Research And Application Of Chrome-free Spraying Passivation Technology For Tin Plate

Tin plate is the low carbon steel plate that have a surface which coated with a thin layer of metal tin,with strong corrosion resistance,good formability and other characteristics so that widely used in food canning,packaging materials and other industries.During the production process of tin plate,after tin plating and soft melting,in order to prevent the tin plate from oxidation and yellowing,and improve the performance of acid and sulfur resistance of tin plate,it need to be passivated.At present,the most commonly used method of passivation is to use chromate cathode passivation which containing hexavalent chromium for treatment.However,hexavalent chromium in chromate and waste liquid that discharged in the production process will cause harm to the environment and human body.On the basis of a cooperative project with a steel plant,this project developed a set of technology and equipment that using spray passivation,applied low-toxicity chrome-free passivation solution to the production line,and produced products that could replace chromate passivation.The main contents and research results are as follows:(1)Firstly,determine the inorganic-organic composite passivating liquid system mainly composed of Ti and Zr compounds and other complexes.On the premise of minimizing the modification of the existing production line,the chromate free passivation process was added,and the traditional electrolytic passivation and dip rinsing processes of chromate were abandoned.The chrome-free passivation process of tin plate is treated by spraying-extrusion-curing process,the chromate passivation tank is left empty,and the strip steel is sprayed passivation directly after soft melting and pre-treatment,realizing the technical application of process improvement,it can be switched between chromate passivation and chrome-free passivation according to different product requirements;(2)After determining the process flow and technical equipment,in order to obtain the specific process parameters of the key equipment rotating disk spraying device,used the CFD software ANSYS-Fluent for numerical simulation.In order to control droplet size and uniformity,a two-dimensional model of the rotating spray plate was established,and the centrifugal atomization characteristics of the rotating spray plate were analyzed by changing the speed of the spray plate,the distance between the spray plate and the steel plate,the distance between two spray plate and the flow rate.The droplet size,droplet velocity and droplet position distribution in atomization field with different variable parameters were obtained.The simulation results show that the droplet crushing effect is better with the increase of rotating speed,and the droplet size can be reached when the rotating speed is 6000 rpm.The closer the distance between the plate and the spray plate and the distance between the spray plate,the more concentrated the droplet distribution.The atomization uniformity can be improved by increasing the number of spray plates.The simulation results provide the theoretical basis for the application of the spray device,and obtain the droplet surface with good uniformity,so as to achieve the requirements of uniform atomization of passivation liquid;(3)Take the non-passivated and chrome-passivated tin plate from the on-site production line,make the chromium-free passivation sample in laboratory,at the same time build the offline platform of spraying equipment.The performance of chromium-free passivation tin plate was evaluated by film characterization,energy spectrum scanning,electrochemical corrosion resistance test and paint film adhesion test.It is found that the plate making of this set of technological equipment can ensure the uniformity of passivation liquid spraying and effectively control the film weight per unit area,and finally meet the requirements of some application products.