Abstract: This invention relates to portable machines for welding together individual thermoplastic sheets in situ. The machine heats different and opposing thermoplastic sheets using independently controlled electric, radiant heat sources and then compresses the sheets beneath an endless compression belt to complete the weld thus forming a unitary membrane.

Abstract: This invention relates to machines for heating and joining thermoplastic resin sheets and more particularly relates to a portable machine which fuses together the overlapping edges of large stationary sheets as the welding machine travels along the overlapping edges. The machine is moved along the opposed edges of the sheet at a velocity which is changed so that the velocity is substantially proportional to the instantaneous temperature of the heat source. The machine is therefore accelerated or decelerated in accordance with the selected velocity change algorithm which is exponentially in the preferred embodiment.