Effect of Molecular Structure of Lubricating Oils on their Frictional Behavior.

In order to establish the relationship between the chemical structure of fluid lubricants and their friction characteristics under elastohydrodynamic (EHD) conditions, a number of chemically defined fluids were tested in a twin-disc machine. Thereby new synthetic lubricants of the polycycles type were developed which have a high traction coefficient. The measurements showed that no direct relationship exists between the viscosity under atmospheric conditions and the friction characteristics under EHD-conditions. Modul substances among the saturated alicyclic and heterocyclic compounds with a steric hindrance in their molecular mobility show high traction coefficients. Lubricants with ″stiff″ molecules as represented by the Stuart-Briegleb spherically indentated models are less dependent on normal load and circumferential surface velocity of the twin-disc machine. A new gauging method has been developed which permits the elimination of the effect of roughnesses of the test discs on the friction measurements, thereby achieving ″friction equivalent surfaces″ .