Abstract
The limiting state of the marine medium speed diesel engine crankshaft occurs as a result of the influence of three basic factors: kinematics error, plain bearings wear, and fatigue of material. A kinematics error causes deformation of the crankshaft, uneven wear of bearings and material fatigue. The crankshaft deformation is monitored by radial runout of the crank journal and change of distance between crankwebs. The legitimate values of deformation are defined by the manufacturer and tested in practice. According to the data taken from the literature, there has been analyzed the process of the crankshaft bearings wearing. The main reason is found an abrasive wear of plain bearings. The uneven wear of crankshaft necks results in their ovality and conicity. Non-cylindrical shape of the neck is the principal reason of plain bearings faults. The phenomenon of the crankshaft fatigue has been studied. Exceeding warning limits of crack length and area on the neck surface, which is mentioned in diesel technical service and repair manual, will result in changing crankshafts with cracked necks. The different types of diesel crankshaft fatigue destruction have been educed. The problem of crack development inside a crankshaft has been studied. The estimations of limiting depth of neck craking are offered based on the results of emergency fatigue fracture of crankshaft, taking into account recommendations of firms-manufacturers and experience of repair. The estimations of crankshaft neck cracking average speed have been given on the basis of study of emergency situations. An example of successful renewal of crankshaft with deep cracks has been demonstrated. After magnetic particle or dye penetrant testing it has been recommended to use the crack depth gauge RMG 4015. Crack control experience has been investigated in the course of the process of 8NVD48A2-U diesel crankshaft neck surface cracking by a decreasing of diesel load.
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