Foam welding apparatus

In an insulation applying apparatus comprising in cooperative combination a first support means, a means to propel the first support means about the periphery of an object to be insulated, an insulation depositing means supported by the first support means and selectively moveable relative to the first support means, the depositing means adapted to trace a generally spiral path over at least a portion of an object to be insulated, means to heat surfaces of adjacent thermoplastic foam strips to a temperature sufficient to fuse the thermoplastic foam strips together, the improvement which comprises the means to heat surfaces is a generally planar heating element of sufficient size to engage surfaces of adjacent thermoplastic foam strips, the heating element having a first generally unheated leading end, a second or heatable trailing end, the heat element having a first or tank side and a second or exterior side, the heating element defining a plurality of generally L-shaped interdigitated slots, the slots being generally parallel to the ends and sides of the heating element, the heating element defining an electrical serpentine path, the heating element being of electrically conductive material and defining a region of greater electrical resistance adjacent the trailing end and means to maintain the heating element in generally fixed lateral relationship relative to the foam strips being welded.