Metal flakes appearing on atomic method. What is this?

[peetersm 120]

This is really strange. I am getting what looks like an accumulation of tiny metal flakes only at the tip of my atomic method pulls. I've already done about 7 pulls and each time I am seeing this. I am not seeing any metal flakes or dust anywhere else in the path (extruder teeth, bowen tube, etc). The outside of my nozzle looks fine, before the pull the filament looks like it's coming out really nice and cylindrical, after the pull when I look down inside the nozzle I see shinny clean looking inside of my nozzle. BUT when I look at the pull I get these strange flakes only on the tip (see photos below). I can scratch the shiny flakes off the tip of the pull and they are fine and power like.

Has anyone else seen this? What could be going on?

Should I keep using the atomic method until this goes away (I've done 7 already).

--more details-

My printer started to slightly under extrude about 30 minutes into a 5 hour print job and at about 1:30H the under extrusion had become so bad I stopped the job. I was trying out a new spool of "Taulman Clear In-PLA - 2.85mm / Clear". I suspected nozzle issues so I have been doing atomic method pulls with some of my trusty ColorFabb PLA/PHA Traffic Red (a spool that about 80% used up and has been super reliable for me)

--------photos-------------------------------------

[peetersm 120]

Here's a photo after I scraped at the flakes with my finger nail and spread some down the side.

[amedee 338]

There is nothing like that in the UMO hot end...

I would suspect it came with another filament and accumulated in the nozzle...

[SyntaxTerror 343]

That's really odd. Looks just like solder.

[jonatanrullman 17]

That's really odd. Looks just like solder.

 

It does look like solder. 60/40 solder melts at slightly below 200 degress and pla is typically printed at 210-240 in an UM2.

It's a long shot but could there be trace amounts of solder contamination in the Taulman spool that melts and accumulates in the nozzle?

[SyntaxTerror 343]

If it really IS solder, I have to wonder how on earth it got there. It really, really does look like solder that's been heated long enough to burn off all the flux.

No matter. If we assume that whatever it is melts in the nozzle... it would be a reasonable assumption that you could get rid of it with some desoldering wick and either a soldering iron or a heat gun.