The International Association of Classification Societies (IACS) has approved an intermediate shaft with tensile strength of above 800N/mm2 for the first time. The component – manufactured by Japanese casting and forging company Kobe Steel – was designated as a ‘Special approved material’ by Class NK, which recommended it for consideration under IACS’ unified Requirements (IR).
The development of intermediate shafts, which transmit power from the engine to the propeller shaft, has previously been limited by the Unified Requirements, which specify a maximum strength of 800N/mm2.
High-strength steel is desirable for the components in order to suppress the torsional vibration that results from the low-speed, high torque rotation design of new large ship engines.
Kobe steel – which supplies ship components including built-up crankshafts, solid crankshafts, intermediate shafts and propeller shafts – can manufacture intermediate shafts of up to 950 N/mm2. Components are inspected and assured using proprietary quality control systems including the automatic ultrasonic testing and, for crankshafts, quantitative digital evaluation of the contact area.
“Under IACS Unified Requirements it is now possible to design intermediate shafts of higher strength,” the company said in statement.
“Shafts of the same diameter will be better able to cope with large torsional vibrations and intermediate shafts of smaller diameters are also possible, saving on weight.”
Source: Kobe Steel
