Abstract: Resin tubes having thick walled portions and thin walled portions are formed by providing a specially configured orifice on an extruder and varying the rate at which the extruded resin tube is pulled from the extruder. The orifice is shaped to form a thin tubular opening and a thick tubular opening communicating with one another, the thick tubular opening being adjacent and down-stream of the thin opening. When the extruded resin tube is pulled at a high speed the thin tubular opening is filled with resin that passes through but does not fill the thick tubular opening. At the slow pulling speed the resin fills at least the open-end portion of the thick tubular opening thereby forming a thick walled portion of the resin tube.

Abstract: An annular groove is formed in the periphery of thermoplastic pipe near an end thereof by combining the forces of a fluid under pressure and a rigid expandable core mold. A pipe is heated, softened and placed over a core mold having an extensible portion. The extensible portion is in the retracted state initially and presents no obstacle to the placement of the pipe on the core mold. A space is provided internally of the pipe and is sealed by parts of the core mold whereby the application of a fluid pressure pushes outwardly on the inner periphery of the pipe. At the same time or subsequently the extensible portion of the core mold is extended to provide additional pressure to and to shape the latter internal periphery of the pipe.

Abstract: Resin tubes having thick walled portions and thin walled portions are formed by providing a specially configured orifice on an extruder and varying the rate at which the extruded resin tube is pulled from the extruder. The orifice is shaped to form a thin tubular opening and a thick tubular opening communicating with one another, the thick tubular opening being adjacent and down-stream of the thin opening. When the extruded resin tube is pulled at a high speed the thin tubular opening is filled with resin that passes through but does not fill the thick tubular opening. At the slow pulling speed the resin fills at least the open-end portion of the thick tubular opening thereby forming a thick walled portion of the resin tube.