| 摘要 |
<heading lvl="0">Abstract of Disclosure</heading> A metal ring having a greatest circumferential length is held in the shape of a substantially true circle, and other metal rings are arrayed in the order of increasing circumferential length toward the metal ring of the greatest circumferential length. At least three holder rods are lowered into the metal rings to hold the metal rings in substantially coaxial alignment with each other. Presser rods are pressed from outside of the metal rings toward the center of the metal rings, thereby deforming the metal rings into a shape including curved portions projecting radially and having a reduced diameter. The deformed metal rings are delivered successively in the array from terminal ends of the presser rods into the metal ring of the greatest circumferential length. The deformed metal rings that are released off the presser rods restore their original shape within the metal ring of the greatest circumferential length, and are laminated to the metal ring of the greatest circumferential length.
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