Stick welding and electrode selection
The construction industry is extremely diverse, and some of the trades don’t feature welding as a core competency in their day-to-day work. However, equipment breaks, and it’s likely welding will be needed get it back up and running. Or maybe you have some downtime and want to reinforce areas that you know are prone to damage.
One of the most common processes for field welding repair is Shielded Metal Arc Welding (SMAW), or stick. Stick electrodes are self-shielded and cut down on the amount of equipment needed—no need to haul in a gas cylinder, hose and regulator. It also provides adequate protection of the weld bead in outdoor applications where wind interferes with shielding gases. Flux cored (FCAW) welding is also a great option for field repair, but for the sake of this article we will focus on stick.
Choosing the correct replacement/filler material is critical to all field repair applications. Operations should replace all materials with one that meets or exceeds the strength of the parent material. Each application varies in mechanical properties such as required strength, ductility, wear resistance, impact strength, and tensile strength. An exact material match ensures weld quality and longevity, and avoids premature failure and unwanted downtime.
Common electrodes used in stick welding are 6010, 6011, 6013, 7018 and 7024 with the most common diameters ranging from 1/8- to 5/32-in. Each of these electrodes offers all-position welding capabilities (except 7024). The first two digits of a stick electrode represent the “as welded” minimum tensile strength: 6010 provides 60,000 psi tensile strength, for instance. The third digit represents the acceptable welding positions for each electrode (1 = all positions, 2 = flat or horizontal only, 3 = flat, horizontal, vertical down and overhead). The fourth digit refers to the coating type and the type of welding current (alternating current (AC)/direct current (DC)) that can be used with the electrode. Here’s a brief rundown of each electrode typically found in this application (courtesy of Hobart Brothers):
- 6010: All position electrode only suitable with DC power sources. It delivers deep penetration and has the ability to dig through rust, oil, paint and dirt. This electrode features an extremely tight arc, which can make it difficult for inexperienced welders. Excellent for penetration on joints with a tight fit-up.
- 6011: All position electrode for use with AC and DC power sources. It produces a deep, penetrating arc that cuts through corroded and unclean metals – ideal for maintenance and repair. Excellent for penetration on joints with a tight fit-up.
- 6013: All position electrode with a soft arc and minimal spatter, moderate penetration and easily removable slag. Suitable with AC or DC power sources, this electrode works best on newer and clean materials, thinner materials and wide root openings.
- 7018: All position electrode with a thick flux and high iron powder content, which makes it one of the easiest electrodes to use. These electrodes produce a smooth, quiet arc with minimal spatter and medium arc penetration. It produces strong welds with high impact properties (even in cold weather). You can use 7018 on carbon steel, high-carbon, low-alloy and high-strength steel base metals. Suitable with AC and DC power sources.
- 7024: For flat or horizontal welding with an AC or DC power source, this electrode contains a high iron powder content that helps increase deposition rates. Performs well on steel plate that is at least ¼-in. thick and can be used on metals that measure over ½ in.
Welding equipment selection
Selecting the right machine for stick welding is based largely on the diameter of electrodes used. A 1/8-in. electrode welds up to 145 amps, while a 5/32-in. electrode offers optimal performance at about 180 amps. Therefore, a welding generator with a 100 percent duty cycle at 250 amps offers enough welding power to meet most needs.
Contractor’s Note: For heavy-duty repairs and space savings on maintenance trucks, contractors should consider a combination welder/generator/air compressor. These machines not only feature welders and generators, but also include self-contained rotary screw air compressors for running air tools and plasma cutters. The Trailblazer 302 Air Pak, for instance, offers 26 CFM of air (up to 160 PSI) at 100 percent duty cycle. This machine also has a battery jump/charge option built in, to give field mechanics another tool to combat idle equipment.
Preparation of the weld joint
Once you’ve obtained the right filler metal alloy and welding machine, cut the steel to its required size and bevel the edges at a 30-degree angle for better welding penetration. For heavier sections of material experts recommend leaving a small face or “land” at the bottom of the joint. After beveling your edges, grind along the surface until the bottom portion is about the thickness of a nickel.
Cleanliness of the welding joint is critical. While some welding electrodes are more forgiving than others, it’s never wise to leave any contaminants behind. Operators must grind or wipe away all rust, oils, and paints prior to welding—failure to do so will lead to a failed or weakened weld.
Once the piece is in place, preheating the weld area may be necessary. Preheating minimizes shrinkage stresses and distortion; all of which might cause cracking when applying an extremely hot welding arc to cold steel. Preheating is typically required on all material thicknesses when the carbon content of mild steel exceeds .40 percent. Consult your material supplier for specific material/process requirements.
To preheat, an oxy-fuel torch outfitted with a special "rosebud" tip to widen the flame is recommended. Preheating temperatures vary based on the material to be welded. A temp stick (or heat crayon) can be used to gauge the temperature as it changes. Temp sticks come in various temperature values and, when applied to material being heated, will change color when the goal temperature is reached. Again, consult your material supplier for specific material/process requirements.
Stick welding recommendations
Bringing all these points together while welding may seem like a lot to think about, but it becomes second nature with practice. These tips are relevant whether you’re repairing a piece of equipment or working on another stick application.
The correct current, or amperage, setting primarily depends on the diameter and type of electrode selected. For example, a 1/8 in. 6010 electrode runs well from 75 to 125 amps, while a 5/32 in. 7018 electrode welds at currents up to 220 amps. The side of the electrode box usually indicates operating ranges. Select amperage based on the material’s thickness, welding position (about 15 percent less heat for vertical and overhead work compared to a flat weld) and observation of the finished weld. Most new welding machines have a permanent label that recommends amperage settings for a variety of electrodes and material thicknesses.
Length of arc
The correct arc length varies with each electrode and application. As a good starting point, arc length should not exceed the diameter of the metal portion (core) of the electrode. Holding the electrode too closely decreases welding voltage. This creates an erratic arc that may extinguish itself or cause the electrode to freeze to the material. Too short arc length also produces a weld bead with a high crown. Excessively long arcs (too much voltage) produce spatter, low deposition rates, undercuts and even porosity.
Many beginners weld with too long of an arc, so they produce rough beads with lots of spatter. Practice will show you that a tight, controlled arc length improves bead appearance, creates a narrower bead and minimizes spatter.
Angle of travel
Stick welding in the flat, horizontal and overhead position uses a “drag” or “backhand” welding technique. Hold the electrode perpendicular to the joint and tilt the top of the electrode in the direction of travel approximately 5 to 15 degrees. For welding vertical up, use a “push” or “forehand” technique and tilt the top of the electrode 15 degrees away from the direction of travel.
Each welder manipulates or weaves the electrode in a unique style. Develop your own style by observing others, practicing and creating a method that produces good results for you. Note that on material 1/4 in. and thinner, weaving the electrode typically creates a bead that is wider than necessary. In many instances, plain, straight-ahead travel works fine.
To create a wider bead on thicker material, manipulate the electrode from side to side creating a continuous series of partially overlapping circles, or in a “Z,” semi-circle or stutter-step pattern. Limit side-to-side motion to 2-1/2 times the diameter of the electrode core. To cover a wider area, make multiple passes or “stringer beads.”
When welding vertical up, focus on welding the sides of the joint and the middle will take care of itself. Pause slightly at the side to allow the weld puddle to catch up and ensure solid “tie-in” to the sidewall. If your weld looks like big fish scales, you moved forward too quickly and didn’t wait long enough on the sides.
The proper travel speed produces a weld bead with the desired contour (or “crown”), width and appearance. Adjust travel speed so that the arc stays within the leading one-third of the weld pool. Slow travel speeds produce a wide, convex bead. Excessively high travel speeds also decrease penetration, create a narrower and highly crowned bead.
Final advice for welding repairs
A few last words of advice. Always remember that you need a good view of the weld puddle. Otherwise, you can’t ensure you’re welding in the joint, keeping the arc on the leading edge of the puddle and using the right amount of heat (you can actually see a puddle with too much heat will roll out of the joint). For the best view, keep your head off to the side and out of the smoke.