An oxygen cutting process that uses an arc between the workpiece and a consumable tubular electrode, through which oxygen is directed to the workpiece.

The oxygen arc process is used in cutting, piercing, and gouging. Mild steel is cut by using the arc to raise the temperature of the material to its kindling point in the presence of oxygen. The combustion reaction that occurs is self-sustaining, liberating sufficient heat to maintain the kindling temperature on all sides of the cut. The necessary preheat at the start of cutting is provided by the electric arc. A schematic illustration of

the process is shown in Figure 0-10.

Applications

Oxygen arc cutting has been used effectively by foundries and scrap yards for cutting mild and low alloy steels, stainless steel, cast iron, and nonferrous metals in any position. The usefulness of the process varies with the thickness and composition of the material being cut. The edges of metal cut by the oxygen arc torch are somewhat uneven and usually require a light surface preparation to make them suitable for welding.

Oxygen arc cutting electrodes were developed primarily for use in underwater cutting and were later applied to cutting in air. In either application, oxygen arc electrodes can cut ferrous and nonferrous metals in any position.

Equipment

Either constant current a-c or d-c power sources of sufficient capacity can be used for oxygen arc cutting. Direct current electrode negative (DCEN) is preferred for rapid cutting. The specially designed electrode holder used for oxygen-arc cutting conveys electric current to the electrode and delivers oxygen to the cut. This is accomplished by bringing oxygen to the electrode holder and passing it through the bore of the electrode into the arc.

For cutting in air, a fully insulated electrode holder is required. When used for underwater cutting, a fully insulated holder equipped with a suitable flash-back arrester is required.

Tubular steel electrodes are available in 5 and 8 mm (3/16 and 5/16 in.) diameter sizes, 46 cm (18 in.) long, with bore diameter approximately 1.6 rnm (1/16 in.) The extruded covering is comparable to a mild steel electrode of AWS classification E601 3. Underwater electrodes are steel tubes with a waterproof coating.

Metallurgical Effects

The oxygen arc method of cutting produces metallurgical effects in the heat-affected zone comparable to those that occur in shielded metal arc welding. The power input approaches that of shielded metal arc welding, but the heat penetration is generally not as deep in AOC because of the faster speed of travel. This produces a somewhat more pronounced quench effect. Metals that do not require a postheat treatment after welding may be severed by this process without detrimental effect. Grades of austenitic stainless steels that are sensitive to corrosion attack when subjected to shielded metal arc welding will be sensitized along the cut when severed by the AOC process.

Oxygen arc cuts in cast iron and medium carbon, low-alloy steels are apt to develop cracks 011 the face of the cut. The extent and frequency of cracking depend on the composition and hardenability of the steel.

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