Comminution of raw materials

The collision mechanics of impact and percussion comminution – Part 2

In numerous machines, the comminution of primary and secondary raw materials is based on the physical effect of collision. This effect is realized by means of the active principles of impact and percussion. These active principles effect four types of collision either between the raw material particles or with machine components: elastic-plastic, rebounding, penetrating and energy-releasing collisions.

Part 2 of the technical article focusses on the widening of the theory of restitution to the theory of collision, enabling its formulation in physical terms. For this purpose, the coefficient of restitution is extended and termed the coefficient of collision. The value range then extends from - 1 to ∞. Here the coefficient of collision from - 1 to 0 characterizes the penetrating collision, from 0 to 1 the elastic-plastic and rebounding collisions and from 1 to ∞ the energy-releasing collision. Comminution is effected in all collision types apart from in elastic-plastic collisions.

Continuation of Part 1 of the technical contribution published in AT 10/2023, pp. 46-56.


4 Physics of collision

High-velocity film recordings of the processes in the process chambers of the comminution machines show different behaviour of particles when they collide with the non-moving and moving work surfaces of the machine as well as with each other. Different collisions result. For the generation of a collision model, the individual collision types must be defined and the subprocesses taking place described in physical terms.


Prof. Dr.-Ing. Dr. h. c. Georg Unland, Technische Universität Bergakademie Freiberg

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