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Causes Of Water-Lubricated Stern Bearings Damage

Open water-lubricated stern bearings have the advantages of no pollution, simple manufacturing, and maintenance. With the development of materials science, a variety of new bearing materials with durable and low friction coefficients are gradually promoted to be used in water-lubricated stern bearings, so there are still broad application prospects. However, due to the large assembly gap of the water-lubricated stern bearing, and the ship being immersed in seawater during operation, the influence of external factors also increases, and the stern bearing damage often occurs.

Analysis of the cause of damage. In addition to normal tear caused by the long-term operation, the purpose of stern bearing damage mainly includes shaft vibration, poor shaft alignment, and unreasonable bearing design. The shafting arrangement generally consists of the straight-line method, the bearing allowable load method, and the bearing reasonable load method. Currently, the shaft bearing alignment method usually adopts the bearing consistent load method. The so-called intelligent load calibration mainly considers the impact of the rise of the main engine when it is hot. A load of each bearing is in the best and reasonable distribution when the main driver is heated. Its essence is to comply with the specified bearing load, stress, rotation angle and other constraints, Through the calibration calculation to determine the reasonable position of each bearing, install the shafting into a prescribed curve state, to achieve a fair load distribution of each bearings.

Shaft system vibration can be generally divided into three categories: shaft system torsional vibration, longitudinal vibration, and slewing vibration. During the construction of the ship, for different ship types and different propulsion shaft systems, the calculation of the torsional vibration, longitudinal vibration and gyroscopic vibration of the shaft system should be submitted to the classification society for approval. For the central propulsion shaft system, it should be ensured that there is no excessively large swing vibration in the standard speed range, no dangerous resonance speed should be generated, and there is no excessive large-amplitude longitudinal vibration in the entire speed range. If the amplitude or stress or torque of the shafting wave exceeds the allowable value for continuous operation specified in the specifications, a speed limit zone should be set, and the machine should not continue to operate within the prohibited area.

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