Improvement in secondary cooling of continuous casting of round billets through analysis of heat flux distribution (original) (raw)
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Tecnologia em Metalurgia Materiais e Mineração, 2014
In the present work, the water flux densities of nozzles with flat jet and full cone jet were experimentally measured using an apparatus in industrial scale that reproduces the secondary cooling of the continuous casting of round billets of Vallourec Tubos do Brasil. A mathematical model for heat transfer and solidification for the continuous casting of round billets was developed applying the experimental water flux density profile, establishing a non-uniform water distribution approach. The mathematical model was validated by experimental measurements of the billet superficial temperature, performed at the industrial plant. The results of the mathematical model using both uniform and non-uniform water flux density approaches were compared. The non-uniform water distribution approach enabled to identify important variations of the heat transfer coefficients and the billet temperatures, especially in the first cooling zone, and to assess more accurately the local effects of the water distribution on the thermal behavior of the strand. The non-uniform water flux density approach applied to the mathematical model was a useful and more accurate tool to improve the comprehension of the thermal behavior of the steel along the secondary cooling.
Inverse Problems in Science and Engineering, 2006
In the present work, heat transfer coefficients (h) along different cooling zones of a continuous caster billet machine were determined during casting of low and medium carbon steels. The effects of casting parameters, such as machine characteristics, the ingot dimension, mold, sprays zones, radiant cooling, melt composition and casting temperature were investigated and correlated with heat transfer coefficients. By using industrial measured billet surface temperatures, linked with a numerical solution of the solidification problem, ingot/cooling zones heat transfer coefficients were quantified based on the solution of the inverse heat conduction problem (IHCP). The experimental temperatures were compared with simulations furnished by an explicit finite difference numerical model, and an automatic search has selected the best theoreticalexperimental fit from a range of values of h. The computer software algorithm has been developed to simulate temperature profiles, solid shell growth, phase transformations and the point of complete solidification in continuous casting of steel billets and blooms. Industrial experiments were monitored with an optical infrared pyrometer to analyze the evolution of surface temperatures during solidification along the machine. The results permitted the establishment of expressions of h as a function of position along the caster, for different steel compositions, casting parameters and melt superheats.
Water Distribution Assessment Applied to Mathematical Model of Continuous Casting of Steel
2017
A mathematical model of heat transfer and solidification for a continuous casting of round billets was developed. The water flux density of the secondary cooling zone was experimentally measured, using an apparatus in industrial scale with two types of nozzles, flat jet and full cone jet. The profiles of water distribution were applied on the mathematical model. The results showed that the water distribution is not uniform in both longitudinal and angular directions owing to the unevenness of the spray and to the curvature effect of the round billet. This non-uniformity causes important variation of the heat transfer coefficients and superficial temperature of the billet, especially in the first cooling zones, where the temperature is higher. The mathematical model was used to simulate a change of nozzle type in the first cooling zone. The results showed that the heat flux and superficial temperature variations were reduced with a full cone jet nozzle in comparison with the flat jet nozzles.
Cooling nozzles characteristics for numerical models of continuous casting
2013
R. Pyszko, M. Přihoda, J. Burda, P. Fojtik, M. Vaculik, M. Velicka, Faculty of Metallurgy and Materials Engineering, T. Kubin, Faculty of Mechanical Engineering, VSB Technical University of Ostrava, Czech Republic, M. Carnogurska, Faculty of Mechanical Engineering, Technical University of Kosice, Slovakia Modelling the temperature fi eld of a continuously cast strand is an important tool for the process diagnostics. The main preconditions for numerical simulation of the temperature fi eld of the solidifying strand are correct boundary conditions, especially the surface condition in the secondary zone of the caster. The paper deals with techniques of determining the surface condition under cooling nozzles as well as their approximation and implementation into the model algorithm. Techniques used for laboratory measurements of both cold and hot spraying characteristics of water or water-air cooling nozzles are described. The relationship between the cold and hot characteristics was fo...
Analysis of Non-Symmetrical Heat Transfers during the Casting of Steel Billets and Slabs
Metals
The current automation of steelmaking processes is capable of complete control through programmed hardware. However, many metallurgical and operating factors, such as heat transfer control, require further studies under industrial conditions. In this context, computer simulation has become a powerful tool for reproducing the effects of industrial constraints on heat transfer. This work reports a computational model to simulate heat removal from billets’ strands in the continuous casting process. This model deals with the non-symmetric cooling conditions of a billet caster. These cooling conditions frequently occur due to plugged nozzles in the secondary cooling system (SCS). The model developed simulates the steel thermal behavior for casters with a non-symmetric distribution of the sprays in the SCS using different boundary conditions to show possible heat transfer variations. Finally, the results are compared with actual temperatures from different casters to demonstrate the predi...
A Fully Coupled Analysis of Fluid Flow, Heat Transfer and Stress in Continuous Round Billet Casting
ISIJ International, 1999
The thermal and vectorial fields in the strand and the temperature distribution in the mold were analyzed with a finite difference method (FDM) considering the effects of turbulence and natural convection of molten steel. The thermo-elasto-plastic behaviors of the strand and the mold were analyzed with a finite element method (FEM) taking into account the ferrostatic pressure dueto the gravity force andthe mechanical behaviors of the strand in liquid phase, mushy zone and~h , phase. The microsegregation of solute elements in steel was assessed to determine some characteristic temperatures and solid, 8-Fe and },-Fe fractions in the mushyzone. The heat transfer coefficient betweenthe solidifying shell and the mold wall was iteratively determined with the coupled analysis of the fluid flow-heat transfer analysis by the FDM and the thermo-elasto-plastic stress analysis by the FEM.With the above procedure, the mathematical model has been developed to predict the possibility of cracks in the strand, originated from the interdendritic liquid film in the mushyzone, through the fully coupled analysis of fluid flow, heat transfer and stress in the continuously cast round billet. The calculated mold temperature and heat flux at various casting speeds showgood agreements with the reported experimental observations.
Research on Intensity of Cooling Continuously Cast Steel by Water Nozzles
Acta Mechanica Slovaca, 2015
The article describes heat removal from the hot surface by water. Method of cooling in a secondary zone of continuous casting of steel has a significant influence on a quality of continuously cast products mainly from the point of view of internal and surface defects. For this reason, a physical model of the secondary zone has been developed at the Department of Thermal Engineering, which enables testing of both water and water-air nozzles. During laboratory modelling cooling effects of a nozzle have been expressed by means of two parameters. Most commonly used parameter is spray intensity, infrequently heat transfer coefficient is determined. In comparison with the cold model the energy and time consumption at measurements on the hot model are several fold higher. Therefore, also was found correlations between the two models.
Heat Transfer Correlations for Secondary Cooling in Continuous Casting
The general term "spray cooling" is for the research presented here limited to the spray cooling of hot surfaces with film boiling, starting at temperatures of about 1200 °C and finishing at the Leidenfrost point where cooling intensity changes rapidly. This is typical area of secondary cooling in continuous casting. Herein, a correlation for Heat Transfer Coefficient (HTC). The most frequently used parameter of water impingement density is in the presented correlation used together with impact pressure to get good results. This study uses both water and mist nozzles. It is shown and experimentally verified why equations based only on the water impingement density cannot provide sufficiently precise predictions of HTC.
Influence of operation parameters on the cooling performance of water/air nozzles
2017
In the secondary cooling zone of the continuous casting process water/air nozzles are used to cool down the strand. The cooling has to be sufficient enough to ensure a certain shell thickness and finally the complete solidification of the material. Further a controlled and uniform cooling strategy is important to minimize the amount of defects in the solidified steel. For the determination of the water distribution and the cooling characteristic of water/air sprays at defined operation parameters the Nozzle Measuring Stand (NMS) at the Montanuniverstaet Leoben is used. In this work the measuring principle of the NMS is explained and the influence of several nozzle operation parameters on water/air sprays, in particular on their cooling characteristic is shown. In a first step the water distribution (WD) at different nozzle distances, water flows and air pressures was determined. Afterwards the heat transfer coefficient (HTC) for every parameter modification was measured. The surface...
International Journal of Engineering Systems Modelling and Simulation, 2010
Thin slab continuous casting process can be controlled by the water flow rate through the copper mould to obtain the proper shell thickness for a given casting speed. To achieve this, 2D model for the liquid metal flow in the strand and water flow through the mould is developed using stream function and vorticity formulation. The main advantage is faster computation, which is very important for process optimisation, and real-time modelling for process control. The funnel type shape of the mould is efficiently taken into consideration by using body fitted coordinate system. The detailed CFD-based model can be used for analysing the process parameters and variables like heat transfer through the mould flux, casting speed and superheat. The model can be easily adapted for wide range of casting process like slab and billet casting and thin strip casting.