| abstract |
The present invention relates to a welding method in the manufacture of a spirally wound tube having a thermoplastic profile (1) of a mainly rectangular cross-section. A hole profile (1) is wound in a screw line form manner on a welding drum (2) simultaneously as profile surfaces (1a, 1b), which are to be welded together are heated with hot air to a desired temperature, whereafter a welding mass (S) is extruded onto the heated profile surfaces (1a, 1b) in two streams along each edge of the profile surface (1a, 1b) and the welding mass coated hole profile portions are pressed together by means of a press roller (10). The invention is characterized in that the welding is performed with a welding head (3) coupled to an extruder and provided with a welding keel (4), which from the outside is inserted between two profile surfaces (1a, 1b) to be welded together. Hot air (L1, L2) is blown out through two pairs of air openings (5, 7) in the welding keel (4) against the edge portions of the profile walls (1a, 1b). A keel nose (9) located between the two pairs of air openings is arranged to guide the four hot-air streams (L1, L2) and to prevent heating of the middle portion of the profile surfaces (1a, 1b). The extruded welding mass (S) is pressed out on the heated portions of the profile surfaces (1a, 1b) through two pairs of welding mass openings (6, 8) in the rear section of the welding keel (4). The welding pressure is maintained on a desired level by regulating the friction between the hole profile (1) and the welding drum (2). |