Silver Fibers show Up when Parts are Rubbed!

[Joel JS]

Hello

I got a strange one here!......... Anybody seen this before???

We are running parts that look fine, and went through preliminary samplings and got approved,.... But now we see this, when you rub the parts with your thumb... always in the same spot, these "silver fibers" appear ......Our customer first noticed when wiping parts before painting w/ alcohol... pictures attached.

- 4 air valve gates, can be sequentially fired,
- mat'l is Bayblend, T65XF, pc/abs
- color pellets added.

I can move the fibers around to different spots by changing the gate sequence, but unable to eliminate. The fibers are always close to end of fill. No other processing that I have tried has had any affect.

*Material supplier has yet to point us in any good direction, basically not sure, fibers were tested and came back with properties very similar to the base resin.!
**Also seen with base resin only, no color added.
*** Switched to resin 0810LG and did not see these fibers, but had other issues with cosmetics, (and just not 100% sure it didn't have this condition since you have to rub the just right to see.. but 90% sure at this point)

Part is colored black, with fibers that look silver, pics attached are a worst case example.

thx,
Joel

[JayDub]

I assume you’ve interrogated the usual suspects – moisture content, mold/melt temps, venting. (You can simulate more aggressive venting by just putting a post-it note on the parting line next to end of fill). The only other suggestion I have would be to slow injection speed right before transfer (enough so you can see a significant difference in the speed and pressure graphs). Double check the vents first, though.

[Joel JS]

Thanks JayDub,

You've inspired me to try something, let me get back to you on my findings.

Joel

[Joel JS]

Hello Group,

Still having this issue, has anybody seen this before?

JayDub, I tried a fill only / short part so there was no gas trap issue and still got the silver fibers.

(I can move them around with different valve gate sequencing but not eliminate)

thx,
Joel

[chrisprocess]

Are the fibers orientated the same direction of flow? Or are they pulling up relative to how they are rubbed?

My best guess is delamination of the material, melt temp/shear (fill speed/ back pressure/gate sizes).
Could just be a bad lot, or a bad material all together.

maybe that surface finish on the steel is just incompatible with this base resin. I would avoid any type of edm suface finish

[nikom]

Chris, why would you want to avoid an EDM finish here?

[Joel JS]

Chris,

Fibers show up when you rub parts in the direction of flow, and the fibers generally appear to be in the direction of flow as well.

It does not look like typical delamination, where you can basically see the material "de-laminating" defect before you rub them.

thx,
Joel

[chrisprocess]

Chris, why would you want to avoid an EDM finish here?

I've experienced various issues with edm surface finish; parts sticking, material gassing/leaching out to steel, vents clogging up (inability to dump gasses) accumulation of gunk, and others.
That said I'm sure some edm surface finishes are of higher quality than others. And I'd bet someone much smarter than me has completed an academic research paper on different types of edm surface finishes and their effects on plastics processing. Generally I've seen much better results with edm surface finishes that have undergone some sort of secondary polish operation. In essence you wouldn't want a smong-like surface finish running plastic parts. Sounds like a recipe for disaster :P

May or may not apply to Joel's issue, just bringing up ideas.

If you could imagine a sponge-like surface finish wouldn't work that great when modling parts.


Chris,

Fibers show up when you rub parts in the direction of flow, and the fibers generally appear to be in the direction of flow as well.

It does not look like typical delamination, where you can basically see the material "de-laminating" defect before you rub them.

thx,
Joel

Yea that's interesting so they appear fine at first but once you rub them the defect occurs.. But only at the end of fill. Almost like the material composition in that region is different than the rest of the part.

[JayDub]

If you look at the process graph, is there a sharp pressure drop at transfer? Just wondering if the flow front is hesitating & causing delamination.

[Joel JS]

JayDub,

The job is not currently running, I did not notice any peculiar pressure spikes on the graph.

thx!
Joel

[nikom]

Chris, thanks for the insight. I'm new to this and we have a lot of molds with an EDM finish. I'll have to keep an eye out for these defects.

[Huw Durban]

Do you still see this defect if the black masterbatch is left out, what is the carrier material of the masterbatch?

[Joel JS]

Do you still see this defect if the black masterbatch is left out, what is the carrier material of the masterbatch?

Yes, the natural base resin still has fibers.

thx! Joel