SMAW Welding Section 8 Unit 26

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SMAW WeldingSection 8Unit 26
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Arc Welding Safety

• Recognize that arc welding produces a lot of
  heat.
• Use equipment according to manufacturers
  recommendations.
• Insure fire extinguishers are available
• Provide a first aid kit
• Use water filled containers to receive hot metal
  from cutting operations.
• Practice good housekeeping
• Use appropriate PPE

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Arc Welding Safety-cont.

• Insure all wiring is correctly installed and
  maintained.
• Remove or shield all combustible materials in
  work area.
• Do not use gloves or clothing which contain
  flammable substances
• Protect others from arc flash.
• Protect equipment from hot sparks.
• Use a fume collector.
• Never work in damp or wet area.
• Shutoff power source before making repairs or
  adjustments, including changing electrode.
• Dont overload the welding cables or use cables
  with damaged insulation.

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Arc Welding PPE

• Helmet
• Shade 10 or darker
• Face protection
• Always wear safety glasses underneath
• Auto helmet recommended
• Clothing
• Long sleeves
• Button up shirt
• Work shoes
• Protective apron, sleeves, jackets or pants if
  available. (Fig 26-6)

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SMAW Process

• The arc temperature over 9,000 oF melts the base
  metal, the wire core and the coating on the
  electrode.
• The high temperature causes some of the
  ingredients in the flux to form a gaseous shield.
• The electric energy is provided by a special
  power source.
• As the weld cools slag forms on top of the weld
  puddle.

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SMAW Power Supplies

• SMAW requires a constant current (CC) of either
  DC or AC.
• Some power supplies will supply both DC and AC.
• Power supply capacity determines the maximum
  diameter of electrode that can be used.

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Equipment
Polarity Switch
Power Cord
Power Supply
Electrode Holder
Power Switch
Electrode
Amperage Adjustment
Amperage Scale
Base Metal (work Piece)
Ground Clamp
Ground Cable
Electrode Cable
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Open Circuit Voltage (OCV)

• Open circuit voltage is the potential between the
  welding electrode and the base metal when the
  machine is on, but there is no arc.
• The higher the OCV a machine has, the easier it
  will be to strike an arc.
• Only adjustable of dual control machines.

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Arc Voltage

• Arc voltage is the potential between the
  electrode and the base metal when the arc is
  present.
• Arc voltage is less than OCV.
• Adjustable on dual control machines.

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Polarity

• The polarity of an object is its physical
  alignment of atoms.
• The term is often used to describe the positive
  and negative ends of batteries and magnets.
• The negative end has an excess of electrons
• The positive end has a deficiency of electrons.

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Five (5) Common Power Supplies

• Transformer
• AC only
• Rectifier
• DC only
• Transformer/rectifier
• AC or DC
• Generator
• DC and/or AC
• Inverter
• AC and DC

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Striking The Arc

• Select the best electrode
• Set the welder (Fig 26-8)
• Turn on welder
• Warn bystanders
• Lower helmet
• Start arc (two methods)
• Brushing
• Tapping

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Brushing Method

• Hold end of electrode about 1/4 - 1/2 inch above
  the surface.
• Lower helmet
• Gently brush surface of the metal with the end of
  the electrode.
• When arc starts, lift electrode 1/8 inch.

• If electrode sticks, twist it back and forth. If
  it does not break loose, release electrode from
  electrode holder.
• Do not shut off the welder with the electrode
  stuck to the metal.

Recommended method for beginning weldors.
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Tapping Method

• Set up welder
• Hold the electrode at the travel angle and 1/4 -
  1/2 inch above the metal.
• Quickly lower the electrode until it touches the
  metal and then lift it 1/8 inch.

More difficult method to learn
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Arc Welding Bead Nomenclature
Electrode
Flux
Gas shield
Electrode metal
Slag
Penetration
Molten puddle
Bead
Base metal
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Running Beads

• Practice running stringer beads
• No weaving or pattern.
• Remember the electrode burns off as the weld is
  made.
• Speed used should result in a bead 2-3 times
  wider than the diameter of the electrode.
• Cool metal between beads.
• Practice holding a long arc for a couple of
  seconds after striking the arc.
• Preheats the weld
• Practice filling in the crater.

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Five (5) Factors of Arc Welding

• Heat
• Electrode
• Electrode angle
• Arc length
• Speed of travel

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Five (5) Factors1. Heat

• The arc welder must produce sufficient heat
  (electric arc) to melt the electrode and the base
  metal to the desired depth.
• The amount of heat produced is determined by the
  amperage.
• Amperage is limited by the diameter of the
  electrode and the capacity of the welder.
• The amount of heat needed to complete the weld is
  determined by several factors

• Excessive heat.
• Electrode easier to start
• Excessive penetration (burn through)
• Excessive bead width
• Excessive splatter
• Electrode overheating

• Insufficient heat.
• Hard to start
• Reduced penetration
• Narrow bead
• Coarse ripples

• Thickness of the metal
• Type of joint,
• Electrode type
• Electrode diameter
• Weld position

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Five (5) Factors2. Electrodes

• The SMAW process uses a consumable electrode.
• Electrode must be compatible with base metal.
• Electrodes are available for different metals.
• Carbon steels
• Low alloy steels
• Corrosion resisting steels
• Cast irons
• Aluminum and alloys
• Copper and alloys
• Nickel and alloys

• Another useful group of electrodes is
  hardsurfacing.
• NEMA color coding
• System of of colors on the end or dots on the
  bare wire indicating the class of electrode.
• Not very common today.
• AWS numerical coding
• Most popular method.

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American Welding Society (AWS) Classification
System

• The AWS system distinguishes the tensile
  strength, weld position and, coating and current.
• Manufactures may and do use there own numbering
  system and produce electrodes that do not fit in
  the AWS system.

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Welding Currents

• Not all electrodes are designed to work with all
  currents.
• Common SMAW currents.
• Alternating Current (AC)
• Direct Current straight polarity (DCSP) or (DCEN)
• Direct Current Reverse polarity (DCRP) or (DCEP)

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Arc Welding Electrode Flux

• Flux A material used during arc welding,
  brazing or braze welding to clean the surfaces of
  the joint chemically, to prevent atmospheric
  oxidation and to reduce impurities and/or float
  them to the surface. (British Standard 499)
• Seven (7) Classifications of Flux constituents
• Protection from atmospheric contamination
• Fluxing agents
• Arc initiators and stabilizers
• Deoxidizes
• Physical properties of the flux
• Fillers and metallic additions
• Binders and flux strength improvers

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Electrode Grouping

• Electrodes are also grouped according to there
  performance characteristics.
• Fast-freeze
• Mild steel
• Quick solidification of weld pool
• Deep penetrating
• Recommended for out of position welds
• Deep penetrating arc
• Fast-fill
• Highest deposition rate
• Stable arc
• Thick flux
• Flat position and horizontal laps only

• - Fill-freeze
• General purpose electrodes
• Characteristics of fast-freeze and fast-fill
• Low hydrogen
• Welding characteristics of fill-freeze
• Designed for medium carbon and alloy steels

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Selecting Electrode Size

• The optimum electrode diameter is determined by
  the thickness of the base metal, the welding
  position and the capacity of the welding power
  supply.

• A diameter of 3/32 or 1/8 inch can be used on
  metals up to 1/4 inches thick without joint
  preparation.
• ROT the diameter of the electrode should not
  exceed the thickness of the metal.

• A smaller diameter is usually recommended for out
  of position welding.
• When completing root passes in V-joints, a
  smaller diameter maybe used and then a larger
  diameter is used for the filler passes.

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Electrode Storage

• Electrodes are damaged by rough treatment,
  temperature extremes and moisture.
• The should be kept in their original container
  until used.
• They should be stored in a heated cabinet that
  maintains them at a constant temperature.
• The storage of low hydrogen electrodes is very
  critical.
• Designed to reduce underbead cracking in alloy
  and medium carbon steels by reducing the the
  amount of hydrogen in the weld pool.
• The flux is hydroscopic--attracts moisture (H2O).
• Moisture in the flux also causes excessive gasses
  to develop in the weld pool and causes a defect
  in the weld caused worm holes.

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Five (5) Factors3. Electrode Angle

• The electrode angle influences the placement of
  the heat.
• Two angles are important
• Travel
• Work

• The travel angle is the angle of the electrode
  parallel to the joint.

• The correct travel angle must be used for each
  joint.
• Beads 15o from vertical or 75o from the work.
• Butt joint 15o from vertical or 75o from the
  work.
• Lap joint 45o.
• T joint 45o.
• Corner 15o from vertical or 75o from the work.

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Five (5) FactorsElectrode Angle-cont.

• The work angle is the angle of the electrode
  perpendicular to the joint.

• The appropriate angle must be used for each joint.

• Beads 90o
• Butt joint 90o
• Lap joint 45o
• T joint 45o
• Corner 90o

• The work angle may need to be modified for some
  situations.
• For example, a butt joint with two different
  thickness of metal.

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Five (5) Factors4. Arc Length

• The arc length is the distance from the metal
  part of the electrode to the weld puddle.
• The best arc length is not a fixed distance, but
  should be approximately equal to the diameter of
  the electrode.

• Arc length can be adjusted slightly to change the
  welding process.

• Excessive length
• Excessive spatter
• Reduced penetration
• Poor quality weld

• Insufficient length
• Electrode sticks
• Narrow weld
• Poor quality weld

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Five (5) Factors5. Speed of Travel

• The speed of travel (inches per minute) is an
  important factor when arc welding.
• The best speed of travel (welding speed) is
  determined by several factors
• The size of the joint,
• The type of electrode
• The size of the electrode
• The amperage setting on the machine
• Deposition rate of the electrode (cubic inches
  per minute)
• The deposition rate of an electrode will change
  with the welding amperage.

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Five (5) Factors5. Speed-cont.

• The ideal speed can be calculated using the
  volume of the joint and the deposition rate of
  the electrode.

• Step one determine the area of the weld.
  (Assuming 1/16 inch penetration.)

• Step Two knowing the deposition rate of the
  electrode, determine the welding speed.
  (Deposition rate 2.5 in3/min.)

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Five (5) Factors5. Speed-cont.

• The correct welding speed is indicated by the
  shape of the ripples.

Too slow excessive width, excessive penetration
Too fast narrower width, elongated ripple
pattern, shallow penetration.
Recommended width 2-3 times diameter of
electrode, uniform ripple pattern, full
penetration.
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SMAW Joints
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Square Groove

• A butt joint can be completed with a groove
  welded on metal up to 1/8 inch thick with a
  single pass on one side, with no root opening.
• Electrode manipulation should only be used to
  prevent burning through.

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Square Groove Thicker Metal

• A groove weld on metal up to 1/4 inch thick can
  be welded with a single pass on one side but, if
  possible, it should be completed with a single
  pass on both sides.
• Metal this thick requires a root opening to
  achieve adequate penetration.
• Electrode manipulation will reduce penetration.

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Single V Groove Weld

• Butt joints on metal greater than 1/4 inch thick
  require joint preparation.
• Note that the groove does not extend all the way.
  A short distance, called the root face, is left
  undisturbed.
• The amount of joint preparation is dependent on
  the diameter of the electrode and the amperage
  capacity of the power supply.
• Several different combinations of passes can be
  used to complete this joint.

Note this is the principle use of pattern beads.
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T-Joints
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Information

• In a T-joint the two welding surfaces are at an
  angle close to 90 degrees from each other.
• The welding side and number of passes uses
  depends on the thickness of the metal, the
  welding access and capacity of the power supply.
• Common joints include.
• Plane T
• T with joint gap
• Single preparation
• Double preparation

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Plane T-Joint

• The plane T joint is very useful for thin metal.
• Can be completed at angles other than 90 degrees.
• Can be completed with metal of different
  thickness.
• The work angle must be changed to direct more
  heat to the thicker piece.

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T-joint--Thicker Metal

• When the metal thickness exceeds 1/8 inch the
  recommendation is to gap the joint.
• Improves penetration
• May not be necessary if larger diameter electrode
  is used and sufficient amperage is available.
• The need for a joint gap varies with the type of
  electrode, but should not exceed 1/8 inch.

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T-joint Single Single Bevel

• As with other joints, thicker metal must have
  joint preparation to achieve full penetration
  with smaller diameter electrodes.

• Several different preparations can be used. A
  popular one is the bevel.
• A bevel can be completed by grinding or cutting.
• The bevel joint can be completed with electrode
  manipulation or no electrode manipulation.
• When when electrode manipulation is used to fill
  the joint, the first pass should be a straight
  bead with no manipulation.

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T-joint Double Bevel

• The double bevel T-joint is recommended for metal
  1/2 inch thick and thicker.
• The root passes should be with not manipulation,
  but the filler passes can be completed with
  either straight beads or patterns beads.
• Alternating sides reduces distortion.

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Weld Defects
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Common SMAW Defects
Under Cutting
Porosity
Hot Cracks
Slag Inclusions

• Hot cracks
• Caused by excessive contraction of the metal as
  it cools.
• Excessive bead size
• May also be found at the root of the weld.
• Slag inclusions
• Long arc
• Incomplete removal of slag on multipass welds.

• Undercutting
• improper welding parameters particularly the
  travel speed and arc voltage.
• Porosity
• Atmospheric contamination or excess gas in the
  weld pool.

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SMAW Weld Defects-cont.
Incomplete fusion
Toe cracks
Microcracks
Underbead cracks

• Toe Cracks
• Excessive heat and rapid cooling.
• Underbead cracks
• Excessive hydrogen in weld pool
• Microcracks
• Caused by stresses as weld cools.
• Incomplete fusion
• Incorrect welding parameters or welding
  techniques.

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Questions