TPi July 2016

Pipe welding

High power welding of downpipes Information supplied by Jana Müller, Kjellberg Vertrieb GmbH

need to have high toughness and bending strength. These properties are not only required on the construction site: the seams have to prove their quality in the factory. After welding, each downpipe is expanded at one end by up to 2mm, creating a sleeve that is used later on the construction site as a connecting element. If the seam quality is insufficient, the seam will tear during expansion. Other pipes are further processed into pipe elbows. For this purpose, they are bent up to an angle of 85°, and after cutting to length are also equipped with a sleeve. Despite the double load on the seam – bending and stretching – there is a greater danger of tearing during the expansion of the sleeve, according to Mr Hanke. What is done in the factory with even force by a mechanical pipe expander, requires the plumber’s skill when processing leftover pieces on the construction site. The lower the temperatures, the more susceptible to cracking the weld seams are. To prevent this from happening, Kjellberg carried out a detailed process analysis, and together with Umicore identified the optimum welding parameters for the InFocus process. The general conditions for the welding process are given by the three existing production lines. Regardless of the welding process, the production lines could produce at a maximum throughput speed of 7.5m of pipe per minute. While welding with InFocus, this speed is no problem, and the potential of the lines can be fully exploited. In comparison to conventional TIG welding this means an increase of the welding speed by 50 per cent without major modifications on the production line. The cuts shaped as pipes have a small weld gap similar to conventional TIG welding, making the use of filler materials unnecessary. The titanium zinc cuts are welded with alternating current and argon as shielding gas. Forgoing the use of expensive helium reduces the production costs. When the coil is not too oily, the process runs smoothly and stably over the entire length of the coil. A stable

Umicore Bausysteme GmbH in Gatterstaett, Germany, produces downpipes and gutters of different diameters, and also elements for roof drainage systems from copper, aluminium and titanium zinc. Its main products are titanium zinc pipes and gutters, which are available under the trade name Vmzinc, with different surfaces such as Natural-Zinc, Quartz- Zinc, Anthra-Zinc, Pigmento and Azengar. 2,500km of pipes with diameters between 60 and 120mm and lengths between 1 and 4m are produced yearly on three production lines; 80 per cent of the pipes are made from titanium zinc. This also means that 2,500km of seams have to be welded. The source materials are strips with a length of approximately 2.2km, which are unrolled from the coil, formed into endless pipes, welded edge to edge, and finally tailored. The production facilities operate in multi-shift production. However, demand is growing, and production manager Torsten Hanke discussed with his colleagues how it would be possible to produce even more downpipes in less time. “The bottleneck is the welding of the longitudinal seams,” said Mr Hanke. “With conventional TIG welding the A 2.2km mill-finish titanium zinc strip is processed into downpipes in a continuous process (Photo credit: Umicore)

welding speed is only about 5m/s.” The company’s specialist welding distributor suggested trying a new process: the high-performance TIG-welding process InFocus, from Kjellberg. It was not necessary to invest in new power sources, because the existing ones could be used after they had been upgraded with efficient cooling systems. The technology carrier is the InFocus welding torch. With its highly focussed arc it is a tool that achieves weld seams with a quality similar to plasma or laser welding. InFocus is a high-performance TIG process for welding low-alloyed and high-alloyed steels, non-ferrous metals and galvanised sheets at high speed. Welding of thin sheets is also possible, as well as welding of thick sheets, up to 10mm in one layer. The process runs reliably and spatter-free, and the weld seams are characterised by an even seam surface of high quality, a small heat-affected zone and low distortion. Umicore has high demands on the quality of the weld seams: in addition to an absolutely smooth seam surface and a well-developed root, the seams Production manager Torsten Hanke (left) is responsible for the introduction of the InFocus process, together with the operator Marco Stottmeier The expansion of the sleeves on the welded copper pipes can clearly be seen

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Tube Products International July 2016

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