Non Return Valve Leaking

[Rojan]

Hi guys,

One of the setters called me to show that the screw bottoms out when processing PA6. We did a static nonreturn valve test and the result was that it leaks. I repeated the same procedure for PP and there was no leak at all. The screw and barrel were regenerated a few months ago - the ID of the barreal and OD of the screw were increased by 0,2 mm as one of the maintenance guys told me.

Do you think there might be too much clearance between the check ring OD and the barrel ID? What are the recommendations for these clearances? The screw is 60 mm in diameter. Except for this clearance I know there might be other causes, but I would like to check the clearance when we take out the screw.

Robert

[rickbatey]

This could be the result of simply running the barrel heats too high for the PA6. You don't mention if either of these resins are glass filled. You also didn't mention decompression settings either. The PA job may run very little compared to the PP one.
BTW I know on an Engel the sealing ring can be turned backwards and not seal properly against the seat. So confirm if it's properly assembled. Also when the refurbishment occurred was the screw tip assembly replaced?
Rick

[brentb]

Different resins flow differently, like sometimes flash where others don't. So some may show a "bad' NRV,where others don't. LCP can really uncover even micro NRV defects!

KOM

brent

[Rojan]

Rick,
The PA6 melt temperature was 265 deg C - I measured that. None of the resins are glass filled. I played with decompression for PA6, but it didn't work. The one thing that I didn't check was moisture content. The resin was dried 5 hours in a dehumidifying dryer with dew point set at -40 deg C. When purging I saw the melt to be normal, not watery.

I will confirm the assembly when they take the screw out. I know that the screw tip assembly was refurbished.

Robert

[Joel JS]

Robert,

My maintenance guy showed me a spec sheet for barrel clearance guidelines......for a 2 1/2 " screw, the new part clearance is .007-.010", and max wear clearance is .030".

Hope that helps,
Joel

[tbramel]

Go to Reiloy's website. They have a lot of good information about screws and barrels. I have attached a file for spec's on screw and barrel wear.