Chapter 32
Oxyacetylene Welding
© 2012 Delmar, Cengage Learning
Objectives
• Explain how to set up and weld mild steel
• Make a variety of welded joints in any position on
thin-gauge, mild steel sheet
• Make a satisfactory weld on small diameter pipe
and tubing in any position
• Explain the effects of torch angle, flame height,
filler metal size, and welding speed on gas welds
© 2012 Delmar, Cengage Learning
Introduction
• Oxyacetylene welding
– Limited to thin metal sections or when portability is
important
– Today almost exclusively used on thin metal
– One of the arc welding processes is most often
used for welding thicker metal
– Some arc welding processes are replacing the gas
welding processes on thin metals
© 2012 Delmar, Cengage Learning
FIGURE 32-1 Gas metal arc welded (GMAW) on 16-gauge mild steel.
Larry Jeffus
© 2012 Delmar, Cengage Learning
Mild Steel Welds
• Characteristics
– Easiest metal to gas weld
– Welds with 100% integrity possible
– Secondary flame shields molten weld pool from the
air
– Atmospheric oxygen combines with carbon
monoxide to produce carbon dioxide
– Carbon dioxide forces surrounding atmosphere
away from the weld
© 2012 Delmar, Cengage Learning
Factors Affecting the Weld
• Torch tip size
– Controls weld bead width, penetration, and speed
• Torch angle and angle between inner cone and
metal
– Effects speed of melting and size of molten weld
pool
• Welding rod size and torch manipulation
– Control weld bead characteristics
© 2012 Delmar, Cengage Learning
FIGURE 32-5 Flashing the flame off the metal will allow
the molten weld pool to cool and reduce in size.
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© 2012 Delmar, Cengage Learning
Characteristics of the Weld
• Key points
– Molten weld pool must be protected by the
secondary flame
– Weld crater susceptible to cracking
– Number of sparks in the air increases just before a
burn-through
– Burnout does not happen to molten metal until it
reaches kindling temperature
© 2012 Delmar, Cengage Learning
FIGURE 32-6 Building up the molten weld pool
before it is ended will help prevent crater cracking.
Larry Jeffus
© 2012 Delmar, Cengage Learning
Outside Corner Joint
• Flat outside corner joint
– Made with or without filler metal
– One of the easiest welded joints to make
– Filler metal not needed if sheets are tacked
properly
– If added, filler metal is added uniformly
© 2012 Delmar, Cengage Learning
Butt Joint
• Flat butt joint
– One of the easiest welded joints
• Place two clean pieces of metal flat on the table and
tack weld both ends together
• Point the torch so that the flame is distributed equally
on both sheets
• When both sheet edges have melted, add the filler
rod in the same manner
© 2012 Delmar, Cengage Learning
Lap Joint
• Flat lap joint
– Easily welded with basic manipulations
– Use caution when heating the two sheets
• Both sheets start melting at the same time
– Direct flame on bottom sheet away from top sheet
– Filler rod added to the top sheet
– Gravity pulls the molten weld pool down
© 2012 Delmar, Cengage Learning
Tee Joint
• Flat tee joint
– More difficult
– Uneven heating
– Large percentage of welding heat is reflected back
on the torch
– Angle torch in the direction of weld travel
– Adjust flame to be somewhat oxidizing
© 2012 Delmar, Cengage Learning
Out-of-Position Welding
• Characteristics
– Welds performed in position other than flat
• Vertical
• Horizontal
• Overhead
– Somewhat more difficult than flat welds
© 2012 Delmar, Cengage Learning
Vertical Welds
• Characteristics
– Most common out-of-position weld
– Control the size of molten weld pool
• If molten weld pool size increases beyond the shelf,
the pool will overflow
– Watch the trailing edge of the molten weld pool
• Prevent dripping
– Less vertical the sheet
• Easier the weld
© 2012 Delmar, Cengage Learning
FIGURE 32-46 Vertical weld showing effect of too much heat.
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© 2012 Delmar, Cengage Learning
FIGURE 32-49 Butt joint at a 45° angle.
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© 2012 Delmar, Cengage Learning
FIGURE 32-51 Some vertical tee joints are
easier for right-handed or left-handed welders. ©
Cengage Learning 2012
© 2012 Delmar, Cengage Learning
Horizontal Welds
• Rely on weld bead to support molten weld pool
– Shelf must be built up under molten weld pool
• Weave pattern
– Completely different than any other position
• Sheet may be tipped back
– 45 degree angle for stringer bead
© 2012 Delmar, Cengage Learning
Horizontal Stringer Bead
• Considerations
– Start with a small bead and build to desired size
– Too large a molten weld pool is started
• Shelf does not have time to form properly
• Weld bead will sag downward and not be uniform
– There may be an undercut of top edge
• Overlap on bottom edge
© 2012 Delmar, Cengage Learning
Overhead Welds
• Considerations
– Wear proper personal protection
•
•
•
•
Leather gloves
Leather sleeves
Leather apron
Cap
– Molten weld pool
• Held to sheet by surface tension
– Weld direction
• Matter of personal preference
© 2012 Delmar, Cengage Learning
Stringer Bead
• Considerations
– Place metal at a height recommended by your
instructor
– With the torch off, your goggles down, and a rod in
your hand, try to progress across the sheet
• Use several directions until you find the direction that
best suits you
• Change the height of the sheet to determine the
height that is most comfortable
© 2012 Delmar, Cengage Learning
FIGURE 32-56 Overhead.
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© 2012 Delmar, Cengage Learning
Mild Steel Pipe and Tubing
• Mild steel pipe and tubing
– Both small diameter and thin wall can be gas
welded
• Process for both are usually the same
• Thin-wall material does not require a grooved
preparation
– Gas welding is used on both pipe and tubing to
make bicycles, hand rails, works of art, etc.
© 2012 Delmar, Cengage Learning
Horizontal Fixed Position 5G
• Requires little skill development after completing
the horizontal rolled position 1G welds
– Torch height and angle skills help 5G position
• As the weld changes from overhead to vertical, the
weld contour changes
• Overhead bead shape controlled by:
– Stepping the molten weld pool
– Moving the flame and rod back and forth
© 2012 Delmar, Cengage Learning
Horizontal Rolled Position 1G
FIGURE 32-58 1G position. The pipe is rolled horizontally. The weld is
made in the flat position (approximately 12 o’clock as the pipe is rolled).
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© 2012 Delmar, Cengage Learning
Horizontal Fixed Position 5G
FIGURE 32-65 5G position. The pipe is fixed horizontally.
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© 2012 Delmar, Cengage Learning
Vertical Fixed Position 2G
• Vertically fixed pipe requires a horizontal weld
– Skill required for the 2G position similar to
horizontal butt joint
FIGURE 32-69
2G vertical fixed
position.
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© 2012 Delmar, Cengage Learning
45º Fixed Position 6G
• Considerations
– Careful manipulation of molten weld pool is
required
– Weld progresses around the pipe
• Changing from vertical to horizontal to overhead to
flat
• Not completely in any one position
– Combination of compound angles makes the 6G
position difficult
© 2012 Delmar, Cengage Learning
FIGURE 32-71 6G position. The pipe is inclined at a 45° angle.
© Cengage Learning 2012
© 2012 Delmar, Cengage Learning
Thin-Wall Tubing
• Technique similar to welding a stringer bead
around a pipe
– Penetration not a concern: welding proceeds as if
you were making a stringer bead on pipe
– Penetration is required: weld will have a keyhole
© 2012 Delmar, Cengage Learning
FIGURE 32-73 The keyhole in the root of the
joint helps to ensure 100% root penetration.
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© 2012 Delmar, Cengage Learning
Summary
• Learning to control heat input to weld is important
– Changing torch angle, height, or travel speed
• Oxyacetylene welding
– Process of preference for part-time and amateur
welders
• Most common problem with OFW welding
– Heat and weld distortion on large weldments
© 2012 Delmar, Cengage Learning