There are two main types of galvanizing processes: hot-dip galvanizing and cold-dip galvanizing. Cold galvanizing is also called electro-galvanizing. Judging from the pH value of the galvanizing bath, there are two main categories: alkaline galvanizing and acidic galvanizing.
Alkaline galvanizing
Alkaline galvanizing process means that the pH value of the plating solution is alkaline. However, due to different complexing agents, it is divided into two types: cyanide zinc plating and zincate zinc plating. Cyanide galvanizing is a very old plating type. There are three main components in the plating solution: the main salt zinc oxide, the complexing agent sodium cyanide and the conductive salt sodium hydroxide (commonly known as caustic soda). There was no brightener in early cyanide plating solutions. With the improvement of people's aesthetic requirements, brighteners that have a brightening effect are added to the cyanide zinc plating solution. The cyanide zinc plating process is stable and the coating is meticulous. Good dispersion ability of plating solution. According to the different sodium cyanide content, it is divided into three types: high cyanide, medium cyanide and low cyanide zinc plating. The biggest disadvantage of cyanide galvanizing is that it is too toxic and seriously harmful to the environment.
Zincate galvanizing is a galvanizing process that has developed rapidly in the past 30 years. Its main components are zinc oxide as the main salt, sodium hydroxide as the complexing agent and conductive salt (commonly known as caustic soda). In order to obtain a fine bright coating with good dispersion ability, a brightener must be added. Although this process is not as stable and meticulous as the cyanide galvanizing process. But its biggest advantage is that it is cyanide-free. Much less harm to the environment.
Acid galvanizing
The pH value of the plating solution is 4-6. It uses zinc chloride as the main salt and ammonium chloride as the complexing agent and conductive salt. Citric acid and nitrilotriacetic acid are auxiliary complexing agents. Polyethylene glycol and thiourea are used as coating refiners. The coating obtained from this plating solution is fine and has good dispersion ability. The plating solution has low toxicity. However, the main disadvantage is that the plating solution is unstable and the ammonium chloride gas emitted is very corrosive to the electroplating equipment. Current efficiency is also lower. Strong sensitivity to impurities. Narrow operating temperature range. It has been basically eliminated by the potassium chloride galvanizing process.
Potassium chloride (or sodium chloride) galvanizing process
Potassium chloride (or sodium chloride) galvanizing process is a new cyanide-free galvanizing process developed in the 1980s. Its main component is: zinc chloride main salt, the general usage content is 70-90g/L. Potassium chloride is used as conductive salt, and the usage content ranges from 140-280g/L, which can be adjusted according to different needs. Boric acid is used as a pH buffer to stabilize the pH between 4.6-5.6. Since this plating solution works at room temperature, the solubility of boric acid is not high, and the general content is controlled at 25-30g/L. The advantages of potassium chloride galvanizing are stable plating solution, bright and delicate coating, low cost, high current efficiency and non-toxicity. The disadvantage is that the dispersion ability of the plating solution is slightly worse than that of alkaline zinc plating, and the brittleness of the coating is also higher.