Apparatus for welding heat fusible material

Welding apparatus for producing an ultimately continuous weld line between sheets of heat fusible material, said apparatus comprising a supporting frame, at least two pairs of welding electrodes, means for mounting each pair of said welding electrodes on said supporting frame, said mounting means including means for moving the electrodes of a said pair relative to each other between a clamping position and a disengaged position, each said mounting means being movable along a predetermined path on said supporting frame in a material advancing direction together with material being welded by said respective electrode pairs and in the opposite direction, means for moving the material to be welded along said paths in the material advancing direction with one pair of electrodes being in the clamping position and with the other of said pair in the disengaged position and moving in said opposite direction, means for activating each said pairs of electrodes to carry out a welding cycle while each said pair of electrodes is being moved in the material advancing direction along their respective paths, one pair of electrodes being located to form a series of collinear spaced line welds and the other pair being located to form line welds which join the said series to thereby from a continuous line weld.