Using energy-saving welding machines and emission-reduced welding processes makes the construction of renewable-energy plants both environment-friendly and economical. Wind power is an important market; with a one-third share, it is already the number-one renewable energy resource in terms of power generation. In Germany alone, there are almost 25,000 wind turbines.
Wind turbines might not look particularly big from a distance, but their size is striking close up, as anyone who has seen a rotor blade being transported on the motorway can confirm (a Siemens B75 blade for a 6MW offshore turbine is 75m long).
It goes without saying that the turbine’s brake needs to be proportionally large in size, as it is one of the most important components and needs to comply with very specific requirements of automated operation under a variety of conditions.
The brake, which can be up to 4m in diameter, protects the wind turbine from turning too fast; it also act as both a holding brake and an emergency-stop brake.
One of the biggest manufacturers of these components is the Danish company Valmont SM, which is part of the American company Valmont Industries.
Based in Roedekro, southern Denmark, it has a 650-strong workforce producing parts for a variety of power plants, including wind plants, for which it supplies constructional steelwork for the towers; Valmont also manufactures the rotary housing, complete with integrated brake discs.
In the past year, about 600,000 man-hours — half the company’s time — were spent on welding tasks and processing 100,000 tonnes of steel.
At Valmont, the focus in virtually all areas is on welding. Around 50 welders are involved in the construction of rotor housings, with six of them working exclusively on fabricating brake discs.
Frede Holdt Jensen, welding engineer and project manager at Valmont, says: “We manufacture the brake discs by cutting four ring segments out of a large steel plate in order to keep wastage to a minimum. The quarter arcs are then mounted on a clamping table, so that they can then be connected together to form one circular piece.”
Carl Petersen — Valmont’s technical welding specialist and welding supervisor for offshore projects and rotor housings — says that for the past two years, the company has been using the ForceArc welding process from the German company EWM AG (
www.ewm-group.com) to weld the discs. “I read about this welding process in a trade journal almost three years ago. After that, everything happened very quickly.
The welding tests carried out on the brake discs were fully satisfactory, so we ordered four Taurus 451 Synergic S welding machines from EWM — quickly followed by another two.”
Cutting costs
The power sources are used to join the four pieces to make one brake disc, which involves welding S355 structural steel in thicknesses of 50 and 60mm. To do this, Valmont uses a T466MM1H5 flux-cored wire electrode and an M21 shielding-gas mixture.
Previously, MIG/MAG welding with flux cored wire only allowed the use of a 60deg included angle, but the welding experts at Valmont were able to reduce this angle to 34deg with the EWM process. Welding procedure tests show that it would be possible to work with an angle of 30deg, but the current solution is both satisfactory and very profitable.
Mr Jensen says: “This allows us to make a cost saving of 30% overall. With ForceArc, we have been able to shorten the weld preparation time and the entire production time for the welding of a brake disc by up to 30%, which equates to a considerable saving in a high-wage country like Denmark.
"In addition to reducing power consumption, we have cut weld material consumption by as much as 50%, as fewer passes are now required due to the smaller included angle.”
The energy-reduced, heat-minimised joining process also results in less distortion. Previously, welders had to turn the workpieces three times; they now only need to do it twice, which means a greater reduction in down-time.
Mr Petersen adds: “Another significant benefit is the reduction in errors. In fact, errors in the joining process are no longer an issue for us — and quality has improved considerably.”
This view is also shared by the six welders involved in disc manufacture. Although initially a little sceptical about changing their familiar practices, they were soon won over by ForceArc — in particular, the significantly less time spent on welding, the reduction in the number of weld passes needed, and the absence of errors.
While Valmont continues to rely on submerged arc welding for seams more than 1m long and when joining thicknesses of 20mm and more (plus partly on the TIG joining process for finishing), it is now planning to switch to the ForceArc MIG/MAG process for the manufacture of other components for wind-energy plants.
Mr Jensen says: “The prospect of achieving savings similar to those we’ve seen when welding the brake discs is obviously very attractive. Purchasing the EWM welding machines was certainly worthwhile, and they paid for themselves very quickly through their efficiency.
"Overall, ForceArc has helped reduce working time to the extent that welding activities now account for only a small part of the whole manufacturing process; this is a very important factor for further improving competitiveness.”