208 



BELL SYSTEM TECHNICAL JOURNAL 



was reduced to No. 24, two gauges, in one draw. The soft copper per- 

 mitted a double reduction at the first die, but the elongation dropped 

 during the operation to less than 1 per cent; the second reduction on 

 this test was from No. 24 to No. 26 gauge and the pull required for this 

 pass practically coincides with the breaking strength of the wire. Wire 

 drawing under such conditions is impractical because the annealing 

 operation is much more expensive than drawing hard wire from No. 22 

 to No. 24 in two passes. 



20 Lbs. 



30^ 



25% 



15 Lbs. 



10 Lbs. 

 15 



5 Lbs. 



5< 



O LBS.O?^ 



22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Die Size 

 1 2 3 4 5 6 7 8 9 to n 12 13 14 15 (6 (7 18 RtouciioN 



Fig. 18 



Figure 18 illustrates the results obtained when drawing annealed 

 wire with A.W.G. reductions. The large margin of safety between 

 the pull required and the breaking strength of the material again dis- 

 appears after two reductions. Fig. 19 '' illustrates practical drawing 



' Slight irregularities in the curves are clue to variations from the mean in the 

 diameters of the dies used during the test. 



