Performance evaluation for aged environmentally adapted lubricants in bronze-steel sliding contacts

Environmentally adapted lubricants (EALs) are becoming of increasing interest to the industry as legislationdemands the replacement of mineral oil lubricants. However, little or nothing is known about the infl uence ofageing on the performance of these fl uids in mixed and boundary lubricated tribological contacts. In this study,samples of three fully formulated lubricating oils, both in their ‘unaged’ form and ‘aged’ by means of an oxidationprocess in the laboratory, were utilized in a detailed study whereby variations in relative lubrication performancewere examined. Standard laboratory pin-on-disc equipment was utilized in order to allow comparisons tobe made and the defi nition of conclusions for a sliding tin bronze on steel contact. This simulated the interactionbetween an oil-lubricated bronze bushing and steel shaft as found in the vane adjustment mechanism of a Kaplanturbine. X-ray photoelectron spectroscopy analysis was employed to assess the effect on surface layer structuralchemistry. Results showed, for the specifi c application being investigated, that EALs continue to function wellin terms of their friction and wear performance even at high acid numbers