212 BELL SYSTEM TECHNICAL JOURNAL 



It has not been possible to definitely establish any quantitative 

 relationship as to the effect of high speed drawing on the wear of dies 

 except that about the same number of million feet of wire may be ex- 

 pected from a properly lubricated die irrespective of the drawing speed. 

 Under such conditions, the high speed die naturally runs a shorter time, 

 but length of life is not the important factor; tonnage of a satisfactory 

 quality with a minimum plant and labor investment is the prime con- 

 sideration. 



Figure 22 shows a diamond before drilling, a stone drilled and lapped, 

 ready for mounting, and a die in the final mounting ready for use. 



Figure 21 gives an outline of the shape of the working surfaces of a 



wire drawing die. 



Annealing 



Hard copper wire is obtained by using the wire as it comes from the 

 wire drawing machine. This same wire may be softened by annealing, 

 or medium-hard wire can be produced by annealing hard wire at such a 

 point in the drawing operations that the final draws will give the 

 desired degree of hardness. ^° 



In a recent commercial type of annealing furnace, Fig. 23, wire may 

 be bright annealed, but it requires a drying operation in order to re- 

 move the water through which it passes in leaving the furnace. The 

 retorts of these furnaces are water-sealed and filled with steam to ex- 

 clude the outside atmosphere, which would discolor hot copper. To 

 obtain bright wire, it is passed under water into the retort to exclude 

 the air and is generally taken out and cooled under water or in an at- 

 mosphere of steam or gas, which excludes oxygen until the wire is 

 relatively cool. 



A special steam seal annealing furnace for small spools of wire was 

 developed on an experimental basis from which the wire was obtained 

 bright annealed and free from moisture. In this furnace the spools 

 were submerged in water to displace the air, raised into the charging 

 end which was under water, thence to the muffle to be heated, and then 

 along a cooling tube to the discharge opening. Air was excluded from 

 the retort and cooling chamber at the discharge end by means of a 

 steam jet. 



The success of the small furnace led to the construction of a larger 

 machine (Fig. 24) for annealing cable wire on spools. The spools are 

 placed in perforated metal baskets which are charged into the furnace 

 at a specified time interval, pushing each other through the retort and 

 along the cooling tube to the discharge end. 



'0 "Experiments in the Working and Annealing of Copper," F. Joiinson, Journal 

 Institute of Metals, Volume XXVI, No. 2, 1921. 



