Patent GB-669779-A (GB)
Title: Improvements in or relating to electric cables or other insulated electric conductors
Inventor: CLOTHIER GEORGE DONALD
IPC: H01B7/16
Filed: 1949-08-05
Abstract: 669,779. Cable-making machines. PYROTENAX, Ltd. July 24, 1950 [Aug. 5, 1949], No. 20408/49. Class 36. An apparatus for the manufacture of an electric cable of the type in which a metal sheath is separated from one or more conducting cores by pulverulent insulating material comprises means for feeding powdered insulating material to the interior of a sheath tube, a ram within the sheath tube, means for imparting relative longitudinal movement to the ram and the sheath tube so that the powder is subjected to a compressive thrust, and a frictional abutment which offers resistance to the compressive thrust and which will yield when the thrust exceeds a predetermined value to permit the sheath and the ram to move together under the thrust. The apparatus may be arranged vertically and is supported above a well B in the ground which is deep enough to take the length of the sheath tube C. A fixed shroud tube D is suspended from a bracket A<SP>1</SP> in alignment with well B, and is long enough to house the sheath C within it. Bracket A<SP>1</SP> also carries bars A<SP>2</SP> for supporting a pneumatically operated cylinder E which is given a vertical reciprocating motion. A tubular ram F extending downwardly within the sheath C is connected to the base of cylinder E. The insulating powder is fed to the sheath C through the interior of the ram F, which is provided at its upper end with a feed opening. The powder may be fed from a hopper G by means of a plunger G<SP>1</SP> which is reciprocated in synchronism with the ram drive. The lower end of the tubular ram F (Fig. 4), is provided with a detachable head H having ports H<SP>1</SP> therein through which the powder can escape into sheath C. The lower end of the ram is closed by a plate having apertures for the passage of conducting cores C<SP>1</SP>, and a disc H<SP>3</SP> is clamped below this plate. The disc H<SP>3</SP> is provided with apertures closely fitting the cores C<SP>1</SP>, and is made of material which will not adhere to the cores. The lower end of the shroud D, which has slits D<SP>1</SP> to give it slight flexibility, is provided with a liner D<SP>2</SP> of friction material which fits closely around the sheath C. The pressure exerted by this liner on tube C is controlled by an internally studded ring J, one of the studs J2 being adjustably mounted so that the friction on the sheath C can be varied. The sheath C is initially lowered into well B and then raised so that the upper end slips over the end of the ram within the liner D<SP>2</SP>, the friction grip having been loosened, until the lower end of the sheath is just below the lower end of the ram. The cores C<SP>1</SP> are then inserted within the ram, and their lower ends secured to an anchoring plug C<SP>3</SP> which is clamped to the lower end of sheath C. Packing C<SP>5</SP> may be provided against the inside of plug C<SP>3</SP>. The friction grip is tighened and the apparatus operated. The ram reciprocates idly while a small quantity of powder is being fed into the tube C during the upward movements of the ram. The powder builds up on packing C<SP>6</SP> until it comes in contact with the ram face at the bottom of a downward stroke, when the friction grip is loosened slightly. During the downward stroke of the ram the compressive thrust of the ram on the powder increases as the powder becomes more tightly packed, until it exceeds the resistance of the friction grip, which will then allow the sheath C and cores C<SP>1</SP> to slip downwardly with the ram until the end of the downward stroke, the sheath and cores thus being driven downwards into well B in a step by step movement. When the sheath tube is nearly filled with compacted powder the machine is stopped and the friction grip loosened to allow the sheath tube to be pulled clear of the ram. The upper end of the sheath is sealed and the workpiece thus formed is removed from well B in readiness for a drawing down operation.