Silicone alternative - less viscous

Question

Silicone alternative - less viscous

drodrig (Mechanical)

(OP)

5 Sep 19 16:56

Hi there,

I've used silicone to seal an aluminium feed through where two PCBs go in. Just "normal" silicone.

The result wasn't good. There are holes. The silicone doesn't fill the gap properly. Later we will have small - thin volumes and it won't work either.

Attached a picture.

Is there any alternative less viscous?

thanks
regards,

Compositepro (Chemical) · Answer 1 · 2019-09-05 17:20:55

Your problem is mainly one of workmanship, which takes experience. With this type of sealant you have to place a smooth bead and then not touch it until it cures or you end-up with this mess. Silicone can be obtained with any viscosity you wish. It can be water thin or gum rubber. The viscosity has to match the application and the application process. Your sealant is designed to be non-sagging. You need to use appropriate tools as well, such as a caulking gun.

IRstuff (Aerospace) · Answer 2 · 2019-09-05 21:04:28

Seems to me that there are lots of other things that aren't necessarily optimized, such as
> gap size being filled -- seems large compared to the apparent bead size
> gap depth -- cab't tell from the photo how thick the sealant is in the PCB longitudinal axis
> the uniformity and consistency of deposition, mentioned above
> overlap -- while the bead overlaps well with the PCB, it doesn't appear to completely fill the gap
> possibly the need for form works (like for concrete) to constrain the sealant until it cures
> constraining the components during deposition and curing

Have you determine any common factors on where the holes form?

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3DDave (Aerospace) · Answer 3 · 2019-09-06 00:05:06

There are better dispensers available to help put the silicone where it's desired.

ProEpro (Mechanical) · Answer 4 · 2019-09-06 11:35:22

RE: Silicone alternative - less viscous

ProEpro (Mechanical) 6 Sep 19 11:35

https://www.mcmaster.com/74965a21

drodrig (Mechanical) · Answer 5 · 2019-09-06 11:52:17

The silicone is too dense; it was put in one shot with the gun, but it didn't flow.

The aluminium part and the PCBs where held during the pouring with some 3D printed brackets to keep everything in place.

The geometry is driven by the needs of the system, everything is very packed and the filling with sealant (the silicone) has the last priority.

I'll look for less viscous silicone

cheers,

TugboatEng (Marine/Ocean) · Answer 6 · 2019-09-28 20:58:15

Dow Corning 734 is a low viscosity flowable silicone that will flow into gaps and smooth itself out after application.

drodrig (Mechanical) · Answer 7 · 2019-09-30 11:24:46

I just saw a video, it looks good

What can I use to close the gap underneath?

With tape there are always small holes and the silicone will flow out

TugboatEng (Marine/Ocean) · Answer 8 · 2019-09-30 19:13:11

The 734 is still fairly viscous. I would suggest experimenting with it. You may not need to take any extra steps.

drodrig (Mechanical) · Answer 9 · 2019-10-01 08:25:08

Ok,

I'm trying also now with Omnivisc 1050

thanks,

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Silicone alternative - less viscous