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This is amazing – I don’t know how many lifetimes it would have taken me to figure all this out. Thanks so much.
I’ve got a bunch of questions again and I’m sure you’re quite busy, so no worries if you don’t respond right away
What was the 5 Bar suggestion based on?
Does it change for different types of plastic?
Surely the thickness of plastic matters too – 1mm would presumably need much less than 50mm, regardless of surface area. Is there some sort of scientific guideline/formula for it?
You settled on 1.8 Bar based on success at that pressure with the book press.
What criteria did you use to judge it to be a success? Just visual inspection? Lack of bubbles? Proper shape? Actual stress testing the material properties?
Did you try less pressure to see if it would work? More pressure to see if it would be better?
I ask all this because I have been browsing all sorts of plastic manufacturing textbooks recently and they seem to say, in accordance with intuition, that a visual inspection is a very poor and misleading way to judge output quality – differences are at the molecular level and show up in stress testing.
Ive got other questions and thoughts on the jack, frame design (steel thickness requirements), moulds etc… But will leave that for later.
Good luck with finishing the thesis! We definitely need to chat when you’ve got time – there might be a job in it for you scaling this up in the developing world as well as helping us tinker with other stuff to help improve lives in a cost effective, creative and empowering way
This is wonderful! I’m hoping to build something similar and hope you can answer some questions!
Any idea of what sort of pressure you are able to exert with that screw mechanism (also, what is it technically called)? Would welding on longer arms (or even just putting pipe over them as “cheater bars”) make sense? Is it even important in your experience?
Do you have an idea of what went wrong with the failure sheets?
What sort of thicknesses have you produced?
Do they seem like they would be viable for building things – furniture, etc…?
Hey there, I have a slew of questions/thoughts now that I’ve reviewed the posts and videos a few times. Hope you have time for them!
I noticed you previously used a book press. I was thinking of doing something like this with a single jack. How did that go? Why did you switch to the 4 hydraulic jacks? Was the pressure insufficient?
What sort of pressure are each of those jacks capable of? Do you have any rationale for what pressure is needed or did you just choose those at random? Do you think the rig you built would be able to withstand more force?
I bring this all up because any literature I can find on compression moulding seems to say a minimum of 200psi is needed, which would be over 200 tons of pressure for a sheet that size, which is obviously absurdly out of reach for us. However, most literature on compression moulding is for thermosets, as thermoplastics seem to not be done this way, so maybe that makes a difference. I’m just trying to get an idea for what sort of pressure I should try to build for.
You said somewhere that the thickness of the sheets is variable, which suggests you just allow the pressure to do its thing rather than have some sort of stopper in place to make an exact height. This is probably the correct way to do it, as limiting the height would limit the pressure on the plastic and presumably result in a worse product. However, you also said there was some thin flashing, which is typical of a compression process, but also means that the pressure on the plastic is literally leaking out.
I suppose a real industrial process would use a specific measurement of plastic and the mould design would allow for flashing while also keeping the correct pressure – perhaps just a trial and error process for the likes of us?
Have you tested the sheets in any building processes yet? Do you think they could benefit from additional pressure? Could you get away with much less?
Or am I overthinking all of this and its a forgiving/flexible process? Whatever the case I’m just going to tinker with some scrap metal and see what happens. But I’d like to have at least some rationale for what I’m doing.
Thanks for the feedback!
I think I’m going to go ahead and tinker with my idea for a while though – I really want to make this cost efficient for the developing world, and I assume electricity is a major cost in this process.
I’m going to try to do some sort of rocket stove heat exchanger – use the stove to efficiently incinerate (organic) garbage (they burn it all anyway) and heat some sort of oil, which will then slowly (and hopefully somewhat stably and accurately) heat up a very large vat of plastic (with some sort of stirring device inside), which I can then use to fill one mould at a time. I figure once its all melted, it will stay melted almost indefinitely and can just add enough for a new sheet for each one poured. Ideally it would result in a fairly quick turnover between moulds and a reasonably high output of sheets that we can then do a lot of cool stuff with.
Efficient/clean cookstoves are part of my project anyway, so might as well tinker with both at once!
I’ll be sure to post progress here in a new thread!
Do you know of any good Introductory level resources for learning about plastic manufacturing? I’d love to get a slightly more technical understanding of temperatures, compression pressures, etc… for different types of plastics.
This looks fantastic. Any progress in the past few months?
Thanks for sharing all this!
Version E is exactly what I was planning to do – i think a large vat would allow for faster production and likely more energy efficient. Could even use various heat sources – rocket stove to incinerate other garbage, for instance. Would take some effort to fine tune the temperature though – may a liquid heat exchanger or something.
I’ll definitely take some inspiration for the press from you though!
Have you finished the paper? I’d love to see some of the results for pressure, temperature, etc… of various types of plasitc.