Electrolytic tinplate corrosion
Corrosion of metal packaging products is due to the electrochemical instability of the material in the corrosive contents. Electrolytic tinplate The main corrosion resistant material is the coating of the can body, the tinplate tinplate and the iron layer, and the top cover and bottom cover with the coating. As the metal packaging products have a certain shelf life, when the electrolytic tinplate empty tank design corrosion life is greater than the shelf life to meet the production requirements, to ensure that food and beverage in the shelf life of the quality and safety, excessive corrosion margin is the quality of excess, Product economic cost. In order to take into account the design life and economic savings at the same time, electrolytic tinplate production of three cans of raw materials and technology with precise requirements to maintain product quality and stability.
Experimental work shows that electrolytic tinplate three-tank coating, tin layer and iron layer is the main corrosion protection barrier, stable raw materials and reasonable technology to meet the vast majority of real tank products corrosion resistance requirements. Related research also found that some products of the tank occurred in the early corrosion time, due to the type of corrosion and the occurrence of different locations, the pace of development is very different, and some real cans within a few weeks have rust, and serious Even in the corrosion after a few months there will be corrosion perforation phenomenon, and some real can corrosion can continue until the shelf life will not occur after the corrosion perforation. Electrolytic tinplate production and storage process often found in the real tank shelf life before the tank will appear corrosion phenomenon, the main form of corrosion is divided into uniform corrosion and local corrosion two categories. Local corrosion phenomenon on the tank quality and safety hazards, serious can lead to the tank during the shelf life occurred in the corrosion perforation leak.
1 uniform corrosion
Uniform corrosion, also known as comprehensive corrosion, corrosion phenomenon distributed throughout the metal surface, the metal surface corrosion rate of the same parts of the same, the metal surface is more uniform thinning, and the metal surface no obvious differences in corrosion form, such corrosion due to its Occurs on all surfaces, easy to find and control. Electrolytic tinplate corrosion is more common in the corrosion phenomenon is uniform corrosion, mostly occurred in the top of the neck necking area, the bottom of the bottom of the deformation zone and the location of the weld reinforcement area.
2 localized corrosion
Local corrosion, also known as uneven corrosion, due to the uneven chemical properties, such as dissimilar metals, surface defects, concentration differences, stress concentration or uneven environment and other factors, the formation of local batteries and corrosion. Local corrosion of the anion, the anode can be distinguished, local corrosion concentrated in a specific location, a sharp occurrence, rapid corrosion of materials damage, electrolytic tin cans of the local corrosion easily lead to perforation leakage phenomenon. Local corrosion is characterized by diversity. According to the damage caused by local corrosion, this type of corrosion can be divided into galvanic corrosion, pitting corrosion, corrosion, corrosion, corrosion, corrosion corrosion, fatigue corrosion or selective corrosion Types of.
The local corrosion of electrolytic tinplate is mostly concentrated in the weld zone or the bottom cover expansion ring, in which the bottom of the tank corrosion is the main area of corrosion perforation, the black uniform corrosion area of the center of the corrosion hole, compared with the uniform corrosion area, corrosion hole Area is very small, is a typical local corrosion phenomenon, corrosion continues to develop will lead to corrosion of the tank perforation.