PULP INSULATION FOR TELEPHONE CABLES 9 



Wire Cleaning 



The supply wire comes to the machine on spools. It is spooled on 



the wire drawing machine and annealed on the spool. The surface of 



this wire, annealed with the drawing compound on it, seems to act 



somewhat as a repellant to wet pulp and causes a ragged, broken 



insulation. This is probably due to a surface tension effect. This 



action caused considerable trouble in the early stages of the work as 



the blame was placed on polishers, pulp, felts, or anything but the wire 



surface. Finally it became apparent that the surface condition of the 



wire was a large factor and the trouble was eliminated by passing all 



the bare wires through an A.C. electrolytic cleaner between the supply 



stand and the wet machine. 



Tensions 



Fine gauge copper wire is soft and easily stretched, pulp insulation 

 in the wet form possesses very little strength, and in the dry form its 

 elongation is much lower than spirally wrapped ribbon insulation; 

 hence it is necessary at every step in the process to maintain minimum 

 tensions in order that the wire may not be stretched and the insulation 

 opened. Devices have been developed that are quite efficient in 

 holding tensions within the safe range. 



Pick- Up 

 In the early operating stages the pick-up from the mold was at times 

 ragged and uneven and the sheet formation not all that could be de- 

 sired. It was found that these conditions could be materially improved 

 by the addition of a very small amount of soap to the pulp suspension 

 immediately before it reaches the machine. 



Polishing 

 In connection with the operation of polishing the sheet down to a 

 circular insulation it has been found that a water content of approxi- 

 mately 72 per cent is preferable to a dryer or wetter sheet as it seems to 

 felt down and form a more homogeneous insulation. The polisher 

 itself has required a considerable amount of development work to 

 insure a continuous uniform product and avoid stripping when a lump 



or break in the sheet occurs. 



Drying 



Several methods of drying pulp insulation were given a thorough 

 trial but a completely satisfactory drier did not prove a simple thing 

 to find. Finally, however, it was discovered that very rapid drying 

 caused less shrinkage than slower drying, and so resulted in a less 

 dense insulation. As a low density insulation is very desirable 



