Choosing and justifying the correction method for marine diesel crankshafts

Abstract

The crankshaft is considered as the main part of a marine internal combustion engine. As the object of research, the crankshaft of the 6CHN 31.8/33 diesel engine used on ships as the main marine engine is chosen. The reasons leading to the violation of the geometry of the longitudinal axis of the crankshaft are determined. The cases of crankshaft deflections exceeding the permissible values are systematized. A maximum deflection of 4.10 mm is recorded with an acceptable value of 0.03 mm. The fourth frame neck is marked, which accounts for the largest number of curvatures of the longitudinal axis of the crankshaft. The dependence of the deflection value on the number of the frame neck and the repair size is determined. The thermal correction with heating by an oxygen-gas flame of the crankshaft approved and used at repair enterprises of JSC Russian Railways is considered. It is noted that the neck heating temperature during thermal correction is significantly higher than the temperature at which structural changes occur in the shaft material, and spot heating can lead to stresses exceeding the tensile strength of the shaft material. A thermomechanical correction of crankshafts based on the phenomena of creep and stress relaxation is proposed. It is proposed to calculate the force with which we act on the shaft according to the formulas of the resistance of materials, and to control the magnitude of the stress by calculating the deflection arrow. The necessity of continuing research in the field of operational reliability of crankshafts of marine internal combustion engines after their restoration by thermomechanical correction based on the phenomenon of creep and stress relaxation is confirmed.