How to identify type of plastic, then repair

Hi,
I have a remote car door control, and a piece of the plastic case has been snapped off. The piece has one of the key-ring loops at the top. The other loop is on the undamaged half of the case.
Can find no markings which seem to identify the plastic type. Inside the case, maybe written by hand in white paint, is 2c, and below that, 23. Any other markings are FCC and Canadian radio compliance codes, etc. The maker is DENSO.
Markings as on exterior of cover: FCC ID:HYQ1512S, CANADA:1551 102 326, RSS - 210, DENSO.
The broken piece is large enough to work with, about 1 1/8" long and 3/4" wide. The break is roughly a straight line, the edges are ragged and don't fit together tightly. Some unknown person has in the past tried to repair with what looks like plastic model cement. It hasn't held, and I've peeled the cement off.
After Googling a lot, I still don't know how to identify the type of plastic, and how make a solid repair. Using "Ambroid ProWeld Professional Plastic Welder, For styrene, Butyrate, ABS & Acrylic (Lucite or Plexiglas)" the parts are together now, but not very securely.
Working from the inside so it looks ok, would hot glue gun material work? Or use a soldering iron tip to smooth and seal the edges? (I've not had good results with this in the past)
Help would be welcome.
Thank you! Dugie
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Dugie wrote:

I found that black ABS cement worked for the broken fender on my wifes scooter. This is the glue used for black drain pipes which you can get at any hardware store. For me it was trial and error until I found the right glue. You know its right when the glue will mar and soften the plastic and then harden back when it cures. Try on an inconspicuous place first. I used cut up pieces of a credit card to reinforce the joint. I also used purple primer on the parts before gluing but don't know if primer is needed.
Kevin
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On Thu, 22 Nov 2007 16:31:31 -0400, "Dugie"

of PVC, so you might try the solvent used for PVC plumbing.
I've had pretty good luck on things like this by first gluing it with polyurethane glue (gorilla glue) and then taking a small piece of aluminum window screen cut to bridge across the gap and then using a soldering iron to heat the screening and press it into the melted plastic. Done on the inside, you don't see it, but the screen reinforces the break so it is very strong. I've even used a few short pieces of small diameter bare wire instead of screen when there isn't room to use the screen.
HTH,
Paul F.
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Nice idea, I'll remember that next time I need to do a repair.
wrote:

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wrote:

as reinforcing bond. You could identify plastic by solvent and burning tests but this would consume some of it. I would probably just use a two part epoxy recommended for plastic.
Frank
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Many of these things are made with ABS, but I think the Ambroid should have worked then. Could have been poor application or stale glue. Or a different plastic altogether.
Touch a spot on the inside with nail polish or acetone. If the plastic softens, _fresh_ airplane glue or the ambroid should work. I've had extremely good success on ABS housings with ABS pipe glue.
You could hedge your bets with a PVC/ABS transition plumbing glue. But the ambroid should have been roughly equivalent to that...
Many plastics can't be solvent welded (eg: polyethylene). These are the plastics that feel slippery and (usually) somewhat softer than the rigid plastics. You can thermal weld many, but not all of them. I've not had much success with it either. Practise a lot first. The trick is slow heat to ensure that the _whole_ bonding surface softens.
There are some plastics that are just plain difficult to bond with anything. Eg: except for some unusual situations, once a delrin or nylon part is broken, it stays broken.

A high temp glue gun might do just enough thermal weld plus "backing" to work.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
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Chris Lewis wrote:

and the value of your time, with the cost of a replacement keyfob off ebay or similar. Unless you have to go to the dealer to reprogram them (in which case you could just swap out the already-programmed guts from the old one), it should cost less than 20-25 bucks, based on a quick search. Chevy Prizm, right? Is it the one that is really a Toyota, or one of the others? Maybe the remote for the 'twin' model would work.
And yeah, I do understand the challenge of repairing something people said is unrepairable, and the elation when you succeed.
Me, I'd just rivet a metal strap to the back and punch a hole in it, rounding off the corners as needed to not cut through my pants pockets. Or if there is room in the case, drill a small hole and thread a loop of nylon cord thru it, holding it in place with a knot on the inside. (Like the wrist strap on a cheap camera or toy radio.) Lotsa ways to McGyver a workaround.
aem sends...
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There's nothing exotic about a $3 tin of plastic plumbing pipe glue or a stick of high temp hotmelt glue (if you have the gun).
At least I didn't suggest West Epoxy ;-)
[Tho the "sample kit" isn't that expensive.]

There is that. I got two matching fobs for $30 (Blazer), and the programming instructions cost another $6.
If you can't find programming instructions, programming at the dealer can cost $100 or more. _Each_. Yipes!

SOs tend not to like McGyver'd solutions ;-)
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
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Dugie, I sell various forms of plastic on ebay including delrin and nylon ( under the name surplusdealdude, if anybody's looking for small plastic offcuts btw).
It's very unlikely that this piece is delrin - it would more likely be a polyproplylene or polyethylene, since those are the standard types of plastic they use for this type of item. These plastics are impossible to glue, even with epoxy, largely because their surfaces are "oily" - that's what gives them their smooth finish.
If the fob was delrin, it would feel like a piece of rock to the touch. It would also be impossible to glue if it were delrin.
If it is Delrin, do not try to heat the edge with a soldering iron. Delrin emits very noxious fumes when it is heated (it's a formaldehyde derivative) and I know of 2 cases where it made people quite sick even with a short exposure.
Most likely this is impossible to glue back together. Welding it with a soldering gun will also likely not work - you need precise temperature control to weld plastics together and all you'll do is ignite the surfaces and make a mess.
Building up the back with epoxy would be a great solution, but you'll have to make sure that the epoxy has something to bond to , because it won't bond to the plastic. Maybe you can bond it to the inner workings and build it up, layer by layer.
Overall, the best idea is to buy a cheap replacement, either on ebay or at an auto wrecking yard and get it reprogrammed.
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