Clean metal cuts better than corroded or growth-encrusted metal. Steel covered with ordinary mill scale and one or two thin coats of paint may be cut easily. Thick scale, thick paint, barnacles and similar marine growth make cutting difficult and should be removed. An ordinary paint scrapper is useful in removing light scale and paint; however, for heavier growths, a high-pressure water jet cleaning tool may perform the cleaning process satisfactorily. If possible, it is important to clean both sides of the metal before cutting. Obstructions on the opposite side of the metal will clog the cut and prevent the cutting jet from blowing through. If inaccessible, striking the area to be cut with a heavy sledge hammer may sufficiently loosen scale on the opposite side.
2-2.9 Steel-Tubular Electrode Cutting Technique (Thick plate). When cutting steel plate that is 1/4-inch thick or greater, use the drag technique (see Figure 2-3) and proceed as follows:
a. Insert the electrode into the collet opening until it bottoms out against the washer. Tighten the collet nut. To start the cut, hold the electrode perpendicular to the surface to be cut and hold the oxygen trigger down to get a steady flow. Place the tip of the electrode against the work and call for SWITCH ON. If necessary, withdraw the electrode slightly and tap it against the work to start the arc.
Thick, gauntlet-type rubber gloves in good condition, worn over a pair of playtex-type gloves afford the best protection against electrical shock. They should be secured at the wrist to prevent slag from entering the glove. In cold water, wet-suit gloves in good condition, worn over surgical gloves are equally effective.
b. As soon as the cut is started through the full thickness of the plate, drag the electrode along the desired line of cut and keep it perpendicular to the work. Hold the electrode with the free hand as if holding a pool que, approximately Four inches from the tip for a more stable cut. The tip of the electrode should be pressed against the advancing lip of the cut. Pressure should be exerted in two directions: inward to compensate for electrode burn-off and forward to advance the cut.
Before beginning the cut, the diver should visually check the oxygen flow while holding the electrode in a horizontal position. Holding the oxygen for approximately 20 seconds allows time for enough cutting-gas pressure to build up along the full length of the hose. To ensure a clean cut, at least a 6-inch stream of oxygen should be issued from the electrode tip.
c. Low oxygen pressure, high travel speed and uncontrolled manipulation are typical causes of back-flare that result in incomplete cuts (see Figure 2-3d). In such cases, the area must be chipped and cleaned and the cut restarted.
d. When the electrode has burned down to within 3 inches of the collet nut, break the arc, release the oxygen trigger and call for SWITCH OFF. When the phone talker has confirmed SWITCH OFF, tap the electrode twice to make sure the switch is off. Loosen the collet nut 1/2-turn and blow the cutting stub from the torch by squeezing the trigger. Insert a new electrode and repeat the starting procedure.
2-2.10 Steel-Tubular Electrode Cutting Technique (Thin plate). When cutting steel plate which is 1/4-inch thick or less, use the following technique. This technique is slightly different from that used on thick plate.
a. Instead of maintaining the electrode tip in the cut and pressing against the lip of the advancing cut, the tip should barely touch the plate surface as it advances along the line of cut. (See the technique illustrated in Figure 2-4.)
b. When visibility is poor, an alternate technique can be used. Hold the electrode perpendicular to the plate until the cut is started through the full thickness. Then, angled at approximately 45o to the plate and in the direction of the cut, proceed as if cutting a thicker plate. The effective thickness of the plate is increased and normal pressure can be applied to the electrode. (See alternate technique, Figure 2-4.) -
Pushing the electrode into the hole too fast will result in a shower of spatter, which may damage the diving equipment and/or result in a blow-back.
2-2.11 Piercing Holes in Steel Plate. Holes can be easily pierced in steel plate using steel-tubular electrodes. The following technique is recommended:
a. Touch the plate lightly with the electrode at the desired point. Hold the oxygen trigger down and call for SWITCH ON.
b. Hold the electrode stationary for a moment, withdrawing it momentarily as necessary to start an arc and permit melting of the steel tube inside the covering.
c. Push the electrode slowly into the hole until the plate is pierced.
This technique has been used to pierce holes in 3-inch steel plate without difficulty (see Figure 25). A hole slightly larger than the electrode will be produced. The hole can be enlarged by working the electrode in and out in a sawing motion. A similar technique may be used with exothermic electrodes.
2-2.12 Steel-Tubular Electrode Cutting Technique (cast iron and non-ferrous metals). Cast iron and non-ferrous metals do not oxidize; therefore, underwater cutting essentially becomes a melting process. There is no chemical reaction of the oxygen and the base metal. Therefore, the only benefit realized by the oxygen is the mechanical effect of blowing the molten metal away.
Since the melting process takes place only in the immediate vicinity of the arc, the following procedure is recommended:
a. Using a sawing motion, manipulate the electrode in and out of the cut.
b. For thin plates, electrode manipulation is not necessary since the procedure is virtually the same as when cutting thin, ferrous metal.
c. Maximum current (up to 500 amperes if available and provided the safety switch is rated to carry such a load) is recommended since the cutting is dependent upon the melting action of the arc.
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