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Herrlisheim, France

Evans R.D.,Timken Co. | Barr T.A.,Timken Co. | Houpert L.,TIMKEN Europe | Boyd S.V.,Timken Co.
Tribology Transactions | Year: 2013

Smearing damage was created on cylindrical roller bearings (CRBs) using a laboratory test protocol that required alternating the load zone direction according to a square wave function. The experimental goal was to compare the wear protection afforded by various surface treatments, including vibratory superfinishing (ES20), black oxide treatment, and special tungsten carbide-reinforced amorphous hydrocarbon roller body coatings (WC/a-C:H). The only bearing treatments that did not smear in these severe tests were the WC/a-C:H bearings. Black oxide and ES20 bearings experienced smearing with the same frequency as untreated bearings, albeit to different degrees of microscopic damage. The test rig was instrumented to measure cage slip, which provided insight about the roller-raceway slip dynamics during the tests via kinematic calculations. The CAGEDYN bearing dynamics model was used to simulate the experimental smearing test conditions, and it provided encouragement that accurate prediction of smearing risk may be possible in the future with further development. © 2013 Copyright Taylor and Francis Group, LLC. Source

Biboulet N.,University of Lyon | Houpert L.,TIMKEN Europe | Lubrecht A.A.,University of Lyon
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | Year: 2013

Based on previous studies concerning pressure perturbations due to indents in dry and elastohydrodynamic lubrication contacts, this article presents the indented contact stress distribution and risk integral calculations. Different stress criteria are discussed and an equation predicting the risk integral is proposed. © IMechE 2012. Source

Balan M.R.D.,Technical University Gheorghe Asachi | Stamate V.C.,Technical University Gheorghe Asachi | Houpert L.,TIMKEN Europe | Tufescu A.,Technical University Gheorghe Asachi | Dumitru Olaru N.,Technical University Gheorghe Asachi
Applied Mechanics and Materials | Year: 2014

Based on a theoretical model and an experimental methodology for defining the friction torque in a modified thrust ball bearing having only 3 balls and presented in [2], the authors experimentally investigated the influence of the ball diameter on friction torque when operating in mixed and full film lubrication conditions and maintaining the normal load, the race curvature and oil viscosity constant. The experiments were realized using ball diameters between 7.938 mm and 3 mm corresponding to maximum Hertzian pressure between 0.264 GPa and 1 GPa and a rotational speed between 60 rpm to 240 rpm. The experiments confirmed that the measured friction torque can be explained using hydrodynamic rolling force relationships respecting the transition from IsoViscous Rigid (IVR) to ElastoHydrodynamic Lubrication (EHL) regime presented in [2]. © (2014) Trans Tech Publications, Switzerland. Source

Balan M.R.D.,Technical University Gheorghe Asachi | Stamate V.C.,Technical University Gheorghe Asachi | Houpert L.,TIMKEN Europe | Olaru D.N.,Technical University Gheorghe Asachi
Tribology International | Year: 2014

Authors propose a theoretical model and an experimental methodology for defining the friction torque in a modified thrust ball bearing, operating in mixed and full film lubrication conditions. The friction torque was measured at low loads and large Λ parameter range using a spin-down method. A comprehensive analytical bearing torque model is described using elastic rolling resistance, curvature effects, inertia forces, disc-air resistance and ball-races hydrodynamic rolling forces, the latter explaining 98% of the final bearing torque. Several sets of hydrodynamic rolling force relationships respecting the transition from IVR to EHL lubrication regime were tested. Final numerical results are shown to be very close to the experimental ones in both full film and mixed lubrication conditions. © 2013 Elsevier Ltd. Source

Houpert L.,TIMKEN Europe
Tribology Transactions | Year: 2016

ABSTRACT: Hydrodynamic effects are responsible for a dimensionless load increase ΔW (relative to the load WHertz calculated in a dry contact) calculated primarily as a function of the dimensionless rolling element–race geometrical interference Δ/Rx, dimensionless speed, and radii ratio. The final load (W = WHertz + ΔW) is therefore never nil, even in cases when the geometrical interference is negative or nil, which corresponds to a Hertzian load nil. The final load is calculated by solving the following dimensionless algebraic relationship: (Formula presented.) , where δ is the elastic deformation (function of the load and radii ratio) calculated using a Hertzian relationship and H is the dimensionless film thickness, again a function of the load and radii ratio but also dimensionless speed and material parameters, the latter being included in piezoviscous-rigid (PVR) and piezoviscous-elastic (PVE, also called elastohydrodynamic or EHD) film thickness relationships. Advanced new curve-fitted relationships are also suggested in this article for calculating miscellaneous Hertzian parameters, such as contact dimensions, maximum pressure, and deformation. A detailed survey of several film thickness relationships was conducted covering different lubrication regimes: isoviscous-rigid (IVR, found at low dimensionless load and speed), PVR, and EHD (high dimensionless load and low dimensionless speed). It has been shown that the IVR regime prevails when Δ/Rx is negative or nil and the radii ratio is large (as found in roller bearings); hence, an IVR approach can be suggested for numerically calculating ΔW. A powerful set of curve-fitted relationships is then suggested for easily calculating ΔW. A simplified approach based on a previously published analytical solution of ΔW applicable to line contact (LC) but used here in a sliced point contact (PC) was also tested after having demonstrated that LC results (for H and δ) can be used in slices for retrieving (within 10%) PC results on H and δ. This result is surprising given that the exponents used for calculating H and δ differ substantially in LC versus PC. In addition, a new IVR thermal correction factor was developed for better calculating the film thickness. Although very small, ΔW can be responsible for a moderate bearing preload and torque increase, calculated using previously published IVR hydrodynamic rolling forces when the dimensionless speed is high and the bearing clearance is small or nil. Hydrodynamic effects, both normal and tangential to the contact, also contribute to the roller speed decreases in the unloaded zone of a bearing, so there is no need to consider large drag force to explain this drop. Previously published roller drag force relationships may therefore overestimate these forces when calibrated versus tests by not considering the rolling element–race hydrodynamic effect described herein. © 2016 Society of Tribologists and Lubrication Engineers. Source

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