Papers by Keyword: Mixed Lubrication

Abstract: This paper presents the effect of surface roughness in line contact under isothermal soft mixed lubrication with non-Newtonian based on Power law viscosity model. The time independent modified Reynolds equation, elasticity equation and the load capacity of asperities equation were numerically solved using finite different method, Newton-Raphson method and multigrid multilevel methods to obtain the film pressure profiles, film thickness profiles and contact pressure in the contact regions. The simulation results showed that the the amplitude of surface roughness has a significant effects on the film pressure, film thickness and surface contact pressure in the contact region. The minimum gap between surface, friction coefficient and asperity load increase when the amplitude of surface roughness increases. For increasing surface velocity, the minimum gap between surface increases but asperity load decreases.

Abstract: Within past 20 years, high surface qualities of cold strip were demanded by automotive industry and electrical engineering. Main purposes of cold rolling processed are to provide high quality surface and generate appropriate roughness for different customs. Emulsion is a common coolant used in cold rolling processes, Properties of base oil in emulsion, concentration, roughness of work roll, rolling speed and reduction are important parameters, which dominate the surface qualities of cold rolled strip. Hence, a powerful cold rolling model which can describe complicate tribological behavior in roll bite is required. In this article, a cold rolling model which integrates roll deformation and mixed lubrication in inlet zone and biting area was developed. The thickness of oil film, fraction of contact area and coefficient of friction in roll bite are calculated.

Abstract: With consideration of asperity contact, the minimum oil film thickness and friction power loss are calculated by simultaneous solution of the dynamics, blow-by and lubrication of piston ring pack. Take the piston ring pack in the first cylinder from the free end of a six-cylinder diesel engine for example, results show that the asperity contact takes place at all of the compression rings and oil ring; the minimum oil film thickness is 1.04μm at the top ring; the total friction loss power is 0.94kW, the top ring accounts for 37.2%, the second ring accounts for 33.0%, the oil ring accounts for 29.8%.

Abstract: This paper investigates the effect of the plastic deformation of surface asperities on the interface friction in metal forming involving multi-scale deformation with random surface topography. The equivalent interfacial layer (EIL) introduced by the authors previously was used to integrate the Reynolds equation with the plastic deformation of the randomly distributed surface asperities. The contributions of solid-lubricant interaction, lubricant viscosity and microscopic deformation were therefore included efficiently in a conventional macroscopic finite element analysis. The merit of the method was demonstrated by an investigation into the metal strip rolling, whose friction, lubrication and pressure distribution are otherwise hard to be characterized accurately.

Abstract: This paper presents the performance characteristics of two surfaces in line contact under isothermal mixed lubrication with non-Newtonian liquid–solid lubricant base on Power law viscosity model. The time dependent Reynolds equation, elastic equation and viscosity equation were formulated for compressible fluid. Newton-Raphson method and multigrid technique were implemented to obtain film thickness profiles, friction coefficient and load carrying in the contact region at various roughness amplitudes, applied loads, speeds and the concentration of solid lubricant. The simulation results showed that roughness amplitude has a significant effect on the film pressure, film thickness and surface contact pressure in the contact region. The film thickness decrease but friction coefficient and asperities load rapidly increases when surface roughness amplitude increases or surface speed decreases. When the concentration of solid lubricant increased, friction coefficient and asperities load decrease but traction and film thickness increase.

Abstract: The average flow model proposed by Patir and Cheng offers a great convenience for the mixed-lubrication analysis of rough surfaces. The pressure flow factor introduced by Patir and Cheng helps to analyze the influence of roughness on the average pressure and average flow of a lubricant between surfaces. This paper reports how to reasonably choose initial pressure in computing the pressure flow factor. The numerical results show that the pressure distribution and further pressure flow factor value are sensitive to an initial pressure in solving the pressure flow factor, and the initial pressure of a constant value is not suitable for the pressure flow factor calculation for a measured surface with many sample points. Meanwhile, the pressure flow code is demonstrated by the comparison of the pressure obtained numerically with the analytical solution of pressure.

Abstract: Tribology plays an important role in sheet metal forming processes relating to near net shape production processes and achievable surface qualities. Nearly every process is realized by using characteristic lubricants affecting the tribological system to achieve the desired results. Deterministic structures on sheet surfaces can result in less friction and higher drawing ratios. This is caused by hydrostatic pressures build up in closed lubricant areas and hydrodynamic pressures due to the lubricant motion especially in thin fluid films [1, 2, 3]. Friction mechanisms in the mixed lubrication regime are not fully understood till today. The numerical simulation of flows in lubricant pockets and their influence on surface evolution are promising ways to gain more knowledge of the lubricant behavior in tribological systems. Therefore, this paper shows results of combined numerical and experimental approaches. The described simulations of closed lubricant pockets on surfaces identify influencing parameters. Strip drawing experiments are done to verify the simulations. The influence and the importance of local pressures due to viscous effects in the lubricant are considered as well as the necessity to use fluid-structure-interactions to simulate the behavior of lubricants in the tribological system.

Abstract: The average Reynolds equation and average clearance equation of circular translational polishing (CTP) under the quasi-stable mixed lubrication state are set up in polar coordinates. The distributions of fluid pressure and contact pressure during polishing are numerically analyzed by solving simultaneously these equations along with the contact pressure equation. The effects of various process parameters on hydrodynamic performance of CTP are analyzed. By comparing the distributions of periodic average pressure along radial direction under fully and partially lubricated states, we conclude that carefully controlled CTP under mixed lubrication is beneficial to improving the surface quality and planarity of the wafer.