Radial Ball Bearings Research Articles

AN EFFECTIVE MODEL FOR CALCULATING THE NONLINEAR RIGIDITY OF BALL BEARINGS

An analysis of the features of the static calculation of the spindle assembly for stiffness, taking into account the stiffness of the supports, was carried out. It is noted that during the static analysis of spindle shafts, approximate reference values of the rigidity of supports - rolling bearings are usually used. which can give an error in estimating the stiffness of the support up to 50%. The paper presents an analysis of the modified Jones-Harris method for calculating the stiffness of bearings, which provides an increase in accuracy due to new constants in the dependencies for the radial stiffnesses of support and support-thrust ball bearings. The finite element models used instead of the Hertzian contact model in the modified Jones-Harris model in the contact problem "rolling element - bearing rings" more accurately reflect the geometry and stiffness of the bearing raceways, which allow obtaining more accurate constants for the nonlinear stiffness model of ball bearings. The advantage of the modified model is the possibility of automatic calculation of the technological gap in the bearing and the speed of rotation of the shaft. The calculation of the stiffness of SKF bearings showed greater accuracy, which is confirmed by comparison with the experiment. The results of the stiffness calculation obtained for a number of SKF bearings can be successfully used for practical stiffness calculations of radial and radial thrust ball bearings of other firms, the structural and technological characteristics of which correspond to the characteristics of the SKF bearings considered in the work.

Comparison of fatigue life behavior between deep groove radial ball bearings possessing conventional and micro-grooved outer races operating under dry condition

A comparative study on fatigue life of deep groove radial ball bearings possessing conventional and micro-grooved outer races by experimental investigation is discussed in this paper. This research has been carried out to explore and understand the fatigue life of a micro-grooved ball bearing (MGB) with a circumferential micro-groove on outer race by conducting long duration tests under dry condition (i.e. wiping out the applied grease from the races by using tissue paper and lint free cloth) and compare the results with same size SKF BB1B 420206 conventional bearing (CB) at the identical operating parameters. Frictional torque (FT), bulk temperature, and overall vibration level of the test bearings (CB and MGB) at the maximum load zone have been measured at 800 N ( pH = 1.7 GPa) radial load and 1800 rpm (4.2 m/s) for the entire duration (7.8 million revolutions) of the experiments. Comparison of the surface conditions of the bearing components by means of the captured scanning electron microscope (SEM) images, roundness and deviation in profile of the races measured by co-ordinate measuring machine (CMM), and photographs captured before and after the experiment indicates lesser damage of the MGB components as compared to the conventional cases. Moreover, the initiation of fatigue failure in CBs is faster as compared to the MGBs for the same test condition, indicating longer bearing life in MGBs as compared to the CBs.

Friction Coefficient during Five-Phased Start-Stop Tests of PEEK-PTFE Hybrid Radial Ball Bearings Reaching 50 c° under 487N at 600rpm in Air

Start-stop rolling contact fatigue tests of PEEK-PTFE hybrid radial bearings were carried out, to investigate the influence of start-stop heat cycle on the friction coefficient of PEEK-PTFE hybrid radial bearings. It was found in all start-stop tests, the temperature of sample side increased as the friction coefficient increased. RCF cycles to reach 50 °C of the third start-stop phase clearly increased from the second start-stop tests, and then kept constant value.

Comparison of Acoustic Noise and Vibration in Ball-Bearing-Supported Motors and One-Axis Actively Positioned Single-Drive Bearingless Motor With Two Radial Permanent-Magnet Passive Magnetic Bearings

This study experimentally investigates the acoustic noise, vibration, and power consumption in a one-degree-of-freedom actively positioned single-drive bearingless motor, which has radial passive magnetic bearings (RPMBs) and compared to an identical stator part and rotor shaft with radial mechanical ball bearings. For the experiment, three test motors were set up: (a) a bearingless motor with two RPMB, (b) a motor with two ball bearings without an axial preload, and (c) a motor with two ball bearings with an axial preload. Motor (a) under test had one-axis active positioning and the radial movements were supported by RPMB made of cylindrical permanent magnets. Conversely, in motors (b) and (c), the radial and axial movements were supported by ball bearings, and there was no production of active axial force. The experimental results confirmed that the levels of acoustic noise, stator vibration, and input power consumption were significantly lower in motor (a) than those in motors (b) and (c). In the analysis section, dynamic models of the bearingless motor with RPMB and motor with ball bearings were designed and simulated using MATLAB <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\backslash$</tex-math></inline-formula> Simulink. The low radial stiffness in RPMB was found to contribute to acoustic noise and vibration reductions. Thus, this article presents an example of a one-degree-of-freedom actively positioned bearingless motor with RPMB that realizes reductions of acoustic noise, stator vibration, and input power consumption.

STUDY OF THE BEARING FRICTION INSIDE ON A MOBILE COUPLING JOINT

The mobile couplings are used in movement and torque transmission between two main shafts usually and have a wide application in transportation and machining systems. These mobile coupling must undertake the shafts misalignments that could appear, usually in the transversal plane and in the longitudinal plane. The friction which appears in coupling’s joints between the involved parts has an important influence on their dynamic behaviour, wear and lifetime. A solution to reduce the friction inside the mobile coupling is to place bearings in joints. The paper presents some general aspects on mobile tripod couplings and following this, using the inside relative movement in joints between parts and corresponding adequate bearing, the friction coefficient is studied. There are considered two cases for the studied radial ball bearings: a sealed one and a non-sealed one. The measurements are accomplished by using a tribometer for different radial loadings and rotational speeds of the inner ring of the bearings. In the final part of the paper, the results present the exploitation conditions of the bearings which assure small frictional loses. According to the obtained results, in order to gain small frictional loses, the mobile tripod coupling with external contacts are suitable to be used in the case of high loads, with small influences on the frictional behaviour of the rotational speeds.

Performance improvement of a radial ball bearing using a micro-groove on stationary outer race

For achieving improved lubrication in a radial ball bearing (BB1B 420206), a circumferential micro-groove inside the stationary outer race has been conceived based on finite element analysis to facilitate the availability of grease and to reduce the stresses at the contacts and it has been fabricated to conduct the experiments. To understand the effect of this micro-groove filled with grease on the film formation, frictional torque, and bearing dynamics, experiments were performed for measuring these variables at different operating parameters ( pH = 0.35–1.2 GPa; speed = 1.4–4.2 m/s). Capacitance based approach, load cell, and miniature accelerometer have been employed to measure the film thickness, frictional load and vibrations, respectively. The results achieved with bearings with micro-groove on outer races have been compared with bearings having the conventional races at the identical operating parameters. Reductions of 14%–41% in vibrations, up to 11.2% increase in film thickness (i.e. 11% reduction in the capacitance), and in the range of 15%–30% reduction in the frictional torque have been obtained as compared to conventional bearing cases.

Effect of grease grades on the tribological and vibrational behaviours of a radial ball bearing: Conventional vs. micro-grooved outer races

Comparative tribo-dynamic studies of radial ball bearings possessing micro-grooved and conventional outer races, employing three different grades of lithium soap-based greases (NLGI grade 000, 2 and 3), are presented in this paper. This research has been conducted to explore and understand the effectiveness of grease grades on the performance parameters in the presence of a circumferential micro-groove on the outer race as compared to conventional case. Indication of lubricating film thickness formation (in terms of capacitance), frictional torque, vibrations, and rise in temperature have been assessed for the conventional and micro-grooved outer race bearings at different operating parameters ( pH = 0.9 to 1.4 GPa; speed = 1.4 to 4.2 m/s). The micro-grooved bearings (MB) provided the indication of better lubricating film formation in terms of capacitance reduction in the range of 11–19% as compared to the conventional bearing (CB) cases. However, the reduction in frictional torque, vibration and rise in temperature magnitudes have been found in the range of 14–26%, 6–23%, and 10–24% respectively, as compared to the CB cases.

Influence on Tribological Behavior of PEEK Composite Film Layer on PEEK-PTFE Bearings with Artificial Defect in Dry Condition

In order to explore influence on tribological behavior of PEEK composite film layer in PEEK-PTFE composite radial alumina ball bearings, rolling contact fatigue tests were performed by using the PEEK bearing’s inner rings with the artificial defects in dry condition. When rotation speed and applied load were 600 rpm and 98 N, the number of cycles of the PEEK-PTFE bearings reached 1.0×107 fatigue cycles. The artificial defects with 0.02 mm depth on the raceway surface of the PEEK inner ring was covered with PEEK composite film accumulation.

An exploration of frictional and vibrational behaviors of textured deep groove ball bearing in the vicinity of requisite minimum load

In case of lightly loaded radial ball bearings, failure mechanisms other than fatigue such as smearing of raceways due to increased frictional torque and vibrations often prevail. Hence, attempts have been made herein for reducing the frictional torque and minimizing the vibrations of a radial deep groove ball bearing employing surface textures at the inner race. Nanosecond pulsed laser was used to create texture (involving micro-dimples having different dimple area density) on the inner race of test bearings. Using an in-house developed test rig, frictional torque and vibrational parameters were measured at different speeds and light loads (i.e. in vicinity of 0.01C, where C is dynamic load capacity of radial ball bearing). Significant reduction in frictional torque and overall vibrations were found in the presence of micro-dimples on inner race at light loads irrespective of operating speeds. Even without satisfying the minimum load needed criteria for the satisfactory operation, substantial reduction in smearing marks was found on the races of textured ball bearings in comparison to conventional cases.

Friction Coefficient and Wear of PEEK-PTFE Hybrid Radial Ball Bearings under Dry Conditions

In this paper, in order to investigate friction coefficient and wear of PEEK-PTFE hybrid radial bearings, rolling contact fatigue tests were performed under radial loads ranging from 93N to 387N at 600rpm in dry conditions. It was found that friction coefficients were 0.013 to 0.032 throughout the tests. Operation temperature followed the change in the friction coefficient, and PEEK-PTFE radial ball bearings exhibited stable performance even though the temperature locally approached 100 °C due to frictional heat. Moreover, wear loss of bearing components excluding alumina balls increased exponentially with increase of load.

Relation between groove and friction in PEEK-PTFE radial ball bearings under dry conditions at 1200rpm

Relation between groove and friction in PEEK-PTFE radial ball bearings under dry conditions at 1200rpm

Axial Load Capacity and Stresses in Combined Loaded Radial Ball Bearings (Dept.M)

An interactive and easy to use simulation tool has been developed to simulate and depict normal loads, contact angle, normal deformations, and stresses at any angular position of the rolling element for combined loaded radial ball bearings. The importance of this work comes from the ability to determine the contact angle and induced normal toad at any angular position. The main objective of this work is to lower stresses within the bearings, consequently, bearing fatigue life which is governed by stress level is significantly affected, showing that the lower the stress level the higher the service lifetime. This work is intended to serve both design and maintenance engineers.

Grease film thickness measurement in rolling bearing contacts

Rolling bearings are the second most used machine components. They work in what it is called elastohydrodynamic lubrication regime. The geometry of rolling element bearings makes the direct measurement of the lubricant film thickness a challenging task. Optical interferometry is widely used in laboratory conditions for studying elastohydrodynamic lubrication however it cannot be used directly in rolling element bearings thus the only suitable methods are electrical techniques. Of these, film thickness measurement based on electrical capacitance of the contacts has been used in the past by a number of authors. One of the limitations of the capacitance method, when used in rolling bearings, is that it cannot distinguish between the contacts of every rolling element and raceway on one hand and on the other between the inner and outer ring contacts. In the present study the authors used an original test rig which can measure the film thickness for only one ball and separately for the inner and outer rings of a radial ball bearing. This paper thus shows for the first-time results of the lubricant film thickness, at the inner and outer raceways, in grease lubricated rolling bearings.

The effect of outer ring elastodynamics on vibration and power loss of radial ball bearings

Ball bearings are an integral part of many machines and mechanisms and often determine their performance limits. Vibration, friction and power loss are some of the key measures of bearing performance. Therefore, there have been many predictive analyses of bearing performance with emphasis on various aspects. The current study presents a mathematical model, incorporating bearing dynamics, mechanics of rolling element-to-races contacts as well as the elastodynamics of the bearing outer ring as a focus of the study. It is shown that the bearing power loss in cage cycles increases by as much as 4% when the flexibility of the outer ring is taken into account as a thick elastic ring, based on Timoshenko beam theory as opposed to the usual assumption of a rigid ring in other studies. Geometric optimisation has shown that the lifetime power consumption can be reduced by 1.25%, which is a significant source of energy saving when considering the abundance of machines using rolling element bearings. The elastodynamics of bearing rings significantly affects the radial bearing clearance through increased roller loads and generated contact pressures. The flexible ring dynamics is shown to generate surface waviness through global elastic wave propagation, not hitherto taken into account in contact dynamics of rollers-to-raceways which are generally considered to be subjected to only localised Hertzian deflection. The elastodynamic behaviour reduces the elastohydrodynamic film thickness, affecting contact friction, wear, fatigue, vibration, noise and inefficiency.

Researches and Finite Element Simulations of Radial Loading Deformations Applied to Steel Ball Bearings

The appearance of quick wear of rolling paths and rolling elements (balls) through contact fatigue phenomena and through surface defects lead to a decrease in the life of ball bearings in service. One of the causes is the interruption of the lubricating film between surfaces with relative motion under load conditions and high speeds, which leads to plastic micro-deformations and micro-welding between contact surfaces. Diagnosing defects by visual observation involves disassemble of the bearing and is an ineffective method of investigation in serial production. In this context, the necessity of: (i) comparative study of the stresses to which two types (100Cr6 steel and 100CrMnSi6-4 steel type) of radial ball bearings are subjected, (ii) the influence of contact between the ball and the inner ring during rotation, and (iii) the analysis with Finite Element Method (FEM) of the deformations occurring at the application of radial bearing forces. FEM is a current approach to real phenomena in mechanical assemblies, which allows a validation of study assumptions; the results of FEM can lead to the detection of tribological causes of increased bearing wear at inner ring to bearing balls contact. In this paper, FE simulation of radial loading deformations was performed in SolidWorks software using the Simulation module and the stresses and deformations in the bearing rings for the two materials were obtained. It has been found that the stresses that appear during simulations are similar for both materials and do not exceed the limits allowed for heavy duty steel bearings.

Experimental and theoretical investigations of heat generation in radial ball bearing

The purpose of a radial ball bearing (RBB) is to support radial loads and to reduce the rotational friction. However, during its operating conditions, an unanticipated and vicious heating of balls in RBB takes place which results in the degradation of its performance as well as accuracy. For this reason, it is important to calculate the heat generation in the bearings because if generated heat is not dissipated from the bearing surface, it causes a temperature rise in the inner race and gives rise to premature failure. In the present work, experimentally, heat generation is calculated by varying the bearing failure parameters such as external load, load position, and rotational speed. Furthermore, a theoretical model is proposed for estimation of heat generation in the RBB. Later, a correlation between the experimental and theoretical model is carried out. Ultimately, the proposed model demonstrates better in estimating heat generation up to 0.45 m of load position without cooling condition. On the other hand, the predicted heat generation above 1.8 N of the external load has a minimal deviation with experimental values at with cooling condition. A better agreement is observed between experimental results and the theoretical model.

TESTING A PROTOTYPE FRICTION DRIVE TRANSMISSION

The article presents research on the mechanical properties of a drive system using an innovative mechanism converting rotary motion to progressive motion. The operating principle of the mechanism uses the friction-based transmission of drive from the motor to the drive shaft by means of two oppositely arranged unidirectional clutches. A side effect of such a solution utilized in the mechanism is the possibility of shifting the couplings while transmitting torque. The clutches were combined with a mechanism converting rotational motion to linear motion by utilizing friction between radial ball bearings and the shaft. This has resulted in an innovative mechanism for converting rotary motion to progressive motion, with the drive source being bound with a “friction screw” (a “slide” screw). A characteristic feature of this solution is the fact that there is no need for the nut to rotate in order to achieve progressive movement. Known solutions are based on a rotating nut and a fixed shaft system. The mechanism uses a fixed pitch nut, but it is possible to use a regulated pitch nut as a possible modification of the mechanism at a later stage of the system development. The main advantage of the mechanism tested is the possibility of uncoupling, which occurs when the maximum force transmitted by the nut is exceeded. This force is related to the friction force resulting from the pressure exerted by angularly shifted ball bearings on the drive shaft. The bearings are a substitute for the screw line in the classical ball screw mechanism. The research results presented in the article give an overview of the mechanical properties of the solution developed. The article also presents the influence of rotational speed and load on the mechanical parameters of the drive. The application of the described invention as the basis of the linear motion mechanism driving the tool of a surgical robot is a safe solution with unique and desirable characteristics.

Study of the Radial Vibrations of a Rotor of a Leak-Proof Electric Pump Engine

This paper considers the nonlinear transverse vibrations of the rotor of the low-power electric motor fastened with radial ball bearings. Amplitude-frequency characteristics are obtained that determine the resonance conditions. It is shown that it is the nonlinear stiffness characteristic of the rotor ball bearings that determines the rotor compound vibrations appearing due to emergence of subharmonic vibrations.

Load Capacity of a Radial Ball Bearing with Increased Radial Clearance

A method is proposed for calculating the load capacity of a radial ball bearing with increased radial clearance.

Experimental and theoretical study of friction torque from radial ball bearings

In this paper it is presented a numerical simulation and an experimental study of total friction torque from radial ball bearings. For this purpose it is conceived a virtual CAD model of the experimental test bench for bearing friction torque measurement. The virtual model it is used for numerical simulation in Adams software, that allows dynamic study of multi-body systems and in particularly with facility Adams Machinery of dynamic behavior of machine parts. It is manufactured an experimental prototype of the test bench for radial ball bearings friction torque measurement. In order to measure the friction torque of the tested bearings it is used an equal resistance elastic beam element, with strain gauge transducer to measure bending deformations. The actuation electric motor of the bench has the shaft mounted on two bearings and the motor housing is fixed to the free side of the elastic beam, which is bended by a force proportional with the total friction torque. The beam elastic element with strain gauge transducer is calibrated in order to measure the force occurred. Experimental determination of the friction torque is made for several progressive radial loads. It is established the correlation from the friction torque and bearing radial load. The bench allows testing of several types and dimensions of radial bearings, in order to establish the bearing durability and of total friction torque.