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Research Papers: Multiphase Flows

Isothermal Modeling of Meniscus Oscillation in the Continuous Strip Casting Process

[+] Author and Article Information
Kevin W. Wilcox1

Department of Mechanical Engineering,  University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canadak.wwilcox@unb.ca

A. Gordon L. Holloway

Department of Mechanical Engineering,  University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canadaholloway@unb.ca

Andrew G. Gerber

Department of Mechanical Engineering,  University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canadaagerber@unb.ca

1

Corresponding author.

J. Fluids Eng 133(12), 121304 (Dec 23, 2011) (13 pages) doi:10.1115/1.4005426 History: Received July 20, 2010; Revised October 25, 2011; Published December 23, 2011; Online December 23, 2011

In the continuous strip casting process a meniscus forms a compliant boundary between the casting nozzle and transporting conveyor. Movement of this meniscus during casting has been shown to create surface defects, which require extensive cold work to remove and limit the minimum thickness for which sections may be cast. This paper discusses experimental work conducted to test an analytical model of the meniscus oscillation. A high frame rate shadowgraph technique was used on an isothermal water model of the casting process to observe meniscus motion, and thus allow the calculation of meniscus frequency, amplitude, contact points and contact angles. Both natural frequency and flow excited tests were conducted. Natural frequency tests were also conducted using mercury which has a nonwetting contact angle typical of molten metals. The experimental results were found to be in good agreement with the predictions of theory for both wetting and nonwetting conditions. The experimentally verified analytical model for meniscus motion is valuable to the design of a continuous casting process because it describes the effect of geometrical parameters on meniscus motion and thus provides an opportunity to mitigate the effects of boundary motion on surface quality.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Geometry of the strip casting process showing the aluminum-air meniscus which forms between the casting nozzle exit and transporting conveyor

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Figure 2

Position of the meniscus between the casting nozzle exit and the moving conveyor. The upper meniscus edge may attach to the step edge or recess as shown.

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Figure 3

Meniscus motion when the contact line is fixed and curvature change is accommodated by a change in contact angle. Exaggerated for clarity.

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Figure 4

Meniscus motion when the contact angle is fixed and curvature change is accommodated by a change in contact line. Exaggerated for clarity.

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Figure 5

Meniscus stiffness as a function of dimensionless head, η, and contact angle, φ, for the fixed contact line case. β = 20°.

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Figure 6

Meniscus stiffness as a function of dimensionless head, η, and contact angle, φ, for the fixed contact angle case. β = 20°.

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Figure 7

Meniscus stiffness, which is determined by the contact angle for the recessed cases. Experimental stiffness values should fall between the two limits.

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Figure 8

Integral of squared velocity, ∫V2dV̶, and average channel velocity, V¯22, calculated from CFD simulations over one meniscus oscillation. Results are for the h2  = 20.2 mm, L = 90 mm water case.

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Figure 9

Effective channel slenderness calculated from Eq. 5 using the CFD results in Fig. 8. Results correspond to the h2  = 20.2 mm, L = 90 mm water case. The dashed line is the average effective channel slenderness, which is calculated by weighting the effective channel slenderness at each time step by the fluid energy per unit mass, ∫V2dV̶.

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Figure 10

The expected shape of the aluminum-air meniscus in the caster is compared to a water-air and mercury-air meniscus to be used in the experimental model. Note that the mercury meniscus has been inverted for the sake of comparison.

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Figure 11

Experimental model for natural frequency tests. The dashed region indicates the location of the backward facing step and meniscus. Not to scale.

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Figure 12

Experimental model for flow excited testing. The model is the same as that for the natural frequency tests with the addition of the flow circuit. Not to scale.

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Figure 13

Region of interest in the experimental model. The dashed region specifies the control area where movement of the meniscus under the step causes a change in the control area size with a change of meniscus radius.

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Figure 14

Water-air meniscus underneath the step during a natural frequency test. The step height is 3.5 mm.

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Figure 15

Response from a typical natural frequency test using water, plotting the area behind the meniscus, Acv

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Figure 16

Side view of the meniscus during one cycle of a natural frequency test. With the exception of the near wall regions, the meniscus is two dimensional. Comparison of frames shows that the meniscus moves in unison with no observable three dimensional modes. Time zero is an arbitrary time set to the beginning of the cycle.

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Figure 17

Contact angle and contact line motion along the wall for the typical natural frequency test with water shown in Fig. 1

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Figure 18

Measured values of natural frequency for water with four different channel heights h2 . Theoretical results are calculated from Eqs. 14,15 using M = 0.73.

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Figure 19

Measured values of natural frequency for mercury with three different channel heights h2 . Theoretical results are calculated from Eqs. 14,15 using M = 0.34.

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Figure 20

Power spectral density (PSD) of the time series of the area behind the meniscus, Acv for all flow tests. Amplitude uncertainty is approximately 11% of nominal amplitude, frequency bin resolution is 0.013 Hz.

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Figure 21

Channel flow energy due to meniscus oscillations

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Figure 22

PDF of the average channel velocity fluctuations derived from Eq. 16

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