Mold's creation == material PVA == work in progress

... formula” creates cycles of temperature by itself. Period is 1min 20 sec and period is stable, even after 20 minutes it stay amplitude and period the same.

To repro situation needs to compile firmware (Sprinter) and monitor temperature in ReplicatorG. 

That is definitely creates a problem with extruder in case: for PVA stating flow point is 180C, starting coagulation temperature for PVA is 200C.

Setting target temperature to 190 makes extruder jam when temperature drop to 180, and melt flow index = 0. That make pressure inside extruder jump, and small jam created.

On another hand when temperature reach 200 it coagulates PVA on a surface of extruder (that will contribute to a jam in a future).

Firmware with PID enable (I do not know correct name = “#define PIDTEMP 1” uncommented) is not capable to print PVA without jam.

To avoid problem need to find solution ether by releasing extra pressure, or by different algorithm of regulation.

Tried setting HEATER_CHECK_INTERVAL to 50 ms – amplitude of cycle dropped to +-5C, period was same, and I believe this is not because of algorithm as it is – just coincidence – when I debugged formula in spreadsheet – in each interval of time it jumped for one bigger value for heater_duty to a smaller value. With 50ms looks like it just “skipped” some of that jumps. When I tried different interval it just returned to same +-10C.

For a plastic with more stable parameters of melt flow index (PLA/ABS) that problem with temperature regulation in extruder is not big impact – plastic flows in a range of +-10C and index is different but varies not much.

Also checked “regular” temperature control (with PIDTEMP commented out) in this case when temperature reaches 191 it switches off, when it is low then 190 –then it is on. Cycles become shorter, and temperature variation is  +-5C.

Then I did experiments with heat absorber (I hold heater by big pliers – good contact and good heat adsorption). PID formula works better then on-off algorithm when there is a flow of a heat to cold pliers, when pliers become hoot (around 60 C – temperature when plastic insulation on pliers did allow  to hold it in hands more) then “on-off” started to work better.

Definitely to improve extruder for 3D printer needs to control temperature better then +-5C.

Task by itself is interesting not only for dissolvable mold creation, but also for a temperature control in vacuum when only radiation of a heat can be done for “heat flowing out”.

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