Corrosion Cause Analysis of Electrolytic Tinplate
1 body corrosion protection system
The corrosion protection system of electrolytic tinplate is composed of organic coating / tin layer / iron layer triple protection structure, the initial corrosion of the real tank is mainly for the protection of the coating, the middle of the tin-based protection, mainly for the late iron protection, Shelf life of the tank corrosion protection, coating protection play a major role. In the use of real cans most of the electrolytic tin cans to meet the shelf life of the quality requirements, only a small amount of real can occur corrosion perforation. Electrolytic tinplate corrosion is closely related to the contents of the package, when the contents of the package with partial acidity, high salt content and sulfur-containing protein and other characteristics, making its contents corrosive strong. Although the organic coating can prevent the contents of the liquid and metal contact, but usually because of the existence of pores, placed for some time after the liquid infiltration and metal contact, the occurrence of tin solution. The tin layer itself is relatively stable, but in the corrosive content, and the presence of nitrate or sulfur ions dissolution rate is large. After a period of time will expose the metal iron, constitute tin - ferroelectric couple, to speed up the dissolution of iron. Electrolytic tinplate corrosion resistance depends largely on the coating porosity and defects, tin layer blunt and thickness and iron thickness.
2 coating failure
Coating performance depends not only on the type of coating and its own properties, but also on the coating process. Metal surface pretreatment cleanliness, coating thickness, coating cure and coating adhesion are the main factors that affect coating performance. For different contents of the product, the appropriate coating and reasonable production process to ensure the stability of real tank products have an important role.
3 tin layer failure
Electrolytic tin cans and tin will be filled with oxygen in the tank when filling, reducing the content of the contents of the opportunity to be oxidized. The effect of the reduction of tin on some of the light fruit flavor and color has a good preservation effect, so the use of prime cans to better keep the contents of the flavor and color, brown change slightly, the taste of the quality of the better, The term is thus extended. However, the uniform acidity of tin, nitrite and nitrite caused by the abnormal fast de-tin, tin sulfide corrosion will lead to the gradual thinning of the tin layer. In order to enhance the corrosion resistance of tin layer, usually tin layer need to passivation treatment to reduce the tin layer dissolution rate, so to enhance the tin layer passivation film is to improve the corrosion resistance of iron cans important measures.