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윤활유의 수분혼입 및 베어링강의 표면 조도가 구름접촉 피로수명에 미치는 효과
허태현 ( Tae Hyeon Heo ),심충기 ( Chung-ki Sim ),김홍석 ( Hong Seok Kim ),신기훈 ( Ki-hoon Shin ),정성균 ( Seong Kyun Cheong ) 한국안전학회(구 한국산업안전학회) 2017 한국안전학회지 Vol.32 No.1
A large amount of research has been performed on the rolling contact fatigue(RCF) life of bearings, since it directly affects the safety and reliability of mechanical systems. It is well known that rolling contact fatigue life is influenced by several parameters including contact pressure, oil contamination by water or metal particles, and the surface conditions of bearings. However, the detailed damage mechanisms involved in rolling contact fatigue have not been clearly identified yet. In this paper the effects of water contamination of the lubricant and surface roughness of bearing steel on the rolling contact fatigue life were investigated. Two types of specimens with different surface roughness values were prepared through turning and lapping operations. They were tested under two different lubrication conditions, i.e. oil lubricant with 100% of oil and the water contaminated condition with 80% of oil and 20% of water using the rolling contact fatigue testing machine. The surface damage induced by the rolling contact fatigue was observed by using atomic force microscope(AFM). Experimental results show that the rolling contact fatigue life, L<sub>10</sub> was reduced by 24 to 33% depending on the lubrication condition. The reduction of fatigue life in the range of 53 to 57% was also observed at different surface roughness conditions.
RCF 시험을 통한 KTX 윤축베어링의 분해 정비 주기 평가
심대섭 ( Dae Sop Sim ),허태현 ( Tae Hyeon Heo ),박영일 ( Young Il Park ),김홍석 ( Hong Seok Kim ),신기훈 ( Ki Hoon Shin ),정성균 ( Seong Kyun Cheong ) 한국안전학회(구 한국산업안전학회) 2016 한국안전학회지 Vol.31 No.1
KTX wheelset bearings have thus far been maintained in accordance with the maintenance system of French national railway company, SNCF. The overhaul cycle time (OCT) of KTX wheelset bearings is now 1.4 million km in mileage. This value, however, has not been validated in Korea that has much different railway environments with France. In fact, it is impossible to validate OCT of wheelset bearings directly because they are disassembled and cleaned only when some faults are detected. In this paper, the accuracy of the current OCT value was evaluated indirectly by investigating the effect of grease lubricants on the bearing life. Five grease samples (one new and four aged greases) were used in this study. Four aged greases of different conditions were obtained from four wheelset bearings whose mileages were about 0.3, 1.2, 1.3, and 1.8 million km, respectively. Each grease sample was then injected into the RCF (Rolling Contact Fatigue) tester and fatigue lifetime was experimentally estimated. In addition, the wt% of Fe in each grease sample was analysed. The experiment results reveal that the bearing lifetime is inversely proportional to the mileage of grease sample while the wt% of Fe increases with the mileage of grease sample. Based on the experimental results, it can be concluded that the current OCT value is appropriate for the first overhaul of wheelset bearings. However, further validation is required to determine the second and third OCT values.