Tutorial: Evaluating your Plastic Welds

5/14/2019

TRIAC ST being used to repair a car bumper

It’s important to evaluate each plastic weld to ensure your final product is strong and resilient. Particularly when speed welding with a hand tool, small defects in a single weld can be magnified as beads are built up to the base material’s thickness. Several key indicators allow you to evaluate your welds without the need for destructive tests.

Correctly welded seams:

Slight flattening of the welding rod
No notches between the welding layers
For PVC:
- Foamy to smooth bead
- No discolouring (e.g., brownish colour)
For PE, PP, PVDF:
- Smooth double bead on both sides
- Dull surface in the area of the welding zone

Example of a correctly welded seam.

Flawed welding seams:

No building of bead or welding rod still round
- Temperature too low
- Speed too fast
- Welding force too small
Notches between the welding layers
- Distance between the layers is too large
In particular with PVC: brownish discolours of the welding bead
- Temperature too high or speed too slow
In particular for PE, PP, PVDF: shiny welding zone
- Temperature too high or speed too slow

Tutorial: Evaluating your Plastic Welds

Correctly welded seams:

Flawed welding seams:

Recommended Further Reading:

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