firmware feature request - help stop blocked nozzles

I had a problem with a blocked nozzle the other day. I think it was caused by the hotend being up to temperature but not printing , for an extended time. I realised, after getting the printer ready to print, that I needed to modify the item, this took some time to change it in openscad, generate the stl and then slice. All this time the plastic in the hotend was cooking.

I wonder if it is feasible to have the firmware reduce the hotend temperature, after a fixed period of time, if a print has not been started.

might save others from having to clean out a blocked nozzle.

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

Quote
appjaws1
I had a problem with a blocked nozzle the other day. I think it was caused by the hotend being up to temperature but not printing , for an extended time. I realised, after getting the printer ready to print, that I needed to modify the item, this took some time to change it in openscad, generate the stl and then slice. All this time the plastic in the hotend was cooking.

I wonder if it is feasible to have the firmware reduce the hotend temperature, after a fixed period of time, if a print has not been started.

might save others from having to clean out a blocked nozzle.

Sorry to hear that, but in a way good that it tends to confirm that cooking plastic does cause blockages. I have only had 2 blocked nozzles in the 15 months I have had the Ormerod (doing at least an average of an hour printing per day, probably more). Both happened shortly after a "cooking plastic" situation. The first time was after the extruder started slipping and wore a groove in the filament, and the second when the Bowden tube came unscrewed during a print, so neither would have been prevented by the firmware mod. you suggest. In the first case I noticed after about 10 minutes, and the second after about 15 minutes, so it doesn't take long - at least with ABS at 230 degrees.

It may be something to investigate more fully if getting a second nozzle, because the standby temperature will need to be lower than the temperature that is likely to cause such a blockage. In that respect the mixing type arrangement would be better than separate hotends.

Meanwhile I have 2 spare nozzles ready in case it happens again. Cleaning the nozzle is a hit-and-miss affair that could take many hours, but a nozzle can be changed in 15 minutes or so.

Dave

Dave,
Thank you for your reply.
I can see that in the circumstances when you have experienced a blockage, the printer would just carry on thinking it was printing correctly, even though no filament was actually extruded.

This request would have helped in my blockage circumstance, although perhaps I should have reduced the temperature manually but I just did not consider a long wait when ready to print as being a problem.
What do you think would be the minimum time to pause a print without the filament cooking too long or the safe time to have the printer hot and ready prior to starting a print?
I wonder what the science is behind keeping filament molten for extended periods?
Would ABS, PLA and specialised filaments react in the same way?

I will order spare nozzles, sound advice.

Paul

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

I'm trying to work out a specification of the required behaviour.

1. Is this only a problem with ABS, or does PLA also cause problems if left molten for too long?

2. What should be the trigger for reducing temperature? E.g. extruder temp greater then X for the last Y seconds, and no extruder motion during that period.

3. What temperature should the extruder be reduced to when this feature is triggered?

4. Should we warn the user that the temperature has been reduced, if so, how?

5. Should we rely on the user to reset the temperature before printing, extruding etc.? If not, under what conditions should we reset the temperature to its previous value?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Personally I've left my hot end on with PLA for well over 45 minutes without any issue.

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pandionx
Personally I've left my hot end on with PLA for well over 45 minutes without any issue.

ditto PLA 60 minutes at 195C - no problem with nozzle after that, and the extruder was active during those minutes



Erik

Quote
dc42
I'm trying to work out a specification of the required behaviour.

1. Is this only a problem with ABS, or does PLA also cause problems if left molten for too long?

2. What should be the trigger for reducing temperature? E.g. extruder temp greater then X for the last Y seconds, and no extruder motion during that period.

3. What temperature should the extruder be reduced to when this feature is triggered?

4. Should we warn the user that the temperature has been reduced, if so, how?

5. Should we rely on the user to reset the temperature before printing, extruding etc.? If not, under what conditions should we reset the temperature to its previous value?

1. I must admit that this has not happened to me with PLA, but at the same time I'm not sure if I have left the ormerod running with no movement for any length of time.
2. I would suggest a trigger time of 5 minuets, or maybe a user input time could be used. What do other users think?
3. I have not had this problem with the standby nozzle, which I have set at 155 C, so maybe that could be the reduction temperature.
4. Maybe a colour change on the current temperature reading on the web control and PanelDue, or flashing reading, or both. On pronterface, a message could be sent to the log.
5. If the temperature reduction has been triggered then a print should not be able to start or continue until the previous operating temperature has been reached and is stable.

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pandionx
Personally I've left my hot end on with PLA for well over 45 minutes without any issue.

That is encouraging, as I said in the original post I'm not sure what happens to ABS or PLA if left molten for any length of time. Do we have any experts who could provide an insight?
However, as a safety feature it would make sense to reduce the hot end temperature if the machine is idle.

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

From what I can find, ABS should remain unaffected by repeated melting, and does not suffer chemical decomposition until heated to about 390 deg C. [www.journalamme.org]

However that paper concentrates of the properties of repeated injection moulding of ABS, and would not have examined whether small solid particles might be formed if kept molten for several minutes, though it does show that there is a one-time change in tensile strength, which could be related. There is also the possibility of some sort of reaction between the molten ABS and PTFE tube in the nozzle. My experience was that the blockage occurred a fair time after the heat event, with the blockage getting gradually worse over the following two prints, which may suggest that the blocking particles formed on the walls of the PTFE tube rather than the body of molten plastic, and broke away at a later time.

Dave

I'm not an expert in polymer chemistry, but I did take quite a few chem classes in collage quite recently (though I opted not to take hard-core polymer chem).

I wouldn't be surprised if heating a small volume of filament for an extended period of time would cause the polymer chains to either link together or break apart, precipitating a solid which would block the nozzle; esp. when many of these filaments are designed to undergo some change upon extruding, i.e. we want super flexible filaments, so they don't break in the bowden tubes, but we want the prints to be nice and solid. Sometimes things are added to these filaments to get these ideal properties, and they might be breaking down under these conditions too (after all, the chemists who design these aren't thinking that the filament will be at these temperatures for 30 minutes)

On the other hand, it could be the dyes added to the filaments that are breaking down from the heat. They might be 'burning' and clogging the nozzle with chunks. This could explain the reason why some people have no issues, while others do... and why the issue can happen with different plastics.


As far as solutions, I see the use in having a failsafe for this in the firmware but I'm not sure what numbers would be reasonable.... I suppose ideally someone would figure out how long filaments could cook before this is a problem, but it would result in many many clogged nozzles.
Another option might be to extrude a small volume of filament every x minutes, although that could cause a mess, ruin a print, or burn someone who's hanging out under it for some reason.

Sounds like this often happens before a print is started, maybe setting up end g-codes to retract the filament would prevent a lot of this?

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shadow651
Sounds like this often happens before a print is started, maybe setting up end g-codes to retract the filament would prevent a lot of this?

I doubt it, because retracting the filament does not remove all the plastic from the nozzle, and so what remains would probably be enough to cause the issue.

My suggestion would be that if the extruder is up to temperature and there has been no extruder movement movement for a minute minute, turn the heat down on the nozzle (maybe down to the bed temperature). When an extrusion command arrives, turn the heat back to the set temperature and wait for it to reach that temperature before executing the move command.

Dave