CABLE DESIGN AND MANUFACTURE 199 



or capstan sheaves was cause for replacement of the sheaves and adjust- 

 ment of the machine. A photograph of the stranding area is shown in 

 Fig. 3. 



EXTRUSION OF INSULATION 



To avoid possible contamination of the polyethylene insulating com- 

 pound in the extruder-hopper loading area, a pressurized enclosure pre- 

 vented entry of air-borne dust and dirt, and the containers of poly- 

 ethylene compound were cleaned with a vacuum cleaner before being 

 brought into the hopper area. A fine screen pack placed in the extruder 

 reduced the possibility of contamination in the core. 



In passing through the extruder, the central conductor was payed-off 

 of a large reel with controlled tension, into the pay-out capstan, through 

 an induction heater, through a vacuum chamber, and thence into the 

 cross-head of the extruder. The induction unit heated the central con- 

 ductor and provided means for controlling the shrinkback of the core 

 insulation and the adhesion of the conductor to the insulation. Shrink- 

 back is a measure of the contained stresses in the insulation. 



On the output side of the extruder, the core was cooled in a long sec- 

 tionalized trough containing progressively cooler water from the input to 

 the output end. The annealing of the polyethylene in the cooling trough 

 also served to hold the shrinkback of the core to a low value. The extru- 

 sion shop is shown in Fig. 4. 



An important addition to the extrusion operation consisted of the use 

 of an improved servo system to control the extruder automatically to 

 attain constant capacitance per unit-length of coaxial. The system used 

 is described in a subsequent section. 



RUNOVER EXAMINATION 



Following extrusion, the core was subjected to continuous visual and 

 tactual examination in a rereeling operation called "runover". The pur- 

 pose of the runover operation was the detection of inclusions of foreign 

 material in the dielectric and the presence of abnormally large or small 

 core diameters. Core not meeting specification requirements was cut 

 out or repaired. 



In addition to visual inspection of the cable, examination of short 

 lengths of core was made at regular intervals with a shielded source of 

 light arranged to illuminate the interior of the dielectric material. Provi- 

 sion of this internal illumination facilitated detection of particles of 

 foreign material well beneath the surface of the core. Strip chart records 



