What Does Double Dip Galvanizing (DDG) Mean?
Double dip galvanizing (DDG) refers to an industrial process used to protect large surface areas of iron, steel and other metals from corrosion. It is characterized by fully or partially submerging the substrate metal into a zinc bath at approximately 460°C (860°F) to form zinc carbonate (ZnCO3). The resulting compound possesses corrosion resistant properties.
Corrosionpedia Explains Double Dip Galvanizing (DDG)
Double dip galvanizing involves three steps to meet completion: preparation, galvanization and inspection.
DDG preparation involves the thorough cleaning and impurity removal from the surface to be treated. Grease removal, chemical treatments and physical adjustments are part of the cleaning process. Chemicals such as hydrochloric acid and zinc ammonium chloride are used to prepare iron surfaces.
After preparation, the actual process of galvanization is performed. This is characterized by substrate immersion into molten zinc to form a protective zinc-iron layer. This stage of completion is vital to prevent galvanic corrosion, which is the damage that occurs when two different metals are in contact in an electrolyte; the more noble metal is protected and the more active metal tends to corrode.
After galvanizing, the structure is inspected for coating thickness and appearance to ensure uniformity in protection across the substrate's surface.