Effect of surface temperature on tribological behavior of PTFE composites

Abstract

Tribological behavior of PTFE is highly affected by fillers used to improve its mechanical characteristics and depends on the ability of the material to maintain its integrity in the working conditions. Specifically, in the case under study, the heat generated by friction was modelled as a heat flow coming from a source at the contact surface in static condition. Considering that a heat flow is also supplied to the samples during a Differential Scanning Calorimetry (DSC) analysis, where crystallinity of material is evaluated, a correlation between thermal characteristics of the material, its structure and tribological behavior is presented.

Study of PTFE composites tribological behavior

“…At regime, formation of a transfer films with high crystallinity on the counterparts causes the relatively steady friction coefficient in the sliding process even with the presence of fillers. As previously explained by the authors in [13] the transfer film and consequently the friction properties are greatly influenced by the prevailing interfacial temperature and also the kinematics of the relative motion between two bodies. It is well known how self-lubricating nature of PTFE originates from the low activation energy for the motion of PTFE molecular bonds.…”

“…For the composites 1, 2 and 3, being the estimated mean contact temperature along the test around 60-70 1C (as reported by the authors in [13] and verified experimentally by Tzanakis in [27]), it is possible to say that the small crystals formed by nucleation at lower temperature are destroyed resulting in flakes separation: from the DSC analysis in Fig. 6, in fact, it can be seen that crystallization of pure PTFE starts at low temperatures, therefore the crystals are less resistant (higher wear) than those grown up at higher temperatures.…”

“…Crystallization is easier when no more than 20% in weight of macro-fillers is present (composites 1, 4, 6, and 7). DSC analysis allows the study of the friction process of energy balance, that is, to establish that friction conditions affect both total friction work and ratio between quantity of energy stored and the quantity of heat generated [13,21].…”

“…Generally the fillers improve the wear resistance from 10 to 500 times and increase the thermal conductivity from 2 to 3 times [3,4]. In a previous study [13] the authors have found the increment in thermal conductivity and diffusivity of PTFE composites improve their wear resistance to adhesion. A direct dependence of wear resistance from the thermal properties of PTFE composite was found by Khedkar et al [9] and by the authors in [26].…”

Frictional heating calculations for polymers

“…In a previous study, the authors highlighted the importance of estimating flash temperature at the contact surface of a polymer rubbing against steel (Conte et al [1]). Subsequently a calculation method based on experimental tests was developed using Tian and Kennedy's equations (Conte et al [2]).…”