V4 Shredder Single Axis – [INDEX+BLOG]
This is the main blog where the updates for the development will be shared and general questions will be answered and discussed. Beside that, there are a few important sub-topics which I will give you an overview in here:
First a short overview about certain Sub-Topics of the development:
So here the Development Blog starts:
I’m Friedrich from Germany – a Industrial Designer and Engineer. I will work on the next revision of the Precious Plastic shredder in Eindhoven until the beginning of the next year.
As most of you know there are some things about the shredder which can be improved to build a more reliable/productive and safer machine. The recent weeks I ran some tests with the current shredder, a fast-spinning shredder and a double axis shredder to compare them against each other.
Some points which we are sure we want to improve:
Right now we have a max output of ~10kg/h – to run a workshop or small business with our shredder we need at least 40-50kg/h. The goal should be to shred in half a day (or less) the complete plastic for a week.
The next version should not jam that often as the current shredder does. This is not just a problem of the motor power only but also concept related. Furthermore we want to implement automatic reverse (Torque detection) and back to normal operation.
This is very related to the topic of reliability, due it is not possible to build a save shredder if it is not processing the input material in a reliable manner. The shredder should run without any correction of the user during the shredding process. The shredding blades must not be accessible during the operation, this is ensured by mechanic constraints or sensors.
Some of you report a fast wear down of the shredding blades. The new version should have a way to reduce the necessary time for maintenance and changing of blades. I will try to increase the lifetime of the blades by optimizing tolerances, cutting angles and material selection.
The revision of machines will come with a guideline for a easier part-selection process depending on personal needs.
So how will we start?
Our biggest problem right now is the huuge variety of plastic we recycle – 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.
I found a different concept from our existing one which i want to adapt to a smaller size shredder. I think it can solve the problem about the big variety in the best way. The biggest benefit of this shredder type is that, the process is more reliable and you can throw in even bigger rests of plastic like left-overs from the extrusion machine or half injected parts.
Its called single shaft shredder which looks like those ones here:
Of course our shredder will be a bit smaller 😉
The build will be similar to the current one (stacked blades on a hex-shaft) – just the blades will be between 10-20mm thick, to assemble the teeths on them. The width will be the same for all, but the length will be adjustable to your needs (education vs. production)
What do you think about this concept?
@davehakkens, in real communities, you know, companies, comparatives there is something they call proposals, votes, etc… of course it requires to open up, some transparency, etc… and I wonder if that is soo much an army thing now, why nobody got actually asked or showed what the next steps are and should be.
It’s also not exactly a VERSION – 4. From what I see is VERSION 3 got abandoned and community input pretty much ignored all the way long and what I see in v4 doesn’t fix, meet or improve anything I had or have on my table.
as said, I would have expect more compact, cheap, light, more availability, real improvements, etc.. I bet with you one in 1000 is able, capable, willing to open this container thing/story workspace. unfortunately, we never saw analytics, updated stats, …
just saying, go ahead, see in version 154 🙂
Let me say that I love the creativity of the brainstorming process. Great ideas here for the shredder mechanisms.
That said, @brettc post was eye opening. Looking at that Aliexpress vendor, they appear to have a shredder that meets many of the V4 goals for $1000 USD delivered to your port. https://www.aliexpress.com/item/Easy-use-plastic-bottle-crushing-machine-shredder-grinder-crusher-shredder-plastic-price-plastic-crusher-price/32851194919.html If that works, building a new machine from scratch may not be worth the effort. I view the PP project as developing an accessible recycling workflow. If one of the machines is already available at a reasonable cost, it is worth investigating. At least obtaining one (or finding someone who has one) and using it as a benchmark for the inhouse development seems like a reasonable path. It may be that the final answer is the modification of one of these machines for different power source, or for cleanliness, etc. It is difficult to develop a lower cost machine that does the same thing as a low cost off the shelf product.
Perhaps the Aliexpress machine is a piece of junk with low reliability, or the vendor is not reliable, or some other problem, but it does set a cost benchmark for a machine of that size
hmm good point @cgoflyn since we never ask people for feedback before we start a new version, like really never. After that we always keep our plans super secret, so no one that helps out has a clue what we are going to do. And obviously during the development process nobody can see where we are up to every month, making it impossible to share suggestions. Because we really don’t want people doing that.
But to be fair. YES we actually do have a filter. We listen carefully to committed members, with a real profile (not 5) that share constructive feedback in a proper way.
A professional shredder price in my country is starting from 10 K euro.
If V4 will cost 2-4k i think it will be a great achievement. About Aliexpress and Alibaba, i think we all know the stories and the quality. I know somebody with a experience with a Chinese producer and this one provide the product at what quality hi desired – more money better quality, low budget – nice junkie.
Don’t stop and don’t be disappointed. You will not be able to thank everyone. Whoever wants to improve their product alone.
@euromarketo, if you search auction / ebay / craiglist for ‘plastic granulator’, you can see the range for shredders is 2-5 K. no matter what you have to say about ali-express : a larger manufacture gives you 10000% more for your money. they have solid and pretty cheap supplies and sometimes decades long record to build such machines for and with their clients. it’s unthinkable that a guy in a garage can build the same value for the same price.
@davehakkens, I am happy to see that you finally discovered some basic about community building, so when can we see the first polls ? And sorry about the accounts, wasn’t really aware that credits is more important than substance here 🙂
It would be nice if you seek for professional advice, or gain the needed education to build PP as network, flat and of horizontal structure. Enabling the network to grow (see bazar fees problem) and giving the tools needed (see this useless forum software)
Because instead and it’s obvious you’re more busy with building the ‘Dave Hakkens’ brand or pyramid/monolith instead of doing good for everyone involved or at least recognize what’s actually going on with the folks around here. It also looks that anything which doesn’t pass your imagination or doesn’t fit in your box (or mattia’s ) won’t be implemented, supported or sponsored or developed. You can’t be manager, machine builder or designer at the same time. This [email protected] is also another prove for that.
So yes, please find somebody who can advise you in such things; there is a cirtical mass waiting to be boosted. You have received all the funds for that, so please use it for that. Needless to say PP has been a community effort.
what’s required :
– free trade
– budgets for projects (remote, not in f** Eindhoven)
– software to enable networking (what you gave here is just a rotten piece of crap, sorry)
– user – workspaces / show-rooms / bazar
– extendable machine component/catalog
– full transparency: network stats, google analytics, ….
– professional skill sets within the administration – department (replacing you and mattia, please)
– pure community driven decisions, for real.
these things you can find always in open organizations/networks.
For now the output looks already promising. We have to continue to improve the reliability of the operation, redesign the blade inserts and the way of how the inserts are shaped and clamped.
Thicker PP material from our sheetpress is a bit challenging for the moment, but we think that the redesign of the cutting unit will solve those issues.
PS CD Cases: 13,1kg/h (old shredder: ~3kg/h)
PS Random Geometry: 9kg/h
PS plates ~10-15mm thick: 13kg/h
PP DVD Cases: 14kg/h
So considering that we are operating at a shredder-with of 1/3 of the full size, we are on a good way to reach our goal of an 30kg/h average.
Beside that we started a second shredder design of a double axis shredder. We want to know which is the most efficient solution (labor/energy/output) in our small size shredders (compared to the ones used in industry).
You will hear about that as soon as the first CAD design is done in the next weeks.
We are a prototype engineering company in Johannesburg. We just designed a double axial version with the same concept as version 1 shredder but with 3 teeth per cutter. Also we bad the tooth much shorts to the axis of rotation to generate more torque through the cut. we are using a single phase 2.2Kw motor that controlled by our in-house controller that detected when the motor spins to slow (lets say 50% if 1400rpm. I measure with a hall sensor at the fan and glue a magnet on the fan itself. the mass of the magnet is to small to induce a vibration. I was looking at the other alternative to detecting a jam by measuring the raise in current with a simple current transformer.
That sounds really good guys! Do you have more pictures of it? Maybe a video?
There is some development going on at OSE on this as well, so feel free to look there;
It’s been a while we don’t update this topic. We were busy with the development of the V4 Shredder: designing, building, assembling, testing, fixing up, testing again…. So I want to say sorry for that. But it means we have lot of news to tell you about the Single Shaft Shredder development!! We finished and tested the single shaft shredder with triangular blades and rectangular blades.
Triangular blades were hard to manufacture and during the tests some teeth broke because they were not properly welded. Besides, some big pieces of plastic could pass through the rotor (the design has to be improved).
Related with the rectangular blades, they are Hardox 400 made so they were really hard to work with them (drilling, threading). So we decided to weld many of them. The blades that were not welded worked properly.
apologize accepted; just don’t do it again. normal science work involves around 40 hours on the job, 20 hours to publish a new paper and another 20 hours for volunteer activities whilst still working on a few pet projects.
yes please, no hardened steel; mild steel can be processed and hardened on demand; in this case easy to grind or cut a knife mount and weld or bolt a grinded HSS blank on it; easy also for our buddies in the more urgent countries.
Could you describe what is in the first image (IMG_9762.jpg)?
The performance with the rectangular blades was very good, shredding around 16kg/h (with a 140mm width shredder, not bad). We did the test without a sieve and the size of the flakes was quite good. However, there were some big flakes of plastic, but it can be solve by installing a sieve.
Some conclusions drawn from the test:
– Hard to adjust the gap between blades and static blades with the current design.
– Good size of the flakes with thick plastics.
– Some big flakes with thin plastic (bottles).
– The performance and safety increase with a inclined plate (15 dregrees) for the piston.
– Use normal blades (like double shaft shredder) makes simpler the building process of the SSSS.
– It can shred big pieces of plastic, like sheets or beams.
– It never got stuck during the testings.
– Some pieces of plastic can reach the back of the piston
During the tests we measure the current consuption. In some moments, the motor could consume up to 8-10A max, but typically 6A when it is shredding plastic. The nominal current of the electric motor is 6,9A, so the 3kW motor has enough power for the shredder.
Thank you, much clearer
With the rectangular blades, there is nothing to stop them from moving if they come loose, they have no register to locate the insert as you would normally have with this type of design, it is only the bolts that keep them in place. If they come loose, they will damage the stationary plate and possibly the rotor (given that the insert is harder than the rotor)
Considering the cost of the hardened inserts and the complexity of manufacture of the design, as well as the high risk of machine damage if they come loose, why not simply use a one piece blade design made from a high carbon steel that can be hardened on the tooth edge. This has no failure mode relating to loose inserts, and the cost of replacing one entire plate would probably be less than the cost of one insert.
From a risk analysis perspective, if the inserts CAN come loose, they WILL come loose. This means that it is highly probable that for each one of these machines made, it WILL have a failure event where the failure mode is a loose tooth. The worst aspect of this is that the most likely time that this will happen will be immediately after the machine is assembled or shortly thereafter. It should be noted that this probability also increases with the typical contributors – ie inexperience and quality of manufacture – both of which are qualities of your target demographic.
The only advantage that your design has, is that it has replaceable blades. I know that the driver for this was that the blades of the earlier machines had a tendency to wear, but that is simply as they were made from the wrong material (stainless steel) and the blade profile is less than optimum. I think that whilst the general design of the blade profile of the new machine is heaps better than the old set up, they do not need to be made replaceable. It is simply adding extra cost and complexity which far outweighs and perceived benefit they give.
Quick change tooling is only of any benefit in a high production environment where the machine lay on the critical path. i.e. if the machine stops, the entire operation stops. In this case downtime is a problem. However. The usual solution for critical machinery is redundancy. i.e. a second machine.
I think that the original design of stacked blades is fine. it is not a massive job to change one or two blades if there is some damage. And in the case of changing blades due to wear – they will generally all wear at the same rate and so this then becomes a scheduled maintenance issue, which is something that should only be happening infrequently and is also something that you can easily plan for.
Both of these points mean that there is no benefit or even any need for quick change tooling in this machine. It provides the end user with NO benefit.
From a design perspective, your original constraints were to increase throughput and reliability. Both of these are easy to address. For faster cutting you use more blades that have an optimized profile. The optimized profile also helps prevent jamming.
The rotating and static blades need to ‘shear’ the material – like scissors. The old design hooks the material and drags it through the clearance in the plates, this is why it is prone to jamming. Look at any cutting tool and they all operate in the same manner, no matter if they are cutting metal or paper, they all have some kind of shear. This shear also has another advantage – that the point load is only where the blades cross – which is only at one point. This reduces the force required to make the cut. When you use a parallel cutting motion you are trying to cut the entire width of the cutting edge in one go, this requires a much higher force. The angle of this shear is also very important for it to work effectively and is usually material dependant. On your new design, the angle of shear is the angle that the rotating teeth present themselves to the fixed plate – the end of the tooth should touch first.
Increasing the number of cutting edges from two per blade also helps to increase efficiency. Double the amount of cutting edges and you effectively double the amount of work that you can do.
The size of the output is also a big factor. larger shards require less cutting and so can be produced faster.
I personally would love to see a design than could be made with hand tools. Whilst the old design is great and has certainly opened up possibilities, it is still not accessible to a majority of places where this kind of technology is needed. Not that I’m trying to be critical of course, but if it is designed correctly it should be able to be made from either a laser cutter or by someone with basic hand tools. This should be part of the design constraints.
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