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Home : Products : HDPE Joining Techniques
Among the techniques used for welding of polypropylene – butt welding, socket welding and extrusion welding are more commercially popular due to the easy portability of the welding machinery.
 Butt Welding Fittings:
This technique is used for welding pipes made from PE, PP, PVDF etc. The pipes are mounted in the clamps of the butt fusion equipment and checked for initial alignment. The pipe ends are then planed to ensure that they are flat & square. The welding sequence begins when a flat heated plate is positioned between the two pipe ends. The pipes are pushed towards each other until they come into contact with the hot plate and the pressure is increased to give good thermal contact.
The pipe ends melt and the interface pressure forces the molten material outwards to form 'weld beads' at the outside and inside pipe surfaces; hence the term 'bead-up' stage. Then the pressure is reduced to a value sufficient only to maintain the pipe in contact with the hot plate. This allows the melt depth to increase without increasing the size of the weld beads. At the end of this 'heat soak' stage, the pipe ends are pulled away from the hot plate. The hot plate is removed, and the two molten pipe ends are pushed together at the same pressure as used during the initial bead-up stage. This causes further growth of the weld bead and is called the 'bead roll over' stage. The pressure is maintained until the weld is fully cooled and joint is ready
 
 
 
Welding Cycle

The welding cycle is divided in 5+1 different phases:


PHASE 1: Bead formation t1
PHASE 2: Heating up t l
PHASE 3: Change over t3
PHASE 4: Bringing up pressure t4
PHASE 5: Cooling down under pressure t5
PHASE 6: Cooling down out of the  machine t6

t1 = Time requested for the bead formation
       with the Specified wall thickness
t2 = Time requested for the  continual
       heating
t3 = Time requested for the change over
t4 = Time requested for bringing up
       the pressure
t5 = Time requested for cooling down
p2 = pressure during the continual heating
p1 = pressure during the bead formation
        and the cooling down
 
Click here for
Values of butt fusion jointing process.
 
 Extrusion Welding:

The process involves continuously extruding molten thermoplastic material into a weld preparation on the plastic component or structure which is being joined. The extrusion barrel on the extrusion gun is heated along its length, either by cartridge heaters or hot air. A thermoplastic rod or granule feedstock is fed into the rear of the extrusion barrel and the material is heated as it is drawn through the barrel by the rotating extruder screw. The ejected material is shaped to match the profile being welded, and defines the shape and size of the final weld. At the leading edge, hot gas is used to ensure there is sufficient heat in the substrate material to form the weld. Typical welding speeds are 0.5-1.0 m/min.  Extrusion welding is generally used to weld custom fabrications with sheet, nozzles etc.

 
 Flange Connections:

Stub flanges/Pipe ends/ collars as butt welded to each side of a length of pipe after inserting two slip-on metal flanges  (one for each side).  A continuous line can then be made by simply bolting the flanges together which are held securely in place.  A leak proof joint is ensured by inserting an sealing gasket thus providing a demountable joint or to match up with pumps, valves etc .  Primarily used where the pipes may need cleaning later on or may have to be moved from one place to another after use.

 
  Electro-Fusion Welding :

Electro-fusion joining involves an electrically conducting implant being incorporated into the socket and/or fitting to be jointed to the pipe. A high electric current is applied via an appropriate power source and causes resistive heating which melts and fuses the pipe and fitting material.Other methods of welding include infrared, bead and crevice free, friction welding depending on the requirements of the application and ultimate use of the manufactured products.

 
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