1. Shielded Metal Arc Equipment, Setup, and Operation
Chapter 8
Shielded Metal Arc Equipment,
Setup, and Operation

2. Objectives Look at: SMAW Process Basic Electricity (and I mean basic)
Welding Polarity
Open Circuit Voltage (OCV)
Arc Blow
Duty Cycle
Types of Welding Equipment
Chapter #8 – SMAW Equipment Setup and Operation

3. SMAW S = Shielded M = Metal A = Arc W = Welding
Chapter #8 – SMAW Equipment Setup and Operation

4. FIGURE 8-1 Shielded metal arc welding.
American Welding Society
Chapter #8 – SMAW Equipment Setup and Operation

5. SMAW Basic Operating Factors
ARC LENGTH
ELECTRODE ANGLE
SPEED OF TRAVEL
AMPERAGE
Chapter #8 – SMAW Equipment Setup and Operation

6. What is arc length?
THE DISTANCE BETWEEN THE TIP OF THE ELECTRODE AND THE BASE METAL BEING WELDED
Chapter #8 – SMAW Equipment Setup and Operation

7. When running a straight bead, at what angle should the electrode be held?
THE ANGLE FROM THE VERTICAL PLANE IN THE DIRECTION OF WELDING: 20 – 30 DEGREES
THE ANGLE AS SEEN FROM THE END VIEW : 90 DEGREES
Chapter #8 – SMAW Equipment Setup and Operation

8. Welding Current Welding current Electric current
Electricity that jumps across the arc gap
Between electrode end and metal being welded
Electric current
Flow of electrons
Resistance to electron flow produces heat
Greater resistance: greater heat
Air has high resistance
Chapter #8 – SMAW Equipment Setup and Operation

9. Basic Electricity: Voltage Amperage Watts Resistance
Chapter #8 – SMAW Equipment Setup and Operation

10. Electrical Measurement
Units to describe electrical current
Voltage or volts (V): measurement of electrical pressure
Amperage or amps (A): measurement of the total number of electrons flowing
Wattage or watts (W): measurement of electrical energy or power in the arc
Resistance (R): opposes the flow of electrons
Chapter #8 – SMAW Equipment Setup and Operation

11. SMAW Arc Temperature and Heat
Welding arc temperature
Dependent on voltage, arc length, and atmosphere
Heat produced by the arc
Determined by amperage
FIGURE 8-5 Energy is lost from the weld in the forms of radiation and convection. © Cengage Learning 2012
Chapter #8 – SMAW Equipment Setup and Operation

12. Types of Currents (Polarity)
Types of currents used for welding
Direct-current electrode negative (DCEN)
Electrode is negative and work is positive
Direct-current electrode positive (DCEP)
Electrode is positive and work is negative
Alternating current (AC)
Electrons change direction every 1/120 of a second
Electrode and work alternate from anode to cathode
Chapter #8 – SMAW Equipment Setup and Operation

13. Sketch of a DCEP arc welding circuit for SMAW
DCEP = DC Electrode Positive
DCRP = DC Reverse Polarity
DC +
Chapter #8 – SMAW Equipment Setup and Operation

14. Sketch of a DCEN arc welding circuit for SMAW
DCEN = DC Electrode Negative
DCSP = DC Straight Polarity
DC -
Electrode -
Work +
Chapter #8 – SMAW Equipment Setup and Operation

15. Sketch of a AC arc welding circuit for SMAW
FIGURE 8-9 In an alternating current, electrons flow back and forth.
© Cengage Learning 2012
Chapter #8 – SMAW Equipment Setup and Operation

16. What is the determining factor in deciding the polarity to be used for SMAW welding?
The coating on the SMAW electrode
Larger selection of electrodes for DC current
Chapter #8 – SMAW Equipment Setup and Operation

17. Welding Power (CC vs CV)
SMAW process
Requires a constant current arc voltage characteristic
SMA welding machine
Voltage output decreases as current increases
FIGURE 8-10 Constant voltage (CV) and constant current (CC).
© Cengage Learning 2012
Chapter #8 – SMAW Equipment Setup and Operation

18. How can you most easily identify whether an arc welding power source is a CC or CV type by looking at the controls?
CC – Amperage Adjustment only See next slide for photo
Chapter #8 – SMAW Equipment Setup and Operation

19. Chapter #8 – SMAW Equipment Setup and Operation

20. How can you most easily identify whether an arc welding power source is a CC or CV type by looking at the controls?
CV – Voltage Adjustment
- WFS (wire feed speed) Adjustment
- see next slide for photo
Chapter #8 – SMAW Equipment Setup and Operation

21. Voltage
WFS
Chapter #8 – SMAW Equipment Setup and Operation

22. SMAW Welding Machine Types
AC Machines
Portable Engine Driven Power Source (AC/DC)
AC/DC Rectifier
Multi-Process Inverter (AC/DC).
Chapter #8 – SMAW Equipment Setup and Operation

23. 1) AC MACHINES
Chapter #8 – SMAW Equipment Setup and Operation

24. 2) Portable Engine Driven Power Source (AC/DC)
Chapter #8 – SMAW Equipment Setup and Operation

25. 3) AC/DC Rectifier
Chapter #8 – SMAW Equipment Setup and Operation

26. Name three types of arc welding machines.
AC/DC Rectifier
Half Wave Rectification
Full Wave Rectification
Chapter #8 – SMAW Equipment Setup and Operation

27. 4) Multi-Process Inverter (AC/DC)
Chapter #8 – SMAW Equipment Setup and Operation

28. Open Circuit Voltage (OCV)
Voltage at electrode before striking an arc
Maximum Voltage – 80V
The higher the OCV the easier it is to strike an arc
The higher the OCV the increase in chance of electric shock
Newer technology drops OCV below 30V once arc is established
FIGURE 8-11 Electricity can have an initial surge much
like the surge of water when a garden hose nozzle is first
opened. © Cengage Learning 2012
Chapter #8 – SMAW Equipment Setup and Operation

29. Arc Blow
When welding with DC current the arc flares uncontrollably to the side of the electrode instead of straight down
Caused by a constriction of magnetic flux lines
Possible Solutions
Switch to AC
Move work lead clamp
Short arc length and different electrode angle
Change welding direction
Lower current setting
Chapter #8 – SMAW Equipment Setup and Operation

30. Duty Cycle
Percentage of time a welding machine can be used continuously at a specified amperage
Increases as amperage is reduced
Decreases as amperage is raised
FIGURE 8-31 Duty cycle of a typical shielded metal arc welding machine. © Cengage Learning 2012
Chapter #8 – SMAW Equipment Setup and Operation

31. Electrode Holders Characteristics
Should be of proper amperage rating and in good repair
Used at maximum amperage rating or less
FIGURE 8-33 The amperage capacity of an electrode holder is often marked on its side.Thermadyne Industries, Inc.
Chapter #8 – SMAW Equipment Setup and Operation

32. Work Clamps Characteristics Must be correct size for current used
Must clamp tightly to material
Must be in good repair
FIGURE 8-35 A work clamp may be attached to the workpiece. © Cengage Learning 2012
Chapter #8 – SMAW Equipment Setup and Operation

33. Loss Of Welding Power. Loose connections at the power source
Loose connection at the work connector or electrode holder
Splices in the cable
Too small of cable for amperage being used
Broken strands in cable not properly repaired
Enlarge hole in cable lug to fit larger stud size
Use of excessively long cables
Chapter #8 – SMAW Equipment Setup and Operation

34. Briefly explain what is meant by a “stray welding current.”
When some or all of the welding current does not return to the power source through the work lead
Usually results from poor cable connections or work piece connection (cable damage, loose fittings, painted surfaces, etc.)
Chapter #8 – SMAW Equipment Setup and Operation

35. Describe the welding technique used in padding and name three areas where padding may be used.
PADDING TECHNIQUE: THE PLACING OF BEADS OR WEAVES SIDE BY SIDE SO THAT EACH NEW WELD OVERLAPS THE ONE PRECEDING IT
Chapter #8 – SMAW Equipment Setup and Operation

36. Practicing Padding in The Shop
Chapter #8 – SMAW Equipment Setup and Operation

37. PADDING IS USED: SHAFTS SHOVELS GRADER BLADES
Chapter #8 – SMAW Equipment Setup and Operation