Inspired by the Poly Lactic Acid (PLA) extruded from the 3D printer at
only 180 degrees C, I wonder if any have considered melting down the
shedloads of plastic that seem to fill our dustbins these days as a
At first thought, perhaps it would be ideal for mouldings such as the
simulated combination of axleboxes and springs?
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At 2nd thought, 180C is quite high. Will cause serious burns on human skin. And there are serious technical problems. I met a plastics engineer a couple of decades ago, learned a lot about how to make stuff out of plastic. It's not as simple as it looks.
Problem 1: Plastics are very sticky when melted. Must be cast in tightly sealed pressure moulds, they will emit toxic vapours when heated in open moulds.
Problem 2: Making a mould for casting plastics is tricky. Plastics are at fairly high temperatures, the mould must have cooling channels around the mould cavity.
Problem 3: 3D printers must be reprogrammable for different printing materials. AFAIK, the cheaper ones aren't.
That's just a 30 second think....
OTOH, waste plastic can be recycled commercially, albeit at a cost. Raw plastic feedstock is cheapre than recycled. But the recycling cost is in the long run cheaper than dumping the stuff into the environment. Oxidation is very slow. Common plastics are indigestible. They break down mechanically, UV degrades the crosslinks that holds the stuff together, and so on. The net result is plastic flakes that are ingested by small animals, and eventually nanometre scale plastic flakes, which are ingested by microbes. Some plastic-processing microbes will eventually evolve, but not anytime soon.
Have a good day,
Reply to
Wolf K
I make 'machineable wax' for CNC prototyping from plastic milk bottles and paraffin wax - work a treat if a bit time consuming. Melt the wax, cut strips of washed and dried milk bottle and stir into the wax slowly bringing the temp up to about 125-130 deg C - when no more plastic dissolves into the wax you are done. I admit that lately I've been using MDPE and HDPE granules intended for injection moulding, as it makes a quicker job dissolving into the wax.
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Andrew Mawson

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