ELECTRIC WELDING. The heat of an electric arc may be employed in fusing or welding metals, or the heat given out in the body of metal acting as a resistance to the passage of a heavy current, without any arc or spark, may effect that result. The arc method appears to have been first employed by De Meritens in 1881. In this instance leaden pieces designed to be united in the form of storage battery plates were arranged together as an extended positive electrode, and an arc was drawn between them and a negative carbon rod manipulated by means of an operating handle. Part of the heat energy of the arc served to melt the lead and cause union of the adjacent pieces, but much the larger proportion of the energy escaped by radiation and convec tion. The electric arc was thus akin to a gas blowpipe as commonly used in lead-burning in the construction of tanks for the chemical in dustries. Following De Meritens, heating by electric arcs has been applied to the fusing and welding of metals, notably of iron and steel, by Bernardos and Olszewski, Coffin and others. When, as in the Bemardos and Olszewski method, the carbon electrode is made positive to the work, carbon is transported through the arc and is likely to enter the metal undergoing the process, which constitutes the negative pole. This addition of carbon may render iron or steel hard and unworkable, and cause cracks to be formed during the cooling of the fused mass at the joint or filling. By the employment, in stead of carbon, of an electrode of the same metal as that of the work, Slavienoff overcame this difficulty. The gradual melting of the metal electrode furnishes metal for forming joints, or for repairing or supplementing cast ings which are defective; such as those which are incomplete or contain blowholes. More recently the work is made the positive pole and this results in a greater proportion of the energy than formerly being expended in heating the metal undergoing the operation. Inasmuch as the conditions of energy supply for sus taining the arc are but little different from those often found in the commercial operation of arc lamps from constant potential mains, arc welding may often be practised by connec tions made to such mains. A choking or steady
ing resistance is put in series with the fusing arc in a branch from direct current lines at a potential difference of 200 volts or thereabout. With work such as that to which the Bernardos and Olszewski method has been found to be applicable, the current in the arc may vary from 150 amperes up to 500 or more. The potential across the arc itself will generally be from 100 to 150 volts. With the metal elec trode used by Slavienoff the current needed will be greater and the arc potential less than the above amounts. It appears that in certain cases the current may even surpass 4,000 am peres.
While a moderate application of these arc processes for fusing and welding iron and steel has been made, the range of operations to which they are suited is somewhat limited and their success depends largely upon the skill of the workman. He must protect not only his eye sight from the glare of the large arc, but also the surface of his body, and must avoid the irri tating vapors which arise from the flame. At the same time vigorous ventilation cannot be employed, for motion of the air tends to dis turb the arc and render the work more difficult. A large proportion of the energy is radiated or carried off in the hot gases from the arc. To these energy losses must be added that due to the use of the steadying resistance for obtaining stability in the current of the arc. On the other hand the appliances needed for arc fusing or welding are simple and the source of current energy often conveniently found in existing elec tric circuits. One of its most recent uses has been in adding metal to rail surfaces where worn at the joints, particularly street railway rails in situ. A considerable extension of the use of arc welding has recently taken place, owing to improvements in materials and meth ods and to increasing demarid for its use in original construction and repair work.