I recently rebuilt my hot end on the Ender3 after the meltdown which left it globbed up with plastic. The globbing up was not the problem why I had to rebuild it though, but probably the start of why I had to clean it. The heater failed (suspected a weakend wire, and when I went to swap it, I found that the heatbreak was stuck. I could have burned it out, but I had spares so I just rebuilt everything so now it is nice and new, ready to get blobbed up again. However I found that I needed some thermal compound between the heatbreak and the heatsink. I did some research and found that most of the products used for computer CPU thermal grease are not able to sustain temps that a 3D printer hot end will commonly go to. One product that can, and then some is Boron Nitride. I found different companies selling it for different prices, and it several I found indicate that they are made by ZYP Coatings which is based in Oak Ridge, TN (which is also home to Oak Ridge National Laboratory). No idea if there is a reason for that, but chances are there are a lot of smart people in that town, so I would not be surprised if there is some connection. In any case, the Boron Nitride thermal grease looks promising and the cheapest place I could find it was at filamentone.com (no affiliation) and their shipping via USPS was cheap too. The stuff comes in a small metal tube (like a small toothpaste tube), and not the syringe looking dispenser they show on the site. I just installed the heatbreak with the boron nitride paste, and will see how it goes (and will update here if there are issues with heat creep).
The stuff seems relatively safe, but there are some considerations since it is a eye and lung irritant (MSDS here). As a side note, it is nice that they have an MSDS for the stuff, considering most thermal compounds from China that I found on Amazon or Ebay don't even mention one (we could probably learn something about deregulation from China ;-). To be on the safe side, I took the printer outside for the first heatup cycle after installation, and ran a PID tune outside as well, since it was mentioned that "Initial exposure to high temperatures evolves, in small amounts, fumes that may be irritating or corrosive to the upper respiratory system." Though I suspect that "high temperatures" for this stuff is really a lot more than anything my printer is capable of - like 600°C probably. At 240°C which I started it up at, I'd guess it may have boiled off some water since it is 65-70% water. The dust is however an irritant so when swapping the heatbreak or removing it from the heatsink, I would probably wear a face mask or respirator to avoid any dust.
Update 9/23/2021: I was gonna use the Boron Nitride again to rebuild a hot end, and found it was all dried out. It's not super surprising but still disappointing that it did not last in storage. For the record, it was capped tightly in a bag. I don't think for a single use it is worth buying this stuff, and will stick to using the small one time use packets for my printers.
The stuff seems relatively safe, but there are some considerations since it is a eye and lung irritant (MSDS here). As a side note, it is nice that they have an MSDS for the stuff, considering most thermal compounds from China that I found on Amazon or Ebay don't even mention one (we could probably learn something about deregulation from China ;-). To be on the safe side, I took the printer outside for the first heatup cycle after installation, and ran a PID tune outside as well, since it was mentioned that "Initial exposure to high temperatures evolves, in small amounts, fumes that may be irritating or corrosive to the upper respiratory system." Though I suspect that "high temperatures" for this stuff is really a lot more than anything my printer is capable of - like 600°C probably. At 240°C which I started it up at, I'd guess it may have boiled off some water since it is 65-70% water. The dust is however an irritant so when swapping the heatbreak or removing it from the heatsink, I would probably wear a face mask or respirator to avoid any dust.
Update 9/23/2021: I was gonna use the Boron Nitride again to rebuild a hot end, and found it was all dried out. It's not super surprising but still disappointing that it did not last in storage. For the record, it was capped tightly in a bag. I don't think for a single use it is worth buying this stuff, and will stick to using the small one time use packets for my printers.
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