Heat transfer paste

While rebuilding my hotend following the burnout I started to think about heat transfer past (the stuff used to improve contact between processors and heat sinks.
Would these paste stand up to the hotend temps and would they actually improve contact transfer.
Current options are Silicon (normal cheep stuff), Aluminium (probably cause the least issues), Silver and copper past often used on cars.

Anyone got experience in using them?

The usual ones won't handle the nozzle temperature, but they are OK to use between the heatsink and the heat break.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Drat- you're right. All the pastes I can find have a max continuous temperature of 200 C. I was going to use a dab of paste on the thermistor to try and improve the contact, but it doesn't look like such a good idea now. Thermal paste that can't get hot - grumble.

Hmm, looks like copper for lubrication applications has good thermal tolerance, but I'm not sure what its electrical characteristics are. It should have decent thermal conductivity, at least compared to an air gap. Ah, specifically described as 'conducting' for use on battery terminals - no good around the thermistor

Edited 2 time(s). Last edit at 07/18/2015 07:24AM by JamesK.

I don't think you need worry about the thermistor not being up to temperature. The hot end temperature changes relatively slowly, and most of the hot end thermistors we use have low thermal mass (so they will follow temperature changes quickly) and thin leads (so very little heat will be conducted away).

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
The usual ones won't handle the nozzle temperature, but they are OK to use between the heatsink and the heat break.

I thought so but couldn't remember the temps.

Quote
dc42
I don't think you need worry about the thermistor not being up to temperature. The hot end temperature changes relatively slowly, and most of the hot end thermistors we use have low thermal mass (so they will follow temperature changes quickly) and thin leads (so very little heat will be conducted away).

Thanks, was just curious.

You can use high temperature gasket material to lock the thermistor into the heat block. It isn't especially thermally conductive, but it's more conductive than air, and locking the thermistor into the block helps prevent fires caused by the thermistor coming out of the block during a print. Any time you alter the thermistor mount, including by this method, you should rerun the PID autotune and check the result with a thermocouple or test print.

[www.amazon.com] is good to 340C

Two that fit the bill are:-
Fischer Elektronik WLPG is good for 400C but is electrically conductive so not right for thermistor - also quite expensive (data sheet at [www.farnell.com] )
Deep Cool Z5 thermal grease is good for 300C and is non conductive and cheap - get from Amazon:-
[www.amazon.co.uk]

The Fischer compound has an exceptional thermal conductivity at 10.5 W/m-K compared with a pretty average 1.46 W/m-K for the Deep Cool Z5

Thanks for the link to the Z5, I ordered a tube. DC42, you're probably right that it's not needed, but the thermistor (an in-line design) seems like a particularly loose fit in this heater block and it just feels 'wrong' to me. I'll feel happier if I can close that gap up.

You can always wrap it with aluminum foil before inserting it into the block...

Quote
the_digital_dentist
You can always wrap it with aluminium foil before inserting it into the block...

but foil is also conductive!

The main reason why standard thermal grease has a max-temp around 200C is the grease/oil used to mix the nano-minerals in a useful paste.
I bet when we overheat it, the grease will become fluid and bleed out of the hotend ( with a little smoke ) leaving a solid but working mineral coating around the thermistor ( or heater ).

Maybe we could use clay or even toothpaste? The water will evaporate without the smoke.
-Olaf