Abstract
An accurate thermofluids model of aluminum direct-chill (DC) casting must solve the heat-transfer equations in the ingot with realistic external boundary conditions. These boundary conditions are typically separated into two zones: primary cooling, which occurs inside the water-cooled mold, and secondary cooling, where a film of water contacts the ingot surface directly. Here, a simple model for the primary cooling boundary condition of the steady-state DC casting process was developed. First, the water-cooled mold was modeled using a commercial computational fluid dynamics (CFD) package, and its effective heat-transfer coefficient was determined. To predict the air-gap formation between the ingot and mold and to predict its effect on the primary cooling, a simple density-based shrinkage model of the solidifying shell was developed and compared with a more complex three-dimensional (3-D) thermoelastic model. DC casting simulations using these two models were performed for AA3003 and AA4045 aluminum alloys at two different casting speeds. A series of experiments was also performed using a laboratory-scale rectangular DC caster to measure the thermal history and sump shape of the DC cast ingots. Comparisons between the simulations and experimental results suggested that both models provide good agreement for the liquid sump profiles and the temperature distributions within the ingot. The density-based shrinkage model, however, is significantly easier to implement in a CFD code and is more computationally efficient.
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Abbreviations
- A, B, C, D :
-
thermoelastic model coefficients
- C f :
-
empirical coefficient for nucleate boiling
- C p :
-
specific heat at constant pressure
- E :
-
Young’s modulus
- f :
-
mass fraction
- g :
-
gravitational acceleration
- H :
-
enthalpy
- H fg :
-
latent heat of evaporation
- h :
-
heat-transfer coefficient
- K :
-
conductivity
- K 0 :
-
permeability coefficient
- K μ :
-
permeability of mushy zone
- L :
-
ingot cross section length
- \( \hat{n} \) :
-
unit normal vector at solid phase
- p :
-
pressure
- q :
-
heat flux
- Q ′ :
-
water flow rate per unit perimeter
- T :
-
temperature
- u :
-
velocity
- W :
-
ingot cross section width
- α :
-
thermal expansion coefficient of solid phase
- β :
-
thermal expansion coefficient of liquid phase
- γ :
-
surface tension
- Γ:
-
water flow rate
- δ :
-
cooling-induced shrinkage
- \(\epsilon\) :
-
strain tensor
- μ:
-
viscosity
- ν :
-
Poisson’s ratio
- ρ :
-
density
- σ :
-
stress tensor
- air:
-
air
- boil:
-
boiling
- coh:
-
coherency
- cont:
-
contact
- conv:
-
convective
- disp:
-
displacement
- eff:
-
effective
- ext:
-
external
- gap:
-
air gap
- in:
-
inlet
- incip:
-
incipient boiling
- l:
-
liquid phase
- liq:
-
liquidus
- lubr:
-
lubricating film
- mold:
-
mold inner wall
- ref:
-
reference value
- s:
-
solid phase
- sat:
-
water saturation point
- sol:
-
solidus
- surf:
-
ingot surface
- wat:
-
water
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Acknowledgments
The authors acknowledge the financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC), Novelis Global Technology Centre (NGTC), Ontario Centres of Excellence (OCE), and Emerging Materials Knowledge (EMK).
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Manuscript submitted May 14, 2011.
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Baserinia, A.R., Ng, H., Weckman, D.C. et al. A Simple Model of the Mold Boundary Condition in Direct-Chill (DC) Casting of Aluminum Alloys. Metall Mater Trans B 43, 887–901 (2012). https://doi.org/10.1007/s11663-012-9658-y
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DOI: https://doi.org/10.1007/s11663-012-9658-y