OPERATION | ||
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No one can learn to weld simply by reading about it. Skill comes only with practice. The following pages will help the inexperienced welder understand welding and develop his skill. For more detailed information, order a copy of the book “New Lessons in Arc Welding.” (See Book Division section at rear of manual).
The operator’s knowledge of arc welding must go beyond the arc itself. He must know how to control the arc, and this requires a knowledge of the welding cir- cuit and the equipment that provides the electric cur- rent used in the arc. Figure 3 is a diagram of the weld- ing circuit. The circuit begins where the electrode cable is attached to the welding machine and ends where the work cable is attached to the machine. Current flows through the electrode cable to the electrode holder, through the electrode holder to the electrode and across the arc. On the work side of the arc, the current flows through base metal to the work cable and back to the welding machine. The circuit must be complete for the current to flow. To weld, the work clamp must be tightly connected to clean base metal. Remove paint, rust,etc. as necessary to get a good connection. Connect the work clamp as close as possible to the area you are welding. Avoid allowing the welding circuit to pass through hinges, bearings, electronic compo- nents or similar devices that can be damaged.
ELECTRODE HOLDER
WELDING MACHINE
AC OR DC POWERELECTRODE
SOURCE AND
CONTROLS
ARC
WORK
WORK CABLE
ELECTRODE CABLE
FIGURE 3 - The welding circuit for (Stick) shielded metal arc welding.
The electric arc is made between the work and the tip end of a small metal wire, the electrode, which is clamped in a holder that is held by the welder. A gap is made in the welding circuit (see Figure 3) by holding the tip of the electrode 1/16 - 1/8”
Arc welding is a manual skill requiring a steady hand, good physical condition, and good eyesight. The oper- ator controls the welding arc and, therefore, the quali- ty of the weld made.
What Happens in the Arc?
Figure 4 illustrates the action that takes place in the electric arc. It closely resembles what is actually seen during welding.
The “arc stream” is seen in the middle of the picture. This is the electric arc created by the electric current flowing through the space between the end of the elec- trode and the work. The temperature of this arc is about 6000°F (3300°C) which is more than enough to melt metal. The arc is very bright, as well as hot, and cannot be looked at with the naked eye without risking painful and possibly permanent injury. A very dark lens, specifically designed for arc welding must be used with the handshield or headshield whenever viewing the arc.
The arc melts the base metal and actually digs into it, much like water through a garden hose nozzle digs into the earth. The molten metal forms a pool or crater and tends to flow away from the arc As it moves away from the arc, it cools and solidifies. Slag forms on top of the weld to protect it during cooling.
| Covering | |
| Electrode | |
Solidified Slag | Arc | |
Shielding Gases | ||
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Weld Metal 
Base Metal
FIGURE 4 - The welding arc.
BULLDOG® 140