the time and frequency domain parameters. The role of the receiving point for vibration measurements is also investigated. The vibration data for various defect cases including the housing structure effect can be obtained using the finite element vibration analysis in order to develop an optimum monitoring method in condition monitoring studies.     

The application of vibration signature analysis and acoustic emission source location to on-line condition monitoring of anti-friction bearings

The mechanical noise, vibration and heat generated by defects in fabrications, process plant and machinery are a measure of component condition, and once characterised allow on-line assessment of defect severity. Unexpected failures which might threaten the entire production process can thereby be avoided. There is an increasing need for reliable and robust condition monitoring instrumentation with on-line data processing, particularly as the trend contunues towards larger production units with little or no standby capacity for use in the event of unscheduled stoppages due to mechanical failure. This article describes the detection of incipient failure of rolling element bearings by kurtosis and the location of fatigue cracks in slowly rotating bearings by acoustic emission     

The deterioration of lithium greases under the influence of electric current—an investigation

In the present work, we report on the analysis of the deterioration of lithium greases used in rolling-element bearings by X-ray diffractometry (XRD), X-ray fluorescence spectrometry (XRFS), and atomic absorption spectrometry (AAS). These techniques give reproducible, reliable data with which to establish the severity of deterioration of greases recovered from the active zone of bearings. XRD appears more suitable for diagnosing quickly the chemical changes that have occurred in the soap residue of greases, even in small quantity, than other analytical and performance evaluation techniques. Fresh lithium greases, their chemical composition, and the formation of new compounds in the greases have been investigated after use in rolling-element bearings run in the presence of electric fields, and also under pure rolling friction conditions without electric fields on a roller-bearing test rig. The deteriorated greases recovered from various motor bearings have also been analysed and the results are compared with those for the greases from the test bearings. X-ray diffraction analysis shows that the chemical composition of the soap residue of the fresh lithium grease, lithium stearate (C₁₈H₃₅LiO₂), does not change in bearings operated without the effect of electric fields, under pure rolling friction. However, lithium iron oxide (Li₅FeO₂) peaks were detected after prolonged operation of the bearings. On the other hand, under the influence of electric fields, the chemical composition of the grease changed to lithium palmitate (C₁₆H₃₁LiO₂), and peaks of gamma lithium iron oxide (Γ-LiFeO₂) and lithium zinc silicate (Li_3.6Zn_0.2SiO₂) were detected. The surface of the bearings was found to be corroded after operation under electric fields. AAS showed a considerable increase in the lithium percentage, and lithium carbonate and lithium hydroxide in the used greases in aqueous solution, compared to the fresh grease The investigations reported in this paper, together with study of damaged/corrugated bearing surfaces, offer potential in diagnosing the cause of bearing failure in teh presence of electric fields, and in establishing the severity of deterioration of the lithium greases used in the bearings.     

Condition monitoring of naturally damaged slow speed slewing bearing based on ensemble empirical mode decomposition

There have been extensive studies on vibration based condition monitoring, prognosis of rotating element bearings; and reviews of the methods on how to identify bearing fault and predict the final failure reported widely in literature. The investigated bearings commonly discussed in the literatures were run in moderate and high rotating speed, and damages were artificially introduced e.g. with artificial crack or seeded defect. This paper deals with very low rotational-speed slewing bearing (1–4.5 rpm) without artificial fault. Two real vibration data were utilized, namely data collected from lab slewing bearing subject to accelerated life test and from a sheet metal company. Empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) were applied in both lab slewing bearing data and real case data. Outer race fault (BPFO) and rolling element fault (BSF) frequencies of slewing bearing can be identified. However, these fault frequencies could not be identified using fast Fourier transform (FFT).     

双层滚动轴承热学特性研究

磁悬浮轴承系统通常采用滚动轴承作为保护轴承。基于传热学、滚动轴承摩擦学以及转子动力学等理论,建立一种用两个滚动轴承组成的双层保护轴承(Double-decker auxiliary bearing,DDAB)的热学模型,通过建立热传递方程,计算轴承的摩擦热和温度分布,研究DDAB的热学特性。研究内容如下:建立双层滚动轴承(Double-decker rolling bearing,DDRB)的热传递模型,推导热传递阻抗和热传递方程,计算DDRB在普通运转条件下达到热平衡时的温度分布;研究不同结构、载荷、转速、润滑剂粘度、材料属性等参数对轴承温升的影响,并对比其与普通轴承在相同工况下的热学特性;建立试验台,实际测量轴承的温升,研究不同结构形式和润滑参数条件对于轴承热学特性的影响,探讨可以降低发热的主要措施。研究结果表明:DDRB的径向载荷和内圈转速直接影响轴承摩擦力矩的大小进而影响轴承的发热,在相同工况下DDRB比普通滚动轴承的内圈温升要小5%～20%,外圈温升要小10%～30%;结构、润滑剂粘度、材料的热学性能对轴承内外圈温度分布影响较大,润滑剂的填装量在轴承空间的1/3,采用Z形结构、铝制中圈、陶瓷滚动体等...     

Rolling Bearing Service Life Based on Probable Cause for Removal—A Tutorial

In 1947 and 1952 G. Lundberg and A. Palmgren developed what is now referred to as the Lundberg-Palmgren model for rolling bearing life prediction based on classical rolling-element fatigue. Today, bearing fatigue probably accounts for less than 5% of bearings removed from service for cause. A bearing service life prediction methodology and tutorial indexed to eight probable causes for bearing removal, including fatigue, are presented that incorporate strict series reliability; Weibull statistical analysis; available published field data from the Naval Air Rework Facility; and ～224,000 rolling-element bearings removed for rework from commercial aircraft engines. Bearing service life L_serv can be benchmarked and calculated to the bearing L₁₀ fatigue life as follows: L_serv = X^1/m L₁₀, where X is the number of bearings removed from service because of fatigue divided by the total of all bearings removed from service regardless of cause and m is the Weibull modulus of the bearings removed from service. The most conservative bearing L₁₀ service life calculation is obtained assuming an exponential distribution where m = 1.1. Of the ～224,000 commercial engine bearings removed from service for rework, 1,977 or 0.88% were rejected because of fatigue. From the Naval Air Rework Facility bearing data, eliminating rolling–element fatigue as a cause for removal, the L₁₀ service life of these bearings would increase by approximately 3%.     

Determination of magnetic flux density on the surfaces of rolling-element bearings as an indication of the current that has passed through them—an investigation

This paper introduces a theoretical model to determine the developed magnetic flux density on the inner and outer surfaces of the inner race and outer race, and on the surface of rolling-elements of a rolling bearing operating under the influence of an electric current. The flux density, analytically determined, is compared with that of the flux density developed on the surfaces of races and rolling-elements of bearings tested on the bearing test-up under the influence of an electric current. The magnetic flux density on the surfaces of damaged bearings of motors and alternators has also been measured and the theoretical model is used to determine the amount of current flow through the damaged bearings. The current flow through the bearings, thus established, has been compared with that of the current evaluated by the measurement of shaft voltage and bearing resistance. The model has the potential to ascertain the cause of failure by current passage and to establish the amount of flow of leakage current through the bearings by determining the magnetic flux density on the surfaces of rolling-element bearings. The current flow, thus established, together with the measurement of the shaft voltage, allow the bearing impedance to be established.     

Rolling-Element Bearing Internal Temperatures

The internal temperature distribution within tapered rolling-element bearings was investigated. A simple experimental procedure using thermocouples for the stationary outer race and a temperature-sensitive medium on the moving components was used to determine bearing operating component temperatures. Circulating oil was used to lubricate the bearings. Temperatures for two different loads and three taper conditions (simulating bearing misalignment) are given. Corresponding contact pressure distributions and the calculated EHL films are shown. The correlation between temperatures and changes in pressure distributions, as well as their calculated effects on the lubricant film, can be easily seen.     

Analysis of whirl speeds for rotor-bearing systems supported on fluid film bearings

There are several numerical approximations for vibration analysis of rotor bearing systems and the most popular approach is the Finite Element Method. In the light of the above it is proposed to undertake a study on the dynamic behaviour of Timoshenko beam supported on hydrodynamic bearings incorporating internal damping using FEM model. Critical speeds are estimated for synchronous whirl at different operating conditions using Campbell diagrams. It is observed in the analysis that in addition to the natural whirl frequencies, for every spin speed another whirling frequency appears in the solution, which is around half the spin speed. In case of fluid film bearings, half whirl is very common phenomenon. In case of dynamic coefficients evaluated using short bearing approximation, it is observed that these additional frequencies are of the same order as that of the synchronous whirling frequencies. The additional frequencies around half the spin speeds are found using only finite bearing dynamic coefficients; this clearly indicates the deficiency in the use of short bearing approximation in similar work.