230 



THE APPLICATION OF ELECTRIC WELDING 



It will be observed that D. C. and A. C. results are quite evenly distributed above and 

 below the resultant curve, as is also the case with results with bare and covered electrodes. 

 But the beneficial effects of employing heavy current are distinctly evident with respect to all 

 the four mechanical characteristics on which the tests were made. Considering, for a minute, 

 the chart showing the relation between the tensile strength and welding current, we see that if 

 the weld is made with some 90 amperes, the most probable value for the tensile strength is 

 only some 43,000 pounds per square inch, whereas if the weld is made with 180 amperes, the 

 most probable value of the tensile strength of the resulting weld will be nearly 50 per cent 

 greater, namely, well above 60,000 poundsi per square inch. Similar ratios of importance hold 

 with respect to the bending test, torsion test, and the per cent elongation at fracture. 



The following schedule shows the distribution of the total of twenty welds in different 

 classes : 



Bare (12) 

 Covered (8) 



^ Direct current (9) plotted as white circles. 



I Alternating current (3) plotted as black circles. 



j Direct current (2) plotted as white .squares. 



I Alternating current (6) plotted as black squares. 



The twenty observations were divided into three groups: "A" for eight welds made with 

 ISO to 175 amperes; "B" for six welds made with 105 to 145 amperes; "C" for six welds 

 made with 83 to 94 amperes. 



As already stated, there was no attempt on the part of the committee to suggest to the 

 proprietors or users of systems or electrodes, the current to be used, or any other conditions, 

 and it is fair to conclude that in each case the conditions employed were believed by the makers 

 of the weld, or by the operators, to be the most suitable conditions. 



The average values obtained for Groups "A," "B," and "C" are shown in the following 

 table : — 



I conclude that the reason for the wide use of 100 amperes and less, for a weld of these 

 proportions, is that there are more operators who can make superficially good-looking welds 

 with such a current than there are operators who can manage currents of twice their value. 



It is very important to note that, with sufficient skill on the part of the operator, not only 

 will the high-current weld be made more quickly, but it will also have much better mechanical 

 characteristics. In so far as these various conclusions are correct, they emphasize the import- 

 ance of concentrating on the development of automatic welding machinery, since it is reason- 

 able to assume that, with such machinery, higher speeds can be obtained, which, as we have 

 seen from these results, are associated with higher currents which in their turn are associated 

 with better welds. 



