206 THE APPLICATION OF ELECTRIC WELDING 



For heavy plates it is advisable to vee half-way through from both sides if prac- 

 ticable. 



The current varies to some extent with the thickness of plate and type of elec- 

 trode, bare electrodes, requiring a higher amperage than covered. 



5. The kind of current, whether alternating or direct, has occasioned consider- 

 able controversy, and while a direct current of a given open circuit voltage will per- 

 mit of a slightly greater length of arc, the advocates of the alternating current claim 

 that, since proper fusion depends upon the maintenance of a short arc, alternating 

 current is preferable as the arc itself will break if lengthened too much. 



As, however, efificient welds can be made by either, the question is more one of 

 economy, ease of operation and convenience in the supply of current. This will be 

 briefly referred to when describing the types of apparatus. 



6. The amperage should be adjusted to suit the size and type of electrode and 

 will be found to increase slightly with the thickness of material being welded ; if too 

 great for the size of electrode used the fusion will not be uniform and steady, the 

 electrode itself tending to "spatter,'' while if the amperage is too small, a proper 

 fusion temperature will not be reached. 



The voltage increases with the length of arc and, in order to prevent this length 

 becoming greater than is desirable for efficient welding, a number of machines and 

 controls have been designed which automatically break the current if the arc is 

 drawn out beyond the desired length. The range of length of arc usually adopted is 

 from 1/8 inch to 3/16 inch and the voltage varies from 15 to 25 with bare elec- 

 trodes and from 30 to 40 with some types of covered electrodes. 



7. The skill of the operator or human element is still the most vital factor, and it 

 is probably because of this that arc welding is known as an art rather than a science. 



The density of current, and therefore the heat density of the arc, decreases as 

 the length of the arc increases ; a short arc, in general, results in a high tempera- 

 ture and virtual vaporization of the metal, while a long arc is apt to lead to the 

 deposition of large drops or "beads" of electrode accompanied by oxidation. Con- 

 sequently a varying length of arc naturally results in a lack of uniformity in the 

 character of material in the weld. 



As, however, scientific investigation determines the effect of each of the above- 

 mentioned variables, it will be possible to predetermine and specify with more exact- 

 ness the ideal conditions under which a successful weld is assured, assuming that the 

 arc is held at constant length. Until such time we must remain largely dependent 

 upon the skill of the operator, not only in maintaining the constant length of arc, 

 but also in determining a most desirable current adjustment for the work in hand. 



It may be interesting at this point to mention that automatic, self-feeding weld- 

 ing machines have already been designed and are now being experimented with. 

 These machines will not only eliminate the factor of varying length of arc but will 

 result in a considerable increase in speed of operation. 



An illustration of the type of work done by a stationary automatic welder man- 

 ufactured by the Automatic Arc Welding Company of Detroit, Michigan, is shown 



