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Research Papers

A Calorimetric Method for Determination of Solid Fraction During Solidification in a Linear Electromagnetic Stirrer

[+] Author and Article Information
P. Kumar

 George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30318

H. Lakshmi

Department of Mechanical Engineering,  Indian Institute of Science, Bangalore 560012, India

P. Dutta1

Department of Mechanical Engineering,  Indian Institute of Science, Bangalore 560012, Indiapradip@mecheng.iisc.ernet.in

1

Corresponding author.

J. Thermal Sci. Eng. Appl 4(1), 011006 (Mar 19, 2012) (10 pages) doi:10.1115/1.4005195 History: Received May 17, 2011; Accepted September 23, 2011; Published March 09, 2012; Online March 19, 2012

In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process design parameters such as cooling rate and stirring intensity, and in estimating the total solidification time. In the present work, a new method for estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al–Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with nondendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Scheil’s equation.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of rheocasting apparatus

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Figure 2

Photograph of the rheocasting mould used for experiments

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Figure 3

Mould thermocouple locations

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Figure 4

Stump temperature variation with time

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Figure 5

Mould water inlet and outlet temperature variations with times

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Figure 6

Melt temperature variations with time

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Figure 7

SS tube surface temperature variations with time at different heights measured from the top surface

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Figure 8

Melt top surface temperature variation with time

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Figure 9

Cooling curves at 300 mm in the melt pertaining to different thermocouple locations (radial variation) obtained during rheocasting of A356 aluminum alloy (stirring current 250 A, water flow rate 20 lpm, melt pouring temperature 690 °C)

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Figure 10

Cooling curves pertaining to different thermocouple locations obtained during rheocasting of A356 aluminium alloy. (Stirring current: 250 A @ 50 Hz, mould coolant: water @ 20 lpm, melt pouring temperature: 690 °C)

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Figure 11

Temperature history at 300 mm in the melt obtained during rheocasting of A356 aluminum alloy. (Stirring current 250 A, water flow rate 20 lpm, melt pouring temperature: 690 °C.)

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Figure 12

Zoomed portion of the phase change segment of a cooling curve showing the error bar and the maximum error in temperature measurement

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Figure 13

Schematic representation of heat exchange process occurring in mould during rheocasting experiment

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Figure 14

Cooling curves at various depths in the mould without electromagnetic stirring (mould cooled by water @20 lpm, melt pouring temperature 690 °C)

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Figure 15

Effect of electromagnetic stirring on evolution of solid fraction in the melt (water cooled mould)

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Figure 16

Cooling curves pertaining to different thermocouple locations obtained during rheocasting of A356 aluminium alloy. (Stirring current: 250A @ 50 Hz, mould coolant: Air flow rate 100 lpm @ 4 bar, melt pouring temperature: 690 °C.)

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Figure 17

Cooling curves at various depths in the mould without electromagnetic stirring (mould cooled by air: air flow rate 100 lpm @ 4 bar, melt pouring temperature: 690 °C)

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Figure 18

Effect of cooling rate on evolution of solid fraction in the melt with and without EM stirring

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Figure 19

Comparison of evolution of solid fraction obtained by the present method and by using Scheil’s equation

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