Brittle Lead-Free UPVC Fittings

Hello and welcome to CR4.

Lead free and uPVC would not be the cause.

Are the splits "longitudinal"? (in the same directin as the extrusion process.)

Recommendations are

1) Check your material hardness and notched IZOD ratings to verify flexibility is what you expect. Maybe the pipe material is harder than you expected. Leads back to process control in fabrication.

2) Check your "fit" dimensions. Interference fitting could create localised stress showing as splitting. Leads back to process control in your fabrication.

3) Check your adhesive. "Environmental Stress Cracking" is common cause of apparent brittle failure for all plastics. A simple but rough way to do this is to put solvent onto a piece of material and put inside an airtight container. Examine a day later for crazing and cracks.

Enjoy the challenge

If you can afford to do this, have the cracks analysed by a testing laboratory. They would be able to examine the crack with a scanning electron microscope and see if the cracks are from mechanical stress or chemical attack.

Cut through the fittings and look to see if there is even wall thickness throughout. If there are thick and thin sections, the thin sections cool and freeze off before the thick sections. The thin walls have stopped shrinking, while the thick walls continue to shrink, putting high stress into the fitting. The fittings can look fine, but could crack after being exposed to a chemical that would not ordinarily attack it.

When you cut through the fittings, sand the cut surfaces and look for voids or bubbles. These could weaken the fitting. They usually occur in the thickest areas.

To help the thin/thick problem, core the fittings as much as possible to obtain a uniform wall. Place the gate into the thickest area and make transitions from thick to thin as gradual as possible. Make sure the runners and gate are adequately sized for the wall thickness. The molds need to be properly cooled and vented. Cooling lines should be placed close to the part surface and all internal large cores must have cooling running through them. Vents for PVC should be .03 to .07mm deep to remove air without flashing.

Good luck!

Dear Zoomer,

We do the gelation test and the material passes the test.

Meanwhile, we have taken your advice of cutting and checking the wall thickness variation, rectification work is in progress.

what would be the corrections i could do on the processing side?

Regards,

ragotham