208 THE APPLICATION OF ELECTRIC WELDING 



erator without affecting other operators whose welding circuits may be connected to 

 the same generator. 



Figure 2 illustrates the "Naval" type one-arc D. C. portable motor generator 

 set manufactured by the Wilson Welder & Metals Company. This machine has a 

 capacity of 150 amperes at 35 volts, and with the control panel weighs about 1,900 

 pounds. 



2. Stationary transformer sets operating A. C. only, as illustrated in Plate 137. 

 This is a one-arc set manufactured by the Electric Arc Cutting & Welding Com- 

 pany, of Newark, N. J., and, as will be observed, is compact and portable, weighing 

 about 230 pounds, and easily carried by two men. This machine has a capacity of 4 

 kilowatts, is designed to maintain a constant wattage, and can be used with prac- 

 tically any A. C. main supply. 



3. Resistance control. This is the simplest of the three types and consists gen- 

 erally of a simple cast iron resistance grid which reduces the voltage from the main 

 to that required at the arc, the difference being wasted. 



Where the main supply is over no volts, however, it is necessary to employ a 

 motor generator set or rotary converter, or in the case of A. C. current a static 

 transformer, as the waste would be prohibitive. Plate 138 illustrates a complete 

 outfit as supplied by the Quasi Arc Weltrode Company, the weight being about 250 

 pounds. The current for each welder can be taken anywhere from the main with a 

 common earth for all arcs. 



It will be seen, therefore, that there is a great divergence in type, portability and, 

 needless to say, in cost of apparatus advocated by the various manufacturers of 

 arc welding outfits and, since they all claim to make a satisfactory weld, it would 

 appear that the question of selection devolves into one of economy of first cost, 

 power efficiency, and portability. In this' connection it is important to bear in mind 

 that, while the simple resistance method is the least efficient electrically, its overall 

 efficiency is increased, due to the current saving when the arc is broken, and in prac- 

 tice this probably represents about 50 per cent of the total time. 



The cost of wiring the shipway or shop is approximately the same with all 

 systems. 



The average apparatus will work at about 6 to 8 kilowatts per welder when 

 welding, but if low voltage is provided at the mains, there are certain outfits which 

 are said to reduce the consumption to as low as 3^ kilowatts or even less. 



SPEED AND COST. 



Unfortunately there are as yet very little reliable data of a general nature in 

 regard to the speed and cost of welding on straight-line work in the field. Again, 

 there are so many varying factors which enter into the question that any figures 

 can only be considered with due regard to the particular conditions under which 

 they were obtained. 



The following figures have been computed from some data obtained in England 

 by Capt. James Caldwell, R. E., on work done in the field during the construction 

 of an all-welded barge recently built at Richborough. 



