Environmentally acceptable lubricants (EAL) in the maritime industry

Abstract

All dynamic mechanical equipment needs lubrication to perform in a best possible way. In the maritime industry, e.g. ships, many of the most important dynamic mechanical systems are located beneath the surface of the sea. Examples of equipment are thrusters, stern tubes and ship stabilizers. All these components are dependent on proper lubrication to perform optimally and secure a long service-life. In the interface between the seawater moving parts, a seal is required to separate the oil and seawater from each other. Due to new requirements, conventional mineral oil shall be exchanged with an environmentally acceptable lubricant (EAL). In this study dierent elastomers were tested against dierent steels (S355-steel and NiCrsteel) with two dierent oils (Shell Omala 68 and Kl uberbio EG 2-68). The motivation for performing the tests was to identify the tribological properties of the elastomers in the required EAL compared to the oil in use, and occurring mechanisms and the chemomechanical eects of the lubricants in interaction with the seal. The testing was performed at lab scale using a "Pin-on-plate" conguration in a tribomachine. To investigate the eect of the lubricants on the elastomers two soaking tests were performed, and soaked samples were tribologically evaluated. The result from this study showed that the conventional mineral oil give the lowest coecient of friction (COF) when comparing the two oils. When comparing the elastomers, NBR showed a lower COF than FKM. It was concluded that all the elastomers are operating in a boundary/mixed lubrication regime. NBR exhibit higher wear compared to FKM in most situations, exceptions are when adding abrasive particles (Silicon Carbides) to the lubricant and the contact pressure (CP) is low. Transfer of polymer from adhesive wear towards the metal surface could be observed for all elastomers. The results from the soaking tests showed that EAL degrade NBR more than conventional oil and that higher temperatures accelerate the degradation. In the soaking test FKM gained mass from aging. This study gives pointers of expected behaviour in the sealing system.