Chapter 32 Oxyacetylene Welding

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

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

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

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

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

FIGURE 32-5 Flashing the flame off the metal will allow the molten weld pool to cool and reduce in size. © Cengage Learning 2012

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

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

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

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

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

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

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

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

FIGURE 32-46 Vertical weld showing effect of too much heat. © Cengage Learning 2012

FIGURE 32-49 Butt joint at a 45° angle. © Cengage Learning 2012

FIGURE 32-51 Some vertical tee joints are easier for right-handed or left-handed welders. © Cengage Learning 2012

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

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

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

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

FIGURE 32-56 Overhead. © Cengage Learning 2012

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.

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

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). © Cengage Learning 2012

Horizontal Fixed Position 5G FIGURE 32-65 5G position. The pipe is fixed horizontally. © Cengage Learning 2012

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. © Cengage Learning 2012

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

FIGURE 32-71 6G position. The pipe is inclined at a 45° angle. © Cengage Learning 2012

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

FIGURE 32-73 The keyhole in the root of the joint helps to ensure 100% root penetration. © Cengage Learning 2012

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