Getting to Know Flux-core Wire

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.

sino welding contains other products and information you need, so please check it out.

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 Core Wire Uses, Types, and Characteristics

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.

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 Shielding Gases

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.

Equipment Requirements for Flux Core Wire

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.

Proper Technique

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.

Storage Requirements

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.

Are you interested in learning more about Flux Cored Wire Self-shielded? Contact us today to secure an expert consultation!

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.

Final Thoughts on Flux Core Wire

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.

By: Hobart Brothers

Self-shielded Flux Cored Arc Welding (FCAW) has proven itself a viable welding process for structural steel erection, heavy equipment repair, bridge construction, and ship and barge construction. It offers high deposition rates, a wide range of mechanical properties and good weldability among other desirable features and benefits.

That doesn&#;t mean, however, that it&#;s free of challenges and difficulties. This article examines common pitfalls encountered during the normal course of self-shielded FCA welding, along with trusted ways to correct them.

Wire Feed Problems: Birdnesting and Burnback 
Easily one of the most common problems with flux-cored arc welding, especially on construction sites, wire feed stoppages and malfunctions are more than just an annoying source of down time. Birdnesting and burnback can prematurely extinguish the welding arc and create irregularities that may weaken the weld bead.Birdnesting is a tangle of wire that halts the wire from being fed.

Often the result of incorrect drive roll tension, birdsnesting
(as seen here) can be a frustrating source of downtime.

Fix a bird&#;s nest by flipping up the drive roll and pulling the wire back out of the gun. Trim off the affected wire and re-thread it through the feeder and back to the gun. Incorrect drive rolls, tension settings, blockages in the liner, improperly trimmed liners (too short/burred/pinched) or the wrong liner (too small or large for the electrode diameter) are all sources of birdnesting.

FCAW wire is a tubular consumable and therefore is much softer then GMAW solid wire.  The correct drive rolls for FCAW wire are knurled V groove drive rolls.  With the correct drive roll, the correct tension must also be used.  Too much tension will flatten the wire and will not allow the wire to feed through the contact tip, causing a birdnest. To set the proper tension, a good technique is to start by releasing the tension on the drive rolls.  Increase the tension while feeding the wire into the palm of your welding glove and continue to increase the tension one half turn past wire slippage. Blockages in the liner can also cause birdnesting. Replace the liner if you find a blockage. Always trim the liner according to the manufacturers direction and be certain you are using the correct size liner for your electrode.

Burnback is the formation of a weld in the contact tip that occurs when the wire feed speed is too slow or if the gun is held too close to the workpiece. Correcting this problem is easy: increase wire feed speed and the distance of the gun from the workpiece (the contact tip should be no further than 1 1/4-in. from the metal). Also remember to replace the contact tip if burnback occurs.

Porosity and Wormtracking 
Porosity is a small pocket of gas caught in the weld metal that can appear at any specific point on the weld or along its full length. This discontinuity&#;whether internal or on the surface of the weld bead&#;significantly weakens the structural integrity of any weld.

A dirty workpiece also causes porosity. Clean the surface of the base metal toremove rust, grease, paint, coatings, oil, moisture and dirt prior to welding. You can also use filler wire with added deoxidizers to &#;clean&#; the weld.

This image shows a combination of porosity and worm tracking, 
both outcomes of too much voltage.

Additional causes of porosity include welding wire that extends too far from the contact tip (the wire should extend no more than 1 1/4-in. beyond the contact tip). Impurities in the base metal, such as sulfur and phosphorous in steel, can be a further cause or porosity, remedied by changing the base metal to a different composition (where specifications allow).

Worm tracking are marks on the surface of the weld bead that are caused from the gas that is created by the flux in the core of the wire. The gas causes worm tracking when there is excessive voltage for a given wire feed setting/amperage. To prevent worm tracking, use the manufactures recommended parameters for a given wire diameter.  If worm tracking does occur, reduce your voltage by increments of one half volt until the worm tracking is eliminated.

Slag Inclusions 
Slag is a naturally occurring part of flux-cored welding, caused when the molten flux from the core of the wire solidifies on top of the weld. Slag inclusions occur when the slag gets trapped inside of the weld metal, creating the potential for weakened weld components and reduced serviceability. These inclusions can be caused by incorrect weld bead placement, incorrect travel angle, low heat input, or poor interpass cleaning.

Weld bead placement is critical when making multiple passes on thick sections of metal, especially on the root passes of plug welds or wide v-groove openings. Careful consideration must be paid to providing sufficient space in the weld joint for additional passes, particularly on root joints requiring multiple passes.The travel angle of self-shielded FCA welding can also cause slag inclusions. In general, if slag inclusions are caused by incorrect travel angle, you should increase your drag angle.

In the flat, horizontal, and overhead positions your drag angle should be between 15 and 45 degrees.  In the vertical up position, your drag angle should be between 5 and 15 degrees. To low of welding heat input may also cause slag inclusions. Always use the manufactures recommended parameters for a given wire diameter. If slag inclusions still occur, increase the voltage until the inclusions cease.

Undercutting and Incomplete Fusion
Undercutting occurs when a groove melts in the base metal next to the toe of the weld and is not adequately filled by the weld metal. This discontinuity creates a weaker area at the toe of the weld and could cause cracking. To correct this problem, reduce the welding current, decrease the welding arc voltage and adjust your electrode angle as needed. Reduce travel speed so that the weld metal completely fills the melted-out areas of the base metal and/or pause at each side of the weld bead when using a weaving technique.

In addition to increasing the current and slowing travel speeds, 
a beveled joint can greatly reduce the chance of incomplete 
penetration.

Incomplete fusion (or lack of fusion) is the failure of the weld metal to fuse completely with the base metal or the preceding weld bead in multi-pass applications. Incorrect electrode/work angles that cause the weld metal to get ahead of the arc can be the culprit and should be adjusted accordingly. For proper welding angles follow these steps: To prevent incomplete fusion, place the stringer bead in its proper location at the joint, adjusting the work angle or widening the groove to access the bottom during welding. Keep the arc on the trailing edge of the welding puddle and remember to use a correct gun angle drag of 15 to 45 degrees. If using a weaving technique, momentarily hold the arc on the groove sidewalls when welding.

If correcting the electrode/work angle does not remedy the problem, check to see if the electrode is getting ahead of the welding puddle. Simple adjustments, such as increasing travel speed or using a higher welding current, will correct the problem.

A dirty workpiece could also be the cause of the problem. Always clean  the surface of the base metal prior to welding to remove contaminants. If you suspect insufficient heat input could be contributing to incomplete fusion, select a higher voltage range and/or adjusting the wire feed speed as necessary.

Excessive Penetration / Lack of Penetration 
Excessive penetration occurs when the weld metal melts through the base metal and hangs underneath the weld; it is often caused by excessive heat input. To correct the problem, select a lower voltage range, reduce wire feed speed and increase travel speed.

Lack of penetration is the shallow fusion between the weld metal and the base metal. An obvious cause (and exact opposite of excessive penetration) is insufficient heat input. Selecting a higher wire feed speed, a higher voltage range and/or reducing travel speed are viable remedies. Lack of penetration can also be caused by improper joint preparation and/or from the material being too thick. Joint preparation and design must permit access to the bottom of the groove, while also allowing you to maintain proper welding wire extension and arc characteristics.

Final Considerations 
Quality self-shielded FCA welds are the result of good welding technique, the proper choice of parameters and the welder&#;s ability to identify a problem quickly and rectify it. Armed with some basic information, you can aggressively tackle the most common problems associated with self-shielded FCA welding without sacrificing time or quality.

Want more information on Cast Iron Stick Electrodes? Feel free to contact us.