The Transition from Static to Dynamic Boundary Friction of a Lubricated Spreading and a Non-Spreading Adhesive Contact by Macroscopic Oscillatory Tribometry

Christof Koplin,Raimund Jaeger,Sherif Ahmed Abdel-Wahed,Matthias Scherge

doi:10.3390/lubricants7010006

Christof Koplin, Raimund Jaeger + Show 2 more

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https://doi.org/10.3390/lubricants7010006

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Abstract

Lubricated poly(ether ether ketone) (PEEK) and polyamide (PA46)–steel tribosystems were investigated. They show a complex but systematic transition behavior from static to boundary friction, to dynamic friction or to mixed-lubrication. Nonstandard macroscopic oscillatory tribometry as well as gliding experiments were carried out. A previous study showed that the surface and interfacial energies of PEEK, lubricant and steel can indicate trends in the tribological behavior. In the current study, these findings are confirmed for PA46 and a wider range of lubricants. It was shown that a reversal of the order of the work of spreading of two lubricants by switching from PEEK to PA46 as polymer component in the tribological system also resulted in a reversal of the coefficient of friction (COF) at low gliding velocities for these systems. The adhesion threshold of PA46 with the non-spreading lubricants water, glycerine, a water–glycerine mixture, ethylene glycol and poly-1-decene decreased with increasing solving tendency of the lubricants in contrast to the previous results for spreading lubricants for PEEK. Furthermore, the onset of forced wetting was studied for lubricants with different surface and interfacial energies and viscosities η. In general, a 1/η dependency was observed for the velocity which marks the onset of forced wetting. This agrees with theoretical models.

Highlights

Loaded components that are used in mechanical engineering or in the automotive industry can be made from thermoplastic polymers in order to obtain light weight and energy efficient products or components which exhibit a superior performance with respect to noise, vibration and harshness
poly(amide) 46 (PA46) with the non-spreading lubricants water, glycerine, a water–glycerine mixture, ethylene glycol and poly-1-decene decreased with increasing solving tendency of the lubricants in contrast to the previous results for spreading lubricants for poly(ether ether ketone) (PEEK)
Spontaneous spreading of the lubricant into the contact surface between the tribopartners is expected when the overall transition will form exotherm energy

Summary

Introduction

Loaded components that are used in mechanical engineering or in the automotive industry can be made from thermoplastic polymers in order to obtain light weight and energy efficient products or components which exhibit a superior performance with respect to noise, vibration and harshness. The use of polymers in tribological applications requires a profound understanding of the friction and wear behavior of polymers [1]. In particular the tribology of lubricated polymer-steel contacts is complex and remains an area of active research. The complexity partially arises from the interaction of polymer, lubricant and the steel frictional partner. The observation of polymer transfer [2] and the “temperature hot spots” [3] of the polymer during frictional loading in lubricated systems indicate that adhesive friction contributes to the tribology of polymers. Physico-chemical interactions between the frictional partners play an important role in particular in the area “left of the Stribeck curve” [4], i.e., in the boundary friction regime. Experimental techniques which focus on the tribological behavior in the boundary friction regime can Lubricants 2019, 7, 6; doi:10.3390/lubricants7010006 www.mdpi.com/journal/lubricants

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