"Welding" Plastic

What is the best way of "welding" or joining two pieces of plastic? The type of plastic I'm using is the translucent material used in milk containers.

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fretted6 years ago
At the bottom of the bottle, there must be a tiny triangle with a number and/or some letters. If you tell us what's the number (and/or the letters), we will be able to know exactly what type of plastic it is.
BrianKT (author)  chooseausername9 years ago
There are quite a few numbers. There is a 2 in the triangle and 163 above that. To the right of the 163, there is 80522-1100.
fretted BrianKT6 years ago
Kiteman BrianKT9 years ago
The "2" is the important number - that means the plastic is HDPE (high density polyethylene).

It is a thermoplastic (so it can be melted without changing it into a new substance). It is resistant to many solvents, so solvent-based glues (like those used for joining PVC pipes) will not work well. You can weld it with heat, as long as you are careful not to get it too hot (molten HDPE is flammable).

I would try "spot welding" with a soldering iron, or laying sheets on a heat-resistant surface, overlapping the edges and gently running a soldering iron down the overlap to heat-seal them.

I would also practice first, using scraps or unimportant bottles.
BrianKT (author)  Kiteman9 years ago
Okay, thanks for the information!
Watch out for the fumes, too!
Use the tip for high detail, use the thing that holds the tip (the thick part) so you don't have to worry about the tip
. Kiteman's method works well as long as the weld will not be getting much stress. For a strong joint, you need pressure to thoroughly fuse the two pieces, as per Rishnai.
Rishnai9 years ago
If you have access to both side of the joint, make like the factory and hot-press. I'm tooling around with an istructable on it now, but the gist of the process is to overlap, press with some sort of metal die against a smooth metal surface, heat the die. If you don't have access to both sides, it is much tougher, and the plastic on the far side of the joint may want to curl away from you.
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