Study On Tribological Problems In Water-lubricated Compound Rubber Stern Tube Bearing

As one important part of a ship propulsion system, the water-lubricated rubber stern tube bearing has great effects on shipping navigation, security, covert, and economic and so on. Although water-lubricated rubber stern tube bearings have been used for more than one hundred years, its basic research is still staying primary stage, especially in the aspect of the mechanism of friction-induced vibration. Therefore, there is of great significance theory and military application value on studying water-lubricated stern tube bearing material development, theoretical and experimental research on friction-induced noise generation mechanism which were based on the reduction of vibration and noise.Funded by National Natural Science Foundation of China, this paper concentrates on key tribological problems of marine water-lubricated rubber stern tube bearings such as friction properties, and friction-induced vibration. The main contents of this dissertation are listed as follows:(1) A nonlinear analysis model of friction-induced vibration for water-lubricated rubber stern tube bearings was established. At the same time, the paper analyzed the stability of the model and got the digital solution. The vibration displacement curve changing with time t was deduced. The impact of factors such as pressure, temperature was analyzed.(2) The mixture of powder of UHMWPE and graphite was blended into NBR to develop a new kind of compound rubber with cost-effective, low-friction performance. The physical and mechanical properties, coefficient of friction of the compound which is knowed as SPB-N have satisfied the ship industry standards of the People’s Republic of China CB/T769——2008, and requirements of the U.S. military standard MIL-DTL-17901C (SH). The local maximum project pressure of SPB-N could reach0.70MPa.(3) For the reasonable experimental design and improvement of the test rig, the block tests for SBR and SPB-N are carried out respectively in a very close manner to simulate the full-size bearing friction. Variations of coefficient of friction with speed were measured under different projected pressure, with different thickness or hardness of rubber layer of test blocks. And a brief analysis is given to the mechanism of action. To distinguish prominent impact factors among the hardness, thickness of the rubber layer and its interaction on the friction performance of blocks, the orthogonal analysis of two-factor interaction was carried out. The results indicate that the coefficient of dynamic friction of the test block decreased with the rubber layer thickness and hardness reduction. Both have an impact on water-lubricated rubber bearing friction performance. Among the three factors which are rubber layer thickness, hardness, and their interactions, the influence of thickness of rubber layers on friction properties is the most significant, followed by hardness factor. Priority should be given to ensuring the rubber layer thickness during water-lubricated stern tube bearing design. The test blocks of the compound rubber SPB-N had superior low-speed performance because of its excellent self-lubricating properties.(4) Using a high-speed camera, the generation mechanism and influencing factors of stick-slip induced vibration of test block rubber layer in the process of axial rotation are studied. Orthogonal experiment method is used to distinguish which the main factor among speed, project pressure, the rubber layer hardness, thickness, and lubrication conditions and so on is. The test results show that the influence of the factors is sorted by size as follows:lubrication conditions, project pressure, and the hardness of the rubber layer, the thickness of the rubber layer. In the sufficient lubrication, increasing the hardness of the rubber layer, or decreasing the project pressure ratio and the thickness of the rubber layer could reduce rubber bearings stick-slip effects.(5) Friction and vibration tests of ship water-lubricated stern tube bearing are carried out on stern tube bearing test rig. At the same time, speed, load, hardness of bearing material, and variety of materials are analyzed on the effects of bearing friction performance. Test data are close to theoretical calculations and the block test results, which verify the theoretical analysis.