The Metallurgy of Fillet Wiped Soldered Joints* 



By E. E. SCHUMACHER, G. M. BOUTON, G. S. PHIPPS 



THE seriousness of the present tin scarcity has stimulated large con- 

 sumers of this vital metal to develop drastic conservation measures in 

 order to extend the available supplies to cover the emergency period. 

 By devising new soldering methods and alloys the Bell System has contrib- 

 uted a substantial share in the tin conservation efifort. Fortunately, the 

 changes, as far as can now be determined, have not introduced weakness 

 into the soldered joints. Some of the new procedures now used were already 

 in the process of development at the onset of the emergency, while others 

 were devised under its stress. In some instances, the newly developed 

 solders were found to be more ditBcult to use than the alloys previously 

 available, and would not have been introduced under normal conditions. 

 One major change made that previously had been under consideration will 

 result in large tin savings. Unless service difiliculties are encountered, this 

 modification gives promise to remain after the emergency has passed. The 

 change involves a reduction in the amount of solder placed on a wiped joint 

 between the cable sheath and the sleeve. Instead of the customary full 

 size wiped joint a wipe of fillet proportions is formed. Through this change, 

 a solder saving of over 60% per joint can be realized. 



Plumbers and cable splicers have for many years joined lead pipes and 

 cable sheath by a soldering process called "wiping." The name is an apt 

 description of the operation. In wiping a joint the sections to be united 

 are heated by pouring molten solder over their surfaces and manipulating 

 the resulting semi-liquid mass by wiping with cloth pads to a well rounded 

 symmetrical form such as is shown in Fig. 1. The operation requires con- 

 siderable skill on the part of the splicer and close control of the solder com- 

 position. At first consideration, the problem of tightness in such joints 

 seems simple but experience shows that even under the best conditions the 

 fissures frequently found in the solder occasionally link to form a path that 

 allows leakage to occur. In the case of telephone cables not maintained 

 under gas pressure, such leaks permit the entrance of water to wet the paper 

 covered conductors, thereby impairing the insulation value and causing 

 service interruptions. By going to an extreme and wiping ofif all the solder 

 in excess of a fillet, it has been found that many causes of porosity are elim- 

 inated. Figures 2 and 3 show cross sections of joints wiped the old and new 



* Reprinted from Metals Technology, A.I.M.E., 1943. 



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