“Shredder” and “Crusher” are not synonyms. They represent two fundamentally different mechanical principles of material failure. Choosing the wrong one is the most common engineering mistake in recycling plant design.

Related equipment: single shaft shredder, double shaft shredder (plastic & metal).

1. Shear Failure (The Shredder)

Mechanism: Two opposing edges pass each other with zero clearance (Scissors).
* Physics: $\tau = F/A$. The machine applies torque until the Shear Strength of the material is exceeded.
* Best For: Ductile & Elastic Materials.
* Examples: LDPE Film, Car Tires, Rubber, PP Ropes, Copper Wire.
* Why: If you hit a tire with a hammer (Impact), it bounces. You generally need to hold it and cut it (Shear).

2. Impact Failure (The Crusher / Granulator)

Mechanism: A high-speed object collides with a stationary or slow-moving material (Baseball Bat).
* Physics: $E = \frac{1}{2}mv^2$. The machine transfers Kinetic Energy into the material until the Fracture Toughness is exceeded.
* Best For: Brittle & Rigid Materials.
* Examples: Glass bottles, Rigid PVC Pipes, Bakelite, Stone, Concrete.
* Why: If you try to shear concrete, you destroy the blade. You generally need to shatter it with impact.

3. The Hammer Mill (The Liberator)

Mechanism: Swinging hammers on a high-speed rotor.
* Role: Liberation. It doesn’t just cut; it smashes composite materials apart.
* Best For: E-Waste & Scrap Metal.
* Example: An electric motor. A shredder would cut it into chunks of copper-steel mix. A hammer mill smashes it until the copper winding unravels from the steel stator, allowing downstream separation.

Selection Matrix

References

[1] “Principles of Comminution,” Chemical Engineering Handbook. Principles of Comminution
[2] “Impact vs Shear in Waste Processing,” Waste Management World. Impact vs Shear in Waste Processing