Someone emailed us last month asking for a “shredder for 800 kg/h of PP.” No material description. No feed size. No idea what the output fed. I asked what they were shredding and they said “plastic, obviously.”
That is a real problem with this word. Triturador gets used for anything that makes things smaller, from a two-shaft machine eating car bumpers down to a granulator chewing bottle necks. Ask three suppliers for a shredder and you will get three completely different machines, all correctly called shredders.
So here is the definition, written the way I wish every buyer would read it before sending an enquiry.
A resposta curta
A shredder is a low-speed, high-torque size reduction machine. It reduces material by shearing, tearing and impact, and it produces a coarse, irregular output sized by a screen — a largest-piece limit, not a uniform particle size.
Four things in that sentence carry all the meaning, and each one separates a shredder from something else:
| Property | What it means | What it rules out |
|---|---|---|
| Low speed | Rotor turns slowly, typically 70–120 rpm | Not a granulator (hundreds to 1000+ rpm) |
| Alto binário | Force over speed — it tears rather than slices | Not a crusher (fast, light cuts) |
| Shear, tear, impact | Material is pulled apart between moving and fixed knives | Not a grinder (abrasion) |
| Screen sets a ceiling | Output is “nothing bigger than X”, not “exactly X” | Not a mill (tight particle distribution) |
That last row is the one that saves people money. If you need a tight, uniform particle size, a shredder alone will not give it to you — you want a crusher after it.
How a shredder actually works
The mechanism is not complicated, and knowing it explains most of the behaviour people find surprising.
- Material is fed into a hopper above the rotor.
- A rotor fitted with knives turns slowly. On our S Series that is 73 rpm on every model, from the 22 kW S600 up to the 90×2 kW S1800.
- Moving knives pass fixed counter-knives, and material caught between them is sheared and torn.
- A screen sits under the rotor. Pieces small enough to pass the holes fall through. Pieces too big stay in the chamber and get hit again.
- On single shaft machines, a hydraulic pusher keeps feeding material onto the rotor. Without it, hollow or springy parts simply bounce on top.
Step 4 is the one to remember. It is why a shredder’s screen sets a maximum, not a target — the same point we made in the shredder screen size article, where the practical rule is to size the hole from whatever machine comes next.
Step 5 is why a “shredder” that will not take your material is often a feed problem, not a power problem.
The parts that matter
| Part | What it does | Number worth knowing |
|---|---|---|
| Rotor | Carries the moving knives; sets working width | 600–1850 mm on the S Series |
| Moving knives | Do the cutting; indexable and rotatable | 30 to 172 depending on model |
| Fixed counter-knives | The anvil the moving knives shear against | Usually 2 on single shaft |
| Ecrã | Decides the largest piece that can leave | Φ40–Φ80 typical on shredders |
| Hydraulic pusher | Forces material onto the rotor | 5.5–7.5 kW on the S Series |
| Hopper | Holds feed; its opening limits what fits | SC600 800×500, SC800 850×630 mm |
Two of these are routinely ignored and routinely cause problems. Hopper opening decides whether your material goes in at all — this is the whole argument in the drum shredder article, where a 200 L drum at Ø580 mm simply does not fit a machine with a 500 mm opening. Ecrã decides what comes out.
The four types, and what each is actually for
This is where the word gets muddy, so here is the clean split.
| Tipo | Rotores | Speed | Resultado | Ideal para |
|---|---|---|---|---|
| Single shaft | 1 + pusher | Baixo | Sized by screen, fairly uniform | Plastics, purgings, lumps, drums |
| Double shaft | 2, intermeshing | Muito baixo | Coarse, irregular | Bulky, mixed, contaminated feed |
| Double rotor | 2, co-rotating | Baixo | Pre-crushed, uniform | Film, woven, fibrous material |
| Four shaft | 4 (2+2 stages) | Baixo | Two-stage in one pass | Hard, abrasive, high-security feed |
For plastics, the overwhelming majority of jobs land on single shaft. It is the machine most plants mean when they say “shredder,” and it is what we build the S Series around.
We covered the comparison in depth in single shaft vs double shaft and in the double shaft guide, and the pipe-specific case in the P Series.
Shredder vs crusher vs granulator
The other half of the confusion. All three reduce size; they sit at different points.
| Triturador | Crusher / granulator | |
|---|---|---|
| Speed | Low, 70–120 rpm | High, hundreds of rpm |
| Action | Shear, tear, impact | Clean cutting, slicing |
| Typical screen | Φ40–Φ80 | Φ8–Φ15 |
| Resultado | Coarse, irregular, a size ceiling | Small, fairly uniform |
| Role in a line | First stage, takes big things | Second stage, does the sizing |
| Power feel | Binário | Speed |
The rule of thumb I give every buyer: the shredder makes big things manageable, the crusher makes small things uniform. Asking one to do the other’s job is the most expensive mistake in this industry.
If the distinction matters to your purchase, the crusher screen article covers the second stage properly, and the three-machine comparison takes them one by one.
The numbers that define a shredder
When you compare machines, these are the specifications that actually mean something. Values shown are our S Series, so you can see the real spread.
| Modelo | Rotor width mm | Usable intake mm | Speed rpm | Main motor kW | Hydraulic kW | Weight kg |
|---|---|---|---|---|---|---|
| S600 | 600 | ~500 | 73 | 22 | 5.5 | 2800 |
| S800 | 820 | ~720 | 73 | 37/45 | 5.5 | 3700 |
| S1000 | 1030 | ~930 | 73 | 55 | 5.5 | 5000 |
| S1200 | 1230 | ~1130 | 73 | 75 | 5.5 | 6800 |
| S1400 | 1450 | ~1350 | 73 | 90 | 7.5 | 8300 |
| S1600 | 1650 | ~1550 | 73 | 75×2 | 7.5 | 11000 |
| S1800 | 1850 | ~1750 | 73 | 90×2 | 7.5 | 14000 |
Note the usable intake rule: rotor width minus 100 mm. It comes up constantly when someone is deciding whether a machine will swallow their material, and it is the first number I check on any enquiry.
What a shredder is not
Worth stating the negatives plainly, because these are the misconceptions that lead to bad purchases.
- A shredder is not a sizer. It gives you a maximum, not a uniform grade.
- A shredder is not a dust-free process. Dry material at the discharge will generate fines.
- A shredder is not quiet on hollow parts. Sealed containers failing inside the chamber push a machine past 100 dB(A) — see the noise and dust article.
- A shredder is not defined by motor power. Torque, rotor width and hopper opening decide what it can take.
- A shredder does not remove contamination. Steel, sand and rubber all go straight through and damage knives.
FAQ
What is the definition of a shredder?
A shredder is a low-speed, high-torque size reduction machine that reduces material by shearing, tearing and impact, producing coarse output limited by a screen. It is a first-stage machine: it makes large material small enough for the next step.
What does a shredder do to plastic?
It tears plastic into coarse pieces, typically 20–80 mm, depending on the screen. It does not produce uniform granules — that requires a crusher or granulator downstream.
Is a shredder the same as a crusher?
No. A shredder runs slowly with high torque and produces coarse, irregular output. A crusher runs fast, cuts cleanly and produces small, uniform particles. In a recycling line they are consecutive stages, not alternatives.
What are the main types of shredder?
Single shaft, double shaft, double rotor, and four shaft. Single shaft is the standard choice for plastics; double shaft suits bulky mixed feed; four shaft handles hard or abrasive material in one pass.
What speed does a shredder run at?
Typically 70–120 rpm for the rotor. Our S Series runs at 73 rpm on every model. That is far slower than a granulator, which runs in the hundreds or thousands of rpm.
How is shredder output size controlled?
By the screen under the rotor. The hole diameter sets the largest piece that can leave, not the average size. Choose the hole based on what the next machine can accept.
Where to go from here
If you are choosing a machine rather than defining a term, start with how to spec a single shaft shredder: rotor width, hopper opening and screen are the three that decide whether a machine fits your job. For throughput expectations, the capacity article shows why the brochure figure rarely matches the floor, and the installation requirements article covers floor, power and foundation before you commit.
SLECOTECH (Streamline Eco Tech) designs and manufactures industrial shredders, granulators, washing lines, and complete plastic recycling systems. The company is based in Yuyao, Zhejiang, China, and exports to more than 30 countries. Send us the material, the feed dimensions and what the output needs to feed — that is enough to tell you which definition applies to your job, and which machine fits it.
See the single shaft shredder range, ou the SC Series if you want shredding and crushing on one frame.