Topcoatings (Duplex systems)

A duplex system is the combination of a diffusion galvanised coating (base coat) and an organic coating (top coat). These systems are generally used when products are permanently exposed to an exceptionally aggressive environment or for aesthetic or functional reasons.

Top coatings can be applied to the sherardised product by painting, spraying, dip spinning, electrostatic or catophoresic processes without pretreatment.

The service life of a duplex system is determined to a considerable extent by the mutual bonding of the coatings and the base material. The zinc-iron alloy produced by the diffusion galvanising is bound inseparably with the base material.

The microcrystalline surface of the sherardised product anchors the organic coating. In the event of damage to the top coat, the underlying zinc-iron layer means no base material corrosion of the top coating can occur.

Sherardised products with a top coating are resistant to more than 1000 hours of salt spray testing in accordance with ISO 9227, without any base material corrosion occurring.

In the case of maritime applications, Sherart has duplex systems on a PTFE basis with a corrosion-resistance of more than 2000 hours.