NEW COPPER WIRE DRAWING PLANT 



105 



by the difference in area, will give the total pounds pull required to draw 

 to the size selected. 



Capstan diameters are determined to secure minimum slip, and from the 

 die diameters selected the pull through the dies is calculated. The horse- 

 power for the main motor is determined from these die pulls and capstan 

 speeds, to which is added machine and motor losses. 



As the drawing machine is required to start up and accelerate under full 

 load, a high torque squirrel cage induction motor was selected. This type 



Z 70 



9, 50 



uj 40 



Fig. 12 — Relative acceleration curves of main and takeup motors 



of motor accelerates to full speed very rapidly, whereas the acceleration 

 of the torque motor for the takeup is very much extended and would there- 

 fore result in very high slip between the wire and capstan. It was there- 

 fore necessary to introduce some auxiliary means to assist the torque 

 motor to come up to speed. This has been effectively accomplished through 

 the introduction of a magnetic clutch for coupling together the main and 

 takeup motors during the starting period. This clutch is energized as 

 soon as the starting button is operated and before the contactors for the 

 main motor make contact. A time relay releases the magnetic clutch as 



