Abstract: Annular articles are produced by cold extruding a tubular ductile cast iron piece through a female die to desirably change the shape of at least an axial portion of the piece. The invention is based on the discovery that the nodular carbon content of ductile cast iron, amounting to, e.g., 10-12% by volume, represents voids of no structural strength in the metal and aids in working the metal in the cold, without damage, to that extent required for extrusion. Application of an extrusion load adequate to bring the metal to the yield point results in all of the metal in the die exhibiting plastic flow. Since the metal is in an annular configuration of decreasing diameter during extrusion, it is subjected to large hoop compression forces which cause the carbon modules to flatten and be arranged in planes which, in the case of an article of circular transverse cross section, are substantially radial relative to the extrusion axis. The iron grains are similarly reshaped and oriented.

Abstract: A method of producing continuous lengths of coilable corrugated wave guide of rectangular cross-section which comprises forming a smooth-wall metal tube with a uniform wall thickness along the entire length and around the entire periphery, and transversely corrugating the walls of the tube along crest and root lines that form a substantially constant perimeter length around any cross-section of the corrugated tube taken perpendicular to the axis of the tube at any point along the length of the tube. In one embodiment, the corrugations of intersecting walls are offset at their intersection so that the crests of the corrugations of each wall meet the roots of the corrugations of the adjacent wall at each corner, with zigzag crests along the corners providing rigidity.