Shredder efficiency

For a future project, we are looking for shredder efficiency and also for waste processing (read cleaning, shredding, sorting).
The coming weeks I will post several tests and outcomes of shredding different materials and also different waste compositions.
My research about cleaning will be updated in this topic.

For this project I used the shredder built by @peter-bas.
See pictures below

The motor is 1.5 kW and makes 1430 rotations a minute. With the gear, slowing down 20 times, results in 71.5 rotations a minute for the shredder.


Material: PP
Amount: 2.7
Method: Shred
Preparation time: –
Prep amount/h: –
Shred time: 60 min
Shred processing kg/h: 2.7
Remarks: Big PP products. Broke it down into smaller pieces during shredding process. Thick walled plastic is difficult to recycle.

That’s great news @khebizi
Thanks for sharing




Hello dears, after all those changes the shredder is working again with high performance (better than before )  in fact we processed around 30 kg in 4 hours with no problems , the shredder jammed 03 times only because of the thick plastic near the bottles opening we are this time checking the blades heat and cooling them using water each 5 kg
Best regards.

@mohammede335 good morning, i have replaced the threaded rod with a black steel one, also untightened all the bolts and it is working as it was before, conclusion : the problem was because of the low quality of the threaded rod.
Thank you for your reply.

@khebizi salem Kamel hope you’re doing well, i think that it’s because of low quality of the threaded try with the black steel one hope works for u.




Hello dears,
first of all i want to thank you all for your useful replies.
i was not actif during last months because of the covid-19 pandemic and our country’s curfew.
the comment in the table is very correct, this is really what i am facing, once i make some money i will switch to 3 kw motor.
for the threaded rod bending please check the picture attached to this post.
Best regards.

hi Kamel nice work from you, and we really appreciate your efforts on documenting the shredding process, well i have test your motors and torque details on the ( will it shred doc ) and the result looks so clear that the shredder will jam little bit, this why we are alimenting our shredder with a 3kw motor and we will put the documentation about very soon. wish y all the best luck



Hello dears, i assambled the shreeder again and started working with, i have passed around 40 bottles than it started to jam every 5 bottles again, however the blades are sharp and it is cutting better than before, i figured out another issue ” the threaded rods supposed to hold the reverse knifs”.
In fact those two rods bended and it seems that the reverse knifs went down by 0.5 cm, i bought a brand new one made of 8.8 steel i will change it today and let you guys know.
Best regards

Hi there Kamel!

I did not check the drawing yet (no time) but out of your description it would be assumable that the problem indeed is caused by too high friction.
Check the gaps between knives with a filler gauge for starters.
This evening I’ll check the drawings if there is any given tolerance besides the general ones. You bought a 8.8 rod, so check the tightening torque and do not overtighten it. (google some torque tables).
Keep me posted….!



hello dears,
thank you for your replies, i tested the shreeder yesterday afternoon, in fact it has nothing to do with the motor, the problem was the blades ( it got rounded ) i had to sharp those blade to 60° angle.
i didn’t got time to reassemble everything.
those blades are made of normal and non stainless steel, i am thinking to use those ones to their max than switch to hardox knifes.
i will keep you guys informed with the future results
Best regards and thanks again.
ps: i have no pictures because yesterday i got engin grease all over my hands

Hello khebizi,

Is your shredder (according the PP design) equipped with stainless steel blades?
Because of the higher thermal expansion for stainless steel type 304 the friction between the blades will increase fast, resulting eventually in jamming of your shredder.
Of course it will cause wear and the sharpness of your blades will be affected fast too leading to a more jams.
My advice would be, if you intend to shred high volumes upgrade to the pro version.
Otherwise you could choose to replace the stainless steel blades with hardox blades or even better, mild steel blades cladded with a hard layer….

Hope my answer brings some ideas to you!

Hello @khebizi

PET is known for being pretty hard to shred. My guess is that your shredder blades are no longer sharp and the edges of the knives got rounded. Plus, if the blades get too hot after running for an extended period of time, the heat will cause the plastic to bend instead of being cut.

My advice would be:

#1 – Let the shredder rest for a few min between shredding cycles to let the blades cool off

#2 – Dissasemble the shredder and grind the edge of all knives to make a 30° cutting edge, that way the shredder will cut easier through plastic. There was a tutorial somewhere around the forum with pictures of the end result but I can’t find it right now



hello everyone,
i recentlly built a shreeder 1.5 kw 380v 70rpm, after being able to shred around 150 kg the shreeder is starting to jam often.
in fact last day i was able to shred PET around 15 kg in 40 minutes at this time the blades were very hot and the shreeder started to jam
– i have two thoughts in mind :
maybe it is because of the overheat !
maybe the blades are no more sharp.
today i will try and see what is the issue blade sharpness or heat , and i will let you informed.

@xxxolivierxx, @davehakkens seems to be often asked, please make it sticky or at least easy to find, thx. g.

The setup we use (see begin post) is working good. I am not a shredder expert but I know that the gear/reducer is important.
Check out this topic

Hi, I’m David from Congo.
We would like to start a project locally and we will be working exclusively with PET or PP bottle and HDPE bottle cover. Our goal is to reach an average of 200 Kg per day (25 Kg per hour). What is the motor configuration you can advice us.

Thank you very much to help us potting in place because plastic waste management it is a big issues here (look at the picture)

I did more tests and there I all the results in this spreadsheet.
I think that we can build on this spreadsheet to get a better idea of the different shredder capabilities. So feel free to add your shredder experience. And do not forget to fill in your shredder specs. I did never work with an open spreadsheet on a forum so curious how it goes.

Conclusion so far:
It highly depends on the type of products how fast you can process. Also experience has an influence on the results. So this is not a set average but an estimation of the shredder capabilities.

PP small items: 12 kg/h
PP big items: 4.5 kg/h
HDPE small items: 33 kg/h
HDPE big items: 9 kg/h
PET bottles: 7.5 kg/h

Hi @imuh
Never mesured the temp on the blades. I think it stays under melting temp.
PET has a bit higher friction coefficient than PP and HDPE. Or because it is tougher, so it stays longer in the shredder.

Hey @mathijsstroober

It is interesting to note the heat on the blade while schredding PET; do you think it could be linked to the fact it is a very dense type of plastic ? Also do you think you could measure that blade temperature ? would be interesting to know if the schredder actually starts to create mini-melting points (which would be bad considering PET needs to dehydrate before reaching melting point)