항공용 고속 롤러베어링의 냉각 방식에 따른 작동간극 변화

박지수 한국트라이볼로지학회 2023 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.39 No.4

In this study, the expansion, stress, and operating clearance of bearing elements during operation are observed using the inner/outer ring temperature test data of a 3.0×106 DN-class roller bearing. The operating clearance characteristics of inner-/outer-ring cooling (IORC) bearings are compared to those of inner-ring cooling (IRC) bearings. For IRC bearings, the thermal expansion of the outer ring is the most important factor in clearance variation. As a result, the operating clearance is less than the initial clearance of 61 μm, and the operating clearance decreases to 0.5 μm at 25,500 rpm. Conversely, the temperature of the outer ring of IORC bearings is lower than that of IRC bearings, so the operating clearance is kept smaller. When the coolant flow rate to the outer ring is approximately 1.5 to 2.0 L/min, the temperature difference between the inner and outer rings is minimized and the operating clearance is maintained at a significantly lower level than IRC bearings. Small operating clearances are expected to be effective in reducing cage slip and skid damage in roller bearings. The results and analysis procedures of this study can be utilized to design of bearing clearance, lubricant flow rate, and assembled interference in the early design stage of aerospace roller bearings.

볼 베어링의 구름 요소 주위 유동 특성에 대한 해석

조준현(Jun Hyeon Jo),김충현(Choong Hyun Kim) 한국트라이볼로지학회 2012 한국윤활학회지(윤활학회지) Vol.28 No.6

Various bearings such as deep-groove ball bearings, angular-contact ball bearings, and roller bearings are used to support the load and to lubricate between the shaft and the housing. The bearings of potential rolling systems in a turbo pump are the deep-groove ball bearings as comparing with the bearings with rolling elements such as cylindrical rollers, tapered cylindrical rollers, and needle rollers. The deep-groove ball bearings consist of rolling elements, an inner raceway, an outer raceway and a retainer that maintain separation and help to lubricate the rolling element that is rotating in the raceways. In the case of water-lubricated ball bearings, however, fluid friction between the ball and raceways is affected by the entry direction of flow, rotation speed, and flow rate. In addition, this friction is the key factor affecting the bearing life cycles and reliability. In this paper, the characteristics of flow conditions corresponding to a deep-groove ball bearing are investigated numerically, with particular focus on the friction distribution on the rolling element, in order to extend the analysis to the area that experiences solid friction. A simple analysis model of fluid flow inside the water-lubricated ball bearing is analyzed with CFD, and the flow characteristics at high rotation speeds are presented.

일회성 터보엔진용 구름 베어링의 저장 수명 예측에 관한 연구

김선제,김동민,홍순호,민성기 한국추진공학회 2022 한국추진공학회지 Vol.26 No.6

Operational reliability of the single-use turbo engine for guided weapons must be guaranteed even after long-term storage. Rolling element bearings have a great influence on the operational reliability of the turbo engine, however changes in micro dimensions of bearings by an oxide layers on rolling elements and raceways may cause failures after long-term storage. In this study, changes in dimensions of bearings were measured and roughness of rolling elements was used for estimating the storage life. Storage life estimation was performed via two kinds of methods, Weibayes method and random sample generation method. The results of two methods were compared and their characteristics were analyzed. This study will contribute to establish an efficient maintenance schedule for the single-use turbo engine. 유도무기용 일회성 터보엔진은 장기간 저장 후에도 운용 신뢰성이 보장되어야 한다. 터보엔진의 운용 신뢰성에 큰 영향을 미치는 구름 베어링은 장시간 저장에 의해 궤도면 및 전동체에 산화층이 형성될 수 있으며, 이로 인해 미세 치수의 변화를 유발하여 고장이 발생할 수 있다. 본 연구에서는 실제 장기 저장된 일회성 터보엔진 베어링을 획득하고, 전동체 조도의 열화 데이터를 이용하여 저장 수명을 예측하였다. 저장 수명은 와이베이즈(Weibayes) 분석 방법과 선형 열화식의 계수를 난수로 생성하는 난수 생성 기반 분석 기법을 통해서 예측하였다. 본 연구에서는 두 가지 수명평가 방법의 결과를 상호 비교하고 이에 따른 장단점을 분석하였다. 향후, 추가적인 장기저장 시편을 확보하고, 명확한 고장 조도 기준을 수립하면 베어링의 저장 수명 예측정확도를 높일 수 있을 것이며, 터보엔진의 효율적인 정비 주기 설정에 기여할 수 있을 것이다.

소형 고속 구름베어링의 연료윤활 특성 연구

김기태(Kitae Kim),김성균(Sungkyun Kim) 한국추진공학회 2008 한국추진공학회 학술대회논문집 Vol.2008 No.11

초소형 가스터빈에 사용되는 소형 고속 구름베어링의 연료윤활 특성을 실험적으로 조사하였다. 윤활유로는 항공용 가스터빈에서 사용되는 MIL-PRF-7808 터빈오일과 항공용 가스터빈의 추진연료로 사용되는 JP-8 연료를 사용하여 운용특성을 비교하였고, 시험용 베어링으로는 내경 17 mm의 깊은 홈(deep groove) ball bearing과 내경 20 mm의 원통형(cylindrical) roller bearing을 사용하였다. 베어링의 연료윤활에 따른 특성을 비교하기 위하여 오일 및 연료를 공급하며 고속베어링 시험을 수행할 수 있는 시험 장치를 개발하여 하중, 냉각공기 온도, 윤활유량 및 회전속도를 변화시키면서 시험을 수행하였다. 30,000 rpm에서 70,000 rpm까지 회전속도를 변화시키면서 시험한 결과 깊은 홈 볼베어링은 축하중과 회전속도가 증가하는 경우 베어링 케이지에 마모가 발생하였으며 마모상태는 오일윤활보다 연료윤활시 마모가 더 많이 발생하였고 본 베어링의 속도한계인 59,000 rpm까지는 연료윤활로 운용이 가능하다는 것을 확인할 수 있었다. 연료윤활의 경우가 오일윤활의 경우보다 베어링 온도가 더 낮은 것을 알 수 있었는데 이는 베어링의 냉각특성이 연료윤활인 경우가 오일윤활의 경우 보다 더 좋기 때문이라 판단된다. 본 실험을 통하여 소형 항공용 가스터빈의 주축 베어링 윤활방식으로 연료윤활 방식이 적용 가능함을 확인할 수 있었다. A parametric study was carried out to find the fuel lubrication performance of high speed small rolling element bearings. Both MIL-PRF-7808 turbine oil and JP-8 aircraft fuel were used as the lubricant to compare the operational characteristics. 17 mm inner diameter deep groove ball bearing and 20 mm cylindrical roller bearing were used. A high speed bearing test rig was developed and the testing was done with varying applied load, cooling air temperature, lubricant flow rate, and speed. Fuel caused more cage wear than oil for ball bearing with increasing axial load and rotational speed. The bearing temperature using fuel was lower than that using oil, and this seems to be the result of the high cooling capacity of fuel. According to various tests, the fuel lubrication is applicable for the lubrication on the main shaft bearings of expendable small gas turbines.

웨이블릿 변환이 접목된 포락처리를 이용한 구름요소베어링 결함 진단

김병수(Byeong-Su Kim),김원철(Won-Cheol Kim),김영찬(Young-Chan Kim),구동식(Dong-Sik Gu),김재구(Jae-Gu Kim),최병근(Byeong-Keun Choi) 한국마린엔지니어링학회 2009 한국마린엔지니어링학회 학술대회 논문집 Vol.2009 No.-

Acoustic Emission (AE) technique is a non-destructive testing method and is widely used for the early detection of faults in rotating machines in these days, because the sensitivity of AE transducers is higher than normal accelerometers. So it can detect low energy vibration signals. The faults in the rotating machines are generally occurred at bearings and/or gearboxes which are the principal parts of the machines. To detect the bearing faults, envelope analysis was studied and presented for several decade years. And the researches showed that AE had a possibility of the application in condition monitoring system(CMS) using the envelope analysis for the rolling element bearing. And peak ratio (PR) was developed for expression of the bearing condition in condition monitoring system using AE. Noise level is needed to reduce to take exact PR value because the PR is calculated from total root mean square (RMS) and the harmonics peak levels of the defect frequencies of the bearing. Therefore, in this paper, the discrete wavelet transform (DWT) was added in the envelope analysis to reduce the noise level in the AE signals. And then, the PR was calculated and compared with general envelope analysis result and the result of envelope analysis added the DWT.

동적 응답 기반 합성곱 신경망 모델의 구름 베어링 스폴 결함 분류 및 물리적 궤적 특성 시각화

황미경(Mikyung Hwang),최민석(Minseok Choi),오현석(Hyunseok Oh) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

In this paper, the spall defect caused by fatigue, which is the main cause of failure, was applied as a direct feature for rolling element bearing condition monitoring. The various signal processing methods are used for the spall size estimation. However, in order to extract the physical trajectory of the spall defect, a filtering method for removing a background noise and interference is required, which required expert-based theory and domain knowledge. Therefore, to overcome this limitation, convolutional neural network structure was applied. A physics-based artificial intelligence model that reflects the text data of load and rotational speed is proposed in the deep learning model. Classification performance was verified for five conditions with different entry-exit angle of the defect bearing. In addition, we provided an explanation for the existing classical method by class activation map to visualize a specific frequency band and the time at which rolling element passes through the defect.

상용 해석 소프트웨어 간 구름베어링 성능 예측 결과 비교

Robert Taylor,김동현(Donghyun Kim) 한국추진공학회 2022 한국추진공학회 학술대회논문집 Vol.2022 No.5

다양한 속도 조건 하에서 진동센서와 음향방출센서의 구름 베어링 고장 진단 성능 비교

김수지(Su J. Kim),윤병동(Byeng D. Youn) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

Rolling element bearing is essential mechanical components in the operation of the rotating system. The failure of the rolling element bearing leads to a stop of the entire rotating system. Therefore, there have been many researches to monitor and diagnose the condition of bearings. In the process of condition monitoring, the rotational speed of the bearings is one of the most important operating conditions. As the speed of rotation decreases, the energy and dynamic characteristics generated by the bearing are weakened. This makes it difficult to apply the conventional diagnosis techniques using the shaft rotation frequency and bearing characteristic frequency. In this case, it is common attempt to use acoustic emission sensors instead of accelerometer for low-speed bearing condition monitoring. In this research, we compare the diagnostic performance of vibration and acoustic emission sensors under various RPM conditions. High-Frequency Resonance Technique (HFRT), which is the most representative method to diagnose bearing failure using vibration signal, are used. Also, the diagnostic parameters for acoustic emission sensored signal are extracted from the raw signal by using several signal processing techniques. Through this study, we could suggest a guide for diagnostic transducer selection under various rotational speed.

가스터빈용 고속 롤러 베어링의 내/외륜 냉각 방식에 따른 작동틈새 분석

박지수(Jisu Park),김동현(Donghyun Kim),유경원(Gyongwon Ryu) 한국유체기계학회 2022 한국유체기계학회 학술대회 논문집 Vol.2022 No.11

개선된 DET 기반 효과적인 결함 특징을 이용한 고 신뢰성 저속 구름 베어링 결함 검출

정인규,강명수,최병근,김종면 한국차세대컴퓨팅학회 2014 한국차세대컴퓨팅학회 논문지 Vol.10 No.3

본 논문에서는 저속으로 동작하는 구름 베어링의 다중 결함 조기 검출을 위해 결함 특징 추출, 효과적인 특징 선택, 선택된 특징을 이용한 결함 분류의 세 단계로 구성된 결함 진단 기법을 제안한다. 1단계에서 이산 웨이블릿 변환을 이용하여 미세성분으로부터 통계적 결함 특징을 추출하고, 개선된 DET(distance evaluation technique)를 이용 하여 추출한 결함 특징 가운데 베어링 다중 결함 검출에 효과적인 특징을 선택한다. 마지막으로 선택된 특징을 인공 신경망 회로의 일종인 SFAM(simplified fuzzy artmap)의 입력으로 사용함으로써 결함을 진단한다. 본 논문에 서는 제안한 결함 진단 기법의 성능을 분류 정확도 측면에서 평가하며 종래의 DET를 이용한 특징을 선택한 결과와 그 성능을 비교함으로써 제안한 기법의 성능 우위를 검증한다. 실험 결과 개선한 DET에 의해 선택된 결함 특징을 이용할 경우 분류 정확도가 97.36%로 종래의 DET에 의해 선택된 특징을 사용한 분류 정확도(62.08% ~ 95.13%)보다 높은 것을 확인할 수 있었다.