Cast iron, stainless steel and non-ferrous metals do not oxidize; therefore, underwater cutting becomes a melting process. The exothermic process develops tip-temperatures in excess of 10,000 oF, which is sufficient to melt these materials with ease. The following technique is recommended:
a. Keep the tip firmly buried in the puddle. Using a sawing motion, manipulate the electrode in and out of the cut.
b. To cut thick, non-ferrous metals, create a puddle and keep the electrode tip slightly below the surface of the molten metal. Every few seconds, push the cutting electrode deeper into the molten pool to wash out and blow the molten metal through. Increase the oxygen pressure at the electrode tip to 110 psi for metals over 3 inches in thickness (see Table 2-2).
2-3.6.2 Exothermic Cutting Technique (Concrete, Rock and other Non-Conductive Materials). When cutting non-conductive materials, a striker plate attached to the ground cable is necessary to strike an arc. The striker plate is placed next to the material to be cut. Call for SWITCH ON, squeeze the trigger slightly, drag the electrode across the striker plate and the electrode will ignite. Once the electrode is ignited, maintain the oxygen flow. Call for SWITCH OFF. If electrode ignition is lost, reignite it from the striker plate by repeating the procedure. Each subsequent electrode must be ignited from the striker plate in the same manner. The following procedure is recommended:
a. For best results, use the 3/8-inch electrode. Ignite the electrode with a striker plate.
b. Press the tip into the material to create a molten pool. As the material melts, periodically move the electrode in and out to allow the oxygen to blow the molten material away.
2-3.6.3 Exothermic Hole Piercing. Exothermic electrodes can be used to pierce holes in plate using the same technique as described for steel-tubular electrode.
2-3.7 Trouble Shooting. Oxy-arc, especially exothermic cutting relies on an unobstructed oxygen flow to be most effective. With inadequate oxygen flow, the rod will burn but not produce the desired cutting effect. Since the actual cutting result is derived from the volume of oxygen reaching the target, any restriction in oxygen flow will decrease efficiency.
2-3.7.1 Symptoms. The following are indications of an oxygen-delivery problem:
a. Oxygen jet at electrode tip less than 6 inches.
b. Electrode burns down in approximately 60 seconds of continuous use and cuts less than 12 inches of 1/2-inch plate.
2-3.7.2 Probable causes. The following are possible causes to an oxygen flow problem:
a. Regulator incapable of delivering 70 cfm.
b. Torch incapable of delivering sufficient flow. Older torches; those designed for 5/16-inch electrodes will not flow sufficient oxygen volume.
c. Torch obstruction, such as dirt in oxygen passage, a damaged flashback arrestor, clogged or burnt monel screen or a damaged oxygen flow valve.
d. Oxygen hose too small, using 1/4- or 5/16-inch hose or a clogged or obstructed 3/8-inch hose.
In all the above cases the regulator pressure will appear normal. There simply is not enough oxygen volume to allow the electrode to cut properly.
2-3.7.3 Locating and solving the problem. The following steps will likely isolate the problem:
a. Shut off electrical power to the torch.
b. Remove electrode from torch and blow through electrode to check passage.
c. Disconnect the oxygen supply line at the torch handle and flow oxygen through the hose. If the flow rate is weak the problem is likely a faulty regulator or a clogged hose. Check each independently and clean, repair or replace as necessary. If the flow rate is strong at the hose end then:
d. Check the torch collet washer to ensure it is in proper position, that it is the correct one for the electrode being used and that it is not obstructing the oxygen passage.
Washers for 5/16-inch electrodes and smaller will significantly obstruct the oxygen flow.
e. Remove flashback arrestor and monel screen from torch and inspect. Replace as nec-essar y. Blow oxygen through the valve and torch to ensure a clear passage.
This should complete the checkout of a low flow problem. Reassemble and recheck to ensure that the problem has been solved.
2-3.8 Post-Dive Maintenance. After each use, rinse the torch in fresh water and dry it. Disassemble and inspect the flashback arrestor and monel screen for corrosion damage due to electrolysis or clogging. Frequent clogging or screen burn-out indicates either insufficient oxygen pressure or burning the electrode shorter than the minimum 3-inch remainder. Replace any damaged parts (see Figure 2-6a, b or c as applicable). All equipment should be thoroughly dry before storing. Secure hose ends with caps or tape to keep out debris. Store all equipment in an oil-free environment. Electrodes which have been exposed to salt water will rust. They should be rinsed with fresh water, blown dry and stored separately to prevent damage to other rods.
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