Patent GB-698511-A (GB)
Title: A process and apparatus for making helical coils of flexible thermoplastic rod
Inventor: MONCRIEFF LESLIE JOHN
IPC: B29C53/12
Filed: 1951-03-16
Abstract: 698,511. Making helical coils of thermoplastic rod. BRITISH CELANESE, Ltd. March 14, 1952 [March 16, 1951]. No. 6393/51. Class 87 (ii). A process for making helical coils of thermoplastic rod comprises winding the rod in a temporarily softened condition into a helix on a winding surface that is rotated about an axis enclosed by said surface and moving the helix parallel to said axis along and off said surface, the periphery of said surface at the winding point being greater than at any point beyond it, so that at every instant the nearmost turn of the helix is of greater perimeter than any of the preceding turns and tends to slip along said surface in a direction parallel to said axis. A mandrel 10 tapers down to a cylindrical part 12 and has an extension 13 of smaller diameter and is mounted for rotation by means not shown. A tube 17, fixed inside a hollow shaft 16, surrounds the part 12 of the mandrel and is slightly greater in internal diameter than the diameter of the part 12 plus twice the diameter of the thermoplastic rod 35. The mouth 18 of the tube is flared. The shaft 16 is rotated at the same speed and in the same direction as the mandrel and is driven by a belt pulley 20. A cam 21, fast on the shaft 16, engages, a roller 22 carried in a fixed bracket 23, a spring 25 exerting a suitable thrust on the pulley 20. The tube 17 carries a ring 29 with slots in which fingers 31 are pivoted, clockwise movement of the finger being positively limited by the slots and anti-clockwise movement resisted by springs 33. A few turns of the thermoplastic rod are wound by hand on the mandrel so that the free end is within the tube 17 and the end leading to the supply of rod leaves the taper in the region of the point 38. Hot air is blown from a pipe 37 to soften the material. When the drives of the mandrel and shaft 16 are set in operation the rod starts to form into a helix. As the reciprocating tube 17 moves towards the tapered end of the mandrel the fingers 31 pass over the coils of the helix. But on the return stroke they enter a space between the coils and prevent the coils that have entered the tube from slipping back out of it. Thus the helix is gradually cooled as it passes through the tube, assisted if desired by cold air, and is guided by the extension 13 to the place of discharge. The surface of the mandrel may be longitudinally grooved to reduce its area of contact with the rod. The fingers 31 may be replaced by star wheels rotatable in one direction only. Instead of reciprocating the tube and shaft, the tube only may be reciprocated, being splined to the shaft. The mandrel may reciprocate instead of the shaft and/or tube. The apparatus may be used in a lathe adapted for the purpose. An example is given of coiling a rod of cellulose acetate, but other cellulose derivatives may be used, also polyethylenes, polyvinyl compounds, polystyrene, acrylates, nylons, polyethylene terephthalate and poly-4-amino-1, 2, 4-triazole. Several ends of the rod can be wound side by side on the mandrel to give a multi-starthelix. Instead of being softened by heat the rod may be softened by a volatile liquid softening agent, e.g., for cellulose acetate, a mixture of ethanol, acetone and water in the proportions 43:23:34 by volume. Applications mentioned are book-binding, covering telephone instrument leads, toys and decorations. The rod is preferably but not necessarily circular in cross-section. The Provisional Specification mentions rotating the tube slightly faster than the mandrel.