Height of Water Pool in the Roll Nip of Secondary Cooling Zone in Continuous Slab Caster: Application of Open Channel Hydraulics

In continuous casting of steel, the strand is cooled in the upper part of the secondary cooling zone with water sprayed by nozzles towards the strand surface. The water accumulates in the nip of the lower roll of a roll pair, forming a water pool which then drains off towards the ends of the roll. In the present work, open channel hydraulics was applied for computation of the water pool height in the nip between roll and strand in continuous slab casting. The differential equation describing the change of pool height for the spatially varied flow with increasing discharge was solved with the Runge–Kutta technique using as boundary condition the pool height at the end of the nip. The effects of the Manning friction factor n and the energy coefficient α were determined in sets of computation. It was shown that the hydraulic theory could predict water profiles in the nip of continuous casting rolls to a good approximation.

Comparison of Optimization-Regulation Algorithms for Secondary Cooling in Continuous Steel Casting

The paper presents the comparison of optimization-regulation algorithms applied to the secondary cooling zone in continuous steel casting where the semi-product withdraws most of its thermal energy. In steel production, requirements towards obtaining defect-free semi-products are increasing day-by-day and the products, which would satisfy requirements of the consumers a few decades ago, are now far below the minimum required quality. To fulfill the quality demands towards minimum occurrence of defects in secondary cooling as possible, some regulation in the casting process is needed. The main concept of this paper is to analyze and compare the most known metaheuristic optimization approaches applied to the continuous steel casting process. Heat transfer and solidification phenomena are solved by using a fast 2.5D slice numerical model. The objective function is set to minimize the surface temperature differences in secondary cooling zones between calculated and targeted surface temperatures by suitable water flow rates through cooling nozzles. Obtained optimization results are discussed and the most suitable algorithm for this type of optimization problem is identified. Temperature deviations and cooling water flow rates in the secondary cooling zone, together with convergence rate and operation times needed to reach the stop criterium for each optimization approach, are analyzed and compared to target casting conditions based on a required temperature distribution of the strand. The paper also contains a brief description of applied heuristic algorithms. Some of the algorithms exhibited faster convergence rate than others, but the optimal solution was reached in every optimization run by only one algorithm.

Application of “flat’ closed-bottom submerged nuzzles for decreasing rejections of slabs because of longitudinal cracks

In the process of steel continuous casting it was discovered, that due to relatively small distance between a submerged nuzzle and a mold walls, formation of “scull crust” takes place in the area of small and big radius of the billet. It resulted in deterioration of heat-away in mold, conditions are formed for origination of longitudinal cracks following its further opening in the CCM secondary cooling zone. To decrease the number of rejections continuously casted slab billets due to existence of longitudinal cracks, it was proposed to use “flat” closed-bottom submerged nuzzles. It was shown, that in contrast to cylindrical form of a series closed-bottom submerged nuzzle, the proposed one has rectangular section with chamfered butt facet in the are of nuzzle submerging into the mold melt, which enables to ensure better fluidity of slag-forming mixture between the nuzzle and the mold walls. This effect results in onsiderable improving evenness of heat-away. To confirm the effectiveness of the pilot submerged nuzzles application, in 2019 their pilot-industrial tests were accomplished in the campaign of casting of carbon and peritectic steels to produce 200 mm thick slabs at CCM No. 4. In the process of the tests when casting various steels, the same slag-forming mixtures were used. As a result of the tests the decrease of rejections of continuously casted slabs due to longitudinal cracks formation was confirmed.

Computational experiment on determination of load on the rollers of continuous casting machine

The article is devoted to calculations of load on rollers of a curvilinear continuous casting machine during bending of the ingot in the levelling section. The calculation takes into account the elastic and plastic characteristics of metal and the flexibility of the roller apparatus. Determination of load on rollers together with meeting other requirements such as reducing the cooling water consumption, minimizing the energy consumption enables optimizing the technology of slab cooling in the secondary cooling zone (SCZ) and obtaining metal of the required quality.

MATHEMATICAL MODELING OF THE PROCESSES OF THE FORMATION OF CAST UNITS IN THE CONTINUOUS CASTING OF STEEL

Проведен теоретический анализ процессов формирования литых заготовок при непрерывной разливке стали. На базе проведенного анализа разработана математическая модель для изучения термосиловых процессов, происходящих в кристаллизаторе и зоне вторичного охлаждения машины непрерывного литья заготовок (МНЛЗ). Методом математического моделирования определены параметры теплообмена и затвердевания исследуемых заготовок вдоль ее технологической оси. В качестве переменного параметра при формировании заготовок рассмотрена интенсивность теплоотвода в зоне вторичного охлаждения. Установлено, что математическое моделирование достаточно адекватно воспроизводит процессы формирования реальной непрерывнолитой заготовки, что позволяет рекомендовать предложенную модель для проведения исследований и оптимизации условий теплообмена в зоне вторичного охлаждения МНЛЗ. A theoretical analysis of the formation of castings in the continuous casting of steel. Based on the analysis, a mathematical model has been developed for the study of thermoforce processes occurring in the mold and the secondary cooling zone of a continuous casting machine (CCM). The parameters of heat transfer and solidification of the studied blanks along its technological axis are determined by the method of mathematical modeling. The intensity of the heat sink in the secondary cooling zone is considered as a variable parameter in the formation of blanks. It is established that mathematical modeling adequately reproduces the processes of formation of a real continuouscast billet, which allows us to recommend the proposed model for research and optimization of heat exchange conditions in the zone of secondary cooling of continuous casting machines.