Hot Dip Galvanizing
Hot dip galvanizing dates back to the 1800s for the protection of steel. It is the process of applying a zinc coating to fabricated iron or steel material by immersing the material in a bath consisting primarily of molten zinc. Galvanizing is considered a factory-controlled metallurgical combination of zinc and steel that provides corrosion protection in a wide variety of environments. It also provides cathodic protection where the zinc sacrifices itself to protect the base steel. Galvanizing has had a proven history of industrial success as a method of corrosion protection in countless applications. It can be found in almost every industry where steel is used.
The 8 Step Process
- Preparation - First the surface of the product must be properly prepared. This entails the removal of all oil, grease and soluble paints with a hot alkaline cleaner. Sandblasting may be necessary if other finishes such as mil varnish and paint coating exist.
- First Rinse - This is a water rinse before going to the pickle tank.
- Pickling - Next the steel is pickled in an acid bath in order to remove scale and rust. We have an acid capacity of five sulfuric acid tanks, two hydrochloric tanks, and one caustic tank.
- Second Rinse - After pickling, it is then rinsed in a tank of approximately 7-10% acid solution to prepare it to be galvanized.
- Preflux - Zinc ammonium chloride is used in the final flux step of the surface preparation. Fluxing removes oxides and prevents further oxides from forming on the surface of the material prior to galvanizing and promotes the zinc bonding of the zinc to the materials surface.
- Galvanizing - Once the product is fully prepared it is immersed in a bath consisting of a minumum of 98% pure molten zinc. The kettle temperature is maintained at about 840°F. Fabricated items are immersed in the kettle long enough to reach kettle temperature. The articles are slowly withdrawn from the galvanizing kettle and the excess zinc is removed by draining.
- Cooling - The galvanized item is then air-cooled.
- Inspection - The most important method of inspection for galvanized material is visual. Then it is checked for thickness, uniformity and adherence of coating, and appearance.