Method and apparatus for forming a corrugated fluoropolymer tube

An apparatus for forming a corrugated fluoropolymer tube from a fluoropolymer tube, said apparatus comprising:

• a mandrel having a longitudinal axis for supporting a tube comprising extruded fluoropolymer without corrugations or convolutions;
• and
• a device for exerting an external force on an outer surface of the tube on the mandrel, the external force exceeding an elastic limit of the fluoropolymer to form corrugations having adjacent peaks and roots by displacing material from the roots at a temperature below the melting temperature of the fluoropolymer, while maintaining a smooth inner surface of the tube;
• wherein
• the mandrel has a first cylindrical portion and a flaring portion that extends to a second cylindrical portion, the second cylindrical portion having an outer diameter which is larger than an outer diameter of the first cylindrical portion to expand the tube;
• and
• the device for exerting external force comprises a plurality of rotatably mounted thread rollers adjacent to and circumferentially distributed around the flaring portion and/or second cylindrical portion of the mandrel, the thread rollers having rotational axes that are substantially parallel to the longitudinal axis along the mandrel and a flight in a transverse orientation relative to the longitudinal axis along the mandrel and disposed at a pitch angle thereon;
• and
• arranged such that the outer surface of the tube is expanded by the flaring portion and is forced into the flights of the thread rollers to displace fluoropolymer of the tube in a cold forming process to form corrugations having adjacent peaks and roots.