Development of Novel Air-knife System to Prevent Check-mark Stain on Galvanized Strip Surface

Yoon, Hyun Gi; Chung, Myung Kyoon

doi:10.2355/isijinternational.50.752

Cited by 11 publications

(13 citation statements)

References 12 publications

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“…They revealed that such a pattern of periodical pressure distributions moves alternatively sideways and together with the longitudinal feed of the strip, it forms the sag lines of checkmark pattern on the surface. In a recent study, 13) they further showed that the snaky coating defect can be avoided by suppressing the periodic variation of the surface pressure by utilizing a secondary parallel gas jet adjacent to the main jet. On the other hand, it was demonstrated that other surface defects can be improved by controlling the aluminum content and temperature of the bath 14) or stirring the molten zinc in the bath.…”

Section: Cfd Analysis Of Sag Line Formation On the Zinc-coated Steel mentioning

confidence: 99%

CFD Analysis of Sag Line Formation on the Zinc-coated Steel Strip after the Gas-jet Wiping in the Continuous Hot-dip Galvanizing Process

Yoon

Chung

2011

ISIJ Int.

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of the coating thickness for long wavelength perturbations. Ellen and Tu 3) have suggested a non-dimensional model that takes into account the surface shear stress and their model gives significantly more accurate prediction of the final coating thickness. Also, Tu and Wood 4) have experimentally demonstrated that the final coating thickness depends on both the pressure and shear stress distributions on the strip surface. Although Tuck and Vanden-Broeck.5) and Yoneda 6) suggested that the final thickness depends on the surface tension and the shear stress on the strip, recently Gosset and Buchlin 7) have shown that the surface tension does not play any role in determining the final coating thickness.There have appeared several numerical simulations of the gas wiping process to predict the final coating thickness by using CFD. One of the recent studies is that by Lacanette et al. 8,9) who numerically simulated the final coating thickness by using volume of fluid-large eddy simulation (VOF-LES) modeling. Their results were satisfactorily compared with their experimental data. They found that the coating thickness is independent of the nozzle-to-plate distance when it is smaller than 8 times of the nozzle slot width. Myrillas et al. 10) tried to validate a model for the gas jet-liquid film interaction in the gas wiping process. In their study, they found that two-phase numerical simulations using LES is more suited to model of the complex interaction than k-e turbulence model. Through these previous studies it can be concluded that the dominant factors affecting the final coating thickness are pressure gradient and shear stress on the strip.So far, most of the previous studies were focused on the average final coating thickness along longitudinal direction and their numerical and mathematical models are made in two-dimensional domain. In spite of its good productivity and easy control of the zinc coating thickness, however, the coated film surface after gas wiping has frequently three dimensional surface defects such as dents, blow lines, peculiar features and sag-lines.11) Therefore, in order to obtain a uniform coating on the strip, it is necessary to investigate in details the three dimensional character of the coated surface after the gas wiping process.Among these surface defects, the sag lines (or snaky coating) cause many problems such as irregularity in the electrical and thermal characteristics and the diffused reflection on the coated surface. The snaky coating is that with an oblique patterns appearing on the coated film surface after the gas wiping process. Depending on its seriousness, the snaky coating is usually classified into five grades as shown in Fig. 2. The arrows in Fig. 2 indicate the moving direction of steel strip. The first grade indicates that no sag line is observed on the surface. In the surface pattern of the 2nd grade, rather short sag lines appear irregularly, thus a pattern of sag lines is vaguely discernible. On the other hand, the 3rd-5th grade snaky coatings reveal oblique...

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Section: Cfd Analysis Of Sag Line Formation On the Zinc-coated Steel mentioning

confidence: 99%

CFD Analysis of Sag Line Formation on the Zinc-coated Steel Strip after the Gas-jet Wiping in the Continuous Hot-dip Galvanizing Process

Yoon

Chung

2011

ISIJ Int.

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“…One such example is the horizontal air-knife system that removes excessive molten zinc from both surfaces of a vertically moving steel strip that is drawn from a molten zinc bath. Recent studies of twodimensional plane impinging jets [12,13] reveal that spanwise vortices appear along the transverse direction of the twodimensional plane jet and the centers of the span-wise vortices move alternatively right or left almost periodically. And since such alternating vortex tubes impinge on the moving steel strip, the surface pressure distribution along the transverse direction is almost cyclical.…”

Section: Introductionmentioning

confidence: 99%

Large eddy simulation of flow characteristics in an unconfined slot impinging jet with various nozzle-to-plate distances

Yoon

Chung

2011

J Mech Sci Technol

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“…Additionally, they are used to provide humidity to foods in the food sector [1][2][3]. Air knives are commonly used in the continuous hot dip galvanizing procedure, a coating technique in the steel industry [4][5][6][7][8][9][10][11]. The paper industry is one with effective use of air knives in the thermal paper production process where a very thin layer of chemicals is spread on paper [12].…”

Section: Introductionmentioning

confidence: 99%

Experimental verification of the feasibility of the CFD approach in an air-knife

Altay

Yaman

2022

THERM SCI

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Air knives with very different nominal values are used for various purposes in the industry. The uses of air knives include the painting and coating stages of automobile semi-finished products, as well as many stages related to food production. One of the important sectors among these is the continuous hot-dip galvanizing process, which is a coating technique in the steel industry. In addition, the chemical coating process on paper as a very thin layer is another research topic. The most critical process needed in these sectors is to ensure a homogeneous air-flow at the expected air speed of the air-knife. These determine whether the coating on the steel or the chemical layer on the paper is homogeneous at the desired thickness. In this study, it is aimed that the air-knife can reach the expected values (speed and homogeneous distribution) with the expected tolerances, the shortest time, cost, and the least production process error. First, a design has been made so that this knife can blow air at the desired speed and homogeneously. For this, the most appropriate modeling and design values were created and analyzed with the CFD. The analysis and evaluations of the design were confirmed as a result of the measurements made on the prototype. This study shows that the inclusion of this type of modeling and analysis in the rapid product development process has an important role in minimizing cost and time.

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Development of Novel Air-knife System to Prevent Check-mark Stain on Galvanized Strip Surface

Cited by 11 publications

References 12 publications

CFD Analysis of Sag Line Formation on the Zinc-coated Steel Strip after the Gas-jet Wiping in the Continuous Hot-dip Galvanizing Process

CFD Analysis of Sag Line Formation on the Zinc-coated Steel Strip after the Gas-jet Wiping in the Continuous Hot-dip Galvanizing Process

Large eddy simulation of flow characteristics in an unconfined slot impinging jet with various nozzle-to-plate distances

Experimental verification of the feasibility of the CFD approach in an air-knife

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