HotEnd Clogs [Cannot make it work]

Hello,

I'm getting crazy about the Hot End. I'm unable to make it work properly. I think I've found the correct design (because the plastic doesn't breaks the nozzle) but it's not printing right. I explain it.

I ended with a design that heats the end of the nozzle. This seems to be best because if I set the nichrome wire around the barrel it makes the plastic melt in the middle and cannot get enough force to push the plastic through it. So it gets blocked.



The design is simple:

It has a nozzle with the nichrome wire of 8mm diameter with a hole of about 0,5mm in one side. It has hole of 6mm on the other side where the barrel goes in, a second hole is drilled inside the 6mm hole of about 4mm. Here is where the internal barrel goes in.

The barrel has two tubes, one of about 4mm diameter (internal barrel) and one of 6 mm. One inside the other. This is because it's a pain redo the threads of the barrel if it get blocked by the plastic. This way I only have to insert one inside the other. And it also let's me adapt the nozzle to the plastic diameter.

The termocouple is on the nozzle. Between aluminium and nichrome wire, near the exit hole (0'5mm one).



Okey. The problem is that if I put the temperature from 160ºC-225ºC I can put plastic inside the extruder and the plastic goes through the other side but it clogs after a pair of cm of plastic extruded.

It blocks in the nozzle. This is what I get when I recover the plastic.




As you can see on the right of the image there is a little piece of plastic at the end. This is what blocks the plastic going out.

Maybe something with temperature or the plastic used. Can you help me?

I have few ideas:

• Maybe the plastic does not get enough temperature fast enough
• Maybe the hole of the nozzle is too small

What do you think?

I uploaded a small draw of the design.



I have to say that it doesn't matter the temperature I set, but from 190º to 225ºC I'm able to push the plastic with a tube (doing a lot of force) and I get it extruded in the other side. What I don't reach to understand is why I need to do this big force. That's why the plastic does not extrude.

If I get the temperature up, more than 240ºC plastic get harder. I think because cristalization.

Hope someone gives some input. I read a lot to reach this point but don't know what else to do. And I want to Do it Myself. :-)


Best regards,

Edited 1 time(s). Last edit at 12/30/2012 04:32PM by gaguilar.

looks lie your hotend has no thermal barrier mechanism and has a really long non static meltzone, which would explain why it extrudes a little bit but jams up

I can't see any thermal insulator to confine the heat to the hot end. If you have a long gradual thermal gradient you end up with plastic with a rubbery consistency in the middle that expands and grips the barrel.

See [hydraraptor.blogspot.co.uk] for why it doesn't work.

See [hydraraptor.blogspot.co.uk] for an all metal design that did work.

---

[www.hydraraptor.blogspot.com]

Hello thejollygrimreaper,

What do you mean with "non static meltzone"?

It has no thermal barrier because it's a prototype. I thought that the thermal barrier was only there to prevent extruder plastic (gear and rest of components) to melt.

I will try to short the barrel while testing.

nophead Wrote:
-------------------------------------------------------
> I can't see any thermal insulator to confine the
> heat to the hot end. If you have a long gradual
> thermal gradient you end up with plastic with a
> rubbery consistency in the middle that expands and
> grips the barrel.

That's because it was a prototype. But maybe you are right and I need a thermal insulator.
I will try to shorten the barrel so I can do some tests to see if this makes easier to extrude.

But think that the hot end will be clogged by the piece of plastic that you can see in the picture. This piece of plastic is in the 0,5 mm hole, not inside the barrel. What I want to say is that the barrel never get blocked. That's why I like this design.

I think that the barrel does not get much temperature because it's built on aluminium.


Will take a look to your links. Thank you a lot.
>
> See
> [hydraraptor.blogspot.co.uk]
> -point.html for why it doesn't work.
>
> See
> [hydraraptor.blogspot.co.uk]
> ve.html for an all metal design that did work.

Aluminium is an extremely good conductor of heat. That makes it a terrible material for a thermal barrier.

Greg Frost Wrote:
-------------------------------------------------------
> Aluminium is an extremely good conductor of heat.
> That makes it a terrible material for a thermal
> barrier.

Hi Greg, is not for the barrier but for the rest of the nozzle.

Hello again,

Something here at the forum gave me a clue...

[forums.reprap.org]

They say that a supplier is selling an J-Head extruder with a extremely long extruder hole. 3mm. And it should be as much of 0,5mm. I think mine is larger than 3mm, hahahaha.

I will drill it a little bit and try again. Let's see what happens.

Quote

I thought that the thermal barrier was only there to prevent extruder plastic (gear and rest of components) to melt.

It is also to stop the filament melting too soon so it remains hard until it gets to the heater where it then melts rapidly.

---

[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> I thought that the thermal barrier was only there
> to prevent extruder plastic (gear and rest of
> components) to melt.
>
> It is also to stop the filament melting too soon
> so it remains hard until it gets to the heater
> where it then melts rapidly.

Great. My problem is that I'm unable to find good plastic barrier in Spain. In fact, everything is hard to get. I'm looking for alternatives.

Thank's for the explanation.

Hello again,

I've redone the nozzle. I've set three holes inside, plus the extrusion end (0,5mm):

• External hole. 0,1-0.5mm.
• Next to 1,5mm that will heat the plastic.
• Next to 4mm with inner diameter of 3mm (this holds the barrel) inside nozzle.
• Next to 6mm threaded. This will join external barrel to nozzle.

I've reduced height of the external hole to 0,2mm. And force you have to do to push plastic is greatly reduced. Thank you for the clues.

I can extrude some centimeters more and when It clogs, and I push the plastic inside, the force I have to do is a lot less.
But I get still the clog.

The clog gets bigger with temperature. From bottom to top. 250ºC, 225ºC, 200ºC, º190C. But the force I have to do to push the plastic out is bigger as temperature decreses.




I think that the clog is produced because the internal hole is not exactly the same that the diameter of the plastic. Do you think this can be a reaseon? The plastic has less diameter than the internal hole and it clogs instead of extrude.

What else can be?

Thank you in advance.

idealy for 1.75mm filament you want a hole of 2mm
with 3mm you want a 1/8th(imperial) or a 3.2mm hole

Quote
idealy for 1.75mm filament you want a hole of 2mm
with 3mm you want a 1/8th(imperial) or a 3.2mm hole

This is for the barrel diameter I suppose, right?

yes