[time-nuts] Re: Potting compound advice needed

[Javier Herrero]

Hello,

Probably Mupsil was a typo. Mapsil 213B is a silicone-based coating also 
approved (at least by ESA) for space applications.

Regards,

Javier

On 11/11/21 5:56, Lux, Jim wrote:
> On 11/10/21 5:31 PM, Gerhard Hoffmann wrote:
>> A customer of mine uses Solitane, another one Mupsil.
>> I just wrote down the names in case I might need it.
>> Probably more for coating boards in space apps, no idea
>> if it fits.
>>
>>
>> Am 10.11.21 um 23:40 schrieb Richard (Rick) Karlquist:
>>> I am looking for help choosing a potting compound that
>>> has the following properties:
>> _
>
>
> Yeah, the solithane (that's the name we use) is more used to repair 
> conformal coatings, stake fasteners, stick wires down to the board, 
> glue components to the board so it will survive vibe (think tall 
> skinny things, with the vibe in the plane of the board).  Fairly 
> fluid, cures fairly quickly, low outgassing, and most important for 
> space - someone else used it and it worked without causing a 
> disaster.   There probably is a potting version of it, and I'll ask 
> one of the M&P folks at work tomorrow what they think about Rick's need.
>
> I've not heard of Mupsil, but we use a lot of Nusil - silicone 
> elastomers, often with alumina particles in it, as a thermal bonding 
> material. Say you've got a box with a fairly flat surface that you 
> want to clamp to another fairly flat surface. The problem is that 
> tightening the fasteners deforms both surfaces (unless you've got a 
> zillion of them) so the thermal contact area is just around the 
> fastener, and there is a perhaps a gap everywhere else. Spaceflight 
> people hate "perhaps" so they say, ok, put a thermal gasket in there 
> (hey, many of us have used a mica washer and silicone grease between 
> part and heat sink, right?).  You can get elastomeric thermal gaskets 
> from Chomerics and similar companies, but they actually have the same 
> problem with clamping force. You tighten the fasteners, but to get the 
> required clamping force over the WHOLE gasket, you need a lot of 
> fasteners, or a lot of force, and you're back to the deformation problem.
>
> So the answer is "thermally conductive glue" - you slather a thin 
> layer on, tighten the fasteners, which then causes the alumina 
> particles to poke into the surfaces on both sides, and hey - good 
> thermal conductivity.  Of course, if you need to take it off, you need 
> to get in there with a wire saw and that's "not fun".
>
> I will say the nifty-est thermal connection was a sort of velvet made 
> of carbon fibers. Carbon fibers have very high thermal conductivity. 
> You bond that furry velvet to both surfaces, and when you put it 
> together, the fibers slide along each other and make good contact 
> along their length, and there's millions of them. You aren't depending 
> on clamping force - it's the springyness of the very stiff fibers that 
> provides the contact force, and as you can imagine, it can tolerate a 
> lot of misalignment and gaps.
>
> The actual stuff was developed originally to make a very optically 
> absorbing black coating over wide bandwidths - all those fibers bounce 
> the light around. And as a laser load (instead of the proverbial stack 
> of razor blades.  It was then was used to coat mannequin forms, for 
> displaying lingerie for Victoria's Secret, of all places, because it 
> was very rugged and didn't shed lint.  There's a whole exotic trade 
> secret about how they make the velvet - there's some sort of 
> electrostatic technique to making the fibers stand on end while 
> they're bonded, and some other exotic trick to getting them all the 
> same length, and so forth. I kept trying to use it in space (it is 
> *so* much easier than glue, gaskets, or zillions of fasteners), but it 
> never took -> 1) nobody else had used it before and 2) everyone was 
> worried about little conductive fibers shedding and floating around 
> into places they shouldn't be.  Again, in the space world, no matter 
> how tedious and painful, if it worked before, we can do it again. 
> thermally conductive glue may be a pain, but it's "known to work".
>
>
> For those of you doing bolted joints..  thermal conductances are 
> around 0.1 to 1 W/K -
>
> You want to google a chapter called "Mountings and Interfaces" by 
> Gluck and Baturkin - It's in Spacecraft Thermal Control Handbook 
> Volume 1. but there's tons of copies floating around the web, and it's 
> a great handbook reference for "just what is the thermal resistance 
> with a 4-40 screw through that TO-220 tab onto an aluminum chassis"
>
> It's one of those references which everyone cites.
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