Factors to Consider When Choosing a Tubular Electrode
When choosing a tubular electrode - whether flux-cored or metal cored - the objective is the same as with any application: 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 over solid wire.
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In order to choose the best tubular electrode, users need to consider some of the basic factors relevant to any welding application.
Base Metal
Users first need to bear in mind the type of base metal being welded, including the base metal chemistry and strength. In many cases, the choices for a tubular electrode will be quickly narrowed down due to the chemical composition of the base metal; there are simply fewer options, for example, when welding on many of the low alloy steels.
In addition to the base metal, users will need to consider the service conditions of the weldment. Specifically, they will need to determine whether low temperature impacts are required, whether a color match is necessary and/or if there are other specifications that could limit filler metal options. A resource such as “Prequalified Base Metal-Filler Metal Combinations for Matching Strength,” can help identify the compatibility or “weldability” of pre-qualified base metals in regard to their corresponding filler metals.
It is also recommended that users discuss their selection with a supplier or manufacturer of tubular electrodes in order to make an informed choice.
Users then have to consider the general surface condition of the base metal itself. If the base metals surface contains mill scale, rust, cutting fluid or has been primed, users can choose to invest the time necessary for pre-cleaning the base metal through grinding or other physical means. However, doing so naturally incurs additional labor costs and decreases productivity. The other option is to use a tubular electrode formulated with added deoxidizers that can efficiently weld through rust and other surface conditions without sacrificing quality. Tubular electrodes with high levels of deoxidizers are manufactured in both “flux cored” and “metal cored” wires. The “metal cored” versions eliminate a slag deposit and also have lower fume generation, a feature that also makes them a great alternative to flux cored and solid wires when encountering poor base metal surface conditions.
The decision between these options is not an easy one and may require a trade off on the users’ part. While using a metal cored wire with added deoxiders can reduce the cost of labor for pre-cleaning, these wires are designed primarily for flat and horizontal position welding and have specific gas mixture requirements compared to a solid wire. Users will therefore have to determine if their applications and gas availability fit within these welding parameters before choosing a specific metal cored wire.
Gas
Similar to base metals, the tubular electrode a user chooses can be narrowed down quickly based on the gas available. If a weld shop or company only has a bulk CO2 delivery system, operators will be limited to using a flux cored wire specified for use with CO2 and one that will provide the desired weld properties within the parameters of that gas—a choice that depends largely on the application at hand. Speaking to a welding supply distributor can help narrow down the flux cored wire for use with CO2.
Even in combination with a flux cored wire, there can be drawbacks to using CO2 as the shielding gas. While CO2 is inexpensive, it can create spatter that may lead to operator discomfort and it also requires additional post-weld cleanup. Even so, a flux cored wire designed for use with CO2 can create quality welds and improve productivity by increasing travel speeds and reducing rework.
The decision to maintain CO2 as the primary shielding gas for an application will entirely depend on whether companies want to invest the time for post-weld cleanup and whether the spatter has become a major discomfort to the operators.
If the labor cost for post-weld cleanup is a factor, using an Argon/CO2 mixture in combination with a tubular electrode may be a viable alternative. This mixture creates the same quality of welds as with straight CO2, but many operators find that (in combination with the right wire) Argon/CO2 provides a more stable arc and a weld puddle that is slightly easier to maneuver.
It is important to mention that most metal cored wires specifically require the use of a Argon/CO2 mixture of shielding gas and users will need to have a bulk gas delivery system in place to supply these gases. Still, in most applications these wires have a better penetration profile and produce less spatter than solid wire when used with the same gas mixture. Additionally, metal cored wires do not have the slag covering customary to flux cored wires and can further reduce post-weld cleanup time and labor costs.
Argon, however, is more expensive than CO2 and users will have to weigh out the price of this gas. Or more precisely, they will have to determine whether the cost of Argon will significantly reduce the amount of post-weld cleanup and labor costs. They may find that the additional money spent on gas is worth the investment, paying for itself in time saved and increased operator comfort.
As a note: there are also flux cored wires that do not require the use of shielding gas. These “self-shielded” wires produce their own shielding gas in the same manner as stick electrodes. Also like stick electrodes, these wires are noted as producing higher spatter and fume levels. Because they do not need an external shielding gas, these wires are more suited to welding outdoors where an external shielding gas would be more easily affected by wind.
Weld Size and Joint Requirements
The joint position and weld size requirements will cause users to consider what tubular electrode would work bestwithin the said welding conditions. For example, using an all-position wire on applications that only require 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 provide increased performance and cost savings by improving wetting action and deposition rates. Metal cored wires are generally limited to flat and horizontal welding, but have lower fume levels and no slag deposit, which yields less clean up between weld passes and greater operator comfort. For out-of-position welding, all-position flux cored wires will out perform metal cored and solid wire in terms of deposition rate and penetration profiles in applications that are suited to the characteristics of the flux cored wires.
Similarly, choosing an appropriate diameter tubular electrode can have a significant impact on the overall performance, efficiency and cost of a welding application. To maximize such wire use on fillet welds, for example, users may want to use the largest possible wire size to achieve the greatest deposition rate and travel speed possible. On multiple pass welds it may also be possible to reduce the number of passes required to fill the joint. However, even if the number of passes are not 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. Further, a larger diameter wire will cost the user slightly less per pound.
Conclusion
In the end, choosing an appropriate tubular electrode can - from a majority of considerations - reduce the cost of labor and minimize operator discomfort. It can also increase production substantially, but it may not be the right choice for all users or all applications. Ultimately, it’s a matter of preference and resources as to whether it is suitable to use an existing base metal without preparation in combination with a tubular electrode or to invest the time and expense for pre-cleaning. In the same consideration, a company’s decision to use CO2 or Argon in the shop is a matter of individual choice and each has its own benefits and downfalls. If, however, it is found that all factors in a welding application lend themselves to the use of tubular electrodes as opposed to solid wires, it’s important to know that there are always options. And those options, despite a higher initial investment, could be more cost effective in the long run.