Flow Lines?

[The Rookie]

Hello all! It has been too long since I have been on to post any questions/responses.

Today I was taking pictures of PET tubes with extra back lighting for our quality department and they immediately started questioning me about "flow lines" on the part. The parts all pass inspection criteria and are acceptable, however, they want to know why.

I told them that I would get back to them after talking with my team (since I am still a newbie at work and didn't want to misspeak).

My team said that they are flow lines and we always have had them, so I wanted to get other opinions/explanations. I have also noticed these lines before that were slightly discolored and looked a little degraded, but my team said it comes and goes as well.

I am inserting the image to the text and also attaching so that you can see the lines. The lines are very hard to see, so I traced the lines as well as lightening the image in hopes of making it stand out.

[JayDub]

The images are too small for my old eyes to make out much detail, but the defect doesn’t look like what I would call a flow line, it seems to be more related to gate blush.

Can you give us more detail about the mold – cavitation, runner style (hot/cold), gates, etc.? Also, you could run a fill progression to see where the cavity just begins to fill, then compare that to the pressure curve – if you see a dip, there may be a hesitation at the flow front causing the flow line.

That wouldn’t necessarily explain the degraded appearance though, so I’ll take a wild shot in the dark. Degraded material coming off the gate – usually with a smoky appearance – can be associated with valve-gated hot runners. In that case, raising the gate zone temperature by a few degrees (5 or 10 F) will generally show an improvement.

[Joel JS]

Hi,

Well, my old eyes can't see em very well either,....... guessing these are heat related "flow lines,"........ also guessing these are direct gated hot drops??? ...... if so take an actual temperature inside these drops with a mini probe if possible (use hot gloves), I have seen many times the temps are much higher than what you see it showing. I would also minimize suck back so it doesn't pull in too much air prior to shooting again, but has enough so you don't get any drool.

Send the group more information as necessary and I am sure they will help you.

Joel

[chrisprocess]

Are you drying the material? - Same dryer used every time it runs? Over drying will cause degradation and can cause flow lines

[The Rookie]

Sorry for the delay! We are running a 96 Cavity Valve Gated Hot Runner and material is from one dryer and has a minimum of 4 hours of drying. We tested the material for moisture and we were acceptable.


Thanks JayDub for the wild shot in the dark and to check the temperature of the tips Joel.

Next time the press is down and/or they see tubes with these marks I will try your suggestions.


We are running a 96 Cavity Valve Gated Hot Runner
Material is from one dryer and has a minimum of 4 hours of drying

[chrisprocess]

would look into machine down time and throughput of your dryer. PET can degrade easily if dried too long