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"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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10
fretted says: Feb 9, 2011. 11:52 AM
http://www.harborfreight.com/welding/plastic-welders/plastic-welding-kit-with-air-motor-and-temperature-adjustment-96712.html
9
chooseausername says: Jun 27, 2008. 9:17 AM
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.
10
TechnoGeek95 (author) in reply to chooseausernameJun 27, 2008. 10:31 AM
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.
10
fretted in reply to TechnoGeek95Feb 9, 2011. 11:46 AM
http://www.harborfreight.com/welding/plastic-welders.html
169
Kiteman in reply to TechnoGeek95Jun 27, 2008. 10:53 AM
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.
10
TechnoGeek95 (author) in reply to KitemanJun 27, 2008. 10:58 AM
Okay, thanks for the information!
41
Weissensteinburg in reply to TechnoGeek95Nov 22, 2008. 6:50 PM
Watch out for the fumes, too!
3
Sandisk1duo in reply to TechnoGeek95Jul 6, 2008. 7:22 PM
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
3
NachoMahma in reply to TechnoGeek95Jun 30, 2008. 9:42 PM
. 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.
5
Rishnai says: Jun 30, 2008. 8:16 PM
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.
1
8bit in reply to RishnaiDec 13, 2008. 4:00 AM
Let me know when you have it done. I'd definately have a use for that.
5
Rishnai in reply to 8bitDec 20, 2008. 8:29 PM
heh, don't wait around for me. It could be a very long while.
1
8bit in reply to RishnaiDec 21, 2008. 8:13 PM
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!
10
11010010110 says: Nov 22, 2008. 5:01 PM
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
21
Thelonelysandwitch says: Nov 21, 2008. 1:13 PM
you can weld it with those wood burning pens. put the 2 things together and go along it with the pen, it works great.
6
zachninme says: Jul 6, 2008. 7:47 PM
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.
22
KentsOkay says: Jun 30, 2008. 10:48 PM
Hmm... Try to heat weld like Kiteman said, or using plastic model cement.
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