Bonding Silicone Rubber to Carbon Steel Sheet

Question

Bonding Silicone Rubber to Carbon Steel Sheet

MintJulep (Mechanical)

(OP)

24 Feb 14 20:41

Conceptually, if I were interested in bonding a silicone rubber sheet to a carbon steel sheet so that it would "never fail", what adhesives and surface preparations should I be looking at?

The surface is big. Roughly 3 meters x 10 meters. Ideally I'd prefer no seams, but that doesn't seem likely.

Because the surface is big, a cure in place application would not seem possible.

I anticipate the surface to be a bit convex in short direction and generally straight in the long direction.

I anticipate that the surface will not be perfectly smooth. It will be 1 or 2 mm thick sheet spot welded to stringers at maybe 500mm spacing. There will probably be seam welds in the steel sheet.

The entire exterior surface will be exposed to sun and weather. Horizontal. Four seasons. The interior will be climate controlled - except of course when the climate control system is turned off, at which time the interior will be hotter than the outside if it's hot outside, and the same as the outside if it's cold outside.

I cannot tolerate a failure that allows moisture to migrate into the bonding surface.

I cannot tolerate a failure that allows an edge, corner or seam to lift.

I do not trust the installing work force to perform the specified surface preparation correctly.

I do not trust the installing work force to follow the adhesive application procedure correctly.

I'm reasonably sure that given these constraints this is an impossible application. But I'd like to investigate anything might have a chance of working.

berkshire (Aeronautics) · Answer 1 · 2014-02-25 01:49:11

Mint,
Have you talked to RELTEK ?
B.E.

You are judged not by what you know, but by what you can do.

CoryPad (Materials) · Answer 2 · 2014-02-25 07:55:13

Lord has special primers for bonding metal to rubber:

http://www.lord.com/products-and-solutions/adhesiv...

btrueblood (Mechanical) · Answer 3 · 2014-02-25 10:18:30

CoryPad is steering you in the right direction. But, you said: "I cannot tolerate a failure that allows moisture to migrate into the bonding surface" - I would say, then don't use silicone rubber. Silicones have a very high permeability to water and water vapor - ever use a clear silicone caulk in the bathroom? You end up seeing the mold growing along the bondline and in the corner crevice. Use an EP rubber instead, it has better resistance to weather, UV and moisture - there are huge numbers of flat roof membranes done in EPR, and a number of manufacturers of the stuff to choose from.

MintJulep (Mechanical) · Answer 4 · 2014-02-25 10:54:38

Thank you for the insight re permeability btrueblood.

I need a degree of resistance to "sparks" - think welding or plasma cutting sparks although that is not the actual source.

I don't think the typical roofing membrane materials are up to that challenge.

Ultimately I think an adhered membrane of any material is a DOA concept for multiple reasons.

btrueblood (Mechanical) · Answer 5 · 2014-02-25 16:33:38

Ok, silicone might work for that, at least better than the fuel source that epdm is - is the membrane likely to be soaked in water for long periods of time, or is it only an occasional thing?

Then again...would a membrane with a cover fabric of fiberglass or the like work? It's possible to bond epr to most fabrics, again I'd look at Lord co. for guidance on what might work. With enough insulation between the rubber membrane and the fire, you might be able to make it work.

Also, it's possible that other polymers might work that have inherent flame retardancy or ability to be formulated with flame retardants (PVC, like is used in most wire insulation jackets would be a guess). The problem with PVC is that the fire retardants tend to leach out over time, and I think that gets accelerated by water.

MintJulep (Mechanical) · Answer 6 · 2014-02-25 21:45:04

Rain and such should not puddle. Wet leaves sitting on it are a possibility. And then there is this stuff called snow and ice in the winter.

BTU content, smoke generation and the toxicity of the smoke are under strict regulatory limits in the application. That makes many synthetic rubbers difficult, PVC is right out because of the toxicity of combustion break-down products.

Maybe some sort of ceramic loaded coating.

btrueblood (Mechanical) · Answer 7 · 2014-02-26 09:39:31

RE: Bonding Silicone Rubber to Carbon Steel Sheet

btrueblood (Mechanical) 26 Feb 14 09:39

Ah, yes, the holy grail: flexible ceramic.

MikeHalloran (Mechanical) · Answer 8 · 2014-02-28 18:31:43

Rolled roofing := felt + tar + tiny white or colored stones,
applied with hot tar under it and in the seams,
over a layer or two of tarpaper, bonded and sealed with hot tar.
Fairly common on flat roofs in Florida.

Older alternative is two layers of tarpaper,
adhered and sealed with hot tar,
covered with pea gravel bedded in hot tar.

The hot tar is the secret ingredient.
Cold adhesives are not even close to as good.

Mike Halloran
Pembroke Pines, FL, USA

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Bonding Silicone Rubber to Carbon Steel Sheet