Crushing and Grinding
- Weight percentages of material greater than 50% of the maximum size are about 50% for roll mills, 15% for tumbling mills and 5% for closed circuit ball mills.
- Roll crushers are made either smooth or with teeth. A 24 in. toothed roll can accept lumps of 14 in. diameter. Smooth rolls have reduction ratios of up to about 4. Speeds are 50-900 rpm. Capacity is about 25% of the maximum corresponding to a continuous ribbon passing through the rolls.
- Hammer mills beat the material until it is small enough to pass through the screen at the bottom of the casing. A reduction ratio to 40 is feasible. Large units operate at 900 rpm, smaller ones up to 16,000 rpm. For fibrous materials, the screen has cutting edges.
The information is arranged by commonly recognised categories. In some instances, definitions and general statements have been included for clarity.
