Most Common Weldable Thermoplastic Materials
HPDE (High Density Polyethylene)
High density Polyethylene welds very well and is the most common form. Other densities include low, medium, high and ultra high molecular polyethylene (UHMW). The low density is much softer and more flexible and also welds well. You can weld a higher density with a lower density rod, but you cannot weld a lower density with a higher density rod. If you identify a polyethylene with a burn test and you think it is high density but it will not weld, it is either ultra high or a cross-linked material. The UHMW requires a special welder, rod, and tip for proper welding.
Polypropylene rod will easily separate from the substrate in the “wetted” or melted state and must be held in place until the clear color on the surface turns back to its original appearance. Also, the rod will not soften all the way through and will remain stiff, making welding in and out of corners and around outside corners difficult. If multiple welds are run, such as in the corner of a tank, relieve stress in the areas by heating the weld and the tank walls on either side of the weld and then cool it slowly by covering it. This process is called “annealing” and it will add years to the life of your weld.
CPVC (Chlorinated Polyvinyl Chloride)
CPVC will produce a good weld if you sand and scrape both the rod and the surface to be welded to remove the coat of plasticizer that leaches from the CPVC material. (removing it with chemicals either softens the material or leaves a residue). More heat must also be concentrated on the substrate when hand welding CPVC. BE careful to guard against scorching, which will weaken the weld considerably.
PVC (Polyvinyl Chloride)
Scorching or discoloration of PVC will weaken the weld. To avoid this problem, either reduce the power or heat by increasing the air flow, or increase your welding speed. If backwelding pipe fittings, never attempt to weld over cement; first remove cement by grinding or other means.
PVDF (Polyvinyl Fluoride)
PVDF welds by hand or automatic feed tip at 890° F and is very strong. All welds of PVDF will provide good performance for more years if annealed. After welding, heat the weld and the substrate around it and allow to cool slowly by covering.
ABS (Acrylonitrile Butadiene Stryene)
ABS has a good esthetic value and can be finished by sanding and painting.
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