Which Adhesive/bonding for glass and stainless steel?

[gophaster]

I am building some small 316/316L stainless steel enclosures that will house underwater closed circuit cameras. They have 38mm diameter round openings where a 42mm diameter disc/glass lens will be bonded from the backside directly to the 316 stainless housing. The lens will be flat as will the stainless steel. The housings will be submerged in ocean water to about 3-4 feet depth for extended periods of time.

I have used some standard two part Loc-tite epoxy for this and it actually works well (no leaks) but I am concerned about long term use if the epoxy will break down over time. Is there some type of adhesive that is best suited for this application?

Thanks for any leads!

[PAR]

Epoxy will not break down with exposure to water, but will with exposure to UV. Painting the exposed epoxy will prevent UV damage.

[wardd]

have o ring grooves cut in the lens or housing outside a bolt hole pattern

make sure the bolts are sealed too

makes replacement simpler

[marshmat]

gophaster,

Wardd's suggestion of O-rings and bolts will certainly make future repairs much easier than an adhesive system would.

There are specialized, silicone-based adhesives designed specifically for structural adhesion of glass to metal, that can handle flexing and pressure variations without springing a leak. (Example- Dow Corning 895, the stuff that's used to glue those giant windows onto the sides of office towers.) They're expensive and tricky to use, though.

[gophaster]

wardd and marshmat, I have no reason to ever remove the glass from the stainless.... I actually prefer a permanent bond here.

I will look into the dow corning 895. Thanks

[PAR]

If I had to choose an epoxy I'd recommend West System's G-Flex, but honestly, I think most any marine rated epoxy will work. G-Flex will have a better elongation rate, which may be desirable in some conditions.

[gophaster]

Par, the Gflex product looks very promising I have used west systems in the past but I never have used/seen that product. It mentions metal but not glass so I sent them an email to see what they say. Thank you for the lead.

[wardd]

what if the rim of the lens was wrapped with a piece of fiberglass tape to form a bezel and then that bonded to the metal?

[Petros]

The problem with your proposed arrangement is the metal and glass expand and contract at different rates, putting a lot of stress on the bonding material. Eventually I think most epoxies will fail due to the temp cycling, epoxy is too brittle for this application, and it become more brittle with time.

Polyurethane adhesives stay flexible, I would find the type used to glue windshields on to car bodies. Consider the extreme temp conditions an auto windshield sees on a daily basis, the black polyurethane adhesive they use must be tough. It is applied fairly thick to allow the temp expansion of the metal car body while still staying attached to the glass.

I would also suggest the rubber o-ring or even a flat rubber gasket with a screw mounted flange. With that you separate the attachment from the sealing of the joint. The rubber o-ring or gasket will stay pliable and the mechanical fasteners will hold it together.

Good luck.

The G-Flex PAR mentioned is the right choice if it has never to be opened again.
Different flexing is just theory, we bond metal and wood with Epoxy since decades (and there is much more difference in flexing) without any problem.

Regards
Richard