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Old 01-10-2018, 12:22 PM   #1
Curious.George
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Default Reassembling solvent-welded cases

I often have to pull apart solvent-welded plastic cases (wall wart, brick, device enclosure, etc.)

But, putting them back together -- in a way that doesn't look amateurish -- is always a challenge.

I've tried different adhesives to minimize the "sloppy mess" but they always, still, look like they've been taken apart and reassembled...
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Old 01-10-2018, 12:43 PM   #2
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Default Re: Reassembling solvent-welded cases

The solvent they use to bond plastic water piping and such is good and stronger than cyanoacrylate super glues, it does take a bit of practice to a) get the wall wart apart cleanly and b) glue it cleanly. Less is more is my rule.
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Old 01-10-2018, 01:48 PM   #3
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Default Re: Reassembling solvent-welded cases

polypipe
from plumbing shops.
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Old 01-11-2018, 01:01 PM   #4
Curious.George
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Default Re: Reassembling solvent-welded cases

Quote:
Originally Posted by stj View Post
polypipe
from plumbing shops.
The solvent-style adhesives don't work. The act of cutting the case open, removes (destroys) material. So, the resulting case is "shorter" than the original. If there are internal structures (e.g., heatsinks, metal frames, connector shells) that neatly fit inside the case, you can't squeeze down on the shell to bring the two cut surfaces close enough together to come in contact with each other.

Adhesives that aren't viscous enough flow straight through the gap between the two half-shells.

So, you need a viscous adhesive that, itself, will cure to be as strong as the case itself -- acting like a "filler" as well as adhesive.

I've found many of these. But, their viscosity makes them hard to apply cleanly; excess inevitably slops over the exterior of the case. And, cuz the case is plastic, any solvents strong enough to clean up the mess end up dissolving the external surface features of the case (e.g., remove the textured finish)

While the reassembled case may be physically intact, it very obviously looks like a patch job!

I don't do these kind of repairs for a living so if I'm doing it, it's:
- because I couldn't just rescue a compatible device
- for a close friend that I'd like to have a "quality" result
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Old 01-11-2018, 01:34 PM   #5
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Default Re: Reassembling solvent-welded cases

I have some stuff called Plastic Weld. Administered with a syringle/needle it's fairly mess free. Capillary action does its thing and the glue melts the top later of plastic.
Crack rather than cut the case open and it works well.
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Old 01-11-2018, 03:37 PM   #6
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Default Re: Reassembling solvent-welded cases

polypipe is a gap-filling gel.
plastiweld is like water.

different tools for different jobs.

or use dark silicone??

Last edited by stj; 01-11-2018 at 03:38 PM..
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Old 01-11-2018, 04:15 PM   #7
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Default Re: Reassembling solvent-welded cases

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Old 01-11-2018, 07:12 PM   #8
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Default Re: Reassembling solvent-welded cases

yes, used the silver version on my 12v test supply.
not a good idea for customer gear though!
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Old 01-11-2018, 10:47 PM   #9
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Default Re: Reassembling solvent-welded cases

Quote:
Originally Posted by stj View Post
polypipe is a gap-filling gel.
plastiweld is like water.

different tools for different jobs.

or use dark silicone??
Polypipe is the name of the company. They do solvent for ABS or PVC or do you mean something else ? https://www.mrcentralheating.co.uk/s...nt-small-125ml
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Old 01-11-2018, 11:05 PM   #10
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Default Re: Reassembling solvent-welded cases

that link looks like the stuff i had.
didnt know it came in black though!!
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Old 01-11-2018, 11:14 PM   #11
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Default Re: Reassembling solvent-welded cases

Quote:
Originally Posted by stj View Post
that link looks like the stuff i had.
didnt know it came in black though!!
Ill give it a try. It's certainly cheaper than Plastic Weld, that somehow manages to evaporate out of a sealed glass bottle.
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Old 01-12-2018, 12:58 AM   #12
Curious.George
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Default Re: Reassembling solvent-welded cases

Quote:
Originally Posted by stj View Post
polypipe is a gap-filling gel.
plastiweld is like water.

different tools for different jobs.

or use dark silicone??
The silicone may be a win -- if I can find a dispenser with a small enough "nozzle" (as you typically only want a 1/16th inch bead to fill the gap).

Or, maybe get a bunch of disposable syringes (large bore plastic tubes instead of needles) and consider each to be a one-use product.

Then again, maybe the syringes would work with the epoxy as well? The problem there is always going from the mixed two parts to "application" without getting all sorts of it on the outside of the case (if you could squirt it into the gap it might be a win as it is reasonably viscous and 5 minute setting times are manageable)
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Old 01-12-2018, 10:35 AM   #13
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Default Re: Reassembling solvent-welded cases

I just repaired a Macally PS-AC4, i just used clear rtv silicone all around the edge, worked perfect, I have used crazy glue but found it won't hold well, in one case I used 5 min 2 part epoxy, It worked good too, none of these products will really stick that well to plastic so there is no problem opening them again if needed.
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Old 01-12-2018, 10:49 AM   #14
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Default Re: Reassembling solvent-welded cases

put tape on the edges of the case,
apply the stuff, smooth it down with a card.
then peel the tape off - clean finish.

i use shitloads of masking tape - a thousand uses for that stuff.
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Old 01-13-2018, 02:14 PM   #15
Curious.George
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Default Re: Reassembling solvent-welded cases

Quote:
Originally Posted by stj View Post
put tape on the edges of the case,
apply the stuff, smooth it down with a card.
then peel the tape off - clean finish.
Then the sides of the case differ, in appearance/texture, from the face and back of the case. Plus, you've "scraped" the side to have square edges instead of the rounded ones typical on most injection molded cases (as well as removing the draft angle that was present on the original sides).

And, you have a couple of places where you've had to work-around the power inlet and outlet while not trying to let the original surface/texture peek through (cuz you've obliterated it, elsewhere along the sides).

If, instead, you confine your adhesive to the gap between the two half-shells, you can make the adhesive look like it was intended to be the "original" adhesive. That's why I take the effort to use hot knife or thin saw blade to cut the case in half -- so the only missing plastic lies in the gap.

I'm going to start looking for disposable syringes -- preferably small barrels so they don't need a lot of adhesive to be effective -- and try using them as applicators. Similar to the fancy solder paste dispenser that I use with my Leister.
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Old 01-14-2018, 08:09 PM   #16
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Default Re: Reassembling solvent-welded cases

I haven't had much success gluing these types of cases. Were I to try another, I'd probably just print a replacement case on the 3d printer and I'd design it to assemble with screws.
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Old 01-15-2018, 03:10 AM   #17
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Default Re: Reassembling solvent-welded cases

you can probably buy good cases, but company's like VERO and Hammond dont sell stuff cheap!
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Old 01-15-2018, 04:31 PM   #18
Curious.George
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Default Re: Reassembling solvent-welded cases

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Originally Posted by clearchris View Post
I haven't had much success gluing these types of cases. Were I to try another, I'd probably just print a replacement case on the 3d printer and I'd design it to assemble with screws.
These are G-jobs, for friends. I'm not going to spend hours measuring the guts and designing a suitably sized enclosure to house it -- then print it. They can go buy a replacement if it gets to that point! Hence the reason I opt to just find a similar replacement (often same make/model) and gift it to them -- to save me the time of disassembling, repairing and reassembling.

It took me an hour to do this process most recently for a set of three power supplies. I figure the average of 20 minutes per supply is cost (time) effective -- it will take me that long to dig through a gaylord full of power supplies in search of a suitable replacement (THREE such replacements).

But, I'd like not to have to be apologetic about the appearance of the results! (actually, these came out "decent" -- though you can tell they were repaired)
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Old 01-15-2018, 04:35 PM   #19
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Default Re: Reassembling solvent-welded cases

drill holes for cable ties .will also let some heat out .
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