Demand for wind power is expected to grow rapidly over the next 20 years. However, wind turbine technology needs to evolve. Engineers are currently struggling to make the devices larger, taller, less expensive , more reliable and more efficient.
The average wind turbine contains up to 8,000 parts that must be assembled. Towers and rotors are the largest and most basic components.
Towers typically consist of large tubular structures. Plated steel sheets are rolled into rings and joined together with submerged arc welding. However, “developments in electron beam, hybrid arc and laser welding processes are being explored,” says Chris Bagley, power industry program manager at The Welding Institute (TWI). “The tower sections are typically fabricated into cans about 20 meter long and then bolted together through internal flanges.
“This is an industry that needs to build large, high-capital items in a production line manner,” explains Bagley. “In this respect, it may be compared to aerospace. However, the current players tend to have a traditional ‘project build’ approach and face a challenge in moving to become factories.”
According to Bagley, tower fabrication typically relies on mature assembly technology, but “there is great potential for advanced robotic welding to be developed.” On the other hand, blade manufacturing tends to be the most innovative and highly secretive area of the wind turbine industry.
Rotor blades are typically made from fiberglass and other composite materials. “[Manufacturers] are facing increasing component size and associated joining and mold technology issues,” says Bagley. “Blades over 70 meters [long] are now being designed.
“As well as having to join long lengths of blade [consisting of] leading and trailing edges to tight tolerances to assure aerodynamic conformance, [manufacturers] face a significant challenge in ensuring uniform resin spread when fixing the internal spars to the blade skins,” Bagley points out. “A lot of blades are made using hand lay-up. Automated solutions from aerospace or automotive, such as robotic tape layers, could be brought to bear here. Vacuum infusion techniques are starting to be used more widely.”
Traditionally, two-component epoxy adhesive has been used to bond the two halves of the blade together. “Over the past few years, manufacturers have become very interested in faster setting, less brittle adhesives,” says Brian Dorenkott, focus segment manager - alternate energy at Henkel Corp. “[We] anticipated these demands and developed two major new adhesive technologies.
“The two-component urethane family of products offers gap-filling capabilities, flexibility and cure speed adjustability,” claims Dorenkott. “The methyl methacrylate product family is very fast, reduces labor costs, and has outstanding strength and economics.”
According to Dorenkott, most wind turbine blades are assembled manually and adhesive is applied with putty knives. “Assembly is currently a very inexact process with imperfect quality control,” he explains.
As a result, some blade manufactures have begun to move toward automation. “The industry recognizes the need to automate the assembly process to achieve low-cost mass production,” says Frost & Sullivan’s Chan. “Companies like MTorres and MAG Industrial Automation Systems are currently pursuing the development of automation concepts and systems.” However, the design of the blade has to be changed to suit the process. A
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