1. Selecting and Using Arc Welding Equipment
Unit 26
Selecting and Using Arc Welding Equipment

2. Shielded Metal Arc Welding
Welding process that uses electrodes
Also called arc welding or stick welding
Advantages
Electricity and welders relatively inexpensive
Works with ordinary 240-volt wiring
Available in a portable form
Fast and reliable
Can also be used for heating, brazing, and hardsurfacing

3. Electricity for Welding
Ampere or amp: rate of flow of electrical current in a conductor
Conductor: material that permits electrical current to move through
Volt: measure of electrical pressure
Watt: measure of energy available
Formula: W × V = A or W = V/A
Transformers: convert high voltage and low amperage to low voltage and high amperage
Alternating current: reverses direction of flow cyclically

4. Electricity (continued)
60-cycle current: electricity that reverses its direction of flow 60 times per second
Generator: produces direct current
Direct current: flows in one direction only
Polarity: the direction of the flow of electricity in the welding circuit
Straight polarity: DC current flowing in one direction
Reverse polarity: DC current flowing in opposite direction

5. Welding Equipment AC welders DC welders Welding cables
Electrode holders and ground clamps
Welding table and booth
Cleaning equipment

6. NEMA Color Coding NEMA: National Electrical Manufacturers Association
Colored markings are placed on electrodes in three areas: the exposed end of metal rod, exposed surface, flux near exposed rod
Most manufacturers stamp the AWS classification number on each electrode instead of using the color-code system

7. AWS Numerical Code AWS: American Welding Society
Code condenses information into a four- or five-digit number for mild steel electrodes
First two digits: give tensile strength
Two right-hand digits: list the type of welding the electrode is capable of doing
Third digit: the welding positions the electrode can be used in
Fourth (or fifth) digit: the depth of penetration and/or welding current

8. Important Terms Arc welder: produces current for welding
Arc: discharge of electricity through the air
Welder: person who welds
Electrodes: flux-coated metal welding rods
Slag: layer of burned flux and impurities
Duty cycle: percentage of time that a welder can operate without overheating
Electrode holder: spring-loaded device with insulated handles used to grip a welding electrode

9. Important Terms (continued)
Ground clamp: spring-loaded clamp attached to an electrical cable
Chipping hammer: steel hammer with a sharp edge and/or point
End marking: color coded on end
Spot marking: color coded on a bare surface
Tensile strength: the amount of tension the finished weld can withstand
Carbon arc torch: holds two carbon sticks and produces a flame from the energy of an electric welder