African Fusion

With the worldwide introduction of its innovative laser-sealed cored wires during Schweissen & Schneiden 2017 in Germany, filler metal specialist Böhler Welding marked a new milestone in the evolution of the metal-cored arc welding process.

For the first time on an industrial scale, Böhler Welding has started using laser technology to hermetically seal cored wires produced from strip. This enables a new welding consumable to be produced that combines the exclusive advantages of both folded and seamless tubular cored wires.

Böhler Welding is dedicating a new fabrication facility to the production of its Diamondspark L-Line (laser line) of ultra-low hydrogen metal-cored wires for applications with stringent requirements on productivity, safety and weld quality, such as the robotic welding of high-strength steel. Moreover – now with in-house expertise in three different cored wire fabrication technologies – Böhler Welding has the option of selecting the best production route for specific consumable applications in the field, rather than a limited offering of run-of-the-mill products.

One manufacturer – three fabrication technologies

The availability of three different fabrication technologies – folded, tubular seamless and laser-sealed seamless wires – enables Böhler Welding to tune cored wire properties precisely to the intended application field.

Bohler Diamondspark Laser sealed FC wireFolded cored wires are produced by filling a U-folded strip with dry minerals, closing it to a round cross section and drawing down it to its final diameter. These can have a butt or overlap seam. The strips are relatively thin, so there is a lot room inside of the folded cored wire for minerals and alloying elements.

The melt-off rate of the thin, current conducting tube is high, as it generates a lot of resistance heating at a given welding current (I2R-effect). This translates into high weld deposition rates. A major disadvantage, however, is the seam running along the length of the wire, which is not airtight and it can, in time, pick up moisture. On welding, this translates into the inclusion of unwanted hydrogen in the weld metal, which is a potential hydrogen cracking risk.

For the same reason, folded cored wires cannot be copper-coated, as liquid from the copper bath would leak through the seam into the mineral core. Also, folded cored wires need a special surface treatment to improve wire feeding properties and current transfer between the contact tip and wire, but these can never fully reach the consistent quality level of copper-coated wires.

Folded flux- and metal-cored wires are ideal for high deposition rate mechanised welding of unalloyed steel in the PA or PB position. All-positional rutile flux and metal-cored wires are available for manual and mechanised/robotic welding of stainless steel, nickel-base alloys and for hard facing and corrosion resistant alloy (CRA) cladding.

These wires are used for welding applications such as: construction equipment fabrication; offshore constructions and pipelines; petro-chemical process equipment; process equipment in the pulp, paper and food industries; automotive exhaust systems and hydro turbines.

Tubular seamless cored wires are produced by vibration filling of a dry powder mix into a resistance-welded tube, before drawing the tube down to its final diameter. Since the tubes have a slightly thicker wall than folded strip, less room is available for minerals and alloying elements. The melt-off rate of the slightly thicker tube wall is a little lower as a result of the lower resistance heating in the current conducting tube and, therefore, the weld deposit rate is lower. The overriding advantage, however, is that there is no seam running along the wire length and, therefore, the seamless cored wire is absolutely air and moisture tight. Weld metal hydrogen is very low; guaranteed in EN class H5 and AWS class H4.

Furthermore, there is no problem passing the seamless cored wire through a copper bath to copper-coat the wire in order to optimise wire feeding properties, current transfer and contact tip wear.

All-positional seamless rutile-cored wires are available for manual and mechanised welding of unalloyed and low-alloyed steel grades covering: normal strength steel; high strength steel; low-temperature steel; creep and weather resistant steels.

Basic cored wires for welding creep resistant steels in the PA, PB or PC position are available, along with the premium UTP AF ROBOTIC seamless tubular copper-coated wires and a comprehensive range low and medium alloyed wires for maintenance and repair use.

As well as for FCAW, seamless cored wires are also be successfully used for submerged arc welding.

Typical applications include: building and civil construction, shipbuilding, offshore construction, pressure vessels, pipelines and wind towers.

Laser-sealed seamless cored wires from Böhler Welding are truly state-of-the-art. By using a laser seam welder to hermetically seal a folded cored wire before drawing it to its final diameter, Böhler Welding combines the advantages of both the folded and seamless cored wire fabrication technologies into a single product. The laser-sealing technology allows strips to be used with a thickness between those of folded and seamless tubular types and the resultant wire products feature medium to high filling volumes.

Laser-sealed cored wires are absolutely air and moisture tight and are copper-coated. Vacuum annealing is applied as an extra step in fabrication to ensure ultra-low-hydrogen weld metal – at the typical level of solid wire (~1.0 ml H2/100 g of deposited weld metal).

Because Böhler Welding has invested in setting up completely new, state-of-the-art fabrication lines, all employing modern production technologies, the seamless laser-sealed cored wires truly represent the future of high-tech welding consumables.

Laser-sealed all-positional metal-cored wires are ideal for robotic welding of normal strength, high strength and ultra-high strength steels for critical applications including: cranes and other lifting equipment, lightweight truck trailers, concrete pumps, railway bogies and lorries, automotive plants and wind towers.

The availability of three different cored wire fabrication technologies – folded, tubular seamless and laser-sealed seamless – allows Böhler Welding to select the optimal fabrication technology for the intended application. Table 1 outlines the specific advantages and limitations of the three technologies.

Diamondspark: a world-class range

The Diamondspark sub-brand has been given to the full range of seamless, copper-coated cored wires produced by Böhler Welding to underline the company’s leading role in this area and to emphasise the quality levels of its products. The fabrication method – T‑line for seamless cored wires and L-line for laser-sealed seamless wires – has been attached to the Diamondspark brand in its product brochures, certificates and labelling.

The Diamondspark T-line tubular seamless cored wire range has over 40 mainly all-positional rutile and basic flux-cored wires with excellent weldability. The rutile fast freezing slag system provides high welding productivity in positional welding and weld metal hydrogen produced if using these wires is within EN class H5 and AWS class H4.

The Diamondspark L-line includes a growing range of laser-sealed metal-cored wires with superb characteristics for high duty cycle robot welding. Weld metal hydrogen is at the level of solid wires (~1 ml/100 g WM) for absolute safety in hydrogen-critical applications, such as the welding of high and ultra-high strength steel.

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