New type of slewing bearing for ship crane

Abstract: 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.