3
and when combined with power curves (Powell, 2006)
results in three different operating modes as shown in
Figure 4. For grinding optimization, the relevant AAM sig-
nals are shown below.
Liner Damage Level (LDL)
A measurement that indicates the extent of damage (wear)
occurring in real-time on the liners. A high LDL (70)
value indicates a higher probability of fracture in both the
liners and grinding media (balls) due to ‘steel-on-steel’
impacts and empty mill condition. Conversely, a low LDL
(30) number indicates very low ‘steel-on-steel’ impacts
resulting in over-protection of the liners/media. By oper-
ating the mill in this manner, the mill can be overfilled
and potentially overloaded in a short period of time. The
optimal point therefore is somewhere in between these two
limits (LDL ≈ 50), operating where the Beach Boys would
call ‘good vibrations’.
Impact Angle (IA)
This measurement indicates the angle at which the grind-
ing media impacts inside the mill. The Impact Angle (IA)
helps identify the optimal point of impact for maximum
grinding efficiency. Figure 3 illustrates how the Impact
Angle (y-axis) changes as a function of mill speed (x-axis)
for specific liner wear, ball charge, and ore characteristics in
a 38 ft SAG mill. The DEM simulations, shown in the fig-
ure, provide insight into why the IA does not change much
below 8.8 RPM, as the impact occurs under the Toe. As the
mill speed increases beyond 8.8 RPM, the IA decreases, and
the impact shifts over the Toe of the load.
This variable is a function of mill speed and enables the
determination of the real-time optimal mill speed, resulting
in the highest possible throughput for the current process
operating conditions (Impact Grinding). Additionally, this
variable can be leveraged to facilitate Attrition Grinding
when the process requires significant reductions in material
size or when upstream/downstream limitations are present.
Fill Toe Angle (FTA)
This corresponds to the degree or point inside the mill
where the toe of the load is located.
Impact on Toe (IOT)
Another measurement indicating the difference in degrees
between the Impact Angle (IA) and Fill Toe Angle (FTA).
Ideally IOT should be zero to maximize impact grind-
ing. For maximizing attrition grinding or under-throw-
ing media, a negative IOT is preferred. A positive IOT
indicates an over-throwing situation which may be more
beneficial in AG mills but is not desirable in SAG or ball
mill grinding, because the balls will be hitting the liners
(‘metal-on- metal).
Fill Level Enhanced (FLEN)
This measurement indicates the optimal volume for effi-
cient grinding. It dynamically adjusts to changes in ore,
grinding media levels, slurry density, and liner wear. This
parameter can range from empty (50) to an overload con-
dition (95).
Jb/Jc Ratio (JbJc)
This measurement indicates the ratio of the ball charge (Jb)
to the total charge (Jc) which includes the grinding media
and slurry. This is a fundamental measurement for maxi-
mizing grinding efficiency independently of the ball charge.
Figure 3. Impact Angle as a function of Mill Speed
and when combined with power curves (Powell, 2006)
results in three different operating modes as shown in
Figure 4. For grinding optimization, the relevant AAM sig-
nals are shown below.
Liner Damage Level (LDL)
A measurement that indicates the extent of damage (wear)
occurring in real-time on the liners. A high LDL (70)
value indicates a higher probability of fracture in both the
liners and grinding media (balls) due to ‘steel-on-steel’
impacts and empty mill condition. Conversely, a low LDL
(30) number indicates very low ‘steel-on-steel’ impacts
resulting in over-protection of the liners/media. By oper-
ating the mill in this manner, the mill can be overfilled
and potentially overloaded in a short period of time. The
optimal point therefore is somewhere in between these two
limits (LDL ≈ 50), operating where the Beach Boys would
call ‘good vibrations’.
Impact Angle (IA)
This measurement indicates the angle at which the grind-
ing media impacts inside the mill. The Impact Angle (IA)
helps identify the optimal point of impact for maximum
grinding efficiency. Figure 3 illustrates how the Impact
Angle (y-axis) changes as a function of mill speed (x-axis)
for specific liner wear, ball charge, and ore characteristics in
a 38 ft SAG mill. The DEM simulations, shown in the fig-
ure, provide insight into why the IA does not change much
below 8.8 RPM, as the impact occurs under the Toe. As the
mill speed increases beyond 8.8 RPM, the IA decreases, and
the impact shifts over the Toe of the load.
This variable is a function of mill speed and enables the
determination of the real-time optimal mill speed, resulting
in the highest possible throughput for the current process
operating conditions (Impact Grinding). Additionally, this
variable can be leveraged to facilitate Attrition Grinding
when the process requires significant reductions in material
size or when upstream/downstream limitations are present.
Fill Toe Angle (FTA)
This corresponds to the degree or point inside the mill
where the toe of the load is located.
Impact on Toe (IOT)
Another measurement indicating the difference in degrees
between the Impact Angle (IA) and Fill Toe Angle (FTA).
Ideally IOT should be zero to maximize impact grind-
ing. For maximizing attrition grinding or under-throw-
ing media, a negative IOT is preferred. A positive IOT
indicates an over-throwing situation which may be more
beneficial in AG mills but is not desirable in SAG or ball
mill grinding, because the balls will be hitting the liners
(‘metal-on- metal).
Fill Level Enhanced (FLEN)
This measurement indicates the optimal volume for effi-
cient grinding. It dynamically adjusts to changes in ore,
grinding media levels, slurry density, and liner wear. This
parameter can range from empty (50) to an overload con-
dition (95).
Jb/Jc Ratio (JbJc)
This measurement indicates the ratio of the ball charge (Jb)
to the total charge (Jc) which includes the grinding media
and slurry. This is a fundamental measurement for maxi-
mizing grinding efficiency independently of the ball charge.
Figure 3. Impact Angle as a function of Mill Speed