I m facing a black line in center cavities of bottle only process is IBM mat HDPE wall thickness is gt 1mm for less thickness it is not observed even without color it is not seen any suggestion

sounds like burnt material at first point of injection, or too hight injection speed for the first few mm, lower nozzle temps maybe, or speed up process? due to idle? maybe also a put a reverse taper in nozzle orifice

Material is not Burnt out!! Nozzle Temp also varried up & down!! No improvement.

Cycle time has limitation to speed up or delayed!! For IBM process!! Not beyond a certain limit!! It is also tried out!! But same result!!

Any more suggestions?? And can u find the culprit???

are the black lines on the knit line of moulding?

it just sounds like oxidisation, material adhering to the barrel somewhere, and degrading? a lower temperature should help it? are you using hot runner? maybe in the manifold? but as you know that in itself will cause other problems, process may just have to be re adjusted to compensate

also are you using regrind? remember the properties are not the same and the anti oxidents are at a lower level due to heat processing,

No!! I use only Virgin!! HDPE 5502BN Marlex from Phillips!!

i have seen hotspots before even though barrel temps say otherwise, also hot runner systems can have hotspots due to lack of maintenance or poor cooling flow in one area, , you only need one to cause a problem, if it were the material itself it would be all over mouldings, this problem looks specific to the first part of the injection process, hope you find an answer sanjay,