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Getting bubble free Acrylic joints

Michaelx

Plastic
Joined
May 8, 2021
Hey everyone

I'm trying to build a watertight acrylic box. Unfortunately I've very little success welding clear acrylic joints despite the edges being flat.

Extra info -

I'm using Cast Acrylic with 6mm to 14mm thicknes. Here is the dilemma-

1. With Weld On 3 or Acri-bond 105 the curing is quick and easy but leaves bubbles.
2. With Acrifix 0192 which is a UV reactive I get optically clear bonds but due to being viscous it gets out of the edges and you can't wipe it without leaving marks. The result is while the joint look clear the sides look hideous.

Any help is appreciated. Thanks.

~Mike
 
Get some methylene chloride and a small syringe or the little solvent bonding bottles that tap plastics sells. Set your joint up and flow the meth into the joint by dragging the needle tip along the insideedge of the joint. The meth is like water viscosity wise- let capillary action draw it into the joint gap. The smoother your edges are (machined our routed) the better the joint will be. The pros don't use Weld On. You can slow the meth down evaporation wise by adding a little acetic acid to it- just a tiny amount.
 
I haven't done much of this myself, but I remember being told that it is a good practice to pre-wet the edge to be joined, soften it up, then position, and then drag the needle with the solvent, and I was told to use either chloroform or dichloroethane
 
I regret not buy a welding iron for plastic. It was hot air or something and you weld pieces together like for metal.
Not exactly what you are doing but with skill the joints would look good.
 
Dan from Oakland has it right generally. There is a noticeable difference also between dichloroethane (aka ethylene dichloride), as jz79 mentions, and methylene chloride. Ethylene dichloride is a slower-acting solvent (and was classified as a carcinogen way back when), and if the joint is fixtured correctly to allow some soak time, you can achieve clear and quite strong bonds. Use of shims to keep the spacing consistent allows for filling the controlled space with solvent, allowing it to work for some bit of time (TBD based on your process), then pulling the shims and letting the bond zone collapse to make the joint, This will typically push out any air bubbles and some softened acrylic. It's a balancing act to determine shim thickness and soak time for good cosmetics vs. material squeeze-out. Methylene chloride can also be used in the same way (as Dan points out, best with acetic acid, I like 10% by volume), but the difference in volatility and viscosity gives some different parameters to work with.

I built a lot of museum-grade display cases using this type of bonding. As a secondary process, for joint cleanup on the outside, leave .015-.020 of the horizontal panel sticking proud of the outside plane of vertical panel, then rout the excess off after the joint is cured. This cleans up the external squeeze-out and allows for some post bond edge polishing if needed.
 
Had a short stint at a sign making company, they made Perspex shop signs, they sent me (being quite young) to the chemist to pick up a bottle of chloroform which they used to stick letters, went to local chemists, aka boots the chemists asked for a bottle of chloroform, the only thing I got was a ride to the police station in the back of a police car, apparently they frown on young men buying chloroform.
Mark
 
I've not tried it, but my Pa had it on good authority from his friend the local pharmacist that asking for industrial chloroform makes all the difference. I've still got his bottle of it - remarkably it hasn't all evaporated in twenty years, unlike my bottle of dichloromethane which seems to evaporate through the plastic of the bottle and disappears in a couple of months.

The pharmacist also said that a smear of soft soap round a ground glass stopper seals it effectively. That's real potassium-based soft soap of course. I've no idea if any of the modern detergents would work as well.

George B.
 








 
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