New type of slewing bearing for ship crane

MacGREGOR (SWE) AB Crane division, located in Örnsköldsvik, Sweden, is part of the Cargotec Corporation. MacGREGOR develops and manufactures cranes for shipboard cargo handling. A typical MacGREGOR ship crane consists of four main modules, the pedestal, the foundation, the crane house and the jib. The slewing bearing connects the crane house to the foundation, allowing the crane to rotate around its vertical axis. If the bearing should fail and split, the crane house will fall down which is a safety issue. The current slewing bearing design requires a narrow flatness tolerance of the foundations top surface which complicates the assembly process. The purpose of this project was to investigate the possibility to use a double slewing bearing design in order to create a safer and more easily assembled crane. Initially, a problem analysis was performed in order to understand the scope of the project. A series of ideas were developed through brainstorming sessions and discussions with handpicked personnel at MacGREGOR. The ideas were narrowed down and refined into concepts. The concepts were evaluated and ranked by predetermined criteria derived from the needfinding process. Two of the concepts were chosen to be further investigated in the detail design phase, where it was found through numerical calculations that due to the stiffness of the top bearing, not enough moment could be distributed to the lower bearing for the design to be feasible. Therefore, finite element analyses were made of the stay connecting the bearings in order to find a stiffer design, however the results only confirmed the numerical calculations. When it became clear that the moment distribution to the lower bearing was insufficient an alternative design was examined in order to solve the safety issue with a more effective approach. A safety hook concept was discarded earlier in the project since it fell outside the delimitations. However, since it now seemed as a realistic alternative it was investigated in order to remedy the safety issue. An internal safety hook design was produced. Finite element analysis and numerical calculations suggested that the design would have to be rather robust. The weight of the hooks implied that the assembly could be difficult. It is therefore recommended to design an external safety hook solution.<p>Validerat; 20101217 (root)