Friday, October 17, 2014

Galvanized surface pretreatment

In order to get a good layer of zinc, steel surface must be very clean, rust, iron oxide, and this will reduce the adhesion properties of the coating, prevent binding of iron and zinc. Therefore, before plating steel surface preparation must be carried out. The process includes a general degreasing, washing, pickling, and then washing with water. Also included in the dry storage of galvanized, painted solvent.

The purpose is to remove grease clarinet skim the surface, dirt, steel pickling plant so as not to affect the results, degreasing can be achieved by burning or caustic, often caustic. Alkaline cleaning solution is an aqueous solution containing about 10-12% NaOH, the temperature is 70-80 ℃. Cleaning time is 8-10 minutes.

The purpose is to remove pickling steel surface oxide skin, the acid is generally used sulfuric acid and hydrochloric acid, sulfuric acid pickling effect depends on the temperature, the effect of hydrochloric acid depends on the concentration of H ions. The pickling solution is an aqueous solution of sulfuric acid containing 10-15% sulfuric acid at a temperature of 60-80 ℃, hydrochloric acid pickling solution containing 10-15% aqueous hydrochloric acid, at a temperature below 40 ℃, the pickling time is usually 30 minutes. The advantage of hydrochloric acid is that it can operate at room temperature, removing the oxide scale capability, less erosion of the base metal by absorption of the hydrogen gas and small in the possibility of contamination of the residue of carbon black, ferric oxide generated acid matter, dark angle, easy to remove, no effect on zinc from galvanized perspective, hydrochloric acid is more appropriate. However, the low sulfuric acid prices, easy regeneration, therefore, countries choose pickling solution under different circumstances, the United States and more with sulfuric acid, hydrochloric acid and West Germany, multi-purpose. Adding an appropriate amount of inhibitor in the acid, the acid can etch the surface of the pure steel decreases, so that the contact is reduced with hydrogen in the steel pipe. In addition, also reduce acid consumption and mist generated, the amount inhibitor is typically 0.1-0.5%. Usual amount inhibitor is generally 0.1-0.5%, commonly used inhibitor of water such as plastic.

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