A recycling shredder reduces bulky waste by low-speed, high-torque tearing rather than fast knife cutting. Selecting one is a question about material shape, not about motor power: soft film, rigid drums, long pipe and mixed bulky waste each need a different rotor, a different feed arrangement and a different cutter geometry.
That is worth saying plainly because most shredder enquiries start from the wrong end. Buyers arrive with a throughput figure and a budget, ask which model fits, and get a recommendation based on kilowatts. Throughput matters, but a machine correctly sized in kW and wrongly matched to the shape of the material will jam, wrap, bridge or wear out its knives at a rate that makes the throughput figure irrelevant.
So work through it as a series of forks. Answer each one about the material you actually have — not the material you hope to buy next year — and the machine type falls out at the end.
Start Here — What Shape Is Your Material?
Everything downstream depends on how the material behaves inside a cutting chamber, and there are four behaviours worth distinguishing.
| If the material is… | The problem in the chamber is… | Which points to… |
|---|---|---|
| Soft film, bags, baled waste | It wraps around the rotor and bridges above it | Single-shaft with forced feeding |
| Rigid drums, crates, pallets | It bounces on the cutters instead of being gripped | Twin-shaft, interlocking rotors |
| Long pipe, profile, extrusion offcuts | It will not fit the hopper and cannot be fed continuously | Single-rotor designed for long feed |
| Anything where the next stage needs a fixed size | A shredder has no screen deciding when a piece may leave | Screen-controlled machine, or a crusher after it |
Notice that none of those rows mentions polymer type. Whether the material is PP or HDPE affects knife wear and the pelletizing stage at the far end of the line, but it barely affects which shredder you need. Shape does almost all of the work in this decision. The place shredding sits in the wider sequence is covered in the plastic recycling process from bale to pellet.
Rotor Speed Is the Spec That Tells You What It Can Swallow
Before the individual forks, one number separates the four families more usefully than power does, and it is the one most quotations bury at the bottom of the table.
| Family | Rotor speed | Installed power | Throughput | Built for |
|---|---|---|---|---|
| DS twin-shaft | 8–15 rpm | 15×2 – 75×2 kW | 400–4,000 kg/h | Drums, crates, pallets, purge lumps |
| LPS long-pipe single rotor | 40 rpm | — | 800–2,000 kg/h | Pipe up to ∅630 and ∅1,100 mm |
| SS single-shaft, horizontal pusher | 72 rpm | 22–90 kW | 200–1,500 kg/h | Baled film, controlled output size |
| YPS single-shaft, swing arm | 74 rpm | 55–110 kW | 500–2,000 kg/h | Loose, light, irregular loads |
Low speed buys torque. A twin-shaft machine running at 8–15 rpm is turning roughly five times slower than a single-shaft at 72–74, and that is what lets it bite into a 200-litre drum instead of skating across it. The trade goes the other way too: the slow machine produces coarse, irregular output, and the fast machine gives you a screen and a size.
Read the table as a shortlist rather than a ranking. A DS1600 will not do a better job on baled film than an SS600 — it will do a worse one, because film needs a ram pushing it onto the rotor and a twin-shaft has nothing to push with. All four families run Siemens PLC control, so the difference genuinely is mechanical rather than a specification tier.
If It Is Soft — Film, Bags and Baled Waste
Film is the material most often mismatched, because it looks like the easiest thing on the list and behaves like the hardest.
Two things go wrong. First, film wraps: it catches on a rotor shaft and builds up until the machine stalls, and clearing it is a manual job with the power locked out. Second, film bridges: a hopper full of bags forms an arch above the cutters and simply sits there while the rotor spins in empty space underneath.
Both are feed problems, not cutting problems, and the answer is forced feeding. A single-shaft shredder with a horizontal hydraulic pusher has a ram that drives material against the rotor continuously, so nothing can bridge. The rotor turns against a fixed bed knife with a screen underneath, which also gives a controlled output. For baled film this is usually the correct first machine.
The alternative geometry is a YPS swing-arm single-shaft shredder, where a pivoting arm presses the charge down onto the rotor rather than pushing it horizontally. It suits loose, light and irregular film loads, and it handles a hopper that is being fed by a conveyor at an uneven rate.
Whichever you choose, remember that shredding is only the first of film’s problems. Washed film holds water in every fold, and it is too light to feed an extruder screw, which is why a film line ends in a pelletizing machine with a compactor rather than a plain extruder, and why a washing line for soft plastics is built differently from a rigid one throughout.
If It Is Rigid — Drums, Crates, Pallets and Purgings
Rigid material has the opposite problem. It does not wrap and it does not bridge; it bounces. A 200-litre drum dropped onto a single rotor will ride on top of the cutters, taking impact without being gripped, until something breaks.
What grips it is two rotors turning towards each other at slightly different speeds. A DS twin-shaft shredder has interlocking cutter discs on both shafts that bite into a large rigid object and pull it down between them. The speed difference between the two shafts is what creates the tearing action and stops material simply riding along. This is the standard first machine for drums, IBC cages, crates, pallets, thick-wall mouldings and hard purging lumps.
Twin-shaft machines run slowly, and that is deliberate. Low speed with high torque produces less dust, less heat and less noise than trying to achieve the same reduction with speed, and it is far more tolerant of the occasional metal fastener that no sorting stage caught. The trade-off is output size: a twin-shaft shredder produces coarse, irregular pieces, and its discharge screen where fitted runs 20–100 mm rather than anything a wash line would call flake.
Drums in particular carry a second consideration that has nothing to do with the shredder: whatever was inside them. The full sequence for that stream is in how HDPE drums are washed and reprocessed into pellets.
If It Is Long — Pipe and Profile
Pipe, window profile, conduit and extrusion offcuts fail the hopper test. A six-metre length of pipe cannot be dropped into a standard shredder hopper, and cutting it down by hand first is slow, is a genuine injury risk, and adds a labour cost to every tonne before the machine has even started.
A LPS single-rotor shredder for long pipes solves this at the feed end rather than the cutting end. It is built to accept long material fed lengthwise and draw it in progressively, so the operator loads a full length and the machine consumes it. The two sizes take pipe up to ∅630 mm and ∅1,100 mm respectively, at 800–2,000 kg/h.
The point is not that other shredders cannot cut pipe — they can, once it fits. The point is that the pre-cutting labour is a permanent cost on every tonne for the life of the plant, and it usually exceeds the price difference between the machines within the first year.
Shredder Blades and Screens — Where the Running Cost Actually Is
Two specifications decide what a shredder costs to own, and neither appears prominently in most quotations. This is also the part buyers ask about after the machine is installed rather than before, which is the wrong way round. What follows is the running cost; the purchase side sits elsewhere, where what a shredder costs against the rest of the line is set out machine by machine.
Blade steel, and why the grade is a feed decision
Shredder blades are consumables, and the grade is chosen against what is in the feed rather than against the polymer. The two properties trade directly against each other: hardness resists abrasion, toughness resists impact, and no steel maximises both.
| Machine | Blade steel quoted | What that suits |
|---|---|---|
| DS twin-shaft | 9CrSi, D2, or tungsten carbide | Carbide for abrasive filled material; 9CrSi where impact from unexpected metal is the bigger risk |
| SS single-shaft | D2 or SKD11 | High wear resistance on abrasive but reasonably clean feed |
Those are the grades quoted on the two families where they are published. For the YPS and LPS machines the grade is specified per order against the feed description, and it is worth asking for it in writing rather than assuming it carries over from another model.
The failure modes are opposite and both are expensive. A hard, brittle blade meeting a steel fastener chips, and a chipped blade damages its neighbours and the bed knife before anyone notices. A tough, softer blade running in abrasive filled plastic simply goes blunt, at a fraction of its expected life, and the first symptom is throughput quietly falling rather than anything breaking. Tell the supplier what contamination the feed realistically contains, including the things you would rather not admit are in it, and let the grade follow from that.
Blade life is driven far more by what is in the feed than by hours run, which means the biggest lever on this cost sits upstream at the sorting stage, not in the purchase decision.
Screen aperture, and why finer is not free
On any screen-controlled machine, the screen is the throughput. Halving the aperture does not halve the output — it reduces it disproportionately, because material has to be recut until it passes.
It also helps to see where a shredder screen sits relative to everything downstream. A shredder discharge screen runs 20–100 mm. A heavy-duty crusher runs 8–100 mm. The washing line then wants flake at 12–20 mm for PET, 8–16 mm for rigid and 60–100 mm for film. Specifying a shredder screen finer than the crusher behind it will ever need is a quiet, permanent tax on capacity — one of the easiest specification errors to make on paper and the hardest to notice afterwards.
Both consumables should be in the business case from the start, alongside the electricity and the downtime to change them. They belong in the same column as the items covered in what adds up in plastic recycling plant cost.
How much contamination to expect is not guesswork either. The US EPA’s material-specific data on plastics gives a realistic picture of what post-consumer streams contain, and the APR Design Guide sets out the quality criteria the flake eventually has to meet — both are better inputs to a blade-grade decision than a throughput target.
If You Need a Controlled Output Size
This fork catches people who chose correctly on shape and still ended up with the wrong line.
A twin-shaft shredder gives you coarse pieces, and coarse is fine if the next stage is a washing line that can handle it or a compactor that will densify it anyway. It is not fine if the next stage needs consistent 12–20 mm flake, because there is nothing in a twin-shaft machine deciding when a piece is small enough to leave.
There are two ways to get a controlled size, and they are not interchangeable:
- Use a screen-controlled shredder. Single-shaft machines run a screen below the rotor, and nothing exits until it passes through. The screen aperture sets the output. This works when the material suits a single-shaft feed in the first place.
- Put a crusher after the shredder. Two machines in series: the shredder makes bulky waste handleable, then a heavy-duty crusher running a 8–100 mm screen cuts the coarse pieces to a defined flake size. This is the standard arrangement for drums, crates and anything that starts genuinely large, and it is what produces the regrind buyers actually specify — see plastic regrind and how buyers judge its value for how that output gets priced.
Trying to get both jobs out of one machine is the most expensive false economy in this category. A crusher fed with oversized material jams and wears its knives fast; a shredder asked to hit a tight size specification runs at a fraction of its rated throughput because the screen becomes the bottleneck.
If it is not plastic at all
Shredders are shape machines, not polymer machines, and the same geometries handle other waste streams. Scrap tyres need a tyre shredder built for steel-belt reinforcement, which chews conventional cutters. Mixed bulky waste, wood, cable and general factory refuse fall to an industrial shredder specified for an unpredictable feed. The selection logic is identical: describe the shape and the worst thing likely to be hidden in the load.
Three Ways This Goes Wrong
Buying a crusher when the material is oversized. A crusher is cheaper than a shredder of comparable throughput, and on a specification sheet it looks like the better value. Feed it drums or baled film and it jams within the first hour, because a high-speed rotor and a screen were never designed to grip something that large. The shredder is not an optional first stage on bulky waste; it is what makes the crusher viable.
Choosing twin-shaft when the output size actually matters. Twin-shaft machines are impressive to watch and genuinely robust, and they get specified on that basis. If your next stage needs a defined flake size, a twin-shaft machine alone will not give it to you, and you will end up buying the crusher anyway — after the layout has been fixed and the floor space allocated.
Sizing on motor power instead of feed geometry. Two machines with identical installed power will behave completely differently on the same material if one has a hydraulic pusher and the other does not. Power determines what a machine can cut once material reaches the rotor. Feed geometry determines whether it reaches the rotor at all, and that is where most real-world throughput is lost. If you are still assembling the full machine list, what machines are needed for a plastic recycling line covers what sits either side of this decision, and the full range is on the plastic shredder machine category page.
Frequently Asked Questions
What shredder can shred plastic?
Single-shaft, twin-shaft and long-material shredders all handle plastic; the right one is chosen by the shape of the feed. Single-shaft with forced feeding suits film and bagged waste, twin-shaft suits drums crates and pallets, and a single-rotor long-feed machine suits pipe and profile up to ∅1,100 mm.
What are plastic shredder blades made of?
Tool steel, with the grade chosen against the contamination in the feed rather than the polymer. Twin-shaft machines are quoted in 9CrSi, D2 or tungsten carbide; single-shaft machines in D2 or SKD11. Carbide resists abrasion best and chips if it meets metal; tougher grades survive impact and blunt faster in filled or gritty material. Ask for the grade in writing against your own feed description, since it does not carry across from one model to another.
How often do shredder blades need changing?
It depends far more on what is in the feed than on hours run. Clean single-polymer material can go a long time between changes; material carrying sand, glass fines, mineral filler or the occasional metal fastener wears or chips cutters much faster. The first sign of a blunt set is usually throughput drifting down rather than anything failing, so it is worth logging output against hours. Sorting quality upstream is the biggest single influence on blade life.
What size output does a recycling shredder produce?
Coarse. A shredder discharge screen runs 20–100 mm where one is fitted, and a twin-shaft machine without a screen gives irregular pieces rather than a controlled size. A crusher after it runs 8–100 mm, and the washing line downstream wants 12–20 mm for PET, 8–16 mm for rigid and 60–100 mm for film. If a specific flake size is in your buyer’s specification, the crusher screen is what delivers it, not the shredder.
Do shredders make pellets?
No. A shredder tears material into coarse pieces without applying heat. Pellets are produced by melting clean, dried material in an extruder, filtering the melt and cutting it, which happens at the very end of the line. A shredder sits at the beginning.
What is the difference between a shredder and a granulator?
Speed and what decides the output. A shredder runs at 8–74 rpm depending on type, tears bulky material and produces coarse pieces. A granulator or crusher runs far faster, cuts against fixed blades and holds material until it passes a screen, producing 8–20 mm flake. Most lines handling bulky input need both, in that order.
Do I need a shredder and a crusher, or just one?
One machine is enough when the input already fits the crusher throat, as with small offcuts, or when the next stage does not need a controlled size. You need both when the material starts large — drums, crates, baled film — and the downstream process requires consistent flake.
Can one shredder handle both film and rigid plastic?
It can process both, but not equally well. A single-shaft machine with a hydraulic pusher will manage rigid material below its torque limit while remaining good on film; a twin-shaft machine handles rigid far better and struggles to feed light film consistently. If both streams are significant volumes, the honest answer is usually two machines.
The fastest way to get this right is to skip the model numbers. Send photographs of the material as it arrives, say where it comes from and what the next stage has to receive, and we will tell you which fork you are on and what it means for the rest of the line.
