Effect of the type and concentration of lubricating additives on the antiwear and extreme pressure properties and rolling fatigue life of a four‐ball tribosystem

Abstract

AbstractTests were performed on two different four‐ball testers. The first was used to determine antiwear (AW) and extreme pressure (EP) properties at sliding friction. The second was used to assess the surface fatigue (pitting) life at rolling movement. Lubricating oils of various chemical compositions were tested. A base mineral oil was blended with two different commercial packages of lubricating additives of AW and EP types. The AW additives contained ZDDP and were blended with the base oil at 0.2 and 3wt %. The EP additives were organic compounds of sulphur and phosphorus, blended with the base oil at 1 and 10wt %. It is shown that AW additives not only improve AW and EP properties but also — at 0.2% — are beneficial for the fatigue life. An increase in the concentration of AW additives leads to an improvement of AW and EP properties but — for one of the packages — reduces the fatigue life. EP additives — at 1% concentration — significantly improve EP properties, and to a lesser extent AW properties. Such a concentration of EP additives has no influence on the fatigue life. An increase in the concentration of EP additives leads to a further improvement of EP and AW properties. However, this is accompanied by a considerable decrease in the fatigue life. By using a scanning electron microscope and energy dispersive spectrometer for analysis of the worn surface, mechanisms of action of various lubricating additives under different friction conditions were identified. Copyright © 2006 John Wiley & Sons, Ltd.