Underwater shielded metal-arc cutting is a simple process. It employs a stick-type electrode but can be accomplished with almost any waterproofed, mild steel electrode. Shielded metal arc has the following advantages over oxygen-arc cutting processes:
a. It can cut corrosion and oxidation resistant steels and non-ferrous metals of all thicknesses.
b. It can be used when no oxygen is available.
2-5.1 Principles of Operation. Shielded metal-arc cutting is a process in which the metal is cut by the intense heat of the arc. The heat melts a localized area of metal, forming a small molten pool. The pool will not flow enough to produce a good cut due to the rapid cooling from the quenching effect of the surrounding water. Therefore, the tip of the electrode must be manipulated to push the molten metal out of the kerf.
2-5.2 Materials. The equipment and materials required for shielded metal-arc cutting are the same as those used in shielded metal-arc welding, which is described in detail in Chapter 3. Commercially waterproofed rods are listed in Table 2-9, however, they are more expensive than surface electrodes. For extended cutting using this process, consideration should be given to the more economical on-site waterproofing of surface electrodes covered in Appendix E, paragraph E-5.1.
2-5.3 Waterproofing Electrodes. The Andersen Easy weld #1 and BROCO SofTouch are both commercially prepared waterproof electrodes and have passed Navy welding qualification testing. The other electrodes used in underwater cutting are essentially surface welding electrodes. Before being used underwater, they must be waterproofed to protect the covering from deterioration by sea water. Although many paints, varnishes, shellacs or tapes have been satisfactory for waterproofing, the materials listed in Table 2-9 have proven to last longer in sea water.
The waterproofing materials are applied by dipping the electrode into the solution and allowing the coating to dry. See Appendix E for detailed waterproofing instructions.
2-5.4 Underwater Shielded Metal-arc Cutting Techniques. The diver should understand that this process merely melts the metal and does not oxidize or consume the metal as in oxy-arc cutting. The molten metal will not run out of the cut on its own, but must be pushed out by manipulation of the electrode tip. By paying careful attention to the molten pool, the diver can master this process in a short period of time. This technique can be used effectively for cutting of steel, brass, copper and other copper-based alloys.
Table 2-9. Material Requirements for Underwater Shielded Metal-Arc Cutting
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