Abstract
KEYWORDS
high-performance coatings, tribology, internal combustion engines.
ABSTRACT
The replacement of the commonly used couple rod-bushing/piston-pin with a coated pistonpin would especially apply to large diesel engines which require very long maintenance intervals and should withstand millions of kilometres. The method used to evaluate the classic system (rod-bushing/steel piston-pin) and the new system (steel rod/coated pin) was tribo-analysis. Friction and wear processes between the piston-pin and the rod-bushing have been investigated using a Wazau tribometer. The tribometer simulated (in real time or accelerated modus) the mechanical working conditions of these engine components. The materials chosen for the classic system were a steel disc (for the piston-pin) and bronze pin (for the rod-bushing). The new system consisted of a chrome-coated disc (for the coated piston-pin) and a steel pin (for the rod). The high performance chrome-coating, Topocrom, is developed by the Swiss company WMV of Winterthur and has a particular surface geometry consisting of chrome spheres (calottes), with the ability of retaining very well lubricating material in extreme working conditions.1 Various tribometer tests, using several lubrication systems (fluid, half-dry and dry) and two motion types (tribo-rotation and tribo-oscillation) have shown that the friction coefficient measured at the classic system (steel/copper) was lower that the one measured at the newsystem (Topocrom/steel). The difference between these two systems was made by the low wear values measured for the chrome-steel system. In order to achieve longer maintenance intervals (very important for large diesel engines) the use of high performance anti-wear coatings is a very good option. Tests results have shown that chrome coatings cause less wear, thus extending the durability of highly stressed engine components.