A Master’s Thesis In Martial Physics And Chemistry

Along with the development of the large-scale mechanical equipment, it is morestrict for important parts. Bearings and bushings are important wear parts on largeequipment in metallurgy, mining, electricity, etc. They not only withstand greaterpressure, alternating stress and shock loads, but also encounter the friction, the role ofwear, high working temperature and multi-corrosive effects of media types. Ordinary tinor lead Chiba’s base alloys, and cast iron base bearing materials can’t be satisfied withthe requirements now. High lead bronze alloys have excellent dry friction properties,high thermal conductivity, fatigue resistance and anti-seizure properties, and are widelyused in the bearings.This paper reviewed the research progress of high lead bronze alloy by centrifugalcasting nowadays, summarized the key technology for preparing high lead bronze alloys.The impact of centrifugal casting process such as centrifuge speed, pouring temperature,mold preheat temperature, casting temperatures, the content of lead, S and RE to leadsegregation, microstructure and properties of the high lead bronze alloy were researched.and the optimum process conditions of preparation of high lead bronze alloy bycentrifugal casting was determined.Observing and analyzing the microphotograph of alloys by metallographicmicroscope. Results show that: when S was not added, lead was lump or banded and itled to serious lead segregation. However, when S was added, compounds Cu2S were formed, which uniformly distributed on the grain boundary and increased incessantlybeing like a net, therefore they hindered the lead segregation. With the increasingquantity of S being added into, lead segregation became lighter. After3.0%S wasadded into high lead bronze, the lead segregation was the lightest and the distributionwas the most uniform, and what’s more, the grain was refined; After adding RE, theform of Pb became a strip or block into punctate or spherical, distributed evenly. Withincreasing amount, the degree of segregation of lead decreased. After adding2.0%RE,degree of segregation of lead became the minimum, lead presented spotty distribution.Contracting the microstructure and properties of high lead bronze. Microstructure:adding S element, lead mainly show the uniform punctate distribution; adding RE, leadgranule size is larger, mainly in the shape of spherical. Hardness: when S addition is3%(optimum adding quantity can improve lead segregation effect), hardness increasedfrom44.2to52.7; adding rare earth hardness increased, increased marginally, REaddition is2%, the hardness of only46.7. Density: the difference is small density. Whenthe addition content of S was3%,9.123g/cm3; rare earth addition of2%,9.108g/cm3.