Comminution energy and power reqs and basic operations

Rittinger’s Law

energy required for particle size reduction is directly proportional to the area of new surface created

in actuality, energy req is usually 200-300 times theo

unlikely that energy requirement and surface created are related

Kick’s Law

Based on stress analysis theory for plastic deformation

energy required for any comminution process is proportional to the volume ratios of particle feed to particle product

unrealistic, 10 to 1 micrometer should not be equal to 1m to 10cm

Bonds Law

energy required to reduce particle size is proportional to the inverse square root of the size

Bond’s Work index

Defined as the energy required to reduce the size of unit mass of material from infinity to 100 microm in size

determined experimentally, material type dependent, final product size independent

Holmes and Hukki

derived a general formula including all size reduction laws as cases

Apply Rittinger’s Law

for small particle sizes (ultra fine grinding)

Apply Kick’s Law

for large particle sizes (coarse crushing, crushing)

Apply Bonds Law

for intermediate particle sizes (most common range for industrial grinding processes)

Crushing

breaking large pieces of material into smaller pieces

Jaw crusher

used for coarse size reduction

operate by compressing the material between two plates, one fixed, one moving

Gyratory crushers

conical head gyrating inside a larger conical shell, crushing the material as it moves downward

Cone crushers

secondary to tertiary crushing of gyratory crushers

Grinding

using abrasion and shear forces to reduce size

Ball mills

Cylindrical devices for fine grinding, tumbling balls to ground the material

Rod mills

long rods as grinding media, rolling and cascading action

Hammer mills

rotating hammers to impact and break the material into smaller pieces

Cutting

size reduction using a sharp knife

Cutting machines

required particle of specified shape, using sharp blades or edges

Attrition

rubbing or scraping reduce size

Attrition mills

rubbing or grinding of particles against eachother, small fragments are removed at surface

Impact

size reduction by striking against another surface

Impact crushers

principle of rapid impact to shatter the material, using hammers or blowbars

Compression

size reduction using rollers or plates to crush materials

Compression crushers

apply a force to the particles, fracturing along their weakest planes