Vibration Monitoring to Diagnose Incipient Seizure of Crosshead Bearings

A technique to monitor abnormal vibration of crosshead bearings in large two-stroke diesel engines has been developed using a dynamically loaded bearing seizure test rig. The test rig is able to simulate the load pattern and oscillatory motion of the actual crosshead bearing. Normal vibration spikes occur around crank angles of -90deg and +90deg where the oscillating speed is zero. When the lubrication condition deteriorates, an abnormal vibration spike caused by severe metal-to-metal contact is frequently generated at a crank angle of +90deg where the oil film thickness is a minimum. If careful measures against seizure are carried out immediately after detecting abnormal vibration, the bearing surface would be able to recover, thereby avoiding severe metal-to-metal contact damage. Thus the early detection of abnormal vibration can be effective in preventing seizure of the bearings.