HotEnd Resistors Silicone Alternative ??!?

[MarioMas]

Hi all, i just starting to build my V2 but i can't find the Permatex Ultra Copper RTV in Italy.

This silicone have particular thermal property or is like a Normal Hight temp silicone.
I mean, is it particular thermo conductive?

I have a Arexon Motorsil in my toolbox; usually i use it in my motorcycle silencer near the motor head, i think it could be a good replacement for the Permatex.

[Nylocke]

The whole special thing about it is it has particles of copper embedded in the silicone to better conduct heat. I, like you, was unable to find some with copper, so I just used some high temp silicone and it worked well enough for me.

[Captain Starfish]

And yet I've read how shite even the copper stuff is as a conductor.

Wrap aluminium foil around the resistor to get as tight a fit into the slot as you can, maybe even put a little heatsink paste on it as you slide it in. Then put a dab of X in either end - not to smother it but just to hold it in place.

X needs to be elastic, needs to cope with 350º at least (don't want to go anywhere near its breakdown temperature), and needs to be able to be pulled out if you ever want to replace the resistors.

[dpmacri]

The whole special thing about it is it has particles of copper embedded in the silicone to better conduct heat. I, like you, was unable to find some with copper, so I just used some high temp silicone and it worked well enough for me.

It does NOT contain copper -- that's just the color . The main thing is that it's "Ultra High Temp" -- rated up to 700F (371C). From the Permatex website:

"The Ultra Copper® is a silicone product and is copper in color. It does not contain any copper or other metal and it is not electrically conductive. For additional information, go to the Ultra Copper product page [hyperlink to 81878 product page] and view the TDS."

[Nylocke]

Oh, sorry I was mistaken, I saw the picture on the assembly manual and it looked like there were particles of copper in it. I never read into it because I couldn't find it locally, sorry to be misleading.

[Eaglezsoar]

The whole special thing about it is it has particles of copper embedded in the silicone to better conduct heat. I, like you, was unable to find some with copper, so I just used some high temp silicone and it worked well enough for me.

It does NOT contain copper -- that's just the color . The main thing is that it's "Ultra High Temp" -- rated up to 700F (371C). From the Permatex website:

"The Ultra Copper® is a silicone product and is copper in color. It does not contain any copper or other metal and it is not electrically conductive. For additional information, go to the Ultra Copper product page [hyperlink to 81878 product page] and view the TDS."

That is correct, and it also is not thermally conductive. It is an insulator whose whole purpose was to hold things like the thermistor in place because
it has one and only one quality that we need, it can take the heat without breaking down. Now we have Seemecnc holding resistors in place with a huge coating of the stuff because they somehow mistakenly felt that the stuff conducts heat. People this stuff does not conduct electricity, it does not conduct
heat, it does not contain any copper, and small amounts of it should be used to hold in the thermistors and a little on the end of the resistors to help them
not to move. This stuff is rubber in a tube. Would you wrap your resistors in rubber to hold them in the holes? Please use the Silicone Ultra Copper only for holding things and in minimal amounts.

[mhackney]

Just some input: I've used Ultra Copper in the past, along with other high temp silicones. Although it is true that it won[t break down at our printing temperatures IT WILL ultimately debond/separate from the aluminum hot end and that can create a problem - especially if the the thermistor then loosens or, heaven forbid, falls out. I don't trust silicone any longer on hot ends and either use cartridge heaters and the skew in thermistor or add a protective wrap of Kapton tape.

[Captain Starfish]

^^ This.

When I do my next round of updates on my RMax for the hotends so they can use the spools of nylon and TGlase languishing unused and unloved in my stock pile, it will be screw-in and cartridge all the way.

[Eaglezsoar]

^^ This.

When I do my next round of updates on my RMax for the hotends so they can use the spools of nylon and TGlase languishing unused and unloved in my stock pile, it will be screw-in and cartridge all the way.

+1 on that!

[Flateric]

You can also use dental ceramic as a paste to "cement" things into place. I have been doing this for a good long time now with great success. It also cures almost instantly when you heat up your hotend, which is a

I simply asked my dentist for a bit with a little of the curing liquid and he gave me a whole bottle and a whole packet of the powder, this made me suspect he earns too much money, LOL.

[guanu]

That is correct, and it also is not thermally conductive. It is an insulator whose whole purpose was to hold things like the thermistor in place because
it has one and only one quality that we need, it can take the heat without breaking down. Now we have Seemecnc holding resistors in place with a huge coating of the stuff because they somehow mistakenly felt that the stuff conducts heat. People this stuff does not conduct electricity, it does not conduct
heat, it does not contain any copper, and small amounts of it should be used to hold in the thermistors and a little on the end of the resistors to help them
not to move. This stuff is rubber in a tube. Would you wrap your resistors in rubber to hold them in the holes? Please use the Silicone Ultra Copper only for holding things and in minimal amounts.

First, we do not feel that it conducts heat... I know I've never said that.... and we use lots on the resistors because if they arent fully coated and the channels the resistors are in arent filled, you can end up with an air channel going to the resistor, get a hotspot, and have the resistor blow.. they need to be fully encapsulated in it for them not to blow, so yes, we do use lots on it to make sure this doesnt happen as best we can... we've even coated the whole heating block in it and other high temp silicons we have been testing with... and it doesnt matter if you coated the whole heating block with 1/4" of the stuff, if anything that will keep the heat in the heating block... but no, we never said it conducts heat (at least I havent).. its better to use more than too little and blow a resistor.. so no, do not use "minimal amounts" to avoid killing resistors... not that I would know, I've only tested with about a dozen or so different amounts and even open air with a set screw...

eagle, dont take this as me being mean, I do not mean to come off that way, I just dont want people to put on too little and end up with a blown resistor.. so if that sounded mean, I'm sorry.

Guanu

[Polygonhell]

I stopped using silicone after I built an H1, it's messy and of questionable value IMO. In fact the only place I've ever heard it espoused in by SeeMeCNC.
You do need to take up any air-gap with the hotend if you are using resistors, wrapping in foil is sufficient for that, though it's a pain in the ass.
The other issue as MHackney says is it doesn't bond well to the Al and the thermistor can slip out without you noticing, leading to increased hotend temperatures without a failsafe, this is how I lost my first hotend.

I just wrap the heater in Kapton and occasionally if I'm feeling particularly adventurous or I'm having issues with a fan pulling too much heat out of the heater I'll run some silicone tape around the outside.

[NorthOfSkepty]

I second avoiding that stuff. I think it's ok to use it as a thermal compound but don't trust it as an adhesive on it's own, (As described in the manual). Just a couple days ago I had my thermistor pop out a hair after cleaning my nozzle. Long story short I did a good job of installing it, cleaned the hot end first, took my time, ensured sufficient application, no airbubbles, etc. But all it took was a small bump to have it pop out and ruin my hot end. Use kapton or silicone tape to keep everything nice and secure. BUT this is a big but, if you do use a tape of some kind you'll need to be creative with your wrapping or preferrebly you will have to insulate those leads coming off of the heat resistors with PTFE to ensure you don't short anything out while wrapping the hot end. I ordered a Jhead from hotends.com as a replacement, but including in my shopping cart were PTFE insulators for the leads

[Eaglezsoar]

Ceramic cartridges have been out for some time now and thermistors can be encapsulated in a Male-Female Threaded Hex Standoff with some high temp
epoxy and there is no need to use one drop of the RTV silicone. An example of a threaded thermistor and ceramic cartridge is here.

[MarioMas]

Wow, i made a hot Topic

I think that the best way to lock the thermistor is in fact the threaded capsule, this method is the only one can guarantee optimal thermal conduction and retention over time; also is easy to replace and made at home.

An other question is a method to keep in place the resistors.

My first idea was to roll they in a aluminum sheet and put in place keeping care to not short circuiting the resistor;
also the two resistor configuration is theoretically a good idea, the Ohm value is higher on a hotter resistor and the energy flow to the colder, an other pro (but I'm not sure of this) is that the parallel resistor helve the Ohm value stretching the resistor life.

Tomorrow i should go to the store to buy a copper screw (M4 or M6) for realize my thermistor capsule with hight temp epoxy.

[Demolishun]

don't trust it as an adhesive on it's own

I am assembling my hot end (putting wires on it) and the thermistor popped out. I don't think the rtv is a good solution for holding it in. It is not act like it was "stuck" to the metal at all.

I am thinking I may get some JB weld to hold it in. It supposed to handle 500F (correction 600F for the 2 part epoxy). Any thoughts on using JB weld? Any experience with it?

Also, how does this copper screw work? Do you hollow it out? What holds the thermistor?

[Demolishun]

Alright, I am going to try using JB Weld (2 part version) that handles 550F according to package. In places online it says 600F so I am guessing the 550F is a CYA statement on the package. 550F is 287C Celcius. So that should be enough. If not I will report back.

Also, I took a 4-40 tap and tapped the thermistor hole slightly. Then I took a 4-40 screw and finished tapping the hole as mush as I could. So when I epoxy the thermistor in place it has plenty of stuff to grab onto. So even if the epoxy does not bond to the metal it will have a nice mechanical fit. I think this would help people using the High Temp RTV as well. The mechanical ridges of the threading would keep the RTV held in place mechanically. You don't need a tap either. I just had one handy. Using a 4-40 screw (in the kit) would work just fine to tap that hole.

[Captain Starfish]

Wait, you've JB-welded your thermistor directly into the hot end?

Please do post up when one of the legs snaps and you need to replace it.

For anyone else, the idea is to tap the hole in the hot end then JB-weld the thermistor into the end of a screw or something so you can replace the whole thing.

[Demolishun]

Since JB Weld and the glass thermistor are weaker than carbide steel, then I can just drill and re-tap the hole. The only reason I tapped the hole in the first place is because it a convenient way to roughen the surface for the epoxy. There is nothing permanent about it. In addition there is the option to drill a hole on the opposite side and put a thermistor there.

Adding a steel screw would just add a place for a hot spot anyway. Since steel tends to hold heat very well versus aluminum. On top of that mixing different metals together and adding energy will cause corrosion at the joint. Corrosion joints have bad heat transfer. Bad heat transfer is bad temperature reading. I guess one could us brass, but you still have corrosion issues.

So, the different problems caused by having a screw to mount are probably just as many as not having a screw.

However, by that time I may end up already having mounted a E3D hot end. In the end (in this case, the hot end) it just doesn't matter.

[Demolishun]

Update on JB Weld holding thermistor:
When I hold my hand on the aluminum of the hot end (off of course) I can watch the temperature change on the NOZ reading very fast. So the sensitivity of the thermistor seems to be good. I am getting reasonable concurrence of temperature between my NOZ and BED thermistors. At room temperature they are about 0.1 to 0.2 degrees apart (21.2 and 21.1).

I have not gotten to the point on my machine to heat up the hot end. Right now I am learning to use Repetier-Host. When I actually print something or test the hot end I will give my results then.

[Demolishun]

Update on Printing ABS with JB Weld Holding Thermistor
Well, I don't have anything to report other than it works and works well. No smoke, nothing. I have not printed PLA or other higher temp plastic yet. I will be soon.