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Polystrene compactor/Extruder

This topic contains 8 replies, has 3 voices, and was last updated by  Andy Noyes 1 month ago.

charlie charlieuk

Polystrene compactor/Extruder

08/12/2017 at 01:52

Currently are local area does not have any way of recycling polystyrene however it is possible to get it recycled by a number of companies. The Problem with polystyrene or eps is it is over 80% air so storage and transporting it in standard expanded form is not cost or environmentally effective so it has to be compacted to do so. The best for of consolidation is to melt it back down to a solid plastic which luckily happens at relatively low temperatures around 150-200deg. It is possible to buy commercial machines but not only are they expensive but they normally run on 3phase power.

My hope is to try and build a machine that can melt polystyrene effectively and efficiently while trying to keep the build costs down.

I’m not 100% sure if I should go the screw route or more of a piston style plunger style method or any other way for that mater.

if it was a screw I am thinking can be something very similar that is used for hard plastics which design is obviously well documented however it would have some sort of grinder above the hoper to brake it down to small peace’s before entering the screw.

Being so light I’m not to sure exactly how it will react

As it contains so much air I’m thinking the compaction screw could probably have quite a course thread so as to process the eps faster.

If anyone has any ideas they would like too add to this I would love to hear them.

I’m thinking of trying to 3d print a prototype screw however I have come a bit stuck at the first hurdle in that I cant figure how to draw the variable pitch thread in fusion360. if anyone has any tips on this I would love to hear them.

Many thanks

warrior
08/12/2017 at 13:20

I think this might have been thought of before, but what about a pair of heated rollers that melt the EPS and squash all the air out, producing a thin sheet directly?

The other way to make a compression screw is to keep the thread pitch the same and vary the depth of the channel.

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starter
08/12/2017 at 14:48

Hi thanks for the reply I have spent a long time searching for a diy solutions but not found anything that has beet taken all the way to a working machine. I had not thought about heated rollers my fear is it would stick to them so I guess you would need something to scrape it it off.

I had noticed some screw use the same pitch with a varied depth and others use a variable pitch and some use both, I guess there are reasons for this? are they known?

many thanks charlie

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starter
08/12/2017 at 16:15

This was the post hole orgar I purchased for £8 just to play with, the only problem is its 80mm dia and I cant find a tube that it will fit in

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warrior
08/12/2017 at 17:55

@charlieuk

Yeah, even if you do find a suitable tube, you won’t be able to heat up all the plastic well enough.

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warrior
08/12/2017 at 22:08

Don’t give up on that auger too soon, it might just work. At that diameter you might be able to get away with a welded tube as a barrel and the seam might not make much difference. If you can find a way to gradually build up the core of the auger (weld on bits of tube?) that will give more compression which both introduces more heat and mixes the material, distributing the heat more evenly. You might need a lot of torque to turn such a screw though.

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starter
09/12/2017 at 16:48

I think the best thing for the auger is to try and put it on a lathe to reduce the diameter to fit a tube( would need to get it down to 73mm I think which isn’t a huge loss. to do so on my lath I would probably have to reduce the length a little too still probably ok for testing.

Im not sure if its going to be better to head the polystyrene when its nice and light and fluffy of once it has been compacted a little.

with eps having so much air and reducing in volume I believe 90:1 could perhaps it be more of a two stage machine were there is a screw feeding a heat box were it melts down onto a screw and then a small screw extrudes it out.

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starter
14/12/2017 at 02:44

I had a go at putting the screw on the lathe and surprisingly it worked quite well and I have been able to turn it down so now although smaller I should be able to get it to fit a tube once I can fine a nice seamless bit.

at the moment im thinking along the lines of maybe a two stage machine the first heater to de bulk and then a second to do the compact further and extrude.

once I get the tube I will try and get a large band heater or two and see if I can get it up to the 150deg it needs to start reducing the foam.

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warrior
14/12/2017 at 13:41

What’s your length to diameter ratio now? Most compression/extruder screws are designed with a L:D ratio of 20:1, though it will probably still work if you’re some way off of this, and EPS might behave differently anyway especially for the fist stage where your mostly squashing air out.

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