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, previ- ously presented in Part I of this article, was used in combination with a three-dimensional (3-D) finite- element 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 phenom- ena 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 para- metric evaluation of the casting-speed limits that two compact-strip process (CSP) casters with dif- ferent 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 [1] where m is the actual amount of slabs produced in a suffi- ciently 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 min- imize 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 pro- duction rate and minimum downtime often conflict with each other, since high-speed operation may be associated with A = m M = E(uptime) E(uptime + downtime) faster, unexpected, and unrecoverable loss of control of the process, which may lead to machine stoppage and downtime. Any action that can demonstrate the capability of reducing the frequency of stoppage/downtime events in the plant is certain to receive much attention from plant personnel. Unplanned line stoppages are clearly deleterious, as they typically involve significant machine downtime and expen- diture of resources, as one must dislodge the troubled slab and ready the machine to resume operation. There are a num- ber of reasons why the operation of a continuous casting machine may halt. Two common situations include break- outs and bulging. This article is concerned with understanding how the second phenomenon may result in the formation of a “whale” that plugs the slab at the pinch rolls during the compact strip processing of thin slabs. As shown by the results reported on Part I of this article, [2] high temperatures and large temperature gradients exist across the thickness of the continuously cast shell. Specifically, [2] through most of its travel down the caster, the outside shell temperature fluc- tuates around 1000 °C and, before the completion of solidi- fication, the shell exhibits a temperature gradient of the order of 20 °C/mm. Solidified steel subjected to these extreme conditions is very soft and deforms easily even under slight stressing when unproperly contained by rolls, either because they are excessively separated or are misaligned. Bulging is the unconstrained swelling and sagging of a continuously cast product, which results in the loss of align- ment of the strand with the roll gap. For slab casting, if the misfit between the bulged slab and the roll gap is severe enough, the slab is unable to continue its motion and becomes stuck between rolls, leading to a line stoppage. The problem is common enough that thermal models have been used to METALLURGICAL AND MATERIALS TRANSACTIONS B VOLUME 35B, JUNE 2004—561 J.E. CAMPORREDONDO S., Doctoral Student, F.A. ACOSTA G., Associate Professor, and A.H. CASTILLEJOS E., Professor, are with the CINVESTAV-Unidad Saltillo, Saltillo, 25000, Coahuila, Mexico. Contact e-mail: hcastill@saltillo.cinvestav.mx E.P. GUTIÉRREZ M., Clinical Asso- ciate Professor, is with Rensselaer at Hartford, Hartford, CT 06120-2991. R. GONZÁLEZ DE LA P., General Manager Steelmaking and Rolling Works, is with HYLSA, S.A. de C.V., San Nicolas, N.L., México. Manuscript submitted November 24, 2003.