I am currently working on an underwater sensor. I want to fill the voids in the housing with some kind of substance that ensures that no water will pass through the housing and into the equipment the sensor will be mounted in. I have tried epoxy, but it doesn't stick to the PEEK housing at all. (see picture) It just peels right off. I need a low viscosity compound that can be injected through a needle with about 1.25mm ID, that has good adhesive properties with PEEK plastic. It should withstand quite high water pressure before water seeps through between the compound and the PEEK housing.
Thanks for any replies.

 

Cyanoacrylate ? Melted wax ? Some times I used oil, liquid silicone lubricant. Pressure is of no concern if no bubbles embedded.

 

It sounds like you need a sealer, not a potting compound. Also surface prep will be critical for a good bond. Check out 3M 5200, it's an excellent sealant/adhesive, just check if it will stick to your material. The quick cure version is ever so slightly thicker than the regular cure version. Apply it before you assemble the parts for the best result, the working time is sufficiently long.

If you want the tube to last a long time (for any sealer product in a tube), when you're finished for the day, fill the cap with thick grease, squeeze a little bit out of the tube onto a paper towel (waste it), then IMMEDIATELY screw the cap full of grease onto the tube. It's very important that you waste a little bit before screwing the cap on, so that you get rid of any that has already interacted with the air and started to cure. Now the tube will keep for a very long time, just waste a little bit before the next use.

 

Also if you get anything in a tube, I very highly recommend a tube key, it makes application soooo much easier. For example, this Amazon link.

 

Cyanoacrylate ? Melted wax ? Some times I used oil, liquid silicone lubricant. Pressure is of no concern if no bubbles embedded.

If cyanoacrylate means super glue I don't think it will suit my application very well. I need something with at least 20 minutes of work time. Also the largest cavity is about 3mm wide.

It sounds like you need a sealer, not a potting compound. Also surface prep will be critical for a good bond. Check out 3M 5200, it's an excellent sealant/adhesive, just check if it will stick to your material.

I need something with quite low viscosity that can be injected through a 1.25mm ID needle, tho.

 

I need something with at least 20 minutes of work time.

Use the same glue dentists use. Can be cured with ultraviolet lamp after your work time. There is many types, as :
----> https://www.ebay.com/itm/2926006230...208b71cd787&rpp_icid=5d3227c402783208b71cd786

 

Use the same glue dentists use. Can be cured with ultraviolet lamp after your work time.

Only problem is I can't use UV light because the glue is on the inside of the housing :/

 

While it wouldn't stick to the PEEK housing, it should protect the interior of your project, any of the marine greases. They are formulated to be water resistant, and should/could fill the cavity around your electronics.

https://www.google.com/search?channel=fen&client=firefox-b-1-d&q=marine+grease

 

While it wouldn't stick to the PEEK housing, it should protect the interior of your project, any of the marine greases. They are formulated to be water resistant, and should/could fill the cavity around your electronics.

I need something that will withstand water pressure.
I guess I can try west marine epoxy.

 

If cyanoacrylate means super glue I don't think it will suit my application very well. I need something with at least 20 minutes of work time. Also the largest cavity is about 3mm wide.


I need something with quite low viscosity that can be injected through a 1.25mm ID needle, tho.

The long cure 5200 may be thin enough if you use a short needle and have patience. Can you not coat everything before assembly? The long cure 5200 gives you plenty of work time. The fast cure 5200 skins in 1-2 hours, the long cure takes a bit longer. Info here: https://www.3m.com/3M/en_US/p/d/b40066996/

 

I should note that the sealant/adhesive will not be in contact with water. The sealant should therefore not rely on humidity to cure.
It is only meant as a fail-safe so that should the o-ring fail, the entire device the sensor is mounted in will not fill with water.

I've added two pictures of a sensor I had laying around. It seems to use some kind of epoxy since it's hard to the touch. It does not however stick to the housing. When i cut the shaft into pieces it came right out.
So maybe it's not so important that the compound I choose to make my sensor watertight will stick to my housing?

The compound used in the pictures also seems to have been pretty thick before it cured, since all of it stayed in the shaft and didn't drip or run.

I think I will try West System Six10. Any thoughts?

 

You turned down my idea of marine grease. and now you say -

I should note that the sealant/adhesive will not be in contact with water.

The grease is water resistant and the only way it wouldn't work very well is if the water was rushing through the sensor. It works in wheel bearings and prop shafts on inboard motors, s o can't see it not working in a mostly sealed environment. It isn't like your normal everyday chassis grease, it's very sticky.

 

The sensor will go deep under water so in the event of an o-ring failure grease wouldn't prevent water from moving through the sensor and into the equipment.