Super Fitness Health BlogFacts About The Hot Dipped Galvanizing Process
Hot dip galvanizing process involves three basic steps namely: surface preparation, galvanizing process, and the process of inspection.
The process of surface preparation is the most vital step in the entire process. In most circumstances, inadequate or incorrect preparation of the surface will cause the coating to fail before its expected service lifetime ends. This step in the galvanizing process has its own means of quality control because zinc will not metallurgically react with a surface that is unclean. Any inadequacies or failures in the steel surface preparation will instantly be noticeable when the steel is taken out from the tub of molten zinc, because unclean area will not be coated and corrective measures must be immediately taken.
The surface preparation process for hot dip galvanizing consists of three the following three steps: degreasing, acid pickling, and fluxing.
Degreasing:
A biological cleaning bath, hot alkali solution, or mild acid bath will remove organic contaminants like paint stains, dirt or dust, oil, and grease from the steel surface. A degreasing bath won’t be able to get rid of epoxies, welding slags, vinyls, and asphalt. So these types of materials must be removed through the process of sand-blasting, grit-blasting, or other mechanical means before steel is forwarded to the galavanizing department.
Pickling:
A dilute solution of ambient temperature hydrochloric acid or hot sulfuric acid can remove oxidation and miss scale from the surface of steel. As an alternative to degreasing, this process can also be done using air blasting sand, abrasive cleaning, grit, or metallic shot onto the surface of the steel.
Fluxing:
Fluxing, the last step in surface preparation process for galvanizing serves two purposes. It gets rid of any residual oxides and deposits a protective layer onto the surface of the steel to prevent more oxidation from developing 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 of molten zinc. The steel being galvanized undergoes fluxing on its way into a molten zinc bath. In the dry method on the other hand, the iron or steel is submerged or pre-fluxed in a molten solution of zinc ammonium-chloride. The iron or steel is then dried before dipped in molten zinc.
Galvanizing Process
In the hot dipped galvanizing process, the steel material is immersed in a molten zinc tub. The bath contains at least 98% pure zinc and is heated to about 840 degrees Fahrenheit.
While the steel item is immersed into the molten zinc bath, the zinc reacts with the iron in the steel material to form a series of iron/zinc inter-metallic alloy layers. When the fabricated item coat growth is completed, it’s slowly taken out from the molten zinc bath, and the excess zinc is removed by vibrating, draining, and/or centrifuging.
The metallurgical reaction will still continue even after the steel or iron product is withdrawn from the zinc bath, as long as the it stays near bath temperature. The galvanized item is cooled by leaving in open air or immersing in water or a passivation solution.
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