STRUCTURAL COMPONENT DEVELOPMENT OF 3-LAYER CYLINDERS FOR SUPERCONDUCTING GENERATORS .1. SELECTION OF LAYER-BONDING METHOD AND DEVELOPMENT OF LONG LARGE-GAUGE 3-LAYER CYLINDRICAL STRUCTURE

The warm damper, a component located outermost in a rotor of the super conducting generator, is intended to shirt off magnetic fields of the armature and bear large bending stresses due to electromagnetic force. So it is required to have both high conductivity and sufficient stren gth against bending stresses. Meeting these requirements is a promisin g three-layer cylindrical structure composed of a highly conductive cy linder sandwiched between cylindrical high-strength nonmagnetic stiffe ners, so that only middle cylinder bear high conductivity and outer an d inner ones bear most of the bending stresses. Candidate materials fo r the middle is Cu-Cr, and for the outer and inner is A286, a iron-bas e superalloy. To realize this three-layer cylindrical structure, the f irst step is to select a method of bonding the three layers and the se cond step is to research and develop large structures. Using test ring s (300 mm in O.D. x 500 mm in axial length) made to a reduced scale, l ayer bonding tests were carried out in the present study to investigat e three bonding methods: explosion bonding, brazing, and diffusion bon ding. The two methods other than brazing were selected because they in volved few defects and provided high bonding strength. When manufactur ing long large-gauge warm dampers, deformations due to bonding must be uniform and bonding strength must be thermally stable so as to join t hem axially by three-layer welding. The two methods were compared for these requirements and finally diffusion bonding was chosen. As the la st step, diffusion bonding rests were carried out with a mock-up warm damper model, which was the largest diffusion-bonded cylinders that ev er made. The size of the model was 885 mm in O.D. and 2800 mm in axial length, and the layer bonding strength was evaluated, proving that su fficient layer bonding strength could be obtained together with unifor m deformations.