Pipe Joining Techniques
Holding / Cooling
In butt fusion, ends of the pipes to be joined are brought together in a dedicated butt fusion machine. The end
faces are squared up by planning with a mechanical trimmer, later to be heated with thermostatically controlled
non-stick heater plate.
Once the ends melt, the faces are pressured together and allowed to cool. The butt fusion process produces weld beads on the interior as well as the exterior of the pipe. These can be removed easily to produce a smooth bore or outer surface. Inspection of beads should be a mandatory check on the weld
Values of Butt Fusion Jointing Process.
|Pipe wall thickness (mm)||Heating element temp°C||Equalisation at P = 0.1 N/mm 2 Height of bead (mm)||Heating time (s) at P = 0.01 N/mm 2 for various materials||Change over time (s)||Time (s) to reach full jointing pressure||Cooling time (s) under jointing pressure P = 0.15 N/mm 2|
|PP / PPH||PVDF|
|4.3-6.9||210||0.5||70- 40||5||5- 8|
|7.1 - 11.4||205||1||90 - 120||6||8 - 10||10- 20|
|12.2- 18.2||200||1||180 - 290||120- 150||8||10- 15||20-30|
|20.1- 25.5||195||1.5||-||10||15- 20||25-38|
Used mainly to fabricate PP and PVDF piping systems and involves the use of a socket type fitting.
The welding cycle is split into two phases, heating and cooling. To heat the outside surface of the pipe being welded, a socket mounted on a hot plate is used. A spigot is used on the opposite side of the hot plate, to heat the interior of the injection molded fitting. Both the fitting and pipe are heated for a set 'heating time'. Once the heating process is complete, the heated pipe and fitting are removed from the socket and spigot, and pushed inside the fitting, producing the weld. Depending on the pipe size, this process is carried out by hand (< 50mm OD) or on a mechanical/hydraulic machine (> 63mm OD).
Values of Socket Fusion
|PP / PPH||PVDF|
|Pipe OD||Pipe insertion depth (into fitting)||Min. Wall (mm)||Heating time (secs)||Cooling time (secs)||Min. Wall (mm)||Heating time (secs)||Cooling time (secs)|