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.