Changing emission legislation limits are challenging the engine developers in many aspects. Requirement to improve combustion and engine efficiency have resulted in increased loads and higher levels of abrasive particles within the engine environment. Concerning piston rings and piston ring grooves, such engine modifications are leading to critical tribological conditions and side wear is becoming a key issue in the design of these components.
Historically one of the most common forms of side wear protection on piston rings has been chromium plate. This solution has limitations on durability (low thickness) and on topography (rough surfaces). In response to these limitations, nitrided stainless steel top rings have been used to improve the side protection; it is harder and typically has a smoother surface finish when compared to chromium coating. However, in the next generation of truck engines, the tribological conditions also point to limitations on some applications for nitride treatments. For these abusive conditions a new solution has been developed using thermal spray technology. Thermal spray technology combines high coating thickness capabilities with reduced wear for both rings and pistons.
Special engine test procedures were designed to evaluate side wear solutions under severe operating conditions. The competing ring technologies were then evaluated with thermal spray coatings presenting the best performance. Long term tests are also presented showing improved durability of thermal spray coatings on the side face.