Welding procedure and welding equipment

The invention relates to a welding device and a method for welding metal or plastic belts, in particular endless belts. The belt (1) welding device comprises a belt guide system, a tensioning system, a drive system and a welding system (2). The tensioning system is designed so that the belts (1) are subjected to mechanical stress at least during the welding process in the welding area. The method of welding belts (1) by the above-mentioned welding device comprises the steps of guiding at least two belts (1) in the welding direction, tensioning the belts in the welding area, longitudinal welding of at least two belts (1) along the longitudinal axis, preferably at mutually facing edges, being under tension, and moving the belt (1) stepwise or continuously relative to the welding system (2), while the process of welding the tensioned belt (1) continues stepwise or continuously.