Inefficient shredder blades

Precious Plastic Machine Development
#1

I’ve spent a couple of days now to investigate the Shredder blades. I realize that the blades are rather inefficient and also expensive to produce since it requires laser or plasma cuts, totaling 120-200 euro, (here in Catalonia). These longer knifes also require more motor power since they more likely to get stall since the smashed plastic can’t really escape….

When looking at industrial shredders, they all share the same design :
2 – 3 cylinders (drive shafts) with short stick-outs, the knifes! I was looking at car, wood and plastic shredders. Always the same. To adopt this findings, I figured that the dual shaft variant with short stick-outs are quite easy to produce, you could use a 4th axis, or even just an angle grinder. Car shredders have replaceable knifes with the shape of a small box.

I guess you already know that, I just wanted to confirm that the mentioned variant is more established and requires less machining and also less power

any thoughts or experiences on this ?
g

#2

@mc007 Yep, there are several inefficient aspects about the PP shredder. The tips of the knives will get dull easily, the tolerances between each knife are too tight, having 3 steel thicknesses instead of just 1 make the final costs way bigger than it should, the opening is not big enough, the teeth are too big which makes them more fragile plus increase the amount of torque required by the motor, etc… etc… etc…

#3

One of my favourite youtubers just purchased a shredder with dual axles and several short-toothed discs made with 1/8″ thick steel (I think) and requires very little torque for shredding:

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#4

Hi Jrizzato,
thanks! Yes I watched them all 🙂 Looks like I have to keep trying. I’m currently
designing a different shredder idea but in it’s design very close to industrial shredders: 2 cylinders with replaceable knifes (in the shape of a box), very similar to car shredders. That way it won’t need laser cuts, just a CNC mill, or with some luck, an angle grinder only.
The last industrial plastic shredder I saw with that design was running at least at 500 RPM which could be also a $$ saver since it requires a less expensive reducer.

#5

Hi, I think you should watch this video:

At minute 2:52 you can see several attempts to achieve the best versatile shredder. I do not think that any other versión of any other shredder is gonna be easy to build, all them requiere custom laser cutted parts (if want to do it right), and in all of them you are going to face alignmet issues, etc. Although, I do agree that shorter blades could have been more efficient, several people (including my self) have build the shredder and it is working perfectly fine.

#6

right, thanks precious mate. I hope i can build something easier, for now i keep going investigating the idea to carve in/out a cylinder for replaceable blades.
happy shredding,
g