hot-end-thermal-management [Bukobot 3D Printer Instructions & Docs]

===== Hot-end Thermal Management  -  Discussion Page =====


Ideas for how best to do thermal management on the hot-end should go here.

Insulation, air flow from the fan, how to debug heating problems...

-------------

Consider the hot end:

{{wiki:jitsbuild:hot-end.png}}

The brown insulator in the middle is the thermal boundary.  The part below it is to be kept hot.  The part above it is to be kept cool.

Don't allow the air flow from the fan to hit the part below.  Any part of it.  (But if the thermal barrier overheats, you may have to modify this policy.)

The part above, on the other hand, must be kept cool, so hit that with the airflow.

(Note that the fan mount can be mounted in various different positions, and this will change the air flow.  The latest model of the fan mount can be mounted in three different positions.)

You need to construct somehow a thing that will keep the airflow where it is needed, and away from where it is not.  (Polyimide tape applied to the bottom surface of the multi-lobed aluminum part right above the thermal boundary would be a good place to start, although that alone is probably not enough.)

In addition to the air flow from the fan, convection currents will naturally arise next to the hot part, and carry heat away.  Anything you can do to stop this flow, or slow it down, will probably help.

Hot air rises, so a box open on the bottom but closed on the top can contain it.  Construct such a box, out of materials that can withstand the high temperatures.  Polyimide tape is provided, but you could use additional materials.  Obviously, you must provide a way for those four wires to escape from the box, without letting too much air leak through.

Just putting some tape around the heater block (the rectangular part near the bottom) may not fully solve the problem.

There is some concern that completely enclosing all of the metal parts below the thermal boundary may cause the brown insulator at the boundary to overheat.

The best way to insulate the hot end is a matter of active discussion.  Solutions that are demonstrated to work well should be shown here.

Remember that a solution that works today may not work on a much colder day.  Experimentation required.


----------------

Proper heating cannot occur unless everything on the hot end is wired up properly.  That's four wires, two from the heater resistor and two from the thermistor.  None of these wires is polarized.

If you power down everything, you can use an ohmmeter to check the wiring.  The spot nearest to the hot end where you can touch a wire is right next to where it enters the terminal block on the X carriage.  Measure the resistance between that point and the place where the wire connects with the controller;  it should be near zero.  To probe the thermistor from the controller end, pull the thermistor connector off the controller just far enough to reach under it and touch the pin with the probe.

Alternatively, you can measure the resistance across each resistor from the controller.  From there, the heater resistor should be about 7 ohms and the thermistor should be thousands of ohms (this one varies a lot, depending on the temperature of the room).

If you get significantly wrong numbers, like infinity or zero, check the wiring.  Make sure you haven't hooked wires up to the wrong places.  Make sure you have good contact between the each wire and its terminal inside the terminal block.

If you have dual extruders, make sure you haven't gotten one extruder's thermistor connected to the other extruder's thermistor connector on the controller.  Likewise, make sure you haven't got the heaters swapped.  Decide which extruder is going to be #1, and which is #2, and be consistent all the way through.  (The thermistor connectors on the Azteeg are marked strangely, which can be confusing, so check the Azteeg docs for which connector is which.)

To make sure your thermistors are working properly, you can do a sanity check with a high-temperature thermometer  (infrared, or a meat thermometer?).  Get your user interface running on your computer, power up your hot ends and see what the computer thinks the temperature is.  Then measure the temperature of the heater block with another thermometer and see if it agrees.  Remember to properly convert between degrees C and F if necessary.

Make sure the 115V/230V switch on the side of your power supply is set correctly for your location.

Check that the spade lugs are solidly crimped onto the cable that connects the power supply to the controller.  Check the power supply voltage at the power supply screw terminals (-V to +V) and at the controller screw terminals;  they should be nearly the same even when the extruder is being heated.

=== one way of insulating the hot-end ===

Insulating the underside of the heated platform didn't use up all the insulating fabric material, so the remainder is used for the hot end.  The paper backing is peeled off, and the fabric put down sticky side up:

{{wiki:jitsbuild:hotend1.png}}

The adhesive on the fabric will not be used to stick the material to the hot end, as that would make it difficult to remove.

The sticky side has been covered with polyimide tape, with the tape extending off the edges:

{{wiki:jitsbuild:hotend2.png}}

Turning it over, fold the tape over:

{{wiki:jitsbuild:hotend3.png}}

Both sides have been covered with tape:

{{wiki:jitsbuild:hotend4.png}}

Start chopping it up.  Sections to be cut out are marked with a suitable writing instrument;  pencil works poorly, as do many kinds of pen.  Here, a fine-tip black permanent marker was used.  After each cut, the marks are wiped off with alcohol;  if not removed now, they may burn off in an undesirable way the first time the hot end is heated. Alternatively, draw cutting lines on the backing paper and then cut the pieces before removing the backing paper.

After each cut, and after the ink is removed, more tape is used to seal off the cut edges:

{{wiki:jitsbuild:hotend5.png}}

One strip 19mm wide is made, and one 14mm wide.

More cutting, resulting in two pieces:  74 x 14 mm, and 45 x 19 mm. 

{{wiki:jitsbuild:hotend6.png}}

If you need to insulate two extruders from the initial 75mm strip you should cut the 19mm strip in half so that you have a 37 x 19mm (x 2 pieces) and a 75 x 14mm (x 2 pieces). In this case the 19mm piece won't be long enough to cut a full 10mm hole as described below but you will still be able to create a perfectly functional cover. 

A hole is cut.  It is 10mm in diameter, with its center 7 mm from one end.  It should be centered along the centerline, better than this:

{{wiki:jitsbuild:hotend7.png}}

Put it on top of the heater block:

{{wiki:jitsbuild:hotend8.png}}

Narrow pieces of tape hold it in place as it is folded over the end of the block and underneath it:

{{wiki:jitsbuild:hotend9.png}}

The remaining 14mm piece is wrapped around the three uncovered sides of the block, and taped in place.  Additional layers of tape are wrapped around in various directions, taking care to keep the tape off the conical nozzle.  None of the tape or insulating fabric should extend below the bottom of the nozzle:

{{wiki:jitsbuild:hotend10.png}}

Looks like rubbish, but it insulates the heater block fairly well.

Another alternative to taping the 19mm piece of material to the heater block itself is to instead tape it to the other 14mm strip. The position of the 19mm piece in this option is adjusted so that it extends down the side of the heater block to match the width of the 14mm skirt (which is put around the other three sides as described above). This should give the appearance of a continuous skirt all the way around the heater block which is subjectively a slightly neater looking. The bottom of the heater was left open primarily again for aesthetic reasons (the cooling fan won't reach the bottom and heater block is now insulated on all the other sides). 

{{:buildrob_hot_end_thermal_management_1.jpg?400}} {{:buildrob_hot_end_thermal_management_2.jpg?400}}

The threaded tube above the heater block is left uncovered, so it can be cooled.  If it were covered, the thermal barrier (the brown material above it) would probably overheat and leak molten plastic.

//The contents of this page may be re-used under any of the following licenses:  The [[http://creativecommons.org/licenses/by-sa/3.0/|Creative Commons Attribution-ShareAlike 3.0 Unported License (CC BY-SA 3.0)]], or the [[http://www.gnu.org/copyleft/fdl.html|GNU Free Documentation License (GFDL, version 1.2 or later)]].//
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