NEW COPPER WIRE DRAWING PLANT 99 



be drawn and the speed at which it could be wound onto a reel. The 

 maximum drawing speed was considered to be that speed where the stress 

 set up by centrifugal force would equal the safe stress for copper of 25,000 

 lbs. per sq. in. A maximum drawing speed of 27,400 ft. per minute was 

 determined by the following calculations: 

 Let W = Weight of drawn copper wire per cu. in. in lbs. = .3212 

 (A.I.E.E.) 

 V = Speed of wire in feet per second. 

 G = Acceleration due to gravity. 



1. Stress in Wire due to Centrifugal Forces = S 



^ 12 X W X F- ^ 12 X .3212 X V' ^ . ^ ^2 

 G 32.2 



2. Maximum Wire Speed Considering Only Stress Due to Centrifugal 



Force. The speed at which 5" would produce a stress of 25,000 lbs. 

 per sq. in. 



^ = 4/7^ = 456 f.p.s. or 27400 f.p.m. 



L197 



With the possibility of a range of speed of 1 to 1.8, the stress set up in the 

 reel rim at a wire speed of 27,400 f.p.m. would equal 62,000 lbs. per square 

 inch when the wire is being taken up on the core of the reel, and the rim 

 running 80% faster. Since this speed and resulting stress are above the 

 safe limit for low carbon steel, a speed of 12,000 f.p.m. was selected which 

 provided a factor of safety of approximately five to one. The stresses set 

 up in the wire and reel rims for the various speeds are shown on diagram, 

 Fig. 5. 



The horsepower requirement of the torque motor for the takeup is made 

 up of three components: 



1. Tension in Wire 



2. Bearing Friction for Takeup 



3. Reel Windage. 



Wire should be taken up on the reel under sufhcient tension to offset that 

 created by centrifugal force. The tension in the wire resulting from cen- 

 trifugal force is shown on diagram. Fig. 6, and is determined by taking the 

 stress in copper wire at 12,000 ft. per minute. Fig. 5, and multiplying this 

 by the area of each size of wire. The tension in the wire changes for each 

 size of wire and remains practically constant throughout the entire reel; 

 therefore, the horsepower required to take up wire on the reel remains 

 constant from the core to the outside of the reels, the speed of the reel 

 slowing down with the build-up of wire on the reel. The lower curves on 



