GB724346A - Improvements in or relating to the manufacture of mineral insulated metal sheathed electric cables - Google Patents

Abstract

724,346. Cables. O'NEILL, A. E. July 14, 1953 [May 7, 1953], No. 12759/53. Class 36. A mineral-insulated cable having a ductile metal sheath is made by compacting powdered insulant about conductors a passing through a nozzle 9, applying one or more ductile metal sheathing strips 10 in concave form to the compacted core issuing from the nozzle 9 and closing the strips 10 around the core, then annealing the cable and subjecting it to a reduction process. The conductors a pass through apertures in a spacer plate 4 and through a reciprocating vibrator or ram 5 in hopper 3. The ram 5 slides in a non-magnetic guide 6 and may be operated by one or more electromagnetic coils 7, 8. Nozzle 9 forms a continuation of guide 6 which is surrounded by insulating material which falls into the nozzle. The metal strip 10 is formed into U-shape by rolls 12 and applied around the tapered end of nozzle 9, the edges of the strip then being brought together about the core by welding rolls 13. Alternatively the sheath may be formed of two metal strips, each of semi-circular cross-section, the edges of which are welded together. A second strip formed from strip 101 may be applied over the first sheath, a thin film of a high melting- point sealing medium being applied between the sheaths. The sides of the hopper and the walls of the sheath may be vibrated by vibrators 14, 15. The hopper 3 may be closed and contain a dry gas above the insulant, the walls of the hopper being heated to dry any air occluded in the insulant. The cable core may include a hollow tube containing nitrogen or other gas under pressure.