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Bearing Design in Machinery Episode 3 Part 6

Tham khảo tài liệu 'bearing design in machinery episode 3 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | catastrophic failure because the tough core minimizes undesired crack propagation. In addition M50NiL can operate at higher speeds is more wear resistant has higher tensile stress higher fracture toughness and lower boundary lubrication friction than AISI M-50. 13.19.2.3 DD400 For instrument ball bearings corrosion resistance is very important. A stainless steel DD400 has been developed for precision miniature rolling bearings and small instrument rolling bearings. Corrosion resistance combined with adequate hardness has been achieved by increasing the quantity of dissolved chromium in the material. However corrosion-resistant stainless steels have reduced fatigue resistance and they are applied only for light-duty bearings. The composition of DD400 is 0.7 C 13 Cr and it is martensitic stainless steel. DD400 replaced AISI 440C 1 C 17 Cr which was used for similar applications. DD400 demonstrated better performance in comparison to AISI 440C in small bearings. The most important advantages are better surface finish of the races and rolling elements better damping of vibrations and improved fatigue life. These advantages are explained by the absence of large carbides in the heat-treated material. 13.20 PROCESSES FOR MANUFACTURING HIGH-PURITY STEEL In addition to the chemical composition the manufacturing process is very important for improving fatigue resistance particularly at high temperatures. For critical applications such as aircraft engines there is a requirement for fatigueresistant materials with a high degree of purity. It was realized that there are significant amount of impurities in the bearing rings and rolling elements in the form of nonmetal particles as well as microscopic bubbles from gas released into the metal during solidification. In fact these impurities have an adverse effect equivalent to small cracks in the material. These microscopic cracks propagate and cause early fatigue failure. Therefore a lot of effort has been directed at developing .