nuclear power
The cable has an external diameter of about 40 mm and is supplied in huge coils each 750-m long.
Preparing the Cable
“After passing strict acceptance tests, including testing in a vacuum chamber,” Barutti said, “the first operation consists of unwinding the cable from the transport coil, straightening it, washing it, and then sanding the surface of the outer coating
demanding for the details that have not been machined. In this process stage, we use a Leica Absolute Tracker AT901 with a Leica T-Scan laser scanner. The 22 turns of the double winding have to meet tolerances in the order of few tenths of a millimeter on the 3D form error, and the total length of the turn has tolerances of a few parts per million throughout the full length, which is also the most complex size to be measured.”
Ghosted cutaway drawing of the toroidal magnet.
with special equipment. The last stage of the forming sys- tem—the most important and complex one—makes the cable bends so as to produce the two turns of each coil, the upper and lower one, in the air without using jigs. In this stage, the material is not superconductive yet and can be handled, bent and formed at will. As the coils are going to change their shape after the subsequent baking required to achieve cable super- conductivity, strict inspection for shape and overall length is essential from this stage. “We must achieve the exact original shape that only after deformation as a result of this baking will become the intended shape. And all this with tolerances that are really
“Thanks to special procedures developed in cooperation with Hexagon Manufacturing Intelligence technicians during the equipment installation,” Caserza explained, “with the laser scanner we detect the geometry of each turn at completion of bending and before proceed- ing with the next one, we examine the full length and shape in order to make any compensations that might be necessary on the next one, and achieve the correct shape and length. We then make a full check of the shape of the winding obtained.” Once the bending stage has been completed, the double winding is ready for heat treatment. A 28- day baking cycle involving various stages and temperatures in a special atmosphere-controlled oven, will give the material superconductiv- ity characteristics. From now on, in all subsequent processing stages,
the big winding needs to be handled with extra care. The superconductive material becomes extremely fragile after crystallization and any mechanical strain on it might cause breaks and impair its performance.
Controlling Deformation “The heat treatment,” Caserza said, “has been de- signed to keep winding deformation under control, but it is still necessary to check the actual shape of every winding before going on with the next part of the process. We also have to make very precise adjustments to the mount- ings that keep the windings’ shape to prepare them for
32 — Energy Manufacturing 2016
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