Seam welder for thermoplastic coated fabric

A seam welding machine for thermally welding overlapping edge portions of coated fabric panels, comprising a guiding head having slots which are open at their laterally outer ends and closed at their inner ends and extend inwardly from the opposite sides of the head to overlap each other past a longitudinal axis of the head for guiding overlapping edge portions of two panels into a nip area, a hot air welding tip directed into said nip area, upper and lower pressure rolls mounted behind said nip area and upper and lower drive belts mounted behind said pressure rolls and drivably connected thereto to press said overlapping edge portions together into a seam, said machine behind said guiding head being laterally open in the plane of the said seam to allow unrestrained passage of panels of unrestricted width, and means for rollably supporting said machine with said overlapping guide slots close to the ground, and further comprising a variable speed motor for driving the upper drive belt and pressure roll, and a torque motor for driving the lower drive belt and pressure roll at a following speed matching the speed of the upper drive belt and pressure roll.