Abstract
In the continuous-casting mold, the mold powder in contact with the liquid steel surface forms a liquid slag layer. The flow along the steel-slag interface generates shear stress at the interface, waves, and leads to fingerlike protrusions of liquid slag into steel. Reaching a critical flow velocity and thereby shear stress, the protrusions can disintegrate into slag droplets following the flow in the liquid steel pool. These entrained droplets can form finally nonmetallic inclusions in steel material, cause defects in the final product, and therefore, should be avoided. In the current work, the stability of a liquid-liquid interface without mass transfer between phases was investigated in cold model study using a single-roller driven flow in oil-water systems with various oil properties. Applying the similarity theory, two dimensionless numbers were identified, viz. capillary number Ca and the ratio of kinematic viscosities ν 1/ν 2, which are suitable to describe the force balance for the problem treated. The critical values of the dimensionless capillary number Ca* marking the start of lighter phase entrainment into the heavier fluid, are determined over a wide range of fluid properties. The dimensionless number ν 1/ν 2 was defined as the ratio of kinematic viscosities of the lighter phase ν 1 and heavier phase ν 2. The ratios of kinematic viscosities of different steel-slag systems were calculated using measured thermophysical properties. With the knowledge of thermophysical properties of steel-slag systems, Ca* for slag entrainment as a function of v 1/v 2 is derived. Assuming no reaction between the phases and no interfacial flow, slag entrainment should not occur under the usual casting conditions.
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Abbreviations
- 1:
-
lighter phase
- 2:
-
heavier phase
- m:
-
model
- c:
-
continuous-casting mold
- w:
-
water
- o:
-
silicone oil
- Fe:
-
liquid metal
- Sl:
-
liquid slag
- *:
-
critical condition
- Ca:
-
capillary number (dimensionless)
- d :
-
droplet diameter [mm]
- Fr:
-
froude number (dimensionless)
- f :
-
frequency (s−1)
- g :
-
force of gravity (m s−2)
- L :
-
characteristic length (m)
- Re:
-
reynolds number (dimensionless)
- u :
-
fluid velocity (m s−1)
- We:
-
weber number (dimensionless)
- α :
-
angular acceleration (rad s−2)
- η :
-
dynamic viscosity (kg m−1 s−1)
- θ :
-
angle (deg)
- ν :
-
kinematic viscosity (m−2 s−1)
- ν 1/ν 2 :
-
ratio of kinematic viscosities (dimensionless)
- λ :
-
scale factor (dimensionless)
- Π:
-
variable of dimensionless group
- ρ :
-
density (kg m−3)
- σ :
-
interfacial tension between model liquids/ steel-slag (mN m−1)
- ω :
-
angular velocity (rad s−1)
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Acknowledgment
The author would like to thank Prof. S. Seetharaman for the fruitful discussions in the last stage of article preparation and D. Ryabov for performing the PIV measurements. This research was supported by the DFG (German Research Foundation) research funding organization under project No.: SCHE675/10 and SCHW1168/2. This is gratefully acknowledged.
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Manuscript submitted December 19, 2011.
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Hagemann, R., Schwarze, R., Heller, H.P. et al. Model Investigations on the Stability of the Steel-Slag Interface in Continuous-Casting Process. Metall Mater Trans B 44, 80–90 (2013). https://doi.org/10.1007/s11663-012-9749-9
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DOI: https://doi.org/10.1007/s11663-012-9749-9