DEVELOPMENTS IN MANUFACTURE OF COPPER WIRE 213 



Fig. 23 — Water seal annealing furnace 



Inspection of Raw Material and Finished Product 



Wire bar made from electrolytic refined copper is used as a material 

 in the manufacture of wire. This material is practically free from silver 

 and other elements which ordinarily exist in the ore, and which have a 

 detrimental effect on the electrical or physical properties of the finished 

 product. A small percentage of silver " seriously affects the annealing 

 qualities of the wire. Traces of other impurities have a very detri- 

 mental effect on the wire drawing properties. During the refining 

 process, the molten bath is oxidized in order to carry off the foreign 

 material in the form of slag, and it is very important that the oxygen 

 content be later reduced to a very small point if bars of proper set are 

 desired. Fig. 25 shows three photomicrographs of wire bar containing 

 varying amounts of cuprous oxide. ^^ Ordinarily the surface condition 

 on top of the bar is a good index of the oxygen content. If the bar is 

 level set or slightly convex on top, it is usually a satisfactory material. 

 If it is low set or concave, it usually contains a large amount of copper 



" "Effects of Silver on the Recrystall ization Temperature of Copper," Caesar and 

 Gerner, A. S. M. E., Volume 38, 1916. 



1- "Microscopic Structure of Copper," H. P. Pulsifer, Mining and Metallurgy, 

 January, 1926. 



