Study On Stress Model And Capacity Improvement Technology Of Sink Roll In Hot Dip Galvanizing Process Of Strip Steel

In recent years,with the upgrading of China ’s manufacturing industry,the demand for galvanized thin sheet is increasing,and the product quality is also increasing,so there is a need to improve the production capacity and production efficiency of the hot dip galvanizing unit.However,in the process of strip speed increase,the sink roller group in the zinc pot often occurs stuck and skidding problems,resulting in an increase in the incidence of surface defects of strip products,seriously reducing the production efficiency of the unit and hindering the improvement of production capacity and product quality of the unit.Therefore,the hot dip galvanizing sink roll group is taken as the research object in this paper,the force model of the sink roll group is established,the mechanism of stuck and slip of the sink roll group is explored,the critical conditions of stuck and slip of the sink roll group are established,and the shaft end structure of the sink roll group is optimized.It is of great theoretical significance and practical value to improve the production capacity of the hot dip galvanizing unit.Firstly,the working principle and process characteristics of the sink roll group were fully considered,and the stress state of the sink roll group with tension under the high temperature environment of molten zinc was analyzed.The friction coefficient of the roll surface was expressed by the empirical function of the zinc slag deposition thickness.The strip element method and the simplified model of the simply supported beam were used to establish the contact pressure between the strip and the roll,the friction driving torque,and the shaft end friction resistance torque model.The mechanism of zinc liquid on the sink roll group was studied,and the viscous resistance model of the sink roll group was constructed by dividing the boundary layer around the strip and the roll.Considering that the shaft end was the weakest area of the sunk roll group,the bending,torsion and thermal deformation models of the sink roll group under multiple loads in complex environment were established by means of solid mechanics and heat transfer theory,and the influence factors of the sink roll group are quantitatively analyzed.Then,the gap between the shaft end of the sink roll group was analyzed,and the mechanism of the stuck and slip of the sink roll group was explained.The expression of the gap between the sleeve and the bearing bush and the maximum bearing capacity model of the roll shaft end under the zinc liquid environment were constructed.It is proposed for the first time that the rotational power factor was used to characterize the working ability of the sinking roll group,and the critical criterion for the slip between the strip and the roll surface was established.In the case of different zinc slag content in the gap between the sleeve and the bearing bush,the critical conditions of roll stuck and slip were studied by taking the roll rotation power factor as the index.The factors affecting the stuck and slip of the sinking roll in the steady state and acceleration and deceleration operation of the sink roll group were studied respectively.Subsequently,the optimization models of the diameter of the roller neck,the corresponding sleeve and the bearing bush were constructed with the safety factor of the shaft end structure of the sinking roller and the rotational power factor of the roller as the objective function respectively to improve the working life and working ability of the sinking roller group.The optimization model of the width of the roller neck and the corresponding shaft sleeve with the rotational power factor of the sinking roller as the optimization objective function reduced the accumulation of zinc slag,accelerates the discharge of zinc slag and reduces the hooping force of zinc slag on the sink roller group.The optimization model of the surface roughness of the bearing bush and the sleeve was optimized by taking the change of the surface roughness of the sleeve of the roller as the optimization objective function,so as to reduce the wear degree of the bearing bush and sleeve and the thermal deformation of the shaft end.In order to minimize the friction resistance between the scraper and the roll surface,the optimization model of the roll surface fit between the scraper and the sink roll group was optimized with the fit degree as the objective function,and the corresponding optimization process of these four optimization techniques was given.Finally,the force model of the sinking roll group in the hot galvanizing process and its ability improvement technology are applied to a hot galvanizing C108 unit as an example.The effect of the technology is verified by the combination of online tracking and offline tracking.Taking the typical three specifications of strip steel produced by the unit as an example,the application effect of the technology is analyzed and compared from three aspects: the surface quality of the finished strip,the running speed of the strip,the wear of the sleeve,the bearing bush and the blade of the scraper.The results show that it achieves the desired effect through optimization that the maximum amplitude of strip vibration is obviously reduced in the process of the strip speed increase,the surface quality of the finished strip products is obviously improved,and the corresponding defects are effectively controlled,the running speed of strip steel is increased from less than 120m/min to more than 130m/min,and the wear of sleeve,bearing and scraper edge of each roll of sink roll group is well controlled.