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What are you sealing in the resistor and thermistor with on your block style heater core?

Posted by SCphotog 
What are you sealing in the resistor and thermistor with on your block style heater core?

I noticed that Nophead uses fire cement, I saw someone use high temp RTV and another used high temp epoxy. What is everyone using? Also what are you insulating the bare wires with? I assume a fiberglass braid is used. Where would one order that from?
Re: What are you sealing in the resistor and thermistor with on your block style heater core?
July 20, 2011 04:13AM
I currently use glass rope adhesive to stick the thermistor and heater. Initially this did not work but I discovered it had separated inside the bottle, so I was only getting a thin liquid instead of a thick cement like adhesive. I removed the nozzle and stirred it and got much better results.

The resistor can also be jammed in with AL foil for good heat conduction. You have get the number of turns just right. Too thin and it falls out, too thick and it damages the resistor.

I haven't found a source of fibreglass braid. I used some a long time ago that I recovered from something else but it soon blackened. I currently use PTFE sleeving.

I have used automotive exhaust pipe cement to hold in my thermistor and resistor. Its a grey ceramic paste available at auto parts stores for repairing leaky exhaust systems.

For the thermistor wires I have been sandwiching the wires between two layers of Kapton.

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I use aluminum encased power resistors in my hot end. Although they have screw mount holes for M2, I just put a bit of heat sink compound on the flat bottom, and fasten it with kapton tape.

The thermistor is similarly mounted from the opposite side of the block. I spread the wires out in a Y shape, and make them parallel about 1/4" apart, and then I wrap them in kapton right up to the glass bead. I place the glass in direct contact with the nozzle and block where they meet, and wrapp the entire thing in several layers of kapton. The tape is a good insulator, that keeps the block hot, but allows the fan to cool other parts of the extruder without draining too much heat (if you use fans, I don't).
Can heat sink compound take temperatures up to 250C? I saw that some of them are only rated to less than 200C.

The compound I am using is rate to 240C. I don't really care if it dries out though. It does seem to work at filling any voids, which are probably not that big to begin with.
OK. Thanks. I didn't think about this before. I'll do this too when I get the chance. It turns out that the Startech silicone heat sink compound that I have is also good to 240C.
I use silicone, the type that is used between the engine block on automobiles. Its usually rated 310C. It can be found usually on any random gas station or car engine shop.

I consider this a pretty good and versatile material for hot end purposes. Its very cheap, probably cheapest for this temperatures. It sticks good enough to almost anything (metal), just makes just a little fume when curing first time. When no longer needed it can be "peeled" off with a cutter blade.

I also use it to cover the entire heated block (not just for thermistor) - hoping for some kind of insulation.
And i use it to cover the wires of everything there, thermistor and resistors aswell - hoping for both insulation and less temperature-oxidation of wires, especially for resistors leads in this case.

Inside in between the heater and resistor i use just 1-2 turns of kapton tape, as i had a short at some point between my 2 resistors and the heated block material.

Edited 1 time(s). Last edit at 07/24/2011 07:24AM by NoobMan.
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