Multi-layer Cr coating with Al2O3(MCC) and Mo plasma sprayed coating are widely used for the piston ring coatings of the large bore marine diesel engine. Each of these coatings has its merits and demerits. The coating life of MCC is much longer than that of Mo plasma sprayed coating, whereas the scuffing resistance of MCC is lower than that of Mo plasma sprayed coating. The ship owners request the coating life of over 2.5 years (maintenance dock interval) these days. However, even MCC, the coating life is not enough. Furthermore, the scuffing problem of the cylinder liners and the piston rings is also one of the most important subjects in order to secure reliability due to the high cylinder pressure and the low quality fuels in these days. Therefore, both of the long coating life and scuffing durability is desired. Wear and scuffing mechanism of MCC and Mo plasma sprayed coating are studied in this study. According to the mechanism, the new concept for the innovative coating which has much longer coating life and much durability to the scuffing is proposed.
In the starved lubrication regime, the film thickness can be much less than the fully flooded film thickness. The film thickness reduction is related to the inlet meniscus distance. The inlet meniscus and the film thickness can be computed for a given inlet film thickness distribution which is generally non-uniform. The inlet film thickness distribution, which is essentially the outlet film thickness distribution of the previous contact, is affected by the surface tension. In this paper, a modified Coyne-Elrod boundary condition is used to calculate the inlet film thickness distribution, taking the surface tension into account. A numerical analysis of EHL point contacts is carried out and solutions of the inlet meniscus and the film thickness are presented. At lower capillary numbers, side bands formed by reflow in the outlet region can replenish the contact owing to reflow in the inlet region. At higher capillary numbers, the side bands move away from the center of the track and the inlet distance decreases. This is a main cause of starvation in EHL point contacts. A good agreement is found between the numerical solutions and experimental results.