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A Study of the Influence of Air-knife Tilting on Coating Thickness in hot-dip galvanizing

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Journal of Thermal Science 2009年第3期18卷 262-267页

作者： Tae-Seok CHO Young-Doo KWON Soon-Bum KWON School of Mechanical Engineering Kyungpook National University

Gas wiping is a decisive operation in hot-dip galvanizing process. In special, it has a crucial influence on the thickness and uniformity in coating film, but may be subsequently responsible for the problem of splashing. The progress of industry demands continuously the reduction of production costs which may relate directly with the increase of coating speed, and the speed up of coating results in the increase of stagnation pressure in gas wiping system in final. It is known that the increase of stagnation pressure may accompany a harmful problem of splashing in general. Together with these, also, from the view point of energy consumption, it is necessary to design a nozzle optimally. And there is known that the downward tilting of nozzle using in air knife system is effective to prevent in somewhat the harmful problem of splashing. In these connections, first, we design a nozzle with constant expansion rate. Next, for the case of actual coating conditions in field, the effects of tilting of the constant expansion rate nozzle are investigated by numerical analysis. Under the present numerical conditions, it was turned out that the nozzle of constant expansion rate of p = having a downward jet angle of 5^0 is the most effective to diminish the onset of splashing, while the influence of small tilting of the nozzle on impinging wall pres- sure itself is not so large.

关键词： Air-knife Constant expansion rate nozzle Impinging pressure Wall shear stress hot-dip galvanizing Coating thickness Splashing

Influence of Air-Knife Wiping on Coating Thickness in hot-dip galvanizing

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Journal of Iron and Steel Research International 2012年第6期19卷 70-78页

作者： ZHANG Yan CUI Qi-peng SHAO Fu-qun WANG Jun-sheng ZHAO Hong-yang College of Information Science and Engineering Northeastern UniversityShenvan110004LiaoningChina University of Science and Technology Liaoning Anshan 114000LiaoningChina Angang Steel Co Ltd Anshan 114021LiaoningChina

In hot-dip galvanizing process, air jet wiping control is so crucial to decide the coating thickness and uni- formity of the zinc layer on the steel strip. The mathematical models developed predict the zinc coating thickness as a function of pressure and shear stress. The required pressure and shear stress profile on the strip surface were calcu- lated using regression analysis, and carried out using numerical simulation as FLUENT, a finite element analysis software. The influences of the outlet pressure, the nozzle to strip distance, the slot opening, the edge baffle plate, as well as the tilting angle of air knife were discussed. Combining with these results and regression analysis on the practical data, four first-order polynomial multi-parameter models were established for different targeted coating thicknesses with better regression coefficients. The validated model was used to carry out sensitivity analysis to de- termine the favorable controlling regime for the air jet wiping process.

关键词： hot-dip galvanizing air knife air jet wiping numerical simulation coating thickness

Recent development of UHSS and its hot-dip galvanizing processes in Baosteel

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Baosteel Technical Research 2023年第1期17卷 2-10页

作者： JIN Xinyan WANG Li Research Institute Baoshan Iron&Steel Co.Ltd.Shanghai 201999China State Key Laboratory of Development and Application Technology of Automotive Steels(Baosteel) Shanghai201999China

Baosteel has excelled in automotive steel sheets in the past three *** has made a significant contribution to the development of China’s automotive industry by producing a wide range of high-quality steel *** milestones achieved by Baosteel automotive steel sheet were briefly *** current challenges in producing ultra-high strength steel(UHSS),especially hot-dip galvanized UHSS,were *** most current advancements in UHSS and the corresponding hot-dip galvanizing processes were *** galvanizability of Si-Mn-added QP steel and DP steel, Mn-added TWIP steel, and Al-added low-density steel has been improved by different techniques in Baosteel.

关键词： ultra-high strength steel(UHSS) hot-dip galvanizing automotive steel sheet Baosteel

Study on the Wiping Gas Jet in Continuous galvanizing Line

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Journal of Thermal Science 2011年第3期20卷 242-247页

作者： Yong-Hun Kweon Heuy-Dong Kim POSCO Technical Research Laboratories 699 Gumho-dong GwangyangJeonnam 545-090 Korea School of Mechanical Engineering Andong National UniversityAndong 760-749 Korea

In the continuous hot-dip galvanizing process, the gas-jet wiping is used to control the coating thickness of moving steel strip. The high speed gas-jet discharged from the nozzle slot impinges on the strip, and at this moment, wipes the liquid coating layer dragged by a moving strip. The coating thickness is generally influenced on the flow characteristics of wiping gas-jet such as the impinging pressure distribution, pressure gradient and shear stress distribution on the surface of strip. The flow characteristics of wiping gas-jet mentioned above depends upon considerably both the process operating conditions such as the nozzle pressure, nozzle-to-strip distance and line speed, and the geometry of gas-jet wiping apparatus such as the height of nozzle slot. In the present study, the effect of the geometry of nozzle on the coating thickness is investigated with the help of a computational fluid dynamics method. The height of nozzle slot is varied in the range of 0.6mm to 1.7mm. A finite volume method (FVM) is employed to solve two-dimensional, steady, compressible Navier-Stokes equations. Based upon the results obtained, the effect of the height of nozzle slot in the gas-jet wiping process is discussed in detail. The computational results show that for a given standoff distance between the nozzle to the strip, the effective height of nozzle slot exists in achieving thinner coating thickness.

关键词： Gas-Jet Wiping hot-dip galvanizing Impact Pressure Coating Thickness

Experimental and Computational Studies on Coanda Nozzle Flow for the Air Knife Application

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Journal of Thermal Science 2007年第2期16卷 164-169页

作者： Soon-Bum KWON Dong-Won LEE Young-Doo KWON School of Mechanical Engineering Kyungpook National University1370Sankyuk-dongDaegu 702-701Korea

To control the film thickness of zinc in the process of continuous hot-dip galvanizing, it is known from the early days that the gas wiping through an air knife is the most effective one. The gas wiping using in galvanizing process brings about a problem of splashing from the strip edge for a certain high speed of coating. So, in the present study, the effects of the deflection angle of Coanda nozzle on jet structure and the distribution of impinging pres- sure at the plate surface are investigated numerically and experimentally. In numerical analysis, the governing equations consisted of three-dimensional time dependent full Navier-Stokes equations, standard k-ε turbulence model to solve turbulent stTess and so on are employed. In experiment, 16 channel pressure scanning valve and 3-axis auto traversing unit are used to measure the impinging pressure at the strip surface. As a result, it is found that the smaller the deflection angle for the same nozzle slit of air knife is, the larger the impinging pressure is. To reduce the size of separation bubble and to enhance the cutting ability, it is recommendable to use an air knife with the Coanda nozzle.

关键词： Air knife Coanda effect edge splashing gas wiping hot-dip galvanizing impinging jet

Change Rules of Γ_2 Particles in hot-dipped Zn-Ti Coating

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Journal of Iron and Steel Research International 2014年第3期21卷 396-402页

作者： Yan GUI Qiao-yu XU Yan-ling GUO Guangzhou Panyu Polytechnic South China University of Technology

hot-dip Zn-Ti galvanizing can restrain the excess growth of the coating which has better corrosion resist- ances than hot-dip pure Zn. The change rules of Г2 intermetallic compound in hot-dip Zn-Ti galvanizing is investiga ted by immersion time, titanium content and the slag test using scanning electron microscopy （SEM）, energy dis- persive spectroscopy （EDS） and X-ray diffraction （XRD）. And the mechanism of nucleation and growth of Г2 inter- metallic compound is analysed. The results show that, when adding 0. 05mass% titanium to the zinc bath, the Г2 particles form in the η layer, which nucleate by obtaining Ti atoms from the phase and Fe atoms from the dissol- ving ζ phase layer. Moreover, the more titanium is added into the bath, the more and bigger Гz particles appear. The Fz particles in the coatings grow up noticeably with prolonging the immersion time.

关键词： hot-dip galvanizing Zn-Ti alloy bath Г2 phase particle

Influence of Ni-electrodeposited Pretreatment on Galvanized Coatings of Reactive Steels

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Journal of Wuhan University of Technology(Materials Science) 2007年第2期22卷 221-224页

作者：车淳山 College of Materials Science and Engineering South China University of Technology

Four types of steel sheets containing 0.04%, 0.09%, 0. 14% and 0.36% Si, respectively, were electrodeposited with a nickel layer of 3 tam in thickness and then galvanized in molten Zn at 450℃ for various periods of time. The formation and growth of intermetallic compound layers on the surface of the samples were investigated by SEM and EDS. The experimental results show that the method of Ni-electrodeposited pretreatment can distinctively restrain the over-growth of the galvanized coatings of reactive steels and get eligible coatings with a proper thickness, bright appearance and strong adherence. EDS results indicate that a series of Ni-Zn intermetallic compounds γ′, γ and δ, are first formed on the surface of the samples. With a prolonged immersion time, the F2-Fe-Zn-Ni and δ-Fe-Zn are formed accompanied by the gradual disappearance of γ′, γ and δ2 layer. After a longer immersion time, the lumpy ζ- Fe-Zn occurs between δ and liquid Zn and the F-Fe-Zn does between steel substrate and δ. Subsequently, ζ is in the form of a continuous and compact layer. The method of Ni-electrodeposited pretreatment changes the formation of Fe-Zn intermetallic compounds, which delay the growth of lumpy （and promote the growth of compact δ. Consequently, the abnormal growth of reactive steels is eliminated.

关键词： hot-dip galvanizing electrodepositing Ni reactive steel intermetallic compound

Bottom dross defect and its transformation behavior during the galvannealing process

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Baosteel Technical Research 2020年第3期14卷 1-11页

作者： JIN Xinyan LIN Chuanhua QIAN Hongwei ZHANG Jun Research Institute Baoshan Iron&Steel Co.Ltd.Shanghai 201999China State Key Laboratory of Developmeni and Application Technology of Automotive Steels(Baosteel) Shanghai 201999Chtna Baosteel-NSC Automotive Steel Sheets Co. Ltd.Shanghai 200941China

Bottom dross obtained from zinc bath and the typical bottom dross defects on galvanized and galvannealed coating were metallographically *** simulations with different holding time were conducted,and the bottom dross transformation behavior during the galvannealing process was *** fast diffusion between bottom dross particles and the surrounding zinc occurs during the galvannealing process,resulting in the formation of an Al-containing Zn-Fe intermetallic outburst structure at the defect *** thicker and harder coating will cause a shiny spot on the coating surface and a deep dent on the substrate after being temper rolled.

关键词： hot-dip galvanizing bottom dross galvannealing

Investigation and improvement of tiny spot defects on hot-dip galvanized automotive steel sheets

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Baosteel Technical Research 2024年第2期18卷 32-38页

作者： GE Zhiyong YANG Bo YANG Jiwu Baosteel Zhanjiang Iron&Steel Co. Ltd.Zhanjiang 524072GuandongChina

The causes of tiny spot defects on the surface of hot-dip galvanized automotive steel sheets were studied using scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS),and effective control measures were *** results show that rubbing against the top roller after galvanizing is easy due to the local thickness of tiny spot defect location coating;therefore,the surface morphology is different from the normal *** kinds of defects,namely zinc slag,small slivers,and pitting,are likely to cause local thickening of the coating after galvanizing,leading to the formation of tiny ***,resolving the three types of defects can effectively control the generation of tiny spot *** them,due to the hereditary nature of the small sliver defect,focusing on its control and supervision is necessary.

关键词： hot-dip galvanizing tiny spot zinc slag pitting small sliver