New Approaches on Material Design for High-Performance 2-Stroke Engine Bearings

When looking at the performance criteria of bearings for the application in Two-Stroke engines, properties like emergency running capabilities, embedability and the fatigue properties are vital to the performance of these engines. The typical approach is to use materials with a soft Tin matrix and hard intermetallic phases commonly known as “Babbitt” alloys. In a second, more recent approach, Aluminium alloys with elevated Tin content are more and more often chosen. Babbitts outmatch any bearing alloys by their outstanding tribological performance but have very limited mechanical properties. Oppositely, the Aluminium alloys have substantial higher strength but leak somehow with regard to emergency running properties. Whereas the poorer running properties of Aluminium Alloys can be overcome by using suitable running-in coatings, the strength increase of the Tin matrices of Babbitts is rigorously limited by the production technology of spin casting and the ban of hazardous alloying elements such as Cadmium. In order to satisfy the needs of engines manufacturers for a material which combines the advantages of Aluminium- and Tin-base alloys, a new approach which combines both metallurgical alloy development and process technology redesign is necessary. By a fundamental process analysis, the limiting effect with regard to alloy tuning of the existing production technology for steel-babbitt bearing shells will be shown in this paper. Further more, new process routings with the effect of enabling the production of Babbitt bearings with never practized alloy compositions with enhanced mechanical properties are presented.