GB1293906A - Improvements in or relating to sealing rings - Google Patents

Abstract

1293906 Piston rings; shaft seals WELLWORTHY Ltd 5 Nov 1969 [7 Nov 1968] 52842/68 Headings F2B and F2T [Also in Division C3] Sealing rings are made from a length of synthetic plastics material which has a cross-section generally corresponding to that of the rings, is wound around a mandrel a plurality of times to form a helix and then cut to form separate rings, the plastics material being treated to retain its ring shape. In the embodiment shown in Fig. 1 for making a split piston-ring, granulated or powdered, filled or unfilled, P.T.F.E. 1 is compressed and sintered in a press 2 prior to extrusion by a ram 3, the P.T.F.E. being heated by heaters 4. The P.T.F.E. is continuously extruded through a die 5 to form a bar 6 which is coiled whilst still hot around a mandrel 7. After cooling, the coiled P.T.F.E. bar is cut by a cutter 8 so that separate rings are formed by each coil 6a, 6b &c. The external surface of the coiled bar may be machined to the finished size before or after cutting. Instead of coiling the bar 6 around the mandrel 7 whilst still hot it may be allowed to cool and, before or after reheating, coiled around the mandrel and then heat treated, e.g. by induction heating the mandrel by a fluidized heating medium, so that the rings retain their form when cut and removed from the mandrel. To form a circumferentially continuous ring, a split-ring 11, produced as previously described, is inserted in an outer metal ring 12 and urged outwardly by an inner split-metal ring 13. The P.T.F.E. ring 11 is then heated to a temperature between 200‹ and 390‹ C. to cause it to plasticize and expand so that its free ends 15 abut and weld together. The ring is then cooled rapidly and removed from the rings 12 and 13. In a further embodiment, a bar of extruded P.T.F.E. is wound when cold to an undersize diameter and then cut, the undersize diameter being selected so that the ring after cutting tends to pause during opening at the desired finished ring diameter. In another embodiment, the rings may be formed from strips cut from a sheet of extruded P.T.F.E. The P.T.F.E. bar may incorporate a core of springy material. The invention may be applied to spiral or helical seals and may be used for sealing between relatively reciprocable and/or rotatable members.