XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3951
manipulating the mill speed based on the IA as the liner
wears, as shown in Figure 7.
Impact Angle for New and Worn-Out liners
In Figure 5, the effect of liner wear on IA is also illustrated
for a 36-foot diameter SAG mill. In this case, the mill speed
is included in the graphic and 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 shows 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 horizontal 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/increas-
ing IA).
In Figure 5, 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,
therefore, 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 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 directly affects the media throw (trajec-
tory) 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 the most energy. Typically, between 130° and
140° IA.
Impact Angle in a Fixed speed AG Mill
Figure 6 shows the IA measurement on a new/different
30-foot diameter fixed-speed AG mill. This graphic displays
all three sensor signals: feed-end, middle and discharge-end
of the mill’s shell. The trend indicates minimal wear mea-
sured by the IA at ~125° around 10/2022 due to the reline
of the mill. By 10/2023, the IA is ~135° due to the liner
wear for the three shell sensors. With the new reline on
10/2023, the IA is back to ~125°. The full liner cycle in this
fixed-speed AG mill is about one year. The IA keeps increas-
ing (low throw) as the liner wears in the mill’s feed, middle
and discharge sections.
Figure 4. Impact Angle (IA) change versus Liners Wear—40 ft SAG Mill
manipulating the mill speed based on the IA as the liner
wears, as shown in Figure 7.
Impact Angle for New and Worn-Out liners
In Figure 5, the effect of liner wear on IA is also illustrated
for a 36-foot diameter SAG mill. In this case, the mill speed
is included in the graphic and 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 shows 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 horizontal 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/increas-
ing IA).
In Figure 5, 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,
therefore, 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 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 directly affects the media throw (trajec-
tory) 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 the most energy. Typically, between 130° and
140° IA.
Impact Angle in a Fixed speed AG Mill
Figure 6 shows the IA measurement on a new/different
30-foot diameter fixed-speed AG mill. This graphic displays
all three sensor signals: feed-end, middle and discharge-end
of the mill’s shell. The trend indicates minimal wear mea-
sured by the IA at ~125° around 10/2022 due to the reline
of the mill. By 10/2023, the IA is ~135° due to the liner
wear for the three shell sensors. With the new reline on
10/2023, the IA is back to ~125°. The full liner cycle in this
fixed-speed AG mill is about one year. The IA keeps increas-
ing (low throw) as the liner wears in the mill’s feed, middle
and discharge sections.
Figure 4. Impact Angle (IA) change versus Liners Wear—40 ft SAG Mill