Every plastic recycling line needs a crusher. That’s not the question. The question is which one, and that’s where people screw up.
Here’s how most buyers pick a plastic crusher. They call three suppliers. Each one quotes a machine with a bigger motor or a wider rotor than the last. They pick the biggest number that fits the budget. It arrives, they hook it up, and within a month they’re fighting one of two problems: the machine chokes on their material, or it’s way more machine than they need and the knives wear out faster than they should.
Neither problem is the machine’s fault. It’s a selection problem.
The motor and rotor size are the last things you should look at, not the first. This article is about the specs that actually determine whether a crusher works for you, and how to match one to your material without guessing.
## First, Understand What a Crusher Actually Does
A plastic crusher — also called a granulator — is a high-speed rotor machine. Knives are mounted on the rotor, spinning at 300 to 600 RPM. They cut against fixed bed knives. A screen underneath controls the output size. Material gets pulled in, sheared between the rotor and bed knives, and pushed through the screen when it’s small enough.
The whole job is size reduction. Big irregular scrap in, uniform small flakes out.
A crusher is a finishing machine. It works on material that’s already been reduced to a manageable size by a shredder. Feed a crusher whole purge lumps and you’ll destroy it. The crusher wants flake and small scrap. That’s its lane.
## The First Question: What Are You Actually Feeding?
Before any spec matters, you have to know your material. Not vaguely. Specifically.
**The type of plastic.** PP and PE are easy on a crusher. ABS, PS, fine. Nylon, PC, and anything glass-filled are hard on knives. PET is tough and abrasive. Know which you’re running, because it decides knife material and motor size.
**The form it arrives in.** Whole parts? Sprues and runners? Film and bags? Pipe sections? A crusher for rigid scrap is configured differently than one for film. Film needs different rotor geometry and often a different feed approach. If you’re feeding mixed rigid and film, that’s its own setup.
**The contamination level.** Clean factory scrap is easy. Post-consumer material with dirt, sand, labels, and residual contents is abrasive and needs more knife steel and often a magnet upstream.
**The throughput you need.** Kilos per hour. This decides the rotor width and motor. But here’s the thing — most plants overestimate their real throughput need. They quote the peak, buy a machine for the peak, and run it at 40 percent capacity most of the time.
## The Specs That Actually Matter
### Rotor width vs. the size of your biggest piece
The rotor width determines how wide a piece can be fed. A 600 mm rotor takes pieces up to about 600 mm wide. If your biggest part is 500 mm, a 600 mm rotor fits. If your biggest piece is 900 mm, you need a 1,000 mm rotor.
Match the rotor to your largest regular piece, not the average. The average piece is what feeds most of the time. But the largest piece is what jams if you undersize.
### Screen size controls output, and output is not optional
The screen underneath decides the flake size. 6 mm to 20 mm holes. This is the spec that determines whether your output feeds your downstream process.
If the crusher feeds an extruder or molding machine, you want regrind around 8 to 12 mm. If it feeds a washing line or a pelletizer, you have more room — 12 to 20 mm might be fine. Smaller screen means more time in the chamber, lower throughput, more knife wear. Run the largest screen your downstream tolerates.
### Knife count and knife material
More knives on the rotor means more cuts per revolution, which means smaller flakes at a given speed and lower dust. Fewer knives means bigger bites, higher throughput, coarser output.
Knife steel matters if your material is abrasive. D2 for clean polyolefins. DC53 for engineering plastics and filled grades. Tungsten carbide for heavy glass-filled material — but only if your feed is clean of metal, because carbide shatters on impact.
### Motor power for your toughest material, not your average
A 37 kW motor handles PP all day. Feed it glass-filled nylon and it stalls. Size the motor for the hardest material in your mix. If you run 90 percent PP and 10 percent glass-filled nylon, size for the nylon. The 10 percent is what will trip the breaker and stop the line.
## The Specs That Don’t Matter (Despite the Brochures)
**RPM, quoted as a headline number.** A crusher at 580 RPM isn’t inherently better than one at 420 RPM. It depends on the rotor diameter and knife geometry. Higher RPM gives more cuts but more heat and more knife wear. The number alone tells you nothing.
**”Heavy-duty” claims.** Every brochure says heavy-duty. It’s a marketing word, not a spec. Look at rotor shaft diameter, bearing size, and chamber wall thickness if you want to judge ruggedness. Those are numbers you can verify.
**Brand name over fit.** A famous brand running the wrong configuration for your material loses to a no-name brand running the right one. Fit beats brand every time.
## Common Selection Mistakes
**Buying a crusher when you need a shredder first.** If your scrap is whole purge lumps, big parts, or anything over about 50 mm in its largest dimension, a crusher alone won’t do it. You need a shredder to make the first cut, then the crusher to finish. Trying to feed whole parts into a crusher destroys knives and stalls the rotor.
**Oversizing the machine.** A bigger crusher costs more, uses more power, and — counterintuitively — wears its knives faster per kilo processed when run well under capacity. The knives spend more time spinning against a thin material layer at higher RPM than necessary. Right-size it. 70 to 80 percent of rated motor amps during normal operation is the sweet spot.
**Ignoring the screen.** People pick a crusher and never think about the screen until output comes out wrong. The screen is half the machine. Match it to your process, not the default that shipped with the unit.
**Forgetting the metal.** Post-consumer and even some in-house scrap contains bolts, screws, and small metal bits. A magnet on the infeed costs a few hundred dollars. It saves you from replacing a rotor and a set of knives.
## The C Series: Matching a Crusher to Your Line
The C Series granulators from SLECOTECH run from the C600 at 30 kW up to the C1200/800 at 132 kW. Six models, rotor widths from 600 to 1,400 mm, screen sizes from 6 mm up.
We configure each machine around the actual material. Rigid PP and PE get standard D2 knives. Engineering plastics and filled grades get DC53. Film and bags get a rotor setup designed for that feed. Screen size is chosen for your downstream process, not a default.
The machines have water-cooled bearing housings for continuous running, sound-damped enclosures to keep the shop floor quieter, and easy-open chambers for fast cleaning between color or material changes.
If you’re setting up a crusher for the first time or replacing one that’s not performing, send us your material type, piece sizes, and target output. We’ll tell you which model fits and what screen and knife config to run. If you need a shredder before the crusher, we’ll say so.
## FAQ
### What’s the difference between a plastic crusher and a granulator?
Same machine. Different regional names. “Granulator” is common in Europe and in technical writing. “Crusher” is common on factory floors in Asia. Both mean a high-speed rotor with knives cutting against fixed bed knives, with a screen controlling output. Neither should be confused with a shredder, which is a slow, high-torque primary reduction machine.
### Do I need a shredder before my crusher?
Only if your scrap is bigger than the crusher can handle. If pieces are under about 50 mm, a crusher alone works. If you have whole parts, purge lumps, or pipe sections, you need a shredder first. The shredder makes the coarse cut; the crusher finishes to uniform regrind.
### What screen size should I use?
Depends on your downstream process. 8 to 12 mm for direct extrusion or molding reuse. 12 to 20 mm if it feeds a washing line or pelletizer. Run the largest screen your process tolerates — smaller screens cut throughput and wear knives faster.
### How do I keep knife life up?
Match the knife steel to your material. D2 for clean polyolefins, DC53 for filled and engineering plastics. Keep the rotor-to-bed knife gap at the manufacturer spec, usually 0.2 to 0.5 mm. Run a magnet to keep metal out. And don’t oversize the machine so much that it runs underloaded at high RPM.
### How do I know what size crusher I need?
Work backward from throughput. How many kilos per hour do you need to process at peak? Then pick the rotor width that matches your largest piece and the motor that handles your toughest material. If you’re unsure, 70 to 80 percent of rated motor amps during normal operation is the right operating point. If you’re at 40 percent, the machine is too big.
## More Questions
### Can one crusher handle rigid plastic and film?
Yes, but it needs the right rotor configuration. Film requires a different knife setup and often a different feed approach than rigid scrap. If film is a significant part of your mix, tell your supplier. A machine configured for rigid scrap alone will struggle with film.
### What about PET bottles?
PET is tough and slightly abrasive. A crusher handles it fine with the right knives — usually DC53 or better — and a screen suited to your flake target. Wash first or crush first depends on your line. For bottles with labels and caps, crushing first, then washing the flake, is common.
### How much does maintenance cost?
Realistically, budget for knife rotation and replacement, screen wear, and occasional bearing service. Knife life varies hugely by material — from a few hundred hours on glass-filled to a couple thousand on clean PP. Screens are consumables, replaced every few knife sets. Maintenance is a recurring cost, not a one-time purchase. Size your machine right and it’s manageable.
### Should I buy an enclosed or open crusher?
An enclosed, sound-damped crusher is quieter and contains dust better. It costs more. An open machine is cheaper but noisier and dustier. If your crusher sits near operators or in a shop where noise and dust matter, the enclosure is worth it. If it’s in a remote corner of the plant, an open machine saves money.