1. Chapter 32
Oxyacetylene Welding

2. 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

3. 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

4. FIGURE 32-1 Gas metal arc welded (GMAW) on 16-gauge mild steel.
Larry Jeffus

5. 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

6. 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

7. 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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8. 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

9. FIGURE 32-6 Building up the molten weld pool before it is ended will help prevent crater cracking.
Larry Jeffus

10. 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

11. 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

12. 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

13. 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

14. Out-of-Position Welding
Characteristics
Welds performed in position other than flat
Vertical
Horizontal
Overhead
Somewhat more difficult than flat welds

15. 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

16. FIGURE 32-46 Vertical weld showing effect of too much heat.
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17. FIGURE 32-49 Butt joint at a 45° angle.
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18. FIGURE Some vertical tee joints are easier for right-handed or left-handed welders. © Cengage Learning 2012

19. 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

20. 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

21. 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

22. 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

23. FIGURE Overhead.
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24. 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.

25. 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

26. Horizontal Rolled Position 1G
FIGURE G 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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27. Horizontal Fixed Position 5G
FIGURE G position. The pipe is fixed horizontally.
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28. 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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29. 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

30. FIGURE 32-71 6G position. The pipe is inclined at a 45° angle.
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31. 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

32. FIGURE 32-73 The keyhole in the root of the joint helps to ensure 100% root penetration.
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33. 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