| 摘要 |
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). The preheated thermoplastic material (28) is conducted one way along a first contact surface (63) by means of at least one metallic fusible plug (58) in a liquefaction zone (54) having metal contact and is conducted back the other way along a larger second contact surface (65) after being at least partially liquefied. The application device for the continuous protective film (20) is designed in the form of a doctor blade (82) encompassing a reservoir (84) for the liquefied thermoplastic material and a front comb (86) for doctoring off excess conveyed plastic, said comb (86) extending perpendicular to the direction of travel (26).
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