Butt fusion technique

PTFE (and other fluoropol5miers) tubes and lined pipes are welded by the butt fusion technique (Fig. 

PTFE (and other fluoropolymers) tubes and lined pipes are welded by the butt fusion technique (Fig. 14.45). A uniform bead is required for the formation of a strong butt weld. The two ends of the plastic tubing are cut back to obtain square ends. The pipe ends are faced together by a device such as the one shown in Fig. 14.46 which allows the application of a measured axial force to the tubes. A heated plate or a clam shell heater can be used to heat the ends of the tube. An important step is to thoroughly clean and wipe the ends of the tube with acetone or another solvent. 

Techniques, used by the gas and water industries to join and repair pipelines, include butt fusion, electrofusion socket welding and socket jointing (309). The study of bond strength testing for solvent joints in piping systems has noted extreme sensitivity to minor variations in sample preparation (259). 

In the extrusion welding technique, the mating parts are heated by pressing onto a metal heater which is held at 250°C-270°C and which has been surface-treated (usually with PTFE) to minimize adhesion. For butt welding, the heater is a flat plate for spigot and socket welding, there are male and female surfaces. The ideal pressure on the hot surface is 50-60 kPa, and the time should be sufficient for the fusion of the material to a depth of 4-5 mm at the contact surface. The heating unit is removed and contact is made under a pressure of ideally 0.06 to... 

Standard inspection techniques should be followed for assessing quality of butt and electro fusion joints... 

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