Numerical Simulation and Cold Modeling experiments on Centrifugal Casting
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in a centrifugal casting system, and understanding the complex flow process is a must for the production of defect-free castings. In the real-life casting process, it is impossible to study the fluid behavior because of the opaque nature of melt and mold. Therefore, the numerical simulation of the process is a better alternative to understand the physics and to carry out a parametric study on the effects of different operating parameters of the process. The analysis also allows an easy and quick assessment of optimization of the rotational speed for centrifugal casting. This article focuses on the numerical simulation of fluid flow in centrifugal casting process to estimate the optimum speed required to produce a defect-free hollow cylindrical casting. The melt poured initially into the mold has low viscosity, and as the molten metal cools, its viscosity increases and the melt tends to lift along the rotating cylindrical surface. At the same time, KESTUR SADASHIVAIAH KEERTHIPRASAD, Assistant Professor, and PUDUKOTTAH GOPALIENGAR MUKUNDA and SEKHAR MAJUMDAR, Professors, are with the Department of Mechanical Engineering, Nitte Meenakshi Institute of Technology (NMIT), Bangalore 560064, Karnataka, India. Contact e-mail: [email protected] MYSORE SEETHARAM MURALI, Professor, is with the Department of Mechanical Engineering, Rashtriya Vidyalaya College of Engineering (RVCE), Bangalore 560079, India. Manuscript submitted January 27, 2010. Article published online December 7, 2010. 144—VOLUME 42B, FEBRUARY 2011
it has a tendency to fall off the mold top until the mold attains a critical rotational speed. During this process, the melt cools and solidifies on the inner surface of the mold and simultaneously the melt, with enhanced viscosity, is picked up along with the mold wall to form a hollow cylinder. The feature involved during these processes is fluid flow; therefore, it is to study fluid flow to understand the parameters that influence the centrifugal casting process. Another important factor that affects the centrifugal casting process is the rotational speed of the mold. On the one hand, excessive speed of rotation produces a high tensile stress in the outer periphery of the casting which eventually results in longitudinal cracks.[1] Furthermore, high rotational speeds can even cause the mold itself to fail. On the other hand, low speed of rotation leads to defective formation of the cylinder. Determination of the optimum (critical) speed is, therefore, crucial to ensure a defect-free product using centrifugal casting. When the mold rotates, it is an usual practice to talk in terms of ‘‘G’’ or the number of times gravity force to which casting or melt is subjected from the rotation of the mold (G = centrifugal force/gravitational force). A rich variety of flow patterns has been observed within a rotating cylinder partially filled with a particlefree liquid that, beyond a critical rotational speed, completely coats the cylinder surface.[2–4] An analytical description of the fluid flow in a partially filled cylinder rotating at or
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