| 摘要 |
A process for preparing the end of a pipe for drawing over a drawing mandrel, including the following steps: (a) inserting a preforming mandrel into an end of the pipe, the preforming mandrel having a first section having a diameter which is substantially smaller than the inside diameter of the pipe to be drawn, a third section having a diameter which is substantially the same as the inside diameter of the pipe to be drawn, and a second section between the first section and the third section, the second section tapering from the diameter of the third section to the diameter of the first section; (b) rolling the pipe with a set of non-driven rolls while the rolls revolve around the pipe and move axially from the first section of the mandrel to the second section of the mandrel and radially inward to from a constriction in the pipe; (c) rolling the pipe with the rolls while the rolls revolve around the pipe and move axially over the second section of the mandrel toward the third section of the preforming mandrel and radially outward so that the pipe has a wall thickness which is continuously reduced as the diameter of the mandrel increases toward the third section; and (d) rolling the pipe with the rolls while the rolls revolve around the pipe and move axially over the third section of the preforming mandrel so that the pipe has a wall thickness which remains constant over the third section to the end of the pipe. The preforming mandrel is then removed so that a drawing mandrel can be inserted and the pipe can be drawn through a drawing mill. Apparatus for practicing the invention is also disclosed.
|
