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Frequently blocked hot-end? Here's my solution

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Posted (edited) · Frequently blocked hot-end? Here's my solution

I have a UM2 with Olsson block, and print mostly with ABS, but what I am about to say could apply to any machine and material.


I bought my UM2 in 2014, and began with PLA, but soon switched to ABS for its superior strength (not to be confused with stiffness), working temperature, and resistance to water. This is because most of my models have mechanical rather than ornamental use, and can easily be strengthened by using an acetone-dipping technique.


After a couple of months I began suffering regular hot-end blockages resulting in under-extrusion and slipping of the feeder motor. I was running my machine almost 24/7, and found I had to perform an atomic-pull on a weekly basis. Eventually, the original nozzle/block would not clean out properly and I had to remove it for more rigorous attention. I did this a couple of times, and also replaced the teflon insulator. Fed up with doing this, I bought a replacement hot-end block and temperature sensor because I was unable to remove it from the block, and eventually broke it trying to get it out. After a couple of months this new part started misbehaving like the original necessitating frequent atomic cleaning.


I was now into my second year of use, and the Olsson block appeared. This seemed a sensible upgrade as it had interchangeable nozzles so I purchased one, together with a new Bowden tube, i2K insulator and yet another temperature sensor. At first, all seemed OK, but ultimately I began to get recurring nozzle blockages.


It seemed then, that the problem was independent of the hot-end design, and I wondered if the temperature calibration of the nozzle was incorrect. I have a contactless (infra-red) thermometer that I have previously used to measure bed temperature, and an accurate thermocouple pyrometer (photo attached). Attempting to measure the nozzle temperature on its outer surface was inconclusive - the infra-red device seemed incapable of detecting such a small object, and the thermocouple bead did not contact the nozzle well enough to get a consistent reading. So, I realised that  I need to place the probe inside the nozzle itself to get an accurate reading.


First, I needed confidence that the thermocouple device was reasonably accurate, so I placed the probe inside my kitchen fan oven together with an oven thermometer and set the oven temperature to about 220degC. When the pyrometer reading settled to a constant value, I opened the oven door and quickly noted the oven thermometer reading, and took a reading with the infra-red device. To my amazement, they were all within 2 degrees of each other at 225degC. So I was confident that the thermocouple device should give a reasonably accurate result.


I now returned to the UM2, and removed the filament and Bowden tube from the hot end, and inserted the thermocouple probe right to the bottom of the nozzle. I then did a series of tests, setting the temperature in 10deg steps from 200 to 250deg. In every case, the temperature was 20degC higher than I had set it to. So, when I had set the temperature to 260degC, the actual temperature was more like 280degC. No wonder I was getting blockages - caused by carbonation of the filament which is notoriously difficult to remove.


I have now been running my UM2 with nozzle temperatures set 20deg lower than required and, over the last (nearly) 2 years I have not had one instance of nozzle blockages. The only times I have used an atomic pull is when changing to different type or colour of filament to ensure the hot-end has been purged. Incidentally, I only use nylon for the atomic pull - by far and away the best material for doing this.


Thermocouple Pyrometers like this can be bought on Amazon quite cheaply if you would like to check your own printer.


Edited by vitalsparks
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Posted · Frequently blocked hot-end? Here's my solution

Great post!


Or... you could just lower the temperature if you keep getting ABS converting to that gummy material.


And if you aren't getting good layer adhesion then you need to either increase nozzle temp or air temp or lower an speed.


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    Posted (edited) · Frequently blocked hot-end? Here's my solution
    On 3/10/2019 at 5:02 AM, gr5 said:

    Or... you could just lower the temperature if you keep getting ABS converting to that gummy material.


    That's what my measurements showed, but it is reassuring for me to know exactly what that temperature is, especially when I occasionally change to a different material like T-Glase or PolyFlex. With ABS, and various other materials, carbonation turns the material into a hard crust that lines the inside surface of the hot-end and, when eventually minute particles break away, this is what can clog the nozzle. In my experience, an early warning sign is the slipping of the feed motor as the carbon builds up, increasing the pressure required to force the filament through the hot-end - due to increased friction against the walls I would guess.


    On 3/10/2019 at 5:02 AM, gr5 said:

    And if you aren't getting good layer adhesion then you need to either increase nozzle temp or air temp or lower an speed.


    With my favourite ABS (ABS-X from 3DFilaprint) I set the temperature to 235deg (actual 255deg) and a bed temperature of 80deg. I get excellent layer adhesion, and no evidence of warping (an attribute of ABS-X). I rarely turn on the fan, except when printing very small objects.


    Edited by vitalsparks
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    Posted · Frequently blocked hot-end? Here's my solution

    Hi vitalsparks,

    Have been reading your interesting post and did the same test as you did when reading the temperature inside the nozzle using chromel alumel thermo couple. I did this because it was convenient, as I did a check of the hot end after some 2o hour printing with nylon first time at 256 deg. Celsius.


    Here is the result from my setup:

    Set Temp. UM2        Nozzle Temp. UM2    Measured temp ext. instrument.
    deg. C                       deg. C                         deg. C
    30                              30                               31
    50                              49                               50
    100                            100                            100
    150                            150                            151
    200                            200                            200
    230                            231                            231
    250                            249                            249
    255                            254                            254


    I was kind of surprised after this good/excellent result, however, this is actually confirming my experience with those sensors. The Platinum PT100 is used "mostly" in the aviation as an absolute temperature reference among a few others.


    Here is some pictures of my setup and most important values:




    The hot end with the thermo couple inserted into nozzle tip.




    The adjusted temp is 100 deg. Celsius.





    The adjusted temp is 200 deg. Celsius.




    The adjusted temp is 230 deg. Celsius.




    The adjusted temp is 250 deg. Celsius.




    The adjusted temp is 255 deg. Celsius.



    Why this difference?


    When I built my printer, I was using copper paste in between the heat shell and the heat block. I've also used copper paste between the PT100 shell and the heat block.


    As there's a little space (for expansion) between the mounting hole's for the heat shell and the PT100 temp sensor it is a good practice to fill up the space (clearance) with copper pasta.

    Copper pasta have excellent properties for this use as:
    Good thermal conductivity (air pocket is a very poor heat conductor).
    Good electrical conductivity

    Corrosion resistance

    Copper paste also prevent corrosion and burning of parts, but you still will need to preheat the nozzle for change or removing hot end from the attachment frame.




    Metal device:       Relative Conduction:
    Copper                 394
    Silver                    418
    Aluminum            238   (The cold junction frame attachment and cooling frame)
    Stainless  steel     13      (The nut holding the heat block and housing the TFM coupler).

    PS. I'm also using copper paste in between the nozzle tread and in between the steel nut  tread mounted onto top of heat block. NB; Be careful here to avoid copper paste into the filament area/side..   Note Well..
    Just for the record; I'm still using a 24 W heat element, even printing with nylon at 256 deg. C!
    This is just because my setup is far more efficient, due to much better heat conduction!

    (To check the calibration of the PT100 sensor, put the sensor into clean water with ice cubes that's need to be stirred to keep this mixture at zero deg. Celsius. Your Ultimaker nozzle temp should read 0 deg, C.  (A precision resistor with 100 Ohm should read zero deg. C as well. 0.5% tolerance or better is needed).
    Do the same with boiling water, will show 100 deg. C here.. )


    Maybe this little modification might be something for you, unless you have something else in error.






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    Posted · Frequently blocked hot-end? Here's my solution

    I tried ice water and boiling water and the temp probe was quite far from 0C and 100C so I don't recommend that.

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    Posted (edited) · Frequently blocked hot-end? Here's my solution

    Hi Folks,



    The 0 deg. Celsius and an ice mixture with clean water have been a preferred method in laboratories as long as I can remember..

    This is the recommended reference in the aircraft standard practice manual as well, used for certain temperature calibration checks.


    For the boiling water there might be some adjustment, -that I forgot to mention..

    Cause, this is valid only at sea level when at "standard atmosphere pressure" (1013.25 hPa (previously named millibar)).


    Here is a calculator to be used for finding the air pressure (for those living at some (high) altitude. This calculator is using standard pressure at sea level as reference, so a barometer showing absolute pressure is nice for this setup..




    I'm living about 45 m above sea level, so it is not that far off..


    By the way, almost all smartphones today have a pressure sensor giving the pressure in hPa, so using this **) calculator will give you a correct value for the boiling point. Just input a value that's according to the pressure, then see the correct boiling point (in deg. Celsius) for water at this pressure. This temperature should match the reading at the nozzle temperature on your UMX using PT100 temp. sensor.


    Note: If the pressure is very hi, you might need to use negative altitude eg. -100 m.  


    The Fluke 8060A is a precision instrument, crocodile clamp that's gold plated I've used in this "experiment", just to see this is the way to check a PT100 for correct reading, vs. the specs. So the easy way to do this is to connect the PT100 to the printer so you can see the temperature directly, the temperature should be only one digit of if any, when using PT100A version.


    Here is the PT100 specs, temperature vs. resistance:



    Here is some pictures of the setup:




    This picture show the resistance in the measuring wiring is: 0.15 Ohm. 




    By pressing the REL button, the instrument reading point is at the point the two small clip is attached.

    This take away the error instrument wires can make.




    Here is the reading when the PT100A probe is immersed in the ice bath (using a food thermos).

    Reading is within specs..




    Here is the PT100A sensor inside a water boiler, sure boiling.

    The reading here is a little say lo, perfect would be 138.51 Ohm according to the spec sheet for the PT100A.


    The fluke is reading 138.44 Ohm, a little less than expected but not far..


    However, the pressure according to my S9+, is: 1006.33 hPa so this need some correction.

    If you use the app, altitude vs. boiling point you find the correct boiling temp for this actual pressure.

    We find the altitude that match closest to 1006.33 is 57m, then we read 1006.4 hPa. As we cannot set 1/00 hPa, this is the closest we can do. So this give us a a boiling temperature at 99.82 deg. Celsius.


    If we use the value from the instrument, 138.44 Ohm and use the linearity between 99 and 100 deg.C, our temperature is 99.79 deg.C.


    Well, this altitude difference was not that much, but at a few thousand will for sure give a clear relation ref. pressure/water boiling temperature.


    The measured difference here is only 0.03 deg. Celsius, and only 0.21 deg. less than 100 deg.C.









    Edited by Torgeir
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