Crusher blades are the knives inside a plastic crusher. They cut scrap plastic into small pieces that can be washed, melted, and used again. In North America, the same machine is usually called a granulator or a grinder.
The blade shape and the blade steel decide three things: how clean your output is, how much dust you make, and how long you run between blade changes. This guide covers the main types of crusher blades, the steels they are made from, and how to pick the right set for your plastic.
What Are Crusher Blades?
A plastic crusher uses two sets of blades.
- Rotary blades: These are bolted to the rotor and spin with it.
- Fixed blades: These are bolted to the wall of the cutting chamber and do not move.
The plastic is cut each time a rotary blade passes a fixed blade. It works like a pair of scissors. A screen under the rotor keeps the plastic in the chamber until the pieces are small enough to fall through.
The number of blades grows with the size of the machine. One manufacturer’s range runs from 9 rotary and 2 fixed blades on a small model to 34 rotary and 9 fixed blades on a large one.
The names change from region to region. The parts do not.
| Term | Also called |
|---|---|
| Crusher blade | Granulator knife, grinder blade |
| Rotary blade | Rotor knife, fly knife, moving blade |
| Fixed blade | Bed knife, stator knife, dead knife |
Main Types of Crusher Blades
Crusher blades are grouped by shape. Each shape suits a different kind of scrap.
| Type | Shape | Best for |
|---|---|---|
| Flat blade | One long straight edge across the rotor | Hollow and thin-walled items such as bottles and containers |
| Claw blade | Short, stepped blades set in a staggered pattern | Thick, hard pieces such as lumps, sprues, and thick-walled parts |
| Sheet (paddle) blade | Wide blades set on paddle-style holders | Sheet, strip, shells, and hollow parts |
| Film blade | Sharp flat blades run with a tight gap | Film, bags, and woven sacks |
| V-type blade | Blades set at an angle to form a V | Spreading the cutting load on larger machines |
Flat blades
Flat blades are long straight knives for plastic cutting. They cut across the full width of the rotor. They work well on light, hollow items that need a clean slice.
Claw blades
Claw blades take many small bites instead of one long cut. This puts the force on a small area, so the machine can cut thick material without stalling. They are the usual choice for hard lumps, sprues, and heavy injection-molded parts.
Sheet and film blades
Sheet blades handle flat and hollow shapes that would bounce off a claw rotor. Film blades need a very sharp edge and a tight gap. If the gap is too wide, film folds over the edge instead of being cut.
Crusher Blade Materials
The steel decides how long the edge lasts and how well it handles shock.
| Steel | What it offers | Where it fits |
|---|---|---|
| D2 (also sold as SKD11 or 1.2379) | High wear resistance and good edge life | The most common choice for plastic crusher blades |
| T10 carbon tool steel | Lower cost, sharp edge, less wear resistance | Soft, clean plastics such as PE and PP |
| H13 | More toughness and shock resistance, less wear resistance than D2 | Scrap with a risk of impact or contamination |
| High-wear and powder metal grades | The longest edge life at a higher price | Glass-filled and very abrasive plastics |
D2, SKD11, and 1.2379 are the same type of steel under American, Japanese, and German names.
Hardness matters as much as the grade. D2 crusher blades are usually hardened to between 56 and 60 HRC. Blades for fine granulation can go up to about 62 HRC. A harder blade holds its edge longer, but it also chips more easily.
One more point. D2 is not stainless steel. If you crush wet or washed plastic, the blades can rust. Dry them and oil them before storage.
How Blade Angle and Gap Affect the Cut
Two settings change how a crusher cuts, even with the same blades.
- Cutting angle: Blades that meet at an angle cut a little at a time, like scissors. This lowers the cutting force. The pieces come out more even, with less powder.
- Blade gap: The gap between the rotary and fixed blades must be small and equal along the full length. Thin film needs a tighter gap than thick, rigid parts.
Many crushers let you adjust how far the blades extend from the rotor. Use that adjustment to bring the gap back to the machine maker’s setting after every sharpening. A crusher with sharp blades and a wide gap still cuts badly.
How to Choose Crusher Blades for Your Plastic
Match the blade to the material first. Then match it to the machine.
| Plastic | Blade steel | Blade type |
|---|---|---|
| PE and PP parts | T10 or D2 | Flat or claw, based on wall thickness |
| PET bottles | D2 | Flat |
| ABS, PS, and PVC | D2 | Claw for thick parts, flat for thin ones |
| Nylon (PA) | D2 or a high-wear grade | Claw |
| Glass-filled plastics | D2 or a high-wear grade | Claw |
| Film and bags | D2 | Film blades with a tight gap |
When you order replacement blades, have these details ready:
- The machine make and model
- Blade length, width, and thickness
- Hole positions and hole sizes
- The edge angle
- The steel grade and hardness you want
- How many rotary and fixed blades you need
If you do not have a drawing, a worn blade is enough. Our custom blade fabrication team can work from a sketch or a sample.
Signs Your Crusher Blades Are Worn
Worn blades show up in the output before you can see the damage on the edge.
- More dust and fines: Dull blades smash the plastic instead of cutting it.
- Uneven pieces: Long strips and oversized chips start to appear.
- Higher motor load: The machine draws more current as the blades dull.
- More heat: Plastic starts to smear or stick inside the chamber.
- More noise: The cut sounds rougher and louder.
- Visible nicks: Chips on the edge leave uncut lines in the material.
Blades usually fail early for one of three reasons. The blade quality was poor. The scrap contained metal, stones, or other hard objects. Or the machine was overloaded.
How to Make Crusher Blades Last Longer
A few habits add a lot of life to a blade set.
- Keep metal out. Sort the scrap and use magnets on the feed. One bolt can chip every blade in the chamber.
- Sharpen the full set together. All rotary blades must stay the same height. If one blade is taller, the gap has to be set to that blade, and the others cut with a wider gap.
- Reset the gap after every sharpening. Sharpening removes steel, so the gap opens up.
- Do not overfeed. A crowded chamber heats up and wears the blades faster.
- Store blades dry and oiled. This prevents rust on the edge.
- Keep a spare set. You can swap blades in one stop and sharpen the worn set without a rush.
For a closer look at matching blades to a machine, read our guide on how to select plastic granulator blades.
Need Crusher Blades Made to Your Spec?
Edgemills makes custom industrial blades from your drawing, sketch, or worn sample. We work with D2 tool steel, M2 high-speed steel, tungsten carbide, and CPM grades. Each blade is heat-treated to the hardness your plastic needs, measured on the Rockwell scale.
Tell us your machine, your material, and the problem you want to fix. Get a quote, and we will take it from there.
FAQs
What is the difference between crusher blades and granulator blades?
They do the same job. Both cut plastic scrap between rotating blades and fixed blades inside a screened chamber. “Crusher” is the common name in Asian markets. “Granulator” and “grinder” are more common in North America and Europe.
What is the best steel for plastic crusher blades?
D2 tool steel is the most common choice. It has high wear resistance and holds an edge well on most plastics. Soft, clean plastics can run on lower-cost carbon tool steel. Glass-filled and very abrasive plastics often need a high-wear grade.
Can crusher blades be resharpened?
Yes. Crusher blades can be reground many times. Sharpen the whole set together so every blade stays the same height. Then reset the gap between the rotary and fixed blades before you run the machine.
Should I use claw blades or flat blades?
Use claw blades for thick, hard, and solid scrap such as lumps and sprues. Use flat blades for hollow and thin-walled items such as bottles and containers. If you run both kinds of scrap, pick the blade that suits the material you process most.