Kobe Steel Ltd. received special approval from Nippon Kaiji Kyokai (also known as ClassNK or NK) to use 1.05 as the K-factor for calculating the design fatigue strength of crank throws, a key component in marine crankshafts. Japan’s Kobe Steel succeeded in applying a die-forging method to manufacture ultra-large crank throws with cylinder diameters of 80 cm (31.5 inches) or more. The method increases fatigue strength by 20% compared with conventional forging. These are used in engines for the world’s largest container ships and tankers.
The die-forging method enables Kobe Steel to supply high-strength, lighter-weight components with an approved 5% margin in fatigue strength in the design phase. Having already received the same ClassNK approval for small and medium-sized throws, Kobe Steel is the only company in the world to receive certification for the full range of throws for use with two-cycle engines.