Polypropylene Welding
Polypropylene Welding
(OP)
We currently have a rectangular shaped water tank made of polypropylene. The tank is a large tank designed to hold 3,000 and 4,500 gallons of water. The majority of the tank welds are welded using extrusion welds.
We are looking to redesign the tank and the new tank would have more complex weld joints (v-groove, double v-groove, lap welds). We don't fully understand why the current welds meets our needs, but they do. I'm trying to understand what occurs when you weld PP and how the strength of the weld will change with the new weld configurations in efforts to predict that the new design will meet our requirements.
I have taken some cross sections of the current weld design and am unable to see any effect of the weld on the parent material, like you would see in a metallographic sample. Are there other ways to evaluate polymer welds?
Any information on welding PP and how to design proper joints would be appreciated!
Thanks in advance for your assistance.
We are looking to redesign the tank and the new tank would have more complex weld joints (v-groove, double v-groove, lap welds). We don't fully understand why the current welds meets our needs, but they do. I'm trying to understand what occurs when you weld PP and how the strength of the weld will change with the new weld configurations in efforts to predict that the new design will meet our requirements.
I have taken some cross sections of the current weld design and am unable to see any effect of the weld on the parent material, like you would see in a metallographic sample. Are there other ways to evaluate polymer welds?
Any information on welding PP and how to design proper joints would be appreciated!
Thanks in advance for your assistance.





RE: Polypropylene Welding
When you weld a polymer you need to heat the polymer long enough and hot enough so that the polymer chains can flow together and re-entangle in the new configuration. Full strength will not be achieved quickly even if the weld looks fine because polymer chains move slowly (viscous). Heating more will help to a degree but too much heating will shorten the polymer chains and lessen the strength.
Filled polymers tend to have problems at the join because the filler forms weld lines with low strength. Therefore, I would expect an unfilled polymer to have lower strength at the weld, far lower than for the rest of the part (up to 80% lower strength for example). So, use unfilled polymer if you can.
Chris DeArmitt
RE: Polypropylene Welding
I've attached a hand sketched drawing of the current tank and the new proposed design. Is there any information out there that suggests one weld joint is better than another for polymer weld design? Sorry the drawings are so crude.
RE: Polypropylene Welding
Chris DeArmitt
RE: Polypropylene Welding
RE: Polypropylene Welding
The shapes obtainable are also limited to some degree, but the material strength should still be stronger than a simple weld of PP sheet.
Regards
Pat
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