The advanced technology in wind turbines depends a lot on conventional manufacturing techniques, such as welding. One welding-machine manufacturer, AMET Inc, Rexburg, Idaho, (ametinc.com) recently called on a linear motion and assembly technology company, Bosch Rexroth, to help build a new generation of custom welding machines for the wind industry. Such welding equipment is used to build turbine towers up to 90-m high. Typically, a machine rolls a metal plate into a cylinder called a can that measures about 9-ft long by 8 to 15-ft diameter. Another machine then welds along longitudinal seams to complete the can and then circumferentially to join cans.
An Amet welding machine makes a circumferential weld on a can that will eventually become part of a wind turbine tower. A CKK linear slide is hidden behind the green arm.
The welder is usually suspended from a guide rail for outside welding. In each case, most of the machine is stationary while the weld head moves small distances on two and three axes, both along and across the seam. A linear control actuator at the end of a horizontal arm determines the motion of the weld head.
AMET’s goal is to build a dependable welder that makes accurate longitudinal and circumferential submerged arc welds. There were several challenges. One was to assure smooth and precise (within 0.01 in.) control of the weld head, and avoid improper welds that need rework. Another was to provide precise control in a dirty environment. “This form of welding generates a tremendous amount of particulates, especially flux dust, that cause problems with components such as linear actuators,” says AMET Engineering Manager Craig Dees. “We must be sure linear-motion components stand up to this harsh environment, especially inside the can.” The company also wanted strong linear-motion components (dynamic loads are in excess of 20,000 Newton) with light weight in a compact size. Another challenge was to support smooth weld-head acceleration, up to 3 m/s2, and travel speeds of 1.5 m/min.
The company turned to a Rexroth distributor, Northwest Motion Inc. (www.nwmotion.com), which recommended the CKK line of linear actuators. The units precision-ground, hardened steel guide rails were specified for the guide rail that carries the suspended weld head for outside welding.
The seal on the CKK slide units protect the module from pitting, a problem in other actuators caused by welding debris.
AMET now specs the CKK 20-145 linear actuators for their welding systems, in 490 and 590-mm lengths. “The sealed rolling strip on these slides is a big advantage,” says Dees. “Many other linear designs use less durable fabric or rubberized bellows to keep the rolling strip clean.”
The compact slide makes machine assembly smoother and easier than with previous designs. Also, the CKK modules provide a guideway with a dynamic load capacity up to 61,000 N, and it’s highly stable. The module is said to resist impact and stress as well as sparks and contaminants, further increasing uptime.
Dees says another feature that cuts machine-build time is that modules are complete and prepackaged with built-in dual ball rails and a ball-screw drive. “The modules are precision-machined at the factory so we don’t need to do any extra work ourselves,” says Dees. What’s more, he says, the slides cut two weeks off previous 14 week build schedules because they arrive when needed. WPE
Filed Under: News, Turbines
