Metals

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28 pages, 4033 KiB

Open AccessArticle

Modeling Air Aspiration in Steel Continuous Casting Slide-Gate Nozzles

by Hyunjin Yang, Hamed Olia and Brian G. Thomas

Metals 2021, 11(1), 116; https://doi.org/10.3390/met11010116 - 8 Jan 2021

Cited by 16 | Viewed by 4402

Air aspiration is an important cause of nozzle clogging and inclusions in final products of continuous casting of steel due to the presence of metal oxides (such as alumina) which occur through the reoxidation of molten steel. This problem is most likely to [...] Read more.

Air aspiration is an important cause of nozzle clogging and inclusions in final products of continuous casting of steel due to the presence of metal oxides (such as alumina) which occur through the reoxidation of molten steel. This problem is most likely to occur when the flow control system (slide-gate or stopper rod) causes the pressure inside the nozzle to drop below atmospheric pressure, drawing gas into the system through possible cracks or gaps in the refractory walls. In this work, a 1-D pressure-energy model of the complete metal delivery system from the tundish to the mold is developed to predict the pressure distribution and throughput under dynamic operating conditions and varying clogging conditions. The energy balance approach includes pressure losses in the slide-gate, wall friction, and nozzle geometry variations, including the effects of multiphase flow due to argon gas injection. The model also predicts air aspiration, oxide inclusion formation, and the time for clogging shutdown. The predicted pressure distribution is verified with a three-dimensional numerical simulation of multiphase turbulent flow, and is validated with plant measurements. Parametric studies with different submerged entry nozzle (SEN) designs revealed that a smaller SEN diameter may lessen negative pressure by redistributing the pressure loss from the slide-gate to the entire nozzle through increased friction losses. Under negative pressure, a submillimeter-thin gap was shown to cause considerable air aspiration. Clogging shutdown times were evaluated for several scenarios under static and dynamic operating conditions. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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12 pages, 3537 KiB

Open AccessArticle

Bubble Formation by Short Plunging Jet in a Continuous Casting Tundish

by Sheng Chang, Zheng Liu, Zongshu Zou, Lei Shao and Baokuan Li

Metals 2020, 10(12), 1590; https://doi.org/10.3390/met10121590 - 27 Nov 2020

Cited by 2 | Viewed by 2065

Abstract

A short plunging jet technique was developed to produce small bubbles in continuous casting tundish, with argon sealing, in order to promote the removal of inclusions smaller than 50 μm. The liquid steel coming out of the ladle shroud is accelerated and vibrated [...] Read more.

A short plunging jet technique was developed to produce small bubbles in continuous casting tundish, with argon sealing, in order to promote the removal of inclusions smaller than 50 μm. The liquid steel coming out of the ladle shroud is accelerated and vibrated by gravity, leading to gas entrainment. This novel approach is free from bubbles growing along the nozzle surface due to the poor wetting condition, which is applicable to producing small bubbles in liquid steel. Water modeling was carried out to investigate the impact of the free-fall length on gas entrainment by a short plunging jet. The results show that gas can be entrained into the liquid bath with a free fall longer than 15 mm. Part of the entrained gas is separated from the gas sheath by the rough surface of the inflow stream, forming initial bubbles. These initial bubbles are further refined into small ones of 0.4~2.5 mm due to the turbulent flow in the pouring region. The cylindrical shield can effectively isolate the surface fluctuation caused by the short plunging jet; thereby, a stable slag layer in the tundish can be maintained during gas entrainment. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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19 pages, 4233 KiB

Open AccessArticle

A 1D Analytical Model for Slag Infiltration during Continuous Casting of Steel under Non-Sinusoidal Mold Oscillation

by Hyunjin Yang

Metals 2020, 10(10), 1389; https://doi.org/10.3390/met10101389 - 19 Oct 2020

Cited by 4 | Viewed by 2520

Abstract

A 1D analytical model for slag infiltration during continuous casting of steel is developed to investigate the slag behavior in the mold–strand gap. The superposition principle and Fourier expansion are applied to obtain the analytical solution for transient slag flow under arbitrary mold [...] Read more.

A 1D analytical model for slag infiltration during continuous casting of steel is developed to investigate the slag behavior in the mold–strand gap. The superposition principle and Fourier expansion are applied to obtain the analytical solution for transient slag flow under arbitrary mold oscillation including non-sinusoidal oscillation mode. The validated model using literature data partially explains several controversies such as slope of slag film channel, mechanism of non-sinusoidal mold oscillation, and timing of slag infiltration. The model shows that a converging slag film into the casting direction is required to open the mold–strand gap if compression is applied in between. Also, model calculations imply that higher slag consumption is achievable from non-sinusoidal mold oscillation by means of the increase of film thickness through longer positive pressure with higher peak pressure. The model demonstrates a time difference between slag flow and pressure near the meniscus and the discrepancy in timing of infiltration between previous works is attributed to the mismatch. The model provides a concise but reliable tool to understand slag infiltration behavior and design mold oscillation settings. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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11 pages, 2173 KiB

Open AccessArticle

Investigation and Minimization of Slag Spot Surface Defects in Continuous Casting of High Carbon Steel Billets through Statistical Evaluation

by Yong-feng Chen, Li Zhao, Xiao-tan Zuo, Qun-nan Tao, Hong-biao Zhang, Hai Li, Qiang-qiang Wang and Sheng-ping He

Metals 2020, 10(7), 878; https://doi.org/10.3390/met10070878 - 1 Jul 2020

Cited by 1 | Viewed by 5233

Abstract

Slag spot surface defects often appear during continuous casting of high carbon steel billets due to the solidification characteristics of molten steel in the mold. To target the problem of surface slag spot defects that occur frequently during the continuous casting of high-carbon [...] Read more.

Slag spot surface defects often appear during continuous casting of high carbon steel billets due to the solidification characteristics of molten steel in the mold. To target the problem of surface slag spot defects that occur frequently during the continuous casting of high-carbon steel strands, we analyzed the influence of molten steel superheat, accumulated service time and the water inlet temperature of the mold, the size of the submerged entry nozzle and the physical and chemical properties of the mold powder on the slag spot defects. The production practice shows that by adjusting the superheat of molten steel to 30–35 °C, the water inlet temperature of the mold is stable at 33–35 °C. To adjust the internal and external diameter of the immersion nozzle to 30–70 mm, the viscosity and melting temperature of the mold powder were adjusted from 0.45–0.55 Pa·s, 1100–1140 °C to 0.15–0.25 Pa·s, 1020–1060 °C. The final billet surface quality was improved significantly, the billet surface was smooth, the oscillation marks were relatively smooth and regular and the slag trench ratio was reduced from the original maximum of 40–50% to less than 1%. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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12 pages, 6906 KiB

Open AccessArticle

An Approach for Modelling Slag Infiltration and Heat Transfer in Continuous Casting Mold for High Mn–High Al Steel

by Jie Yang, Dengfu Chen, Mujun Long and Huamei Duan

Metals 2020, 10(1), 51; https://doi.org/10.3390/met10010051 - 26 Dec 2019

Cited by 9 | Viewed by 3793

Abstract

To clarify the characteristics of slag infiltration and heat transfer behaviors in the meniscus region during the casting of high Mn–high Al steel, a mathematical model of a continuous casting mold that couples fluid flow with heat transfer, and solidification is developed. The [...] Read more.

To clarify the characteristics of slag infiltration and heat transfer behaviors in the meniscus region during the casting of high Mn–high Al steel, a mathematical model of a continuous casting mold that couples fluid flow with heat transfer, and solidification is developed. The model is based on the change in slag composition and properties caused by the steel/slag reaction. The formation and evolution of the meniscus profile and slag films for different mold fluxes during mold oscillation are described. The results show that the rapid growth of the slag rim with a high Al₂O₃ content approaches and deforms the meniscus so that a series of casting problems such as slag infiltration blocking, large fluctuations in heat flux, and even meniscus breaking occur in the continuous casting process. Predictions are in good agreement with plant measurements. These findings provide an improved understanding of the complex phenomena occurring in the meniscus region and give new insights into the evaluation and optimization of mold flux properties for high Mn–high Al steel casting. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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20 pages, 3617 KiB

Open AccessArticle

MgO Refractory Doped with ZrO₂ Nanoparticles: Influence of Cold Isostatic and Uniaxial Pressing and Sintering Temperature in the Physical and Chemical Properties

by Cristian Gómez-Rodríguez, Daniel Fernández-González, Linda Viviana García-Quiñonez, Guadalupe Alan Castillo-Rodríguez, Josué Amilcar Aguilar-Martínez and Luis Felipe Verdeja

Metals 2019, 9(12), 1297; https://doi.org/10.3390/met9121297 - 1 Dec 2019

Cited by 9 | Viewed by 4340

Abstract

The chemical environment and the internal conditions of the furnaces and ladles are extremely aggressive for the refractories, so metallurgical industries demand refractory linings with greater durability and resistance to avoid unforeseen stoppages and to reduce the changes of the furnace lining. Therefore, [...] Read more.

The chemical environment and the internal conditions of the furnaces and ladles are extremely aggressive for the refractories, so metallurgical industries demand refractory linings with greater durability and resistance to avoid unforeseen stoppages and to reduce the changes of the furnace lining. Therefore, the current work aims to evaluate the impact of the additions of ZrO₂-nanoparticles (1, 3, and 5 wt. %) in magnesia-based bricks. A comparative study of the physical and chemical properties in bricks obtained using two cold pressing techniques (uniaxial and isostatic pressing) and two sintering temperatures (1550 and 1650 °C) was carried out. The microstructure and crystalline phase characteristics obtained after the heat treatments and the slag corrosion test was studied using scanning electron microscopy/electron dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The results reveal that the sample with 5 wt. % of ZrO₂ nanoparticles (obtained by cold isostatic pressing and sintering at 1650 °C) has the lowest porosity and greatest resistance to penetration of blast furnace slag. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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13 pages, 4670 KiB

Open AccessArticle

Influence of EMS on Asymmetric Flow with Different SEN Clogging Rates in a Slab Continuous Casting Mold

by Bin Li, Haibiao Lu, Yunbo Zhong, Zhongming Ren and Zuosheng Lei

Metals 2019, 9(12), 1288; https://doi.org/10.3390/met9121288 - 29 Nov 2019

Cited by 11 | Viewed by 3225

Abstract

Submerged entry nozzle (SEN) clogging is a troublesome phenomenon in the continuous casting process that can induce the asymmetric mold flow, and thus, lowering the steel product quality. In this paper, a mathematical model coupling the electromagnetic and flow fields, was developed to [...] Read more.

Submerged entry nozzle (SEN) clogging is a troublesome phenomenon in the continuous casting process that can induce the asymmetric mold flow, and thus, lowering the steel product quality. In this paper, a mathematical model coupling the electromagnetic and flow fields, was developed to investigate the influence of the SEN clogging rate on the flow field and the influence of electromagnetic stirring (EMS) on the asymmetric mold flow. Slag entrapment index R_c was introduced to quantify the possibility of slag entrapment, and symmetric index S was introduced to quantify the symmetry of the flow field. The results show that as the SEN clogging rate increased, the slag entrapment index R_c increased, while the symmetric index S decreased. EMS can greatly improve the symmetry of the flow field with SEN clogging, but it cannot remove the asymmetric phenomenon completely because the stirring intensity should be controlled below the safe level to avoid slag entrapment. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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13 pages, 3426 KiB

Open AccessArticle

Effect of CaF₂ on the Viscosity and Microstructure of CaO–SiO₂–Al₂O₃ Based Continuous Casting Mold Flux

by Xingjuan Wang, Hebin Jin, Liguang Zhu, Ying Xu, Ran Liu, Zhanlong Piao and Shuo Qu

Metals 2019, 9(8), 871; https://doi.org/10.3390/met9080871 - 8 Aug 2019

Cited by 11 | Viewed by 5348

Abstract

In this study, a CaO–SiO₂–Al₂O₃-based continuous casting mold flux was designed using the FactSage thermodynamics software to determine the composition range of CaF₂. The viscosity characteristics of the mold flux were determined using a rotating [...] Read more.

In this study, a CaO–SiO₂–Al₂O₃-based continuous casting mold flux was designed using the FactSage thermodynamics software to determine the composition range of CaF₂. The viscosity characteristics of the mold flux were determined using a rotating viscometer. The results show that the constant temperature viscosity at 1300 °C decreases gradually as CaF₂ content is increased from 3% to 11% in the CaO–SiO₂–Al₂O₃-based slag. Viscosity is reduced from 0.854 to 0.241 Pa·s, viscous the flow activation energy is reduced from 157.74 to 114.34 kJ·mol⁻¹, and the break temperature is reduced from 1280 to 1180 °C. Furthermore, when the CaF₂ content is increased from 3% to 11%, the number of nonbridging fluorine bonds (Al–F structure and Si–F structure) in the melt increases to 287, the number of bridging fluorine bonds (Al–F–Al structure, Si–F–Si structure, and Si–F–Si structure) is only 17, and the network rupture of fluorine ions in the system is larger than the network formation. Consequently, both the degree of polymerization and viscosity are reduced. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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15 pages, 7209 KiB

Open AccessArticle

Quasi-Symmetric Transfer Behavior in an Asymmetric Two-Strand Tundish with Different Turbulence Inhibitor

by Bin Yang, Hong Lei, Yan Zhao, Guocheng Xing and Hongwei Zhang

Metals 2019, 9(8), 855; https://doi.org/10.3390/met9080855 - 5 Aug 2019

Cited by 15 | Viewed by 3291

Abstract

The task of the tundish is to supply and distribute the molten steel with the similar temperature and the similar inclusion mass concentration to the continuous casting mold. But it is difficult for the asymmetric tundish to accomplish this task. Thus, the scheme [...] Read more.

The task of the tundish is to supply and distribute the molten steel with the similar temperature and the similar inclusion mass concentration to the continuous casting mold. But it is difficult for the asymmetric tundish to accomplish this task. Thus, the scheme about the asymmetric turbulence inhibitor and the baffle wall with guided holes is proposed to optimize the tundish. In order to have a deep insight into the metallurgical behavior in the asymmetric tundish, numerical simulation is applied to describe the fluid flow, the heat transfer, RTD (residence time distribution) curve, and inclusion collision aggregation behavior. Numerical results show that the predicted temperature and inclusion concentration agree with the industrial experimental data. In the asymmetric two-strand tundish, the asymmetric turbulence inhibitor and the baffle wall with guided holes can extend the mean residence time at the left outlet, reduce the temperature difference between the two outlets, and prompt the inclusion removal rate at the left outlet. Full article

(This article belongs to the Special Issue Mold and Tundish Metallurgy)

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