The technology of nail shooting was improved and used to study the transverse shape of the solidified shell during steel continuous casting. Three locations across the slab width (1/2, 1/4 and 1/8) were measured by nail shooting and which indicated a larger solidification coefficient and longer liquid core in the slab at higher casting speeds. The solidified shell across the slab width direction was non-uniform due to uneven secondary spray cooling. The point of final solidification at locations 1/8 and 1/4 was much longer than the position between the slab centre and location 1/4, leading to a long solidification end of .2 m, which is poor for the application of dynamic soft reduction. A mathematical model was developed to simulate the growth of the solidified shell and which was in good agreement with the measurements measured by nail shooting. Based on the measurements and simulations, the water spray pattern was improved, making the solidified shell more uniform. Dynamic soft reduction was then optimised resulting in reduced centreline segregation.

Ultrathick continuous slab casting is a growing technology, especially in developing countries due to the vast market demand of thick rolled plate. The structure of the submerged entry nozzle is regarded as the crucial factor to determine flow related phenomena in the mould. This article conducts a 0?55 scale water model and a three-dimensional numerical model to investigate the influences of submerged entry nozzle on flow behaviour, temperature field and solidified shell distribution in a 420 mm ultrathick slab mould. Physical and numerical finite volume methods with K-e turbulence model simulations verify that the flow pattern in ultrathick mould is similar with that in conventional slab mould. The diffuse type nozzle fails to increase the surface velocity while easily causing slag entrainment. The four-spout nozzle gives a detrimental effect on shell distribution. The tunnel bottom nozzle is optimal, because it shows a lively surface behaviour and a favourable heat transfer between mould flux and surface flow, and the shell thickness is uniform and thick enough at the mould exit to avoid breakout.

Based on the laser triangulation and machine vision technology, a three-dimensional quantitative inspection method for continuous cast slab surface defects was established, which adopted one laser and two array charge coupled device cameras and an optimal laser stripe imaging algorithm. In addition, the laser scanning system establishing method is described in detail in this paper. A laser stripe edge shape extraction method on the slab surface is proposed that utilises an improved edge scanning extraction model in accordance with the charge coupled device camera frame frequency. The detection accuracy control algorithm is presented and finally the three-dimensional image reconstruction method for slab surface defect shape was also studied. Based on the research work, the possibility of the presented laser scanning system was verified through industrial application experiments in a steel plant.

Based on a basic water cooling model, a novel model with closed feedback loop was developed for online temperature control system (OTCS) to control the strand surface temperature online during steel continuous casting process. The OTCS considered the temperature delay to the casting speed and water flowrate and combined the feedback control model with feed forward control model for the control of secondary cooling water. The online feed forward control with the temperature of molten steel in the tundish and the temperature of cooling water was also considered. A fine adjusting temperature region and an optimal temperature region were applied to the OTCS to avoid big temperature fluctuation during control process and to shorten the adjusting time. A single point OTCS was applied to a slab continuous caster, showing that the slab surface temperature was well stabilised at the target temperature under the control of the OTCS in continuous casting process. During tundish change or big variation of casting speed, the low slab surface temperature could be quickly controlled to the target temperature again by the OTCS within 7 min. The industrial application indicated that the OTCS could reduce the slab surface cracks and aid in increasing productive efficiency in continuous casting.

In this paper, a scanning laser system based on an array couple charged detector (CCD) has been developed to detect and measure quantitatively the morphology and depth of defects on continuously cast billet (CC billet) surface at high temperatures. The technique, based on a linear light scattering method, employs a low power He-Ne laser and a conventional CCD probe and enables a narrow line array laser beam to be projected on the test surface across the width direction on the CC billet surface. In the relative scanning direction between the test surface and the CCD probe, the one-dimensional linear surface image acquired by the CCD sensor at a given shutter time, which exhibits the curvature change of the laser scanning line, can be used to determine the distance morphology according to triangulation principles. Combining with casting speed, a linear laser beam image can be spliced into a two-dimensional surface image that constructs the billet surface profile and detects surface defect shape and depth. Furthermore, it can reconstruct a threedimensional morphology for the billet surface defects in the high temperature condition. Proof of concept experiments have been performed through online measurement of different size defects, and quality tracking on the hot CC billet surface has been implemented.