PULP INSULATION FOR TELEPHONE CABLES 7 



and leave the material in shape to be turned down to the final form. 

 This is done by passing the conductors embedded in the narrow sheets 

 through individual polishers which turn the wet sheet down into a 

 uniform covering of a size determined to a large extent by the amount 

 of pulp deposited in the sheet. These polishers are simply rapidly 

 rotating heads carrying three specially shaped blades so arranged that 

 one blade deflects the traveling wire and sheet from a straight line 

 against the other two with a pressure controlled by the tension on the 

 wire. The wet cylindrical insulation is then dried to about a 9 

 per cent moisture content by a single passage through a horizontal 

 electric furnace 26 feet long the wet end of which is maintained at a 

 temperature of about 1500° F. and the dry or tempering end at some- 

 thing under 800° F. The wires are carried through the drier by a 

 rotary pulling mechanism designed to minimize the crushing or 

 flattening of the dried insulation. This device delivers the finished 

 product to the take-ups for spooling. The machine is operated at 

 about 130 feet per minute. 



Considerable amounts of water are used in the process, for in this, 

 as in all paper making processes, water acts not only as a carrier for 

 the fibres, but it forms some sort of a loose chemical or mechanical 

 combination with them in the beater which is one of the principal 

 factors in determining the final characteristics of the material. The 

 approximate fibre concentrations at the various steps of manufacture 

 are as follows: 



Beater 3.5^% 



Storage 1.3% 



Screen 0.07% 



Cylinder Vat 0.05% 



Polishers 28%; 



Completed Insulation 91% 



Finished Cable 100% 



Some Problems Involved 



In theory the whole process is remarkably simple, but from the 



practical standpoint, many intricate problems had to be solved before 



satisfactory operation was possible. In some cases it was rather 



difficult to segregate the problems for study as there were so many 



variables involved. Gradually, however, these details have been 



cleared up and today operation is quite satisfactory. A brief survey 



of some of the more important problems and their solutions may be of 



interest. 



Continuous Operation 



It is quite essential, from an economic standpoint, that the machine 

 should operate continuously. The fact that the supply spools carry 



