Development of a pre-screening-method for the qualification of environmentally acceptable lubricants for stern tube systems—The evaluation of friction efficiency and scuffing capacity

Abstract

Lubricants for stern tube systems are subject to increasingly stringent requirements in terms of environmental compatibility, as any lubricant leakage leads to contamination of the sea. As a result, interest in environmentally acceptable lubricants (EALs) is increasing. Biodegradable ester lubricants represent a possible alternative to conventional, mineral oil-based lubricants. In addition to environmental compatibility requirements, these ester lubricants must also meet tribological requirements. In this study, suitable tribometers were therefore combined in a pre-screening method to cost-effectively test lubricants for their tribological requirements (friction efficiency, wear protection and scuffing capacity). For this purpose, the contact parameters are transferred from the real conditions in the stern tube system’s journal bearing and from the standardized component tests (FZG for gears and FE8 for rolling bearings) to tribological model tests on a Mini-Traction-Machine (MTM, PCS Instruments). The result of the study is a method for the pre-screening of EALs under the application-related journal bearing and standardized component test conditions, respectively. The results show an influence of the lubricant composition on the friction efficiency in fluid friction as well as the transition point from fluid to mixed friction. Furthermore, an influence of the lubricant composition on the scuffing capacity could be shown. The results of friction efficiency and scuffing capacity confirm also a high reproducibility for those pre-screening tests.