Marine engine nodular cast iron crankshaft

Abstract

The present invention discloses a marine engine nodular cast iron crankshaft, which comprises: a main journal arranged on a cylinder, a connection rod neck connected with a connection rod big end hole, and a balance block, wherein rolling fillets are respectively undercut on positions of journal transition fillets formed by the main journal and the connection rod neck with the balance block. The marine engine nodular cast iron crankshaft has the following characteristics that: the structure is simple and reasonable; fillet rolling is adopted to strengthen the crankshaft so as to improve a fatigue strength; and the fillet does not require fine grinding processing after rolling strengthening, and it can be ensured that beating deformation is qualified, such that processing property of the marine engine nodular cast iron crankshaft is better than processing property of the nitrogenization crankshaft, and cost is low.

Description

technical field [0001] The invention relates to the field of engines, in particular to a nodular cast iron crankshaft of a marine engine. Background technique [0002] The crankshaft is the main rotating part of the diesel engine. Its rotation is the power source of the engine and the source power of the entire mechanical system. When the crankshaft is working, it must bear huge bending and torsional combined loads. Therefore, the crankshaft is required to have high fatigue strength and reliability. The commonly used materials for the crankshaft are forged steel and ductile iron. Most of the crankshafts used in marine diesel engines over 6,000 tons are forged steel crankshafts, and there are also a small number of ductile iron crankshafts. In order to improve the fatigue strength of large crankshafts, steel crankshafts usually undergo quenching and tempering treatment, and forged steel crankshafts with higher strength requirements also undergo neck surface + fillet quenchin...

AI Technical Summary

Problems solved by technology

In order to improve the fatigue strength of large crankshafts, steel crankshafts usually undergo quenching and tempering treatment, and forged steel crankshafts with higher strength requirements also undergo neck surface + fillet quenching and strengthening treatment. Although steel crankshafts have high strength and good reliability, but It is expensive, accounting for 20-30% of the cost of the whole machine

At present, large-scale marine ductile iron crankshafts are treated by normalizing or surface nitriding strengthening, but the fatigue strength of this ductile iron crankshaft is much lower than that of forged steel crankshafts, which can only reach 60% of the strength of steel crankshafts, and there is a problem of poor reliability; At the same time, the crankshaft that has reached the final size of the finished product is prone to bending deformation after the final high-temperature nitriding treatment, which makes the runout out of tolerance. For example, a certain type of marine ductile iron crankshaft with a length of 2000mm is treated with surface nitriding strengthening treatment. The technical requirements require the crankshaft to deform and run out after nitriding Or not greater than 0.15mm, but actually more than 20% of the crankshaft nitriding deformation runout is greater than 0.25mm and is facing scrapping

Therefore, although the current manufacturing cost of large-scale marine nodular iron crankshafts is 40% to 50% lower than that of forged steel crankshafts, due to quality problems such as low safety factor, poor reliability, and low product processing pass rate, it is seriously limited to replace steel crankshafts on a large scale. Use and apply to larger power marine engines and generators

In addition, the crankshafts used in large ships at present adopt a large fillet structure according to the needs of the strengthening process. Because this structure needs to grind the journal surface and fillets at the same time, the grinding process is difficult, so the production efficiency is also low.

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