Vapor Polishing Polycarbonate

[Peroni]

I'm trying to vapor polish some polycarbonate sight glass windows without much success. I've got the methylene chloride, a hot plate, flask plus all the proper PPE recommended for working with this particular chemical.

The part is 3/16 thick with a pocket in one side so the actual "sight" portion of the disk is 1/16 thick. It's the floor of that pocket I need to make optically clear. The other side didn't get machined so it's still clear and the outer edge does not matter.

I've tried dipping the part which worked great for a few seconds before drying to a cloudy finish. I first tried vapor polishing in a beaker but all that happened was the part melted and again turned cloudy when dry. Next I tried a flask and directed the vapor to the surface I wanted to polish and nothing happened to it. The edges of the pocket got polished and rounded over but the actual surface I wanted to polish didn't change. Parts were cleaned with soap and water several times with a final DU water rise and handled with gloves. Material was certified US made from Piedmont Plastics. What in the world am I doing wrong? I really wanted to do this in house vs sending the job out esp as I've only a couple parts.

 

[Dan from Oakland]

Given that meth does a poor job solvent bonding polycarb, I'm not surprised that the vapor polishing is not going well for you. Meth works great to vapor polish cast acrylic parts in my experience. Best bonding of polycarb was using a mixture of meth and tetrahydrofuran. Not sure about using it for vapor polisning. A quick google search suggested using Weldon #4 for vapor polishing polycarb..... you might look into that approach.

 

[richardbt]

High humidity can cause clouding on lacquer finishes when drying. Maybe this is what is happening when the polycarbonate solvent is drying.

 

[jccaclimber]

I've seen that done with Weld-On (maybe #4?) as the solvent. I've had pretty good success with flame polishing as well, but for small areas without melting everything around it it's a lot easier with a really tiny torch, as in a hypodermic needle sort of small.

Note, I'm not sure what your definition of "optically clear" is, but know that these processes are good at taking haze off, but not so good at anything bigger like turning/milling marks. If you just need to see through it that doesn't matter, but if you need a nice clear window to actually see what's going on you'll need to start pretty smooth to begin with.

It's a lot more work, but I've had good luck with Novus on both PC (and acrylic) despite the label saying that it's not for use on polycarbonate.

 

[Peroni]

High humidity can cause clouding on lacquer finishes when drying. Maybe this is what is happening when the polycarbonate solvent is drying.

You are likely right it is humid as can be here and has been for several days. I finally got good results by baking the parts for a few hours then doing the vapor polish. Used Weld On 3 which the msds says is 70-95% Methyline Chloride by weight.