Analysis of thin-slab casting by the compact-strip process: Part II. Effect of operating and design parameters on solidi
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6/5/04
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Analysis of Thin-Slab Casting by the Compact-Strip Process: Part II. Effect of Operating and Design Parameters on Solidification and Bulging J.E. CAMPORREDONDO S., F.A. ACOSTA G., A.H. CASTILLEJOS E., E.P. GUTIÉRREZ M., and R. GONZÁLEZ DE LA P. The mathematical model to compute the thermal evolution and solidification of thin slabs, previously presented in Part I of this article, was used in combination with a three-dimensional (3-D) finiteelement thermomechanical model to analyze how actual operation conditions can lead to excessive deflection and jamming of the slab shell at the pinch rolls. The models suggest that these phenomena arise from a sudden loss of control of the metallurgical length stemming from the coupling of inappropriate steel superheats and casting velocities to deficient heat-extraction conditions at the mold or secondary cooling system. The bulging deformation was calculated with an elastic and creep model that takes into account the temperature distribution across the shell thickness and the different times that shell elements have to creep exposure, i.e., according to the time that rows of elements require to reach their current position in the casting direction at a given casting speed. The last point was simulated by varying the duration of application of the ferrostatic load to the inside surface of each row of elements. The conditions forecast by the models as being responsible for excessive bulging agree very well with those present during the occurrence of these events in the plant. Since bulging after the last containment roll is a major limitation to productivity, this article also presents a parametric evaluation of the casting-speed limits that two compact-strip process (CSP) casters with different supported lengths may have as a function of steel superheat, mold heat-extraction level, water flow rate of the spray and air-mist nozzles, and slab thickness.
I.
INTRODUCTION
THE effectiveness or availability[1] (A) of a thin-slab continuous casting line can be defined as A
E(uptime) m M E(uptime downtime)
[1]
where m is the actual amount of slabs produced in a sufficiently long period of time, M is the maximum amount of slabs that can possibly be produced in the same time, E(uptime) is the expected amount of uptime, and E(uptime downtime) is the expected amount of uptime plus downtime of the machine. Clearly, to optimize production, one must try to approach the maximum possible production rate and minimize the expected amount of downtime. Production can be maximized by operating the machine at capacity, i.e., casting the largest possible section at the highest possible casting speed exempt of unprogrammed downtime. Casting managers and operators try to reduce the downtime by ensuring that the machine is stopped as infrequently as possible, besides for regularly scheduled maintenance. The maximum production rate and minimum downtime often conflict with each other, since high-speed operation may be associated with
J.E. CAMPORREDONDO S., Doctoral Stude
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