Room temperature cure epoxies

Why is it necessary to cure at room temperature?

I have some excellent epoxy that will grudgingly cure at room temperature, but it works much better if it is cured at 10 or 20 degrees F above room temperature. It cures faster and stronger if warmed.

–B.G.–

There is a part that cannot be removed that includes UHMWPE fibers, so I would need any heating to be very controllable. And I don't have a way to controllably heat a long CF tube.

Loctite Hysol and West System epoxies have been recommended to me. Loctite Hysol 9430 seems like a good candidate, but it appears that it is only available in large quantities (2 lb cans). I was just wondering if anyone had any first hand advice about any specific products.

Colin,
It kind'a depends on what you are looking for. There are several epoxies that will work, all should be considered high strength.

MAS, System-3, as well as several 5 minute epoxies. JB weld is fairly heat proof. Then the older grey goo (I forget the real name.)

Mostly, none will bond to Ultra High Molecular Density plastics, though. These require special surface treatments for only a medium bond, at best. Often keys can be formed that will lock in a part, even if it does not bond well.

Check out the various web sites to find out more about fillers and thickening agents. I usually use sawdust in my boats, metal grinding dust in metal stuff, allowing an hour or so of wait time…depends on what type of hardner you have.

Not really an expert, but I have been using epoxies for many years, off and on.

Epoxy used to be my go to glue.
Then I disovered that it can degrade the bond in carbon fiber composites.
Then I discovered that urethane glues often hold better than epoxy, especially with composites and plastics.
Experiment first is what I do now with all bonding projects.

Thanks for the tips. I hadn't realized that bonding carbon composites with epoxy can pose a risk to the epoxy matrix underneath.

I don't plan to bond UHMWPE. I'm working on a center pole for a mid and I'd like it to have a few other uses (fishing pole, hiking pole, etc.), so I'm attaching some aluminum hardware.

I've had good luck with urethanes, too. I'll keep them in mind. I might do an experiment with one of the Hysol urethanes and Loctite E60HP epoxy, and see how they fare. Thanks again for the input.

Common epoxies like Araldite
Co-polymer adhesives (silicone/PU)
Eclectic E6000

But don't expect any adhesion to PE from almost anything.

Cheers

If you can get an epoxy like Bob suggested, without knowing your project I would imagine a blowdryer would be able to to raise the temp the necessary amount without worrying too much about damaging anything. If you're project can't handle 120F I'd question it's stability as a whole (but then again I live in AZ so I expect everything to survive 180F!)

CURE 24 hours at 77°F(25°C), or 2 hours at 140°F(60°C), or one hour at 180°F(82°C).

That's what I had in mind. I've generally warmed it to roughly 120 F and left it that way overnight.

I've been using the same stuff for over thirty years. Miller Stephenson 907 Epoxy.

I've used it for permanently mounting ski binding screws. Once set, I have never had screws fail. If I absolutely need to break the epoxy joint, I heat up the screw with a pencil torch and then torque it like crazy.

–B.G.–

PM sent, check your email. In my PM I forgot to mention that all of those are room temp cure epoxies, but you'll see that when you look at the spec sheets.

The only conceivable way that an epoxy adhesive would damage a carbon fiber component would be the following:

1) Carbon fiber is laid up with a resin that has amazingly poor resistance to solvent such as xylene

2) Epoxy adhesive used contains copious amounts of solvent

3) Adhesive is applied overly thick such that the outer surface skins over and the balance entraps the remaining solvent

4) Over time this entrapped solvent could attack the epoxy used to lay up the carbon fiber component

This is all pretty unlikely and can be mitigated completely by using a 100% solid epoxy. Araldite is a decent epoxy with middle of the road adhesive and tensile strength. As others have stated, getting a bond to polyethylene is extremely difficult. I would recommend the following to maximize adhesion:

1) Flame the PE part in order to increase the surface energy available for any adhesive to bond to.

2) Roughening the flamed PE with carding cloth in order to produce a "wooly" surface. You are creating significant extra surface area for the epoxy to bond to.

These two steps significantly increase the adhesion of epoxy to polyethylene. With a good adhesive you can expect around 200 psi tensile shear adhesion. As a bonus, you can condition the flamed and roughened PE with a nice solvented epoxy. The solvent will very slightly attack the PE and carry a very thin epoxy into the PE thus increasing the bond strength. Hope this helps but if there are any follow-up questions let me know.

I appreciate the input about bonding a cured epoxy surface (CF composite) using epoxy.

I guess I should clarify about the PE. As I said before, I am not bonding any PE parts. There will be no glue in contact with anything made of PE at any stage of this project.

I hope to bond aluminum to a carbon fiber tube, and I am wary of heating the tube in a way that is not very controllable (with a hair dryer, say) because the tube has a permanently affixed PE part on it already and I don't want to risk damaging that. I only mentioned the PE part to answer a question from Bob about my room-temperature cure requirement.

So, I'm interested in epoxies that will achieve a high bond strength on those surfaces (aluminum and CF/epoxy tube) after a room temperature cure (even if room temperature curing takes a week or more). Thanks to several good suggestions, I have a list of products to consider, and I think I might just commit some scrap material to a series of experiments.

You will want to roughen the aluminum to a >3 mil angular profile prior to bonding with the epoxy. This can be done on small areas by roughening with 80 grit or coarser sand paper. Ideally you would use 80 grit followed by something like 36 grit believe it or not. You want to make as many mechanical keys as possible for the epoxy to bed into. Bead blasting (if it is an option) should be avoided like the plague since it peens the surface rather than create the tortuous cavities that you are after.

The CF/epoxy part does not need the same roughness of profile, 1.5 mils is sufficient there. This can be accomplished by roughening with 120 grit but 80 grit isn't going to hurt anything. You want to wash away any surface dust with copious amounts of MEK, MIBK, or acetone and a short-bristle brush. A cheap 1" chip brush with the bristles cut to 1" long works great. Leaving the bristles long leave the brush far too soft to do the job properly. It is important to select something which evaporates completely and does not leave any residue which may act as a release agent. After surface preparation, avoid touching anything with naked hands since oil from skin will diminish the bond obtained. There isn't much worry about how fast you apply the epoxy after surface preparation since the fresh aluminum surface will oxidize almost instantly in the presence of oxygen and the aluminum oxide film is tightly adherent. The story is very different for steel in which best practice is to begin the application within 8 hours.

Colin,

I forgot the mention that you can control the thixotrope and viscosity of any epoxy by adding fumed silica (trade name cabosil) to the base prior to mixing the two components together. Enough fumed silica will make a thin coating into a paste.

A common trick for slightly raising the temperature in a controlled and cheap fashion is to make a box out of pink insulation board and put an electrical light inside with the epoxy to be post cured. A 60 watt bulb in a small space can be an effective heater. It takes a little trial and error to size the box and bulb to produce the desired temperature but keep it in mind should you not find a suitable room temperature cured epoxy.

Within the Belzona product range the best selection would be 1821 which is only sold in 1kg units and you might expect to pay around $300 for the kg. Keep in mind these materials are not sized or priced for small consumer projects. It actually works out to be cheaper than JB Weld on a $/mL basis. If you need to be put in touch with your local distributor I can arrange that. I would imagine you will do fine with a smaller volume of a less robust adhesive though.