The photo shows the placement of the bearings and gears inside the nacelle of the wind turbine. Photo: Mogens Hvid
WhiteWind continues as part of the research in the strategic research
centre REWIND that ended June 2017. “What we discovered and
demonstrated in REWIND,” says Marcel Somers, “was that when
we introduced compressive residual stresses in the surface, we
were actually able to avoid cracks as a consequence of rolling
contact fatigue.” An important focus of WhiteWind is understanding
and optimizing the surface treatments to bring about controlled
compressive residual stress distributions in the bearings.
“We are using a different process now than in REWIND, because we are
using stainless steel for the bearings,” Thomas L. Christiansen tells.
“In industry, a specific stainless steel quality called Cronidur does not
show these failures when applied on a small scale. For this reason,
they have an interest in a large scale version for wind turbines. Instead
of a material that is difficult to apply to large scale, we have chosen
stainless steel, a material we have investigated for several years. By
developing a new surface treatment, we will design durable bearings.”
The process will be carried out in collaboration with the partners Vestas
and SKF. “This idea was born in our research environment several years
ago, and our spin-out company Expanite will take it to the market. They
are actually the project leader of WhiteWind,” Marcel Somers relates.
The problem with the bearings is not just happening in wind turbines.
He recently visited a helicopter factory where they experience the
same issues with the rotor: “The bearings showed the same problems
with white etching cracks as the wind turbines, so this is really a
generic problem. Finding a solution will eventually affect several
industries,” concludes Marcel Somers.
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The photos show typical failure and damage of bearings which can be
induced by so-called white etching. White etching cracks start below the
surface and eventually leads to severe damage. The specific occurrence
of the damage is difficult to predict, and the cracks may cause a complete
breakdown of the wind turbine.
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