I’ve more or less cracked the problem of regrinding the material into usably small granules, and my flat-plate sanwich toaster is capable of melting and fusing the granules into solid sheets.
The challenges I currently face are:
Getting the quality consistent - I’ve tried pressing the the material into a template, but that didn’t work very well. I’ve tried moulding pieces the size of the whole platter, but they end up lacy and porous at the edges - probably because I can’t exert enough pressure over a very large sheet of material to be able to form it into a uniform solid.
Also, HDPE has quite a noticeable coefficient of expansion - As long as I let my panels cool inside the machine, they come out beautifully flat, but that does impose limits on the rate at which I can produce them, and possibly their consistency of size when cooled…
My goal (which I’m starting to see recede into infinity) is to be able to make consistently-sized solid panels of remanufactured plastic that I can weld together into larger sheets, to cut out the pieces to make a small canoe. I’m convinced it’s not impossible, just technically difficult.
I toyed with the idea of setting up some kind of rotational moulding process in a rotisserie oven, with a cube-shaped mould, the faces of the resulting objects then being available to cut out and use as panels, but I dont think it will work only rotating in one axis.
So… what to do? I’ve stopped work now to think about it. Can anyone suggest any avenues of further progress?
Mangetout, you are really, truly awesome. That is the coolest thing I have seen in such a long time. That kind of project is the hallmark of an innovative and brilliant mind. Just look out for the fumes, okay?
Maybe somebody over at MAKE magazine can help you out.
While this won’t help with your boat building, those panels look like decent floor tiles, especially suitable for a playroom.
Other than that, I got nothing. Except I had a flashback to a toy I had in the 60s called a Thingmaker, which required the child using it to melt plastic sheets with a VERY hot appliance. Ah, the glory days before toy safety regulations…
I had a bit of a breakthrough last night - and I’ve worked out a way, I think, of manufacturing continuous strips of the material.
I’ll have to cut the front lip off the sandwich toaster, but that’s OK - it was cheap and I’ve accepted the possibility of writing it off for this project…
What I plan to do is construct a press adjacent to the front of the sandwich toaster at exactly the same level - so I can slide the melted material out of the hot press and clamp it in the cold press to prevent buckling while it cools.
If I use silicone-impregnated baking paper, this also separates from the plastic during cooling - then I should be able to place the baking paper back on the hot press, slide the ragged end of the plastic sheet back onto the toaster, add more plastic and melt a new section onto the edge, then bring this out and clamp, etc.
The major wins with this (if it works, which I am fairly confident it will) are that the press can be kept hot (so it should be cheaper to run, and the whole process should be fairly fast), and I’ll be creating a single continuous strip of plastic - so the only welds I need perform will be on the chines of the boat, when I construct it (and these will be reinforced with timbers on the inside of the same joints).
The other big win is that with the double-press method, the product is just much more uniform in texture - and the source material doesn’t even need to be finely ground - for last night’s experiment, I mostly used flakes from milk bottles just cut to approximately 1cm square with scissors.
Fumes aren’t generally a problem, as HDPE is a pretty benign material, unless charred - and it seems that the top temperature of the sandwich press happens to be optimal for melting the plastic without burning it. I’ll probably set up some kind of extractor hood though, just in case.
Overlaps should work for thin layers, but for the sorts of welds I’m looking at, the process comprises butting the pieces, cutting the join to a V-profile, then applying directed heat (hot air gun, with a very small nozzle) at the base of a rod of matching material pushed into the gap - if all goes well, the stiffness of the rod allows it to be fed into/along the joint as it melts, and as the edges melt to unite with it.
Ideally, I’d prefer to lap the edges and use ultrasonic welding, but that requires some specialist kit.
So why not use big cookie sheets and do this in the oven? You could get sheet metal cut to fit on top of the cookie sheets to act as a press. You’d be able to get much larger sheets, plus you could do several at a time.
I have done some smaller-scale stuff in the oven, but the plastic tends to start burning, as the heat is applied in the form of hot air and thus is a longer process - applying heat by conduction seems to work rapidly enough to keep the plastic semi-molten, but without burning.
My oven probably wouldn’t accommodate anything significantly bigger than I can make on this press (it’s about a foot wide), plus the oven is in the kitchen, which happens to be upstairs in my house. I’d probably get in trouble with the missus if I set up production there.