Clean out impurities
Cleaning removes the impurities that get absorbed into the metal during weld; if they stay behind, they compromise the repair. If cleaning isn’t possible, avoid mending a repair with a MIG welder. Use a stick welder and a 6011 rod. Also, slow your travel speed down. This allows time for gas bubbles to boil out of the molten weld before these impurities are trapped inside the weld.
Hydrogen is the worst weld-destroying impurity around. Because it is everywhere (in water, dirt, rust, paint, manure, grease), hydrogen is a huge challenge for welders. What can be done to gun down hydrogen? Clean, clean, and clean some more. Hydrogen, along with high-residual stress and crack-sensitive steel, may result in cracking hours or days after welding.
Keep the Globular transfer and Spray arc transfer
Globular transfer (short arc): Voltage, amperage, and feed speed are higher than the standard short circuit mode. This results in large globs of wire expelling off the end of the wire to enter the weld puddle. This mode provides deep penetrating welds on thick material, but it produces a lot of spatter.
Spray arc transfer: The volts, amps, and wire speed are higher than in globular mode. It produces a stream of tiny molten droplets that spray across the arc from wire to metal. For true spray transfer, you’ll need to use argon-rich gas. Spray arc allows the use of large-diameter wire, so a lot of metal is deposited, and you get a great-looking bead. It can only be used on flat or horizontal fillet welds; its puddle is very fluid. Be sure to change your gun’s nozzle to a unit that is about 3 inches long or longer.
Rules on angle, direction, and speed
One of the amazing aspects of welding is that even a novice welder can experience some success. If it produces slag, you drag. In other words, you drag the rod or wire when welding with a stick or flux-core wire welder. Otherwise, you push the wire with metal inert gas (MIG) welding.
With wire welding, hold the gun at a 10° to 15° angle into the direction you are pushing the weld. With stick welding, maintain a 20° to 30° lead angle in the dragging direction. With a fillet (tee) weld, hold the rod or wire (regardless of weld process) at a 45° angle between the two pieces of metal.
Adjust travel speed so that the welding arc stays within the leading one third of the weld pool. For wire (flux-core or MIG) welding, With stick welding, look to keep that distance between the rod tip and work piece. The arc length should not exceed the diameter of the core of the electrode.
Watch the welding puddles and ridge (where the molten metal solidifies). When wire welding (MIG or flux-core). A too-slow travel speed produces a wide, convex bead with shallow penetration that also deposits too much metal. On the other hand, a too-high travel speed creates a shallow weld that produces a narrow and highly crowned bead. Most travel speeds for various joints are well below 40 inches a minute.
MIG gas selection
For MIG welding, the tried-and-true shielding gas of preference is 100% carbon dioxide (co²). It is economical and gives you deep penetrating welds.
Yet, there are times to invest in more expensive shielding gases, which include:
- 75% argon and 25% co² for producing nice-looking welds (100% co² produces a lot of spatter) and for welding at high amperage levels.
- 85% argon and 15% co² for welding heavier plate steel or for using on metal that has a lot of mill scale or rust.
- 90% argon and 10% co² for spray transfer welding and for heavy or thick sections of metal.
- 100% argon or an argon/helium mixture for welding aluminum.
- 90% argon, 7.5% helium, and 2.5% co² for welding stainless steel.
The increasing presence of aluminum in ag equipment is forcing the issue of making repairs to the metal. The good news is that any wire welder can handle aluminum, and the process is relatively easy to learn. But there are some rules that you must follow, says Hoes. Those rules include:
- Buy U-groove drive rolls that support the wire but don’t crush it. Do keep drive-roll adjustment on the loose side.
- Replace the cable liner using a Teflon, nylon, or similar liner product.
- Use only argon or argon-helium gas.
- Select an aluminum filler wire that is 3/16 or 1/6 inch in diameter. These larger wires are easier to feed down the gun cable.
- Employ a contact tip approximately .0115 inch larger than the diameter of the wire.
- Remove grease, oil, manure, or dirt by using an organic solvent such as acetone, a mild alkaline solution like strong soap, or a citrus-based degreaser. Avoid strong alkaline or acid cleaners.
- Brush the repair using a new stainless steel wire brush (only used for aluminum welding jobs) to remove the oxidized aluminum that occurs naturally on the surface of the metal. Aluminum oxides melt at 3,700°F., while the base metal melts at 1,200°F. Oxides on the repair surface will inhibit penetration of the filler metal.
Manufacturers are increasingly turning to the use of hard-to-weld metals like high-strength steel, particularly in tillage implements to reduce their weight. When repairing high-strength steel, it is crucial to prepare by first removing all rust, paint, grease, and moisture to get down to bare metal. Next, preheat the repair site prior to welding.
The higher the carbon content of the steel (common in high-strength steels), the more preheating that’s required. Preheating is required to prevent postweld cracking. Employ a small-diameter, low-hydrogen electrode, such as a 7018 stick rod, when repairing high-strength steels. Finally, keep your welding travel speed slow; this keeps the weld puddle molten by giving hydrogen gas bubbles time to boil out. The result is a better finished weld.