When electric current is properly supplied to a cathodic steel strip immersed in an electrolytic solution containing metallic ions, the metallic ions lose their electrical charges by combining with electrons and precipitate on the cathodic surface as metallic atoms. A continuous electroplating line is composed of pretreatment equipment, plating equipment, and post-treatment equipment. The functions and construction of the pretreatment and post-treatment equipment are almost identical to those used in a hot-dip line. To ensure uniform, efficient plating, it is important to supply the plating solution to the whole strip surface at high speed and with uniformity. As plating proceeds, metallic ions are lost from the plating solution. Quick resupply of these lost metallic ions is essential for uniform, high efficiency plating. In order to obtain a uniform plating thickness, it is necessary to ensure that the composition of the plating solution supplied to the whole strip surface should be uniform. It is also necessary with electroplating equipment to minimize the electrode distance between the strip and the anode in order to reduce electric resistance and hence power consumption. For this purpose, plating cells of the various types shown in the figure have been developed and put into practical use. Multiple cells are typically arranged in series to obtain high productivity. Examples of electroplating are zinc, tin and chromium plating. Zinc plating is divided into pure zinc plating and alloy zinc plating such as zinc-iron and zinc-nickel, which are applied to produce electrogalvanized sheets for automobiles, home electrical appliances, and building materials. Tin plate is mainly used in food and beverage cans. The method of joining the can body has changed from soldering to cementing and welding. To reduce the consumption of expensive tin, the production of tin-free steel has increased. Tin-free steel is a surface-treated steel strip with a coating comprising an under layer of metallic chromium and an upper layer of chromium hydrate.