Epoxy / adhesive for hard plastic (headphone hinge) ?

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plastics

I use Weld*On products with lexan and acrylics. It is a solvent as you desc ribe. I imagine that they have products for your plastic.

m/

Good luck.

That's what I use for gluing problem plastics. Seems to work with all the hard plastics and some soft (flexible) plastics. It's a cyanoacrylate adhesive, with some hexane added to soften the plastic. Note that it's not very good at filling gap. With flexible plastics, it does well if the glue joint is very thin and therefore flexible. With a thicker glue line, it will crack and eventually crumble.

Another glue that I've found that works well with hard plastics is Zap-It. It's also a cyanoacrylate adhesive with some manner of solvent to soften the plastic. What I like most about it is that if I use the UV light to cure the joint, I don't need to wait until it hardens. I'll know if I have a decent joint in seconds. One catch is that it works best on transparent plastics, where the UV light can penetrate. However, if the plastic is opaque, just slop on some glue which leaks outside of the joint, harden what's visible with the UV light, and let it sit for about an hour. Even without the UV light, the cyanoacrylate adhesive will harden in less than an hour.

No clue on the other stuff you mentioned as I haven't tried those.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Try the 'burn test' to identify the plastic if its type isn't marked on it

if it's a low surface energy type, there is Scotchweld DP8005, but it's not cheap

Thanks very much b23sunwoodllc, Jef Liebermann, and Andy Burns,

the burn test is great, I'll make a purchase based on those results.

No, unfortunately there is not. Plastics is a huge group of materials with large differences in properties.

If at all possible, find out which type(s) of plastic you are dealing with. Larger plastic parts usually have mark, in a normally invisible location, that indicates plastic type.

If you can't find out, the job is merely a matter of trying different things until you run out of patience.

I do not have personal experience with the products you mention, but if it claims to be able to glue plastics such as PP and PTFE, it might be well worth a try. Those plastics, along with PA (PolyAmid / Nylon), are usually considered practically ungluable.

Your application is a high stress one, so it is possible a glue joint will not be able to last, even with a glue that works. Sometimes, a mechanical repair can be used. Some sort of bracket or clip that is screwed in place, for example.

Plastics can be tricky. The broken surfaces tend to be fairly smooth, which doesn't give epoxy much opportunity to "grab" onto it and make a good mechanical bond.

Also, some common plastics have a "low surface energy" issue - put simplistically (and not quite correctly) this means that the surface of the plastic has relatively few chemically-reactive sites on it, to which the epoxy resin could create a chemical bond.

So, without good mechanical or chemical bonds, you end up with a glue joint that's not held together very strongly, and it breaks apart easily.

I've had good luck on plastics using a thickened epoxy called G-Flex

655. It's sold by West System (a.k.a. West Marine) specifically for use in repairing plastic and fiberglass boats. In my experience it's an excellent all-around repair epoxy for most materials. A friend of mine used it to bond steel pipes and flanges to sheets of granite, after roughing up the granite surface with some emery paper. When he tested it by banging sideways on the pipe with a sledgehammer, the epoxy didn't fail... instead, the granite itself "tore apart" - the rock pulled apart into separate crystals. This stuff has become my "go-to" repair epoxy.

There are two tricks you can/should use when bonding difficult plastics. The first is to roughen the surfaces with some sandpaper, giving the material some "tooth" into which the epoxy can flow and then harden - this gives you a better mechanical bond.

The second is flaming. Take a propane and butane torch set on a fairly low flame. *Quickly* pass the very tip of the flame over the area to be bonded. You don't want to heat the plastic up enough that it melts, or even starts to soften... you simply want to let the tip of the flame oxidize the very surface of the plastic. This helps deal with the "low surface energy" issue, by creating reactive sites to which the epoxy resin can create a chemical bond.

If you buy the West System G-Flex 655 boat-repair kit, you get two very generous tubes of epoxy, some sandpaper, gloves, and "plastic boat repair" instructions which goes through the above procedures in detail. You can buy just the epoxy (without the extras) for a bit less money. It's a more expensive initial purchase than the little tubes you'll find at a hardware store, but it'll be enough to last you for years.

G/Flex 650 is the less viscous mix.

G/Flex 655 is the thickened mixture.

G/FLex 650 can be converted into the thicker G/Flex 655 by adding 406 Colloidal Silica: However, I've never tried it.

Both epoxies require some form of surface preparation. Notice that the adhesion strength increases substantially with sandpapering, alcohol wipe, and flame treating.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Thanks, and I agree, I think I'll glue it and then wrap an aluminum brace around the perimeter to add additional strength.

Thanks Dave.

Thanks Jeff, their video is funny and impressive.

On many of my plastic repairs, I strengthen them be drilling and inserting a 0.025" steel rod that I glue in place. Sometimes two, if it is large enough. Sometimes I temporarily glue it in place to get proper alignment while drilling. It has saved me a lot of time waiting for parts. I also have a drill and tap for a 1-72 screw if that is needed. As you are aware, it breaks where at the point where it needs the most reinforcement.

Mikek

Jeff,

Thanks again, I tried the Loctite above based on your recommendation and the price and it worked great, exactly as you said - it is a great glue for close-fitting parts! I added a 3/4" wide strip of aluminum cut from a rain gutter and screwed that into place around the joint for extra support, covered that with black tape, used the headphones several times, problem solved and it's not too noticeable. Thanks for your detailed reply.

Thanks Mikek, that would make for a very strong joint, if my current fix breaks I'll see if there's enough plastic material to support this approach. Cheers.

I do something similar when desperate. Instead of drill and pin, I use a flexible sewing pin (not a needle) and my soldering iron. I put some gouges in the surface of the pin, heat the pen head, shove the pin into the parts that I want to glue, and wait for the plastic to harden. When done, I cut off the head of the pin with flush cutting diagonal cutters or a Dremel tool with a cutoff disk. If I need pull strength, I use a straightened paper clip instead of a pin. The paper clip metal is softer, so I can use my wire cutters to roughen the surface of the paper clip. I heat instead of glue to assemble the parts because the hole is usually in some inaccessible location that can be reached with a soldering iron, but not a Dremel drill tool.

Another alternative is plastic welding. I modified a spare tip for my SMD hot air desoldering tool by adding a smaller nozzle suitable for plastic welding. So far, it's worked nicely for parts about the diameter of a pencil. However, my attempts at plastic welding small parts usually result in a blob of plastic or a cloud of plastic smog. The next time I get a laptop in the shop to fix, with the usual ultra-thin standoffs broken off by the threaded brass inserts, I'll give plastic welding another try.

Yep. However, my usual problem is finding the broken off plastic piece.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I visited my daughter last week and her Shark vacuum had broke at the neck of the beater bar. (something about gravity and a stairway) No real material to get any screws or pins into it. I used the Super Glue as listed above, >

to preliminarily hold the parts in position. Then after spending the time necessary to sand all the areas where I was to apply the two part epoxy made for plastic. >

I epoxied as much area as I could. After a full days cure, she vacuumed the whole house and it survived. I left specific instructions to let me know if it breaks. If it holds up, I'll call the glue and epoxy winners, because that is a high stress point of the vacuum. Mikek

Nice! (gravity and a stairway : lol)

I've done the burn test, but find I have more confidence if I have a known sample to compare aroma's. Mikek

For those interested in bonding polypropylene.

Mikek

For those into something more mundane for polypropylene: "The activator primes hard-to-bond surfaces such as polypropylene and polyethylene"

Cyanoacrylate adhesive with Heptane solvent for surface preparation (activator). I'm rather surprised that it works as most surface activators (used to increase surface energy and therefore chemical reactivity of low energy plastics) require elevated temperatures.

One big problem for me has been shelf life. I bought a few tubes of the stuff from a local hardware store, only to find that it was near the end of its shelf life. It died in the tube (unopened) a few months later: Shelf Life. From date of manufacture (unopened):

I suggest you check the self destruct date when buying:

Lot Code Explanation: #YDDDX Printed on crimped end on tube # = Disregard Y = Last digit of year of manufacture DDD = Day of manufacture based on 365 days in a year X = Disregard Example: 6061 = 61st day of 2016 = March 2, 2016

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558