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Arc Welding

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Metals and Welding Precautions and Safe Practices Relatively safe compared to other forms of welding 4 areas of concern during arc welding Shock - Fire Burns - Fumes ... – PowerPoint PPT presentation

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Title: Arc Welding


1
Arc Welding
  • Metals and Welding

2
Precautions and Safe Practices
  • Relatively safe compared to other forms of
    welding
  • 4 areas of concern during arc welding
  • Shock - Fire
  • Burns - Fumes
  • Light
  • Heat

3
Prevention of Shock
  • Use a wooden grating on concrete floors
  • Rubber soled shoes are best
  • Danger of shock is increased with higher
    temperature and humidity - perspiration
  • Disconnect power before repairing
  • Qualified electrician should complete maintenance
    and repairs
  • Make sure the machine is grounded
  • Ground clamp paint, rust, grease will prevent
    solid ground

4
Prevention of Shock
  • Use special welding cables with high quality
    insulation
  • Repair solid dont use tape
  • Keep in good condition free of grease, oil, out
    of water, ditches, etc.
  • Electrode holders and cables should be fully
    insulated
  • Turn main switch to welder off when leaving the
    work area
  • Follow usual precautions in handling electric
    power

5
Prevention of Light Burns
  • Eyes
  • Helmet or hand shield with a minimum shade of no.
    10 lens is required (see table on 159-160)
  • Wear safety glasses also
  • Completely screen equipment for arc glare
  • Locate jobs in special rooms or booths
  • Avoid accidental contact on the part of others
  • Skin
  • Completely cover body
  • UV Light will cause sunburn type burn

6
Prevention of Heat Burns
  • Clothing
  • Completely cover body
  • Sparks and heat
  • Cotton clothing is preferred with leather shoes
    and gloves
  • Mark hot metal to prevent others from coming in
    contact with welded pieces
  • Pick up hot metal with pliers or tongues, not
    gloves or hands
  • Dont hand hot metal to instructor or TAs

7
Prevention of Fire
  • Clothing
  • Stand while Arc welding
  • Dont roll cuffs
  • Keep free of oil, grease, etc.
  • Sweatshirts turned inside out
  • Do not weld near flammable materials
  • Proper fire extinguishing equipment should be
    stationed near welding operations

8
Prevention of Fumes Exposure
  • Exhaust systems or breathing apparatus should be
    provided when welding inside
  • Fumes from electrode flux non-toxic
  • Fumes from paint lead content - toxic
  • Fumes from metal coating
  • Zinc (galvanized), Aluminum - toxic
  • Carbon monoxide
  • Carbon dioxide
  • Dust

9
General Safety
  • Good housekeeping
  • Keep area clean
  • Electrode stubs
  • Slag on concrete floor
  • Cables hung up
  • Tools put away
  • Good workmanship in making sound welds is
    essential to that others may not be injured due
    to failure of welded parts

10
Stick Electrode Welding
  • Operation of a miniature electric furnace between
    the grounded base metal and the electrode
  • Arc temperature is about 11,000º F
  • Molten metal must be protected from the air by a
    gaseous shield and/or slag shield
  • Machine settings and operators manipulations
    determine size and shape of bead

11
Successful Arc Welding depends upon
  • Correct metal identification
  • Metal properties vary
  • Correct electrode selection
  • Depends on metal type, thickness and position of
    weld
  • Correct amperage
  • Depends upon electrode type, size, position, and
    metal thickness
  • Influence burn off rate and affect arc length
    and speed of travel

12
Successful Arc Welding depends upon
  • Proper Arc length
  • Influences the amount of heat during the weld
  • Correct speed of travel
  • Determines the width of bead and indirectly the
    strength of the weld
  • Angle of electrode
  • Determines the bead shape and controls slag and
    gas inclusions

13
AC/DC
  • Alternating Current electrons change direction
    every 1/120 of a second (60 cycles per second)
  • Rapid reversal causes the welding heat to be
    evenly distributed on both the work and the
    electrode
  • Direct Current flow of electrons in one
    direction
  • Electrode Negative (DC Straight) electrode is
    negative and the work is positive (high electrode
    melting rate)
  • Electrode Positive (DC Reverse) electrode
    positive and work is negative (produces the best
    welding arc characteristics)

14
Electrode Selection
  • Early arc welding done with bare, low carbon
    steel wire electrodes on DC welders
  • Early 1930s flux coated electrodes
  • Exhaustive research into chemical and physical
    properties and chemical combinations
  • American Welding Society (AWS) has classified
    electrodes to allow for wide choices for many
    applications

15
Classification of Electrodes
  • Classified according to filler metal
    specifications by AWS and ASTM (American Society
    for Testing Materials)
  • Lincoln, AIRCO, Hobart, etc. will all be the same
  • Based upon four factors
  • Minimum tensile strength of the as-welded
    deposited weld metal
  • Type of covering
  • Welding position
  • Type of welding current (AC, DC, DC-)

16
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

17
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

18
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) Pg. 161

19
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

20
Electrode storage
  • Store electrodes in protected place
  • Avoid cracking or chipping flux by bending or
    striking
  • Store in dry place
  • Aluminum and low hydrogen (E7018) should be
    stored in a closed container
  • Old refrigerator works well
  • Low hydrogen electrodes may be re-dried at 300º F
    for non-x-ray welds

21
Function of 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 (E7024)

22
Selecting the Electrode for the Job
  • Fast-Freeze-electrodes - deposits a weld that
    solidifies or freezes rapidly - E6010, E6011.
  • Fast-Fill - deposits metal rapidly - E7018,
    E6024, E6027.
  • Fill-Freeze - characteristics between
    fast- freeze and fast-fill - E6012, E6013,
    E6014.

23
Amperage Setting
  • Influences the rate of metal deposition
  • Influences the speed of welding
  • Bead should be 2x the diameter of the electrode
    wire
  • Type of electrode influences amp. setting
  • Unusual to select the proper setting on the first
    try
  • For ¼ steel, start at 90 amps and adjust from
    there
  • Actual amperage is greatly influenced by arc
    length

24
Striking the Arc
  • Peck Method
  • DC welders
  • Contact the plate with downward motion
  • Scratch Method
  • AC or DC welders
  • Contact by sweeping motion

25
Angle of Electrode
  • Arc has a definite directional force
  • Flat welding
  • Perpendicular from side to side
  • Tilted in direction of travel about 15º

26
Angle of Electrode by Position
  • Tee and Lap
  • 45º side 15-20º lead
  • 6011, 6013, 7024
  • Horizontal
  • 5-10º side 15-20º lead
  • 6013, 6011
  • Overhead
  • 90º side 10-15º lead
  • 6011
  • Vertical up
  • 90º side 0-5º slant
  • 6011
  • Vertical down
  • 90º side 10-15º lead
  • 6013

27
Proper Arc Length
  • Arc welding involves unavoidable changes of arc
    length
  • Must be controlled as much as possible
  • Arc length influences
  • Actual amperage (heat)
  • Appearance of a bead
  • Arc length should be equal to the diameter of the
    wire in the electrode (1/8)
  • Tighter arc will give even penetration, metal
    deposition, a strong bead, and less spatter

28
Proper Arc Length
  • Long arc results in
  • Large globules melting
  • Wavering arc
  • Wide spatter and irregular bead
  • Short arc results in
  • Electrode sticks
  • Poor penetration
  • Convex bead
  • Clag inclusions
  • Irregular bead
  • Use short length for vertical welds

29
Speed of Travel
  • Movement of electrode forward and downward
  • Travel speed influences
  • Bead width
  • Penetration
  • General shape of the bead
  • Use a uniform speed
  • Both hands on the electrode holder
  • Operator comfort
  • Bead should be about twice the diameter of the
    electrode wire

30
Read the Bead
31
Controlling distortion(Volume changes of
expansion followed by contraction during cooling)
  • Do not overweld.
  • Avoid continuous welds.
  • Consider chain intermittent
  • Or staggered intermittent
  • Use fewer beads (passes).

32
Controlling distortion cont.
  • Use 600 included angle on edge prepared joints.
  • Weld near the neutral axis.
  • Use back-step welding.
  • Use wedging.
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