Determination of the Heat Transfer Coefficient at the Metal-Mold Interface During Centrifugal Casting
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HORIZONTAL centrifugal casting is currently one of the most important processes in the industrial production of steel and cast iron tubes. In this process, the molten alloy is poured into a rotating cylindrical mold and is thrown against the internal wall by a centrifugal inertial force that is much larger than the gravitational force.[1] This force causes a pressure gradient in the radial direction, parallel to the heat flux, helping flotation of impurities, and feeding of solidification contraction, eventually improving the metallurgical quality of the casting.[2] Because of rotation, experimental thermal analysis of the centrifugal casting process is more difficult than that of static processes, increasing the importance of the mathematical modeling of heat transfer as an alternative tool. However, to construct useful and realistic heat transfer models, the heat flux at the contact interface between the cast tubes and the cylindrical molds must be known accurately. This heat flux can be defined in terms
SANTIAGO VACCA, Mechanical Engineer, and MARCELO A. MARTORANO, Associate Professor, are with the Department of Metallurgical and Materials Engineering, University of Sa˜o Paulo, Av. Prof. Mello Moraes, 2463, Sa˜o Paulo, SP 05508-900 Brazil. Contact e-mail: [email protected] ROMULO HERINGER, Professor, is with the Department of Materials Engineering, Federal University of Paraiba, Campus Universitario, Joa˜o Pessoa, PB 58051-900 Brazil. MA`RIO BOCCALINI Jr., Researcher, is with the Center for Metallurgical and Materials Technologies, Institute for Technological Research – IPT, Av. Prof. Almeida Prado, 532, Sa˜o Paulo, SP 05508901, Brazil. Manuscript submitted July 12, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
of a heat transfer coefficient, hMM, which depends on several parameters, such as the thickness and the material of the coating on the internal mold wall, and the thickness of the air gap that forms at the metal-mold interface owing to the tube contraction. Values of hMM adopted in centrifugal casting simulations are unreliable and usually arbitrary. Ebisu[3] and Yang et al.[4] assumed an exponential decay for the radiation heat flux at the metal-mold interface. Martinez et al.,[5] Gao and Wang,[6] Kang et al.,[7] Kang and Rohatgi,[8] and Chang et al.[9] adopted constant arbitrary values of hMM, while Raju and Mehrotra,[10] Drenchev et al.,[11] Nastac et al.,[12] and Panda et al.[13] assumed that hMM decreased with time according to an arbitrary equation. Xu et al.[14] assumed perfect contact at the metal-mold interface and Humphreys et al.[15] calculated the heat flux at this interface using thermal resistances, but did not provide the parameters to calculate them. In Table I, the values of hMM adopted by these authors are summarized. In addition to unreliable hMM values, important effects were neglected in some of these models. As examples, in the centrifugal casting of tubes, calculation of the heat loss from the tube inner surface was neglected or oversimplified[3,5–8,12] and the mushy zone was approxim
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