Patent GB-1248831-A (GB)
Title: Process for making corrugated tubing and the product of the process
IPC: B29C53/30
Filed: 1969-08-28
Abstract: 1,248,831. Corrugated flexible tubing. PENNSYLVANIA FLUOROCARBON CO. Inc. 28 Aug., 1969, No. 42959/69. Heading F2P. Annular or helical corrugations, preferably of a sawtooth cross-cut configuration, Fig. 6, are produced in plastics tubing 33, the plastics having an elongation of at least 100%, between 70‹ and 80‹ F., by longitudinally compressing the tube by means of apparatus shown in Figs. 6, 12, so that the wall thickness throughout the corrugations is uniform. The maximum and minimum wall thickness as a percentage of the internal tube diameter decrease from 20 and 10% respectively for a 0À06 inch tube to 2À5 and 1% for a tube of 2 inches or larger, as illustrated in Fig. 21 (not shown), and detailed in the Specification. The internal diameter of the tube is not reduced by corrugating. The sawtooth cross-cut configuration, in which one wall 23, Fig. 6, of each corrugation is shorter than the other wall 24, results in the shorter walls becoming perpendicular to the longitudinal axis as the tube is stretched, Fig. 2, and permits the tube to be bent sharply, as short sides 23 of the corrugations on the inside of the bend move in under adjoining corrugations, while the short sides 23 at the outside make an increasing angle with the long sides 24, Fig. 3 (not shown). As a result there is very little tendency for the tube to spring back from even the sharpest bends. The plastics is preferably polyterafluoroethylene, or a copolymer of tetrafluroethylene with 5 to 35% hexafluoropropylene. Other suitable plastics are polyethylene, flexible polyvinylchloride and irradiated plastic produced from a mixture of polyethylene and polypropylene. In a preferred method of corrugation, tube 33, Fig. 6, is slid over mandrel 32, which is coated with polytetrafluoroethylene 31, lubricated with oil, and has a diameter between 0À005 and 0À03 inch less than the inside diameter of the tube. Tube 33 is anchored at its forward end by collet 34. An annular abutment 38 has a convex face 40 directed toward the rear of the tube, to define the first corrugation, and inclined between 30 and 60 degrees to the axis. The face may alternatively be concave (Fig. 7, not shown) or, less desirably, transverse to the axis (Fig. 4, not shown) so as to produce symmetrical corrugations. The rear of the tube is lightly gripped by collet 42, which is moved forwards by chains 50, Fig. 12, driven by motor 44, thus collapsing the tube into corrugations near the front collet 34, where it is heated (to about 250‹ C. for polytetrafluoroethylene tubes) by heating chamber 53. The heating chamber 53 is moved towards the rear of the pipe by reversible motor 57 so that the corrugations extend down the tube. A clip (Fig. 20, not shown) may be used to keep a portion of the tube uncorrugated. The corrugated tube is then preferably heat set by removing tube and mandrel to a heating medium, e.g. an oil bath, polytetrafluoroethylene tubes being heated to 300-400‹ F. for 10 minutes. Helical corrugations may be produced if abutment (40, Fig. 8, not shown) is mounted on a wobble pivot or ball (41) in a bearing (41<SP>1</SP>), the centre of the ball being on the axis.