Size Reduction

Abstract

In this chapter, the mechanism and factors affecting size reduction process and the laws governing these operations are discussed. Size reduction is a process in which particles with smaller size and large surface areas are formed, which ultimately eases the processing. The chapter explains the size reduction mechanism during compression, impact, cutting, shearing, and attrition. The stress-strain behavior of materials during mechanical failure also plays an important role during size reduction. To evaluate the effectiveness of size reduction operation, analysis of newly formed surfaces and energy involved becomes important. A better understanding of equipment and operation parameters can minimize the overall input energy. The popular size reduction equipments for agricultural produce, viz., hammer mill, ball mill, burr mill, jaw crusher, gyratory crusher, crushing roll, cutter mill, Reitz mill, and colloid mills, are explained using schematic diagrams. The heat generated during size reduction is always a big concern in processing spices and herbs. Hence, advanced size reduction operations like hammer mill with water jackets and cryogenic grinding are used to protect the aromatic and volatile components. In liquid food, homogenization is frequently used to break particulate matter into smaller and uniform particle sizes to form dispersion. The chapter also deals with different size reduction laws.