Study On The Compactness Of Chrome Plate Surface Coating

Metal packaging materials have always played an important role in the packaging field because of its good airtightness,hard texture,good elasticity,good light resistance and good gas barrier properties.Tinplate metal is an important part of packaging materials,but because tin is the main strategic resource,the price is more expensive,and the resources are increasingly exhausted,chrome-plated iron is getting more and more attention.Due to the discontinuous micro-pore defects on the surface of the chrome plate,the service life of the product and the inherent quality of the stored food and beverage are affected.Especially in wet and offshore areas,coupled with a long transport cycle,chrome plate surface quality problems(point rust defects)are more prominent.Therefore,it is important to determine the influencing factors of the surface compaction of chrome plate and to grasp the evaluation method of the density of the plated surface of chrome plate.Based on the chemical etching method,this paper combines the iron ion leaching process on the surface of chrome plate in solution to explore the evaluation method of surface density of chrome plate.The electrochemical evaluation method and the damp heat test were used to study the evaluation index of the plating density of the chrome plate.The XPS analysis,electrochemical test and SEM analysis were used to analyze the influencing factors of the coating density on the surface of chrome plate,and the following conclusions were obtained:1)Evaluation method for the density of plating on the surface of chrome plateCombining the composition of different etching solutions on the surface erosion of chrome plate,the composition of the etching solution is optimized,that is,the etching solution is 1.0mol/L reagent A,1.5%(volume)reagent B,2%(volume)The composition of CH₃COOH and distilled water has an erosion time of 15min,and the porosity of the surface of the chrome plate is relatively stable.The evaluation method can clearly distinguish the quality of the plates of each manufacturer,which is more in line with the actual situation.The damp heat test and the salt spray test show that:excellent(rust area<5%),good(rust area 5%to 20%),poor(rust area 20%to 30%),and inferior(rust area>30%)Three grades;excellent-porosity<1.0 mg/dm²;good-porosity 1.0-1.5 mg/dm²;poor-porosity 1.5-2.5 mg/dm² inferior-porosity>2.5 mg/dm².The detection method can greatly reduce the experiment time,and can quickly make an accurate evaluation of the surface compactness of the chrome plate.2)Effect of electroplating process on the compactness of chrome plateThe difference in compactness of chrome plated coatings produced by one-step electroplating and two-step electroplating is significant.The two-step method is slightly better than the one-step method by the denseness evaluation method.Combined with XPS analy sis,the surface of the coating is a mixture of Cr,Cr₂O₃ and Cr(OH)₃,and both crystal water is present,but the two-step plating can be significantly improved.The content of Cr₂O₃ and Cr(OH)₃ coatings increased,the thickness of the oxide film increased,and the content of crystal water decreased,and the coating showed better compactness.3)Effect of plating system on the density of chrome plate coatingThe compactness test method was used to compare the corrosion resistance of chrome plate produced by NH₄F system,H₂SiF₆ system and Na₂SiF₆ system.The H₂SiF₆ system and the Na₂SiF₆ system are slightly better than the NH₄F system,and the H₂SiF₆ system chrome plate has a low porosity.Combined with XPS analysis,the plated surface of NH₄F plating system has the lowest chromium oxide content,and the surface composition of the coating is more complicated,but the oxide film is thinner,mainly composed of Cr,CrO₃,Cr₂O₃ and Cr(OH)₃,and crystal water exists.H₂SiF₆ plating system and Na₂SiF₆ plating system,the surface of the coating is Cr,Cr₂O₃ and Cr(OH)₃ mixture,there is less crystallization water,more chromium oxide,thicker oxide film,and the coating shows better resistance.Corrosion performance.4)Influence of coating structure,current density and impurity ion concentration on the surface plating density of chrome plateWhen the content of chromium in the metal is the same,the content of Cr(OH)₃ in the oxide film is less,and when the content of Cr₂O₃ is more,the density of the coating can be improved,indicating that Cr₂O₃ plays an important role in the corrosion resistance of the coating.With the increase of current density,the content of oxide film in the coating increases.When the current density is 5A/dm²,the composition of the coating is more complicated,CrO₃ and Cr₂O₃ are present at the same time.When the current density is 10A/dm²,the content of chromium oxide in the coating increases,and the corrosion resistance is also improved.It is better than the chrome plate produced by low current density;when the current density is 20A/dm²,no formation of crystal water is detected in the coating,which greatly increases the corrosion resistance of the coating,but the energy consumption is also increased a lot,which increases the production cost.As the concentration of impurity ions increases,the higher the porosity of the coating,the worse the density of the coating.Therefore,the aqueduct should be cleaned regularly during production,and the plating solution should be replaced to reduce the impurity ion concentration.