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V4 Shredder Double Axis – [INDEX+BLOG]

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Yann lagrenouille

V4 Shredder Double Axis – [INDEX+BLOG]

23/04/2019 at 15:49

Hey community,

We are 3 guys to work on the V4 shredder double axes, Landry ( @landry) from France – a industrial designer and engineer, Paco ( @pacoacu13) from Spain – mechanical engineer, and Yann from France – material engineer.

We work on the Precious Plastic shredder double axes in Eindhoven, and we try to find the best solution for shred some big parts of plastic, also including thick parts like beams and sheets.

The sub-topics will be the same than for the single axis shredder, as most of the technologies will be similar :
Drives (Motors and Gears)
Cutting Technology (Shredding principles and fine tuning)
Feeding System (Hoppers, Conveyer Belts, new Systems)
Control System (Electronics)

The double axes shredder is the most used for different industrial activities, but with different designs for different results. We need something close to an industrial shredder, who can shred different plastic shapes and sizes quickly, and easly in very little plastic chips.

Reliability, Safety & Maintenance
As for the single axis shredder trials, the next version should not jam as often as the current shredder does. Furthermore we want to implement automatic reverse (torque detection) and back to normal operation.
Safety will also be improved by a proper hopper limiting the acces to the blades, and a good “catch” of the plastics for removing any human help in the process of shredding.
Maintenance such as cleaning (between different plastic batch) shall also be considered.

So how will we start?
The main goal we want to achieve, is increasing the shredding capacity, we want something much bigger than the last verion, and that can work all day (at least 7 hours) with no jam and very few human interventions.Our biggest problem right now is the huge variety of plastic that can be found – small/big, thin/thick, flat/geometric and different materials. And most of the shredders are specified on one particular task. E.g. slow running Granulators to recycle runners of the injection process.

Double axis shredders in general seams a very polyvalent option, even if they have quiet some incovenient (like a lot of laser cut parts…), but let’s give it a try at least !

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27/06/2019 at 22:35

So, what we need:

It needs higher torque: it get stuck with cd cases and big HDPE bottles. We want to keep the same power (around 3kW). That means we have to lower the speed to get higher torque. So we need a higher ratio for the gearbox. New blades: Flakes are too big. More teeth and less thickness Hard to clean: The flakes can accumulate in many places of the shredder The gripping is not good: sometimes the shredder can’t catch the plastics. Easy to build: Keep a design easy to assembly with part easy to find.

In the double shaft shredders, the size of the flakes is determined by the number of the teeth and thier respectively width. The new design of the blades is mainly focused to get small flakes and to have a good gripping as well. So we design a shaft with 13 teeths/blade (small flakes) and another one with only 6 teeths (good gripping)

We made also something very easy to build and assembly, we have also include the gears inside the box for more safety

And we have also increase the output and decrease the speed of the motor for answer to the stucks problems

For the specs :

Size of blades: 6 x 130

Shredding dimension: 240 x 300


Power: 2,2 Kw

Output speed: 19 RPM

Nominal torque: 1000 Nm

So we make this new design:


27/06/2019 at 22:50

looks promising; congrats. the recent builds of MorrenTrading use 2 motors (classy) to run such thing. Evtl. they share some details with you. I am still convinced that it’s impossible to get flakes size down whilst keeping an efficient low-power/spec -design; thus the mentioned ‘post-processing’ grinder module (at ~700RPM, 3 classic blades mounted on hexbar)  which only has one challenge : share drive power, via belts or gears. The very extra unit can be done for a fraction, as add-on as said; also enabling PET print right away as well better results for injection & extrusion.

05/07/2019 at 17:09

@landry I like your Shredder, is it possible to have a futur of this one. Is it the next download kit?

05/07/2019 at 19:18

It would be great if the PP team picked some shredder performance benchmarks for comparing the various V3.x and V4 designs. Examples might be “what does it take to jam” 2L coke bottle? HDPE laundry bottle? What thickness PP sheet. Throughput would be good to know as well.

05/07/2019 at 19:51

@s2019, I think i placed a link to the only data we have about in the v3 shredder’s resource section, although the data seems to have little noise. And as far I recon, they are still fighting with flake size, to a degree that comparison isn’t exactly possibly, yet.

05/07/2019 at 21:35

@pex12 , thanks. That’s a great start at a product description. I guess what I was hoping for is the requirements list that is being used to go from the V3 design to V4. The shredder is a supporting piece of hardware that in general does not produce an end product (though it is amazing how many people want to build it first). The shredder requirements come from the other machines and the business plan. With several years of use, there should be an understanding of what the other machines need.

Flake size: I’ve only used a version of the injection machine. For me, flake size has the following trade space. To create monochromatic parts, I often use the largest strips that will fit into the mouth of the tube, going smaller as the compaction process fills the tube. More recently, I used smaller flake size to create more interesting color patterns in the finished part. As I go smaller, I transition from manual feed (needle nose pliers) to using a small hopper. There may be other differences between flake size such as time to melt and time to compact out air bubbles, but I have not captured these. Perhaps this has been evaluated. Given all that, flake size of a couple of square cm is probably the smallest I need. For the compression machine, flake size, in general is driven by color patterns and the ability to remove air during compression. The PP team has done a lot of work on the compression machines. Hopefully they can publish some conclusions on flake size  in the compression machine. The extruder machine is the only one that appears to need a certain flake size to feed properly (probably depends on whether a wood auger or compression screw is used). Again, the past PP work should be able to set a requirement here, Though Paul’s work in the Maldives, feeding rope was interesting.

Materials and thickness: Do you need to worry about shredding PET if you don’t have a recycling process for it? Are you willing to flatten bottles and perhaps cut off the necks for separate processing? What thickness flat HDPE, PP, etc. does the shredder need to pass without jamming?

Throughput: in a small work space, with only one of each machine, there is quite a bit of time spent waiting for plastic to melt and cool down. How fast does the shredder need to be to effectively use that time?

There rest of the parameters (blade width, cutting diameter, tooth profile, shaft speed, shaft torque, etc.) are just trade space to get to a solution.  For example, if you are willing to flatten the feed material then a smaller cutting diameter can allow wider teeth or less torque or…

It would be very informative to see how the V4 effort worked through these (quantitatively) to get to the sizing and design shown above

12/07/2019 at 22:07

Good points, @s2019; thanks. Indeed, we need a more complete guide on PET.. I’ve managed to find a few more DIY and PP shredder variants. In particular, I’ve found a more promising v3.1 candidate, @weedo and he seems to work on a double shaft shredder as well but I have no data on it, yet. Eventually we order just one from him, just to see how it goes 🙂 However; would be interesting to know how many people need a shredder that big. From our side, we don’t know many and I hope we can scale the v4 design down, making it also easier to add the mentioned grinder add-on for PET print.

17/07/2019 at 16:51

Hey community

@rbagg066, yes it will be the next download kit.

We work on it, like you can see 🙂

For assembly it, with all the part, take around 2 hours without the frame and hopper.
We will start the test the 29 July.

20/07/2019 at 10:28

@landry When will we get our hands on this?

21/08/2019 at 00:54

How is progress coming?

21/08/2019 at 11:56

Hello guys, we have design and manufacture the double shaft shreder. Here is our machine

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