330 BELL SYSTEM TECHNICAL JOURNAL 



It was found that the drying time using vacuum ovens was reduced 

 to about one third as compared with hot air ovens, and improved 

 quahty and large cost savings resulted. 



Before the war the average demand for telephone cable in this 

 country amounted to about two hundred million conductor feet per 

 week. During and after the war this demand steadily increased until 

 now it amounts to about six hundred million conductor feet per week 

 or about thirty billion feet per year, requiring annually forty thousand 

 tons of copper wire, seventy-five thousand tons of lead, and six thousand 

 tons of insulating paper. 



Cable-making Machinery 



In planning for the manufacture of this quantity of cable, the design 

 of all machinery was reviewed and changes made wherever possible to 

 improve quality or increase output. 



A great deal of work was done in improvement of insulating ma- 

 chines, and a ten-head vertical type insulator was developed to replace 

 the older five-head horizontal type for non-quadded light gauge wire. 

 In designing the new machine many improvements were incorporated. 

 The old machines had been built to handle relatively strong paper and 

 heavy wires, and studies indicated that to insulate finer wires success- 

 fully with lighter paper, also to run at high speeds without stretching 

 the wire, and to apply a uniform wrapping without backlapping or 

 folding over of the paper and with low breakage per pad the insulators 

 must be rigid, the tension on the wires should be uniform and both 

 supply and take-up mechanisms should operate smoothly. 



The relative floor space per head for the ten-head machine including 

 operator's space is about 60 per cent of that taken by the five-head 

 machine but based on production the relative space per unit of produc- 

 tion is about 50 per cent. The new machine runs at a head speed of 

 about 3,000 R. P.M., carries a 12-in. pad of paper, and in general is a 

 very substantial machine. 



The insulating head, the vital part of the insulating machine, has 

 undergone many changes to accommodate the thinner, narrower in- 

 sulating papers. One of the most important of these has been to 

 improve the tension mechanism which now consists of a very small 

 multiple disc clutch actuated by a system of levers so that a very light 

 but very uniform tension is applied at all times. This is not only 

 making possible the use of smaller paper ribbon but may permit of 

 changes in the composition of the paper with resultant cost savings. 

 This head is shown in Fig. 8. 



Another desirable feature in a paper insulating machine is a bare 



