Shielded Metal Arc Welding

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Shielded Metal Arc Welding
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Safe practices when Arc Welding

• Dont stand in water
• Discard frayed cords and wires
• Keep flammable liquids away from heat
• Dont look at the arc with out a number 10 lens.

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Dress Code

• Wear properly fitted clothes.
• When welding, sleeves should be buttoned and
  gloves should be worn.
• Wear boots or high top Tightly laced shoes.
• Do not wear loose clothing, shirt tails, and
  unbuttoned sleeves around power equipment.
• Do not wear clothes that you do not want to get
  dirty.

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The Arc

• When electrons jump through the air
• When the pressure overcomes resistance
• VA X R

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Parts of the Arc

• Arc stream
• Vaporized metal
• Appears yellow
• Liquid metal
• Appears green
• Arc flame
• Natural gases surrounding arc stream
• Pale red

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Arc Control

• Length
• Angle

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Reverse Polarity(DCEP)

• Electrode positive
• Better penetrated welds

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Straight Polarity (DCEN)

• Electrode Negative
• Used when a high rate of filler metal is
  required.
• EXX2X Electrodes

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Alternating Current

• Stops and starts
• Must have enough voltage restart arc
• Good penetration
• Less expensive

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Classification of Steel Electrodes

• Electrode designated by E followed by a 4- or
  5- digit number
• First two or three digits - minimum tensile
  strength as-welded deposited weld metal expressed
  in thousands of pounds per square inch (1000psi)
• E-60xx - 60,000psi TS
• E-120xx - 120,000 psi TS

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Classification of Steel Electrodes

• Third or fourth digit refers to the welding
  position.
• E-xx1x - all positions
• E-xx2x - flat and horizontal fillet positions
• E-xx3x - flat position only

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Classification cont.

• The fourth or fifth and last digit indicates the
  type of welding current and the type of flux
  covering
• E-xx10 - DC reverse polarity (electrode
  positive) only (cellulose sodium).
• E-xx11 - AC or DC reverse polarity (cellulose
  potassium ) Fast freeze, cutting
• E-xx13 - AC or DC straight polarity (titania
  potassium)

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Factors of Electrode Selection

• Type of metal to be welded
• Thickness of metal
• Position of weld
• Type of power (DC or AC)
• Cleanliness of metal
• Weld bead appearance desired

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Flux

• Improves the performance in handling, storage and
  operation of the electrode
• Floats out impurities
• Directs arc stream (stabilizer)
• Insulator
• Prevents oxidation (slag or gas)
• Holds in heat
• Iron-powder improves striking ability and
  increases metal deposition rate

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Striking the Arc

• Pecking
• Touching electrode to the base metal and moving
  away to proper arc distance. Moving electrode in
  a vertical motion.
• Can start precisely where the weld is to be.

• Scratching
• Moving electrode across base metal then moving
  electrode away to the proper arc distance.
• Dose not work good in tight places

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Common Striking Problems

• Sticking
• Lift electrode and metal
• Break electrode from metal
• Remove electrode from clamp

• Arc is extinguished
• The electrode is moved to far away from the base
  metal after the arc is struck.

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Arc Length

• Longer arc
• Increases Resistance
• Increases Voltage
• Decreases Current
• Decreases filler consumption

• Shorter arc
• Decreases Resistance
• Decreases Voltage
• Increases Current
• Increases filler consumption

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Arc Length

• Should be no more then ¼ inch
• The sound of the arc should sound like eggs
  frying

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Bead Width

• Stringer bead
• Only motion is in the direction of travel
• About 3 times the width of the electrode
• With 1/8 inch electrode should be 3/8 inch

• Weaving bead
• Motion side to side as well as forward
• About 6 times the width of the electrode
• With 1/8 inch electrode should be 3/4 inch

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Stringer Bead
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Weaving Bead
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Electrode Angle

• Should be 15 to 20 tipped forward in the
  direction of travel
• Stringer bead should be at 90 from the base metal

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Travel Speed

• Bead width
• Bullet-nose-shaped ripples

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Restarting

• Strike ark 3/8 inch in front of previous weld
• Move back to crater
• Move forward to finish weld

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Restarting