Abstract: According to the invention, a continuous protective film (20) made of a thermoplastic material is applied to the internal face (68) of the longitudinal weld seam (16) of sheet metal tubes (10). The sheet metal tubes (10) are fed, when the front sides thereof are practically in contact with one another, via the welding arm (12) of a welding machine and an adjacent application arm (18). The continuously fed thermoplastic material is preheated in the area of the application arm (18), is melted, and is directed to an application device (44) after being homogeneously liquefied, said application device (44) applying the liquid plastic in a metered manner across at least the entire width of the weld seam (16).

Abstract: The invention relates to a continuous protective film, consisting of a thermoplastic synthetic material, which is applied to the inner side of the longitudinal weld of sheet metal pipes which are supplied end to end across the welding arm of a welding machine and an adjacent applicator arm. The thermoplastic synthetic material is continuously melted and applied using an applicator nozzle across at least the entire width of the weld. The thermoplastic synthetic material fed continuously is preheated, melted and conveyed to the applicator nozzle in a homogeneous liquid state. The discharge opening of the nozzle is subsequently guided at an adjustable constant distance from the inner side of the longitudinal weld of the sheet metal pipes, and the liquid synthetic material is applied in metered quantities. The melting apparatus for carrying out the process comprises means for guiding the discharge opening of the applicator nozzle. The means are, for example, a follow up roller, a sliding block, or a probe.

Abstract: On the welding arm of a welding machine is mounted a coaxial application pipe with removable transport means and an application nozzle. Into this application pipe is fed a block-shaped hot-melt mass, in the direction opposite the advance direction of the sheet metal tube, guided in direction (V) of the application tube, melted in the area of a narrowing heater, passed through a supply tube to the application nozzle and applied or sprayed as a hot-melt strip to the inside of the longitudinal weld seam of sheet metal tubes.The application of a hot-melt strip is suitable in particular for the protection of the longitudinal seam of a tin-plated can shell.