. The Bell System technical journal . ven cross-section of the conductor. Thequality of the brazes in these components was controlled by a qualifica-tion technique described below in the section on core jointing. The strand was drawn through several forming dies to size the finisheddiameter of the central conductor accurately. No lubrication was usedbecause the removal of the resultant residues, which could contaminatethe polyethylene insulation, was difficult. The taper in the central con-ductor diameter due to the die wear w^as controlled by appropriate re-placement of tungsten carbide dies,
. The Bell System technical journal . ven cross-section of the conductor. Thequality of the brazes in these components was controlled by a qualifica-tion technique described below in the section on core jointing. The strand was drawn through several forming dies to size the finisheddiameter of the central conductor accurately. No lubrication was usedbecause the removal of the resultant residues, which could contaminatethe polyethylene insulation, was difficult. The taper in the central con-ductor diameter due to the die wear w^as controlled by appropriate re-placement of tungsten carbide dies, where used, or by the use of adiamond die where the rate of die wear is less than 1 or 2 micro-inchesper mile. The stranding area in both plants was enclosed and pressurized toguard against dirt and dust settling on the central conductor. A highstandard of cleanliness was maintained for parts of the machine whichtouched the conductor or its components. Undue wear of the guide faces 198 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957. c ao G ■B a 03 03 o3bO C u Sh a;> CO bb 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 inFig. 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 beingbrought into the hopper area. A fine screen pack placed in the extruderreduced the possibility of contamination in the core. In passing through the extruder, the central conductor was payed-offof a large reel with controlled tension, into the pay-out capstan, throughan induction heater, through a vacuum chamber, and thence into thecross-head of the extruder. The induction unit heated the central con-ductor and provided means for controlli
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