8
Impact Angle in a Fixed speed AG Mill
Figure 10 shows the IA measurement now employed on
a new/different 30 foot diameter fixed-speed AG mill. In
this graphic, all three sensor signals are displayed: feed-end,
middle and discharge-end of the mill’s shell. The trend indi-
cates minimal wear measured 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 increasing (low throw) as the liner wears in the
feed, middle and discharge sections of the mill.
Automatic Mill Speed Adjustment for Liner Wear
Compensation
The following case describes a 32-foot SAG mill where the
impact angle (IA) is controlled and maintained around
135° for the entire liner wear cycle. The target IA value is
controlled by adjusting mill motor speed until a point is
reached where IA can no longer be held at the optimal value
due to the limitation of reaching maximum motor speed.
When motor speed hits the maximum limit, the controller
can no longer maintain the desired IA target and instead IA
begins increasing to 150° at the end of the liner cycle cam-
paign. This can be seen in Figure 11 where the blue signal
is Motor RPM and in red the IA. During the first 17 weeks
of operation, the speed is slowly increased to flatten out or
maintain an IA value of ~135°. At week 18, the mill begins
to reach the upper limitation of Motor RPMs. By week 20,
significant wear on the liners has occurred and with the
limitation of reaching maximum motor speed, the control-
ler no longer can maintain the optimal Impact Angle and
thus it begins to drift upward towards 165° indicating that
the liners are worn-out.
Figure 9. New (green)/worn (red) liner impact angle (ia) measurements versus speed -36 ft.
SAG mill
Figure 10. Liner wear/impact angle for feed, middle and discharge regions of a 30ft AG mill
Impact Angle in a Fixed speed AG Mill
Figure 10 shows the IA measurement now employed on
a new/different 30 foot diameter fixed-speed AG mill. In
this graphic, all three sensor signals are displayed: feed-end,
middle and discharge-end of the mill’s shell. The trend indi-
cates minimal wear measured 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 increasing (low throw) as the liner wears in the
feed, middle and discharge sections of the mill.
Automatic Mill Speed Adjustment for Liner Wear
Compensation
The following case describes a 32-foot SAG mill where the
impact angle (IA) is controlled and maintained around
135° for the entire liner wear cycle. The target IA value is
controlled by adjusting mill motor speed until a point is
reached where IA can no longer be held at the optimal value
due to the limitation of reaching maximum motor speed.
When motor speed hits the maximum limit, the controller
can no longer maintain the desired IA target and instead IA
begins increasing to 150° at the end of the liner cycle cam-
paign. This can be seen in Figure 11 where the blue signal
is Motor RPM and in red the IA. During the first 17 weeks
of operation, the speed is slowly increased to flatten out or
maintain an IA value of ~135°. At week 18, the mill begins
to reach the upper limitation of Motor RPMs. By week 20,
significant wear on the liners has occurred and with the
limitation of reaching maximum motor speed, the control-
ler no longer can maintain the optimal Impact Angle and
thus it begins to drift upward towards 165° indicating that
the liners are worn-out.
Figure 9. New (green)/worn (red) liner impact angle (ia) measurements versus speed -36 ft.
SAG mill
Figure 10. Liner wear/impact angle for feed, middle and discharge regions of a 30ft AG mill