LEAD-COVERED PAPER-IXSULATED TELEPHONE CABLE 453 



it passes to the supply ducts in the storage room. The system is so 

 constructed that there are three simultaneous cycles (Fig. 20) : one in 

 which the silica gel is used as an absorbent, the second where it is 

 reactivated, and the third where a freshly reactivated bed is cooled to 

 68° F. Automatic controls switch the air currents into their respective 

 channels at established intervals. The condition of the vital parts of 

 the system is indicated continuously on a control board where tempera- 

 tures, air volumes, and relative humidities ^ are shown. 



Lead Sheathing 



The thoroughly dried cable core passes from the storage oven 

 through a tube, designed to minimize any exposure to outside air, 

 into the press where it receives its protective cover of lead. The 



LEAD CYLINDER 



\ %\ V4 V4 V^ 



Fig. 21 — Cross section of typical die block. 



basic principle of applying lead sheath to cable is illustrated by Fig. 21 



which shows a cross-section of a typical die block. This die block 



consists of a core tube and a die, ring shaped, mounted in a hoUowed- 



out block. This arrangement provides an opening adjacent to the 



cable core which aids in definitely controlling the thickness and 



diameter of the sheath. This die block is placed underneath a large 



cylinder for receiving molten lead, and both are placed in a hydraulic 



press. 



In covering large cable, more than half of the total time is taken up 



in filling the cylinder with lead and cooling it under pressure to a 



point where it can be extruded. The tendency, therefore, has been to 



build presses with larger lead containers, and in turn of larger capacity, 



s Page 134, \'ol. 2, Industrial and Engineering Chemistry, April 15, 1930 — article 

 by A. C. Walker and E. J. Ernst, Jr. 



