RENEWABLE ENERGY Faster rotor blade bonding thanks to new technology
The energy turnaround and the push to expand renewable energy generation is posing major challenges for manufacturers of wind energy plants. To ensure economic viability, efforts are focusing first on improving the availability and productivity of existing production facilities.
H
enkel says that the use of new material technologies is making an important contribution to this, especially in rotor blade production. Traditionally, blade shells and spars have been bonded using two-component epoxy resins. While
these materials reliably meet the extremely high mechanical specifications, they are rapidly reaching their limits when it comes to the automation of manufacturing processes. Henkel’s newly developed polyurethane adhesive - Macroplast
UK 1340, is a PUR adhesive that satisfies the specific mechanical requirements for use in the wind power industry and, on top of this, makes rotor blade production more efficient.
Higher capacity utilisation through faster curing Henkel highlights that one of the major benefits offered by
Macroplast UK 1340 is its accelerated cure speed. Since it is not only highly reactive but also produces less reaction heat, this two component adhesive considerably reduces both the duration and the temperature of the cure phase. Extensive tests have shown that substantial reductions can be achieved in bonding and tempering times. The lower cure temperature also has a positive impact on energy consumption in addition to reducing the risk of stress cracking due to excessive thermal loading. Heat sensitive foam inserts also remain unaffected. Macroplast UK 1340 also satisfies the high mechanical
demands for this application, as confirmed in a variety of tests. The key criterion for achieving the technology shift is described by Nicole Schlingloff, product developer at Henkel: “One absolute essential for wind energy plants is that they have to
be in technically perfect condition. Rotor blades are among the most highly stressed components one can imagine. Even the tiniest flaws can have disastrous consequences, and that can result in high costs for repairs, downtime, or even replacement of complete rotor blades. For all of those reasons, we had to make sure that Macroplast UK 1340 would entirely satisfy the market’s high demands.”
GL approved and IWES tested Macroplast UK 1340 fulfils all the key parameters specified
by Germanischer Lloyd (GL) and Henkel says it is the first PUR adhesive in the world to have obtained GL approval. GL’s requirements for the adhesive primarily relate to its tensile shear strength, resistance to aging, creep behaviour and glass transition. Further evidence of the functional capabilities and fatigue
strength of the processed adhesive was recently furnished when it successfully passed load tests performed by the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES). In a long term test lasting some four months, an ENERCON rotor blade bonded with Macroplast UK 1340 was subjected in Bremerhaven to stresses and strains that would normally occur over a period of 20 years. The bonded joints of the 40 meter long blade passed the static and dynamic tests specified in the IEC 61400-23 standard to determine the rated load and fatigue behaviour of the blade. The test criteria specified for approval of wind energy plants were met without any problems. ENERCON’s own specifications were also satisfied in this blade test.
Real time bolt measurement
An experiment on a wind farm in Texas, USA, has demonstrated new applications for Norbar’s USM-3 ultrasonic bolt meter, which provides precise measurements for the elongation (resolution to 0.0001mm) and load in threaded fasteners from 25mm to over 15m long.
T
he experiment showed how Norbar’s USM-3 ultrasonic bolt meter can provide precise real time measurements of forces affecting a bolted joint, in this case a 2m long foundation bolt on a wind turbine tower. The initial length of the bolt was recorded using the USM-3 meter and a magnetic transducer placed onto the bolt
end. After a while, it could be noted that the elongation measurement seemed to be unstable and the value was constantly drifting. This was because, as the wind increased, it was pushing the tower in the direction of the foundation
bolt, so that the joint was compressed slightly and the elongation decreased. The opposite occurred when the wind decreased. Norbar’s ultrasonic specialist Gregory Young explained: “This ability to read minute fluctuations in the bolt tension, real time,
can be of value to many companies dealing with bolted joint issues. Many sectors such as the automotive industry will also be interested, since real time changes in bolt tension are highly important in automotive engineering.” Ultrasonic measurement performed by the USM-3 works on a ‘time-of-flight’ principle, similar to sonar, with a small
transducer placed on the head or stud end of the fastener sending an ultrasonic sound wave through the length of the bolt and back again, with easy to read data displayed on an LCD screen. The USM-3 incorporates digital signal processing and graphic displays of signal analysis and waveforms, which Norbar says makes it a truly user friendly instrument. Norbar Torque Tools is a specialist in the design, development and production of torque tightening and measuring
equipment. With its UK manufacturing base in Banbury, Oxfordshire, Norbar companies are located in Australia, China, India, New Zealand, Singapore and the USA.
42 Fastener + Fixing Technology • Issue 5 Apr - Jun 2012
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