Resistant coating systems for offshore rotor blades

• Mineral fillers significantly improve the resistance of rotor blade coatings
  to rain erosion
• Specific surface treatment of the high-performance fillers further increases the resistance
• Cost savings due to longer maintenance intervals

Extreme conditions for wind turbines

In the offshore sector, rotor blades for wind turbines should be able to withstand 20 years of operation without impairment. Extreme environmental influences such as snow, hail, rain, salty seawater, heat and UV radiation put a strain on the huge blades. Wind speeds of up to 500 km/h affect the blade tips. This area is therefore a particular weakness of the rotor blade, as the coating at this point is particularly badly eroded by rain erosion, so that the aerodynamics on the blade surface change and performance can decrease.

Rain damages rotors

The impact speed and the size of the raindrops play a major role in rain erosion. HPF The Mineral Engineers, a division of the Quarzwerke Group, carried out rain erosion tests based on real conditions in a miniature simulator. Glass fiber reinforced plastic (GRP) test specimens were rotated around their own axis in the centrifuge at a horizontal rotational speed of 10,000 rpm. For a 22 cm long rod, this corresponds to a speed of the rod ends of 414 km/h. At the same time a vertical load from above with a continuous 3 mm wide water jet was applied to simulate rain. The aim of the tests was to find out whether the use of special high-performance mineral fillers can contribute to the durability of rotor blade coatings. The evaluation of the damage patterns that occurred on the differently coated test rods after different rotation times in the simulation chamber is impressive: These clearly show how the resistance of the coating to rain erosion depends on the filler used.

Increased service life of coating systems for rotor blades

The talc and barium sulfate fillers contained in the starting formulation served as reference fillers in the pore filler. They were successfully replaced in the tests by the silica flours SIKRON^® and SILBOND^® as well as by TREMIN^® wollastonite and MICROSPAR^® feldspar. All the alternatives tested significantly improved the resistance of the test rods to impacting rain drops compared with the reference fillers. MICROSPAR^® feldspar achieved the best resistance. It was shown that a specific surface treatment of the functional fillers further increased the resistance.

Conclusion: Using various high-performance fillers, it has been possible to develop coatings that are resistant to rain erosion.