Kobe Steel Ltd Develops New Die-forging Method for Ship Crankshaft Manufacture

Kobe Steel, Ltd. has developed a new die-forging method to manufacture built-up type crankshafts for diesel engines in ships. The new die forging method offers considerable improvements in design fatigue strength in comparison to the conventional “bending forging” method. Using the new method, Kobe Steel can make near-net-shape forgings for crank throws.

Due to requests to improve fuel consumption stemming from stricter environmental regulations and the high price of ship fuel, the need for “eco-ships” is rising. Two important points in the development of eco-ships are ship development to reduce drag on the hull and engine development to improve fuel consumption and lower exhaust gas emissions.

In engine development, ships are using larger propellers that rotate at slower speeds, driving the need for low-rpm propellers with high output. To meet this trend, long-stroke engines are growing in popularity.  When long-stroke engines are used, the crank throws are longer and heavier than conventional ones, leading to higher load stress on the crankshaft and higher bearing loads.

Kobe Steel has recently developed a new die-forging method using its experience as an integrated crankshaft manufacturer covering all processes of steelmaking, forging, machining and inspection. Incorporating the new forging method and techniques of clean steelmaking, Kobe Steel has successfully increased the fatigue strength of the crankshaft material by 20 percent, compared with conventional forging. As a result, long-stroke crank throws of higher reliability and lighter weight can now be commercially mass produced.

Along with the development of the new die-forging method, Kobe Steel developed automatic ultrasonic inspection technology and numerical inspection technology that digitally evaluates the part where the crankshaft touches the bearing. These technologies provide substantial improvement on the reliability of the crankshafts, which face higher load stress and bearing loads when used with long-stroke engines.

In addition to the new die-forging method, Kobe Steel conducts research and development of advanced materials for marine parts. Responding to customer needs, Kobe Steel is contributing to the advancement of the shipping and shipbuilding industries.

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