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전선이중피복용 동심압출 die내의 고분자 물질의 이동현상에 관한 유변학적 해석
Rheological Analysis of Polymeric Met Flow in a Coextrusion Wire Coating Die
HWAHAK KONGHAK, December 1990, 28(6), 637-643(7), NONE
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Abstract
LDPE와 PS를 피복물질로 사용하는 전선이중피복 공정에서 동심압출 전선피복 die내에서의 고분자 물질의 유동현상을 Newtonian fluid model과 Carreau model을 사용하여 유한요소법으로 수치해석하였다. 피복물질의 상대적 위치의 바뀜과 조업조건의 변화가 유동장에 미치는 효과를 조사하였으며 고분자 물질의 점성분산에 의한 온도상승을 고려하기 위해서 비등온 해석을 수행하였다. 계면의 위치는 점도가 작은 LDPE가 외층 피복물질로 쓰였을 경우에 die의 외벽 쪽으로 더 접근함을 알 수 있었으며, die내의 전체 압력강하는 점도가 큰 PS가 외층을 이룰 때가 LDPE가 외층을 이루는 경우보다 2배 정도 컸으며 각각 전선속도의 0.40, 0.45승에 비례하여 증가하였다. Die내에서의 최고온도 상승은 충격점 부근의 전선표면에서 생겼으며 이는 전선속도가 증가할수록, 점도가 큰 물질이 전선과 접촉하고 있을수록 더 큰 값을 보였다.
This study is to analyze the flow behavior of Newtonian and Carreau model fluids in a coextrusion wire coating die by finite element method. The effects of the change of the relative position of the coating materials and the operating conditions on the flow fields and investigated. A nonisothermal analysis is also carried out to take into ac-count the temperature rise due to viscous dissipation. The interface is positioned closer to the outer die wall when the lower viscous component forms the outer layer. The total pressure drop for the PS/LDPE system is nearly twice as large as that of the LDPE/PS system at the same wire velocity. The wall shear stress increases as the wire velocity increases and the PS/LDPE system has the larger value than the LDPE/PS system for both isothermal and nonisothermal condi-tions. The maximum temperature and the die exit temperature increase as the wire velocity increases. And the tem-perature rise due to viscous dissipation of molten polymer is higher when the higher viscous component forms the in-ner layer.
References
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Han CD, Shetty R, Polym. Eng. Sci., 16, 697 (1976)
Han CD, Rao D, Polym. Eng. Sci., 20, 128 (1980)
Basu S, Polym. Eng. Sci., 21, 1128 (1981)
Caswell B, Tanner RI, Polym. Eng. Sci., 18, 416 (1978)
Mitsoulis E, Polym. Eng. Sci., 26, 171 (1986)
Kim DP, M.S. Dissertation, Seoul National Univ., Seoul, Korea (1987)
Bird RB, Amstrong RC, Hassager O, "Dynamics of Polymeric Liquids," 2nd ed., Vol. 1, John Wiley, New York (1987)
Christie I, Griffiths DF, Mitchell AR, Zienkiewicz OC, Int. J. Numer. Methods Eng., 10, 199 (1982)
Gallaghter RH, Zienkiewicz OC, Oden JT, Cecchi MM, Taylor C, "Finite Elements in Fluids," Vol. 3, Wiley, Chichester, England (1978)
