Tribological properties of additives for water-based lubricants

Fully formulated water lubricating fluids have been thoroughly described in literature. However, the influence of individual additives on tribological properties of these compositions is still not fully clear.In this paper we present frictional, anti-wear and anti-corrosion properties for separate solutions of anti-corrosion, anti-foaming and anti-microbial agents – amines (ethanolamine oligomers, ethylamine oligomers), friction modifiers – glycols (monoethylene glycol, 1,4-butylene glycol) and amine derivatives with longer hydrocarbon chains (3-amino-1-propanol, 4-amino-1-butanol). As a reference, we also performed some tests with pure water.The results show that the additives used in the tests in particular concentrations significantly improve tribological properties of water. The best performance – the lowest friction and no traces of corrosion – was obtained for triethylamine. Ethylene glycol and 1,4-butylene glycol significantly reduced friction, however their anti-wear behaviour was unsatisfactory. Ethanolamines, which combine properties of amines and alcohols showed an increase in friction and corrosion, but significantly reduced wear. The conclusion is that the examined additives can enhance one property of a tribosystem while adversely affecting another.

Research highlights▶ The results suggest that in rolling/sliding contact hydroxyl groups (OH) present at both ends of the additive molecules (Glycols) increase corrosion and wear rate of the steel specimens, but reduce friction. ▶ Amine groups on their own (Ethylamines) significantly improve tribological performance due to a better activation under rolling-sliding contact and to the formation of a more mechanically durable film. ▶ Amine and hydroxyl groups presented together in a lubricant molecule (Ethanolamines and additive mixture) reduced the wear rate and prevent corrosion in the absence of contact but are not good boundary lubrication additives. ▶ The more general conclusion is that the additives in a mixture can enhance one property while adversely affecting another. Furthermore, the presence of an amine group in additive molecules can have a big impact on a water lubricated tribosystem.