Granular Flow - Application
Parameter study of a ball mill
Two-dimensional DEM simulation results have been undertaken of a ball
mill, systematically changing the following parameters to understand their
influence on the mill behaviour (charge motion and power draw):
Mill speed:
Increasing mill speed leads to steadily increasing amounts of cataracting
material and an increasingly angular bi-linear profile to the cascading
free surface. Note that for these lifters significant numbers of
collisions already occur between cataracting material and the liner.
| 60% |
 |
 |
70% |
| 80% |
 |
 |
90% |
| Charge distribution for different
mill speeds (fill level = 30%) |
Fill level:
At a 10% fill level most of the charge is trapped between the lifters. As
the mill is filled, progressively the cascading free surface rises higher
and becomes more angular in shape. The amount of cataracting material is
essentially independent of the fill level, since the same amount of
material is trapped between the lifters for all fill levels.
| 10% |
 |
 |
20% |
| 30% |
 |
 |
40% |
| Charge distribution for different
fill levels (mill speed = 75% critical) |
Lifter shape:
By adjusting the lifter height and face angle, lifter wear can be
mimicked. As the lifter face angle is reduced, and the lifter height
correspondingly decreased, there is a significant reduction in the amount
of cataracting material. The shape of the charge, however, is essentially
independent of lifter shape.
| 85 o |
 |
 |
60 o |
| 45 o |
 |
 |
22.5 o |
| Charge distribution for different
lifter shapes (mill speed = 80% critical) |
Lifter pattern:
The lifter characteristics can be modified by removing selected lifters,
or replacing with lower ones. Reducing the number or height of the lifters
decreases the amount of cataracting material, but does not have a strong
influence on the shape of the charge.
| standard |
 |
|
|
half
number |
 |
 |
hi-lo |
| Charge distribution for different
lifter patterns (mill speed = 80% critical, fill level = 40%) |
|
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