CHAPTER 7 SHIELDED METAL-ARC WELDING AND WEARFACING

The shielded metal-arc welding process, referred to as metallic-arc welding, arc welding, or stick welding, is extensively used in welding ferrous and nonferrous metals. It has many applications for producing a vast assortment of metal products. Shielded metal-arc welding is found in the ship building industry and in the construction industry for fabricating girders, beams, and columns. Because it is easy to use and portable, shielded metal-arc welding is universally used in the repair and servicing of equipment, machinery, and a host of other items.

MANUAL SHIELDED METAL-ARC WELDING

Arc welding provides you the ability to join two metals by melting them with an arc generated between a coated-metal electrode and the base metal. The temperatures developed by the arc can reach as high as 10000°F. The arc energy is provided by a power source that generates either direct or alternating current. The electrodes that carry the current produce a gas that shields the arc from the atmosphere and supplies filler metal to develop the weld shape.

ARC-WELDING EQUIPMENT

A wide variety of welding equipment is available, and there are many differences between the makes and models of the equipment produced by the manufacturers. However, all types of arc-welding equipment are similar in their basic function of producing the high-amperage, low-voltage electric power required for the welding arc. In this discussion, we are primarily concerned with the typical items of arc-welding equipment, rather than the specific types. For specific information about the equipment your battalion or duty station has available, consult the manufacturer's instruction manual. For additional operational information and safety instruction, have your leading welding petty officer explain the operation to you.

The basic parts of a typical shielded metal-arc welding outfit include a welding machine, cables, electrode holder (stinger), and electrodes. The Steelworker also requires a number of accessories that include a combination chipping hammer and wire brush, welding table (for shopwork), C-clamps, and protective apparel.

Before we discuss the different types of welding machines, you must first have a basic knowledge of the electrical terms used with welding.

Electrical Terms

Many terms are associated with arc welding. The following basic terms are especially important.

ALTERNATING CURRENT. - Alternating current is an electrical current that has alternating negative and positive values. In the first half-cycle, the current flows in one direction and then reverses itself for the next half-cycle. In one complete cycle, the current spends 50 percent of the time flowing one way and the other 50 percent flowing the other way. The rate of change in direction is called frequency, and it is indicated by cycles per second. In the United States, the alternating current is set at 60 cycles per second.

AMPERE. - Amperes, sometimes called "amps," refers to the amount of current that flows through a circuit. It is measured by an "amp" meter.

CONDUCTOR. - Conductor means any material that allows the passage of an electrical current.

CURRENT. - Current is the movement or flow of an electrical charge through a conductor.

DIRECT CURRENT. - Direct current is an electrical current that flows in one direction only.

ELECTRICAL CIRCUIT. - Electrical circuit is the path taken by an electrical current flowing through a conductor from one terminal of the source to the load and returning to the other terminal of the source.

POLARITY. - Polarity is the direction of the flow of current in a circuit. Since current flows in one direction only in a dc welder, the polarity becomes an important factor in welding operations.

RESISTANCE. - Resistance is the opposition of the conductor to the flow of current. Resistance causes electrical energy to be changed into heat.