C. Koplin1*, H. Oehler2, B. Schlüter1, I. Alig2, and A. Bormuth3

1 Fraunhofer IWM MikroTribologie Centrum, Wöhlerstraße 11, 79108 Freiburg, Germany,

2 Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF, Abteilung Kunststoffe, Schlossgartenstraße 6, 64289 Darmstadt, Germany,

3 Klüber Lubrication München SE & Co. KG, Tribology Fundamentals and Component Analysis, Tribology & Chemistry, Geisenhausenerstr. 7, 81379 München, Germany

*christof.koplin@iwm.fraunhofer.de

Actuator systems based on gear and spindle drives often use thermoplastics for one or both of the systems in contact [1]. Both are exposed to oils or greases to reduce friction and dissipate heat. Interaction is inherent in all macromolecular systems. All in all, the effect of interaction is difficult to predict, but can be correlated with physically motivated properties and trends through experimental and analytical testing. Tribological sliding friction and wear models are based on descriptions of the manifestations of adhesive [2] and abrasive [3] interaction. Thermoplasts sliding on technical steel surfaces show a complex running-in behaviour, can therefore not be directly attributed to changes in properties. Chosen auxiliary variables µ-stiction and micro-surface hardness are therefore used in these investigations on friction. Further measurement variables are correlated, that are the absorption of oil via weight change m and the viscoelastic moduli via a DMA measurement of G' and G''. E.g. spreading energy Wspreading of polymer, steel and oil is a surface quantity and can be determined via contact angle measurements for industrial systems. It changes the acting adhesion for lubricated systems against the tribopartner [4]. C. Koplin et al. have demonstrated the effect of Wspreading for glassy solidified thermoplastics PA46 and PEEK. For thermoplastic material POM and PK, which are rubbery at room temperature, the characteristics of swelling and rubbery interaction with industrial oils of different polarities were investigated in comparison with PA46. Low spreading energies and subsequently a high spreading ability of the lubricant were found to partially compensate adhesive mechanism for glassy and rubbery but nor for swelling POM. The manifestation of tribologic mechanisms can be assigned to the chosen variables via specific trends in swollen, glassy or rubbery state for friction of lubricated thermoplasts on steel.