Mechanical Operations
Rittinger's crushing law states that

Work required in crushing is proportional to the new surface created
Work required to form a particle of any size is proportional to the square of the surface to volume ratio of the product
For a given machine and feed, crushing efficiency is dependent on the size of the feed & product
Work required to form a particle of a particular size is proportional to the square root of the surface to volume ratio of the product

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Mechanical Operations
Work index is defined as the

Gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the product passes through a 100 micron screen
Energy needed to crush one ton of feed to 100 microns
Energy needed to crush one tonne of feed to 200 microns
Energy (kWh/ton of feed) needed to crush small feed to such a size that 80% of the product passes a 200 mesh screen

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Mechanical Operations
For a non-spherical particle, the sphericity

Is always less than 1
Is defined as the ratio of surface area of a sphere having the same volume as the particle to the actual surface area of the particle
Has the dimension of length
Is the ratio of volume of a sphere having the same surface area as the particle to the actual volume of the particle

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Mechanical Operations
In case of grinding in a ball mill

Its capacity decreases with increasing fineness of the products
All of these
Wet grinding achieves a finer product size than dry grinding
Grinding cost and power requirement increases with increasing fineness of the products

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