Robust Optimization Method of Cylindrical Roller Bearing by Maximizing Dynamic Capacity Using Evolutionary Algorithms

Optimization of cylindrical roller bearings(CRBs)has been performed using a robust design.It ensures that the changes in the objective function,even in the case of variations in design variables during manufacturing,have a minimum possible value and do not exceed the upper limit of a desired range of percentage variation.Also,it checks the feasibility of design outcome in presence of manufacturing tolerances in design variables.For any rolling element bearing,a long life indicates a satisfactory performance.In the present study,the dynamic load carrying capacity C,which relates to fatigue life,has been optimized using the robust design.In roller bearings,boundary dimensions(i.e.,bearing outer diameter,bore diameter and width)are standard.Hence,the performance is mainly affected by the internal dimensions and not the bearing boundary dimensions mentioned formerly.In spite of this,besides internal dimensions and their tolerances,the tolerances in boundary dimensions have also been taken into consideration for the robust optimization.The problem has been solved with the elitist non-dominating sorting genetic algorithm(NSGA-II).Finally,for the visualization and to ensure manufacturability of CRB using obtained values,radial dimensions drawing of one of the optimized CRB has been made.To check the robustness of obtained design after optimization,a sensitivity analysis has also been carried out to find out how much the variation in the objective function will be in case of variation in optimized value of design variables.Optimized bearings have been found to have improved life as compared with standard ones.

A combined experimental and analytical method to determine the EHL friction force distribution between rollers and outer raceway in a cylindrical roller bearing

Friction force is a crucial factor causing power loss and fatigue spalling of rolling element bearings.A combined experimental and analytical method is proposed to quantitatively determine the elastohydrodynamic lubrication(EHL)friction force distribution between rollers and outer raceway in a cylindrical roller bearing(CRB).An experimental system with the instrumented bearing and housing was developed for measuring radial load distribution and friction torque of bearings.A simplified model of friction force expressed by dimensionless speed,load,and material parameters was given.An inequality constrained optimization problem was established and solved by using an experimental data-driven learning algorithm for determining the uncertain parameters in the model.The effect of speed,load,and lubricant property on friction force and friction coefficient was discussed.

Mechanical performance analysis of hollow cylindrical roller bearing of cone bit by FEM

Bearings are key components of cone bit,thus its rapid failure is a major cause of leading to lower life of the bit.To improve the bearing performance and prolong working life,contact mechanics of hollow cylindrical roller bearing of cone bit was simulated.Effects of hollow size,drilling pressure,friction coefficient and fitting clearance on mechanics performance of the bearing were studied.The results show that the maximum equivalent stress of the hollow cylindrical roller bearing appears on the claw journal,and the maximum contact stress appears on the contact pair of the hollow roller.Besides,hollow sizes have a greater impact on the equivalent stress and contact stress of the cylindrical roller,while the influence on the stress of the cone and claw journal is relatively small.With the increasing of the drilling pressure and fitting clearance,equivalent stress and contact stress of bearing parts increase.The friction coefficient has little impact on mechanical performance of the bearing.As the 121/4SWPI517 type hollow cylindrical roller bearing of cone bit an example,the optimal hollow size is 55%,the drilling pressure is 140 kN and the fitting clearance is 0e0.02 mm.

Post-testing measurement of freely movable and diffusible hydrogen in context of WEC formation at cylindrical roller thrust bearings from 100Cr6

Sub-surface crack networks in areas of altered microstructure are a common cause for bearing failures.Due to its appearance under light microscopy,the damage pattern is referred to as White Etching Cracks(WEC).The root causes leading to the formation of WEC are still under debate.Nevertheless,it has already been shown that atomic hydrogen can have an accelerating effect on the formation and propagation of WEC.In addition to hydrogen pre-charging,hydrogen can be released and absorbed during rolling/sliding due to the decomposing of the lubricant and water.The current work focuses on the analysis of the hydrogen content of cylindrical roller thrust bearings after testing in a FE8 type test rig using two different lubricants.Within the framework of this work,two different hydrogen analysis methods were used and assessed regarding their applicability.The results show that the so-called Hydrogen Collecting Analysis(HCA)is more suitable to investigate the correlation between lubricant chemistry and hydrogen content in the test bearings than the Local Hydrogen Analysis(LHA).The measurements with the HCA show a continuously increasing freely movable and diffusible hydrogen content under tribological conditions,which leads to the formation of WEC.Comparative tests with an oil without hydrogen showed that the tendency of the system to fail as a result of WEC can be reduced by using a lubricant without hydride compounds.

Experimental study on impact of roller imbalance on cage stability

This study presents a method for measuring the imbalance in a small-sized cylindrical roller.The roller imbalance was calibrated on the built static-pressure-air flotation measurement machine.The impact of the roller imbalance on the dynamic characteristics of a cage were then studied on the aero-bearing test rig.The displacement spectrums with different roller imbalance of the obtained cage orbits under various bearing speed and radial load were used to evaluate the cage stability.The results show that the cage cannot form a stable operating state at a lower bearing speed with or without the unbalanced rollers.The cage with balanced rollers gradually develops stable motion with the increase of the bearing speed.The existence of a small roller imbalance causes the stability of the cage to deteriorate.With an increase in the bearing speed and radial load,the cage with the unbalanced rollers runs unsteadily accompanied by a high-frequency vibration when the roller imbalance is large enough.The vibration amplitude of the cage in the horizontal direction is greater than that in the vertical direction during an unstable operation,which is similar in the stable status.