Hot gas welding

[N2950H]

I'm interested in fabricating an ATO reservoir similar in style to the Royal Exclusiv Dreambox or Advanced Aquatics units. I'm thinking I'll use the following mateirals:

main body: white PVC or maybe white polycarbonate
window: clear polycarbonate

I'm a metalworker above all else, so my question is about how to seal this thing together. Royal Exclusiv says theirs are hot gas welded and the AA boxes look to be constructed in a similar manner. I'm not suite sure what this method really entails, but if YouTube is to be believed, you basically take a stick of the colored thermoplastic welding rod and run it through a sort of heat gun to seal a joint. Sounds simple enough. Has anyone ever tried this, and maybe recommend a tool or method that worked for you? And can you use this process on dissimlar plastics, like PVC and polycarbonate?

Once I get that sorted out, I'm going to order some material to practice on. I'm looking for an excuse to use my CNC router and I think this will be as good a project as any.

 

[N2950H]

I found a table that indicated welding PVC to PC is rather frowned upon, so I may need to use PVC and acrylic instead. Not a big deal, I just know polycarbonate is less prone to warping.

 

[reefwiser]

You machine your pvc sheets they seal with a pvc welder

 

[bigcheese]

A couple of things.... just like TIG welding thicker metals, if the plastic is thicker you may need to bevel or chamfer the edges of the joint and do multiple passes with the plastic rod to get structural strength.

Agreed on the PVC-PC welding, Not recommended. I would limit your materials to things with similar tensile modulus (stretchiness under load) and coefficient of thermal expansion (how much it grows/shrinks with temperature changes). If you need to have dissimilar materials with widely variable properties, then welding isn't the way to go, stick with silicone.

If you can get your hands on an ultrasonic welder, consider that your best, cleanest weld solution. It uses ultrasonic vibrations to cause friction (and therefore heat) directly at the joint, liquefying the leading edges of the two parts. The resulting bond is as strong as the materials themselves and it's really hard to make a rookie mistake like overheating or melting through.

 

[N2950H]

Appreciate the info, bigcheese. I looked up the prices of those ultrasonic welders, and I think for my one-off fabrication purposes I'll have to stick with the hot gas weld method. I sure do love specialized tools, though...

 

[bigcheese]

Why buy when you can rent...

 

[N2950H]

Why buy when you can rent...

Yeah, that's certainly an option. One thing I noticed in all the ultrasonic videos I watched was that they seem to be used primarily for spot welding. Haven't seen anyone use it on a long run but I'll look into it further. Thanks again, I had no idea this even existed.

 

[Kris B]

Harbor freight sells a few different plastic welders. One uses your compressor for blowing the hot air, the other has a motor/fan built in. I have used the later many times messing around/modifying bumpers on cars with great success. Its a lot like tig/stick welding using a filler rod. Play around a little, get the heat/melt point figured out and its not that hard, especially if you have welding experience.
They also sell another type of plastic welder that is much like a soldier iron that works well, but unless you are doing it on the back side or can sand/grind smooth it can leave a messier finish