1. Shielded Metal Arc Welding (SMAW)
Heat for welding generated by electric arc established between flux-covered consumable metal rod (electrode) and work
Called stick electrode welding
Combustion and decomposition of electrode creases gaseous shield (Gases given off)
Protects electrode tip, weld puddle, arc, and highly heated work from atmospheric contamination
Additional shielding provided by covering of molten slag (flux)
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2. SMAW
American Welding Society
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3. SMAW Advantages Equipment less complex, more portable and less costly
Can be done indoors or outdoors, in any location and any position
Electrodes available to match properties and strength of most base metals
Not used for welding softer metals

4. SMAW Operating Principles
Sets up electric circuit
Includes welding machine, work, electric cables, electrode holder and electrodes, and a work clamp
Heat of electric arc brings work to be welded and consumable electrode to molten state
Heat intense: as high at 9,000ºF at center
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5. SMAW Operating Principle
American Welding Society
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6. Welding Power Sources
Each type of power source has fundamental electrical differences that best suit particular processes
Welding machine
Must meet changing arc load and environmental conditions instantly
Must deliver exact amount of electric current precisely at right time to welding arc
Available in wide variety of types and sizes

7. Four Types of Power Source
Engine-driven generators
Powered by gas or diesel combustion engine
Can be found with a.c. or d.c. electric motor
No longer being manufactured and rarely found
Inverters
Increases frequency of incoming primary power
Constant current, constant voltage, or both
Produce a.c. or d.c. welding current

8. Four Types of Power Source
A.C. transformers
Used to step down a.c. line power voltage to a.c. welding voltage
Transformer-rectifiers
Use basic electrical transformer to step down a.c. line power voltage to a.c. welding voltage
Welding voltage then passed through rectifier to convert a.c. output to d.c. welding current
May be either d.c. or a.c.-d.c. machines

9. Bridge Rectifier

10. Output Slope
Two basic types
Constant current
Constant voltage

11. Current Controls Amperage Voltage Quantity of current (flow)
Determines amount of heat produced at weld
Voltage
Measure of force of current (push)
Determines ability to strike an arc and maintain its consistency

12. Constant Current Welding Machines
Used for shielded metal arc welding and gas tungsten arc welding
Available in both d.c. and a.c. welding current
Current remains fairly constant regardless of changes in arc length
Total Wattage stays the same
Voltage drops as amps increase (dropping arc voltage (DAV) machine)
Enables welder to control welding current in specific range by changing length of arc

13. Open Circuit and Arc Voltage
Open circuit voltage runs between volts (no welding being done, volts high, no amps)
Drops to arc voltage when arc struck
Arc voltages (Voltage generated between electrode and work during welding, voltage lower, amps higher)
Range: 36 volts (long arc) to 18 volts (short arc)
Determined by arc length held by welder and type of electrode used
Arc lengthened, arc voltage increases and current decreases

14. Polarity
Electrode negative and electrode positive used in d.c. welding
DCEN (d.c. electrode negative)
Electrode connected to negative terminal of power source and work connected to positive terminal (current flows from neg to pos) flow from electrode to work = more electrode consumption.
DCEP (d.c. electrode positive)
Electrode connected to positive terminal of power source and work connected to negative terminal

15. D.C. Transformer-Rectifier Welding Machines
Have many designs and purposes
Flexibility one reason for wide acceptance
Deliver either DCEN or DCEP
May be used for:
Stick electrode welding
Gas tungsten arc welding
Submerged arc welding
Multi-operator systems
Stud welding
The Lincoln Electric Co.
Miller Electric Mfg. Co.
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16. Transformer-Rectifier Machines
Have two basic parts
Transformer for producing and regulating alternating current that enters machine
rectifier that converts a.c. to d.c.
Third important part is ventilating fan
Keeps rectifier from overheating
Design improves arc stability and makes it easy to hold short arc which is soft and steady
No major rotating parts so consume little power

17. A.C. Transformer Welding Machines
Most popular a.c. welding machine
Function of transformer
Step down high voltage of input current to high amperage, low voltage current required for welding
Especially suited for heavy work
The Lincoln Electric Co.
Miller Electric Mfg. Co
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18. Advantages of a.c. Power Sources
Reduces tendency to arc blow
Can use larger electrodes
Resulting in faster speeds on heavy materials
Lower cost
Decreased power consumption
High overall electrical efficiency
Noiseless operation
Reduced maintenance

19. D.C. and A.C.-D.C. Inverter Welding Machines
Portable, lightweight, and versatile
May be either constant current, constant voltage or both
Can perform several different processes
Miller electric Mfg. Co.
The Lincoln Electric Co.
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20. Duty Cycle
Percentage of any given 10-minute period that machine can operate at rated current without overheating or breaking down
Rating of 100% means machine can be used at rated amperage on continuous basis
Required by continuous, automatic machine welding
Rating of 60% means machine can be used at its capacity 6 out of every 10 minutes without damage
Satisfactory for heavy SMAW and GTAW

21. Twin Carbon Electrode Holder
Metal shield to protect welder's hand from intense heat.
Two leads are required because the arc is created between the two electrodes.
Larger than the metal electrode holder
The Lincoln Electric Co.
Holder is water cooled
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22. Atomic-Hydrogen Arc Welding
Process in which electric arc surrounded by atmosphere of hydrogen
Gas shields molten metal from oxidation and contamination from the air
Transfers heat from electrode to work
Arc formed between two electrodes
Temperature produced by arc: 7,500ºF
Current supplied by a.c. welding transformer
Hydrogen supplied in cylinders

23. Atomic-Hydrogen Electrode Holder
General Electric Co.
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24. Atomic-Hydrogen Arc Welding
Metal of same analysis as being welded can be deposited
Welds may be heat treated
Unusually smooth, ductile, nonporous and free from impurities
Surface free from scale
May weld hard-to-weld metals
Advantages: increased production, low operating cost, and low maintenance cost