Casting Speed Research Articles

УПРАВЛІННЯ ЗОНОЮ ВТОРИННОГО ОХОЛОДЖЕННЯ З УРАХУВАННЯМ ПРОЦЕСУ КРИСТАЛІЗАЦІЇ БЕЗПЕРЕРВНОЛИТОГО ЗЛИТКА МБРЗ

Four main approaches used in controlling the thermal regime of the secondary cooling zone of a continuous machine were identified: regulation of the ratio casting speed - cooling water flow, control of secondary cooling on the basis of the surface temperature of the ingotbefore entering the SCZ and at its exit, regulation of the temperature of the ingot in each section based on the current value of the temperature of the ingot in the section, the use of mathematical models in a dynamic SCZ control. Controlling the cooling process of the ingot in the secondarycooling zone, taking into account the process of its crystallization in real time by calculating the crystallization parameters and the amount of water in the sections, is a promising area. This approach allows to optimize the water rate in the secondary cooling zone with its optimaldistribution on the surface of the ingot. An algorithm for calculating the set values of the water and air flow rates, depending on the crystallization of the ingot, which are transmitted to the automatic control system of the secondary coolling zone has been developed. Based on the proposed algorithm, software that allows to consider the current thermal state of the secondary cooling zone has been developed in an environment of object-oriented programming. In real time, the program receives the current values of the speed of drawing the ingot, the surface temperature of the ingot in front of the SCZ, the metal level in the mold. The values of static coefficients can be changed within certain limits. To verify the correctness of the calculation results, values corresponding to real production data were entered into the program.

Determination of thermal resistance at mould-strand interface due to shrinkage in billet continuous casting – Development and application of a novel integrated numerical model

An industrial continuous casting process of steel billet is analysed using a novel, integrated numerical model for the heat transfer and solidification of the molten metal as it passes through the mould. One of the major difficulties related to determination of thermal resistance at the mould-strand interface is addressed in the present study. Contrary to empirical or semi-empirical methods commonly used in the industry for determination of the heat transfer at the interface, the present work deals with the determination of the interfacial thermal resistance by adopting a novel mathematical approach. A two-dimensional, transient, finite difference method based code is developed for a plane slice of molten steel moving with a given casting speed down the mould. The resultant solidification and thermal shrinkage are calculated from the temperature distribution and knowledge of the temperature dependent density of steel. The heat transfer from the cast strand to the cooling water is modelled by a network of thermal resistance. The model is validated against experimental data obtained from literature. The numerical results reveal a dominant role of advection of the gaseous mixture of air and other components from pyrolysis of casting oil, in the interfacial gap formed due to the shrinkage of steel, which has not been considered previously in the formulation of thermal resistance. The numerical model is also used to analyse the heat transfer in the mould and the growth of the solidified shell as the strand moves down the mould. In particular, the corner regions of the strand are found to be hotter than the off-corner regions, due to non-uniform heat transfer across the periphery. Also, the effect of casting speed in the mould is found to be dominant in comparison to other casting parameters, such as mould thickness and cooling water velocity.

A Qualitative Study of the Influence of Grooved Mold Surface Topography on the Formation of Surface Marks on As-Cast Ingots of Aluminum Alloy 3003

The effects of the wavelength and orientation of machined grooves on a mold surface, casting speed, and melt superheat on the formation of surface marks on as-cast ingots were studied with an immersion casting tester and copper mold chill blocks. The mold surface topographies included a polished smooth surface, and those with machined unidirectional parallel contoured grooves oriented either parallel (vertical) or perpendicular (horizontal) to the casting direction. The unidirectional grooves were 0.232 mm deep with wavelength or spacing between 1 and 15 mm. The casting speed and melt superheat were between 1 and 200 mm/s, and 10 and 50 K, respectively. Two primary types of surface marks were observed on ingots cast with the copper mold with smooth surface topography, namely the finer and closely spaced ripples (Type I), and the widely spaced but coarser laps (Type II). The latter were more prevalent at the higher casting speeds and melt superheats. Qualitatively, formation of both types of surface marks on the as-cast ingots of the aluminum alloy 3003 appeared to be alleviated by increase in casting speed and melt superheat, and by the use of molds with grooved surface topography. In fact, casting with a mold surface with 1 mm spaced grooves that are perpendicular to the casting direction eliminated the formation of surface marks at casting speeds greater than 1 mm/s. It also improved the uniformity of the ingot subsurface microstructure and eliminated the associated subsurface segregation.

Numerical analysis of local heat flux and thin-slab solidification in a CSP funnel-type mold with electromagnetic braking

In this article, based on the actual monitored temperature data from mold copper plate with a dense thermocouple layout and the measured magnetic flux density values in a CSP thin-slab mold, the local heat flux and thin-slab solidification features in the funnel-type mold with electromagnetic braking are analyzed. The differences of local heat flux, fluid flow and solidified shell growth features between two steel grades of Q235B with carbon content of 0.19%C and DC01 of 0.03%C under varying operation conditions are discussed. The results show the maximum transverse local heat flux is near the meniscus region of over 0.3 m away from the center of the wide face, which corresponds to the upper flow circulation and the large turbulent kinetic energy in a CSP funnel-type mold. The increased slab width and low casting speed can reduce the fluctuation of the transverse local heat flux near the meniscus. There is a decreased transverse local heat flux in the center of the wide face after the solidified shell is pulled through the transition zone from the funnel-curve to the parallel-cure zone. In order to achieve similar metallurgical effects, the braking strength should increase with the increase of casting speed and slab width. Using the strong EMBr field in a lower casting speed might reverse the desired effects. There exist some differences of solidified shell thinning features for different steel grades in the range of the funnel opening region under the measured operating conditions, which may affect the optimization of the casting process in a CSP caster.

Investigation of Non-Sinusoidal Oscillator Driven by Double Servomotors for Continuous Casting Mold

To improve the surface quality and casting speed of the slab further, a new type mold oscillator synchronously driven by double servomotors was proposed in this paper. The experimental prototype was designed and manufactured. For the non-sinusoidal oscillator, the waveform modification ratio could be adjusted during the steel continuous casing operation. Firstly, the working principle of the oscillator was described. Secondly, the rotating rules of the servomotor to realize non-sinusoidal oscillation waveform for entire function were given. Finally, the laboratory experiments were made. The experiment results show that the error of the two-side oscillation curves is smaller and the actual technological parameters are close to the theory and the oscillator can realize non-sinusoidal oscillation well. This kind of non-sinusoidal oscillator provides a feasible scheme for reducing oscillator investment, increasing casting speed and enhancing slab quality.

Physical and numerical modeling of liquid slag entrainment in mould during slabs casting

The paper presents results of physical and numerical modeling of liquid slag entrainment during continuous casting of steel slabs process. The main aim of this work was to determine the critical casting speed and also to specify, which entrainment mechanism is most responsible for transport of slag droplets into steel volume. Physical modeling was based on water-oil model of mould, made on reduced linear scale of Sl = 0.4. In mathematical modeling, Realizable k-ε and LES WALE models were used to describe turbulent motion of water and oil, whereas Volume of Fluid model was used to take into account interactions between phases. It was found, that the main cause of slag entrainment is the formation of von Karman vortex in the vicinity of submerged entry nozzle. The results of laboratory experiments and numerical simulations were compared each other. Both method are a useful tools for modeling of slag entrainment. Great agreement was found between laboratory experiments and numerical simulation carried out using LES WALE model, regarding the shape of the oil and oil entrainment as a result of vortex structures formation. However, in the simulation case using Realizable k-ε model, the oil entrainment hasn’t been modeled for the conditions under consideration.

Optimization of Flow Field in Slab Continuous Casting Mold with Medium Width Using High Temperature Measurement and Numerical Simulation for Automobile Exposed Panel Production

In the present work, mathematical modeling combined with measurement of the velocities near mold surface with rod deflecting method at the high temperature was carried out to optimize the flow field of slab continuous casting mold with medium width of 1230 mm for the production of an automobile exposed panel. The results show that the measured results of the velocities near the mold surface are in good agreement with the calculated results. The velocities near the mold surface increase with increasing the casting speed and decreasing the argon gas flow rate. When the casting speed is increased from 1.0, to 1.3, 1.5, and 2.0 m/min, the flow pattern in the mold is changed from single-roll flow (SRF), to unstable flow (UF), and then to double-roll flow (DRF), the top surface level fluctuations has the smallest value at 1.5 m/min. When the argon gas flow rate is 1 and 4 L/min, the velocity near the mold surface has a moderate value, and the flow pattern in the mold is DRF and the top surface level fluctuation is small and symmetrical. When the submerged entry nozzle (SEN) submergence depth is increased to 200 mm, the velocities near the mold surface decrease, and the top surface level fluctuation becomes small. The optimized flow field in the mold can be judged to be favorable to the surface quality of the automobile exposed panel; if the velocities near the mold surface are relatively small, the flow pattern in the mold is DRF and the top surface level fluctuation is small and symmetrical.

Numerical Simulation of Heat Transfer between Roll and Slab under Dry Secondary Cooling in Ultrathick Slab Continuous Casting

A 3D model of heat transfer between the circular‐distributed water channel roll (CDWCR) and slab during ultrathick slab continuous casting process is established, considering the structure of water channels inside CDWCR and rotating contact between the roll and slab. The results show that the contribution of conduction heat transfer in the heating process of the roll is greater than that of radiation heat transfer, and maximum surface temperature of the roll is 460 K, located at the place where it is right out of contact with the slab, and the change of internal temperature of the roll lags behind the change of surface temperature. The temperature decreases gradually from the outside to the inside in the radial direction. The temperature of the CDWCR inside the circle of cooling water channels is no more than 325 K. The yield strength of CDWCR is analyzed, showing that the strength of the roll meets the requirements of using it in the process. In addition, the orthogonal method is used to analyze the influence factors on CDWCR temperature. The results indicate that the orders of factors affecting more are the contact angle, the slab temperature, the casting speed, and the inlet speed of cooling water.

Thermal characteristics and uniformity of microstructures during temperature controlled mold continuous casting profiled copper alloy strip

Nonuniform temperature field at cross section of profiled billets during conventional continuous casting always results in serious defects and inhomogeneous microstructures. In this paper, a 3D temperature controlled mold continuous casting (TCMCC) model for preparing profiled copper strip was established and verified to calculate the magnetic and temperature field during continuous casting process. Under different controlled temperatures of TCM and casting speeds, the temperature fields in the TCM and melt were numerically calculated, and the variation of temperature fields in the mushy zone was analyzed. The calculated temperatures are in good agreement with the measured values. The results indicate the uniformity of temperature gradient (uG) at the profiled section improves significantly when the controlled temperature of TCM is higher than the liquidus temperature of alloy, further, the uG gradually reaches the minimum and then increases with increasing casting speed. Based on the calculated results, the profiled KFC copper alloy strips with good surface quality were successfully prepared by the TCMCC under controlled TCM temperature of 1423 K and casting speeds of 15–60 mm/min. The value of the uniformity of primary dendrite spacing at the cross section of the profiled strips reaches the minimum with the casting speed of 45 mm/min.

Predicting the Partition of Behavioral Variability in Speed Perception with Naturalistic Stimuli.

A core goal of visual neuroscience is to predict human perceptual performance from natural signals. Performance in any natural task can be limited by at least three sources of uncertainty: stimulus variability, internal noise, and suboptimal computations. Determining the relative importance of these factors has been a focus of interest for decades but requires methods for predicting the fundamental limits imposed by stimulus variability on sensory-perceptual precision. Most successes have been limited to simple stimuli and simple tasks. But perception science ultimately aims to understand how vision works with natural stimuli. Successes in this domain have proven elusive. Here, we develop a model of humans based on an image-computable (images in, estimates out) Bayesian ideal observer. Given biological constraints, the ideal optimally uses the statistics relating local intensity patterns in moving images to speed, specifying the fundamental limits imposed by natural stimuli. Next, we propose a theoretical link between two key decision-theoretic quantities that suggests how to experimentally disentangle the impacts of internal noise and deterministic suboptimal computations. In several interlocking discrimination experiments with three male observers, we confirm this link and determine the quantitative impact of each candidate performance-limiting factor. Human performance is near-exclusively limited by natural stimulus variability and internal noise, and humans use near-optimal computations to estimate speed from naturalistic image movies. The findings indicate that the partition of behavioral variability can be predicted from a principled analysis of natural images and scenes. The approach should be extendable to studies of neural variability with natural signals.SIGNIFICANCE STATEMENT Accurate estimation of speed is critical for determining motion in the environment, but humans cannot perform this task without error. Different objects moving at the same speed cast different images on the eyes. This stimulus variability imposes fundamental external limits on the human ability to estimate speed. Predicting these limits has proven difficult. Here, by analyzing natural signals, we predict the quantitative impact of natural stimulus variability on human performance given biological constraints. With integrated experiments, we compare its impact to well-studied performance-limiting factors internal to the visual system. The results suggest that the deterministic computations humans perform are near optimal, and that behavioral responses to natural stimuli can be studied with the rigor and interpretability defining work with simpler stimuli.

Numerical study of aluminum segregation during electron beam cold hearth melting for large-scale Ti-6 wt%Al-4 wt%V alloy slab ingots

To investigate aluminum (Al) segregation in large-scale Ti-6 wt%Al-4 wt%V (TC4) slab ingots produced by electron beam cold hearth melting (EBCHM), a three-dimensional multiphysics model verified with experimental data in the literature has been established. The numerical predictions qualitatively revealed the macrosegregation tendency of Al in the molten and the solidified region at different casting conditions. It was noticed that Al segregation is slightly influenced by increasing casting speed due to the vertical evolution of the pool shape near the inlet. A promising solution for Al segregation control is to limit the Al evaporation loss by decreasing the pouring temperature. The results suggest that for EBCHM with a casting speed of 8 mm/min, as the pouring temperature decreases from 2273 to 2073 K, the segregation degree Фl increases from 0.70 to 0.96 in the pool. As a consequence, the corresponding segregation degree Фc on the solidified cross-section improves (increases from 0.67 to 0.93).

Effect of electromagnetic casting process on microstructure and properties of AZ31 magnesium alloy

ABSTRACTIn this paper, AZ31 magnesium alloy is cast by applying the semi-continuous casting process with a low-frequency electromagnetic field. By studying the influence of electromagnetic field frequency, excitation current intensity and casting velocity on the microstructure and mechanical properties, the optimum process under oil-slip electromagnetic casting conditions was determined to improve the degree of grain refinement, yield strength, elongation and tensile strength of AZ31 alloy. An improved microstructure refining effect and higher hardness can be obtained with a current intensity af 60 A. The microstructures and mechanical properties obtained for different casting velocities of V = 200 mm/min and V = 230 mm/min at processing parameters of f = 30 Hz and I = 120 A were compared. Our results suggest that a higher casting speed does not lead to grain refinement or improved mechanical properties. Frequency

Optimization of the Gap Parameters of Supporting Rollers of Curvilinear Continuous Casting Machine

A study was performed to determine the influence of technological and design parameters of continuous casting of steel on reducing the thickness of the billet along the technological line of a curvilinear continuous casting machine (CCM) designed by Uralmashzavod OJSC. The effect of carbon content and casting speed on linear shrinkage through the billet’s thickness was investigated. It was established that in all cases there was a discrepancy between the thickness of the billet and the settings used for CCM rollers. This discrepancy can lead to defects in the billet caused by the distortion of its shape (owing to the blow-up under the action of ferrostatic pressure) and to an increase in friction and, accordingly, pulling forces. On the basis of the obtained results, new settings for the rollers on the hard and hydraulic sections were proposed. The use of recommended parameters considerably reduces the discrepancy between the thickness of the billet and the gap of the rollers, which will improve product quality.

Numerical and experimental investigation of solidification structure evolution and reduction of centre segregation in continuously cast GCr15 bloom

ABSTRACT A CAFE model and SDAS model are established in order to study evolutionary behaviour of macrostructure and secondary dendrites on 220 × 260 mm2 bloom cross-section of GCr15 bearing steel, respectively. Based on numerical simulation and experiments, the effects of process parameters on centre ECR and SDAS are investigated. It is found that increase of centre ECR and decrease of SDAS occur with the decrease of superheat and with the increase of M-EMS. The results reveal that M-EMS and superheat exhibit a significant effect on centre ECR, whereas casting speed evidently affects SDAS than superheat. In addition, casting speed has the obvious influence on solidification end, which is closely related with F-EMS implementation. After less than superheat of 25°C and casting speed of 0.8 m min−1 with optimized M+ F-EMS are adopted, centre ECR increases by 11% and the SDAS is effectively refined. Furthermore, centre segregation gets improved as well.

Numerical Simulation on Multiple Physical Fields Behaviors in Billet Continuous Casting with Different Stirrer Positions

A 3D coupled model considering electromagnetic field, flow field, heat transfer, and particle transport is developed to predict the effect of stirrer position on the magnetic field distribution, fluid flow streamlines, temperature distribution, and inclusion removal in 180 mm × 220 mm billet continuous casting process, and the effect of stirrer position on the mold‐level fluctuation and slag entrapment behavior is also studied based on the homogeneous model. The casting temperature of molten steel is 1750 K, and the casting speed of billet is 0.9 m min−1. The results indicate that as the stirrer center position is lowered, the maximum value of the magnetic induction intensity has almost no change, whereas the maximum value of the tangential electromagnetic force initially decreases followed by an increase. With the downward movement of stirrer center position, the decrease rate of central molten steel velocity slows down, and the range of the upper circulation flow zone increases. A lower stirrer center position increases the cooling of the billet and inclusion removal. When the stirrer center position is moved from 515 to 815 mm, the wave height of steel/slag interface decreases from 11.6 to 3.4 mm, and slag entrapment behavior gradually weakens.

Analysis of transient mold friction under different scales based on wavelet entropy theory

The mold friction (MDF) is an important parameter reflecting the lubrication between the mold and slab quantitatively. The mold/slab friction was detected using an online monitoring system on a slab continuous caster equipped with hydraulic oscillators. Wavelet entropy theory was introduced to describe the fluctuation characteristics of the MDF signal in order to quantitatively estimate the mold/slab lubrication. Furthermore, MDF signal and its wavelet entropy were analyzed under typical casting conditions, such as normal casting, different models (to control the relationship among the amplitude, the frequency and the casting speed), changing casting speeds and breakout. The results showed that the wavelet entropy could accurately reflect the overall changing trend of the mold friction as well as the local variation features. Besides, the wavelet entropy of the hydraulic cylinder force and the MDF was compared and analyzed, and the relationship between them was further discussed.

Acquiring High-Quality Oil Casing Steel 26CrMoVTiB under Optimal Continuous Casting Process Conditions

While the solidification macrostructure of continuous cast billets is an important factor influencing the final performance and rolling yield of oil casing steel, the continuous casting process parameters have a direct influence on the solidification structure. This study simulated the solidification process of the continuous casting round billets of oil casing steel using a cellular automaton–finite element (CAFE) model. According to the simulation results, at a superheat degree of 20–35 K, a casting speed of 1.9–2.1 m/min, and a secondary cooling specific water flow of 0.34–0.45 L/Kg, the solidification structure had a relatively high equiaxed crystal ratio and small average grain radius. Guided by the simulation results, this paper establishes optimal process schemes for producing 26CrMoVTiB steel round billets, comparatively analyzes the equiaxed crystal ratio and central shrinkage of round billets produced according to these schemes, and defines the optimal continuous casting process conditions, which are: superheat degree = 25 K, casting speed = 2.1 m/min, and specific water flow = 0.35 L/Kg. When adopting these process parameters, the 26CrMoVTiB steel round billets demonstrate a tiny central shrinkage and an equiaxed crystal ratio of 45.2%.

Mold Oscillating System with Optimized Non-Sinusoidal Oscillation Profile

A mold oscillating system for continuous casting machines has been developed based on a nonsinusoidal oscillation profile with an online oscillation control capability. A new type of the mold oscillating system is proposed comprising two servomotor-driven eccentric shafts. The principle of operation of a non-sinusoidal oscillation system is described. Based on the analysis of the non-sinusoidal oscillation waveform expressed as a piecewise linear function, the angular speed of a servomotor necessary to realize such oscillations was determined. A procedure for calculating process parameters was developed. The model of synchronized control of the casting speed and oscillation frequency was optimized and process parameters were calculated for the deviation factor of 20% and amplitude equal to 4 mm. The mold oscillating systems of sinusoidal and non-sinusoidal type were compared. The advantages of the non-sinusoidal type of oscillating system were shown, which include a decrease in depth of the oscillation marks on the surface of continuous-cast billet, an improvement in the mold-ingot lubrication conditions, and higher quality of continuous-cast billets.

Lattice Boltzmann Method Modeling of Flow Structures and Level Fluctuations in a Continuous Casting Process.

Transient flow and level fluctuations in the mold were simulated using the three-dimensional Lattice Boltzmann Method (LBM). The LBM model was verified by measured data from the literature. The transient flow field and the free surface fluctuations in the mold were simulated. The distributions of the coherent structures were also investigated. The results showed that the behavior of the jets with oscillating characteristics on both sides of the submerged entry nozzle (SEN) played an essential role in the development of the turbulent flow in the mold. During jet diffusion, the coherent vortex ring and vortex rib structures were generated. The vortices at the narrow wall were asymmetrical in the mold, accompanied by the development, dissipation, and extinction of the coherent structures in the turbulent flow. The asymmetric flow affected the free surface fluctuations at the top of the mold. The peak and trough fluctuations on both sides of the SEN alternated thereon. The distributions of the free surface fluctuations were quantified at different casting speeds and SEN immersion depths. As the casting speed was increased, the variations and the velocities of the free surface increased; as the SEN immersion depth increased, the fluctuations and the velocities thereof decreased.

Influence of mould curvature on the metallurgical performances of beam blank continuous casting

ABSTRACT A 3-D finite volume mathematical model was established by customizing pull velocity field function of solidified shell, to simulate the coupled fluid flow, heat transfer, and solidification of beam blank continuous casting, taking into consideration of the effects of mould curvature on the metallurgical performances. When the central impact stream reaches to a certain depth, part of it circulates to scour the solidified shell, causing the remelting of shell at fillet and narrow face centre from about 370 mm down the meniscus to mould exit. The differences of strand surface temperature and shell thickness between inside and outside radius caused by the mould curvature are obvious only at the fillet of the mould exit. The fillet of outside radius having the highest temperature but the thinnest solidified shell is prone to arising quality problems. The metallurgical performances under different casting speed and superheat indicated that the strand surface temperature arises and shell thickness decreases integrally at the mould exit as the casting speed increases. The superheat has the same influence trend as the casting speed does, but the sites it affects are concentrated in the fillet and narrow face centre.