Abstract: 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.

Key words: Air knife, Axial velocity, Strip steel, Tension, Vibration control