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Your experience using solvents to weld plastic? MEK isn't working

A

atod

Experienced Member
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Oct 14, 2010
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New York, NY
Hi,

I'm in the process of fixing a LSI ADM-3A terminal keyboard. Basically, I'm transporting a working keyswitch from a Atari 800 over to the LSI keyboard. My plan was to hole saw drill out both switches (done) and then use solvent to weld the plastic together.

There were a bunch of shavings after drilling and I placed these into the jar below with MEK. Everything sat in MEK overnight soaking and I was surprised in the morning that the plastic did not "melt" into a soft state at all. I tried painting Ambroid Proweld on a piece of the same plastic and it didn't soften either. Ambroid is supposed to handle ABS, Styrene, Butyrate and Acrylic plastic, so it's not one of those.

Has anyone had similar success (or failure) trying to weld plastic together? Any suggestions on other solvents that may work on this application?

Thanks

Pic to follow

img1202t.jpg
 
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Well. First thing would be to try and find out what kind of polymer it is.
From what era is it?
What is the functional solvent in that Ambroid (I am not familiar with the product)?
How rigid is the plastic, on a relative scale?
Do you have some little piece of scrap to burn? Does it self-extinguish? How does the smoke smell?

It might be PVC, in that case you can use THF (but be careful with it!)
 
Have you tried acetone? I've used it with ABS pieces dissolved to make liquid plastic, and it worked very well. If there is no special reason to weld the pieces together you might try superglue as that sticks things pretty well, provided the surfaces are close-fitting and thoroughly clean.

Steve.
 
You can also use accelerator with superglue, which I've found to provide good results when gluing sheets of Lexan.

I use solvent welds with PVC and ABS in plumbing, and that works very well. As mentioned above, you just need to figure out what sort of plastic it is.

Epoxies will work well too. I'm a big fan of JB-Weld, which will stick most A to most B. It will stick smooth metal to smooth glass if allowed to cure properly. We JB-Welded the handle on our push lawnmower once, and I believe the fix outlasted the mower.
 
Jorg said:
Well. First thing would be to try and find out what kind of polymer it is.
From what era is it?
Click to expand...
Mid to late 1970s

What is the functional solvent in that Ambroid (I am not familiar with the product)?
Click to expand...

Texan7R

How rigid is the plastic, on a relative scale?
Click to expand...

Very rigid. Even small pieces will not bend easily like the plastic on my car fender does.

Do you have some little piece of scrap to burn? Does it self-extinguish? How does the smoke smell?
Click to expand...

I'll try that. I'm not sure what that will tell us.

It might be PVC, in that case you can use THF (but be careful with it!)
Click to expand...

Where can THF be purchased? By the way, I thought MEK or Texan7R should be able to weld PVC

Thanks
 
Chuck(G) said:
Given the time period at which the part was manufactured and its need for dimensional stability (no one likes sticking keys), I'll wager that the thing has been cast from polyamide, quite possibly nylon. Here's a little bit on the problems of bonding polyamide

I've heard that there are special polyamide hot glues that work pretty well for this application. You may want to investigate.
Click to expand...

Oh boy, this is not good. I researched solvent welding and Nylon had no solution! I may be forced to thermo-weld. Of course that would also require an expensive thermowelder with nylon plastic "stick".

Any other ideas? I think if epoxy is used around the transported key, it will easily pop out of the hole it's in.
 
I know some convertible tops on cars are made of nylon, and you have to glue on the rear window (so glueing nylon to polycarbonate/glass). Try contacting a body shop or car parts store for the glue used. Gorilla glue might work, fixed most anything I used it on, but it sure is messy... I use it on most things instead of jb weld due to its flexibility. JB when flexed just cracks off, where as gorilla glue just bends back.
 
Thanks Folks. I saw Plastic Surgery and opted not to get it. I found it odd that it was the only product claiming to do the job. Also, it has no filling properties. I ended up filling the keyswitch in with Epoxy. I'm hoping it will catch the irregular surfaces and hold the keyswitch in. I'll update with the results tomorrow.
 
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