Transcript Chapter 4

Chapter 4
Shielded Metal Arc
Welding of Plate
© 2012 Delmar, Cengage Learning
Objectives
• Demonstrate safe work practices
• Demonstrate the ability to strike an arc at a
specific point
• List the problems that can result if the welding
current is set too low or too high
• Discuss how to select the correct diameter of
welding electrode for a weld
• Describe the effects of overheating a weld by
comparing the bead’s shape for width,
reinforcement, and appearance
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Objectives (cont'd.)
• Define arc length, and describe the effects of
using too short or too long an arc length
• Compare a leading electrode angle to a trailing
electrode angle
• Tell what characteristics of the weld bead can be
controlled by the movement or weaving of the
welding electrode
• Demonstrate ten weave patterns for weld beads
• Discuss the importance of positioning the welder
and the plate properly before starting to weld
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Objectives (cont'd.)
• Give the characteristics of the three filler metal
groups E6010 and E6011, E6012 and E6013, and
E7016 and E7018
• Define stringer beads and tell how they are used
• Demonstrate a vertical up stringer bead and a
horizontal stringer bead
• Demonstrate how to make a welded square butt
joint in the flat, vertical up, and horizontal positions
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Objectives (cont'd.)
• On an edge joint, demonstrate how to make a flat
weld, a vertical down weld, a vertical up weld, a
horizontal weld, and an overhead weld
• On an outside corner joint, demonstrate how to
make a flat weld, a vertical down weld, a vertical
up weld, a horizontal weld, and an overhead weld
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Objectives (cont'd.)
• Demonstrate how to make a welded lap joint in the
flat position, a welded horizontal lap joint, a
vertical up-welded lap joint, and an overheadwelded lap joint
• Demonstrate how to make a welded tee joint in the
flat, horizontal, vertical, and overhead positions
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Introduction
• Shielded metal arc welding (SMAW)
– Common method used to join plate
• Also called stick welding
– Provides high temperature and heat concentration
• Allows a weld pool to be built up quickly
– Filler metal from the electrode increases strength
– Minimum equipment required
– High-quality welds can be consistently produced
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Figure 4-1 Striking an arc and running short beads. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning
Effect of Too High or Too Low Current
Settings
• Each welding electrode must be operated in a
specific current range
– Current set too low results in poor fusion and poor
arc stability
• Arc length is very short
• Results in frequent shorting and sticking of the
electrode
– Weld bead at a high amperage is wide and flat with
deep penetration
• Spatter is excessive
• Causes electrode to discolor, crack, low red, or burn
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Electrode Size and Heat
• Welding electrode size depends upon:
– Welder skill and welding codes or standards
– Metal thickness and size
• Small diameter electrodes
– Require less skill, but more time
• Large diameter electrodes
– May overheat: can cause a burn-through
• Chill plate
– Large piece of metal that absorbs excessive heat
© 2012 Delmar, Cengage Learning
Figure 4-9 The effect on the shape of the molten weld pool caused by the heat input.
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© 2012 Delmar, Cengage Learning
Arc Length
• Distance the arc jumps from the end of electrode
to the plate or weld pool surface
– To maintain a constant arc length: electrode must
be lowered continuously
– Narrow range for the arc length to remain stable
– Higher settings must be within the amperage range
for the specific electrode
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Figure 4-11 Welding with too long an arc length. Larry Jeffus.
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Electrode Angle
• Measured from electrode to surface of the metal
– Leading electrode angle: pushes molten metal and
slag ahead of the weld
– Flat position: caution must be taken to prevent cold
lap and slag inclusion
– Rapid cooling: prevents the metals from fusing
together
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Electrode Angle (cont'd.)
• Preventing cold lap and slag inclusions:
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–
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Use as little leading angle as possible
Ensure arc melts the base metal completely
Use a penetrating-type electrode
Move arc back and forth across molten weld pool to
fuse both edges
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Electrode Angle (cont'd.)
• Trailing electrode angle
– Pushes molten metal away from leading edge of
pool
• Solidifies toward the back
– Molten metal is forced away from bottom of weld
• Arc melts more of the base metal
• Reinforces weld
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Figure 4-21 Welding with a trailing angle. Larry Jeffus.
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Electrode Manipulation
• Weaving the welding electrode
– Controls several bead characteristics
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•
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Penetration
Buildup
Width
Porosity
Undercut
Overlap
Slag inclusion
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Electrode Manipulation (cont'd.)
• Weave pattern for each weld
– Personal choice of the welder
– Some patterns are especially helpful for specific
welding situations
– Many weave patterns are available
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Figure 4-23 Weave patterns.
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Position of the Welder and the Plate
• Welder
– Should be in a relaxed, comfortable position before
starting to weld
• Welding helmet is down
– Welder is blind to surroundings
• Several factors led to swaying
– Lean against or hold a stable object
• Find most comfortable angle
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Practice Welds
• Grouped according to:
– Type of joint
– Type of welding electrode
• Instructor or welder
– Selects order in which welds are made
• Students
– Find it easier to start with butt joints
– Flat position allows welder to build skills slowly
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Electrodes
• Arc welding electrodes used for practice welds are
grouped into three filler metal classes
– F3 E6010 and E6011 electrodes
• Cellulose-based flux
– F2 E6012 and E6013 electrodes
• Rutile-based flux
– F4 E7016 and E7018 electrodes
• Mineral-based flux
• Should be the last choice
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Stringer Beads
• Characteristics
– Straight weld bead with little or no side-to-side
electrode movement
– Used to practice maintaining arc length and
electrode angle
– Should be straight
– Easily made once the welder develops the ability to
view the entire welding zone
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Square Butt Joint
• Made by tack welding two flat pieces of plate
together
– Root opening: space between the plates
• Changing the root opening affects penetration
• Excessively large openings can cause burn-through
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Figure 4-43 Square butt joint in the flat position.
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© 2012 Delmar, Cengage Learning
A
B
FIGURE 4-44 (A) After the arc is established, hold it in one area long enough to establish the
size of molten weld pool desired. (B) Weld back over the arc strike to melt it into the weld.
A & B Larry Jeffus.
© 2012 Delmar, Cengage Learning
Edge Weld
• Made by placing the edge of the plate evenly
– Plates should be clamped tightly together
– Make tack welds to hold the plates together
– Size of weld should equal the thickness of the plate
being joined
– Weld bead should have a slight buildup
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FIGURE 4-49 Make tack welds at the ends of the joint.
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© 2012 Delmar, Cengage Learning
Outside Corner Joint
• Made by placing the plates at a 90 degree angle to
each other
– Make small tack welds
– Weld bead should completely fill the V-groove
formed by the plates
– Slightly convex surface buildup
– Back side can be used to practice fillet welds
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Lap Joint
• Made by overlapping edges of the two plates
– Can be welded on one side or both sides with a
fillet weld
– Buildup should equal the thickness of the plate
– Good weld has smooth transition from the plate to
the surface of the weld
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FIGURE 4-69 Lap joint.
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© 2012 Delmar, Cengage Learning
Tee Joint
• Made by tack welding one piece of metal on
another piece of metal at a right angle
– Heat is not distributed uniformly between both
plates
– Most heat should be directed toward the base plate
– Can be strong if welded on both sides
– Flat or slightly concave appearance
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Figure 4-83 Tee joint in the flat position.
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© 2012 Delmar, Cengage Learning
Summary
• Shielded metal arc welding
– Referred to as stick welding
• Stick shape of electrode
• Tendency of electrode to stick to the workpiece
• Difficult to view entire welding zone
– Developing visual skill is essential
• Takes time and practice
• Objectively inspecting work
– Enhances skills
© 2012 Delmar, Cengage Learning