ABSTRACT

The comminution or size reduction process is an important unit operation in the process industries in which solid materials are broken or cut into smaller sizes by the application of mechanical stress. Solids can be reduced in size by crushers and grinders which employ compression, impact, attrition, shear, or combinations thereof. Depending on the degree of

CONTENTS

Introduction ................................................................................................................................. 125 Grinding Energy Requirements ................................................................................................ 126 Primary and Secondary Crushers ............................................................................................. 127

Gyratory Cone Crushers ....................................................................................................... 127 Jaw Crushers ........................................................................................................................... 128 Roll Crushers ........................................................................................................................... 129

Intermediate and Fine Grinders ................................................................................................ 130 Impact Mills ............................................................................................................................ 130

Hammer Mills .................................................................................................................... 130 Centrifugal Pin Mills ......................................................................................................... 130

Attrition/Disk Mills ............................................................................................................... 131 Tumbling Mills ........................................................................................................................ 132

Ball Mills ............................................................................................................................. 132 Tube Mills ........................................................................................................................... 134 Rod Mills ............................................................................................................................. 134 Autogenous and Semiautogenous Mills ........................................................................ 134

Rolling Compression Mills ................................................................................................... 135 Ultra”ne Grinders ....................................................................................................................... 135

Fluid-Energy Mills ................................................................................................................. 135 Agitated Mills ......................................................................................................................... 136

Attritors ............................................................................................................................... 137 Vibratory Mills ................................................................................................................... 139

Impact Mills with Internal Classi”cation ............................................................................ 139 Rotary Cutters.............................................................................................................................. 141 Equipment Operation ................................................................................................................. 141

Open and Closed Circuit Grinding ..................................................................................... 141 Conclusions .................................................................................................................................. 142 References ..................................................................................................................................... 143

particle size reduction desired, the end result is achieved in one or several steps. Devices that are used for size reduction operations can be classi”ed into primary and secondary crushers, grinders, and pulverizers. Explosive blasting is used in many instances for primary size reduction of ore formations into sizes workable by primary crushing machines. The primary crushers are slow-speed machines that reduce the run-of-mine product into 15-25 cm lumps. A secondary crusher reduces these lumps to 5 mm product. Grinders reduce the products of crushing operations into powder. An intermediate grinder typically produces a product that passes a 40-mesh screen. Fine grinders reduce feed into product that passes a 200-mesh screen. Ultra”ne grinders can convert the product of secondary crushers into 1-10 µ product. Cutting machines produce particles with a de”nite size and shape in the 2-10 mm size range.