Prediction and Influencing Factors of Scraper Force of Submerged Roller System in Hot-dip Galvanizing Unit

Summary

In view of the problem that the zinc slag on the surface of the submerged roll system of the hot-dip galvanizing unit is not cleanly scraped, which leads to many roll marks on the surface of the strip, which seriously affects the quality level of the strip products, fully combine the equipment and process characteristics of the hot-dip galvanizing unit. The force analysis of the roller system scraper mechanism is carried out, and the scraper force model under steady-state conditions is established on this basis. Considering the influence of factors such as the fluctuation of the gap between the bushing and the bearing bush, the residual zinc slag deposited on the roll surface, the scraper wear, and other factors in the actual working conditions of the submerged roller system on the scraper force, the scraper force model were revised to make it suitable for unstable conditions. The same applies to the calculation of scraper force under normal conditions. Then, the mechanism of the influence of scraper angle, journal eccentricity, scraper blade wear, and residual zinc slag on the scraper force on the scraper force was analyzed, and the scraper force calculation process was formulated according to the scraper force correction model, and the model was applied to actual production. Three typical specifications of strip steel are selected for scraper force prediction. The relative error between the predicted scraper force and the measured value is less than 15%, and it meets the accuracy requirements of the unit. Finally, the influence of strip production process parameters (strip tension, strip speed, surface galvanizing amount) on the predicted value of scraper force is analyzed by taking the specification A strip as an example. The results show that the scraper force increases with the increase of the scraper angle in a small range (9°~12°); the scraper force increases rapidly and nonlinearly with the increase of the journal eccentricity; the wear of the scraper blade increases reducing the slag removal ability of the scraper; the increase in the amount of residual zinc slag on the roller surface leads to an increase in the scraper force, which is easy to cause the roller system to be stuck or slipped. The scraper force has an approximately linearly increasing relationship with the strip tension, and an approximately linearly decreasing relationship with the strip speed, but the amount of surface galvanizing has relatively little effect on the scraper force.

sunken roll

Introduction

In recent years, with the rapid rise of new economic industries such as smart home appliances and new energy vehicles, hot-dip galvanized strips have been widely used because of their low price and good corrosion resistance. The sunken roll system is the key equipment in the galvanizing process of the hot-dip galvanizing unit, and its working condition directly determines the product quality and production efficiency. Roll marks appear on the surface of the strip after the air knife scrapes zinc, which is due to the large zinc slag particles remaining on the roll surface. Although each roller is equipped with a scraper mechanism, the scraper force is indirectly adjusted by manually adjusting the pressure of the cylinder. If the scraper force is set too small, the surface of the roll may not be cleanly scraped, and if the scraper force is set too large, the roller system may slip or slip. The phenomenon of being stuck, causes the unit to be unable to produce. At present, the unit cannot directly obtain the specific value of the scraper force, so the adjustment process of the scraper force is all qualitative rough adjustment, and quantitative fine adjustment cannot be realized. Therefore, it is necessary to accurately grasp the scraper force of the scraper on the roller surface to avoid blind adjustment. At present, the related research on the hot-dip galvanizing (aluminum) process and equipment mainly focuses on the research on the formation mechanism of hot-dip galvanized sheet defects and its surface quality control. For example, Yue Chongfeng et al. Optimize the addition of a slag accumulation tray to improve the surface quality of the coating; Li Chao et al. used an optical microscope, scanning electron microscope, and energy spectrum to study the microscopic morphology and composition, and conduct point defect classification and analysis of the formation mechanism; Jin Xinyan et al. Scanning electron microscopy studied the morphology and composition of the coating on the surface of the strip with sunken roller groove print defects and analyzed the formation mechanism of the defect; Duan Xiaoxi et al. The measures of occurrence; Wang Yinjun et al. reviewed the classification, composition and formation causes of zinc slag in aluminum-zinc molten pools, and focused on the formation mechanism and research progress of bottom slag in aluminum-zinc molten pools with high aluminum content. However, there are few studies on the doctor blade force of the sink roller system doctor blade mechanism. At present, the control of the scraper force of the sunken roll system and the optimization of the scraper mechanism is effective to control methods for the unit to control the roll marks on the strip surface. The realization of it lays the foundation for the quantitative control of the subsequent scraper mechanism, and this paper conducts relevant research on this problem under this background.

sunken roll

Conclusion

(1) This paper fully considers the equipment and process characteristics of the submerged roll system of the hot-dip galvanizing unit, analyzes the force of the scraper mechanism, and establishes a scraper force model under steady-state conditions; The strip vibration causes the roll journal to fluctuate in the bearing bush, the scraper wear and the thickness of the zinc slag deposit on the roll surface affect the scraper force, and the unsteady condition scraper force correction model is established.

(2) It is determined that the factors affecting the operation of the scraper mechanism include scraper angle, journal eccentricity, scraper blade wear, and residual zinc slag on the roll surface. The scraper force increases as the scraper angle increases. Generally, the scraper angle is set to 9°~12° and a smaller angle is selected; with the increase of the journal eccentricity, the scraper force increases nonlinearly at a faster speed; As the wear of the scraper blade increases, the tangential component of the scraper force decreases, and the scraper’s ability to remove slag decreases; as the amount of residual zinc slag on the roll surface increases, the scraper force and friction increase, which is likely to cause the roller system to be stuck or blocked. slip.

(3) Apply the scraper force prediction model in this paper to the field, formulate the scraper force calculation process, and compile the scraper force prediction software. It is found that the relative error between the predicted value of the blade force and the measured value is less than 15%. In addition, taking the specification A strip as an example, the influence of the strip production process parameters (strip tension, strip speed, surface galvanizing amount) on the predicted value of the scraper force is analyzed. It has a nearly linear decreasing relationship with the strip speed, but the effect of surface galvanizing on the scraper force is relatively small.

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