[vc_row][vc_column][vc_column_text]By Peter Middleton,
Editor, African Fusion
(Editor’s note: Article previously published in African Fusion, November 2007)
“Flux-cored welding is not a new process. It has been around for several decades now,” says Richard Fowles. “The main motivation for flux-cored welding was to get the benefits of flux from the stick welding process coupled with the productivity of continuous wire processes,” he adds. “To that end, it has been well proven and well documented that flux-cored wire
can weld at least four times faster than SMAW/MMAW in terms of arc hours.
productivity advantages of using flux-cored wires for the 6G-positional welding
of pipe at the SAIW Technology Centre open day (Richard is now a welding
engineer at the SAIW).
” Fowles continues: “We have also proved that flux-cored wire is three times faster than solid wire for positional welding. When welding in position using the GMAW process and solid wire, the dip transfer or CO2 process is usually used to lower the heat input and keep the weld pool under control.”
“People seem unwilling to do the basic business calculation, that is to say; what is the actual cost per kilogram of weld metal that I am putting down, based on actual welding speeds that can be obtained with the different processes? So far they have realised that solid wire is faster than stick but a lot of people haven’t yet made the step from solid wire to flux-cored wire,” he exclaims. “If your flux-cored wire is priced right on the market, you can find that your labour input cost per kilogram can be halved as compared to solid wire. This is purely due to the deposition rate in kg/hour. For positional welding with flux-cored wires, your arc-time is slashed,” he tells us.
So what is in the way of the widespread use of flux-cored wires in South Africa? Fowles highlights three possibilities.
“The first thing that is counted against flux-cored wire is the amount of fume generated and that the welder is exposed to,” begins Fowles. “Fume generation rates are far higher than with solid wire and because of the continuous arc, there are also more fumes compared to SMAW.” He points towards very high arc intensities and the continuous nature of the process as reasons for this. The fumes from the flux-cored process, while no more harmful than SMAW fume, are denser because of the higher duty cycles of the process. “This is easily counteracted though, by proper training of welders about how to avoid fumes and the proper use of fume extractors,” he adds.
A second issue inhibiting the process, says Fowles, is labour resistance: “Welders paid by the hour will get through the work more quickly. By welding four times faster, the job gets finished quicker and, welders argue, they earn four times less.”
Thirdly, he identifies a lack of training in flux-cored welding: “When changing from solid wire to flux-cored wire you need a slight change of technique. You need to pull the wire instead of pushing it,” he explains. “The reason for this is that you don’t want to wash the slag into the arc. A lot of people, convinced of the benefits of moving to flux-cored wires, have failed to coach their welders in the technique changes. They end up getting slag inclusions and a lot of rejects because their welders are not properly coached. Then the process is thrown out of the window and it is impossible to get it back,” says Fowles.
We ask about flux-cored weld quality: “If the welds are done properly with flux-cored wire, in the end, you get cleaner weld metal and better mechanical properties because of the cleaning action of the flux additions. You also get better weld bead shapes because of the holding action of the slag.”
“Some flux-cored wires, such as low alloy steels, can actually be made cheaper than solid wire because you don’t need to ask the steel mill to make special billets. You can make up the alloy with flux additions,” Fowles tells us when asked about controlling weld metal composition.
We start to talk about self-shielded wires and the use of gas-assisted flux-cored welding for on-site construction: “There is a demand for self-shielded wire for on-site welding, but it’s only useful in the field. If you are in a workshop “If people have to increase productivity but they can’t because of a gas problem then self-shielded wires will be the natural way to go. This is going to happen.”
wire. A tent has been erected around the tank scaffolding to protect the arcs-hielding
from the wind.
For on-site pipe-line welding in South Africa though, Fowles tells us that gas-assisted flux-cored welding can significantly improve productivity levels. “If you couple gas assisted flux-cored wires with automation, then you are much less reliant on welders. You can reduce your number of welders on a job by half”. Portable Weldycar or Buggo systems enable automatic welding by allowing a torch manipulator to be connected to a pipe using magnets or a track.
We ask him about the wind problem, so often used against the gas shielded welding processes: “In the USA, Europe, and South America, all they do is construct a tent to keep the draught out,” The tent can easily be moved along the site from joint to joint, he tells us. He shows us a photo of a large tank being welded using a Weldycar motion system. Welding is taking place on scaffolding, five stories high. The draught is eliminated by wrapping plastic sheeting around the outside of the scaffolding. “Just eliminate the draught,” he advises.
Fowles tells us that DCD-Dorbyl is a good example of a fabricator that has made the successful shift to flux-cored wires. “They are typically welding material 75mm thick or more at their factory, constructing things like drag line bases. They are using seamless copper-coated wires because of the lower hydrogen values associated with these.” He tells us that these wires are guaranteed to produce less than four milliliters of hydrogen per 100 grams of weld metal or half that of a traditional seamed flux-cored wire.
Some advice from the Miller Electric company, however, may be worth noting “The most important thing to remember is not to fall into the ‘one-size-fits-all’ mindset. Solid wire, self-shielded flux-cored wire and gas shielded flux-cored wire all work well provided they are applied correctly.”[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_empty_space][/vc_column][/vc_row][vc_row][vc_column][vc_btn title=”Printer friendly version” link=”url:https%3A%2F%2Fwww.saisc.co.za%2Fwp-content%2Fuploads%2F2008%2F04%2FMag-Apr08-p35-TechFluxCoredWelding.pdf|||”][/vc_column][/vc_row]
