XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3953
thus, it begins to drift upward towards 165°, indicating that
the liners are worn out.
Pegging Detection
Pegging occurs when rock or spalled balls get trapped in the
openings of the discharge grates. It can vary from minor
pegging to very challenging situations (more than 40%
pegging) where the entire discharge grate is affected/sub-
stantially blocked, as shown in Figure 8.
As described in the previous section, LDLs greater
than 70 indicate the undesired situation of grinding media
overthrow, which in turn produces both liner fractures and
broken grinding media. For optimal operation, LDL is typ-
ically desired to be around ~50.
Figure 9 shows an industrial example of the LDL sig-
nal in a 40-foot diameter SAG mill. In this case, the LDL
reached an extremely high LDL 200 for over 5 hours of
operation, as shown in the red circle. This LDL indicates
an undesired ‘metal on metal’ operation that fractures balls
and liners. When a significant quantity of broken balls is
combined with fine ore, lower density and high mill speed,
pegging has a very high opportunity to develop and the
discharge grates become blinded. The blinding of the dis-
charge grates creates an imbalance or blockage of flow in
the mill.
Luckily, this can be detected with the feed and discharge
trunnion sensors. The Trunnion Vibration Difference is
shown in Figure 9 (gray). Shortly after the Extreme High
Figure 7. Mill Speed Control based on Optimal Impact Angle (IA) in a 32ft SAG Mill
Figure 8. Discharge grate pegging
thus, it begins to drift upward towards 165°, indicating that
the liners are worn out.
Pegging Detection
Pegging occurs when rock or spalled balls get trapped in the
openings of the discharge grates. It can vary from minor
pegging to very challenging situations (more than 40%
pegging) where the entire discharge grate is affected/sub-
stantially blocked, as shown in Figure 8.
As described in the previous section, LDLs greater
than 70 indicate the undesired situation of grinding media
overthrow, which in turn produces both liner fractures and
broken grinding media. For optimal operation, LDL is typ-
ically desired to be around ~50.
Figure 9 shows an industrial example of the LDL sig-
nal in a 40-foot diameter SAG mill. In this case, the LDL
reached an extremely high LDL 200 for over 5 hours of
operation, as shown in the red circle. This LDL indicates
an undesired ‘metal on metal’ operation that fractures balls
and liners. When a significant quantity of broken balls is
combined with fine ore, lower density and high mill speed,
pegging has a very high opportunity to develop and the
discharge grates become blinded. The blinding of the dis-
charge grates creates an imbalance or blockage of flow in
the mill.
Luckily, this can be detected with the feed and discharge
trunnion sensors. The Trunnion Vibration Difference is
shown in Figure 9 (gray). Shortly after the Extreme High
Figure 7. Mill Speed Control based on Optimal Impact Angle (IA) in a 32ft SAG Mill
Figure 8. Discharge grate pegging