화학공학소재연구정보센터
홈 로그인 로그아웃 연락처 사이트맵
Korean Journal of Materials Research, Vol.10, No.10, 703-708, October, 2000
Export Citation
열팽창계수차에 기인된 잔류응력을 이용한 세라믹 캠 팔로우어의 크라우닝 제어
Control of Crowning Using Residual Stress induced by the Difference of Tehermal Expansion Between Ceramic and Carbon Steel in Ceramic Cam Follower
최영민, 이재도, 노광수1
  • 한국화학연구소 화학소재연구부
  • 1한국과학기술원 재료공학과
Youngmin Choi, Jaedo Lee, and Kwangsoo No1
  • Korea Research Institute of Chemical Technology, Taejon, 305-600 Korea
  • 1Korea Advanced Institute of Science and Technology, Tajon, 305-701, Korea
초록
최근에 상용차용 디젤 엔진의 성능 향상을 목적으로 엔진 설계가 급격히 변화되면서 캠 팔로우어(cam follower)와 캠(cam) 사이에 작용하는 접동면 하중의 증가로 접동면에서의 마모가 중요한 문제가 되고 있다. 본 연구에서는 기존의 주절체 및 소결합금 캠 팔로우어에 비해 내마모성이 우수한 세라믹 캠 팔로우어를 개발하였다. 잔류 응력을 완화시켜주는 중간층을 사용하지 않고 질화규소( Si 3 N 4 ) 팁과 중탄소강을 활성납재를 사용하여 직접 접합후 냉각시키는 과정에서 두 모재의 열팽창계수차에 의한 크라우닝(crowning, R) 이 형성되도록 하였다. 접합에 사용한 중탄소강은 열팽창시 이력(hysteresis) 거동을 나타내었으며, A c1 변태점인 723 ? C 이하에서 접합할 경우 원하는 크라우닝이 형성되었다. 접합온도가 723 ? C 이상이 되면 크라우닝 (R) 값이 온도에 따라 지수함수적으로 증가하였으며 이는 중탄소강의 상변태에 의한 열팽창.수축의 이력 특성으로 설명되어질 수 있었다. 규격에 맞는 크라우닝이 형성되는 최적 접합 온도는 700 720 ? C 의 범위였다. 질화규소와 중탄소강의 직접 접합방법으로 접합과 동시에 크라우닝을 형성시키고 제어함으로써 난가공재인 세라믹을 곡면 가공하지 않고도 적당한 곡률을 갖는 저가의 세라믹 캠 팔로우어를 제조할 수 있었다.
As the engine design changes to get high efficiency and performance of commercial diesel engine, surface w wear of the earn follower becomes an important issue as applied load increasing at the contact face between cam follower and cam. We developed the ceramic cam follower made of sili ∞ n nitride ceramic which was more wear resistant than the cast iron or sintered metal cam follower. Ceramic cam follower was made by direct brazing of thin ceramic disk to steel body using an active brazing alloy without the interlayer. In-situ crowning(R), resulted from the difference of thermal expansion coefficient between ceramic and carbon steel after direct brazing without any stress-relieving inter]ayer, could be controlled. When a earbon steel was heated above A c1 point and then c ∞ led, the expansion curve represented a hysteresis. Appropriate crowning was achieved below the A c1 point(about 723 ? C ) and crowning increased with brazing temperature exponentially above the A c1 point. Optimum brazing temperature range was from 700 to 720 ? C . We developed successfully the ceramic cam follower having appropriate crowning and being inexpensive. Also we could successfully control the crowning of ceramic earn follower by hysteresis behavior of thermal expansion of earbon steel during direct brazing process.
Keywords:Si 3 N 4;joining;ceramic cam follower;In-situ crowning;hysteresis behavior of thermal expansion
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