Chapter 11 SMAW: Electrodes Goodheart-Willcox Publisher

Learning Objectives Identify carbon and low alloy SMAW electrodes. List six purposes of an electrode covering. Interpret the AWS electrode identification system. Determine the trial amperage of a welding machine using the rule-of-thumb method. Select an electrode to meet the requirements of a weld. Identify two means of storing electrodes.

Introduction SMAW electrode properties Solid, round metal wires Low-carbon steel Covered (coated) Melting electrode provides filler material Electrode selection depends on several factors

AWS Electrode Specifications

Electrode Coverings Also called flux coverings Purposes Create shield around arc and weld Create flux to clean impurities Create hard slag covering to protect weld while cooling Improve mechanical and chemical properties of weld Provide filler metal Determine current type and polarity in electrode

Effects of Certain Flux Coverings Metallic salts Make weld stronger, more corrosion resistant, or more ductile Iron powder Electrode deposits more filler metal into weld in given length of time Low hydrogen electrodes Deposit minimum amount of hydrogen into weld Help prevent weakened welds

Electrode Sizes Lengths Diameters Diameters (cont.) 9″ (229 mm)

AWS Electrode Identification System for SMAW Electrodes Goodheart-Willcox Publisher

Recommended Polarity Last two numerals of electrode designation indicate recommended electrical polarity

AWS Electrode Suffixes Suffix indicates that alloys have been added to electrode

Low Hydrogen Electron Covering Compositions

Electrode Amperage Requirements Electrode diameter determines amperage required Larger diameter needs higher amperage Manufacturer’s guide provides guidelines Trial amperage Rule-of-thumb method

Rule-of-Thumb Method Steps Determine base amperage for the electrode Determine difference between 1/8″ (3.2 mm) electrode and electrode to be used Convert the fractional difference from step 2 to equivalent fraction with 32 in denominator Multiply the number of 32nds by 30A

Rule-of-Thumb Method Steps (Cont.) Calculate the trial amperage If the electrode diameter is larger than 1/8″, add the answer from step 4 to the base amperage in step 1 If the electrode diameter is smaller than 1/8″, subtract the answer from step 4 to the base amperage in step 1

Welding Procedure Specification (WPS) Used for commercial jobs Outlines how weld is to be made Lists diameter and type of AWS electrode Specifies type of current and current setting or range Not needed for most fabrication, repair, and craft welding Welder or shop owner selects electrode

Factors for Selecting Electrodes Type of metal Metal thickness Groove design Joint alignment Available welding current Welder skill Welding position Deposition rate Depth of penetration Weld bead finish Additional metal properties

Type of Metal Determine tensile strength of base metal Tensile strength of electrode should be as strong as that of base metal

Metal Thickness Consider number of passes needed for metal thickness Weld passes no more than 1/4″ (6.4 mm) thick Wider weld beads needed for thicker metal Electrodes that do not penetrate deeply work well with thin metal E6012 E6013

Groove Design Wide V-groove joint Small-diameter electrode for root pass Larger electrodes for filler and cover passes Narrow bevel-, V-, J-, and U-groove joints Smaller-diameter electrodes for root pass and next few passes

Joint Alignment Poorly designed or assembled joints may have large openings Use electrodes designed to span large root openings E6012 E6013 E7014

Welder Skill Highly skilled welders Less-skilled welders May use large-diameter electrode and high amperage Achieve proper penetration Less-skilled welders Select electrode that allows proper penetration with their level of skill

Welding Position Flat All electrodes Overhead EXX1X EXX4X

Deposition Rate Amount of filler deposited per unit time Measured in pounds or kilograms per hour Achieving high deposition rate Larger electrode diameter Higher amperage DCEP

Depth of Penetration Good penetration on thick metal Deeper penetration E6010 E6011

Weld Bead Finish When good appearance is needed When appearance is not as important E6010

Additional Metal Properties Alloying elements Improve strength Provide corrosion resistance Add other desirable characteristics Low hydrogen electrode coatings Low in moisture Low in hydrogen

Care of Electrodes Keep in shipping containers until used Keep away from moisture Moisture contains hydrogen (H2) Hydrogen weakens the weld Do not bend electrodes

Care of Low Hydrogen Electrodes Store in electrode drying oven Use within specified time after removing from oven Goodheart-Willcox Publisher

Electrode Dispenser Provides temporary storage Protects electrodes while out of oven