Study On Surface Characteristics Of Cold Rolled Sheet And Its Effects On Properties Of Tinplate Coating

Tinplate occupies an important position in food packaging industry.With the continuous reduction of tin resources and the increasingly fierce market competition,the thickness of tinplate gradually appears a decreasing tendency,cold-rolled substrate thinning and tin coating thinning,aimed at reducing costs and improving competitiveness.The thickness reduction of cold rolled sheet means that the cold rolling reduction rate will increase,which will affect the cold rolling plate surface characteristic and the tin plate performance.The thickness reduction of tin coating will affect surface morphology,corrosion resistance of tinplate and finishing.Therefore,the cold rolled steel plate with different rolling conditions is the research object,simulating the production process of tinplate,to observe the physical and chemical properties of cold rolled plate surface evolution and its influence on the properties of tinplate,and to provide important technical guidance and theoretical support for production.Research mainly includes two aspects.The first part,the surface roughness tester and scanning electron microscope(SEM)were used to observe surface features of cold rolled sheet in the electroplating process at different stages in the process,to study the change rule and the influence of each process stage.The second part,Tafel polarization curve,electrochemical impedance spectroscopy(EIS)and contact angle of tinplate with different surface morphology were measured,and X-ray photoelectron spectroscopy(XPS)was used to analyze tinplate surface composition,and effects of tinplate surface morphology on the coating structure,corrosion resistance and finishing were studied.It is found that the rolling process has an important influence on the surface properties of cold rolled sheet.In the process of electrotinning for cold rolled sheet,the reflowing influences and levels the surface morphology most obviously,the roughness decreased about 0.06?m,the number of peaks per centimeter reduced above 20.The tin crystal formed by electrodeposition is uniform and dense,attached to the surface of cold rolled sheet.The effects of alkaline cleaning,pickling,passivation and electrostatic oiler on the surface topography are relatively light.But the alkaline cleaning and pickling can reduce the resistance of cold rolled sheet,improving the activity,oil film will make the tin plate wettability decreased.Research shows that the surface morphology of cold rolled sheet affects tin iron alloy layer,finishing and coating structure.The tin iron alloy layer with small roughness is more uniform and compact.The surface roughness coating adhesion and wettability of the tinplate with big roughness are slightly better.The increase of surface roughness will change the element content and compound proportion of coating,but its elements and compounds are the same.The oxide film is mainly tin oxide,SnO2 and SnO,the passivation film is chromium oxide,Cr2O3 and CrO3,as well as Cr(OH)3 and a small amount of metal chromium.The microstructure of cold rolled sheet has little effect on tin iron alloy layer,and the surface morphology has no obvious correlation with the corrosion resistance of tinplate.