Development of Analytical Equations for Design and Optimization of Axially Polarized Radial Passive Magnetic Bearing

In the present research work, analytical equations have been developed for design and optimization of radial axial polarized passive magnetic bearing (PMB) with single layer for facilitating easy and quick solution, obviating the need of costly software. Seven design variables: eccentricity, rotor width, stator width, rotor length, stator length, clearance, and mean radius were identified as the main factors affecting the design and were thus considered in the development of analytical equations. The results obtained from the developed analytical equations have been validated with the published results. The optimization of the bearing design, with minimization of magnet volume as the objective function, was carried out to demonstrate the accuracy and usefulness of the developed equations

On the integrated degradation coefficient for adhesive wear: A thermodynamic approach

Normal adhesive wear process in tribological components is characterized by a non-linear behavior during the transient running-in stage followed by a constant rate of steady-state wear. Even though the running-in stage of wear has an imperative significance in defining the component's long-term performance, its characteristics have been largely overlooked in the literature. In general, many of the available predictive models do not consider the contact temperature and the variation in the friction coefficient with time. The present work is an endeavor to propose a complete integrated wear model using the principles of thermodynamics. In this regards, an integrated degradation coefficient is proposed which correlates the time-dependent wear rates (at both running-in and steady-state stage), friction coefficient, and the contact temperature. The efficacy of the proposed degradation coefficient compared to established wear coefficient is demonstrated by considering test results using a vertical pin-on-disk apparatus. Results reveal that the degradation coefficient provides a realistic measure of wear during running period

Evaluating Grease Degradation through Contact Angle Approach

Grease is highly susceptible to degradation due to regular usage and the severity of the operating conditions. Degradation can negatively impact the performance of grease-lubricated machinery, demanding frequent maintenance to avoid premature failure of machine elements. Quantification of grease degradation has proven to be a formidable task, for which no accepted standards are currently available. In this paper, we extend the results of a novel approach developed recently for the evaluation of the water-resistant property in grease to quantify degradation. The methodology is based on measurements of the contact angle of a water droplet on the surface of a sample of grease. We report the results of extensive tests performed on different grades of lithium complex greases to evaluate the variation of contact angle values with the composition of grease. The measurements were compared with penetrometer readings to quantify a relationship between the grease consistency and contact angle. Detailed study results are also presented on three types of greases sheared in a grease worker for a different number of strokes: contact angle and the yield stress values were measured and compared. Finally, the tribological characteristics were determined for two greases that exhibited a low or high change in their contact angles