ARISTOTLE UNIVERSITY OF THESSALONIKI
 FACULTY OF ENGINEERING
SCHOOL OF MECHANICAL ENGINEERING
Laboratory of Machine Elements and Machine Design

  

  







DISSERTATIONS

Author: Gatsios Stilianos
Title: Investigation of the physical adsorption of lubricants in mixed film lubrication conditions leading to scuffing
Abstract: Contemporary machine elements are often called to operate in mixed film lubrication regime. Under these conditions one possible mode of failure is scuffing. The adsorption of lubricant molecules on the friction surfaces can significantly reduce the risk of scuffing. The purpose of this work is to study, in a quantitative manner, the role of the lubricant’s physical adsorption on scuffing under conditions close to those found during the operation of gears and bearings. The two-disk test rig of the Laboratory of Machine Elements and Machine Design was used for the experimental investigation, after making some necessary improvements. Additionally, a custom device was created from scratch that allowed for the measurement of roughness onthe circumference of the disks. After conducting friction coefficient measurements in very low sliding speedand considering the effect of lubricant adsorption under these specific conditions, the heat of adsorption for FVA2 lubricant was determined. Next, scuffing experiments were conducted in appropriate conditions using carefully prepared disk specimens and FVA2 lubricant. For each experiment, in every stage, bulk temperature of each disk, friction force and other experimental data were collected and recorded. These data, together with disk surface roughness,were fed into anexisting numerical model capable of solving the contact of two rough surfaces operating in mixed film lubrication regime, resulting in the determination of the pressure distribution. Also, a methodology was developed that allowed for the calculation of the temperature distribution at the interface of the rough sliding bodies. Based on the results of pressure, temperature and activation energy it was made possible to calculate foreach surface in the contact the fractional coverage due to lubricant molecules adsorption. The calculations were conducted both for time-dependent and time-independent adsorption. The results from the theoretical investigation and theprocessing of all exper-imental datalead to the conclusion that the theory of adsorption can be used to describe a hydrodynamic pressure versus temperature curve that serves as a limit between scuffing-safe and scuffing-unsafe regions of operating conditions. It was found that the exact position of the limit-curve can be correlated with the surface roughness.

 

© 2020