How did they do this?

[Ulu]

Acrylic sheet is super easy to bend around the radius if you have something to form it over, like a barrel. You heat it in the oven until it gets soft and then you bend it over the form and let it cool as you hold it there.

Those poly barrels can only be heat fused to other plastic of exactly the same composition and there is no way to glue them chemically like PVC. You can get glue to stick on them for a while but it doesn't fuse.

But you can clearly use a gasket and lots of fasteners and get them to hold water.

Static Pressure at the gasket is under 5 psi. 1/6 the water pressure at my house faucet.

 

[johnnymax]

...I hope you're not planning on stocking them in a similar way to the examples shown. That's just wrong.

I am thinking I could use it when growing out small fry when selective breeding. That is why I need an observation window.

 

[Ulu]

I did a quick search for lexan on Amazon


Clear Polycarbonate Lexan Sheet - 1/4" (12" x 24") for window replacements, signage, display cases, aquarium covers, greenhouses, table protectors, DIY Projects, cabinets, shelves
4.6 out of 5 stars 23
$13.29

Lexan is very tough stuff. The windshield on my bike is lexan polycarbonate, and the eyeglasses I wear are a similar polycarbonate. I use Lexan for all my new lids now. Lexan will soften and bend with heat as well, but it's a bit trickier to get the temp right. Lexan will bubble if you go a bit too high. It also looses strength if overheated. Acrylic like plexiglas is cheaper & more forgiving in that respect.

 

[johnnymax]

Lexan is very tough stuff. The windshield on my bike is lexan polycarbonate, and the eyeglasses I wear are a similar polycarbonate. I use Lexan for all my new lids now. Lexan will soften and bend with heat as well, but it's a bit trickier to get the temp right. Lexan will bubble if you go a bit too high. It also looses strength if overheated. Acrylic like plexiglas is cheaper & more forgiving in that respect.

I learn so much here...

 

[Lepisosteus]

Here I am thinking the question was “how did they stuff so many tilapias into a barrel”.

The window is definitely acrylic. Silicone and bolts as pictured would do the job no problem. To curve it, they likely just put the sheet in a large oven or used an electric acrylic heater and placed it over top of a 55 gallon barrel to cool. That or cut a barrel in half and use the inside as the preform mold.

 

[Ulu]

My Wagner heat gun bends the stuff no problem too. Heck, you can char with it. 8-0

 

[fishdance]

I've made several of these with rotamould (HDPE) rainwater tanks. You definitely need polycarbonate which will flex. It's stronger as well so 6mm is fine for tanks up to 2m depth.

On high windows, it's a good idea to use a stiffening brace on the vertical sides as the tension strength is much lower than the curved top & bottom.

As previously mentioned, use silicon as a gasket. So fairly thick bead in line covering the screw holes but only lightly screwed down until the silicon has cured then tighten further. Curved corners on the opening if your container is thin walled.

I have used acrylic on flat sided tanks. If you use 10mm thick acrylic, you can tap thread (not all the way throygh) and use plastic bolts for a neater look.