BLADE INSPECTION & REPAIR
FEATURE SPONSOR
MINIMISING OPEX WITH BLADE REPAIR STRATEGIES
DIVERSE REPAIR NEEDS
The repair of wind blades present a special set of issues due to the varied types of repairs that may be needed, the wide range of materials available and the physical limitations that complicate repairs. For some repair scenarios the drill & fill technique offers the best balance of composite repair and minimal impact to composite integrity.
Used in filling pre-existing voids or inter-layer de-bonds that have occurred in relatively small areas, drill & fill involves drilling small holes (as small as 3mm) through the composite skin and injecting a specialised two-component adhesive that fills the void and binds the composite layers together.
LIMITATIONS
There are limitations to the usefulness of drill & fill: it is not used as a major structural repair, nor will it address engineering design issues. Drill & fill does however allow for a versatile up-tower repair to a common class of composite
problems before they could potentially cause greater issues.
Not just any adhesive will work for a drill & fill operation. An ideal drill & fill adhesive needs to have a reliable cure mechanism independent of the presence of moisture and under anaerobic conditions that exist. Ideally the adhesive will be thixotropic to allow injection through the small holes used and flow freely through the repair area. In addition, as drill & fill does not allow for cleaning of the surfaces to be bonded the adhesive needs to be fully functional without surface preparation.
A good drill & fill adhesive should be both hydrophobic and immiscible to allow it to displace any liquid water (not ice!) that may have collected in the void.
UNDERSTANDING TEMPERATURE EFFECTS
Since repairs are made up-tower, it is also important to understand the effect
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of ambient temperature on both the cure profile of the repair adhesive and the substrates being bonded. In general lower temperatures will slow the curing process, affect the time to complete repair and affect the flow rate of the adhesive during application making it harder to inject into the repair. Higher temperatures during use will speed the curing process and allow the adhesive to be injected with less pressure.
PROPER USE
In summary the proper use of drill & fill repairs on composite blades can be a useful maintenance tool in keeping the turbine operational with minimal downtime. As with all composite repairs, work closely with your adhesive supplier to understand the features and limitations of their materials.
ITW WindGroup
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