| 摘要 |
571,684. Electric cables. SONNENFELD, H. Oct. 26, 1943, No. 18280/44. Divided out of 570,640. [Class 36] [Also in Groups V and XXXIV] In power cables, the cores are pre-twisted and then insulated by extrusion. The cores 'may be sector-shaped to form the cross-section without fillings. The extrusion machine has a die rotated at a speed related to the lay of the core and the speed of extrusion. The core is passed through a tube 22 whilst the thermoplastic insulation is extruded by a screw 14 through a die 1 fixed in a holder 2 which is mounted on ball-bearings 5, 7 and carries a gear-wheel 12 by which it is rotated. The die is continued as a disc 6 between the extrusion head 4 and its cover 3, the thrust being taken by bearings 7 and by compressed air admitted through a bore 17 to between the disc 6 and cover 3, labyrinth passage's 8 ... 11 and packing 18 being provided. The air may be compressed by a pump 16, after which it may be electrically heated at 36 and passed through a valve 23 and tube 22 to prevent the insulation from entering and carbonizing within the tube 22 after the core length has left it. The insulation may consist of natural or synthetic rubber of or artificial resins such as vinyl or cellulose esters or polymers. The suction from pump 16 may be used by pipe 19 and passages 20 to withdraw air bubbles from the insulation as it passes through cylinder 21. Specification 570,640 is referred to. The Provisional Specification states also that the rotatable die-holder may be used for marking tubes with helical reinforcing ribs.
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