Capable of two-millimeter accuracy, Danish machining tool expert CNC Onsite is launching its Goliath solution in the fall of 2022. Goliath is designed to mill flanges of tower bases, monopiles and transition pieces of up to 10 meters in diameter.
The increasing dimensions of wind turbines operating in harsher offshore environments create engineering challenges for large flange connections that join wind turbine towers to their foundations. To prevent bolts loosening – an issue often associated with significant repair costs and downtime – the connecting flanges must be flat to within millimeters.
“We constantly develop our manufacturing to ensure we can deliver the right products with the right tolerances that the industry requests,” says Klaus Munck Ramussen, senior vice president at Bladt Industries. “With larger flanges, integrating Goliath into our manufacturing process will allow us to continue to do just that.”
A critical mechanical joint within the wind turbine structure, large flanges are technically complex to mount reliably, requiring pairs of matching surfaces fixed in place with bolts. After the manufacturer has welded the flange into the structure – a process that often warps the flange – the surfaces have traditionally been corrected by hand using heat treatment to produce similar skewness. Goliath, however, achieves fine tolerances as part of the production process post welding by milling, grinding and grooving the flanges to create faces with the required structural fit.
“We are proud to support the development of the industry and, by securing the tolerances, we contribute to securing the integrity of these large structures and thereby the production of green power for many years,” Ramussen adds.
“Obtaining a global flatness of a couple of millimeters on a four- to five-meter diameter flange can be challenging enough, but obtaining the same result on today’s eight-plus meter flanges is simply not possible with previous methods,” explains Søren Kellenberger, sales director at CNC Onsite. “Once it is up and running in the autumn, we would not be surprised if we can obtain even better tolerances.”
“Because incorrect bolt tension is so problematic, the industry has long aspired to maintenance-free bolted connections that require two criteria: sufficiently flat flanges and correctly tightened bolts,” adds Kellenberger. “Today, reliable bolt-tightening methods are available to manufacturers. If the flanges are skewed, however, the bolts can still fatigue, even break, potentially leading to a complete collapse of the turbine.”
Designed to work quickly without compromising the high-precision work, the tool carries out some steps simultaneously to save time. In addition to Goliath, CNC Onsite offers a range of in-house flange-facing tools that cover diameters from 1.8 to 10 meters.