1. Glob or spray modes for thick steel
Most farmers may not realize that adjusting the volts, amps, and wire speed on wire welders can produce transfer modes fine-tuned to thick metal. The limiting factor with globular or spray modes is they can only be used on “metal ⅛-inch thick and thicker and only when making flat and horizontal fillet welds,” says Lincoln Electric’s Karl Hoes.
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.
2. Clean out impurities
“Farmers commonly fail to adequately prepare the metal before welding,” says Miller Electric’s John Leisner. “This includes removing paint, rust, dirt, and other surface contaminants, but it also means grinding out cracks.” Leisner readily understands that metal prep is the last thing on your mind when a weld repair is needed at the height of the season or in the middle of feeding livestock.
“I’m not saying the repair area must be absolutely pristine,” he says, adding that aluminum welds are the exception (see tip number 6 on welding aluminum). “At the very least, hit the repair area with a powered wire brush to remove rust and dirt.”
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,” he says.
Hydrogen is welding enemy #1
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,” says Lincoln Electric’s Hoes. “High-strength steels (commonly used on tillage implements), thick sections of metal, and restrained parts are more susceptible to hydrogen cracking.”
3. Rules on angle, direction, and speed
One of the amazing aspects of welding is that even a novice welder can experience some success. However, Hose and Leisner caution that there are some hard-and-fast rules to produce a lasting welding repair.
Push or pull: Here the rule is simple. “If it produces slag, you drag,” says Leisner. 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.
Work angle: 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.
Arc spacing: 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, keep a work distance of ⅜ to ½ inch. With stick welding, look to keep that distance ⅛ inch between the rod tip and work piece. “The arc length should not exceed the diameter of the core of the electrode,” Leisner says.
Speed: Watch the welding puddles and ridge (where the molten metal solidifies). When wire welding (MIG or flux-core), the ridge should be approximately ⅜ inch behind the wire electrode, Hoes says. 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.
4. 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.
5. Farm electrode shopping list
The array of wires and rods sold makes selecting electrodes confusing. Leisner and Hoes give this shopping list of farm electrodes that will cover most repair tasks.
MIG wire: A good overall MIG wire diameter is either .035 (the most common) or .045 inch. But consider a .025 inch when welding thin materials of ⅛ inch or less. The reason is that a smaller-diameter wire welds more stable at a lower current, which provides less arc force and less tendency to burn through the metal.
Flux-core wire: One of the most popular flux-core wires is the E71T-1 as “it’s good for out-of-position (vertical, overhead) welding, offers fast freezing slag, and provides high deposition rates,” Leisner says. If you are welding out of position (an overhead weld), you could go to an E71T-8 wire, says Hoes. If you are welding coated or galvanized metal (such as a grain leg), go with an E71T-14 wire, because it has core materials that explode in the arc. This action volatilizes steel coatings, thus, minimizing weld cracking and porosity. All these wires offer higher deposition rates than stick electrodes, and their slag removes more easily.
Stick electrode: A general-use rod is a 6011 electrode, Leisner says, since it delivers a good penetrating weld. On thicker material that “needs a deeper penetrating weld, move to a 6010 electrode,” he says.
“If you are welding thinner stock where you want less penetration, change to a 6013 electrode.” The most common rod size is ⅛ inch. “Go to a larger-diameter rod for thicker metal and a smaller-diameter rod for thinner metal,” Hose advises.
6. Welding aluminum
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.
Preheat the repair to 230°F. to minimize cracking. Place tack welds at the beginning and end of the repair to aid in preheating and to prevent distortion.
Use a short gun and a straight cable. If you are doing a lot of aluminum welding, consider buying a spool gun.
Push into the weld to reduce contamination and to improve shield-gas coverage.
Weld hot and fast using higher amperage and voltage settings and weld-travel speeds to prevent burn-through.
Fill the weld crater at the end of a weld. Craters are the leading reason aluminum welds crack, Hoes warns. To fill the crater, continue to feed wire at the end of a weld, reversing your direction of travel back over the weld for about 1 inch.
7. High-strength steel mending secret
Manufacturers are increasingly turning to the use of hard-to-weld metals like high-strength steel, particularly in tillage implements to reduce their weight, Hoes says. 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,” Hoes says. “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, adds Leisner. 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.
8. Why do welds crack?
Hoes says welds crack for one or more of the following reasons:
- Not grinding cracks out to their bottom prior to welding.
- Forming undersize beads. Welds should always be slightly wider than they are deep.
- Forming concave or hollow beads. Such welds can lead to cracking down the middle of the bead. Welds should always be convex or humped up.
- Failing to properly clean a repair. Leaving rust, paint, grease, dirt, or moisture on a repair introduces hydrogen into the weld that can promote cracking.
- Not preheating prior to welding. This is particularly required when the steel you’re welding has a higher carbon or alloy content.
- Avoiding the use of low-hydrogen electrodes to repair hard-to-weld steels (high carbon or alloy content).
- Failing to fill craters at the end of a weld.
- Not properly reinforcing a weld repair.
- Not laying down a first bead on multiple pass welds that is of sufficient size and flat or convex in shape. This resists cracking until the later beads can be added for support.
Leisner says rigid parts are more prone to cracking. If possible, weld toward the unrestrained end of such parts and leave a 1/32-inch gap between plates for free shrinkage movement as the weld cools. Peen each bead while it is still hot to relieve stresses.
9. Welding out of position
Gravity is your enemy when working out of position, so counteract its effects (particularly with wire welding) by using a little less voltage and a lower wire feed speed to create a smaller puddle, says Hoes. Reversing polarity to concentrate the heat at the electrode tip results in cooler welding, which lets the weld puddle cool faster to prevent dripping, says Leisner. Here are more tips from both experts on welding out of position:
Horizontal welds: Drop your work angle to either 0° or 15°, and then weld at a steady pace to keep the weld puddle in place.
Vertical welds: On 3/16-inch and thinner steel, weld in a downward motion. This movement can be a challenge, however; the weld puddle can get ahead of the arc and become an insulator, reducing penetration. On 1/16-inch and thicker steel, weld in an upward motion using a side-to-side technique, moving the arc from the right to the center and then to the left to create a triangle.
Overhead welds: Lower the amperage and move quickly to keep the weld puddle narrow. Use a circular motion and a whip action to prevent the weld puddle from spilling away from the weld.
10. When to reinforce
Reinforcing a welding repair is “definitely needed if the crack is in a location where you can’t prep its surface for welding,” says Leisner. “Always reinforce high-stress points, such as a hinge on a folding implement.”
Reinforcement is also needed if a piece has broken more than once in or near the same place as a previous repair, Hoes adds.
When reinforcing, be sure to bevel edges at a 30° angle where the new metal meets the old metal. Doing so provides better welding penetration.
For heavier sections of material, leave a small land (space) at the bottom of the joint. To do this, first bevel the edges and then grind along the bottom of the bevel until it’s the thickness of a nickel.
Here’s a final reinforcement tip. “Material over ¼-inch thick usually should be welded in multiple passes,” Leisner says.