Shielded Metal Arc Welding Equipment

Learning Goals

• We can…
• Identify the component of a Shielded Metal Arc Welding Set Up

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• Compare and contract welding power sources

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• Select the power type and electrode type

Shielded Metal Arc Welding Set Up

Power Source

Constant Voltage (CV) Power Source

An arc welding power source with a volt-ampere relationship yielding a large welding current change from a small arc

voltage change.

Constant Current (CC) Power Source

An arc welding power source with a volt-ampere relationship yielding a small welding current change from

a large arc voltage change.

Arc Welding Power Source Classifications

• The electricity flows from the power source, through the electrode and across the arc, through the base material to the work lead and back to the power source

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• All SMAW machines are called constant current (CC)

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• Three types of arc welding power sources
• Alternating current (AC) power sources

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• Direct current (DC) power sources

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• Combination (AC and DC) power sources

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AC vs DC

• Alternating Current (AC) - the direction of the flow of electrons switches back and forth at regular intervals or cycles

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• Direct current (DC) is electrical current which flows consistently in one direction

DC vs AC Constant Current

Power Sources – AC Transformer

• Also called a buzz box

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• Simplest and cheapest SMAW power sources

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• Transforms high voltage and low amperage, coming in from the power line, to low voltage and high amperage

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• Since alternating current changes direction every half cycle it is known to have no polarity and therefore is capable of producing AC current only

Power Sources – Transformer Rectifier

• Operates like an AC transformer but includes on more step

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• Uses a rectifier or diode in the machine to produce DC

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• Capable of producing either AC or DC current types

Power Sources - Inverter

• Inverter power supplies are the newest innovation in SMAW power supplies

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• An inverter welding power source is a special transformer-type machine

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• It changes incoming ac current to dc, then back to very-high-frequency ac current

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• Inverters make use of new technology to make welding power supplies smaller, lighter in weight and very efficient electrically

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Direct Current Power Sources

• Polarity - The direction that the current flows

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• Direct Current Electrode Negative (DCEN)

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• Direct Current Electrode Positive (DCEP)

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Direct Current Electrode Negative�Direct Current Straight Polarity

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• The electrode is connected with the negative terminal of the power source

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• The electrons flow from the electrode to the work piece

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• About 66% of the heat is from the base metal

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Direct Current Electrode Positive�Direct Current Reverse Polarity

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• The electrode is connected to the positive terminal of the power source

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• The electrons flow from the work piece to the electrode

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• More heat is from the electrode

DCEN vs DCEP

Duty Cycle

Duty Cycle Amperes Time

Available

30% 250 3 Min/10 Min

40% 225 4 Min/10 Min

50% 200 5 Min/10 Min

60% 190 6 Min/10 Min

70% 180 7 Min/10 Min

80% 170 8 Min/10 Min

90% 155 9 Min/10 Min

100% 140 10 Min/10 Min

The duty cycle of a power source is the percentage of a ten (10) minute period that it can operate at the rated output current setting. If the welder is not aware of the duty cycle of his or her machine they may “overwork it”, and cause severe damage to the machine.

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Show What You Know – Part 1!

1. What does DC stand for?
• Direct Current
2. What does AC stand for?
• Alternating Current
3. What is an advantage of DC?
• Ability to select polarity, used in all positions, used with most electrodes
4. What is an advantage of AC?
• Great filler metal deposition rates, faster welding speeds, less expensive
5. Where is the heat coming from in DCEN?
• Base metal
6. What is an advantage of DCEN?
• Quick melting of the base metal, deeper penetration
7. What is an advantage of DCEP?
• Higher filler deposition rate, arc cleaning action
8. What does “duty cycle” mean?
• The percentage of a 10 minute period that it can operate at the rated output current setting

Cables and Terminals

Welding Cables

• Three main cables:
• Power Cable
• Work Lead
• Electrode Lead

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• Provide the path for the welding current to travel through

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• Cables are generally made of copper

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• Cable sizes range from 4 through 4/0
• Smallest = 4
• Medium =0 or 1/0
• Largest =4/0

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• Cable size will depend on amperage level and length of cable

Terminals

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• Lugs – uninsulated terminals

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• Connectors – insulated terminals

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• So, what should I do?
• Make sure connections are tight
• Make sure insulation is in good working condition

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Cable and Connectors

• Concerns:
• If the electrode holder or the work clamp become hot during welding it could indicate:
• Too small of cable
• Loose connections

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• So, what should I do?
• Check all cables for proper insulation & tightness
• Do not weld if there are exposed or frayed wires

Work Clamp

• Must have a ground to allow electricity to flow

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• There are four primary types of ground clamps:
• Permanent
• Spring Loaded
• C Clamp
• Magnetic

Work Clamp

• You may not have a good connection if:
• You are not able to strike an arc
• Your welds are sputtering or spattering

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• So, what can I do?
• Inspect ground clamp

for frayed wires and

loose connections

• Clean ground clamp if

needed

Electrode Holder & Electrodes

Electrode Holder�(stinger)

• Hand held clamping devices that hold the electrode during the welding process

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• Selected according to the machines maximum output rating

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• Should be completely insulated

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• Contain grooved jaws to hold the electrode in play

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• So, what should I do?
• Inspect to make sure the connections are tight and there are no loose or frayed wires
• Ensure that the outside of the holder is insulated and is in good condition

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Electrode Holder

Show What You Know – Part 2!

1. What is the cable called that connects the machine to the work clamp?
• Work lead
2. What is the smallest sized cable?
• 4
3. If the electrode holder or cable is hot, what should you check?
• Proper insulation, tightness, frayed or exposed wires
4. What is the clamp called?
• Ground clamp
5. If my arc does not strike, what should I check?
• Ground clamp tight and cleaned, inspect for frayed and exposed wires
6. What is another name for the electrode holder?
• Stinger

Electrodes

Electrode

• A solid metal consumable electrode covered in flux

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• Composed of two parts:
• Core Rod (Metal Filler)
• Carries welding current
• Becomes part of the weld
• Flux Coating
• Produces a shielding gas
• Can provide additional filler
• Forms a slag

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Electrode Flux

• Purpose:
• Provide deoxidizers & scavengers to clean the weld

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• Produce shielding gases to protect the weld

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• Produce a slag covering to allow it to cool more slowly

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• Provide stabilization to the arc

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• Increase deposit rates

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Electrode Flux

• Common Elements:
• Calcium
• Carbon
• Manganese
• Molybdenum
• Nickel
• Potassium
• Silicon
• Sodium
• Titanium

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Electrode Numbering System

Electrode Numbering System

Electrode Characteristics

“Fast-Freeze” Electrode Group�EXX10, EXX11, EXX22�

• Use in All Positions

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• High Cellulose Coating

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• Deep Penetration, Forceful Arc

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• Light Slag

“Fast-Fill” Electrode Group�EXX24, EXX27�

• High Deposition Rate

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• Flat and Horizontal

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• Heavy Slag

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• Slow Cooling

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• Tight Fit Up Required

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• Good On Poor Surface Conditions

“Fill-Freeze” or “Fast Follow” Electrode Group�EXX12, EXX 13, EXX14�

• Higher Deposition Rates than “Fast-Freeze”

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• Used for All-Position Applications

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• Rutile Based Coatings with the Addition of Iron Powder

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• High Travel Speeds on Sheet Metal Under 3/16” Thick

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• 50/50 Mix of “Fast-Freeze” and “Fast-Fill” Groups

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“Low Hydrogen” Electrode Group�EXX18, EXX28�

• Known Today as the “Code Rod”

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• Mineral-Lime Based Coating – Moisture Sensitive

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• Designed for All Position or High Deposition Welding

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• Moderate to Shallow Penetration

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• Moderate to Heavy Slag

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• First Choice for Welding “Difficult to Weld” Steels

Electrode Selection

• Factors affecting electrode selection:
• Weld groove design
• Required tensile strength
• Base metal composition
• Position of the weld joint
• Rate at which to deposit
• Welding current
• Penetration required
• Metal thickness
• Experience of the welder
• Welding position

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Electrode Diameter

• Diameter is determined by the diameter of the inner core of solid metal

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• Outside diameters may vary considerably as the

amount of flux will be significantly different between

the electrodes of different classifications

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• Most common:
• 3/32”
• 1/8”
• 5/32”
• 3/16”

Electrode Diameter Selection

• Electrode must be small enough to manipulate at the root of the weld

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• Electrode diameter should not be thicker than the base metal

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• Use the largest allowable electrode at the highest acceptable amperage to reduce welding costs

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• Electrodes with diameters of 1/8” or smaller are preferred for out of position welds

Electrode Storage

• Electrodes must be kept dry and away from humidity
• Low hydrogen options like E7018 are particularly susceptible
• Drying ovens or rod boxes are options

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• Drying ovens are not always the best option
• E6010 should not be kept in an oven but should be kept in a relatively dry environment

Machine Set Up

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Sketch and label a picture of a SMAW machine set up with the accessories!

Shielded Metal Arc Welding Set Up

Show What You Know – Part 3!

1. What is the purpose of the flux?
• Clean the weld, protect the weld, cool more slowly, stabilize the arc, increase the deposit rates
2. What are the first 2 numbers on an electrode number?
• Tensile strength
3. What is the 3^rd number on an electrode number?
• Position
4. List one electrode diameter rule.
• Small enough to manipulate, not thicker than base metal, largest at highest amperage, 1/8” or small for out of position
5. What type of environment should electrodes be kept in?
• Warm and dry