TPT January 2008

F ittings, C ouplings & T ubular J oints

Other applications of applying thin-gauge material to large tubular components as a dissimilar coating are also being investigated. The MP joining technology and DRW processes will enable product designers to extensively use tubular sections in various components for cost, performance improvement, and weight reduction. This article was supplied by Menachem Kimchi, Business Development Engineer, EWI (Edison Welding Insititute).

Advances in welding tubular components

Tubular components can offer significant improvements with respect to performance, weight, and cost. Joining technologies like gas metal arc welding (ie MIG welding), gas tungsten arc welding (ie TIG welding), and laser welding, create challenges when welding large volumes of tubular components. Issues include burn-through and the need to move the welding heat source and/or filler metal source around the weld joint in tight spaces. These processes create even greater challenges when joining dissimilar materials and in the welding of tubular components made of coated materials (eg galvanized steel). Edison Welding Insititue (EWI) is involved in the development of two new technologies designed for joining of tubular structures: deformation resistance welding (DRW) and magnetic pulse (MP) joining technology. DRW is a resistance welding process which uses conventional resistance welding machines and forms near instantaneous, leak-tight welds. DRW was initially developed for tube-to-tube joints but this technology extends to tube-to-heavy- section components such as heavy-wall pipes, fittings, and other solid and hollow parts or components. Other applications for DRW technology include hydraulic lines, exhaust systems, and suspension/frame components.

MP joining configures two tubular parts to form a lap-type joint, and provides the opportunity to achieve welding or mechanical joints as required by the application. The weld generated by this technology is characterized as a solid-state weld. The basic requirement of the process is that the outer tube is electrically conductive and possesses contain amounts of plastic deformation capability. The inner tube can be a different material that is either conductive or non-conductive. The passage of a high current discharge through the specially designed coil (or coil bank) creates an induction current (eddy current) in the conductive outer tube. The interactions of the two magnetic fields generated by the primary discharge current and the eddy current result in the repulsion force between the coil and the outer tube. This powerful repulsion force causes the outer tube to impact on the inner tube at a velocity that is sufficiently high to generate bonding in a matter of microseconds. MP joining development work at EWI includes the welding of dissimilar materials for various industries such as automotive, heavy manufacturing, and aerospace. Applications that include welding aluminium alloys to steel are common for MP technology.

Edison Welding Institute – USA Fax : +1 614 688 5001 Email : menachem_kimchi@ewi.org Website : www.ewi.org

Tube and fitting system for thermal installations Eurotubi Pressfitting, from Eurotubi Europa, Italy, is a system of tubes and fittings used for hydrothermosanitary installations, and is suitable for the conveyance of water, gas, and compressed air. The fittings at the extremities of the O-ring seating are able to support high pressures and temperatures over 85°C. Tubes and fittings are assembled through the permanent deformation of the fitting by special pressing jaws mounted on small electromechanical tools. Once pressed, the o-ring ensures hermetical connection. The Pressfitting system combines the reliability of joints with a quick and easy method of laying, as it requires no gluing, threading or welding. A wide range of fittings are available in diameters from 15mm to 108mm in stainless steel 316L, and in diameters from 12mm to 108mm in carbon steel. The quality of materials, constant sealing and duration tests, and rigorous quality control allow the Eurotubi Pressfitting System to obtain conformity within strict European certifications. Carbon steel provides a competitive and innovative solution for thermal installations, offering the same quality provided by traditional copper systems, but at a lower cost. The Eurotubi Pressfitting System is also compatible with most significant brands of fittings. Eurotubi Europa – Italy Fax : +39 0362 41099

fi Figure 1 (below left and right): deformation resistance welding (DRW) tube to a solid part; and bottom (left and right) magnetic pulse weld – aluminium to steel

Email : info@eurotubieuropa.it Website : www.eurotubieuropa.it

124 ›

J anuary 2008

www.read-tpt.com