750 BELL SYSTEM TECHNICAL JOURNAL 



brass, nickel silver and phosphor bronze are used in the manufacture 

 of telephone apparatus as structural members, springs, and bearings. 

 Because of space Hmitations, the parts are necessarily small; many 

 are formed into irregular shapes; spring parts must maintain accurate 

 adjustments and have long fatigue life; certain other parts must 

 resist wear. All requirements are steadily becoming more exacting 

 because of the increasing complexity of telephone systems and it, 

 therefore, became necessary to insure more closely the uniformity 

 of the material used in the apparatus. 



The methods of test developed to check the uniformity of material 

 are of equal concern to both consumer and supplier. Both are 

 interested in a test rapid enough for use in inspection work and also 

 so simple that specially trained men are not necessary for the actual 

 testing. Due to the large amount of material that must be inspected 

 it is necessary that any tests used require little time to apply and be 

 adaptable to modern production methods. Furthermore, close agree- 

 ment in test results is necessary. Since no test method was available 

 fulfilling these requirements, it became necessary either to develop new 

 methods of test or to modify existing methods. In addition, limits 

 were desired that would represent the best quality of material obtain- 

 able consistent with commercial mill practices. 



As a result of this need a cooperative program of tests was laid 

 out which would lead to the drafting of requirements on thin-sheet 

 metals. Those cooperating in this program were associated in the 

 production and use of such material, and each member had already 

 done preliminary work which evidenced his interest in the problem. 

 The group was limited to one producer and one consumer in order 

 that the work might be expedited, and the results that have been 

 obtained justify the plan. 



The results of the investigation are given herein for such value as 

 they may have to the industry. It is hoped that this work may act 

 as a stimulus to others interested in this problem so that ultimately 

 definite standards may result, including the refinements demanded 

 by modern industry. 



The results of the study of the methods of test suitable for high 

 and clock brass sheet of the order of 0.020 in. and thicker are presented 

 and it is shown that the Rockwell tester gives the most reliable 

 information of the several hardness testing machines available at the 

 present time. Methods of operation of the Rockwell hardness tester 

 were worked out by the cooperating laboratories and a method of 

 carrying on tension tests was developed. The limitations in the use 

 of the Rockwell hardness tester for sheet metal are pointed out and 



