Not getting a strong bond in acrylic help please!

[Smertrios]

I have some small acrylic tubing that I have cut so I can solvent weld them back together at angles. Problem is it doesn't take much at all to snap them apart they break at the seam showing how they did not bond well even tho it looked good until I broke it.

I use a mill to cut the angles on the ends so the parts mate perfectly. I use weld-on on the ends then push them together for a few seconds and set them on the table to cure. I come back and inspect, they look good *but* with very little effort they snap apart. So far with all the different things I have tried to get a better "weld" its PVC cement that is easiest and creates a strong bond but I wonder how long that bond will last =<

Anyone tried disolving acrylic in something like weld-on to create a thicker goop to put parts together? One thing I have not tried yet is flame polishing the ends before I solvent weld maybe that would make all the difference.

Anyone tell me whats wrong? Have to clamp them together? <-- that will be difficult for me to do because of the angled cuts and lack of clamps that could hold them together at the angles I have cut.

 

[scott m]

This seems odd. First off, are you sure the tubing is acrylic? Weld-on makes great products...they make different viscosities too... so no need to experiment making a "thicker goop". I'm assuming the angle you're trying to glue would be the high stress area, but to break off so easily after bonding (and curing) doesn't make sense to me. You've tried PVC cement and got a strong bond...was it the same tubing? I'm inclined to think that flame polishing the ends would not help, but if you have a surplus of the tubing, give it a try. Not sure how to answer the clamping question...lots of ways to accomplish clamping + securing but if you've got your pieces to stay at the correct angle after bonding, why clamp? Maybe there is another way to accomplish what you're trying to do/make with the tubing (like bending it using heat).

 

[sross]

weld on #16 is the thicker stuff.

 

[cvermeulen]

Sometimes acrylic bonds are tricky.

1) make sure the cut end of the tubes is absolutely flat. You said you're using a mill so I'm guessing they are pretty good. If there's any doubt try placing some sandpaper on a hard flat surface and gently scrubbing the end of the tube across it so you're sure it's totally flat. Don't bother flame polishing it, that can result in a nice *looking* surface but it doesn't mean that the surface is flat.
2) When I do acrylic seams with flat panels I use the "pin" method. This is a bit involved to explain and I don't know if it would really work for you with your application. The long and short of it is you use pins to create a tiny gap where your seam is going to go. You fill this space with weld-on solvent and let it sit for a few seconds before pulling the pins out and carefully wipe up the excess solvent. This allows the cement to work at the joint a bit and soften it before you press it together. Some adaptation of this might be helpful but again I see how this might be tough to use from what you're describing.
3) How long are you letting it cure? The stuff takes a couple of days to achieve full cure. (though it should be pretty strong in a few hours)
4) Weld-on makes several consistencies. I forget which product number it is, but there is one that comes in a tube and it's quite goopy. It's usually sold anywhere the solvent type is sold. There are also two part structural adhesives that are supposedly good for gap filling and so on but I've never used one.

Hope that helps! Any photos of what you're working on?

 

[cvermeulen]

Also yeah Scott raises a good point. Clear plastic tubing comes in acrylic, polycarb, HDPE, PVC and so on. If you're not certain it's acrylic that could be the smoking gun!