1108 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



of grooved rolls. There are a hundred of these rolls in each plating line 

 and all but a very few of them are equipped with contact brushes to 

 supply cathode potential to the wires in the cells. Because of bearing, 

 roll seal, and brush friction, these rolls offer considerable resistance to 

 turning; this frictional resistance is subject to rather wide variations 

 under service conditions. To limit and control the rate of wear on the 

 roll grooves, and to prevent a build-up of excessive wire tensions in the 

 plating lines, all rolls are positively driven at constant speeds. The rolls 

 are grouped on eight separate drive units, each powered by its own 

 motor, so that each carries a definite portion of the total roll load. The 

 motors are geared in and speed regulated by resistances in the motor 

 control circuits to drive all the contact rolls a little faster than wire 

 speed, each successive group of rolls being also driven slightly faster 

 than the preceding one. This roll overdrive, as a result of wire-to-roll 

 friction, produces a closely controllable pull on each individual wire since 

 the only service factor affecting roll pull is the total wire tension (the 

 consequent wire-to-roll pressure) prevailing in any given part of the 

 plating line. The roll pull on the wire increases wire tensions toward the 

 entry end of the plating line so that the point of highest wire tension is 

 at the supply capstan recess, but the total increase is moderate because 

 most of the roll pull is absorbed in overcoming wire drag through the 

 cells. 



Wire tensions on the approach side of the magnetic supply and capstan 

 are held low in the interest of safety, efficiency and economy. Those on 

 the recess side of the capstan are higher, which means that the capstan is 

 actually pulled by the wire. So that the motor on the capstan does more 

 than just a braking job, it is made to drive the first group of contact 

 rolls, all those in the preparation leg. In this way the supply capstan 

 motor is loaded about the same as other motors in line so that it operates 

 at a comparable point on its characteristic curve, and performs in sub- 

 stantially the same way as the other motors. It is important that this 

 motor be positively loaded so that it ''motors" instead of ''generates" 

 because this motor drives a tachometer generator which controls the 

 entire drive. 



Most of the contact rolls are in the acid leg of the plating line. They 

 are hardest to drive because of their close spacing and the large number 

 of brushes they carry. To safely limit drive chain tensions and produce 

 the desired roll overdrive gradients the acid leg rolls are grouped in six 

 drive units each with its individual motor. These are matched motors 

 with similar load characteristics and they are geared in at comparable 



