Adhesive advice needed

[tkeithlu]

I need to glue a block of optical acrylic to a bronze frame, in a situation in which I need to fill gaps up to a millimeter or so, and I need the gap-filling adhesive to set very quickly, while I hold the acrylic piece in place. The adhesive cannot be runny because the glued surfaces are vertical. So, I need a pasty glue that is going to set up quickly, as in a few minutes. It needs to be thick, almost putty. An epoxy comes to mind, but which one? I tried Gorilla Glue epoxy, and it all ran out of the cracks before setting.

Which glue comes to your mind?

[JPA Cate]

Hi, tkeithlu,

There's a Super Glue that comes in gel form that stays put. I'm thinking you should talk to plastics specialists, or use the Sikaflex they use to glue in large arcylic panels in skyscrapers.

Good luck with it. Those are big gaps to fill, and if the acrylic will be expanding from heat, you need something that will stay flexible, and I doubt the gel super glue does.

Ann

[Wotname]

Originally Posted by tkeithlu

I need to glue a block of optical acrylic to a bronze frame, in a situation in which I need to fill gaps up to a millimeter or so, and I need the gap-filling adhesive to set very quickly, while I hold the acrylic piece in place. The adhesive cannot be runny because the glued surfaces are vertical. So, I need a pasty glue that is going to set up quickly, as in a few minutes. It needs to be thick, almost putty. An epoxy comes to mind, but which one? I tried Gorilla Glue epoxy, and it all ran out of the cracks before setting.

Which glue comes to your mind?

If epoxy is suitable in your application, then you use two epoxies. One slow setting and one fast setting (3 to 5 minutes).

Use a few spots of fast setting epoxy and then the bulk of the glue can be slow setting.

You can fillers to the fast setting epoxy if it is too runny but you got to be quick with the mixing!

This assumes you can hold the item steady for about two minutes until the fast setting epoxy kicks in and holds the item for you.

[Breaking Waves]

https://www.3m.com/3M/en_US/p/d/b40065698/3M has some pretty good structural glazing tapes.

Don't know if they would work for your specific application - but they have quite high near-instantaneous bond strength (some clamping pressure is useful for ultimate strength), and can fill couple mm gaps easily.

[Pauls]

Fumed silica is what is used to thicken epoxies. It is available from a number of suppliers. You can use to thicken an epoxy so that it will not slump.

The 2 epoxy components must be mixed before the fumed silica is added. Because it will take a few minutes to mix in the fumed silica this is not viable with fast setting (5 minute) epoxy.

The ideal solution, as far as epoxy goes, is to use a slower setting epoxy and make something to hold your acrylic in place until the epoxy has gone off.

There are silicones especially made for glazing. guaranteed they will not sag or run. They go off slowly, you will again have to have something to hold the acrylic in place while it cures. A few scraps of wood, glued together perhaps?

[Jim Cate]

Dunno if it would work for you in this application, but I've had good results using hot melt glue gun stuff to hold bits together whilst the epoxy went off. It's quick to apply and set up and easy to remove later when all is solid.

Jim

[HopCar]

I’ve used 3M VHB mounting tapes in other applications. I would go with Breaking Waves suggestion. Avoid epoxy. I don’t think it will bond well with the acrylic, also epoxy is not very flexible and the bronze and acrylic will expand and contract at different rates as the temperature changes.

[AKA-None]

You can buy uv set super glue
It stays liquid until you hit it with uv

I looked at it for a manufacturing project in a former life. Way cool stuff

[Bill Seal]

The coefficient of thermal expansion of acrylic is about 7 times greater than bronze, so you'll have to use a very flexible adhesive or have bulged windows like skylights or hatches.

[Bill Seal]

Originally Posted by AKA-None

You can buy uv set super glue
It stays liquid until you hit it with uv

I looked at it for a manufacturing project in a former life. Way cool stuff

It's what your dentist uses for fillings and cementing crowns

[tkeithlu]

Thanks, folks. That gives me several leads that are new to me, and which I can explore. Expansion may not be too big a problem - the acrylic is a prism in the lens of the Crooked River Lighthouse at Carrabelle, which I maintain. It fell out of the lens when I lifted the lens to get to the ball bearings underneath. The bronze is 1/4" plates that go between the parts of the lens, and form the frame of the bivalve lens. The chunk of acrylic weighs about a pound, and is oddly shaped.