1. Hot-dip galvanizing generally has a thicker zinc layer, about 10um or more, and has strong anti-corrosion capabilities. It is a commonly used galvanizing process.
Electroplated zinc is very thin, about 3-5um. The surface of hot-dip plating is rough and bright, with zinc splatter in severe cases, while the surface of electroplating is smooth and gray (stained).
Galvanized steel sheets manufactured by the electroplating method have good processing properties. However, the coating is thin and the corrosion resistance is not as good as that of hot-dip galvanized sheets.
Cold galvanizing is electro-galvanizing. The amount of galvanizing is very small. Only the outer pipe wall is galvanized (hot plating---both inside and outside). It is only 10-50g/m2. Its corrosion resistance is much different than that of hot-dip galvanized pipes.
2. Chemical industry generally uses electro-galvanizing, which is suitable for small parts; hot-dip galvanizing is generally used for electrical equipment and components, and is suitable for large components and equipment.
Electro-galvanizing, commonly known as cold galvanizing, uses an electrochemical method. A zinc ingot is used as an anode. Zinc atoms lose their electrons and become ions and dissolve into the electrolyte. The steel strip serves as a cathode. Zinc ions gain electrons on the steel strip and are reduced to Zinc atoms are deposited onto the surface of the steel strip to form a coating.
Hot-dip galvanizing is to pickle the steel pipe first. In order to remove the iron oxide on the surface of the steel pipe, after pickling, it is cleaned in an aqueous solution of ammonium chloride or zinc chloride or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to in a hot dip plating tank.
3. There is a big difference in the amount of galvanizing between hot-dip galvanized sheets and electro-galvanized sheets. The galvanizing amount of hot-dip galvanizing cannot be too small. Generally, the minimum is 50~60g/m2 on both sides and the maximum is 600g/m2. The galvanized layer of electro-galvanized sheets can be very thin, with a minimum of 15g/m2. However, if the coating is required to be thicker, the production line speed will be very slow, which is not suitable for the process characteristics of modern units. Generally, the maximum is about 100g/m2. Because of this, the production of electro-galvanized sheets is greatly restricted.
4. There are fundamental differences in the coating structure between hot-dip galvanized sheets and electro-galvanized sheets. There is a slightly brittle compound layer between the pure zinc coating of the hot-dip galvanized sheet and the steel strip matrix. When the pure zinc coating crystallizes, most of the zinc flowers are formed, and the coating is uniform and has no pores. The zinc atoms in the electroplated zinc layer are only precipitated on the surface of the steel strip, and are physically attached to the surface of the steel strip. There are many holes for drying, and it is very easy to cause pitting corrosion due to corrosion properties. Therefore, hot-dip galvanized sheets are more durable than electro-galvanized sheets. preservative.
5. The heat treatment processes of hot-dip galvanized and electro-galvanized sheets are also completely different. Hot-dip galvanized sheets generally use cold hard plates as raw materials, and are continuously annealed and hot-dip galvanized on the galvanizing line. The steel strip is heated in a short period of time. It is also cooled, so the strength and plasticity are affected to a certain extent, and its stamping performance is worse than the same cold-rolled plate after degreasing and annealing in a professional production line. Electro-galvanized sheets use cold-rolled sheets as raw materials, which basically guarantees the same processing performance of cold-rolled sheets, but its complex process also increases production costs. In short, hot-dip galvanized sheets have lower production costs and wider application range, and have become the main variety in the galvanized sheet market.
