Friction Coefficient Of Bearings Research Articles

Study of Frequency Converter Motor Selection Method of Shafting Test Bed

The rotary inertia, speed, acceleration of shafting and the friction coefficient of rubber bearings have an important influence on the calculation of shafting resistance moment, related to the selection rationality of driving motor. In order to guarantee load startup and normal operation of the shafting, by analysing shafting rotary inertia, bearing support force and friction coefficient, calculated resistance moment of the shafting, established the mathematical model of shafting equivalent resistance moment and motor rotational speed, compared the output moment of motor with shafting equivalent resistance moment, so that determined the correct motor model.

Finite Element Simulation of Process Control for Bolt Tightening in Joints With Nonparallel Contact

In this paper, 3D finite element analysis (FEA) is used to simulate and evaluate different process control methods that are commonly used for automating the assembly of bolted joints in a mass production environment. The finite element (FE) model takes into account the thread helix angle of a fastener along with parallel and nonparallel contact surfaces under the bolt head. Simulation includes the torque-only and the torque-turn process control methods for achieving a desired level of the bolt preload at initial assembly of the joint. The torque-only process control option is simulated by applying the target torque at which the tightening process is automatically stopped. On the other hand, a torque-turn or torque-angle method is simulated by first applying a low level (threshold) torque, to the bolt head, followed by turning the bolt head by a specified angle of turn in order to achieve the desired bolt tension. The effect of variables such as thread and underhead bearing friction coefficients and bolt hole clearance is investigated. The FEA simulation provided in this study would be helpful in developing a reliable tightening strategy for joints with nonparallel bearing surfaces.

Force Prediction in Cutting Operations with Self-propelled Rotary Tools Considering Bearing Friction

This paper presents a model to predict cutting force and motion of the rotating insert in cutting processes with self-propelled rotary tools (SPRT). Metal cutting utilizing rotary tools is effective to suppress tool wear and thus it is considered to be suitable to attain high performance machining of difficult-to-cut materials. It is well known that a circular insert attached to a rotational axis is self-propelled due to inclined chip flow on rake face plane by setting certain oblique angle. A resultant insert rotation speed can be easily predicted considering a frictionless rotary axis. However, friction at the rotary axis of SPRTs may not be negligible in practice especially when slide bearings are employed. In order to investigate the influence of the friction at the rotation axis on the rotary cutting process, a new cutting model is proposed. As the friction at the rotation axis causes a decrease in a speed of round insert rotation, an equivalent oblique cutting process is taken into account in the proposed model utilizing conventional theoretical model. In the equivalent process, the tangential component of the resultant cutting force corresponds to the friction force at the rotary axis. The friction force is determined by cutting force component normal to force-bearing mechanism and the bearing's friction coefficient. Considering the equilibrium condition in cutting and friction forces, the resultant cutting force and the insert rotation speed are iteratively computed in the proposed model. Edge force model is also associated with the oblique cutting model, which is not negligible especially in machining difficult-to-cut materials. The developed model is extended to simulate milling processes with SPRTs. The proposed model is experimentally verified, and influence of the bearing friction of SPRT on the process is clarified.

Global Analysis of Polymer Pads in a Bearing Element for a Large-Span Movable Sluice

The contact surface of a hinge suffers huge pressure in particularly bad lubrication conditions. Reinforced polymer bearing pads offers low friction under dry sliding conditions. Load transfer between contact surfaces was studied, showing that the pressure and positions are related to the power output of the loco. The friction coefficient of concave bearings with polymer pads was low, and would not totally failed in a high contact stress. Performances of polymer pads on loads were simulated, and provided a global analysis for the design of the pads.

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.

Effect of PTFE Retainer on Friction Coefficient in Polymer Thrust Bearings under Dry Contact

Polyetheretherketone (PEEK) is a tough semi-crystalline thermoplastic polymer with excellent mechanical properties. While abilities of polyphenylenesulfide (PPS) are similar to PEEK, former material cost was lower than later. Polytetrafluoroethylene (PTFE) is well known because of its low friction coefficient and self lubrication ability. The objective of this study is to observe the friction coefficient of hybrid bearings, PTFE retainer sandwiched with PPS-races or PEEK-races. Rolling contact fatigue tests were performed and in situ friction forces wear measured. It is concluded that the PTFE retainer reduced friction coefficient.

Retraction Note: Effects of boundary slippage on thin-film lubrication between two nonparallel plane plates

Hydrodynamic lubrications between two plane plates with an intersection angle θ have been investigated using the boundary slippage theory, and relations are obtained between dimensionless pressures and coordinate x, between bearing capacity, friction force, friction coefficient and dimensionless slipping size factor. The results show that bearing capacity of two plane plates without boundary slippage significantly increases with increasing intersection angle θ when 0 1°. The results also show that negative pressure occurs in fluid entrance region and bearing capacity decreases, and friction force and friction coefficient increase with the increase of dimensionless slipping size factor.

RETRACTED ARTICLE: Effects of boundary slippage on thin-film lubrication between two nonparallel plane plates

Hydrodynamic lubrications between two plane plates with an intersection angle θ have been investigated using the boundary slippage theory, and relations are obtained between dimensionless pressures and coordinate x, between bearing capacity, friction force, friction coefficient and dimensionless slipping size factor. The results show that bearing capacity of two plane plates without boundary slippage significantly increases with increasing intersection angle θ when 0 1°. The results also show that negative pressure occurs in fluid entrance region and bearing capacity decreases, and friction force and friction coefficient increase with the increase of dimensionless slipping size factor.

Sliding bearings used as seismic dampers with composite self-lubricating materials

The scientific basis for the design of self-lubricating self-aligning sliding bearings with reciprocal motion is presented for the first time. The bearings are used as seismic dampers for bridges, industrial and civil buildings, and oil and gas offshore structures; they are superior to known bearings in carrying and damping capacities. An original experimental-calculation method for determining the life of a frictional pendulum sliding bearing used as a seismic damper is elaborated. It implies the use of the dependences for the wear rate presented in generalized variables. A method for estimating the friction coefficient of frictional pendulum bearings is also developed. The outlook for domestic development of an antifriction self-lubricating coating with preset tribological characteristics is analyzed and the present state of the art is discussed. The studies are based on known developments in the field of tribological materials with account for modern advances in nanotribology. The most promising heat-resistant polymers and fillers, as well as combined mixed antifriction fabrics on their basis, are considered.

Analysis of squeaking on ceramic hip endoprosthesis using the complex eigenvalue method

Abstract A finite element model of the ceramic hip endoprosthesis system is established with ABAQUS 6.7. The generation mechanism of squeaking is studied using the complex eigenvalue method which allows for a stability analysis of the system under friction coupling. Numerical results reveal that a ceramic hip endoprosthesis system has a strong propensity of unstable vibration when the friction coefficient of ceramic bearings reaches to a critical value, which is considered to be the most likely mechanism for squeaking. In the present study μ = 0.15 is proved to be a critical value, below which there is no instability of the system. Furthermore, the resonance of the femoral components at a frequency of 3177 Hz is found to be the source of the unstable vibration in squeaking. On the basis of the etiology of squeaking, two methods for suppressing squeaking are proposed. One method is adding ultra-high molecular weight polyethylene (UHMWPE) damping material in acetabular components, the other is imposing reasonable fixed stiffness on acetabular components. Simulation results show that both methods are effective for increasing the critical friction coefficient from 0.15 to 0.22 and 0.32, respectively, which improve the stability of the ceramic hip endoprosthesis system to a great extent.

Criterion for Preventing Self-Loosening of Preloaded Cap Screws Under Transverse Cyclic Excitation

In this paper, a novel criterion is developed for preventing the self-loosening of preloaded threaded cap screws under cyclic transverse loading. For a known cyclic excitation, the system parameters are used in the formulation of a closed form solution for the minimum fastener preload required for preventing self-loosening. The effect of several key variables is investigated; this includes bearing and thread friction coefficients, cap screw grip length, thread pitch, material, and cyclic amplitude of the transverse excitation. An experimental setup and test procedure are established. Comparison between the experimental and analytical clamp load variation results shows that the proposed criterion can accurately predict the requirements for preventing self-loosening.

Effects of Oscillation Frequency on the Tribological Properties of Self-Lubrication Spherical Plain Bearings with PTFE Woven Liner

The working principle and performance characteristics of a self-made oscillation tribo-tester were introduced. Under different oscillation frequency and pressure conditions, the friction coefficient and linear wear of spherical plain bearings with polytetrafluoroethylene (PTFE) woven liner were investigated. By using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the wear mechanism of the spherical plain bearing was analyzed. The results indicate that with the oscillation frequency increases, the friction coefficient of spherical plain bearings decreased while the wear loss increased. In the high frequency of 4.8Hz, the reduction ranges of the friction coefficient is not obvious with the contact pressure increased, but the effect of contact pressure on the wear of the spherical plain bearing is great. During the experiment, adhesive wear, abrasive wear and spalling wear took place on the surfaces of woven liners.

Effect of Thread and Bearing Friction Coefficients on the Self-Loosening of Preloaded Countersunk-Head Bolts Under Periodic Transverse Excitation

A nonlinear mathematical model is developed for studying the self-loosening behavior of preloaded countersunk threaded fasteners that are subjected to cyclic transverse loads. Torque components acting on the bolt are divided into pitch and resistance torque components; the net torque determines whether or not the bolt will rotate loose under the external excitation. The accumulation of the differential amount of loosening rotation increments is converted into the gradual loss of the bolt tension/clamp load. Although the loosening model incorporates several system variables, this study is focused on investigating the effect of thread and bearing friction coefficients on the loosening of fasteners with coarse and fine threads. Model prediction of the self-loosening behavior is experimentally validated.

Seismic Fragility of Multispan Simply Supported Steel Highway Bridges in New York State. I: Bridge Modeling, Parametric Analysis, and Retrofit Design

This paper studies the dynamic seismic behavior of a typical highway bridge in New York State. The topological layout and structural details of this multispan simply supported steel-girder bridge are identified as the most typical of the New York State Department of Transportation bridge inventory database. Three-dimensional finite-element models of the bridge are established considering the nonlinear behavior of critical bridge components. An in-depth parametric study is carried out to evaluate the sensitivity of the bridge’s seismic response to variations in its structural parameters. The parametric analysis determined that uncertainties associated with the steel reinforcement’s yield strength, the superstructure’s weight, the expansion joints’ gap size, the friction coefficient of expansion bearings, and the concrete compressive strength should be considered during the fragility analysis of the bridge system. The Latin hypercube sampling (LHS) approach is used to obtain representative samples for the f...

Effect of Coating Thickness on the Friction Coefficients and Torque-Tension Relationship in Threaded Fasteners

This paper experimentally investigates the effect of coating thickness on the thread, bearing friction coefficients, and torque-tension relationship in threaded fasteners, as well as an investigation into the effect of coating thickness on surface roughness properties. The torque-tension relationship is highly sensitive to frictional changes. Two different coating thicknesses are investigated using two bolt thread pitch; test data are collected for a preselected level of bolt tension. The experimental setup collects real-time data on the tightening torque, bolt tension, and the corresponding reaction torque. Test data are used for calculating the thread and bearing friction coefficients, as well as the overall torque-tension relationship for two different coating thicknesses. The study would provide an insight into the variation in the torque-tension relationship, which is a key factor that significantly affect the reliability and safety of bolted assemblies in many mechanical and structural applications.

Torque-Angle Formulation of Threaded Fastener Tightening

In this paper, the evolution equations of the bearing and thread friction coefficients are proposed based on mechanical behavior of the bolted joint assembly. The study shows excellent correlation between the proposed model and the experimental results for the breakaway torque values in both the tightening and loosening directions. Evaluation of the torque-angle control of the tightening process is made, and a modified torque-angle control approach is proposed. The effect of friction coefficients on the error in the clamping force prediction is analyzed.

Seismic Fragility of Continuous Steel Highway Bridges in New York State

This paper presents results of an analytical seismic fragility analysis of a typical steel highway bridge in New York State. The structural type and topological layout of this multispan I-girder bridge have been identified to be most typical of continuous bridges in New York State. The structural details of the bridge are designed as per New York State bridge design guidelines. Uncertainties associated with the estimation of material strength, bridge mass, friction coefficient of expansion bearings, and expansion-joint gap size are considered. To account for the uncertainties related to the bridge structural properties and earthquake characteristics, 10 statistical bridge samples are established using the Latin Hypercube sampling and restricted pairing approach, and 100 ground motions are simulated numerically. The uncertainties of capacity and demand are estimated simultaneously by using ratios of demands to capacities at different limit states to construct seismic fragility curves as a function of peak ground acceleration and fragility surfaces as a function of moment magnitude and epicentral distance for individual components using nonlinear and multivariate regressions. It has been observed that nonlinear and multivariate regressions show better fit to bridge response data than linear regression conventionally used. To account for seismic risk from multiple failure modes, second-order reliability yields narrower bounds than the commonly used first-order reliability method. The fragility curves and surfaces obtained from this analysis demonstrate that bridges in New York State have reasonably low likelihood of collapse during expected earthquakes.

Effect of Thread and Bearing Friction Coefficients on the Vibration-Induced Loosening of Threaded Fasteners

This study provides a theoretical and experimental investigation of the effect of the thread and bearing friction coefficients on the self-loosening of threaded fasteners that are subjected to cyclic transverse loads. The friction coefficients are varied by using different types of coating and lubrication. A phosphate and oil coating and an olefin and molydisulfide solid film lubricant are used on the bolts tested. A mathematical model is developed to evaluate the self-loosening behavior in threaded fasteners when subjected to cyclic transverse loads. An experimental procedure and test setup are proposed in order to collect real-time data on the loosening rate (rate of clamp load loss per cycle) as well as the rotational angle of the bolt head during its gradual loosening. The experimental values of the friction coefficients are used in the mathematical model to monitor their effect on the theoretical results for the loosening rate. Experimentally, the friction coefficients are modified by changing the coating or the lubrication applied to the fasteners. The theoretical and experimental results are presented and discussed.

Effect of Lubrication on Friction and Torque-Tension Relationship in Threaded Fasteners

In this research, three types of lubricants are investigated for their effects on the friction and torque-tension relationships in threaded fastener applications. Investigated lubricants included oils, greases, and solid film lubricants that were applied to the threads of the fastener and the nut, and the turning bolt underhead surface as well as the joint surface in contact with the bolt head. The oils tested were mineral oils with different viscosities, i.e. 21cst, 115cst, 1000cst respectively at 40°C. Three types of grease were tested; namely, regular grade, pure nickel special, and heavy metal free grease. For the solid lubricants, an olefinic type, an olefinic base with a polytetrafluoroethylene additive, and an olefinic base with an inorganic additive (Molybdenum disulfide), were applied. Class 8.8 M12 fasteners with both fine and coarse threads were used. The experiments were carried out using a Laboratory Fastener Testing System which measures the input torque, the fastener tension, the thread friction torque, and the angular rotation of the bolt head. The system computes the thread and bearing friction coefficients from the measured data. In each test, the fastener was repeatedly tightened and loosened five times. The tests were also conducted under different tightening speeds, varying from 1 rpm to 100 rpm. The nut factor, the coefficients of thread and the underhead friction were obtained from the experiments. The effects of the number of tightening and loosening cycles, the tightening speed, and the type of lubricant on friction and nut factor were investigated. It was found that lubrication had a significant effect on the friction and the torque-tension relationship in threaded fasteners. Presented at the STLE/ASME International Joint Tribology Conference in San Antonio, Texas, October 23-25, 2006 Review led by Thierry Blanchet

Response time and performance of a high-torque magneto-rheological fluid limited slipdifferential clutch

In this study, the response time and system characterization analyses of a high-torquemagneto-rheological (MR) fluid limited slip differential (LSD) clutch are presented. Theresponse time of the clutch is examined based on the objective of keeping the relativevelocity difference of the shafts of the clutch less than a predetermined threshold value. Theexperimental setup allows the application of an external disturbance to the system, so thatthe relative velocity difference exceeds the threshold value. A velocity-based, closed-loopcontrol system is designed and tested. Additionally, system identification experiments areperformed to determine system parameters such as bearing friction coefficients, dryand viscous torque coefficients. These parameters are utilized in the theoreticalresponse time analyses of the MR fluid LSD clutch. It is demonstrated that theoverall response time of the system varies between 20 and 65 ms as a function ofoperating velocity and electromagnet current, including the response times of thecontroller, solenoid inductance and MR fluid and inertia effects. The responsetime reduces by increasing solenoid current and increasing the operating velocity.