| 摘要 |
1,164,370. Conduits. BLACK, SIVALLS & BRYSON Inc. 2 Nov., 1967 [16 Nov., 1966], No. 49957/67. Heading F2P. A method of forming a conduit for pneumatically conveying polyethylene or other plastics material includes the steps of providing a tube, supporting the side walls of the tube on a mandrel 20 provided with a recess 21 and repeatedly pressing a die 16 on the exterior surface of the sidewall opposite the recess for forming inwardly projecting protuberances 12 at appropriate positions. As shown, the concave impressions 12 are formed on a helix by rotating and advancing the tube a predetermined amount, the wedge-actuated expansion mandrel 20 being locked prior to and released after the forming of each impression. Alternatively, the protuberances may be part helical in form. |
