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"Welding" Plastic Answered

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.



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.

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.


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.

Okay, thanks for the information!

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.

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.

Let me know when you have it done. I'd definately have a use for that.

heh, don't wait around for me. It could be a very long while.

Hey, you know, you could use two clothing irons and some wax paper. Those are pretty easy to come by or borrow. You just might want a jig to hold 'em!

say you want to connect 2 together form it with low heat (hot air or water) to the shape you want before joining put the pieces together fill with sand to make support from inside (so it won't warp) heat with clothes iron thru aluminium foil to make it even or use hot glue it won't warp too much if its filled and you press it to shape from outside immediately after applying hot glue and putting together

you can weld it with those wood burning pens. put the 2 things together and go along it with the pen, it works great.

I'd be weary of any heat-based methods. I once tried to hot glue parts of a milk bottle, and it warped pretty badly. Mind you, the pieces were cut out of the side; so if you were to weld 2 bottoms together, you might have better luck.

Hmm... Try to heat weld like Kiteman said, or using plastic model cement.