FIELD: welding. SUBSTANCE: method includes welding of thermoplastic section by welding head connected with extruder and provided with welding member which is installed between two welded surfaces which are heated with hot air supplied through two pairs of air holes located on the side of welding member facing direction of rotation of hollow section near the areas of section walls on which welded seams are formed. Nose of welding member located between two pairs of air holes directs hot air flows to welding zone to prevent heating of middle areas of section surfaces. After heating of welded surfaces to required temperature, welding mass is extruded onto heated areas of each edge of section surface through two pairs of holes located in middle part of welding member at the level of two pairs of air holes. Areas of hollow sections are present to applied welding mass by means of at least one hold-down roller whose axis runs radially relative to welding drum. In this case welding pressure is maintained at the present level by regulating the friction between hollow section and welding drum. Welding head used for embodiment of the offered method has welding member provided with three main zones: upper welding, central shielding and lower welding ones. Front edge of upper welding zone has one pair of air holes inclined forward for supply of hot air to each welded surface. Located on its rear edge is a pair of holes directed to both sides for application of welding mass to section surfaces heated by flows of hot air. Central shielding zone has welding member nose directed toward. Lower welding zone has a pair of air holes for supply of hot air and a pair of holes for supply of welding mass for formation of internal welded seam. EFFECT: higher efficiency. 10 cl, 3 dwg
