Two technological methods of electrogalvanizing

Two technological methods of electrogalvanizing

Galvanizing process mainly includes hot - dip galvanizing and cold galvanizing. Cold galvanizing is also known as electric galvanizing. Electrogalvanizing is mainly discussed here. There are many kinds of electric galvanizing, various. But from the PH value of galvanized bath, there are two main categories: alkaline galvanized and acidic galvanized.

Alkaline galvanizing

Alkaline galvanizing process refers to the PH value of the bath is alkaline. But because of the different complexing agent, it is divided into cyanide zinc and zinc zinc two. Cyanide galvanizing is a very old type of plating. There are three main components in the plating solution: zinc oxide, the main salt, sodium cyanide, the complexing agent, and sodium hydroxide, the conductive salt (commonly known as caustic soda). There was no brightener in early cyanide plating solutions. With the improvement of people's aesthetic requirements, brightener has been added to cyanide solution galvanized solution. Cyanide galvanizing process is stable and the coating is fine. Bath dispersion ability is good. According to the amount of sodium cyanide content is different, and divided into high cyanide, cyanide and low cyanide galvanized three. The biggest disadvantage of cyanide galvanizing is that it is too toxic and seriously harmful to the environment.

Zincate galvanizing is a fast developing galvanizing technology in recent 30 years. Its main components are the main salt zinc oxide, complexing agent and conductive salt sodium hydroxide (commonly known as caustic soda). In order to obtain a fine bright coating with good dispersion ability, brightener should be added. The main development period of zincate galvanizing in China is the big cyanide-free galvanizing in the 1970s. The famous DPE galvanizing process and DE galvanizing process have been used. Although this process is not as stable as cyanide galvanizing process, meticulous. But its biggest advantage is that it is cyanide-free. It's much less harmful to the environment. Zincate galvanized has a new development, foaming and brittleness defects have been overcome, greatly improved dispersion ability, and cyanide galvanized than the United States.

Acid galvanizing

The PH value of the bath is 4-6. The second result of the great effort of cyanide-free galvanizing in the 1970s was cyanide-free ammonium chloride galvanizing. On par with zincate base galvanizing. It consists of zinc chloride as the main salt, ammonium chloride as the complexing agent and conductive salt. Citric acid and ammonia triacetic acid were auxiliary complexing agents. Polyethylene glycol and thiourea were used as coating refiners. The plating obtained from this solution is fine and has good dispersion ability. The plating solution has little toxicity. But the main disadvantage is that the plating solution is unstable, and the ammonium chloride gas emitted is very corrosive to the plating equipment. The current efficiency is also low. Strong sensitivity to impurities. The operating temperature range is narrow. It has been basically eliminated by 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 composition is: zinc chloride main salt, the general use content is 70-90g/L. Potassium chloride as conductive salt, the use of content from 140-280g/L, according to different needs can be arbitrarily adjusted. Boric acid is used as a PH buffer to stabilize PH between 4.6 and 5.6. Because this bath is working at room temperature, the solubility of boric acid is not high, the general content is controlled at 25-30g/L.

It is impossible to obtain qualified zinc coating by these three components alone. Some additives are needed to obtain a bright, fine galvanizing layer. The advantages of potassium chloride galvanizing are stable bath, bright and fine coating, low cost, high current efficiency and non-toxic. The disadvantage is that the dispersion capacity of the plating solution is slightly worse than that of alkaline zinc plating, and the brittleness of the coating is larger. Nevertheless, potassium chloride galvanizing, as soon as it was available, was universally popular. Development is very rapid, has occupied half of the galvanized Jiangshan. From the market, galvanized process is mainly two kinds of plating: alkaline zincate and acid potassium chloride galvanized. Other galvanizing processes have been dwarfed, slowly out of the historical stage.

There is also a sulfate galvanizing process in acid galvanizing process. Its main component is zinc sulfate, the main salt. Content between 250-500g/L. Alum or aluminum sulfate as conductive salt. The content is between 30-50g/L. Conductive salts are also available with sodium sulfate or sodium chloride. In addition to the above several, but also add some additives, the role is to make the coating fine. At first, dextrin or gum was used, and later some special brightening agents were invented to make the coating brighter and finer. The biggest advantage of sulfate galvanizing is that it can use a large current density (1-5A/dm2) and plating speed is fast. But the disadvantage is that the dispersion ability of the bath is very poor, not suitable for plating more complex workpiece.