help with new tool

[mensite]

we have an new 8 cavity mold and just started it up the other day. after about all day we finally got it running good parts.We are running white pvc material. after about 3 hours we started getting shorts and could not get it to over come it.were running a nissie 500 ton. pressure seems to be good.everything is working like it should.

but one thing is when the screw fills up i notice when it starts to inject the screw comes forward about 3 inches before plastic starts to push. and when it does inject it comes all the way to a nice coushion.just like its makinga whole shot. when the mold opens all the parts are short big time.all 8 parts.


where is the material going??? could the check ring be bad letting the material back flush. please help me out guys

[MIOMY]

If possible watch screw during injection, either through site glass which some nisseis' have or look down throat. If screw is turning during injection that usually indicates wear. Hope this helps.

[brentb]

If possible watch screw during injection, either through site glass which some nisseis' have or look down throat. If screw is turning during injection that usually indicates wear. Hope this helps.

In line with the above, try increasing inject time and see if "cushion" gets smaller.
Are you running a NRV or smear tip screw?

KOM

brent

[mensite]

If possible watch screw during injection, either through site glass which some nisseis' have or look down throat. If screw is turning during injection that usually indicates wear. Hope this helps.

yes the screw does turn some but not alot... no matter how much shot size or pressure we still get shorts. and inject time too. but still , where is the material going. i know its picking up material cause i can see
it flow down at the magnet glass

[pjhall]

When was the last time you had the tip assembly off /checked/measured? A screw pull might be in order to eliminate the tip/check-ring/seat. Turn the holding pressure to zero and see if you can get the part 95-98% full. If you can't even do that it is most definitely a screw / tip /barrel issue.

[moldingppm]

I'm almost going to garuntee that the check ring is bad.

[MIOMY]

Sounds like check ring and possibly barrel worn at the bottom end. Material is flowing back past check ring and pressure is transferred to flights of screw causing rotation during injection.

[Pilot]

or you have a leakage into hot runner chanel :-) ..... Dont worry .. its only plastic :-(

KOM Pilot

[brentb]

or you have a leakage into hot runner chanel :-) ..... Dont worry .. its only plastic :-(

KOM Pilot

Pilot,

Looks like resin is PVC. It doesn't mention a hot runner. If there were for PVC, I'd worry about leakage!

Still don't know if there is a ring tip. Many PVC molders used to employ smear tips on their screws.
KOM
brent

[kelley]

Make sure no one's changed the back pressure setting to zero, that would allow the screw to rotate backwards without pushing material forward.

kelley

[Pilot]

Hi Brent .... you are absolutely right.
But it is Nissei, If is not special screw inside, he has a ring valve.

[ArikB]

Its slipping past the NRV. Pull the screw, mic the barrel and screw, and check the NRV. Also look at your decompression. There needs to be enough so that the NRV seats before the screw hits the melt.