RENEWABLE ENERGY
Handling the demands of wind power
NOF METAL COATINGS EUROPE has developed thin layer anti-corrosion coatings that it says provide worldwide wind power companies with an alternative for protecting fasteners.
T
he zinc flake anti-corrosion technology that NOF METAL COATINGS GROUP has been developing for over 30 years is used across a wide variety of industries, but is especially significant for the wind power sector. Michel Almosnino, chemical engineer in charge of
the wind power market at NOF METAL COATINGS EUROPE in France explains: “The wind power market is one of the most dynamic industries for which our water-borne zinc flake anti- corrosion technology is recognised as being particularly efficient by European and international professionals of the sector. It is a fast growing market with an installed capacity increasing from 25% to 30% yearly worldwide.” The anti-corrosion performance of coatings is essential in big
mechanical structures such as wind turbines, with the fastening of the different elements providing the installation with safety and integrity. “On a 1MW wind turbine, there is about 5 tonnes of bolts,” mentions Michel Almosnino.
The key to innovation The structural element of a wind turbine, the nacelle
mounted on top of the mast, connected to the rotor by the hub, is home to mechanical and pneumatic components as well as some electrical and electronic components necessary for its running. The corresponding fastenings, with diameters between 24mm and 64mm, are subjected to mechanical stress, physical/ chemical and climatic constraints, and have to be protected. NOF METAL COATINGS points out that the anti-corrosion
protection principles (barrier effect, sacrificial protection and passivation) already demonstrated in the fields of automotive, trucks, railway and construction equipment, means that its GEOMET®
zinc flake coatings are able to meet these
requirements. Regarding the control of coefficients of friction, NOF METAL
COATINGS GROUP has developed, with several wind turbine manufacturers, an alternative system for lubricating agents used generally when tightening and untightening bolts. NOF METAL COATINGS’ says that its PLUS®
the coefficient of friction is very low, ranging between 0.06 and 0.09. The tightening torque is therefore lower, thus making the assembly and disassembly easier, particularly during maintenance operations. The coefficient of friction is an essential parameter to control the integrity of the bolted joints.” Michael Almosnino also highlights that the geographical
situation of wind farms is part of the factors that have to be taken into account, meaning that specific tests have to be implemented. In France, the Institute of Corrosion in Brest - French subsidiary of the Sweden Institute of Corrosion, has certified the NOF METAL COATINGS GROUP coatings.
Application process Fasteners for wind turbines are generally large-sized, can
weigh up to ten kilograms and have often complex geometries. That is why it is important to have appropriate industrial technology for application. There are several application processes among which the spraying of parts on racks is the most used owing to its easy implementation on big-sized screws. Another common technology is the dip-spin process on racks. This enables covering hollow spaces and thus avoiding the ‘Faraday cage’ effect linked to the electrostatic spraying application. NOF METAL COATINGS points out that prior to being
coated, the parts are degreased and shotblasted (and not pickled in order to avoid hydrogen embrittlement). The GEOMET®
500 + PLUS® XL anti-corrosion system is a
coating formed from aqueous solutions. It is composed of zinc and aluminium flakes in an inorganic matrix, without chromium. The application of PLUS® lubricated GEOMET®
XL topcoat after the already self- 500 coat reduces substantially the
coefficient of friction to values that are appropriate for the wind sector. The PLUS®
XL lubricated
topcoat ensures the tribological functions needed for the screw-bolt assembly, which when associated with GEOMET® 500, provides an anti-corrosion protection of at least 1,000 hours when salt spray tested according to ISO 9227 standard. Two laboratories, one French the other Spanish, have tested and validated the anti-corrosion and tribological properties. This process involved five assemblies and dis-assemblies being simulated without altering the properties. The result was a reduction of the assembly costs. Michel Almosnino provides details: “Owing to this system,
40 Fastener + Fixing Technology • Issue 5 Apr - Jun 2012 XL topcoat enables, on the one hand to ensure
the required tribologic functions for the screw/bolt assembly and on the other hand to avoid the additional stage of further lubrication which is used frequently and costly. According to specifications parts are coated with a very thin film, with a thickness of between 8µm and 10µm. The last application process step consists of a drying and curing of the coating. “Land or sea-based wind farms are booming, particularly
in the United states, China, India and in Europe - especially in Spain, Germany and United Kingdom with the offshore wind power. Thanks to its global organisation, NOF METAL COATINGS GROUP is able to accompany these changes by bringing its expertise in the thin layer anti-corrosion field.”
www.nofmetalcoatings.com
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