Hot End Question

[taav]

Hey newbie here setting up my first Rostock max

I am about to put together my hot end.
Not 100% sure about what kind of sealant I should use for the resistors.
I don't live in America so I cant get that RTV stuff suggested in the manual.

Can someone let me know what temperature the sealant I get needs to be able to withstand in order to be safe?

Thanks in Advance.

[cambo3d]

if your using the stock hotend. at least 240C minimum.

[lordbinky]

The permatex ultra copper RTV silicone is specced to 371C.

Besides the temperature you need to make sure the silicone rubber (if you still go with a silicone rubber sealant) you use does not contain Acetoxy, which is the most common RTV silicone sealant condensation curing method (the other curing method is an addition system where you add two parts together). Acetoxy releases acetic acid which corrodes the aluminum slightly, and more importantly will corrode the copper wires of the thermistor. Silicone sealants that do not use Acetoxy are commonly referred to as neutral-cure if that makes your search easier ( another example of an appropriate silicone is the ACC AS1805 silicone listed on http://www.intertronics.co.uk/products/acc01.htm)

[geneb]

If the thermistor wires are shielded properly (and they very much should be!), the RTV won't come into contact with the thermistor leads.

g.

[taav]

Thanks guys.

So in short, 240 Celsius minimum.

If I go for silicon sealant avoid Acetoxy.

Oh, and regarding the thermistor leads, the manual suggests using some silicon tape and RTV to make a thermistor sandwich. Doesnt that mean the RTV is essentially contacting the thermistors? Could you offer some insight on what the manual says?

[Polygonhell]

I usually use Kapton for the thermistor, but the same basic principle applies, you just want to tape the legs far enough apart that they don't short out. If your being careful you can wrap one leg in the Kapton, then tape the other to it, but just laying out the legs on the tape is sufficient.
If you have some 1/32in silicone or PTFE tubing you can use that on the thermistor legs instead.

[lordbinky]

For my thermistors, I've slide a piece of kapton down between the legs right up to the thermistor and then just fold it over and trim the excess. This just gives me more confidence and warm fuzzies that the leads aren't going to make contact while minimizing the strain on them to keep them apart. From there I do the standard lay them out on the tape or whatever method of choice that works best for the hotend.

And Geneb is right about the leads shouldn't be coming into contact with silicone, but the nice part is it should be ok even if they do, and on top of that I just don't trust acetic acid to stay in it's place when it evaporates .

It's ok for the RTV to touch the thermistor sides, what's important is the thermistor tip is making clean contact to the metal for maximum heat transfer. Ideally the entire thermistor would be making contact directly, but in practice as long as it's making good enough contact for heat transfer it's fine. When I followed the manual I think it said to put some rtv on the side, and that's to help keep the thermistor in place. You put the RTV on the sides of the thermistor instead of in the hole so the tip of the thermistor stays clean and doesn't have anything between it and the metal.

[geneb]

If you read about a "thermistor sandwich", YOU'RE READING THE WRONG MANUAL. Please see the 2nd edition thread in the official docs forum.

g.

[taav]

Thanks Gened. This new manual is apparently quite recent no wonder I didnt notice it. Thanks so much

Oh I picked up some Sparko Hi-Temp RTV 100% silicone Rubber Gasket maker. It goes upward of 300 Celsius.
Should I be good to go with the rest of the set up?

Anything I should know before I wrap up my construction and start wiring?

[geneb]

That RTV should work just fine.

g.