Heat Shields?

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MDVolle
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Location: Fullerton CA

Heat Shields?

Postby MDVolle » Fri Nov 17, 2017 7:41 am

Has anyone experimented with any type of rigid (thin but probably brass or stainless sheet) shields between the hot and cold sections?

I was trying to devise a way to keep all of the air from the fans away from the hot end and also have a radiant barrier between the hot end and the printed part -

I am not sure if this would work as well as insulating the hot block but I think I could make these parts easily and quickly.

I'm just curious if anyone else has already gone down this path?

The odd appendage on the left corner is my extruder spy cam - there is a small prism in the housing and the camera allows me to see the extrusion process in real time - up close enough to observe even a 0.1mm layer building on a part. Its been an invaluable aid in troubleshooting and tuning - I hope to post the parts at some point but still need to find a currently available and reasonably priced camera - I already had the one I used and it wasn't affordably priced and isn't made any longer.


Thanks

Mark

Heat Shields.jpg

zemlin
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Re: Heat Shields?

Postby zemlin » Fri Nov 17, 2017 12:55 pm

I haven't done anything like this. My expectation is that stainless steel would be the preferred material, as brass conducts heat fairly well. Stainless Steel sucks by comparison - 10%-20% of yellow brass.

AR_LA
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Re: Heat Shields?

Postby AR_LA » Fri Nov 17, 2017 4:16 pm

When people insulate their hot ends, the wrap the top too. Common materials are Kapton polyamide, mica, ceramic, and fiberglass. All are better insulators than brass or stainless.

If you want to use metal, titanium would be a good option. But you can also use some synthetic high temperature gasketing material since all you need to do is cut it straight, then punch a hole for your design.

MDVolle
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Location: Fullerton CA

Re: Heat Shields?

Postby MDVolle » Fri Nov 17, 2017 9:32 pm

Thanks for the thoughts - I know that the stainless wouldn't have a great insulating effect but it should, even with a very minor air gap, redirect a lot of the radiant energy back to the hot end and away from the part and the cool end...

I'm wondering if the radiant block is sufficient without having materials directly contacting the hottest part of the system - I am printing a lot of Nylon and working on PolyCarb, so my hot end is up above 265C a lot.

This would have NO impact on changing nozzles and would disassemble fairly easily, although you would need to drop both hot ends together.

I am considering using mica as the lower shield and skipping the bent up edges (mica is stiff enough by itself). That would offer both radiant protection and insulation.

firesped
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Re: Heat Shields?

Postby firesped » Sat Nov 18, 2017 12:58 pm

actually, I found that you don't want to insulate the top of the heater block. There is a reason for it. the issue is that the excess heat still has to go somewhere and the only out points when you insulate the hotend are the nozzle and the thermal tube. So you are just concentrating the heat in the one place you don't want it. the cold end.
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MDVolle
Posts: 57
Joined: Fri Oct 20, 2017 9:00 pm
Location: Fullerton CA

Re: Heat Shields?

Postby MDVolle » Sun Nov 19, 2017 7:10 am

firesped,
Thanks for the insight - I have been seeing the heater block wrapped in insulation, sleeved in insulation and almost molded into a silicone block but wondered what the pros and cons were.

Part of my thinking was to shield the cold side more than insulate the hot side? I was thinking of just trying to stop the radiant heat moving up into the cold side heatsink but it sounds like even that effort might limit the dissipation from the heater block?

I have ordered some 2mm ceramic "paper" and was thinking of trying that but not wrapping the hot end - just a flat piece - so heat could still rise around it, just not straight up to the cool side.

What would you expect the first signs of trouble to be?
I was thinking of measuring the temp of the heat sink on the lowest flat and seeing if it increased or decreased with the shield.

I have "gooed" a heat tube twice now with PC filament and I will say, I don't enjoy the recovery process - I'de rather be printing than disassembling and melting out my parts... I was hoping this would prevent that, but it sounds like it might make it worse!

Thanks

Mark

zemlin
Posts: 421
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Re: Heat Shields?

Postby zemlin » Sun Nov 19, 2017 1:28 pm

Thermal energy does not seek the path of least resistance. Heat transfer is defined by the temperature differential across an interface and the thermal properties of that interface. In insulating or shielding the hot end, the key will be to ensure the thin-walled heat break is able to do its job. Insulating the break or blocking the air flow from the fan will prevent it from transferring thermal energy into the air and will result in higher temperatures in the throat and more heat being transferred into the cold end.
The temperature of the hot end is controlled by a PID controller. Insulation will mean the hot end loses less heat to the atmosphere and radiation so it will reach the target temperature in less time and require less energy to maintain the temperature. Insulation will not result in 'excess heat' or higher temperatures.
Shielding will have some impact on convection around the hot end so will will act as somewhat of an insulator. It will mainly reduce the radiant energy being transferred from the hot end to the surroundings.

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DrewPetitclerc
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Re: Heat Shields?

Postby DrewPetitclerc » Mon Nov 20, 2017 7:12 am

I found it super easy and it works very well to insulate the hot block to protect delicate parts from excessive heat using a great product from "Z-Temp.
http://z-temp.co/
I used Julia's "Extruder Block Insulator"
http://z-temp.co/products/extruder-block-insulator.html
with safety wire instead of the "high temp o-rings due to space of dual extruders and added some aluminum foil tape on the exterior for resistance to abrasion of insulating blanket.
I have not wrapped the ends yet but I am considering it, just not sure how much it adds to the issue.
20171108_105438.jpg

When using only one extruder at say 260c the unused extruder reads out at 40-50c, about 10 degrees above ambient temp.
This really works great and keeps things clean, I've put these onto both of my "Zortrax M200" and my "UP Plus Pro".

I've also upgraded my cooling fan ducts for less leakage and a better flow across the heat sinks, just thought I would throw this in to.
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