DIAMOND DIES FOR DRAWING OF COPPER WIRE 35 



mo\-al from the metal mounting separated into two sections. The majority 

 of the dies failed in this manner. 



Examination of worn oversize dies invariably shows that the erosion and 

 the effect of the forces incident to wire drawing are concentrated at the 

 pressure ring where the entering wire contacts the reduction area. Here, 

 the abrasive action of the wire and die contacting surfaces, and the disrupt- 

 ing stresses are most evident. An analysis of the forces present in a wire 

 drawing die indicates that secondary stresses normal to the drawing axis 

 are set up in this sector. In dies drilled normal to the HI plane these 

 stresses, coupled with the thermal, impact and fatigue forces converging in 

 this area, would tend to shear the diamond stone parallel to this plane. 

 Overdrawing and poor operating conditions would of course accentuate this 

 effect and bring it about prematurely. 



The previously mentioned dies drilled normal to 110 and 100 planes did 

 not crack in the manner noted above. These failed due to chif>ping and 

 spalling. Cracks, when present, were small and inclined to the drawing axis. 

 Dies drilled normal to 110 plane have cleavage planes parallel to the die 

 hole axis. In one case a stone drilled in this manner cracked along this 

 plane. Data to date indicate that better die life was obtained from these 

 dies than from those drilled normal to the 111 plane. 



The noted studies indicate that the orientation of the drawing hole is of 

 practical importance with regard to stone breakage, the limiting factor of 

 die life. A better understanding of its relation to die performance should 

 achieve appreciable economies. No conclusions have been made as yet 

 with regard to the exact desired orientation of the drawing axis. In Fig. 5 

 is depicted a unit cube of a diamond structure. Here is shown the possible 

 directions of drilling and the location of the cleavage plane. Figure 6 

 shows the diamond crystal faces and planes. 



Whether or not the aforementioned die breakage characteristics are local 

 to our drawing operations and die sizes is not known. We invite comments 

 from other wire manufacturers whose equipment and practices vary sig- 

 nificantly from those used at the Kearny Wire Mill. 



Acknowledgment 



The author wishes to acknowledge and thank Mr. F. E. Haworth, of the 

 Bell Laboratories, for his x-ray determinations and Mr. W. W. Broughton, 

 of the Quartz Crystal Development Group of this Company, for his many 

 suggestions with reference to the crystallographic studies. 



References 



1. "Design and Operation of a New Copper Wire Drawing Plant," H. Blount and J. E. 

 Wiltrakis, Wire and Wire Products, October 1940. Bell Telephone Sj-stem Technical 

 PubUcations Monograph P-1273. 



