| 摘要 |
A method and apparatus for expanding and shaping the end portion of a section of thermoplastic pipe to form a so-called "bell" thereon with a raised annular rib defining a sealing groove. The end portion to be belled is differentially heated to provide an intermediate zone of high temperature and plasticity for the rib, between two zones of lower plasticity for a lip and a barrel, the lip zone preferably being of higher plasticity than the barrel zone, and is forced onto a mandrel with radially expandable internal die sections and closable external die sections for shaping the rib. When the pipe is on the mandrel, the bell is thickened by axial compression, and then die-shaped so that the wall thickness increases progressively with the diameter of the rib. Two alternative differential heating methods are disclosed, one heating the different zones in steps, and one using heating chambers of different intensities in a one-step process.
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