Trailers and their components are constructed from a range of metals including cast iron, stainless steel and aluminium. Iron and steel need protective coatings and even aluminium requires corrosion protection if it is to be submerged in salt water for long periods of time.
There are a range of protective trailer coatings available, but by far the most effective and versatile material is zinc.
The paradox with zinc is that its impermeable layer of zinc carbonate is formed thanks, in part, to oxidisation. Even when a scratch exposes the underlying metal to the elements, zinc oxide re-forms and is deposited over the area, resealing it. Because of this zinc is referred to as self-healing or sacrificial.
Here are the most popular forms of zinc coating:
Hot-dipped galvanisation is the most well-known form of zinc coating. A component is dipped in molten zinc at 460º Celsius causing the zinc to metallurgically bond with the material.
Hot-dipping offers the best zinc protection as it results in the greatest thickness of all the available processes while maintaining a uniform finish.
Under optimum conditions, hot-dipped zinc coating will protect for 70 years or more, far outlasting the trailer itself.
The finish is not as attractive as plating due to its ‘spangled’ fleck pattern. It’s heavier and not suitable for threaded components of M10 or smaller. It’s also unsuitable for components with sustained operating temperatures in excess of 200º Celsius, on high tensile.
With zinc plating, zinc is applied to the component through electrolysis. It results in a coating that is finer than hot-dipping, making it cheaper, lighter and more suited to detailed surfaces.
Due to this thinner coating, plating is not ideal for heavy-duty applications. Plating is more attractive than galvanising due to its lustrous finish.
Dacromet is a cold-dip/spray process that results in a thin coating of zinc similar to that of plating. The components are dipped and spun in a cold zinc solution before they are baked at 300º Celsius.
As the process is far newer than hot-dipping, it is unknown how long Dacromet will last. In addition to improved corrosion resistance, Dacromet protects components from brittleness and has a lustrous finish.
A range of trailer paint preparations are available to protect components against corrosion.
A fairly thick coating can be achieved with zinc paint and theoretically there is no limit in the size of the component to be coated.
However, the quality of the finish is largely dependent on the skill of the painter. As such, painted surfaces cannot achieve the consistency of hot-dipped or plated coatings. Paint is also useful in patching up worn or scratched coatings.
Each process offers advantages but it all comes down to coating thickness. In the words of Finishing.com’s Ted Mooney, ‘zinc is zinc’ – that is to say, the thickness of a zinc coating is directly proportional to its anti-corrosive properties.
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