Under this head come rubber gloves, a leather or rubber suit or apron, a hood of cloth, stovepipe or wood for the head, and a pair of glasses for the eyes. Bear in mind that the operator is manipulating a current of high voltage and also an arc of great heat and dazzling light. A stovepipe hood for the head is rather unsafe because of the danger of shock. The eye-glasses had better be double, of red and green or red and blue glass, because the light is violent.

Practice

In practice the metal piece to be welded is clamped onto the metal table. The positive lead is also clamped onto the table or sometimes directly to the metal piece. The carbon electrode is pressed against the metal piece, and the switch is then closed. The operator, clad in his insulated clothing and hood, then draws the carbon pencil away from the piece about 2 to 4 inches and makes the arc. If the arc goes out or is too intense, the current is increased or diminished at the rheostat.

As with the hot-flame processes, the operator now gives his arc a circular movement, taking care to keep the pencil at least 2 and not more than 4 inches from the work. As the metal begins to melt, he works it into the weld with a stick of melt bar, as in the oxy-acetylene process (see page 97). The weld may also be reinforced with scraps of the kind of metal needed. If the metal is brass or zinc, it is best to cover it with a layer of the proper flux.

A slight variation of the Bernardos system is practised in Sweden in the welding of boiler plate. Instead of a carbon negative, a bar of soft steel is used. The bar begins to melt in about a minute and is then pressed on to the weld and the current cut off. The joint of the two plates has already melted and the bar acts as melt bar. The joint is hammered, and the arc is again sprung and more of the bar melted on.

The details of manipulating the torch and metal in this process are not different from the hot-flame processes. Different metals require different treatment in heating, fluxing, and working. Metals that melt to a liquid will have to be built up with a luting of clay or bricks.

It is claimed for the Bernardos process that the metal at the weld is not injured by the heat or the current if the operator follows directions and uses common sense. Iron welds should not be brittle or hard unless the carbon was originally high.

Samuel McCarthy1 gave the results of comparative tests of the tensile strengths of bars scarf-welded and bars electrically welded. The bars were of several different grades of English iron and steel, of cross-section 2 by 1/2 inches approximately. He claims an advantage averaging 18 1/2 per cent, for the arc-welded bars over the smith-welded bars. The arc-welded bars ran from 73.6 to 92 per cent, of the strength of the original stock.

1 "Bernardos Arc-welding," read before the Inst, of Mech. Engineers, England.

Welded. The bars were of several different grades of English iron and steel, of cross-section 2 by 1/2 inches approximately. He claims an advantage averaging 18 1/2 per cent, for the arc-welded bars over the smith-welded bars. The arc-welded bars ran from 73.6 to 92 per cent, of the strength of the original stock.

The Bernardos process at present is recommended for general repair work, such as boiler-plate repairing, broken castings, cracked parts, etc. The process is handicapped greatly by the violence of the light and heat of the arc, by the limited size of the flame, and by the danger to the operator from the high voltage. As with the hot-flame process, the heating effect is purely local, and one part of the weld may be getting cold while the other part is being welded. Even heating may be obtained by preheating over a gas flame; freedom from shrinkage strains may be had by annealing. The oxy-acetylene flame may be turned on the work from several burners at once. But so far there is but one arc with each welder. It is not likely that two or more arcs will be used together on one job; the only way to increase the size of the work to be welded is to increase the carbon pencil and augment the current. Such increase has sharp limitation.