| 摘要 |
1370679 Flexible plastics pipes F KIRCHNER and H KIRCHNER [trading as FRANKISCHE ISOLIERROHR-u METALLWAREN-WERKE Gebr KIRCHNER] 22 Dec 1971 [29 Jan 1971] 59661/71 Heading F2P A 'plastics pipe 1 has a corrugated wall in which the axial lengths 8 of cylindrical portions 2 are less than their diameter 5 and outwardly bulging corrugations 3 form slots 4 in the pipe interior such that the external width 9 does not exceed the length 8 or three times the average wall thickness of the portions 2 and the internal slot width at the level of the outside diameter of the portions 2 does not exceed the average wall thickness of the portions 2. As shown, the slots 4 are wider towards the bottom than in the region of the outside diameter of the portion 2 and may have flat base portions 6 or this portion may be rounded (Figs. 2, 3, not shown). The external height 10 of the corrugations is preferably from one to three times the width 9, three times the wall thickness of the portions 2 and three-quarters the length 8. The length 8 is preferably three to six times the wall thickness of the portion 2 and twice the width 9 of the corrugations 3 and the radius of the fillet 11 between the corrugations and cylindrical portions 2 is less than half the wall thickness of the portion 2 and preferably from 0À1 to 0À3 times this thickness. The pipe may be made by extruding a plain pipe, e.g. of PVC or polyethylene, and the corrugations 3 are produced in moving mould segments with which the pipe is forced to engage by the application of an excess air pressure in the pipe. In other arrangements an external jacket (25) (Fig. 2, not shown) is attached to the crests (22) of the corrugations and the circumferential corrugations may be replaced by a single helical corrugation (31) (Fig. 3, not shown). |
