PRECISION LOCAL EXPANSION SHAPING PROCESS AND APPARATUS FORMETAL TUBES OF SUBSTANTIAL LENGTH

摘要

Apparatus for local expansion shaping in a precisely located region of the running part of a cylindrical tubular wall of substantial length which comprises a dismantable tubular die which includes an expansion chamber and, on respective sides of said chamber, two cylindrical bearing surfaces whose inside diameter is substantially equal to the outside diameter of the tube to be expanded, taking into account the clearance required to permit the tube to be introduced into the die, the bearing surfaces having different coefficients of friction with respect to the surface of the tube to be expanded. A mandrel which is slightly smaller in diameter than the tube which is to be expansion-shaped is housed within the tube and penetrates into the part thereof which is disposed within the die; it comprises an internal conduit which is substantially parallel to the axis and which may be connected to an external pressure fluid source. By virtue of a radial aperture, the conduit communicates with the annular space between the mandrel and the tube. That space is defined by two regions in which a seal is made as between the mandrel and the tube, on respective sides of the expansion chamber, at the location of the cylindrical bearing surfaces of the die. The sealing effect is in most cases attained by means of sealing joints such as metal or elastomer seals. And a process for expansion shaping of at least one localized region in a running portion of the wall of a tube of substantial length.