A method and apparatus for pre-heating a plastic strip to facilitate plastic welding at a location underground

摘要

An apparatus for lining an underground conduit is disclosed. The apparatus (10) includes an annular frame (40) and a strip guide disposed around and supported by the annular frame (40). The strip guide is arranged to guide a strip (12) around a helical path when the machine is in use. A drive assembly (70) is mounted to the frame (40) for driving the strip (12) so as to present an incoming first edge (16) to an adjacent second edge (18) of a wound convolution of the strip. An extruder (80) is mounted to the frame, the extruder having a nozzle (85) for extruding a molten bead of plastic onto the strip (12). A multi-stage air heater including a first heating stage (50) powered by compressed air and a second heating stage (150) powered by electricity, the multi-stage heater is provided for generating heated air and a nozzle (95) for directing the heated air onto the plastic strip (12) is also disclosed.