Amount Of Current Used

Welding operations are of various kinds and take different amounts of current, depending upon the nature of the material worked upon, the size and shape of the piece, and the sort of operation to be performed. For example, thin steel sheets require less current than thick ones; cutting requires a larger amount of current than welding, etc. As a general rule it may be said that metallic welding operations usually require from 50 to 150 amperes, although thin sheets may be welded with as little as 15 amperes and extra heavy ones may take 185 or 190 amperes; graphite arc welding, on the other hand, averages from 350 to 500 amperes, running from 100 amperes on small articles up to 600 amperes on heavy work. Cutting with the electric arc requires from 300 amperes on small sections up to 1000 amperes or more, the average job taking from 400 to 600 amperes. The nature of the equipment supplying the energy will affect the amount of current required to some extent, those with the best control systems being the most economical.

Plate Welding

The rate at which welding can be done depends upon the article to be welded, its size and shape, material, nature of weld, etc., Table II indicates the speed of welding seams in sheet steel.

Table II. Data On Steel Plate Welding

Thickness

Diam. Electrode

AmPeRES

Seam Welded

28 to 20 gage

18 B. W. G.

10 to 25

30 ft. per hour

18 gage to 1/8.

1/16" diam.

20 to 40

25 ft. per hour

1/8" to 3/16"

3/32" diam.

30 to 60

20 ft. per hour

3/16" to "

1/8" diam.

50 to 100

15 ft. per hour

" to 3/8"

5/12" diam.

75 to 150

10 ft. per hour

Over 3/8"

5/32" diam.

150 to 180

Variable

The figures given in the last column are only approximate, as they may easily be exceeded by an expert operator, but they give a fair average. These apply to seams made by butting the edges of the plates together and welding along in the space between them. The edges of the plates should be beveled sufficiently to allow the filling material to penetrate the full thickness of the plates, Fig. 75, or else a satisfactory weld will not result. Thicker plates than those given may also be welded and the time will vary as the square of the thickness. This is based upon one-fourth of an inch as the standard because that is about the thickest plate which may be satisfactorily welded by going along the seam but once. For thicker plates it is necessary to go along the seam several times in order to fill the slot properly and the area of the slot increases approximately as the square of the thickness when a V-shaped groove is to be filled. When an X-shaped slot, or two V slots, can be formed by beveling the plates on both sides, then the time required to make the weld is cut in two, and the rate of welding varies about in the same ratio as the thickness of the plates. The metallic electrode is used almost exclusively for steel plate and sheet welding, although the graphite electrode is sometimes used for heavy plates, when it is possible to work with the plates laid in a horizontal position, thus preventing the molten steel from running off.

Fig. 75. Fractured Locomotive Hide Frame Cut Out with Graphice Electrode and Welded with Metallic Electrode.

Courtesy of C &C Electrc and Manufacturing Company.

Castings

When castings of iron or steel are to be welded, it is necessary to prepare a large enough space to work in; otherwise it will be impossible to join the pieces throughout their thickness. This is due to the fact that the filling material is not so liquid as that used with brazing and consequently will not flow in a small crack, but must be allowed to run easily into the space. With steel castings, and for some classes of small holes in large iron castings, the metallic electrode may be used but, for most cast-iron pieces and very large steel pieces, it is necessary to use the graphite arc and a melt bar for the best results. For cast-iron welding it is desirable to preheat all but the smallest and simplest pieces before welding in order that the high-shrinkage factor of the metal will not cause cracks when the weld is cooling. It is also good to reheat after welding and allow the piece to cool slowly in order to insure a weld soft enough to machine. A good welding flux is also an advantage when making cast-iron welds in order to help raise the slag and improve the quality of the weld. Iron with about 25 per cent of silicon should be used for cast-iron welding, and steel with from 25 per cent to 40 per cent excess of carbon, manganese, vanadium, or other desired content should be used when welding steel castings containing the elements mentioned.

Copper And Aluminum

Copper and aluminum sheets, bars, and castings may be welded with the electric arc by using the graphite electrode and puddling in the filling. This operation is similar to welding cast iron and can be done only with the work laid in a horizontal position to prevent running. Owing to the necessity for using the graphite electrode instead of a piece of wire, it is evident that thin sheets cannot be successfully welded by this process. But sheets over one eighth of an inch thick have been welded, both of aluminum and copper, and castings as thin as one-fourth of an inch also. It is necessary to build a simple mold of clay around the spot to be welded in order to hold the molten metal, but it is a very simple process and requires but the smallest amount of current which will melt the metal. Large amounts of current tend to burn the material and, if zinc is present (as in brass), it will volatilize or bum out and leave a porous and useless weld. The same thing applies to bronze alloys containing manganese, phosphorous, etc., but in a lesser degree. In other words, when welding alloys of any kind, it is necessary to use that current which is suited to the most volatile element in the mixture. The others will get heat enough to flow sufficiently for all practical purposes in most cases and experience will soon show any operator the best methods of handling any of the alloys.