A customer sent me a photo of a shredder screen last month. Bent, cracked along one weld, holes worn oval. He wanted to know if he should order the same size again or go smaller. “The flakes are too big,” he wrote. “I want finer output.”
I asked what those flakes fed into. A crusher. With a 400 mm infeed. His screen was Φ30.
He had been paying for that Φ30 for two years — in throughput, in power, in blades — for a size his crusher never needed. That is the most common screen mistake I see, and it comes from one wrong idea about what the hole does.
A resposta curta
A shredder screen does not set your output size. It sets the largest piece that is allowed to leave the machine. Material smaller than the hole drops through on the first pass. Material bigger than the hole stays in the chamber and gets cut again. So the hole is a ceiling, not a setting.
Pick the biggest hole your next machine can swallow, then stop. Every step down in hole size costs you throughput, power and blade life, and buys you nothing unless something downstream actually needs smaller feed.
Most single shaft shredders run screens somewhere between 20 mm and 80 mm. Our SC series ships with Φ50 on the shredding stage and Φ10 on the crushing stage, and that pairing is not accidental — I’ll explain it below.
What the screen actually does
The rotor knives cut. The screen does not cut anything. It is a sieve with a hydraulic pusher behind it, and its only job is deciding when a piece is allowed to leave.
A shredder screen is a size ceiling, not a size setting. Anything under the hole leaves immediately. Anything over the hole stays in the chamber and gets hit again.
This is why output from a Φ50 screen is not “50 mm flakes.” It is a mix. A lot of it is 10–25 mm, some is 30–40 mm, and a small fraction is right at 50 mm because that piece happened to be lying flat and slipped through lengthwise. If you sieve the output of a Φ50 screen, the distribution spreads well below the hole diameter.
That matters for two reasons. First, you cannot spec a shredder screen by the flake size you want in your head. Second, you do not need to. If you need a tight, uniform particle size, that is a crusher’s job, and the machine that does it well is cheap compared to what you lose by forcing the shredder to do it.
If you have not read it yet, the crusher screen article covers that side in detail.
The question that decides the hole size: what eats it next
I ask every buyer the same thing: what is the next machine in the line? The answer sets the screen. Nothing else does.
| Next machine after the shredder | What it can swallow | Screen I’d spec |
|---|---|---|
| Second-stage crusher (C Series) | 40–100 mm | Φ50, sometimes Φ60–Φ80 |
| Washing line / friction washer | 30–60 mm | Φ40–Φ50 |
| Direct extrusion or pelletizing | 8–15 mm | Don’t. Put a crusher between them. |
| Nothing — you sell the shred as-is | Whatever your buyer’s contract says | Ask the buyer, not me |
That third row is where most of the money gets wasted. A single-shaft shredder is a coarse machine. Ask it to produce 10 mm and you have turned a 22 kW machine into a 6 kW machine, because most of its power now goes into re-cutting material that is already small enough to leave.
Here is the rule I give people: the shredder’s job is to make big things small enough for the next machine. The crusher’s job is to make small things uniform. Do not swap them.
What a smaller hole actually costs you
Going down one screen size is not free. Four things get worse at the same time.
| Hole size | Largest piece out | Capacidade de processamento | Power per ton | Desgaste da lâmina | Fines |
|---|---|---|---|---|---|
| Φ80 and up | ~80 mm | Elevado | Baixo | Baixo | Very little |
| Φ50 | ~50 mm | Good | Normal | Normal | Some |
| Φ30 | ~30 mm | Noticeably down | Up | Up | More |
| Φ20 | ~20 mm | Way down | Well up | Well up | A lot |
The mechanism is simple. Smaller hole means material spends longer in the chamber. Longer in the chamber means more knife passes on the same plastic. More passes means more kWh per ton, more heat in the knives, and more of your material turned into dust you cannot sell.
The fines are the part nobody budgets for. If you are shredding to sell the regrind, every kilogram that leaves as dust is a kilogram you paid for and cannot invoice. On a small screen with hard material, that number is not trivial.
Hole size by material
Different scrap behaves differently against the same screen. This is what I actually recommend, material by material.
| Material | What it does in the chamber | Screen I’d run | Why |
|---|---|---|---|
| Film, woven bags, raffia | Soft, wraps, mats over the screen | Φ50–Φ80 | A small screen lets film smear across the holes and blind them |
| Purge lumps, sprues, thick gates | Hard, bulky, breaks clean | Φ40–Φ50 | Too big and you ship lumps that jam the crusher infeed |
| Drums, barrels, jerrycans | Hollow, thin wall, collapses | Φ50 | Thin-wall scrap breaks fast; a small screen just slows it down |
| Tubo | Long, wall thickness varies a lot | Φ50–Φ80 | Match the hole to the wall, see below |
| Bumpers, thick-wall mouldings | Tough, thick section | Φ60–Φ80 | Thick sections make wide chips that bridge small holes |
Film is the one people get wrong most often. I have watched a plant run stretch film through a Φ25 screen and wonder why output collapsed every twenty minutes. The film was not being cut, it was being smeared across the screen face until the open area was gone. A Φ60 screen on the same machine ran all day.
The thick-wall trap
This one is worth its own section because it looks like a machine problem and it is a screen problem.
When a knife cuts through a thick wall, the chip it makes is roughly as wide as the wall is thick. Cut a 20 mm wall and you get chips around 20–30 mm across. If your screen hole is Φ30, those chips arrive at the hole sideways, bridge across it, and sit there getting hit again and again instead of dropping through.
Keep the hole at least 2 to 3 times the wall thickness you are cutting. For 20 mm wall, that means Φ50 minimum, Φ60 if the shred is going to be long.
The symptom is easy to spot: the machine pulls steady amps but output drops, and when you open it up the screen face is covered with chips lying flat against it. Not a power problem, not a blade problem. Hole too small for the section.
Plastic shredder screen size vs crusher screen size
These get confused constantly, so here is the side-by-side.
| Shredder screen | Crusher screen | |
|---|---|---|
| Typical hole | Φ40–Φ80 | Φ8–Φ15 |
| It controls | The largest piece that can leave | Particle size, fairly tightly |
| Main risk of going smaller | Throughput collapse, blinding | Power spike, knife heat |
| Main risk of going bigger | Oversize reaching the next machine | Uneven flake, poor bulk density |
| Common mistake | Sizing it like a crusher screen | Sizing it like a shredder screen |
Note the last row. Both mistakes exist and they go in opposite directions. Running a crusher with a shredder-sized screen gives you rubbish flake. Running a shredder with a crusher-sized screen gives you a machine that costs a fortune per ton and never reaches its rated output.
What our machines ship with
The SC series exists partly to end this argument. It is a shredder and a crusher on one frame, with a screen at each stage, so neither one is being asked to do the other’s job.
| Artigo | SC600 | SC800 |
|---|---|---|
| Hopper size | 800 × 500 mm | 850 × 630 mm |
| Shredding rotor diameter | Φ300 | Φ400 |
| Shredding knives (moving / fixed) | 26 / 2 | 42 / 2 |
| Shredding motor | 22 kW | 37 kW |
| Shredding screen | Φ50 | Φ50 |
| Crushing screen | Φ10 | Φ10 |
| Crushing motor | 22 kW | 22 kW |
| Footprint (L × W × H) | 2100 × 1680 × 2008 mm | 2800 × 1950 × 2800 mm |
Φ50 on the first stage is deliberately generous. It lets bulky scrap — lumps, barrels, short pipe — leave the shredding chamber as soon as it is small enough to handle, which keeps throughput up and keeps the knives cool. The Φ10 crushing screen then does the actual sizing, which is what it is good at.
On a standalone triturador de eixo único, the screen is whatever the downstream needs, and we cut it to suit. That is where the table above earns its keep.
Before you order: six questions
- What is the next machine, and what is its largest acceptable infeed? This sets the hole. Everything else is secondary.
- What is the thickest wall you will cut? Keep the hole at 2–3× that.
- Is any of it film or fibre? If yes, do not go below Φ50.
- Do you sell the shred, or process it further? If you sell it, ask what size the buyer’s receiving equipment wants.
- Are you running more than one material? Size for the worst case, not the average. You can always screen down later; you cannot screen up without buying steel.
- Can you get a second screen with the machine? Two screens cost very little next to one week of lost output.
FAQ
What plastic shredder screen size do I need?
Whatever the next machine can take, plus margin. For a second-stage crusher that is usually Φ50. For a washing line, Φ40–Φ50. Do not size it to the flake size you want, because the screen does not control that.
Does a smaller screen give a smaller particle size?
It gives a smaller maximum particle size. The bulk of the output was already well under the hole. You pay in throughput, power and blades for a change that mostly affects the few largest pieces.
Can I change the shredder screen later?
Yes. It is a bolt-in part, and a spare screen is cheap insurance. What is not cheap is discovering you needed a different size after a month of low output.
Why does my shredder slow down on thick pipe?
Most of the time the hole is too small for the wall thickness. Chips as wide as the wall bridge across the hole and get re-cut instead of falling through. Open the screen up to 2–3× the wall.
Should I use a small screen for film?
No. Film smears over a small hole and blinds it. Φ50 to Φ80 keeps the open area clear and the machine running.
What screen does the SC series use?
Φ50 on the shredding stage, Φ10 on the crushing stage. The first stage makes bulky scrap manageable, the second stage does the real sizing.
Where to go from here
If you are still picking a machine, start with how to spec a single shaft shredder — screen size is one input, not the whole decision. If you already run one and the output is off, check the screen before you blame the knives; blade wear gets blamed for a lot of things that are actually screen problems.
Two more that come up in the same conversation: what one machine actually puts out per hour if you are chasing throughput, and how big a lump one machine can take if your feed is bulky. If the shred is only one stage of a bigger plan, the line article covers where each machine sits.
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. If you want a second opinion on the screen size someone has quoted you, send us the material, the wall thickness and what the next machine is — that is usually enough to tell you if the number is right.
See the SC Series shredder-crusher or the C Series crusher for the second stage.