7
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 4. 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 8, 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 is shown to be
increasing and moving towards 180°. This indicates that the
throw is slowly reducing over time as expected. Thus, the
liner trajectory can be seen to be decreasing almost linearly
with increasing IA over the first 3 months of the trend as
well as the second half of the trend (4.5 months). The mill
speed is also shown in the trend for refence. In comparison,
Figure 11 shows the equivalent scenario where the speed is
automatically adjusted to control the IA.
Impact Angle for New and Worn-Out Liners
In Figure 9, the effect of liner wear on IA is also illustrated
for a 36-foot diameter SAG mill. In this case, the mill speed
clustered weekly. A worn-out liner is indicated in red and
new liners in green. With the worn-out liner (red), the
speed has little to no impact on the throw, as measured by
the Impact Angle. The red clusters all look like columns
which show that as speed changes on the y-axis, not much
change is observed for IA on the x-axis. However, in the
green plots, we can see that the clusters have some horizon-
tal change with respect to a change in speed. Specifically,
as speed increases, IA moves towards 90° (higher throw/
decreasing IA) and as speed decreases the values approach
180° (lower throw/increasing IA).
In Figure 9, weeks 14–17 are at the end of the liner
cycle. Note: By week 17, the IA is approximately 146° at
both 8.5 and 9.5 mill RPMs, indicating that the grinding
media is impacting inside the toe of the load due to the
worn-out liners.
Week 18 is when the new liners are installed and there-
fore has two columns of points corresponding to really
worn-out liners (red) and new liners (green). Weeks 19–22
are relatively new liners showing IA responsiveness to
changes in speed. Note: By week 20, we can clearly observe
the impact of mill RPMs on the throw, as measured by
the IA. At 8.5 RPMs, the IA reaches up to 145°, while at
9.5 RPMs, it decreases to 135°. This demonstrates that the
new liner edge profile is directly affecting the media throw
(trajectory) and can be measured via IA. IA can now be
used to tune mill speed to project the grinding media to
the angle where it has most energy. Typically, between 130°
and 140° IA.
Figure 8. Impact Angle (IA) change versus Liners Wear -40 ft SAG Mill
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 4. 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 8, 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 is shown to be
increasing and moving towards 180°. This indicates that the
throw is slowly reducing over time as expected. Thus, the
liner trajectory can be seen to be decreasing almost linearly
with increasing IA over the first 3 months of the trend as
well as the second half of the trend (4.5 months). The mill
speed is also shown in the trend for refence. In comparison,
Figure 11 shows the equivalent scenario where the speed is
automatically adjusted to control the IA.
Impact Angle for New and Worn-Out Liners
In Figure 9, the effect of liner wear on IA is also illustrated
for a 36-foot diameter SAG mill. In this case, the mill speed
clustered weekly. A worn-out liner is indicated in red and
new liners in green. With the worn-out liner (red), the
speed has little to no impact on the throw, as measured by
the Impact Angle. The red clusters all look like columns
which show that as speed changes on the y-axis, not much
change is observed for IA on the x-axis. However, in the
green plots, we can see that the clusters have some horizon-
tal change with respect to a change in speed. Specifically,
as speed increases, IA moves towards 90° (higher throw/
decreasing IA) and as speed decreases the values approach
180° (lower throw/increasing IA).
In Figure 9, weeks 14–17 are at the end of the liner
cycle. Note: By week 17, the IA is approximately 146° at
both 8.5 and 9.5 mill RPMs, indicating that the grinding
media is impacting inside the toe of the load due to the
worn-out liners.
Week 18 is when the new liners are installed and there-
fore has two columns of points corresponding to really
worn-out liners (red) and new liners (green). Weeks 19–22
are relatively new liners showing IA responsiveness to
changes in speed. Note: By week 20, we can clearly observe
the impact of mill RPMs on the throw, as measured by
the IA. At 8.5 RPMs, the IA reaches up to 145°, while at
9.5 RPMs, it decreases to 135°. This demonstrates that the
new liner edge profile is directly affecting the media throw
(trajectory) and can be measured via IA. IA can now be
used to tune mill speed to project the grinding media to
the angle where it has most energy. Typically, between 130°
and 140° IA.
Figure 8. Impact Angle (IA) change versus Liners Wear -40 ft SAG Mill