PVC Moisture content

[futuremolding]

Hi all, we are facing silver streaks issue in PVC molded fittings . we are doing the inhouse compounding and the compounded mix is pelletized and using for molding operation. we are predrying the pelletized material twice @80 degree celcius and the silver streaks issue is going. My question is it possible to accumulate moisture from the compounding operation. we are not storing material in warehouse , we are directly using it from pelletizer. Can anyone help.

[rickbatey]

PVC isn't hygroscopic so I've never seen it dried. I would bet one of your additives is carrying the moisture or its shear or residence generated. For shear, I'd expect a narrow area or sharp corner in the tool is degrading the resin as you inject it. BTW-Do you run this in a cold runner?
Rick

[Jendalf]

Maybe its the extensive drying you describe. Try to reduce it and check the result. ("Too much dry(ing) will kill you :)"

j

[futuremolding]

Hi Rick , we are running cold runner,initial investigation found that the hot mixing breather was blocked and the pelletizing barrel vacuum was not enough .Thanks

[futuremolding]

Single time drying unable to eliminate the silver streaks, whereas two times drying is eliminating the silver streaks effectively.still searching for the root cause.Thanks

[Jendalf]

Ok, tell us more about the process and equipment.
temperatues (setup)
plastification setup
residence time
inj. unit and machine inlet and outlet diameters.
tool runner system

pictures of problem
J