Hot gas welding can be applied to most thermoplastics and is used widely. Like many manual processes, its success depends greatly on operator skill.
Welding equipment is relatively straightforward. In its simplest form, the main component is a hand-held welding gun consisting of an integral blower, a heating element with thermostat and a set of interchangeable nozzles fordirecting hot gas at the workpiece. A filler rod is used and this is made from the same polymer as the components to be welded.
Usually, the gun is fed with air - although for some applications nitrogen gas is used. The temperature of the hot gas stream is typically in the range 200-400°C. With the heated gas directed towards the joint, local melting orsoftening of the components and filler rod take place. A weld is formed when the joint region and filler rod fuse and then cool to ambient temperature.
Extrusion welding, another process for fabrication in plastics, is used on thick sections. Filler material is separately heated in the barrel of a hand-held extruder. Softened or molten material is extruded through a PTFE die intothe joint which has been pre-heated using a hot gas gun mounted on the extruder barrel.
The main advantage of hot gas welding is that the equipment is portable; however, the process can be slow and weld quality is operator dependent. Fabrication of containment vessels and pipework are the main applications.
Copyright by TWI, 1999
