CellTech™ can be welded by normal procedures, such as hot gas, heated tool, bending and welding, friction, etc., using common equipment. Before welding, the part of the sheet to be welded must be properly cleaned with a cleaning agent or by machining. After welding, finishing may be necessary. CellTech™ should be worked very carefully to ensure that the foam structure does not collapse.
Hot Gas (with welding rod)
Hot gas welding (manual or machine) with a welding tip plasticizes the sheet material and the welding rod at the weld. This is accomplished by heated gas, preferably oil- and water-free compressed air (0.3 bar maximum, low-pressure blowers from Leister, Wegener, Zinser, etc.). The sheet material and the welding rod are then joined under pressure. Only skilled specialists should do this type of welding.
A wide range of welding equipment and welding tips are available on the market. We recommend high-speed nozzles, which ensure secure and reliable seams by evenly heating the sheet and welding rod. Semi-automatic welding units with mechanical feeding are suitable for welding in series.
Fillet, single V and double V butt welds are most frequently used with CellTech™ Thin sheets are joined by single V-butt welds, thicker sheets by double V-butt welds. Welding alternately on both sides to avoid distortions should produce double V-butt welds.
It is important to weld with undrawn filler rods at constant pressure and speed. Before using a new welding rod, the weld must be scraped to remove thermally damaged material. To achieve good hot gas welding factors with CellTech™ the temperature1 inside a circular welding nozzle should be 464 – 518°F. For a high-speed nozzle, the inside temperature should be 518 – 554°F.
Heated Tool (Butt Welding)
Circular and sword-shaped tools are used in this welding procedure. The smoothed and cleaned surfaces of the parts to be welded are heated by lightly pressing them against the heated tool until they are plasticized. They are then pressed together. The joints are almost free of tensions and capable of resisting high stress.
This welding method is simple and timesaving. If proper welding conditions (e.g., temperature of tools, intensity of pressure against the tool, intensity of joining pressure, immediate joining after plasticizing) are followed, the welded seam is almost as strong as the material. For CellTech™ the surface temperature of the tool should be 410 – 446°F. For heating, pressure should be 11.6 lbf/in2. For joining, pressure should be 14.5 – 29.0 lbf/in2. Welding tools and equipment must be appropriately adjusted and checked regularly.
During heating, the plasticized material forms a bead. Heating should be stopped when the bead is 1 – 2 mm thick. The heated tool should be pressed lightly against the sheet to avoid squeezing too much of the plasticized material out of the plasticized zone. The plasticized parts must be pressed together firmly immediately after removing the heated tool and until the material has hardened again.
1 These values depend on quantity of penetrated hot air (40 – 60 l/min), welding speed, type of welding rod, induction period of temperature, etc.
2 These values depend on thickness of sheet, heating time, etc.
Bending and Welding
Bending and welding is a modification of butt-welding. Place the sheet on an even surface. Place the heated tool on the sheet along the bending line and intruded into the melting material. The edge of the bar has an angle of 60° for rectangular bending. The bar should enter the sheet up to two thirds of its thickness. Immediately after removing the bar, bend the sheet and weld along the plasticized line.
To produce the necessary pressure on the heated bar, the angle between the edges to be welded should be 15 – 20° smaller than the bending angle. If thick sheets have to be bent, the heating time can be reduced by milling a wedge-shaped groove into the welding line before applying the heated bar with CellTech™.