| Bearing, which forms one of the four friction pairs with shaft journal, is a significant engine component. Its primary functions are to reduce wear and tear between bearing and shaft, and raise longevity of shaft and connection rod. During the use of bearing, due to the effect of three factors: cyclic impact from rotating shaft, hard exterior particles in the lubricating oil, which could lead to score of bearing or journal, as well as minor uncoaxiality with the bearing or shape irregularities of crankshaft journal, which can result in wear partly, the material must possess excellent fatigue strength and good compliance.Bearings of Babbitt Alloy, of which manufacturing technology is usually chosen centrifugal casting, have been widely used in the initial engine. Recently, with faster rotating speed of engine and greater output of power, bearing materials of engine have trended to choose Al-based or Cu-based alloy, and relevant manufacturing processing of bearing adopts roll-bonding and powder metallurgy sintering respectively. Among Al-based bearing materials, a representative alloy contains 20% Sn that distributes in matrix as "isolated island" , which is a typical wear-resisting structure with soft particle embedding hard matrix. This alloy has largely used in bearings of light engine. However, under the condition of widely applying of nodular iron shaft and the general trend of diesel engine in the automobile industry, its disadvantages of poor wear-resisting property and low fatigue strength are exposed clearly. On the other hand, Cu-Pb bearing alloys with higher fatigue property, which adapt to manufacture the bearing of great power diesel engine, but reveals high cost, complicated manufacturing processing, as well as unfriendly environmental behavior, so its application has been limited gradually. Based the situation above, we expect to develop two new type of bearing Al-Si alloys with high properties to extend the using space of conventional Al-based material.In this article, the group of project has analyzed the operating state of bearing and its evolving process, and discussed the principal factors that influence bearing's lifespan. By optimizing of melting, casting, heat treating and roll-bonding, the problems of poor rolling-forming property and bad surface performance, which have exposed in using and producing of bearing, have been tackled basically. Two or three kinds of Al-based bearing alloys with high properties, which adapt to high volume productions of automobile industry, have been developed successfully. These alloy and bearing`s properties have caught up with the counterpart abroad.During optimizing experiment of composition of low silicon bearing material in terms of traditional alloy Al20SnCu, through addition of 2.5% Si that acts as role of solid solution strengthening and decrease of low melting point Sn, the bearing alloy with high wear resistance and good fatigue strength has been obtained. Meanwhile, the companying problem of poor rolling-forming property is also brought out. In order to deal with it, the project group adjusts the processing of rolling and annealing of bearing strip, the production rate raises more than 90% from less than 10%. On the other hand, the group starts the research about Al-Si bearing alloy. By increasing the content of Si to 4~8%, decreasing Sn to 3~6%, as well as adding Zn and other alloying element, the fatigue strength of the developing alloy reaches or approaches the level of Cu-Pb alloy. With improvement of strength, the decline of rolling property is certain consequence, so tackling this problem becomes the importance and difficulty of project exploring. Through replacing the traditional opened-roller with completely-restrained roller, the issue of crack of strip has settled out basically. And industrial production of Al-Si bearing alloy could be achieved. Through research of this project, the whole set of manufacturing technology of Al-Si bearing alloy with high property has been mastered, so the producing technology of bearing has caugh... |
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