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

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

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

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

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

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

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

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

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