Prediction and influencing factors of scraper force for sink roll system of hot dip galvanizing unit

The sink roll in hot galvanizing units blown not clean on the surface of zinc slag leads to the strip surface defects, which seriously affect strip product quality grades. The characteristics of equipment and process of hot galvanizing unit were combined in this paper. Firstly, the force of sink rollers scraper mechanism was analyzed and the model of scraper force was established on the basis of steady state condition. Considering the influence of gap fluctuation between axle sleeve and bearing bush, the residual zinc residue deposited on the roll surface and the blade wear on the blade force in the actual working conditions of sink roll system, the scraper force model was modified to calculate the scraper force under unsteady conditions. Then the influence mechanism of scraper angle, journal eccentricity, blade wear and residual zinc residue on scraper force was analyzed. The calculation process of scraper force was developed according to the scraper force modification model, and the model was applied to actual production. Three typical specifications of strip steel were selected to predict the scraper force. The relative error between the predicted value and the measured value was less than 15%, and met the precision requirement of the unit. Finally, the influence of strip production parameters (strip tension, strip speed, surface galvanization) on the predicted value of scraper force was analyzed by taking strip A as an example. The results show that the scraper force increases with the increase of scraper angle in a small range (9°-12°), and the scraper force increases nonlinearly with the journal eccentricity increasing. The increase of blade wear will reduce the slag removal ability of scraper. The increase of residual zinc residue on the roller surface leads to the increase of scraper force, which is easy to cause the phenomenon of roller system sticking or slipping. The scraper force increases linearly with strip tension and decreases linearly with strip speed, but the influence of surface galvanization on scraper force is relatively small.