DEVELOPMENTS IN COMMUNICATION MATERIALS 



247 



different instruments and it was necessary to allow rather wide limits 

 on each temper resulting in considerable overlapping of the temper 

 tolerances. While tensile strength is usually considered the reference 

 test for cold worked metal, it is necessary to have a test which can be 

 used for more rapid inspection. As a result of our study we were able 



100 



40,000 60,000 aO,000 100,000 120,000 



TENSILE STRENGTH fPSl) 



Fig. 11 — Relation between tensile strength and Rockwell hardness — sheet brass. 



to develop means for maintaining the Rockwell hardness tester to an 

 accuracy within 2 points compared with 8 or 10 points on the sclero- 

 scope. Fig. 11 shows the relation between tensile strength and Rock- 

 well hardness for a rolling series made up by the American Brass Com- 

 pany under carefully controlled manufacturing conditions. This 

 rolling series covered all ranges of hardness and thickness of sheet 

 metal generally used in telephone apparatus. The tension test is used 



