Mechanical Operations
For efficient grinding, ball mills must be operated

At a speed more than the critical speed
With minimum possible small balls
At a speed less than the critical speed
At a speed equal to the critical speed

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Mechanical Operations
Reciprocating screens are normally inclined at an angle of 5° with the horizontal and employ gyratory motion at feed end & reciprocating motion at the discharge end. They are not suitable for the screening of the

Heavy tonnages of rocks or gravel
Dry chemicals
Light metal powder down upto 4 meshsize
Powdered food & granular materials

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Mechanical Operations
For a non-spherical particle, the sphericity

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

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