Continuous Hot-dip Galvanizing Line Research Articles

Root cause analysis of an abnormal groove-clogging failure on sink rolls in continuous hot-dip galvanizing line

In this study, the root cause of an abnormal premature groove-clogging failure on a sink roll in a hot-dip galvanizing line was investigated. Cross-sectional metallurgical characterization was performed on samples obtained from both the groove-clogged and groove-clear sink rolls. Process investigations focused on the Al and Fe concentrations in zinc bath, bath temperature (Tbath), and strip entry temperature (Tstrip). It was found that groove-clogging failure on the sink roll was caused by a large amount of Fe2Al5Znx dross buildup in the grooves, and Tstrip control was the key factor. When Tstrip was consistently lower than Tbath for a long time period during operation, the Fe2Al5Znx intermetallic compounds preferentially precipitated and grew in the locally cooled zinc bath because of the decreased Fe solubility at lower Tbath. When Tstrip was controlled at least 5 ℃ higher than Tbath, the groove-clogging failure was successfully solved.

A fast online estimator of hot-dip zinc coating weight using improved dynamic fuzzy neural networks

The measurement value of the zinc coating weight (mass) of continuous hot-dip galvanizing line often deviates from that of gravimetric method. We employed 17 samples on-line and off-line comparative test, and revealed the deviation is inseparable from the measured value of iron content. In view of influence of the iron content on the phase distribution of the zinc-iron alloy layer, using iron content to make up for the shortcomings of X-ray fluorescence (XRF) fundamental parameter method, the accurate value of zinc coating weight were estimated by dynamic fuzzy neural networks. The results show that the average deviation of the estimated zinc coating weight is reduced from 3.07 g/m2 of XRF to 1.16 g/m2, with an iron content ranging from 5 to 15 %. This estimator is suitable for continuous production lines with fast speed and high control precision.

Oxidation resistance of Al2O3/SiO2 nanocomposite coating on hot-dip galvanized steel deposited by chemical immersion and sol-gel coating

A protective coating against oxidation of hot-dip galvanized (HDG) steel was developed using a solution-based route and its oxidation protectiveness during hot-stamping was evaluated. An Al2O3/SiO2 nanocomposite coating of approximately 500 to 700 nm was developed and successfully processed on a HDG SGC400 steel via a chemical immersion and sol-gel dip coating method. Oxidation tests at 900 °C show that oxidation of the HDG SGC400 steel is effectively suppressed by the Al2O3/SiO2 nanocomposite coating, signifying its potential as a protective coating for HDG press hardening steel. The phase transformation of Al2O3/SiO2 nanocomposite coating at 900 °C was also investigated. Although cracks form inevitably, the Al2O3/SiO2 nanocomposite coating is stable at 900 °C. Specially, the thickness of the composite coating changes slightly and ZnO is confined in the composite coating via the formation of Zn2SiO4 nanoparticles. Finally, this chemical immersion and dipping route to form a nanocomposite oxide coating is in line with the continuous hot-dip galvanizing line for steel industry.

Investigation of the Influence of Proximal Radiation on the Thermal Stresses and Lifetime of Metallic Radiant Tubes in Radiation-Dominated Industrial Furnaces*

Abstract The influence of surrounding (or proximal) radiation on radiant tubes inside a continuous hot-dip galvanizing line was investigated. The furnace chamber, the strip and the neighbouring tubes were considered as the surroundings. A coupled heat transfer model was developed and subsequently validated against experimental measurements. This model was used to calculate the radiation exchange between the tube and its surroundings, and to give the new temperature distribution on the tubes as its output. This result served as an input to an already validated FEM model, which was used to assess the creep behaviour and the corresponding stresses on the tube. Basis of the investigated setups were Alloy 602 p-type tubes operating under burner on/off firing. The results show an increase in creep deformation of the tube when the surroundings were taken into account. Highest creep deformations were observed for setups with a strip, even though these cases showed the lowest maximum tube temperatures. Furthermore, an opposing effect between creep deformation and stresses acting on the tube exists. This is supported by the fact that no definite pattern relating the creep and stresses of a tube was found. Local tube temperature gradients and transient cyclic loading due to burner on/off firing were observed to have a significant influence on the tube's service life.

About Continuous Hot-Dip Galvanizing Line

About Continuous Hot-Dip Galvanizing Line

Elasto-plastic bending of steel strip in a hot-dip galvanizing line

A quasi-static model of axially moving steel strips in a continuous hot-dip galvanizing line is presented. The model provides the bending line of the strip and takes into account the history of elasto-plastic deformation. The numerical integration of the material model of elasto-plastic deformation is algorithmically separated from the solution of the boundary value problem of the bending line by pre-computing sets of one-dimensional candidate relations between the strip curvature and the bending moment. Using this model, the influence of different roll positions in the zinc bath on the mean displacement of the strip at the gas wiping dies and the maximum lateral curvature of the strip (crossbow) can be efficiently calculated and analyzed.

UTILIZATION OF INDUCTION HEATING TECHNOLOGY IN GALVANIZING LINES

Continuous Hot-Dip Galvanizing lines are widely used for the production of coated steel sheets. Quality improvement measures are of great importance for this type of line. A significant proportion of production and quality losses when operating these types of lines occurs when production is transitioning from one strip gauge/thermal cycle to another. Utilizing induction heating technology, in combination with a sophisticated control system, can dramically decrease yield losses during transitions. Dynamic Transition and Production Planning Models have recently been developed for the simulation and control of the continuous hot-dip galvanizing line. The results of this work have been implemented in some galvanizing lines with production rate up to 350,000-ton annual capacity.

Analysis on dominant influencing factors of on-line life cycle in sink roll system and effective improved methods

The continuous hot-dip galvanizing line is performed by threading the steel strip through three rolls of the sink roll system (including sink roll, stabilizer roll and correcting roll) submerged in molen zinc. The premature failure of sleeves and bushings of the three rolls would result in increased cost of production and low production efficiency. According to the on-site investigation of Meishan Iron&Steel Ltd and theoretical analysis, it indicated that the dominant influencing factor of online life cycle was the abrasion between the sleeves and bushings. Insufficient abrasive resistance of sleeves and improper hardness ratio between sleeves and bushings led to rapid abrasion of sleeves. When the sleeves were manufactured by higher hardness materials, the online life cycle was increased from less than 15days to about 20days.

CGLワイピング部における電磁石を用いた鋼板の振動および形状制御

Hot-dip galvanized steel sheets are often used for automobile exterior body panels to enhance the corrosion performance. The requirements for their surface appearance from automakers have become higher recently. Especially, a uniform coating layer of zinc is required. In a continuous hot-dip galvanizing line (CGL), a pair of gas wipers, which are installed just above the zinc pot, is used to control the thickness of the coating layer. The strip vibration at the gas wipers causes the uneven coating thickness in the traveling direction, while the cross-bow of the strip leads to the unevenness in the width direction. The behavior of the strip at the gas wipers should be stable for the uniform coating layer. In order to make the strip stable and flat, a strip vibration and shape control technique using electromagnets has been developed. It greatly contributes to produce hot-dip galvanized steel sheets with excellent surface appearance.

Research on Vibration Control Method of Steel Strip for a Continuous Hot-dip Galvanizing Line

Nonlinear vibration of axially moving steel strip with tension near the air knife box during continuous hot-dip galvanizing process is investigated. A model of strip vibration for cooling section is established. Governing equations of the model are derived through the Hamilton's principle. Effect of speed, tension, molten zinc, oscillation of touch rolls and nonlinear wind load on strip vibration is considered. The reasonability of boundary conditions of the model is confirmed by comparison of results from theoretical method and numerical simulation. Averaging method is employed in solving the equations and obtaining displacement response. The relation between amplitude near the air knife and production parameters is studied and further solutions of vibration control is presented. The research reveals that speed of strip has noticeable effect on amplitude near the air knife. It will be more difficult to reduce vibration with the increase of speed. Larger tension is in favor of keeping away from peaks of amplitude by using speed adjustment. A scheme of vibration control based upon averaging method can meet the requirement of production. A vibration suppression proposal by improving support stiffness of touch rolls is suggested.

Research on the Vibration of Sheet Metal near the Zinc Pot Area in Continuous Hot-Dip Galvanizing Line

Large vibration of the sheet metal near the air knife is one of the main factors controlling the accuracy of thickness of the cladding zinc in continuous hot-dip galvanizing line. Lots of vibration tests are carried out on the strip and main equipments in the zinc pot area of a galvanizing line during downtime and operation in order to diagnose causes of the large vibration of the strip near the air knife. Theoretic foundation of adjustment of control parameters to suppress the strip vibration is established. Main mechanisms of large vibration of the strip are found by the theory of the transverse vibration of axially moving continua. The first one is the resonance of forced vibration induced by support movement aroused by passive rollers’ sloshing in the zinc pot, and the other is the parametrically excited resonance of the strip induced by tension fluctuation enlarged by local structural resonances of the cooling tower.

Real-Time Vibration Control of Steel Strip Immersed in Fluid for a Continuous Hot-Dip Galvanizing Line

A method of combining theoretical analysis with numerical simulation is presented to achieve real-time vibration control of steel strip immersed in fluid during continuous hot-dip galvanizing process. Theoretical and numerical methods are employed to investigate inherent properties of strip and immersed strip, respectively. Multivariate quadratic regression is adopted to fit the ratio of natural frequencies. Keeping inherent frequencies far from excitations is taken as optimization objective, based upon field testing results. Real-time vibration control of immersed strip near the air knife box is carried out by varying production parameters. The results reveal that width, thickness, tension and molten zinc have noticeable and highly nonlinear effect on inherent properties of steel strip. Axial speed of strip is negligible in calculations of natural frequencies. Wind load of air knife moving relative to strip is the principal source of vibration. The approach of combining theory with numerical computation can meet the requirement of real-time vibration control of alloy strip.

On-line Control of Strip Surface Quality for a Continuous Hot-Dip Galvanizing Line Based on Inherent Property of Thin Plate

Theory and method of on-line control for surface quality during continuous hot-dip galvanizing process due to vibration of steel strip near the air knife box are investigated.A model of strip vibration for cooling section is established.Analytic solutions of the model for natural property are obtained by using the Hamilton's principle.Numerical simulations are employed to verify rationality of the model.Basic ideas and solutions for on-line control of surface quality in continuous hot-dip galvanizing are presented,based on field testing results and technique of real-time surface detection.The research shows that tension and velocity of the strip have noticeable effect on natural frequencies and excitation frequencies respectively.They may be regarded as key parameters for on-line control of surface quality.Axial velocity of the strip is negligible in calculations of natural frequencies.Numerical simulations confirm the validity of substituting simple support for contact rolls and stabilizing rolls in the vibration model.Analytic solutions of natural property make it possible to realize on-line control of surface quality.A vibration suppression scheme by improving support stiffness of contact rolls and stabilizing rolls is proposed.

Morphology and antimony segregation of spangles on batch hot-dip galvanized coatings

Spangles produced by batch hot-dip galvanizing process have a rougher surface and a greater surface segregation of alloying element compared with those in continuous hot-dip galvanizing line (CGL), owing to the cooling rate of the former is much smaller than that of the later. Therefore, typical spangles on a batch hot-dipped Zn–0.05Al–0.2Sb alloy coating were investigated. The chemical, morphological characterization and identification of the phases on the spangles were examined by scanning electron microscopy (SEM), backscattered electron imaging (BSE), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The results showed that the coating surface usually exhibited three kinds of spangles: shiny, feathery and dull spangle, of which extensively antimony surface segregation was detected. The nature of precipitate on the coating surface was identified as β-Sb 3Zn 4, The precipitated β-Sb 3Zn 4 particles distributed randomly on the shiny spangle surface, both β-Sb 3Zn 4 particles and dentritic segregation of antimony dispersed in the dendritic secondary arm spacings of the feathery spangle and on the whole dull spangle surface. The dentritic segregation of antimony and precipitation of Sb 3Zn 4 compound are discussed by a proposed model.

갈바어닐링온도변화가 합금화용융아연코팅의 합금상과 마찰특성에 미치는 영향

This paper is aimed to understand the effect of different galvannealing temperatures on the frictional properties and Fe-Zn intermetallic phases of the galvannealed (GA) coatings on steel sheets. Their galvannealing treatments were conducted at 465, 505, 515 and 540℃ for about 10s in the additional heating furnace of an industrial continuous hot-dip galvanizing line. The mechanical and the frictional properties of the coatings were estimated using nanoindentation, nanoscratch, micro vickers hardness tests and flat friction tests, which were performed at contact pressures of 4, 20 and 80㎫. Also, the correlation between the microstructure and the frictional properties of the GA coatings were investigated by SEM observation for the cross-section of the GA coating after and before flat friction tests. The results showed that the mechanical and the frictional properties of the coatings are strongly dependent on their phase distributions and microstructure. Especially, in low contact pressure of 4㎫ the frictional properties of the coatings were dependent on the surface phases and morphology, while in high contact pressure of 80㎫ it was influenced by their mechanical properties based on the dominant phase distributions.

Identification of segregation phase on a batch hot‐dip‐coated Zn/0.1Al/0.2Sb surface

AbstractThe segregation of antimony in a batch hot‐dipped regular‐spangle galvanized coating from a Zn‐0.1Al‐0.2Sb bath was investigated. The samples were characterized by using SEM/EDS. The nature of the segregation phase was determined by XRD as βSb3Zn4. Assisted with SbZn phase diagram, the behavior of antimony during the solidification process of the Zn‐0.1Al‐0.2Sb coating is examined. It is suggested that the coating solidification proceeds in three stages. Owing to the cooling rate of batch hot dip galvanizing process smaller than that of continuous hot dip galvanizing line (CGL), the resulting structure of the segregation phase in current work is βSb3Zn4 instead of metastable ζSb2Zn3 for CGL. Copyright © 2007 John Wiley & Sons, Ltd.

Evaluation of the Annealing Temperature Effect on the Mechanical Properties of a IF Steel by Means of Physical Simulation

Interstitial-free (IF) sheet steels are largely used in automotive deep-drawing applications, as they offer both good formability and adequate strength for auto bodies. In order to improve the corrosion resistance they are usually coated, mostly by hot-dip galvanizing. In the present work two IF steels purposely designed for a specific continuous hot-dip galvanizing line are investigated. The employed methodology, based on physical simulation, is presented and discussed in the paper. Its reliability is demonstrated by comparing some experimental and industrial results. The simulated specimens are tensile tested and the effects of annealing temperature and line speed on their mechanical properties are evaluated.

Numerical Analysis of Fluid Flow and Heat Transfer in Molten Zinc Pot of Continuous Hot-dip Galvanizing Line.

A numerical model adopting a partially staggered grid system for the location of dependent variables has been developed to analyze the fluid flow and temperature distributions in a molten zinc pot of No. 2 CGL of POSCO Kwangyang strip mills. A control volume based finite difference procedure was employed to solve the conservation equations transformed by using the boundary-fitted-coordinate (BFC) system. The calculation results have shown that a change in the steel strip velocity has little influence on the overall flow pattern developed in the pot. The overall temperature distribution was rather uniform as predicted. However, charging cold ingots directly into the pot produced a non-uniform distribution of temperature. The local temperature fluctuations will promote the formation of intermetallic dross particles. It has been proposed that the non-uniform distribution of temperature could be reduced by selecting an appropriate channel inductor position as well as by optimizing the zinc ingot loading position.