THE METHOD OF ROLL SURFACE QUALITY MEASUREMENT FOR CONTINUOUS HOT DIP ZINC COATED STEEL SHEET PRODUCTION LINE

The present paper describes a developed analyzing system of roll surface during the process of continuous hot dip zinc coated steel sheet production line, in particular, adhering problem by transferred inclusions from roll to steel sheet surface during annealing process so called the pickup. The simulated test machine for coated roll surface in processing line has been designed and performed. The system makes it possible to analyze roll surface condition according to pickup phenomena from various roll coatings concerning operating conditions of hearth rolls in annealing furnace. The algorithm of fast pickup detection on surface is developed on the base of processing of several optical images of surface. The parameters for quality estimation of surface with pickups were developed. The optical system for images registration and image processing electronics may be used in real time and embed in processing line

Dross formation mechanism and development of wear resistant scraper in aluminum-silicon-zinc coating bath.

Steel sheet manufacturers across the globe, face a huge loss of production due to the molten metal corrosion of the pot hardware in continuous galvanizing lines. The development of steel sheet with corrosion resistant for more than 30 years using a high aluminum content zinc coating has made an impact in the construction industry. High aluminum content bath (55 wt%) causes severe corrosion of the pot hardware and causes huge repair and replacement cost with frequent stoppages. One of the main reasons for stoppages is the severe dross formation over the submerged hardware (sink roll), which results in poor coating layer over the steel sheet. Complete understanding of the mechanism of the dross formation over the submerged hardware has not yet been completely achieved. In order to establish the dross formation mechanism, an array of tests was performed. Initial inhibition of Al attack by the silicon rich layer and further formation of Fe2Al 5 layer hindering the diffusion of the Al into the substrate were observed. Also, the effect of the hydrodynamic motion of the bathe in the dross formation mechanism was established. A series of tests for efficient removal of the dross formed over the sink roll using high hardness, corrosion resistant materials were conducted at 600°C. After these tests, an efficient scraping process with a potential for energy and cost savings was developed with a better scraper material, resulting in a reduction of 75% in line stoppages

Long-term performance of pot hardware in continuous galvanizing lines

Preliminary comparative wearing tests were conducted on wearguard bearing system against CF3M (casting version of 316L steel), with tungsten carbide laser clad coating, at 30% and 50% production line tension. Tests were also conducted on Stellite 6 against Tribaloy T 400 at 50% production line tension. For each test, periodic measurements of wearing rate, surface microstructure and surface hardness were carried out. An unique dross build-up setup which consists of two sleeves counter rotating against each other was designed to simulate the dross build-up in production line. The chemical composition of the dross material formed and change in sleeve microstructures were analyzed using SEM and EDX.;Microstructural analysis of the CF3M test sleeve revealed that (1) tungsten carbide bearing sleeve-wearing, was mainly due to abrasive wear, (2) ceramic inserts experienced abrasive wear and (3) the existence of intermetallic dross particles formed on the bearing sleeve surface. Microstructural analysis of the Stellite 6 test sleeve revealed that (1) wearing was due to abrasive wear and corrosive wear and (2) the sleeve reacted with zinc bath to form intermetallic compounds

Minimizing Zinc Coating Section Downtime of Continuous Galvanizing Line in Steel Industry

Galvanizing is a technique of smearing a protective Zinc coating on Steel or iron, to avert its rusting. The usual practice to produce galvanized steel is through hot dip galvanizing method. It is a continuous line where annealed sheet is immersed into molten Zn bath with Sink roll assembly guiding the sheet and air knife system maintaining proper coating of Zn onto the sheet. Due to high vibration sink roll bushes get wear frequently and scratches are formed on sheets, as a quality defect. The vibration causing element is to be identify and resolving it reduces the sink roll changing frequency and increases Zn coating section availability time, also minimizes the scratch formation on sheet during coating. The data were collected, analyzed and implemented to increase the availability time of Zn coating section, and thus the productivity. Keywords: Corrector and Stabilizer roll , Cause and effect analysis ,Dross formation, Hot dip galvanizing,  Pareto analysis , Sink roll assembly vibration, Zinc coating

The development of surface treatments on galvanised steel products for the automotive industry utilising a chemcoater

This thesis investigates the development of coatings to be applied via a two-roll roller coating system, a Chemcoater. Novel coatings were investigated to enhance a substrate’s performance and add overall value to the hot-dipped galvanised steel product, by adding fuctionalities such as improved corrosion resistance, enhanced surface passivation and increased surface lubricity. Historically, hexavalent chromate was a common component of coatings for hot-dipped galvanised steel to provide corrosion protection during material storage and transportation. However, REACH law within the European Union prohibited its use due to its intrinsic toxicity and detrimental environmental effects. This legislation accelerated industry and researchers’ attention toward developing alternative, more environmentally friendly processes. Initial investigations included the analysis of current coatings, PrimeCoat and PLT. Both coatings were shown to have similar rheological characteristics and similar thermal stabilities with PLT performing well as a dry film lubricant. A common laboratory polishing unit was adapted to create a novel Pin-on-Disk tribometer, providing an effective and reliable method for measuring the dynamic coefficient of friction of coated substrates. The adapted unit was designed, built, and commissioned according to ASTM G99-17, and it was able to produce repeatable results for measuring the coefficient of friction. An additional investigation showed that sulphate-based treatments could reduce the coefficient of friction of zinc-coated steel substrates. Tests indicated that a neutral ammonium sulphate solution improved lubricity by 15-10%. Ammonium and sodium sulphate treatments were deemed suitable for coil coating, improving the capacity to reduce oil volume and overall production costs. A systematic study was conducted to improve the processability of a one-step hydrophobic coating. The best-performing coating had a contact angle of 146° with a reduced processing time of ~67%, using IPA as the solvent, 2% wt. 1 M NaOH (aq), 0.2 M stearic acid and micro-SiO2 (0.2–0.3 μm). This method significantly reduced processing time and fewer health and safety risks, avoiding the use of toxic chemicals. On further analysis, the coating was shown to be relatively formable and durable, with no significant reduction in hydrophobic performance after 30% strain was induced. Several corrosion analysis techniques showed increased performance in comparison to uncoated hot-dipped galvanised steel samples. These results suggested that the coating could be a viable option for some industrial applications and showed a potentially positive alternative to banned hexavalent chromate options. The chemical constituents of the newly proposed coatings have significantly less toxicity and pose a reduced negative effect on the wider environment and its users

Analysis of energy consumption in continuous galvanizing lines

The pot hardware in continuous galvanizing lines is prone to failure and needs to be replaced quite frequently. This resulted in considerable loss of production time. Also equipment like, the molten zinc pot and annealing furnace cannot be turned off during downtime resulting in considerable energy consumption during downtime too.;A profound study of the energy aspect of the equipment used on galvanizing line was done. A systematic approach was used to collect and analyze the data from galvanizing facilities. A decision support system (DSS) that will take into account all the major energy consuming equipment in a typical hot dip continuous line was developed. This DSS allows the user to model their galvanizing line in Excel(TM) based software. The DSS maintains track of the current production and energy consumption for up to three different processes. It can simulate a scenario to identify the magnitude of benefits that can be obtained as a result of any energy savings measures implemented.;The economic justification of whether or not to replace the hardware can be evaluated with the help of this DSS. Charts pertaining to energy consumed by different equipment groups, total cost of energy spent on natural gas and electricity, MMBtu/ton, tons/year and production time before shutdowns are obtained from the DSS

Improving Galvanizing Bath Hardware

Suspended dross particles in galvanizing bath can interact with moving rolls that guide the strip and eventually accumulate on it. They can cause the roll to function improperly and reduce the surface quality of galvanized steel sheet. In this research, a turbulent flow simulation of a continuous sheet galvanizing bath is carried out using the computational fluid mechanics in Ansys FLUENT to determine the flow profile inside a galvanizing bath. Multiphase flow modeling has been performed to understand the particle-surface interactions by coupling the particulate models for solid phase with computational fluid dynamics for fluid phase. A strong fluid flow along the roll axis, which captures a significant number of dross particles, was found in the 3D bath simulation. It was observed that surface region in which particles agglomerate on the roll reported by the industry is the same as where particles collisions with the roll were observed in the simulation

Heat balance analysis of annealing and galvanneal furnace in continuous galvanizing lines

Galvanizing facilities are highly energy intensive operation with electrical and fuel energy representing a significant share of their total energy usage. Furnaces are extensively used in galvanizing process. Production process expertise along with the energy conservation practices can play a significant role in proper usage of energy at galvanizing facilities. Therefore, benchmarking galvanizing energy consumption and understanding the specific energy consumption by various elements are critical. E-GEPDSS (Enhanced Galvanizing Energy Profiler Decision Support System) was built to identify this specific energy consumption by using heat balance analysis. The use of E-GEPDSS does not hinder the production process and the user may run the model for different set of operating conditions and observe the results. The results obtained from the analysis will help the user to make energy enhancing decisions.;This research involved the analysis of galvanizing operations focusing on the furnace side of energy consumption. The furnace heat balance was built and applied using the data collected from a host company during the plant visit. Sensitivity analysis were done to study the impact of changing process and product parameters on the total heat loss from the system.;From the energy analysis conducted for the furnace equipment at the host facility, it was found that the useful heat absorbed by the product is only 50% of the heat supplied to the furnace and rest of heat dissipates as losses. Heat losses from surfaces, walls, water cooling and stack are significant. Heat loss due to opening and phase change heat loss seem not to be significant. Emissivity, dimensions of the furnace, temperature of the zones, thermal conductivity of insulation materials and the strip temperature at the entry and exit of each zone have significant impact on the total heat loss. In the future, the model will be applied extensively to more galvanizing lines in order to help the galvanizers to have a better understanding about the energy consumption while producing their product

Evaluation of surface mechanical properties of pot hardware materials in continuous galvanizing lines

Pot hardware in continuous galvanizing lines is subjected to harsh and corrosive environment. The application of pot hardware in such conditions can cause surface degradation of the pot hardware materials thereby decreasing their life. The surface degradation can be due to wear, decrease in hardness or change in surface elastic modulus. The 500-lb lab scale test set-up at WVU was used to simulate the conditions existing in the actual continuous galvanizing line.;Ultrasonic equipment has gained immense importance in the field of non-destructive testing. One such instrument that measures surface hardness based on the shift of an ultrasonic frequency was used for measuring the on-site hardness of pot hardware materials. The hardness measured by the instrument is also a function of the elastic modulus of the material. The change in surface elastic modulus was determined theoretically based on the governing equation for the instrument.;The change in surface hardness and elastic modulus was explained and correlated to the corresponding microstructural analyses

Zinc pot bearing material wear rate as a function of contact pressure and velocity

There are currently over 50 galvanizing lines in operation in the United States producing approximately 50 million tons per year of galvanized sheet. Frequently zinc-pot hardware fails which causes production delay, resulting in an economic loss. It takes approximately 3 hours to change the zinc-pot bearings at a downtime cost of {dollar}400/h.;To predict the performance of the submerged bearings, a large number of variables must be considered. These variables include pot chemistry, temperature, line speed and line tension. With these variables it is possible to develop a design guide for sheet mill operators to determine the most cost-effective selection of zinc pot bearing materials/coatings, which will not be the same for all galvanizing lines.;The objective of this project is to measure wear rate of submerged zinc-pot bearing materials as a function of contact pressure and velocity. A small laboratory size-testing machine was developed for this purpose. This machine measures the wear of bearing material samples, submerged in a cup of zinc, in the form of a 1-inch diameter ball rotating against a matched ball seat. The seat and ball can be cast or machined using bearing materials from a test matrix. The seat is placed in a temperature controlled molten zinc bath where load, torque and RPM of the test samples are measured and recorded. From the measured torque the sliding friction coefficient of the bearing materials tested can be calculated. By measurement of the seat radius before and after testing, the wear rate of the material as a function of contact pressure and velocity was determined