Modification design of large-scale compressor crankshaft based on modal and dynamic response analysis

Crack of crankshaft and scuff of bearing have been the bottleneck for the development of large-scale reciprocating compressor. To solve such problems, modal and dynamic response analyses are performed for the crankshaft system. Torsional model shapes and stress status are obtained, which shows that the crack of original crankshaft results from fatigue damage and slight torsional vibration, and two factors result in frequent scuff of the crank bearings. After the diameter is enlarged, the torsional vibration amplitude of crank pin becomes larger, which increases continuously from driving end to free end. At the same time the first order of natural frequency of torsional vibration is increased, and the ratio r between sevenfold rotating speed and the first order of natural frequency is reduced from 1.036 to 1.016, and therefore a stronger resonance vibration occurs. The crankshaft is cut off between 2^nd and 3^rd phase at last and re-connected with two hot assembled plate flanges, rotational inertia-mass is thus enlarged and the ratio r is increased to 1.064. As such the resonance vibration disappears and fatigue life of crankshaft is prolonged effectively.