Sink Roll 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.

Intermetallic Compounds Formation during 316L Stainless Steel Reaction with Al-Zn-Si Coating Alloy

Steel products are coated with Aluminum (Al) and Zinc (Zn) alloys to improve their corrosion properties. Bulk steel products are coated in batches; however, steel sheets are coated by a continuous hot-dip galvanizing process. Steel sheets are guided into and out of the molten Al-Zn-Si (AZ) bath with the help of stainless-steel rolls, known as guiding, and sink rolls. These rolls are subjected to excessive surface corrosion with molten AZ bath and, hence, are replaced frequently. The surface deterioration of the immersed rolls has been a long-standing issue in the galvanizing industry. In this study, 316L stainless-steel (SS) rods are immersed in the AZ alloy at 600 °C. The immersion time varied from 1 day to 7 days under the static melt conditions in the iron (Fe)-saturated AZ bath. Microstructural analysis of the immersed SS samples revealed two distinct intermetallic compound (IMC) layers forming between the SS substrate and AZ alloy. The IMC layer 1 (AL-1) formed between the SS substrate and IMC layer 2 (AL-2), growing in thickness from 68 µm to 120 µm within 5 days of immersion. The AL-2, which formed between AL-1 and AZ alloy after 24 h of immersion, then grew in thickness up to 150 µm with an uneven trend. The AL-1 is composed of Fe2Al5 and that of AL-2 is composed of FeAl3 that were predicted by the FactSage thermodynamic analysis. Crack development between AL-1 and AL-2 layers, and disintegration of AL-2 into the AZ bath, are key findings of this study. A drastic hardness increase was observed because the IMC layers produce a hard and brittle sink roll surface.

Experimental Study on Sliding bearing of Sink Roll in Galvanizing Line

Hot dip galvanizing can effectively prevent the corrosion of steel. With the increasing demand of industry for steel strip, higher requirements are put forward for stable and continuous operation of submerged roller bearings in hot dip galvanizing line. The existing sliding bearings for sink roll of galvanizing line mainly depend on imports, and their service life is about two weeks. Two weeks later, the sliding bearing failed, so it is necessary to stop the line and replace the new bearing, wasting a lot of material cost and time cost. In this paper, zinc liquid corrosion test, high temperature pin-and-disc dry friction test and corrosion wear test were carried out on the materials of sliding bearing pair of submerged roller, mainly alumina ceramic bushing and three kinds of metal sleeves (alloy A, alloy B and 316L stainless steel) under simulated actual working conditions. The status of corrosion and wear in bearing failure was compared and analyzed, and the hydrodynamic lubrication effect formed by zinc liquid under test conditions was considered, and the main failure mechanism was comprehensively analyzed.

Experimental Investigation of Added Mass and Damping on Model of Sink Roll in Fluid Media

Experimental Investigation of Added Mass and Damping on Model of Sink Roll in Fluid Media

Analysis About the Failure Mechanism of the Sleeves in Sink Roll System

Sleeves and bushings were important expendables applied of sink roll system in hot-dip galvanizing lines, but the quick wear failure of the sleeves and bushings could significantly influence the stability the sink roll system and decreased the on-line life cycle substantially. To uncover the quick failure mechanism of the sleeves and bushings, the contact stress and friction coefficient between the sleeves and bushings were analyzed; the results indicated that under the action of high tensile stress in the steel strip, the contact stress between the sleeves and bushings could exceed 100 MPa; at the meantime, high contact stress induced high friction coefficient; in addition, the alloying between zinc and steel could decrease the surface hardness and hard zincilate particles could participated in the abrasion, the sleeves and bushings would come to quick wear failure under the combinations of the factors above.

Development of Sleeve Parts for Continuous Hot Zinc Plating Roll Applied to Wear-Resistant Alloy Cast Steel

Metal casting is a process in which molten metal or liquid metal is poured into a mold made of sand, metal, or ceramic. The mold contains a cavity of the desired shape to form geometrically complex parts. The casting process is used to create complex shapes that are difficult to make using conventional manufacturing practices. For the optimal casting process design of sleeve parts, various analyses were performed in this study using commercial finite element analysis software. The simulation was focused on the behaviors of molten metal during the mold filling and solidification stages for the precision and sand casting products. This study developed high-life sleeve parts for the sink roll of continuous hot-dip galvanizing equipment by applying a wear-resistant alloy casting process.

Stress and deformation of ceramic rolls to produce high quality zinc coated steel sheet

Several ceramic rolls can be used efficiently to produce high quality zinc coated steel sheet used for automobiles. Those ceramics rolls may provide a longer life and reduce the cost for the maintenance because of its large heat resistance and large wear resistance. One example may be seen in sink rolls used in molten zinc bath to manufacture zinc coated steel sheet. Since the rolls are subjected to large thermal stress and mechanical loading, care should be taken for the risk of fracture due to the ceramic brittleness. Moreover, since the sleeve and shafts can be connected only by using small shrink fitting ratio, another failure risk should be considered for the separation of those components [25, 26]. In this paper, therefore, the mechanical and thermal stress and separation condition will be investigated considering the separation of the connected portion. Here, by using the finite volume method the heat transfer coefficient is discussed and by using the finite element method the thermal stress is considered.

Performance of Flow and Heat Transfer in a Hot-Dip Round Coreless Galvanizing Bath

Flow field in a coreless hot-dip galvanizing pot was investigated through a water modeling experiment. The corresponding velocity vector was measured using an acoustic Doppler velocimeter. The flow field of molten zinc in the bath was also analyzed. Steel strip velocities from 1.7 to 2.7 m/s were adopted to determine the effect of steel strip velocity on the molten zinc flow in the bath. A large vortex filled the space at the right side of the sink roll, under linear speed from 1.0 to 2.7 m/s and width from 1.0 to 1.3 m of the steel strip, because of the effects of wall and shear stress. The results of the water modeling experiment were compared with those of numerical simulations. In the simulation, Maxwell equations were solved using finite element method to obtain magnetic flux density, electromagnetic force, and Joule heating. The Joule heating rate reached the maximum and minimum values near the side wall and at the core of the bath, respectively, because of the effect of skin and proximity. In an industrial-sized model, the molten zinc flow and temperature fields driven by electromagnetic force and Joule heating in the inductor of a coreless galvanizing bath were numerically simulated. The results indicated that the direction of electromagnetic force concentrated at the center of the galvanizing pot horizontal planes and exerted a pinch effect on molten zinc. Consequently, molten zinc in the pot was stirred by electromagnetic force. Under molten zinc flow and electromagnetic force stirring, the temperature of the molten zinc became homogeneous throughout the bath. This study provides a basis for optimizing electromagnetic fields in coreless induction pot and fine-tuning the design of steel strip parameters.

Corrosion Resistance Studies of Austenitic Stainless Steel Grades in Molten Zinc-Aluminum Alloy Galvanizing Bath

The corrosion inhibition performance and mechanical behavior of galvanized and heat-treated four newly developed austenitic stainless steel grades and type 316L austenitic stainless steel for application as sink rolls in galvanizing baths of 0.14–0.21 wt.% aluminum was investigated and compared through immersion corrosion test to determine the weight loss between 168 and 504 h, tensile test, and Charpy impact test. The delta ferrite content of the test samples was observed and estimated through optical microscopy, feritscope, and ONRL diagram. Scanning electron microscopy and energy dispersive spectroscopy were used to characterize the surface microstructure, morphology, and chemical composition of the galvanized coating of the steel samples. Result showed that only two of the newly developed stainless steel compositions were selected for use in fabrication of galvanizing hardware based on the comparisons of corrosion and mechanical performances of tested alloys.

Cross Coating Weight Control by Electromagnetic Strip Stabilization at the Continuous Galvanizing Line of ArcelorMittal Florange

In hot dip galvanizing lines, strip bending around the sink roll generates a flatness defect called crossbow. This defect affects the cross coating weight distribution by changing the knife-to-strip distance along the strip width and requires a significant increase in coating target to prevent any risk of undercoating. The already-existing coating weight control system succeeds in eliminating both average and skew coating errors but cannot do anything against crossbow coating errors. It has therefore been upgraded with a flatness correction function which takes advantage of the possibility of controlling the electromagnetic stabilizer. The basic principle is to split, for every gage scan, the coating weight cross profile of the top and bottom sides into two, respectively, linear and non-linear components. The linear component is used to correct the skew error by realigning the knives with the strip, while the non-linear component is used to distort the strip in the stabilizer in such a way that the strip is kept flat between the knives. Industrial evaluation is currently in progress but the first results have already shown that the strip can be significantly flattened between the knives and the production tolerances subsequently tightened without compromising quality.

Intermetallic spike growth mechanisms in 316L stainless steel in contact with molten 55%Al-Zn metal coating alloy

Immersed pot hardware used in 55%Al-Zn metal coating pots is fabricated from austenitic stainless steel grade 316L. This alloy is selected for immersed pot hardware applications because of its good corrosion performance in contact with the metal coating bath. The steel however, can be susceptible to excessive corrosion damage after prolonged service at elevated temperatures. The types of corrosion damage observed in immersed pot hardware include intergranular and pitting corrosion and the formation of cone shaped intermetallic alloy spikes, often referred to as horn growth defects. When 316L reacts with molten 55%Al-Zn coating bath, two distinct interfacial alloy layers are formed. The alloy layers provide a diffusion barrier and minimise excessive dissolution of the steel and prevent the formation and growth of the alloy spikes. Laboratory immersion experiments show that when the two interfacial diffusion barrier alloy layers are absent, alloy spike is promoted. It is also found that the diffusion of aluminium into the substrate steel leads to γ to α-ferrite transformation in the steel resulting in a self-sustaining growth process for continued intermetallic alloy spike growth. The microstructures of the laboratory produced alloy spikes are compared with those observed in sink rolls and other immersed pot equipment. Alloy spike growth mechanisms are discussed together with experimental verification of the proposed alloy spike growth mechanisms.

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.

Study of Selected Properties of Coatings Devoted to Extreme Tribo-Corrosive Conditions

The paper deals with the evaluation of coatings CoMoCrSi and WC-NiMoCrFeCo applied by High Velocity Oxygen Fuel technology from point of view of their suitability for renovation of sink roll in hot dip galvanizing line. The structure of the coatings was evaluated by metallographic analysis. The adhesion of the coatings as-sprayed and after thermal cyclic loading was determined by pull-off test. Wear resistance of the coatings was evaluated by pin-on-disc test in the corrosive environment of 1M aqueous solution of NaCl.

탄소 나노튜브 혼합액으로 봉공처리된 텅스텐 카바이드 용사층의 아연 내부식성에 대한 연구

Abstract An experimental study was conducted to investigate the effect of carbon nanotubes on the zinc corrosion resistance of sealing layer formed on the Tungsten Carbide spray coating. Using the nanotubes, a sealing agent in the form of solid-liquid suspensions was made and applied to the surface of spray coating. A series ofexperiments, consisted of three stages such as preparation of test piece, molten-pot immersion test, and evaluation of micro structure, were undertaken to demonstrate complicated interaction existing between zinc ions and sealing layer containing the nanotubes. Experimental results showed newly developed sealing layer were less susceptible to corrosion and thus coated layer was well protected even in the case of 10 days exposure. Comparison of the micro structure after molten pot test also indicated that carbon nanotubes still remained in the matrix and organized more reliable frame work constituted with boron nitride and chromium compound. It was revealed that carbon nanotubes in the sealing layer played positive role to enhance zinc corrosion resistance in the perspective of both fibrous structure and inherent chemical stability.Key Words : Carbon nanotube, Thermal spray, Sink roll, Corrosion resistanceISSN 1225-6153Online ISSN 2287-8955

MoB–CoCr as alternatives to WC–12Co for stainless steel protective coating and its corrosion behavior in molten zinc

Erosion of sink rolls by molten zinc is one of the most prominent and persistent problems occurring in hot-dip galvanizing industry. MoB–CoCr as an alternative to WC–12Co for stainless steel protective coating resistance to molten zinc was deposited by high velocity oxygen fuel (HVOF). Microstructure and mechanical characterization of the coatings were carried out by SEM, XRD and micro-hardness test. Resistance to thermal shock and molten zinc corrosion of the coatings were also conducted. Results showed that MoB–CoCr coating exhibited a better resistance property to thermal shock than that of WC–12Co. At the same time, the corrosion test showed that lifetime of samples with MoB–CoCr coatings in molten zinc appeared to be longer than that of WC coating. The corrosion resistance of MoB–CoCr coating may be ascribed to non-wettability of MoB–CoCr in molten zinc, which can delay the molten zinc penetration into substrates along the micro-cracks of the coating.

The Research of Permanent Magnet Sealing Technology in Vertical Hot Galvanized Pot

In order to solve the confinement problem of liquid metal, permanent magnet sealing is discussed in this paper, and its principle is introduced. Based on calculations, some helpful conclusions are made, which are important for research on hot dip galvanizing process without sink roll.

Improving the Sink Roll life in Galvalume

Galvalume is a Continuous Galvanizing Line. JSW Ispat Steel Ltd. Kalmeshwar has to frequently replace the sink roll assembly used in Zn-Al tank of the Galvalume. The mean time between replacements is very less as compared to expected mean time between failures (expected MTBF). This is due to deposition of zinc dross on the surface of roller. This result in uneven or improper Zn-Al coating on sheet surface. To avoid this sink roll has to replaced. The frequent replacement of roller assembly results in Stoppage of production, material loss, start-up loss and increased cost of production. This paper proposes an alternative material to extend the life of sink roll. Galvalume is a continuous hot dipping process in which steel sheet is dipped in Zn-Al pot. Zinc pot contains Aluminum (55%), Zinc (43.5%) and Silicon (1.5%). The hot dipping is carried out at 6050 c. The chemical reaction between molten ZnAl alloy with iron at 6050c results in the formation of complex compound “dross”. This dross deposits on sink roll surface. It causes: 1. Uneven deposition of dross on sink roll. 2. Impressions on sheet and variations in coating on sheet. 3. Sheet showing dross Build-up. Due to this quality of sheet is lowered and sheet is downgraded. This downgrading brings financial loss to the company. To avoid this, frequency of roller replacement is increased. However this has following disadvantages: 1. Increased loss of production due to frequent stoppages (During removal and refitting of assembly). 2. Zinc loss due to frequent change of roller assembly. 3. Additional cost of re-machining of sink roll. 4. Increase idle time in the process. The project is aimed at increasing the life of sink roll or extending the time period between the sink roll replacements. The increased time between replacements will help in overcoming the above disadvantages. Sink Roll TheSink roll, is a roll used in molten zinc tank in continuous galvanizing line. It is generally made of SS316L Ferrite free, stainless steel that can withstand extreme temperatures & high corrosion for extended periods of time. It made by centrifugal casting.[11] There body uses different shapes like straight body, crowned and tapered depending upon applications. A variety of groove patterns and pitches are made on the surface as per as customers specifications. Special grooves are provided for carbide coatings. [8] Sink roll or Pot roll immersed in the molten zinc bath is affected by the dross is also attacked by the molten zinc leading to pitting and build ups. All these factors affect the coil surface. Such rolls have very short life. Sink rolls are works in a very corrosive environment, i.e. molten zinc. They typically see temperatures in excess of 6000C for weeks at a time. Materials used are made to withstand this criteria, so they are also difficult to machine.[16] The roll is made of SS316L material. It is a ferrite free stainless steel grade having surface hardness RC 10. The body is a centrifugal cast stainless steel and the end ball/journal is from a static casting. Most of these rolls have no coatings on them. An uncoated roll may last up to 2 weeks, but with carbide coatings and special bushings they laste up to 5 weeks. However for Galvalume the life is reduced drastically due to dross formation (pick-up) and high tempurature ( i.e above 6000 c ). An apparatus called ‘Scrapper’ is installed in a molten metal plating line includes a blade pressed against a roll dipped in a

Numerical Simulation of Flow and Dross Particle Transfer in a 55% Al-Zn Pot

Computational fluid dynamics (CFD) is nowadays a powerful and reliable tool for simulating different flow processes and temperature. CFD is used to analyze the various pot geometries and operative variables in 55% Al-Zn pot of CGL. In this research, different strip velocities were assumed and then shown the flow pattern in the pot that was similar in the different strip velocities. Temperature distribution in the pot depended on inductors and inlet strip temperature at the steady condition. Generation of dross particles and transport models were considered to describe dross particles evolution inside the pot. In order to observe dross influence by scrap location, dross particles were generated upon the sink roll. Floating time of dross particles is different by scraper locations above the sink roll.

Corrosive Wear Behavior of Several Materials Coupled with Si3N4 in the Molten Zinc

In continuous hot dip galvanizing, serving parts working in the molten zinc, such as sink roll, sleeves, etc. tend towards degradation and failure due to corrosion and wear. In this paper, corrosive wear performance of several materials, such as boronized，H13，Co-based alloy and Fe-based alloy coupled with Si3N4 is evaluated with the aid of a self-made test machine of block-column sliding wear. Moreover, the corrosive wear mechanism is analyzed. It has been found that these materials suffered not only considerable wear, but also the corrosion of molten zinc. For boronized layer, the wear is the main reason to cause the failure of work parts under the act of the corrosive wear. For H13, the interaction between corrosion and wear plays a very important role on its failure. For those alloys with bad corrosion resistance such as Co-based alloy and Fe-based alloy, both corrosion of solid solution and wear of intermetallic compound act on their failure at the same time. However, the rate of wear shows no obvious relation to the hardness although wear performance is important. The failure greatly lies on the ratio of the hardness of corrosion products to matrix.

Materials Resistance to Liquid Zinc Corrosion on Surface of Sink Roll

Abstract In this paper, the principles of metal materials corrosion by liquid zinc are reviewed, and the materials resistant to liquid zinc corrosion and techniques of surface modification are compared. Besides, the development of the materials resistant to liquid zinc corrosion is prospected. The spay coatings such as WC/Co, Al2O3, ZrO2-Y2O3. MoB/CoCr etc can effectively improve the properties of liquid zinc corrosion resistance. The MoB/CoCr coating by high velocity oxy-fuel (HVOF) has much higher durability in liquid zinc, and neither formation of the reaction layer and nor decrease in the coating thickness after a test of 600 hours. Therefore, the MoB/CoCr coating is a promising material in increasing the lifetime of sink roll.