Idea on underextrusion

[dieselpower 0]

Wouldn't it be better to only cool the PTFE part? You want to keep your heat in the nozzle, just not in the PTFE cold part of your extruder.

What about a aluminium heatsink or water cooling jacket around a PTFE lining/fitting?

 

[3poro 9]

The sketch seems to add heat conductive material between the heater element and the top of the hot end isolator. I would keep the conductive material to its minimum - as i is more or less in the original design. Instead, the added heat dissipation at the top is a good idea - maybe it could continue higher on the sides of the PTFE part? Not front or rear though, as it would likely prevent air flow around the PTFE.

 

[3poro 9]

Wouldn't it be better to only cool the PTFE part? You want to keep your heat in the nozzle, just not in the PTFE cold part of your extruder.

What about a aluminium heatsink or water cooling jacket around a PTFE lining/fitting?

 

PTFE has fairly high heat resistance, so the impact of a heatsink would be subtle. Also, the temperature difference between the surface of the PTFE fitting and the chamber (right above the heated bed) is not very big.

How about something like this:

Sorry Kris for ruining your nice sketch... My idea is that everything below the green line would remain hot - while everything above it would be cooled as efficiently as possible. As the heatsink is likely to be warmer than the PTFE surface, it would probably make sense to leave the front and the rear of the heatsink open in order to let the 25mm fan to ventilate the PTFE efficiently. Also, because of the difference in surface temperatures, I wouldn't add a heat sink around the PTFE as the hot end isolator might actually radiate heat to it.

I'm planning to get my aluminum plate (the gray one in the picture) anodized, but not from its lower surface - otherwise it will just absorb heat more easily from the nozzle unit.

 

[dieselpower 0]

PTFE has fairly high heat resistance, so the impact of a heatsink would be subtle.

 

Indeed, so every form of cooling, would be rather inefficient....

So maybe a (stainless)steel + aluminium heatsink replacement? Somebody ever tried a full aluminium version?

An anodized finish will add around 4 - 8% to the overall cooling effect using forced air

 

[kris 29]

Yes, you guys are correct. The idea was basically to pull away heat from the PTFE component. PTFE has two advantages; it has low friction and it can handle high temperatures. A significant drawback is the thermal expansion which might cause under extrusion. My hope is that we can overcome these trouble with minimum effort, i.e. without replacing existing parts.

I have hence added a heat sink in the analysis in an attempt to draw heat away from the PTFE. And it seems to work very well. I will post the calculations here in short while. Have a short business trip tomorrow. That heat sink is just an add on that will not require any changes to the existing components...I hope :???:

I think that ultimaker's initial intention was to use the aluminium structure of the extruder as heat sink. That is the reason for the 3rd fan I guess, in order to improve convection. But apparently it is not efficient enough in doing so.

What do you think, I might be wrong here.

 

[kris 29]

The sketch seems to add heat conductive material between the heater element and the top of the hot end isolator. I would keep the conductive material to its minimum - as i is more or less in the original design. Instead, the added heat dissipation at the top is a good idea - maybe it could continue higher on the sides of the PTFE part? Not front or rear though, as it would likely prevent air flow around the PTFE.

 

Absolutely. Will show the results here soon.

 

[kris 29]

Here are the results. I ran a few different models to test out different ideas to knock down the temperature in the PTFE bushing. I did not take into account forced convection (from the fan). I achieved the best results with a heat sink at the top, as originally proposed. In addition reducing the contact area between the PTFE bushing and the remaining components helps. I managed to reduced the temperature in the bushing from 170°C to 110°C (model ptfe_v2_p). I measured the temperature a few millimetres away from the interface to the nozzle, because here the temperature is pretty much unchanged due to the proximity to the heat source.

I have tried not to alter existing components, in an attempt to create a method that can be retrofitted. Currently the heat sink that I added does not fit into the setup. There is too little space. So it has to be reduced in size somewhat.

Important to note: The TG of ABS is around 104°C. Previously we were well above that in the PTFE bushing which means the ABS will loose most of its mechanical properties before it even enters the nozzle. At the moment the spring pushes the bushing firmly against the nozzle. There will be a certain heat transfer. If we would allow for a little gap between these components the temperature in the PTFE bushing will remain around 100°C. See below. Not sure if that would create other problems. But sure worth a try. The bushing would have to rest against the steel nut.

Feedback is most welcome

 

[3poro 9]

What if you lifted the upper heatsink up by just a bit, so that its fins would not touch the aluminium block underneath?

Also, would it be difficult to factor in the impact of the rear fan - just to get an understanding of the magnitude of its impact?

Your idea of reducing contact between the PTFE and the isolator is very interesting. Do you think it would be enough to make the surface of the PTFE a bit knurled? Or, what if the slots were vertical rather than horizontal? I'm just thinking how to lose as little of the PTFE part's rigidity as possible. Of course, an efficient way of minimizing the loss is to keep it cool

 

[kris 29]

I think if the heat sink touches the aluminium block that is not a bad thing. This just increases the cooling area.

Neglecting the rear fan is kind of conservative I guess, since it will improve convection. Now that I think about it, I do not really understand the slotted aluminium block at the back. To me it seems as if it is too far away from the heat source. I think the new heat sink could replace that component completely and reduce temperature in the upper part of the extruder considerably.

 

[3poro 9]

I think if the heat sink touches the aluminium block that is not a bad thing. This just increases the cooling area.

 

I guess the nozzle unit heats the aluminium block significantly, as the nozzle unit is between the steel plate and aluminium block. I would guess the new heatsink could be cooler than the aluminium block.

 

Neglecting the rear fan is kind of conservative I guess, since it will improve convection. Now that I think about it, I do not really understand the slotted aluminium block at the back. To me it seems as if it is too far away from the heat source. I think the new heat sink could replace that component completely and reduce temperature in the upper part of the extruder considerably.

 

For estimating the role of the slotted aluminium block at the back, I really think we would need to understand the impact of the rear fan.

I think the lower aluminium block gets quite a lot of heat from the nozzle unit, also to the rear parts of it. Therefore, I don't think the slotted block is that far.

[dieselpower 0]

Would be nice if we could cool the complete print head system, as there is a known problem when using dual extruders.

The problems we are facing for dual-extrusion UM2 are mechanical right now, not software. Due to a mis-calculation the teflon gets too hot with 2 hotends in there.

 

 

[kris 29]

My guess is that the current heat sink is in the wrong place. It is not efficient in preventing heat moving into the PTFE part. It is also too far away.

[3poro 9]

I agree the current heat sink is not helping to cool the PTFE part. It does, however, help in keeping the lower aluminium block relatively cool. I think the cooling of the isolator (the hollow bolt) needs to be improved - for that, another heat sink is needed. My guess is - it's not optimal to combine the two into one. The aluminium block absorbs a lot of heat from the nozzle unit and I'm afraid it will remain quite hot.

[kris 29]

I agree the current heat sink is not helping to cool the PTFE part. It does, however, help in keeping the lower aluminium block relatively cool. I think the cooling of the isolator (the hollow bolt) needs to be improved - for that, another heat sink is needed. My guess is - it's not optimal to combine the two into one. The aluminium block absorbs a lot of heat from the nozzle unit and I'm afraid it will remain quite hot.

 

You might be correct. Would be interesting to try this out.

 

[3poro 9]

You might be correct. Would be interesting to try this out.

 

Thank you Kris for inspiration - I have worked on the topic a bit and I'll update after some tests:

http://umforum.ultimaker.com/index.php?/topic/6307-um2-twin-tornadoes/

 

[kris 29]

ABS extrudes at 260°C. What happens to residual PLA at that temperature if I switch from PLA to ABS?

Could this potentially clog the nozzle?

Just a thought... :-P

Because I noticed many people experience the problem after changing material, including myself. So maybe there is nothing wrong with the hot end after all.