A NEW DESIGN FOR CROSS-HEAD BEARINGS FOR HIGH-PERFORMANCE TIER II 2-STROKE ENGINES

摘要

The technology drivers for slow speed large bore engines can be summarized as follows: restrictive emission regulations, improvements in reliability, new ship designs and decreasing life cycle costs (fuel efficiency, first cost, maintenance cost). The industry mindset and development experience is traditionally driven by reliability and fuel consumption. The upcoming emission reduction calls for a focus shift and new development processes for the engine builders. The emission reduction increment is substantial and the time is short. Therefore the industry needs fast technology awareness, acceptance and implementation. The new 2-stroke engine generations are subject to continuous performance improvements driven by new and demanding operating conditions. Higher firing pressures are required and result in higher bearing loads and larger bearing sizes. In particular for the cross-head bearing the bearing width will exceeding 400mm. Thus traditional bearing designs no longer meet the requirements. Bearing manufacturers must consequently go to the limits of feasibility. When looking at the performance criteria of bearings for the application in 2-stroke engines, properties like emergency running capabilities, embedability and to certain extend the fatigue properties are vital to the performance of these engines. To meet these demanding requirements a new and extremely robust cross-head bearing design based on tri-metal configuration Steel - Aluminium-Tin 40 - Synthec® for the MAN Diesel & Turbo SE Tier II engine platforms has been developed and successfully tested. The new design is called "Patch-Work-Bearing" and is currently used for long stroke engines with a minimum bore diameter of 400mm. So far, the prefab material for steel backed aluminium based bearings is produced via well-established roll-bonding processes. If it comes to cross-head bearings for the new engine generations with a characteristic bearing diameter to bearing width ratio of approximately 1:1 ordinary processes cannot be used. The process window is already fully exploited with respect to the rolling-mills capability (width and rolling force). Currently in order to produce the needed prefab material a so called explosion bonding process is used, at which the formation of multi-layer materials is based on kinetic blasting energy [1]. Parts with a size of several square meters can be product. Anyway this technology is exceptionally expensive as high safety measures are mandatory and ordinary production facilities are insufficient. It is a single piece production process with many variable process parameters and therefore a stable and high quality level is difficult to achieve. In particular the bonding strength and bonding quality relies on a constant forming process. This paper will focus on a new method to produce prefab material for the production of extra wide cross head-bearings which is not based on the explosion bonding process. The paper gives an insight in the new design of the cross-head bearing and the advantages resulting from that.