What is Hot Dipped Galvanising?
Galvanised Trailers is Trailer Guys. Galvanising is a rather complex process and this article is here to help understand the galvanising process.
Hot-dip galvanising (HDG) is the process of coating fabricated steel by immersing it in a bath of molten zinc. There are three fundamental steps in the hot-dip galvanising process.
- Surface preparation
1. Surface Preparation
A bare metal trailer arrives at the galvanising facility. An overhead crane is used to hang the trailer and run though a series of preparation methods. As a result the trailer is lifted and moved through all three processes. As a result the trailer then goes through a series of three cleaning steps; degreasing, pickling, and fluxing.
- Degreasing : Removal of dirt, oil, and organic residues
- Pickling : An acidic pickling bath removes production mill scale and iron oxide
- Fluxing : Final surface preparation step. Fluxing removes any remaining oxides, and also coats the steel with a protective layer, to prevent any further oxide formation prior to galvanising.
Most Importantly, proper surface preparation is critical, as zinc will not react with unclean steel.
- After surface preparation, the bare trailer is dipped in the molten (500 C) bath of at least 98% zinc
- Then lowered into a kettle. At an angle that allows air to escape from the RHS tubular shapes. The angle also releases air from other pockets to ensure that the zinc can flow into, over, and throughout the entire trailer.
- While immersed in the kettle, the iron in the steel trailer metallurgically reacts with the zinc to form a series of zinc-iron intermetallic layers and an outer layer of pure zinc.
An inspection of the trailers coating is the final step of the galvanised trailers process.
- A visual inspection gives a very accurate determination of the quality of the coating
- Especially relevant is that the Zinc does not react with unclean steel This means that an un-coated area on the trailer will be visible to the naked eye
- In addition, a magnetic thickness gauge is used to verify the coating thickness complies with specific requirements
Why Choose a Galvanised Trailer?
Hot-dip galvanising provides a number of benefits to the steel trailer it protects.
Metallurgically bonded zinc iron alloy layers that are created in the above process. Creates a barrier between the trailer and the environment. It also cathodically protects the steel.
The cathodic protection offered by zinc means the galvanised coating sacrifices itself to protect the underlying base steel from corrosion.
The tightly adhered coating, which has a bond strength of around 3,600 psi. This coating is also extremely abrasion-resistant as the intermetallic layers are harder than the base steel.
Even if the coating is damaged, zinc’s sacrificial action will protect exposed steel up to 7-10mm away.
In addition to the cathodic protection offered by hot-dip galvanising, there are a few other characteristics of the coating which provide longevity.
Reaction. Reaction in the galvanising kettle is a diffusion process, which means the coating grows perpendicular (horizontal) to the surface, ensuring all corners and edges have at least equal thickness to flat surfaces.
Immersion. The complete immersion in the zinc bath provides total coverage of the Trailer Guys Trailer. Including the interior of hollow structures.
Zinc Coasting. Finally, the zinc coating naturally develops an impervious layer of corrosion products on the surface, known as zinc patina. The patina, cathodic protection, complete coverage and all of these other features, provide hot-dip galvanised steel with a long, maintenance-free service life. First maintenance for hot-dip galvanised steel can be seen below.