Uphill oozing, blobs, globs, electrostatics etc. - snafu.

Discussion in 'E3D-v6 and Lite6' started by UlrichKliegis, Jan 25, 2016.

  1. UlrichKliegis

    UlrichKliegis Well-Known Member

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    Some time ago, my supply of PLA of a certain brand was used up, the retailer had closed his shop, time to look around for something different. No problem, enough PLA for all of us. At the same time, I also turned to PETG, and am still fascinated by the quality of the parts made from it.

    At about that time, I started to observe extruded plastic gathering around the cone of the 0.3mm nozzle of my E3D-V6. I run this in an OrdBot Hadron, one of the usual H-shaped printers.

    As I had taken apart my hotend some time ago, I thought - until this morning - that the plastic that collects there around the nozzle outlet, growing slowly to a larger blob engulfing the whole cone of the nozzle, finally even covering the hexagonal part of the brass nozzle up to the heating block was somehow oozing from a less than optimally tightened nozzle, that the pressure within the heating block / melting chamber drives it out between the nozzle and the heat break. After heating the fronted up and removing the nozzle, I saw that the thread of the nozzle and it's top margin looked absolutely clean, no remainders of molten or burnt plastic. Hmm, good news and at the same time bad news. Where does the plastic come from?

    So, I cleaned the nozzle completely, scratched off all baked plastic, gave it a thorough treatment with a brass brush, heated the hotend to 260°C and retightened the nozzle in the aluminium block, leavin a gap of about 0.5mm between the heater block and the brass nut. Restarted printing PETG.

    Of course, the first tracks looked good. I had a very keen eye on the nozzle tip - at first, it was shiny brass, the cone well visible. Then, after a few minutes (laying a ground layer for an object), I saw that the filament sort of flowed upwards very slowly, starting to build up a volume from the nozzles outlet (most of the material of course landing on the heat bed and later on the previous layers), but it formed a sort of thick film that spread upwards and around the cone. This took less than 10 minutes. The drop of molten plastic grew and grew - and finally got stuck somewhere on the building surface, tearing most of it with it, landing as a nasty blob on that surface. Stuck immediately, but was ironed flat by the next pass of the nozzle in the net layer of the infill. That process repeats endlessly. The volume in question is about 50 µl, not much, but enough to be in the way and in the worst case stop the nozzles way - as happened here yesterday.

    So my suspicion that the unwanted drops sipped through the nozzle's thread was wrong, the real reason is pretty mysteroous, though.

    Static electricity comes to mind immediately. At least, in the OrdBot, all essential parts are isolated from each other by plastic rollers, plastic washers etc.So, the extruder carrier is not grounded, neither is the build table nor the frame. All major parts are permanently in motion, and the extrusion of the molten plastic is a feast for a thoertic physicist, electric charge-wise.

    'Wet finger'-grounding the extruder and thus also the hotend showed a surprising effect: The surface of the infill layer that was just printed at that time showed a different surface structure - repeatable.

    I had even the impression, but that may be self-deception, that the aggregated plastic started to flow off during the grounding attempts - but I doubt that myself.

    Has anybody observed something similar? Is it common knowledge and am I the only one who does not know (again)? ;)

    Do you folks at E3D know anything about the influence of static electricity on the building (micro-)processes?

    Any advice and thought is appreciated.

    Thanks, cheers,

    Ulli
     
    #1 UlrichKliegis, Jan 25, 2016
    Last edited: Jan 25, 2016
  2. Dr Jeep

    Dr Jeep Well-Known Member

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    This is pretty fascinating if true, definitely needs some further experimentation I'd say. My K8200 based printer has the hotend insulated by the plastic of the extruder body (I suspect most do) but most of the running surfaces are metal on metal and I've never seen much tendency to generate static, but perhaps it really is a problem on mechanical designs more likely to.

    Ground with a wire on a small ring terminal on the heater cartridge securing screw I say and do a full ungrounded and grounded print.
     
  3. richard sumner

    richard sumner New Member

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    I've been using clear PLA and now starting to use clear PETG. I do see little dark spots in the print, but I haven't caught one in the process of creation. I see these in PETG, but not in PLA. The hot end temps are: clear PETG at 260 C, the PLA at 190 C. I'm using a robo3d with an e3d v7 hot end. The nozzle is e3d brass, 0.3 mm. The PETG is maker filament hd clear glass. Dark spots are most annoying!
     
  4. mike01hu

    mike01hu Well-Known Member

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    Ulrich, that is an interesting observation. I had noticed the collection effect on my K8200 running its standard nozzle. This nozzle is very large compared with the E3D part yet filament coating would appear all over it; I had first assumed it was a condensate but that did not make sense as the nozzle was at the same temperature and it was definitely filament as it wiped off while hot and had the same colour.

    Was it electrostatic? The nozzle on this machine is totally isolated electrically so could accumulate a charge due to the passage of filament through it and wiping over the print surface; of course the filament is a good insulator so no path for the charge to neutralise but I can't think of the physics that would cause the filament to creep over the surface, other than that PLA is exceptionally sticky when fluid so could flow by the whetting process, much like putting a drop of washing liquid in water to get it to cover a surface i.e. breaking the surface tension. As I only used PLA, I smeared a fine layer of silicon grease over the nozzle and this seemed to prevent the problem occurring.

    The other thing that made a difference was ensuring the nozzle face was flat; this made sure that filament did not rise above the set height at the edge of the extrusion, lessening the chance of pickup on the next pass. I flattened the nozzle by placing a sheet of very fine emery paper on the bed and lowering the nozzle to just touch it then gently moving the table in several directions to restore the nozzle surface; this has another advantage in that it ensures that the nozzle is square to the bed surface.

    The next time I fire up the printer for a job I'll hang my oscilloscope x10 probe on the heater block to see if there is any charge.

    Mike
     
  5. UlrichKliegis

    UlrichKliegis Well-Known Member

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    Interesting replies, thanks to all so far. When talking about static electricity, I had also some glueing chemistry in mind. Back in the days (or nights) I spent in the darkroom developing photos (to the younger ones here: It was called photography :) ) I observed some luminescence when peeling off the leading paper that was taped to the 120-sized medium format film. Where film and tape separated, this luminescence could only be seen, it left an interesting exposure pattern on the film too. A physicist told me that at the moment when the two parts are separated, a very high tension between the surfaces is discharged.

    So, my reasoning was and is - does the melting, depositing and re-curing of the plastic material cause some local electrical phenomena? You will almost certainly not be able to measure anything with your o'scope, I could hook up one of my vintage Tektronix boat anchors up there too but am pretty sure that there is no accessible dipole. If there is some electrical field at all, it will be limited to the melting/curing area. What would be the other side - the heat bed, acting as a capacitive electrode? Guess not. The reason, if to be found here at all, will be in the local change-of-state of the plastic material.

    Mike, your nozzle - treatment is interesting, both the abrasion and the silicon-application. Does the silicon not interfere with the sticking capabilities on the heat bed and between material layers? I could imagine that some sort of a microfilm would also spread over the printed part's surface. From boat painting I know the cast-iron rule - never bring silicon close to your brushes, varnishes, surfaces-to-be-painted, even don't think about it!

    I'd be interested to hear from the E3D-folks what they think.

    I mean, it is maybe the same physical effect of adhesion that lets water creep up a piece of a glass's wall - is molten PETG or PLA a polar or unpolar liquid? I'd guess polar. But I surely don't know.

    Ulli
     
  6. UlrichKliegis

    UlrichKliegis Well-Known Member

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    Update: The provider of my PETG filament advised to check the flow rate. His words: If the material creeps up on the nozzle's outside and generates a growing volume there, the flow rate is definitely too high: Some "wetting" by the filament is normal for PETG, but not that abundance. I'll test it later today and will report.
    I am building yesterday's problem case in PLA right now - no problem, no upflow so far. Same nozzle. Oh well...

    Ulli
     
  7. mike01hu

    mike01hu Well-Known Member

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    Yes Ulli, that was my thought before applying silicon grease but it is really no more than a very sparing "wipe over with an oily rag" and certainly not anywhere near the bed. It is a pig to clean off a surface if not wanted so it is definitely a case of "user beware".

    Regarding the nozzle treatment for flatness and level, for most nozzle setups there is no method of adjusting the vertical alignment, so there is total reliance on the flatness of mating surfaces. As you will know, any deviation from parallel to the print surface leaves a wedge shaped gap under the nozzle thus encouraging the extruded filament to be distributed unevenly and can produce a ridge along one side of the track. It is important that the face of the nozzle is also wider than the track width, so my flattening process also ensures that any rounding of the edges of that face are minimised and the full width is available; if not, this will also cause ridges to form on the track edges as well. Any ridges may be flattened by the next pass but can equally be picked up by the nozzle.

    For others reading this, it is important to note that flattening the tip is not an everyday process and only needs to be done after a nozzle or hotend change and this flatness is not a major issue but really addresses filament pickup by the nozzle, which is what this thread is about. Bed levelling has greater effects and any nozzle flattening will be offset by this, so for auto-levelling systems it may not apply.

    Mike
     
  8. UlrichKliegis

    UlrichKliegis Well-Known Member

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    Mike, thanks for the additional information.

    Most important for the time being, I can report that the problem seems to have been solved. In short: Too much material flow, temperature(s) not high enough, sub-optimal infill pattern. I'll report more on one of the next days.
     
  9. mike01hu

    mike01hu Well-Known Member

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    Silly me, I assumed these parameters were OK as they are equally important. Good luck.

    Mike
     

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