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Crushing principles

Why is it shredded?

Different mill types operate according to different comminution principles. The choice of mill ultimately depends on the fracture behavior of the material to be ground.

Hard-brittle materials are mainly crushed by impact, pressure and friction forces, while soft or elastic materials are mainly effectively processed by cutting and shear forces.

For coarse grain sizes above approximately 40 mm, crushers or shredders are usually used. Smaller particle sizes, however, are processed with mills.

In principle, different stress mechanisms can be distinguished when comminuting solids.

Crushing of hard or brittle materials

Compressive stress

In this method, the material is compressed between two surfaces (e.g., the tools of a mill) until it breaks. Examples include jaw crushers and roller crushers.

Crushing-compressive stress
Crushing-impact stress

Impact stress

Here, the particles hit a solid surface at high speed, breaking them down into smaller fragments. This can occur either by the grinding tool itself or by the mill wall. Typical examples are vibratory mills, planetary mills, impact mills, and air jet mills.

Frictional stress

Frictional forces act between the material and one or more surfaces. The material to be ground is essentially ground. Examples of this include disc mills and other attrition mills.

Crushing-friction stress

Shredding of soft, elastic and fibrous materials

Comminution-shear stress

Shear stress

In this method, two or more solid surfaces interact, creating a shear effect. Typically, one surface moves while the other remains stationary.
Examples: Drum mills, cross beater mills, ultrasonic mills

Cutting stress

Here, the material is separated between two or more sharp-edged surfaces. At least one of the surfaces has a cutting edge that divides the material.
Examples: shredders, cutting mills, knife mills

Crushing-cutting stress
Klaus Ebenauer

Ing. Klaus Ebenauer

info@litechgmbh.com
+43 1 99 717 55

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