194 



BELL SYSTEM TECHNICAL JOURNAL 



using rolling mill formulae.^ Based on the design of the mill using 

 the eighteen pass arrangement the first four passes would operate at 

 about 62, 100, 105, and 90 per cent of the safe working load of the mill. 

 These same passes calculated on the basis of the sixteen and fourteen 

 pass arrangement of the more sturdy mill at the Chicago plant operate 

 at 86, 87, 90, 85 and 96, 96, 90, 90 respectively. This indicates that a 

 further reduction may be made in the number of passes in the mill 

 provided roll adjustment is improved. 



Relation between Working and Physical Properties 



It has been often stated that the more passes (i.e. the more gradual 

 working) given the copper, the better the physical qualities of the rod. 

 Actual tests (see Table I) made on representative lots of yl in. rod fail 

 to confirm this impression. 



TABLE I 



The averages indicate that fourteen pass rod is superior in elonga- 

 tion, and better than the total average in tensile strength. 



Cleaning of Rod 



When the coils emerge from the tank through which the rod coiler 

 apron conveyor passes, they are cool enough to handle and after being 

 tied with wire, several are lifted together by a monorail crane, and 

 placed for thirty minutes in a pickling tank containing from 5 to 10 per 

 cent free sulphuric acid, in order to remove the black oxide caused by 

 oxidation of the hot copper in the air during rolling. The solution is 

 maintained at approximately 120° F., and the copper content varies 

 from 1 to 3 grams per 100 c.c. Experiments have shown a difference 

 of less than 10 per cent in pickling time between the minimum and 

 maximum acid used, the greater solubility being obtained from the 

 weak solution. Actual results obtained were checked with Sidell's 



1 " Pass Limitation in Rolling Mill Practice," Machinery, July, 1918. "The 

 Theory and Practice of Rolling Steel," Wilhelm Tafel. 



