How to grind failed prints to pellets?

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How to grind failed prints to pellets?

This topic has 22 replies, 16 voices, and was last updated 1 March 2018 at 23:12 by Neil Wyatt.

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28 February 2018 at 18:19 #343704
Rainbows
Participant
@rainbows
Wanted to steal some knowledge off of the forum.

I have a long term plan to try and make a filament extruder to recycle the rapidly filling box full of broken/failed/prototype prints but before that I need way to pelletise the parts.

First thought was something like a rock crusher but wrote that off because wasn't sure how well it would work with a ductile material instead of rocks.

Second plan was one of these things that look like big paper shredders

but that requires a whole bunch of blades being made.

Anyone got experience or theories to what might make a good pelletizer?
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28 February 2018 at 18:19 #31558
Rainbows
Participant
@rainbows
28 February 2018 at 18:31 #343706
Bazyle
Participant
@bazyle
For small volume you only need 1 moving and one fixed blade. Arrange a screen of the target size curved round the bottom of the blade so that motion lifts larger bits back up for another chop. Mild steel then case harden the teeth. A couple of years ago I did post a link to someone who was selling laser cut blades but don't have it bookmarked.

I haven't got round to a machine yet but am manually cutting milk bottles with scissors to make MDP sheet.
28 February 2018 at 18:33 #343707
Neil Wyatt
Moderator
@neilwyatt
Only musings…

A shredder & extruder would make excellent subjects for MEW.

Not sure a whole load of silver steel blades would that difficult to make, I think a 4" throat would be ample.

Another option is feeding failed prints into our garden shredder! I may experiment with that…

I have seen at least one extruder that uses a wood auger in the feed. As the wires don't flex it would be safe to use a high powered mains heater cartridge, perhaps with a thermal cutout on the block.

Neil
28 February 2018 at 18:39 #343709
Journeyman
Participant
@journeyman
Needless to say someone has already done it see Indestructable

Or here 3D Printing For Beginners

Doesn't go into making the pellets though!

John

Edit: add another link

Edited By Journeyman on 28/02/2018 18:48:19
28 February 2018 at 19:45 #343719
roy entwistle
Participant
@royentwistle24699
Borrow the wifes mincer

Roy
28 February 2018 at 19:53 #343720
John Hinkley
Participant
@johnhinkley26699
. . . . . . . . . or food processor. That should REALLY shred it.

John H
28 February 2018 at 20:34 #343722
martin perman 1
Participant
@martinperman1
Bazle has described the correct shredder, a couple of blades for balance and speed to cut the plastic, as Bazle says a curved screen full of holes to allow the pieces to pass through, the blades of machines I've serviced were straight and relied on shearing action.

Neil,

The plastic parts would most likely bounce around and eventually clog your garden shredder .

Martin P
28 February 2018 at 20:35 #343723
Paul H 1
Participant
@paulh1
Take a look at this site https://preciousplastic.com/ They have created some pretty good machines with lots of info including plans for the build. The shredder is one of the machines there.

Paul
28 February 2018 at 21:00 #343724
Muzzer
Participant
@muzzer
Every time you melt thermoplastic and hold it at that temperature, it degrades. "Regrinding" leftovers and scrap parts generally results in poorer quality parts. In the case of recreating filaments, that would amount to 3 melting cycles.

I'm not saying it won't work but be prepared for a disappointing result. Recycled / regrind material is generally only used where the material properties are not critical and there are usually strict limits on their use – either zero or low % of the total.

Murray
28 February 2018 at 22:28 #343731
duncan webster 1
Participant
@duncanwebster1
Posted by Muzzer on 28/02/2018 21:00:27:

Every time you melt thermoplastic and hold it at that temperature, it degrades. "Regrinding" leftovers and scrap parts generally results in poorer quality parts. In the case of recreating filaments, that would amount to 3 melting cycles.

I'm not saying it won't work but be prepared for a disappointing result. Recycled / regrind material is generally only used where the material properties are not critical and there are usually strict limits on their use – either zero or low % of the total.

Murray

So what does that say about the drive to recycle plastic? I'd happily go back to glass bottles, and have them washed and re-used rather than smashed and remelted. At east with glass and steel you can recycle endlessly.
28 February 2018 at 22:30 #343732
Jeff Dayman
Participant
@jeffdayman43397
It might be worthwhile for a commercial 3D printing service to grind scrap and re-melt / re-extrude filament, if they were processing hundreds or thousands of pounds of scrap a week.

For home use it would be senseless in my opinion to develop a grinder and filament extruder to save a few $ on printing filament.

The materials and motor alone for a grinder would amount to many thousands of $. A grinder for plastics parts will need to have quite heavy construction and a very powerful electric motor to deal with the forces involved in shredding even small plastic parts. By the way, the feed stock pellet / particle size for an extruder cannot just be any old dust or big lumps, in fact most commercial extruder units have closely specified sizes of acceptable feed stock particles, and state that fines (dust) should not be used or the screw can become jammed. I have seen this happen in injection moulding machines and it is no joke to fix. Usually to get decent filament properties and decent extruder performance with minimal hold-up time in the extruder the extruder firm will add some virgin pellets of the same resin to the regrind, as others have mentioned. You will need a source for this extrusion grade virgin resin, hope you can find a bag or two somewhere, it is usually only sold in qty to commercial moulders or extruders.

Commercial plastics grinders make one hell of a racket when operating, and shake the floor and the ground under it, your neighbours will not be impressed if you build a similar but scaled down unit.

Any metal particles from your grinder rotors chipping over time would cause some big problems if they got jammed in your 3D printer or extruder. Commercial moulding machines and extruders usually have magnet systems in the material hoppers to trap any metal particles.

If you ever inadvertently mix PLA and ABS grindings by accident, or other combinations of materials, properties of finished parts and processing of the filament will be a nightmare.

As usual with most plastics technology there is a lot to extruding filament and if it is to have decent properties for 3D printing there is a lot to know to get good results in a controllable process. Iffy filament will result in odd 3D print defects.

Hobby time is short – spend it wisely – don't bother to try and make your own filament. Some sort of model or engine or tooling accessory would be a far better use of your time in my opinion.

Edited By Jeff Dayman on 28/02/2018 22:31:24
1 March 2018 at 08:08 #343743
Old School
Participant
@oldschool
I used to work in the plastic pipe industry most of our production was from recycled HDPE plastic bottles we bought as much granulated material in as we could plus we bought in a processed bales of bottles post consumer waste. Most of our pipes used 100% recycled material but you need the controls and knowledge in place to get a good quality product. The only downside is that most of it is black. Recycling has moved a long way but a lot of companies have not invested the time and money to make a success of it. When I left the industry we typically shipped 40 artic lorry loads a day of fully certified pipe a day.
1 March 2018 at 08:25 #343746
Neil Wyatt
Moderator
@neilwyatt
Posted by Muzzer on 28/02/2018 21:00:27:

Every time you melt thermoplastic and hold it at that temperature, it degrades. "Regrinding" leftovers and scrap parts generally results in poorer quality parts. In the case of recreating filaments, that would amount to 3 melting cycles.

I'm not saying it won't work but be prepared for a disappointing result. Recycled / regrind material is generally only used where the material properties are not critical and there are usually strict limits on their use – either zero or low % of the total.

Murray

Yet practical experience suggests that many people are successfully recycling their filament.

Bear in mind 3D printing melt times are generally for much shorter periods and lower temperatures than for injection moulding.
1 March 2018 at 08:29 #343747
Neil Wyatt
Moderator
@neilwyatt
Posted by Jeff Dayman on 28/02/2018 22:30:33:

The materials and motor alone for a grinder would amount to many thousands of $. A grinder for plastics parts will need to have quite heavy construction and a very powerful electric motor to deal with the forces involved in shredding even small plastic parts. By the way, the feed stock pellet / particle size for an extruder cannot just be any old dust or big lumps, in fact most commercial extruder units have closely specified sizes of acceptable feed stock particles, and state that fines (dust) should not be used or the screw can become jammed. I have seen this happen in injection moulding machines and it is no joke to fix. Usually to get decent filament properties and decent extruder performance with minimal hold-up time in the extruder the extruder firm will add some virgin pellets of the same resin to the regrind, as others have mentioned. You will need a source for this extrusion grade virgin resin, hope you can find a bag or two somewhere, it is usually only sold in qty to commercial moulders or extruders.

Commercial plastics grinders make one hell of a racket when operating, and shake the floor and the ground under it, your neighbours will not be impressed if you build a similar but scaled down unit.

Any metal dust coming through (0.4mm chips are unlikely) will at worst destroy a cheap disposable nozzle.

Neil
1 March 2018 at 08:36 #343748
Neil Wyatt
Moderator
@neilwyatt
It really surprises me that model engineers are saying its pointless or impossible.

I'm afraid the millennials are way ahead of the old fogeys on this one.

Home shredding and filament extruding are both established technologies.

en.wikipedia.org/wiki/Lyman_filament_extruder

http://www.appropedia.org/Recyclebot_v2.3

http://www.robotdigg.com/product/1029/Desktop-Pellet-Filament-Extruder

3dprintingforbeginners.com/how-to-make-diy-filament-for-your-3d-printer/
1 March 2018 at 10:37 #343768
not done it yet
Participant
@notdoneityet
Posted by Neil Wyatt on 01/03/2018 08:36:55:

… I'm afraid the millennials are way ahead of the old fogeys on this one….

en.wikipedia.org/wiki/Lyman_filament_extruder

I’m somewhat surprised at that statement – after looking at the first reference on the quoted link.
1 March 2018 at 10:46 #343770
Martin Kyte
Participant
@martinkyte99762
You can print pellets.

;0)
1 March 2018 at 12:54 #343797
MW
Participant
@mw27036
Posted by Neil Wyatt on 01/03/2018 08:25:49:

Posted by Muzzer on 28/02/2018 21:00:27:

Every time you melt thermoplastic and hold it at that temperature, it degrades. "Regrinding" leftovers and scrap parts generally results in poorer quality parts. In the case of recreating filaments, that would amount to 3 melting cycles.

I'm not saying it won't work but be prepared for a disappointing result. Recycled / regrind material is generally only used where the material properties are not critical and there are usually strict limits on their use – either zero or low % of the total.

Murray

Yet practical experience suggests that many people are successfully recycling their filament.

Bear in mind 3D printing melt times are generally for much shorter periods and lower temperatures than for injection moulding.

This is true,

They are also talking about where regrind is concerned, a very particular problem that only applies to professional industry, and critical applications, neither of which we are doing at home.

I would definitely say that its an interesting thing to look at and experimenting is all part of what should make M.E an attractive hobby.
1 March 2018 at 14:42 #343815
Neil Wyatt
Moderator
@neilwyatt
Posted by not done it yet on 01/03/2018 10:37:00:

Posted by Neil Wyatt on 01/03/2018 08:36:55:

… I'm afraid the millennials are way ahead of the old fogeys on this one….

en.wikipedia.org/wiki/Lyman_filament_extruder

I’m somewhat surprised at that statement – after looking at the first reference on the quoted link.

Touche!
1 March 2018 at 22:30 #343910
Rainbows
Participant
@rainbows
Odd that preciousplastics calls for something in the range of 1.5Kw geared down to 60 RPM where as I doubt the paper shredders match that in any way. Guess its all a case of capacity and duty cycle.

I might be able to beg the use of a plasma cutter but preciousplastic gets theirs laser cut, not sure how acute the difference is.

A hang up I have been having with the extruder is trying to make some sort of quick change barrel so I can swap barrels out and not have to worry about colour or plastic contamination. Might be as easy to just make more than one extruder though

¯_(&#12484_/¯
1 March 2018 at 23:03 #343912
Mark Rand
Participant
@markrand96270
I haven't got much interest in additive machining and probably won't get around to it, unless I decide that it's the best way to make metal casting patterns. However:-

Over the last year I've come to hate my cheap impact garden shredder because it won't do soft stuff. I've taken onboard the fact that the neighbours say their 'quiet' shedder (toothed profile pressing against a spring loaded plate) can't cope with anything big or hard.

I've got some decent sized EN24 bar, some gear cutters and some 2hp motors. I'd like to make a 'proper' shredder that could cope with everything from bedding plants to 2"x4" timber with the odd nail not doing too much harm. Doesn't have to be quick, just thorough…
1 March 2018 at 23:12 #343914
Neil Wyatt
Moderator
@neilwyatt
Posted by Rainbows on 01/03/2018 22:30:20:

Odd that preciousplastics calls for something in the range of 1.5Kw geared down to 60 RPM where as I doubt the paper shredders match that in any way. Guess its all a case of capacity and duty cycle.

We get to choose the size and nature of what we recycle, plus we can be quite happy with modest shredding rates. Finally, we can add pellets of virgin material or unused filament if we want.

Also a huge difference between a reservoir of near-liquid plastic for injection moulding and brief passage of filament through a print head aina far from liquid state.

Neil
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