The Research On Improveing And Optimizingthe Microstructure And Performance Of Spinning Rings

The spinning ring is a kind of steel circular gear. It is a key part of ring-spinning frame to cooperate with spinning traveller to complete yarn twisting and winding process. The performances of rings determine the yarn quality, including balloon stability, hairness, end breakage and so on. And its working life is the main effect on the enterprise benefit. The foreign rings has many excellent characteristics, including the short running-in, high-quality of yarn and 8-years working life of foreign rings. However, the working life of domestic rings is only about 2 years and the yarn quality will be sharply declined after 1-years working life. The performances and working life of domestic spinning rings lags far behind the performances of the foreign. So the almost whole high-end market of spinning rings is occupied by imported product. This monopoly leads to overpricing the foreign spinning rings which unit price is dozen times more than the unit price of domestic spinning rings. And the low-end market of spinning rings is subject to fierce competition, keeping the margins very thin. So the domestic manufacturers of spinning rings are hard to survive. In this work, the differences between the domestic and foreign spinning rings were compared to find the reason why the foreign spinning rings are so good. Moreover, the effects of austempering process parameters on the mechanical property of GCr15 bearing steel were studied to improve the comprehensive performances of domestic spinning rings.Firstly, the differences between the foreign spinning rings and the domestic spinning rings, including the raw material, the microstructure, hardness and volume of residual austenitic grain, surface plating chromium layer, were studied to explore its manufacturing process. Three guiding and valuable differences are found: 1.The kinds of carbide morphology are different. The carbides in foreign rings are nearly ball-like, and the carbides in domestic rings are stub-like and partially polygon-like. Moreover, The 70 percent of carbide size of foreign bearing steel ring is less than 0.6μm, and the 80 percent of carbide size of domestic bearing steel ring is range from 0.3μm to 0.9μm. 2. The volume of residual austenitic grain and hardness are different. The volume of residual austenitic grain in domestic bearing steel ring is 25.62%, and the volume of residual austenitic grain in foreign rings is less than 10%. Although the volume of residual austenitic grain in foreign rings is less than the volume in domestic rings, but the hardness of foreign rings is still lower than the hardness of domestic rings. The Vickers Hardness of bearing steel ring is about 740 HV, and the Vickers Hardness of common domestic ring is higher, reach 800 HV.3. The surface plating chromium layers are different. The average concave curve radius and depth of the foreign coating interface are respectively 0.52μm and 0.57μm, and the average concave curve radius and depth of domestic coating interface are respectively 2.7μm and 0.93μm.The shot peening techniques make a difference between foreign and domestic spinning rings in the surface plating chromium layer, and the differences of the kinds of carbide morphology, the volume of residual austenitic grain and hardness are made by the heat treatment techniques.Secondly, the hardness, microstructures, residual austenite contents and austenitic grain size of bainite/martensite structures were studied using the method of orthogonal experiment to design isothermal quenching process, under different process parameters. Within the test selection, the major factor influencing hardness of GCr15 bearing rings is austenitizing temperature and the minor factor is austempering temperature. The other two factors, austempering time and tempering temperature, have little influence on hardness of GCr15 bearing rings. Moreover, as the quantity of spheroidized particle increases and the size of spheroidized particle decrease, the hardness of GCr15 bearing rings increases. With the elevation of austenitizing temperature, the size of austenitic grain decrease and the volume of residual austenitic grain increase. After the heat treatment, the more carbides are in the original austenite grain, the smaller austenitic grain size is. With the rising of austemping temperature, the acicular bainite organizations are also constantly become longer and wider and the hardness of GCr15 decrease.Finally, the friction and wear performance under the different content ratio of bainite/martensite structure were compared, using the orthogonal table under different isothermal quenching process. The friction and wear performance of traditional tempered martensite, bainite and bainite/martensite were compared. The study shows that bainite/martensite has better wear resistance than the single bainite or martensite in the wear form of spinning rings.