In the materials processing terminology, particle size reduction by mechanical means is called grinding [HOGG01, LYNC05]. Other terms are crushing, milling, or attrition milling. The term crushing is used for bigger end size particles (e. g. about 13-19 mm in diameter); the term milling refers to low micron sizes or below.
Machines used for these processes are often called grinding mills [SCHI10]. The grinding machines can be media mills (tumbling mill, centrifugal mill, stirred-media mill, vibratory mill), impact mills (hammer mill), or fluid energy mills [HOGG01, LYNC05]. Size reduction in crushing processes results from particle fracture under stress [HOGG01].
For size reduction processes, a huge variety of abrasive materials is used such as steel, corundum, glass, nylon, SiC, SiN, tungsten carbide, zirconium oxide, zirconium silicate, etc. [NN12]. Several factors such as abrasive grit size, hardness, specific gravity, shapes, and chemical reactions have to be considered when selecting the grinding media [NN12, SCHI10].
Fig. 4.10 Example shapes of the abrasive particles for vibratory grinding after [ROES12, WALT12]