3950 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
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): A second-generation
measurement indicating the relative volumetric fill level in
the mill. This parameter can range from empty (50) to an
overload condition (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 fundamen-
tal measurement for maximizing grinding efficiency inde-
pendently of the ball charge. This ratio indicates the impact
conditions in the mill low ratio is typically 0.4, a safe
ratio is ~0.65 and a very high ratio is0.85 in some SAG
mills. In this case, the mill speed must be adjusted to avoid
balls and liners breakage, grates pegging, etc.
GRINDING PRINCIPLES
In 2006, Powell and Mainza introduced the power curves
to the grinding industry (Power, 2006). They serve as a
valuable tool for understanding the importance of mill fill-
ing in achieving optimal grinding efficiency under varying
conditions. The most common use of power curves is in
surveys where the process is steady and a single data point
is collected. However, this approach has several challenges
when we are searching to obtain the real-time optimum
operating point in the grinding process, as it has numerous
continuously changing variables and varying mill internal
&surrounding circuit conditions. i.e., changes in ore den-
sity, hardness and size, ball charge, mil speed, wearing liners
and grinding balls, slurry density, discharge blockages, etc.
The introduction of Advanced Analytics Measurements
(FLEN, LDL, IA, FTA, IOT, and JbJc) allows for online
utilization of the power curves every mill rotation. This
advancement opens new possibilities by clearly identifying
and graphically displaying, in real-time, when the mill is
empty, in optimal impact condition, overfilled, or over-
loaded, as indicated in Figure 3.
As the adage goes, “We can’t manage what we can’t
measure.” This is particularly true in grinding: we can’t con-
trol what we can’t measure, and we can’t optimize what we
can’t control. Therefore, to optimize grinding, we need to
prevent it, and for this we need to measure several impor-
tant and relevant variables that drive the grinding actions
inside the mill. The introduction of Advanced Analytics
Measurements provides an opportunity to measure what’s
going on inside the mill, thereby enabling better milling
process control. When combined with traditional power
curves, it is possible to achieve accurate optimal operation
in real-time, despite challenges such as a low stockpile, a
high or low ball charge, coarse/fine ore, hard/soft ore, new
versus worn liners and upstream &downstream limitations
related to other circuits, e.g., flotation capacity, leaching,
etc. This new combination of vibration-derived variables
identifies in real-time whether a mill is empty/underfilled,
overfilled/overloaded, or operating optimally.
INDUSTRY APPLICATIONS
The following plant results illustrate how Advanced
Analytics Measurements (AAM) have been applied to SAG,
AG, and BM operations, including topics such as liner
wear, pegging detection, and Jb/Jc ratios.
Liner Wear -Advanced Analytic Measurement (AAM)
Applications
Liner wear is an inevitable consequence of grinding that
affects the process’s overall performance. In the late 20th
century, variable-speed mills were introduced to compen-
sate for liner wear, minimize impact, and extend liner life.
This is achieved by starting the liner campaign at a lower
speed and gradually increasing the speed as the liner wears
to inject more grinding energy for reduced liner ball throw
(trajectory).
Impact Angle Increase Due to Liner Wear
As previously mentioned, the Impact Angle (IA) is cal-
culated using AAM and indicates the angle at which the
media and slurry land inside the mill. Figure 4 corresponds
to a 40-foot diameter SAG mill in this example. Observe
that the IA increases as the liner wears. Specifically, from
approximately 139° in September to 149° in December,
moving from left to right through the trend. Note: Zero
degrees is defined at the top of the mill when viewed from
the discharge end of the mill. 90° is on the right-hand
side, 180° at the bottom, and 270° on the left, as shown in
Figure 3. The mill was also known to be running in a clock-
wise direction when viewed from the discharge end. Thus,
a higher throw or trajectory would approach 90° while a
lower or reduced trajectory would move towards 180°.
In Figure 4, halfway through the trend (January), the
liners were replaced, and the IA can be seen to reset or
start at ~132°. Then, as the liner wears, the IA increases
and moves towards 180°. This indicates that the throw
is slowly reducing over time, as expected. Thus, the liner
trajectory can decrease almost linearly with increasing IA
over the first three months of the trend and the second half
(4.5 months). The mill speed is also shown in the trend
for reference. Please note that the control strategy for this
operation maximizes the speed of the mill at all times.
There is an opportunity to improve grinding efficiency by
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): A second-generation
measurement indicating the relative volumetric fill level in
the mill. This parameter can range from empty (50) to an
overload condition (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 fundamen-
tal measurement for maximizing grinding efficiency inde-
pendently of the ball charge. This ratio indicates the impact
conditions in the mill low ratio is typically 0.4, a safe
ratio is ~0.65 and a very high ratio is0.85 in some SAG
mills. In this case, the mill speed must be adjusted to avoid
balls and liners breakage, grates pegging, etc.
GRINDING PRINCIPLES
In 2006, Powell and Mainza introduced the power curves
to the grinding industry (Power, 2006). They serve as a
valuable tool for understanding the importance of mill fill-
ing in achieving optimal grinding efficiency under varying
conditions. The most common use of power curves is in
surveys where the process is steady and a single data point
is collected. However, this approach has several challenges
when we are searching to obtain the real-time optimum
operating point in the grinding process, as it has numerous
continuously changing variables and varying mill internal
&surrounding circuit conditions. i.e., changes in ore den-
sity, hardness and size, ball charge, mil speed, wearing liners
and grinding balls, slurry density, discharge blockages, etc.
The introduction of Advanced Analytics Measurements
(FLEN, LDL, IA, FTA, IOT, and JbJc) allows for online
utilization of the power curves every mill rotation. This
advancement opens new possibilities by clearly identifying
and graphically displaying, in real-time, when the mill is
empty, in optimal impact condition, overfilled, or over-
loaded, as indicated in Figure 3.
As the adage goes, “We can’t manage what we can’t
measure.” This is particularly true in grinding: we can’t con-
trol what we can’t measure, and we can’t optimize what we
can’t control. Therefore, to optimize grinding, we need to
prevent it, and for this we need to measure several impor-
tant and relevant variables that drive the grinding actions
inside the mill. The introduction of Advanced Analytics
Measurements provides an opportunity to measure what’s
going on inside the mill, thereby enabling better milling
process control. When combined with traditional power
curves, it is possible to achieve accurate optimal operation
in real-time, despite challenges such as a low stockpile, a
high or low ball charge, coarse/fine ore, hard/soft ore, new
versus worn liners and upstream &downstream limitations
related to other circuits, e.g., flotation capacity, leaching,
etc. This new combination of vibration-derived variables
identifies in real-time whether a mill is empty/underfilled,
overfilled/overloaded, or operating optimally.
INDUSTRY APPLICATIONS
The following plant results illustrate how Advanced
Analytics Measurements (AAM) have been applied to SAG,
AG, and BM operations, including topics such as liner
wear, pegging detection, and Jb/Jc ratios.
Liner Wear -Advanced Analytic Measurement (AAM)
Applications
Liner wear is an inevitable consequence of grinding that
affects the process’s overall performance. In the late 20th
century, variable-speed mills were introduced to compen-
sate for liner wear, minimize impact, and extend liner life.
This is achieved by starting the liner campaign at a lower
speed and gradually increasing the speed as the liner wears
to inject more grinding energy for reduced liner ball throw
(trajectory).
Impact Angle Increase Due to Liner Wear
As previously mentioned, the Impact Angle (IA) is cal-
culated using AAM and indicates the angle at which the
media and slurry land inside the mill. Figure 4 corresponds
to a 40-foot diameter SAG mill in this example. Observe
that the IA increases as the liner wears. Specifically, from
approximately 139° in September to 149° in December,
moving from left to right through the trend. Note: Zero
degrees is defined at the top of the mill when viewed from
the discharge end of the mill. 90° is on the right-hand
side, 180° at the bottom, and 270° on the left, as shown in
Figure 3. The mill was also known to be running in a clock-
wise direction when viewed from the discharge end. Thus,
a higher throw or trajectory would approach 90° while a
lower or reduced trajectory would move towards 180°.
In Figure 4, halfway through the trend (January), the
liners were replaced, and the IA can be seen to reset or
start at ~132°. Then, as the liner wears, the IA increases
and moves towards 180°. This indicates that the throw
is slowly reducing over time, as expected. Thus, the liner
trajectory can decrease almost linearly with increasing IA
over the first three months of the trend and the second half
(4.5 months). The mill speed is also shown in the trend
for reference. Please note that the control strategy for this
operation maximizes the speed of the mill at all times.
There is an opportunity to improve grinding efficiency by