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In an increasingly competitive environment, some contractors in the structural steel industry are converting from stick welding (SMAW) to self-shielded flux-cored welding (FCAW) as one way to improve productivity and to reduce costs. Stick welding has traditionally been the process used on jobsites for major infrastructure jobs, as it is a familiar process to many welding operators, it offers mobility since shielding gas cylinders and a wire feeder are not required.
In recent years, significant technology advancements in both equipment and filler metals have made the self-shielded FCAW process a more viable option for contractors ' one that offers higher productivity, and can save time and money in labor. Self-shielded FCAW wires are now formulated to be easier to use and to provide better weld quality than ever before, making them more appealing to many contractors. While self-shielded FCAW is a faster process that can offer a competitive edge, to get the best results it is important to understand the characteristics of the most commonly used wires for construction applications, as well as proper welding techniques, in order to get the best results.
Common wire classifications
Technology advancements have resulted in self-shielded FCAW wires with improved mechanical properties and welding performance, including better weld pool and arc control, on top of the productivity gains provided by this continuous welding process.
The two most common types of self-shielded flux-cored wires used by contractors for welding in construction applications are those meeting American Welding Society (AWS) E71T-11 and AWS E71T-8 classifications. These wires ' also known as T-11 and T-8 ' are versatile options for structural applications, and are both suited for all-position, general purpose welding.
Choosing the proper equipment when using either type of wire is key. Both the T-8 and T-11 wires should be used with a constant voltage (CV) power source, rather than a constant current (CC) power source. The power received from a CC power source fluctuates too much when using these wires, and can cause inconsistent quality and weld defects such as porosity. Conversely, a CV power source provides the constant voltage needed for smooth arc performance and is particularly adept at adjusting for 'dirty power' on jobsites ' high and low spikes in power generated when multiple loads (like compressors and power sources) are on the same line.
T-8 and T-11 wires should both be operated on DCEN (direct current electrode negative) or straight polarity, which is opposite of most wire filler metals. It is important to note that using the incorrect polarity can result in poor welding performance, including increased spatter levels. In addition to these equipment considerations, suitcase wire feeders ' rugged suitcase-like feeders that encase and protect the wire ' are often used with these wires to improve portability on the jobsite.
Characteristics of T-11 wires
Wires classified as AWS E71T-11 are generally considered easy-to-use and provide a wide parameter window that is forgiving to technique errors, which is particularly helpful for welding operators who are newer to the self-shielded FCAW process.
Contractors should keep in mind that T-11 wires offer no toughness properties, (and they are not required to in order to meet the AWS E71T-11 classification) so they are not as resistant to cracking as something like a T-8 product. As a result these wires are not used for critical welding, however AWS D1.1 Structural Welding Code for Steel does allow the use of T-11 wires for welding on materials less than 1/2 inch thick. They are most commonly used on a construction site for small stitch welds or tack welds.
The typical parameter range when using T-11 wires is between 17 to 22 volts and 50 to 275 amps, depending on wire diameter. If the application allows, using larger wire diameters can provide greater deposition rates for improved productivity. Filler metal manufacturers generally offer these wires in 0.035-inch diameters all the way up to 5/64-inch diameters. During the welding process, T-11 wires require a technique similar to the one used for gas-shielded FCAW wires. A 1/2- to 3/4-inch stickout (again depending on wire diameter) and 10 to 20 degree drag angle will help minimize the risk of slag inclusions and offer the best joint penetration.
This image, depicting a vertical up fillerCharacteristics of T-8 wires
In contrast to T-11 wires, T-8 wires offer very good toughness with no thickness restrictions. Wires under the AWS E71T-8 classification must meet a toughness requirement of 20 foot-pounds at -20 degrees Fahrenheit. For the classification E71T-8 J, the additional 'J' designator indicates that the wire offers increased toughness properties of 20 foot pounds at -40 degrees Fahrenheit, for lower temperature impact strengths.
T-8 wires are often approved for Demand Critical Welds like those that must follow requirements of AWS D1.8/D1.8M Structural Welding Code ' Seismic Supplement. There are two different ways to qualify filler metals to be used for seismic applications under AWSD1.8: qualified to the 'D' designator or qualified to Annex A. If a filler metal is qualified using the 'D' designator there is a 'D' included in the AWS classification, as in the example E71T-8JD H8. When a wire is qualified to Annex A, it can be used for D1.8 applications, but there is simply no 'D' designator in the AWS classification. Annex A allows for more deviation from set parameters for the testing that filler metal manufacturers must complete, but wire qualified to this standard is still approved for use under AWS D1.8. Contractors can feel certain that both classifications of wires will provide the appropriate mechanical and chemical properties, specifically toughness, for the job.
T-8 wires can be more difficult to use than T-11 wires and are less forgiving to technique errors. The T-8 wires produce a very heavy slag that can interfere with the welding arc, which can prevent the weld bead from wetting out properly.
Following a drag technique with the appropriate travel speeds to tie in the weld at the toes is important. For the best results when welding with T-8 wires, the stickout should be longer than with T-11 wires ' 1 inch to 1-1/4 inch ' depending on wire diameter. The general rule is that a larger diameter wire will require a longer stickout. Contractors should note, however, that the smallest available diameter of T-8 wires usually available is 1/16-inch. This is because T-8 wires have a higher fill percentage (the percentage of the wire cross section that is powder), making it more difficult for manufactures to draw the wire down to a smaller size.
The recommended parameter range for T-8 wires is 18 to 23 volts and 200 to 275amps for all-position welding for the range of available diameters.
Storage requirements
As with any filler metals, it is imperative to prevent against moisture pickup when using either T-8 or T-11 wires. With self-shielded FCAW wires like these, moisture can potentially lead to worm tracking in the weld bead, which is a discontinuity similar to porosity. It forms under the slag on top of the weld bead. Properly storing filler metal packages in a dry, enclosed environment ' while keeping the wire in its original packaging ' can help prevent moisture pick-up. Ideally, the storage temperature should be between 40 degrees and 120 degrees Fahrenheit, with a maximum humidity of 80 percent.
Realize advantages with proper training
To get the best results from self-shielded FCAW wires and to meet the appropriate welding code(s), welding operator training and proper certification is essential. It's also important to have a solid understanding of the characteristics and operating requirements of the T-8 or T-11 wires being used in order to weld successfully with them.By taking the proper steps and precautions, contractors can realize many productivity advantages from these wires and ensure that quality requirements of critical structural applications continue to be met.
Flux-Cored Wires for Welding High-Temperature and High-Strength Applications
Solid Wire Versus Flux-Cored Wire: When to Use Them and Why
No single filler metal is suitable for every job. The mechanical and chemical properties of the base material, the required welding position, the available equipment, and the welding operator's skill set, among other considerations, all factor in making the best selection.
When you are seeking to increase productivity through higher deposition rates, flux-cored wires often are a viable option. These wires are known for high performance and weld quality in industries ranging from general fabrication and manufacturing to construction, offshore, and shipbuilding.
Flux-cored wires have unique welding characteristics and requirements, advantages, and limitations. Knowing these can help you determine whether they are the right choice.
Flux-cored wire comes in self-shielded and gas-shielded varieties, some of which are designated for all-position welding (for example, American Welding Society [AWS] E71T-1C), or for flat and horizontal applications (E70T-1C). Both types are gas-shielded and produce a slag that helps protect the liquid weld metal during cooling, but this slag must be removed after welding and between passes.
Contact us to discuss your requirements of Flux Cored Wire Self-shielded. Our experienced sales team can help you identify the options that best suit your needs.
These wires are available for various base materials, including mild steel, low-alloy steel, stainless steel, and nickel alloys. For steel welding, they are available in tensile strengths of 70 KSI for mild steel, as well as 80 to 120 KSI and higher for welding high-strength, low-alloy steel.
Self-shielded flux-cored wires (FCAW-S) produce their own shielding gas when the arc initiates, eliminating the need for an external gas cylinder and making them suitable for use in portable and remote applications. These wires tend to produce slightly higher levels of smoke and spatter than gas-shielded flux-cored wires, but many classifications offer good impact toughness, even at lower temperatures.
Self-shielded flux-cored wires are often employed in lieu of shielded metal arc welding (SMAW) electrodes as a means to increase productivity since they are continuously fed and don't require repeated downtime for changeover. They are generally available in diameters from 0.035 to 7/64 in.
Gas-shielded flux-cored wires (FCAW-G) require an external shielding gas of either 100 percent CO2 or a blend of argon and CO2. They tend to have a higher operator appeal, meaning they are easier to control and to use to produce an aesthetically pleasing weld. They typically are used in a shop setting. When used outside, FCAW-G wires may require a barrier, either a tent or some other means to protect the weld pool, so that the shielding gas doesn't blow away.
Typically available in diameters from 0.035 to 7/64in., these wires can be used instead of solid wires to enhance productivity through higher deposition rates; welding operators can add more weld metal to a joint in less time, especially in out-of-position applications.
Pound for pound, FCAW-G wires typically are less expensive than FCAW-S varieties, which contain additional core materials and alloying elements, but do not require the additional expense for the shielding gas. FCAW-S wires also have a lower efficiency, about 65 percent compared to FCAW-G, which have 75 to 85 percent efficiency. These efficiencies also are lower than solid wires', because a portion of the wire is lost in the slag-forming agents that are discarded during the welding process. These factors should be considered when choosing a welding process.
Both types of wires are classified by usability designators defined by AWS'a number from 1 to 14 or the letter G or GS, which indicates the wire's polarity and operating characteristics.
FCAW-G wires have varying shielding gas requirements, and each type provides specific characteristics. Wires with a "C" designation in their AWS classification ' for example, E70T-1C H8 ' operate with only CO2. Those with a "M" designation, such as E71T-1M, require a shielding gas mix of CO2 and argon, usually a 75/25 percent balance.
Some wires are considered dual-gas and have a "C/M" designations that allows them to be used with both types of gases.
Care should be taken when considering a shielding gas change. While the wire may operate with either shielding gas, altering the gas is considered an essential variable change that can require new welding procedures and testing before use.
Wires operating with 100 percent CO2 offer more weld penetration, but also tend to create more spatter, whereas wires for mixed gases have reduced spatter and smoke, along with a smoother bead appearance. Once again, it is worthwhile to weigh out cost when choosing between the two types of classifications and shielding gases. CO2 is less expensive, but will likely generate a weld that requires more time and labor to remove spatter. Conversely, mixed gases are more expensive, but the welds need less cleaning after completion.
Gaining the best results from flux-cored wires is as much a matter of selecting the right wire for the job as it is having the proper equipment and training to weld with them. Both FCAW-S and FCAW-G operate with a standard constant-voltage (CV) power source set for straight polarity (direct-current electrode negative, or DCEN) or reverse polarity (direct-current electrode positive, or DCEP), depending on the wire formulation.
A common mistake made when setting up equipment to operate FCAW-S is selecting the wrong polarity on the welding power supply. While many wire welding processes operate using DCEP, the majority of FCAW-S wires are designed to operate on DCEN. Always consult the filler metal manufacturer's recommendations for operation.
FCAW-S wires often are paired with a voltage-sensing wire feeder. The welder can set the voltage at the power source but then control the wire feed speed (and therefore amperage) at the feeder. This feature is helpful on large job sites; fewer trips to the power source allows for more welding time. In the event that the welder varies the contact-tip-to-work distance (CTWD), voltage-sensing wire feeders also can help regulate the subsequent voltage variations.
Both wire types require V-knurled drive rolls in the wire feeder to provide smooth wire feeding and consistent weld quality. Flux-cored wire is softer than solid wire and can easily be deformed or crushed if incorrect drive rolls are used.
During the welding process, welders should employ a drag technique. A good drag angle for flat, horizontal, and overhead positions is between 15 and 45 degrees. For vertical-up welds, a gun angle of 5 to 15 degrees works well. A steady and fast enough travel speed keeps the weld pool from getting ahead of the arc, which could lead to slag inclusions.
Welders using flux-cored wires should be sure to use the correct stick-out or electrode extension; self-shielded wires are particularly sensitive to this variable. Depending on the wire diameter and type, the manufacturer-recommended stick-out could exceed 2 in.; check the requirements for each wire.
Improper stick-out can cause issues such as burnback, worm tracking, incomplete slag coverage, and difficult slag removal. Stick-out also is crucial because it provides a level of resistive wire heating, which helps increase the deposition rate. The increase in resistance allows less current to pass through the arc, permitting higher wire feed speeds to be used, and thus increasing the deposition rate.
As with any filler metal, it's important to store FCAW-G and FCAW-S wires in a clean, dry area. Damage from moisture or other contaminants can lead to poor weld quality and likely void the product warranty.
It's a good idea to maintain the same temperature in the storage area as in the welding area. Moving wires from a cold storage room to a warmer weld cell may cause condensation to form on the wires. This condensation can cause the wire to rust and potentially cause porosity and wire feeding problems. If maintaining the same temperature in both spaces is not feasible, allow the wire to acclimate to the temperature of the weld cell for 24 hours before welding.
It also is important to keep the wires in their original vacuum- or hermetically sealed packages until ready for use. For wire already in use, take precaution to remove the spool from the wire feeder, place it in a plastic bag, and store it properly. Remember to remove any wire still inside of the gun if that equipment won't be used for a long period of time. Flux-cored wires, especially in humid climates, can rust inside the gun, requiring the removal and replacement of the entire welding gun liner.
Training is key when using any type of filler metal. Welders new to using flux-cored wires may need additional training and/or certifications for their particular application, for example, converting from an SMAW electrode to an FCAW-S wire for a structural application.
Another example would be converting from an FCAW-G wire to an FCAW-S. While both wires are known as flux-cored, they are in different AWS classifications, and this change could potentially require additional testing and qualification.
Always follow the required work procedures and operating parameters for a given application and flux-cored wire. Combined, proper technique and operation can lead to better weld quality and productivity, while also reducing costly downtime.
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