How to grind failed prints to pellets?

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?

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.

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

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

Borrow the wifes mincer

Roy

. . . . . . . . . or food processor. That should REALLY shred it.

John H

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

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

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.

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

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.

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.

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

www.appropedia.org/Recyclebot_v2.3

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

3dprintingforbeginners.com/how-to-make-diy-filament-for-your-3d-printer/

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

You can print pellets.

;0)

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.

Touche!

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

¯\_(ツ_/¯