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Anyone knows how to make a homemade Bowl Extrusion Machine? Answered

I'm trying to do a new shapes from a used PET bottles. Is possible?

3 Replies

pastprimitive (author)2011-11-26

I have recycled HDPE milk jugs at home. My process was to clean the milk jugs, let them dry overnight so absolutely no water was present. Than I cut them into small pieces by hand with scissors. I then heated some canola oil to about 350 degrees and monitored it vary carefully with a thermometer. I then fed it the plastic chips a bit at a time allowing them to turn clear.

After I had melted enough ( about 12 or so gallon milk jugs) I would take the plastic out with a metal spoon and put it into a tin can coated with oil on the inside to prevent sticking. I would than take a smaller can to compress the plastic in the can to help it form to the shape of the can.

Than I covered it with tin foil, put it in the oven at 350 degrees and over the course of 6-8 hours I slowly stepped the temperature down to the lowest setting on my oven which was like 170 deg F, took it out and let it cool the rest of the way. The slow cooling helps with preventing more air bubbles, and cracking.

My result was a deformed 4" diameter, 5" tall cylinder that was riddled with impurities, and air bubbles. Which I then cut slices from of and turned in my metal lathe to make different dies for a cottage manufacturing process I still use in my business to this day. I was fortunate enough that the many imperfections did not lie in any spot that effected the dies.

The melted plastic was not like thick syrup, but more like a soft clay. Even when I brought it up to 400 deg F in the oil. The oil prevents the plastic from oxidizing (burning).

Anyway I thought this information may help you in deciding what to do with the recycled PET bottles.

My only other comment is that the process is really messy, very dangerous from all the hot oil, melted napalm-like plastic, and obscenely long time spent monitoring the whole affair so it doesn't literally catch on fire and burn the house down.

Not to mention there is a real risk of poisonous fumes depending on the type of plastic. Especially if it oxidizes, but even than some plastics such as, but not limited to PVC and vinyl. When they're melted or burned they put off fumes that can kill you and do other bad things. I was told HDPE would not put off any toxic fumes as long as it didn't oxidize by my brother, but he is no plastics expert. So I would take that with a grain, or maybe a handful of salt.

I hope this helps. I found the process to take a lot of effort, and be very fulfilling on a certain level. But efficient, safe, or economical it was not. Also I did dabble with trying recycled PET bottles. I couldn't get the plastic to melt in a way that was workable the way I wanted it to be. Much more difficult than the HDPE milk jugs.

Side note: HDPE shopping bags did not behave the same way in this process and were useless for me.

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orksecurity (author)2009-10-29

I think I'd look at either poured casting (if you can figure out how to liquify the stuff safely) or at simply re-forming the bottle (see, for example, https://www.instructables.com/id/make_an_art_bowl_from_pet_bottle/)

The "Related" links to the right may have other useful information.

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Re-design (author)2009-10-29

I'm thinking that it's not a project that a diyer would be able to take on unless very lucky with having a well stocked junk yard.

You have to clean the plastic.

Then sort it.

Then melt it without burning it.  Different plastics melt at different temps and some may burn or scorch before others would be melted.  So unless you have a large supply of the plastic that has the exact same qualities then each batch of plastic would have different working characteristics.

You have to have a way to deliver the melted plastic to the machine at the right temperature.  Your machine has to be able to cool it to just the right temp. to form it and the handle it until it as it is cooling.

If you get a jam during the forming you may end up with a machine full of solidified plastic.  So you have to build in some safe guards to prevent this.

I don't know what the EPA would say about backyard plastic factory.  I have no idea what chemicals melting these plastics would release.

I'm not saying that you couldn't do it, I'm just pointing out some things that you may not have thought of yet.

Or -  I may not know what I'm talking about cause I've never tried what you're think of.

Either way good luck.

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