Zinc flake in practical use – approval in the wind industry 12 May 2014

By Mr Jörn Selent, global sales – tiers, Dörken MKS-Systeme

Over the decades, the superior zinc flake systems of Dörken MKS-Systeme have received the approval of nearly all leading manufacturers of wind turbines. The global availability of DELTA-MKS® systems ensures the optimal realisation of specifications with manufacturers and service providers.

Dörken MKS-Systeme

A look at the supply chain reveals that Dörken MKS-Systeme enjoys great popularity with its systems. Approximately 80% of all wind turbine manufacturers and their suppliers currently use DELTA-MKS® zinc flake systems.

These manufacturers of wind turbines or their subcontractors place their trust in DELTA-MKS® systems, as these have proven their longevity in various tests and use scenarios.

The official certification of DELTA®-TONE 9000 and DELTA®-SEAL GZ system by Germanischer Lloyd in particular serves to underscore quality and reliability – including in challenging climatic conditions, with this further highlighted by certification to class C5M (offshore).

In addition to the Germanischer Lloyd certification, further DELTA-MKS systems are also being put through their paces on a FINO offshore wind turbine. In the Baltic region various test pieces (size M24 bolts) are being exposed to every conceivable external influence until 2018. Also, a test at the DIBt is underway, carried out by the BAM (Federal Institute for Materials Research and Testing), that involves the DELTA-MKS zinc flake coating being compared with standard hot dip galvanisation on size M16 and M30 bolts. The components were exposed in March 2012 on the island of Sylt in northern Germany, as well as in Berlin, and have since been examined regularly, with typical corrosion tests also conducted in the laboratory. Interim results from summer 2013 clearly indicate that the components coated with the DELTA-MKS zinc flake systems are functionally at least equal to, optically more appealing than, the hot dip galvanised components. No damage whatsoever can be determined as yet with the DELTA-MKS systems.

Coatings – market and trends
Repairs and breakdowns are expensive. Components are therefore required to function well. The trend is towards higher quality, which for us means higher requirements of coating systems.

Whereas formerly 480 – 720 hours of corrosion exposure as per DIN EN ISO 9227 was required, today, particularly in the offshore field, corrosion exposure times of 1,440 hours are standard.

The portfolio of parts that it is possible to coat has also grown. Where until recently primarily fastening elements in the rotor blade connectors and gondola were coated with zinc flake systems from Dörken MKS, the systems are now also to be found in the tower and foundation areas. In future, the aim is to coat high-tensile pre-stressed bolts.

How does zinc flake technology work?
A coating of zinc flake is a ‘paint’ comprising numerous tiny flakes, primarily protecting components of various kinds against corrosion. The effect of the base zinc enables it to provide active protection against environmental influences – this is known as cathodic corrosion protection. Zinc flake coatings mostly contain a combination of zinc and aluminium flake (as per DIN EN ISO 10683 or DIN EN 13858), bound together via an inorganic matrix.

Even extremely thin coatings – a system of base coat and top coat typically comprises 8μm – 12μm – enable protection of up to 1,000 hours to be achieved against base metal corrosion (red rust) as per DIN EN ISO 9227. Other classic technologies in contrast require a far higher coating thickness in order to offer similar corrosion protection or, due to their application, cannot function in the thinnest micro layer ranges.

The organic top coat DELTA®-SEAL in particular protects the zinc flake base coat and provides a tight sealing against external influences that could otherwise attack a more porous zinc flake coat.

Dörken MKS-Systeme highlights that no hydrogen is generated in the coating process and there is therefore no risk of hydrogen induced stress cracking corrosion. For this reason, zinc flake is particularly well suited for high-tensile steels of the classes 10.9 and 12.9 or from 1,000MPa.

Typical application forms for threaded bolts are spray coating and spin coating.

Claire Aldridge Deputy Editor t: +44 (0) 1727 743 889

Having spent a decade in the fastener industry experiencing every facet – from steel mills, fastener manufacturers, wholesalers, distributors, as well as machinery builders and plating + coating companies, Claire has developed an in-depth knowledge of all things fasteners.

Alongside visiting numerous companies, exhibitions and conferences around the world, Claire has also interviewed high profile figures – focusing on key topics impacting the sector and making sure readers stay up to date with the latest developments within the industry.