Monday, August 24, 2015

6 Useful Tips for Preventing Flux Core Welding Problems (Part 1)

With some tips and practice, you can avoid flux core welding problems and improve your FCAW welds.

See also
6 Useful Tips for Preventing Flux Core Welding Problems (Part 2)

When it comes to structural steel erection, bridge construction, heavy equipment repair, and other same applications, FCAW (Self-Shielded Flux Cored Arc Welding) has been, for many years, a feasible welding process. Unsurprisingly, because it provides high deposition rates, fantastic mechanical and chemical properties and weldability needed for those jobs. Yet, there exist some challenges related to this process. With some tips and practice, you can avert the problems and create qualified welds you need.

In case you are interested in:
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Post Welding Operations to Ensure Productivity

1. How to avoid wire feed welding problems

Common problems at workshops are wire feed malfunctions and stoppages caused by a significant number of downtime. Bird-nesting and burn-back are 2 most notorious types of wire feed welding problems. Those types tend to prematurely extinguish the arc, inducing weld defects. 

Burn-back happens when the wire melts into the ball at the end of contact tip. Most often, it’s the consequence of too slow speed of wire feed or/ and the welding gun held too close to the work-piece. For this problem prevention, make sure you use the proper feed speed and keep a distance of no more than 1 ¼ inch from the contact tip to the work.

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To avoid bird-nesting  - a wire tangle halting the wire from being fed - when FCAW welding, use knurled U or V-groove drive rolls in the wire feeder. Comparatively with GMAW solid welding wire that employs smooth V-groove drive roll, the FCAW wire is far softer because of tube-shaped design. It can compress the wire if you use wrong drive roll.  

Also, setting the right drive roll tension can stave off the wire flattening and being tangled. In order to set the correct tension, start with releasing tension on drive rolls. Raise the tension whilst feeding the wire into the palm of welding glove and keep raising the tension one half turn to pass wire slippage.

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Bird-nesting also results from blockages in the liner, wrong liner used, or inappropriately trimmed liners. Quickly replace the liner if you find out a blockage when routinely inspecting your welding cables and gun. Also, always trim your liner (employing the correct tools) in line with the manufacturer’s recommendations. Make sure that there isn’t any sharp edges or burrs on the liner, and always apply the proper size liner for the diameter of welding wire.

2. How to prevent worm tracking and porosity

As typical weld discontinuities, worm tracking and porosity can weaken the weld integrity. 

Porosity occurs when gas is trapped in the weld metal, and can appear along its full length or at any particular point of the weld. For preventing porosity in welding, get rid of any grease, rust, oil, paint, coatings, dirt and moisture from the base metal before you weld. You can also use filler metals with added de-oxidizers to prevent contaminated welds. Still, those products can’t replace appropriate pre-cleaning. After that, maintain a proper electrode stick-out or extension. Generally, the wire shouldn’t extend more than 1 ¼ inch beyond contact tip.

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To avert worm tracking (also, marks on the weld bead’s surface as a consequence of gas created by the flux in the wire core), avoid immoderate voltage for the wire feed setting as well as amperage. For the best, follow the recommended parameters by the manufacturer of filler metal for the particular diameter of welding wire. In case worm tracking occurs, decrease your voltage by one half volt’s increments until you remove the problem.

3. How to remove slag inclusions

Slag inclusions eventuate when the slag produced by the molten flux in the wire core gets trapped inside the weld. Whatever causes of this problem, they can be averted with appropriate welding techniques.

First, prevent wrong placement of weld bead, especially when making many passes on the thick metal sections. Be sure to give adequate space in the weld joint for added passes, particularly, on the joints in need of multiple passes.

Second, keep up with correct travel speed and travel angle. From 15 to 450º should be the drag angle in the overhead, horizontal and flat positions. For vertical up position, the angle should be in range of 5 – 150º. In case there are slag inclusions at those angles, raise slightly the drag angle. Keep a steady travel speed. If you make too slow travel speed, slag inclusion due to weld puddle getting ahead of the arc will eventuate.

After that, maintain appropriate welding heat input, because too low heat input can be conductive to slag inclusions. Always apply the parameters recommended by the manufacturer for a certain wire diameter. In case slag inclusions still happen, raise the voltage until this problem stops.

Finally, make sure you thoroughly clean between the weld passes, taking away any slag using a wire brush, chipping hammer or grinding before you begin the next weld pass.

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