Consider both when choosing a tubular electrode
July 12, 2005
To choose the best tubular electrode, you should consider some basic factors relevant to any welding application: base metal, gas, weld size, and joint position requirements.
When choosing a tubular electrode—whether it's flux-cored or metal-cored—the objective is the same: Make the most of the wire while investing the least amount of time and labor.
And while any type of filler metal comprises only a small percentage of the total cost of welding, choosing the most appropriate tubular electrode can reap many benefits.
To choose the best tubular electrode, you should consider some basic factors relevant to any welding application: base metal, gas, and weld size and joint position requirements.
First, think about the type of base metal you're welding, specifically, its chemistry and strength. In many cases you can narrow down your tubular electrode choices on the basis of the base metal's chemical composition—for example, fewer options are available for welding many of the low-alloy steels.
In addition to the base metal, you should consider the weldment's service conditions. In particular, you'll need to determine whether the weldment requires low-temperature impacts, a color match, or other specifications that could limit filler metal options. A resource such as the "Prequalified Base Metal-Filler Metal Combinations for Matching Strength" section in theAmerican Welding Society (AWS) D1.1-2004 Structural Codecan help you identify the compatibility or weldability of prequalified base metals in regard to corresponding filler metals.
You also must take into account the base metal's general surface condition. If the base metal surface contains mill scale, rust, or cutting fluid, or if it has been primed, you can preclean the base metal physically by grinding it or use a tubular electrode formulated with added deoxidizers that can help you weld through surface conditions.
Choosing between these options isn't easy and may require a trade-off. While a metal-cored wire with added deoxidizers can help reduce the cost of labor for precleaning, these wires are designed primarily for flat- and horizontal-position welding and have specific gas mixture requirements. Before deciding to use a tubular electrode in this case, you'll need to determine if your applications and gas availability fit within these welding parameters before you choose a specific metal-cored wire.
Speaking of gas availability, you also can focus your tubular electrode selection based on the gas available. If your company has only a bulk CO2delivery system, you'll be limited to using a flux-cored wire that's designed for use with CO2and will provide the weld properties you want within the parameters of that gas—a choice that depends largely on your application.
Even in combination with a flux-cored wire, using CO2as a shielding gas can have drawbacks. While CO2is inexpensive, it can create spatter that may lead to operator discomfort and also may require additional postweld cleanup. On the other hand, a flux-cored wire designed for use with CO2can create quality welds and improve productivity by increasing travel speeds and reducing rework.
The decision to maintain CO2as the primary shielding gas for an application depends on whether your company wants to invest the time for postweld cleanup and whether spatter has become a major discomfort to the operators.
If the labor cost for postweld cleanup is a factor, an argon/CO2mixture in combination with a tubular electrode may be a viable alternative. This mixture can create the same weld quality as with 100 percent CO2, but in combination with the right wire, argon/CO2can help provide a stable arc and a more maneuverable weld puddle.
It's important to mention that most metal-cored wires specifically require an argon/CO2shielding gas mixture, and you'll need a bulk gas delivery system to supply these gases.
Another factor to be aware of is that argon is more expensive than CO2. You'll have to weigh the price of this gas; or more precisely, you'll need to determine whether the cost of argon will reduce the amount of postweld cleanup and labor costs significantly. You may find that the additional money spent on the argon is worth the investment, paying for itself in time saved and increased operator comfort.
As a note, flux-cored wires that don't require shielding gas are available. These self-shielded wires produce their own shielding gas the same way shielded metal arc welding (SMAW) electrodes do. Also, as with SMAW electrodes, these wires can produce more spatter and fumes. Because they don't need an external shielding gas that can be affected by wind, these wires are more suited to welding outdoors.
Joint position and weld size requirements will figure into which tubular electrode will work best. For example, using an all-position wire on applications that require only flat and horizontal welding can lead to a decrease in overall efficiency. Instead, selecting a tubular electrode specially formulated for use on flat and horizontal welds can help improve performance and save costs by improving wetting action and deposition rates.
Metal-cored wires generally are limited to flat and horizontal welding, but have lower fume levels and no slag deposit, reducing cleanup between weld passes and improving welder comfort. For out-of-position welding, all-position flux-cored wires can improve deposition rate and penetration profiles in applications suited to the characteristics of flux-cored wires.
Similarly, choosing an appropriate diameter size for your tubular electrode can affect the overall performance, efficiency, and cost of a welding application significantly. To maximize such wire use on fillet welds, for example, you may want to use the largest possible wire size to achieve the greatest deposition rate and travel speed possible. On multiple-pass welds, it also may be possible to reduce the number of passes required to fill the joint. However, even if the number of passes isn't reduced, the increased travel speed for each pass can lower the amount of labor required to fill the joint and, in turn, lower the overall cost to produce the weld.
Tim Hensley is product manager and Anthony Nikodym is business development manager, tubular division, of Hobart Brothers, 400 Trade Square East, Troy, OH 45373, 937-332-4000,www.hobartbrothers.com.