The Hot Dipped Galvanizing Process

The hot dipped galvanizing process involves three basic steps namely: surface preparation, galvanizing, and the process of inspection.


The process of surface preparation is the most vital step in the whole galvanizing process. In many circumstances, inadequate or incorrect preparation of the surface will cause the coating to fail even before its expected service lifetime ends. This initial step has its own means of quality control as zinc won’t metallurgically react with a surface that is unclean. Any failure or inadequacy in this process will immediately be noticeable when the steel is taken out from the molten zinc bath, because unclean area won’t be coated and corrective measures must be taken as soon as possible. 


Surface preparation for hot dip galvanizing consists of three the following steps: degreasing, acid pickling, and fluxing. 




A biological cleaning bath, hot alkali solution, or mild acid bath gets rid of organic contaminants like paint stains, dust or dirt, grease, and oil from the steel surface. A degreasing bath can’t get rid of epoxies, welding slags, vinyls, and asphalt. So these kinds of materials should be removed by sand-blasting, grit-blasting, or other mechanical processes before steel is given to the galavanizing department. 




A dilute solution of ambient temperature hydrochloric acid or hot sulfuric acid could get rid of rust and miss scale from steel surface. As an alternative to degreasing, this step could also be done using air blasting sand, abrasive cleaning, grit, or metallic shot onto the surface of steel.




Fluxing, the final step in the process of surface preparation for hot dip galvanizing serves two purposes. It gets rid of residual oxidation and deposits a protective layer onto the steel surface to prevent further oxides from building up onto the surface of steel before galvanizing is performed. 


Flux is applied in dry or wet method. In the wet galvanizing process, a layer of liquid zinc ammonium-chloride is floated on top the molten zinc. The iron or steel being galvanized undergoes the process of fluxing on its way into the molten zinc tub. In the dry method, the steel is pre-fluxed or submerged in a molten solution of zinc ammonium-chloride. The steel or iron item is then dried before it’s dipped in molten zinc bath.        


Hot-Dipped Galvanizing Process


In chemical process, the steel material is immersed in a molten zinc tub. The hot zinc bath contains at least 98% pure zinc and is heated to about 840 degrees Fahrenheit. 


While steel is immersed into the molten zinc bath, the zinc reacts with the iron in the steel item to form a series of iron/zinc inter-metallic alloy layers. When the fabricated item coat growth is completed, it’s slowly withdrawn from the zinc bath, and the excess zinc is removed by centrifuging, vibrating, and/or draining.


The metallurgical reaction will still continue after the steel or iron product is removed from the molten zinc bath, as long as the steel stays near bath temperature. The galvanized item is cooled either by leaving in open air or by immersing in water or a passivation solution.  


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