Cause analysis of crankshaft crack & Crank bearing scuff of large-scale reciprocating compressor

The crankshaft of a six-crank reciprocating compressor frequently cracks during operation station. After the diameter of main shaft being magnified, this problem is not solved while new one appears, i.e., the unit vibrates strongly and the Crank bearing scuffs continuously at the 1^st and 2^nd crank. To explain the exact reason and modify the configuration of compressor, analysis of modal and dynamic response is performed for the initial and magnified crankshaft with ANSYS finite element analysis software. The result shows that the crack of crankshaft results from the fatigue damage worsened by torsional resonance vibration, and the crank bearings are scuffed because of the largest torsional vibration amplitude of crank pin, which increases continuously from the driving end to the free end. As the diameter of main shaft is magnified, the first order of torsional vibration natural frequency is increased and thus the frequency ratio r of sevenfold rotating speed to the first order of torsional vibration natural frequency is reduced from 1.036 to 1.016, and therefore stronger resonance vibration occurs. Improved configuration is put forward with reduced diameters of crankshaft and cylinders of each stage. With the fault eliminated, not only the predetermined technical performance is ensured but also lower cost and smaller size of components can be obtained.