Abstract
Using large components made of nodular cast iron (GJS) in wind turbines enables the application of lightweight construction through the high degree of design freedom. Besides the sand-casting process, casting into a permanent metal mould, i.e. chill casting, leads to a finer microstructure and higher quasi-static mechanical properties as well as higher fatigue strength. Unfortunately, in present design methodologies specific fatigue data is only available for sand cast and not for chilled cast GJS. Thus, lightweight design strategies for large, chilled cast components are not achievable, which led to the publicly funded project “Gusswelle”. Based on material investigations of EN-GJS-400-18-LT chill cast, an optimized hollow rotor shaft is developed. The design process and the resulting shaft design are presented. The optimized hollow rotor shaft prototype will be tested on a full-scale test bench to validate the design methodology. The intended validation plan as well as the test bench setup is shown in this paper. Furthermore, the decreasing wall thickness influences the interference fit between main bearing and hollow rotor shaft. Thus, through the applied bending moment, inner ring creep is more probable to occur in the main bearing seat. The creeping behaviour is investigated with finite element simulations and a measuring method is presented.
Highlights
The German federal government plans to expand offshore wind power to a capacity of 15,000 MW by year 2030 to reduce the CO2 emissions [1, 2]
Compared to the conventional sand-casting process, the chill casting technology leads to the formation of a microstructure with smaller graphite nodules due to fast heat dissipation resulting in higher fatigue strength [8]
An optimized hollow rotor shaft made of EN-GJS-40018-LT chill cast is developed with the general optimization goal to save material and component costs, through the application of lightweight design for large cast components in combination with the application of the chill cast technology for nodular cast iron
Summary
The German federal government plans to expand offshore wind power to a capacity of 15,000 MW by year 2030 to reduce the CO2 emissions [1, 2]. Compared to the conventional sand-casting process, the chill casting technology leads to the formation of a microstructure with smaller graphite nodules due to fast heat dissipation resulting in higher fatigue strength [8] Components manufactured with this technology hold a fast solidification in areas near to the chill mould. The project partner Fraunhofer LBF investigates the cyclic material behaviour of chill cast nodular cast iron Based on these material strength results and the raw design, the optimized prototype of the hollow rotor shaft is developed. The scope of this paper is the optimization of a highly stressed component of a wind turbine’s drive train, a hollow rotor shaft, in consideration of the influence of high strength cast material. At the end of the paper, the main conclusions of the work and an outlook are provided
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