PIV and MFC measurements in a
continuous caster mould. New tools
to penetrate the caster black box
P.H. Dauby, M.B. Assar, G.D. Lawson
(LTV Steel, USA)
Objectives
Four objectives are presented in this paper :
– defect samples were analyzed using Scanning
Electron Microscopy to confirm the steelmaking ori-
gin of the defects observed (defective coils were re-
inspected at slow speed).
–
–
–
–
determine to what extent water models reflect actual
casting operations ;
Conclusions
determine the predictability of the steel flow in the
caster moulds ;
•
Water model (PIV data) and actual mould results
(MFC data) are only identical in zero-gas casting condi-
determine to what extent steel flow pattern and velo-
city affect slab quality ;
tions, making it difficult to use water modelling for cas-
ter operation optimization.
identify the main parameters/ countermeasures that
impact slab/coil quality.
• Steel flow in the mould is highly turbulent.
Experiments
• Parameters such as casting speed, argon flow, slab
width and SEN depth significantly affect steel meniscus
velocity and flow pattern (single or double roll).
The two technologies that were investigated during this
research programme are Particle Image Velocimetry
(
PIV) and Mould Flow Control (MFC) :
•
High argon flows (particularly at slow speeds) and
–
PIV is a powerful laser-based technology that was
used on the LTV 0.4 and full-scale water models to
determine water velocities in various simulations of
casting conditions ;
transitory casting conditions such as SEN clogging,
casting speed changes and tundish changes have a great
impact on flow stability.
•
It typically takes two to four minutes following a cas-
–
MFC sensors are magnetic sensors that were installed
on the LTV Cleveland-East 2-strand slab caster to
measure actual liquid steel velocities.
ting speed change for the steel velocities to stabilize at
the new level. After a tundish fly, it may take up to fifteen
minutes for the steel flow to re-stabilize.
In addition, nail boards, X-ray and SEM analyses were
extensively used :
• Steel quality (slivers and pencil pipe) is related to flow
pattern and flow stability, two items that are not directly
predictable from the usual quality event alarms.
–
nail boards (steel/aluminum nails inserted into the
liquid steel) were used to determine steel meniscus
profiles and mould powder/molten slag layer thick-
nesses during casting ;
•
Overall steel quality improvement requires low gas
flow rates and steady casting conditions, making argon
reduction and clogging elimination the primary goals of
any optimization programme.
–
X-ray analysis was used to determine gas bubble/
pinhole locations/densities in as-cast slabs ;
–
–
–
déterminer s'il est possible de prédire les mouvements de
l'acier en lingotière à partir des conditions de coulée ;
l'eau ainsi que des bulles de gaz qu'elle peut contenir. Les
vecteurs de vitesses ainsi déterminés sont ensuite utilisés
pour construire les trajectoires suivies par l'eau et les bulles
de gaz.
déterminer dans quelle mesure les mouvements de l'acier
affectent la qualité du produit fini ;
déterminer quels paramètres et conditions de coulée sont
favorables à l'amélioration de la qualité des brames et des
bobines.
La figure 1 schématise les deux types de trajectoire habi-
tuellement observés. Dans la trajectoire de type « double-
roll », l'eau (ou l'acier) heurte d'abord les petites faces de la
lingotière et se divise ensuite en deux boucles. Il en résulte
qu'en surface de lingotière les vecteurs vitesses sont dirigés
depuis les petites faces vers la busette immergée (SEN).
Dans la trajectoire de type « single-roll », l'eau (ou l'acier)
monte d'abord vers le ménisque et les vecteurs vitesses au
ménisque sont alors dirigés de la busette vers les petites
Mesures PIV (laser) sur maquettes
Dans la technique PIV, un laser combiné à une caméra rapide
(30 vues par seconde) est utilisé pour mesurer la vitesse de
354
La Revue de Métallurgie-CIT
Avril 2001