Basic Shielded Metal Arc Welding SMAW Review Shielded

Basic Shielded Metal Arc Welding (SMAW) Review

Shielded Metal Arc Welding SMAW -process with an arc between a covered electrode and the weld puddle -consumable flux covered electrode 9/18/2020 2

Types of Weld Machines • AC Transformer Welder - current alternates direction 120 times per second

• AC-DC-Transformer rectifier provides either alternating current or direct current

• Motor Generator produces DC current

• Engine Generator produces DC current

Polarity Reverse Polarity(DCRP) Current flows from base metal to electrode. Base metal is negative, electrode is positive.

Straight Polarity (DCSP) Current flows from electrode to base metal. Base metal is positive, electrode is negative.

Current Flow Negative to positive.

Alternating Current (AC) – current alternates its direction 120 times per second Direct current (DC) – electrical current that flows in only one direction

Welding Circuit

Factors That Determine Polarity Electrode Type of flux on electrode

Operating Machine Adjustments Current (amperage) Settings Increasing amps - produces more heat Decreasing amps - produces less heat

Polarity • DCRP (direct current reverse polarity) • DCSP (direct current straight polarity) • AC (alternating current)

Types of Electrodes • • • Mild Steel Low Hydrogen Non-ferrous Hard surfacing Cast iron Stainless steel

Electrode Grouping • Fast-Freeze – weld puddle and slag solidifies quickly. • Least amount of slag • deep penetration Exx 10 Exx 11

• Fast-Fill – weld puddle and slag cools slowly. • thickest flux coating and most amount of slag • limited use to flat groove and fillet welds in the flat and horizontal position Exx 24 Exx 27

• Fill-Freeze – characteristics of fast-freeze and fast-fill. • easy to strike an arc • produces a clean weld with minimum amount of spatter • can be welded in all positions Exx 12 Exx 13 Exx 14

• Low-Hydrogen – characteristics of fast-freeze and fast-fill. • Produce welds with outstanding resistance to cracking under high stresses and vibration-type load conditions • do not contain much hydrogen in the form of moisture in the flux coating or in chemical form E 6015 E 6016 E 6018 E 7016 E 7018 E 7028

Determining Electrode Size Determined by: the diameter of the bare end of the electrode

Bead Size • Width of bead should be 3 times the diameter of the electrode

Purposes Of Flux Coating • • • Stabilizes the arc Shields molten puddle from air Floats impurities out of the puddle Forms slag and slows cooling process Provides deoxidizers and scavengers to prevent porosity of the weld zone • Provides alloying elements for higher weld strength • Provides iron powder to increase deposition rate

AWS Electrode Classification EStands for electrode

First two digits Tensile strength deposited in thousand pounds per square inch

Third digit Indicates weld position 1 = all positions 2 = flat and horizontal positions

Fourth digit Represents special characteristics 1 = current 2 = penetration 3 = type of flux coating

Factors For Selecting Electrodes • • Base metal strength properties Base metal composition Welding current Joint design and fit-up Thickness and shape of the base metal Service conditions and/or specifications Production efficiency and job conditions

Types of Welds • Bead

• Fillet

• Groove

• Plug

Parts of Groove Welds

Parts of Fillet Welds

Types of Weld Joints • Butt

• Corner

• Tee

• Lap

• Edge

Reasons For Poor Welds • Improper • Improper machine adjustment electrode and size electrode movement electrode angle base metal preparation arc length

Parts of Welding Process

Welding Positions • Flat = 1

• Horizontal = 2

• Vertical = 3

• Overhead = 4