Tribological Behaviour of Corrosion Inhibitors in Metal Working Fluids under Different Contact Conditions

The use of different process media such as cutting fluids, coolants, honing oil and washing media in typical machining operations exceeds 5,000 m3 per year. These media support critical functions such as lubrication, corrosion protection, cleaning and cooling, and have an enormous effect on the manufacturing performance. The tribological properties of these media are improved by using additive molecules, which are physically or chemically adsorbed on the surface of tools and workpieces. The additive performance is especially important in water lubricated tribosystems, where the environment is highly corrosive. The role of corrosion inhibitors typically applied is to neutralize the pH of contaminants in the fluid. Ethanolamines and ethylamines are known as ligands which can form chelate bonds with metals via their amino, hydroxyl and deprotonated hydroxyl-groups. In tribology they are widely spread, as corrosion inhibitors and detergents especially for water based lubricants. This study inquires the tribological performance of amine-based solutions in two types of tribotesters which apply different contact conditions. The dissimilar behaviour under rolling and sliding contact is explained in terms of the structure of the adsorbed compounds. Understanding the performance of the first chemisorbed layers of additives on the workpiece provides essential information for optimizing lubrication in aqueous solutions.