10
High and Low-Ball Charge (Jb/Jc) Ratios
One of the most important variables for optimizing the
performance of a grinding mill is the relationship between
the ball filling level (Jb) and the total charge (Jc) which
includes both the grinding media and slurry. Maintaining
a good Jb/Jc ratio is important for the following reasons: 1)
Reducing damage, wear and tear on the mechanical parts of
both the mill and grinding media. 2) Controlling and con-
serving energy consumption. 3) Optimizing mill through-
put. 4) Maximizing grinding efficiency.
Figure 14 shows the Jb/Jc ratio from a 22-foot SAG mill
where the baseline grinding media charge is approximately
12–13%. Under regular process operating conditions, the
Jb/Jc ratio is usually ~0.75 (high impact condition) as
shown initially in Figure 14. In the middle of the figure,
the Jb/Jc ratio increases to over 0.85 (very high impact con-
dition). During this period, the Jb (grinding media level)
was increased by the plant to approximately 15% and the
ore volume (feed) was slightly decreased to compensate for
the increased power draw to stay within mill motor limita-
tions. In this case, the ore portion of the total charge was
too low for the existing ball charge. On the right-hand side
of the figure, we then observe the opposite case where the
ball (Jb) drops to ~10%. The ore volume was then increased
to maintain regular motor power draw operation. In this
case, the ore portion of the total charge was too high for the
existing ball charge. The Jb/Jc ratio dropped to ~0.5 (very
low impact condition).
Hence the Jb/Jc ratio provides an excellent measure-
ment for how to detect when the balance between grind-
ing media and ore is not optimal. When the ideal Jb/Jc
ratio target is achieved, optimal grinding operating con-
ditions occur for current ball charge. Advanced Analytic
Measurements therefore can be used to measure and main-
tain a healthy ratio between media and total charge in real-
time avoiding poor operation.
CONCLUSIONS
Advances in high-volume data processing and Advanced
Analytics Measurements (AAM) allow us to benefit from
vibration sensors attached to grinding mills in new ways
not previously discovered. Examples are the avoiding high
levels is Liner Damage Level (LDL) as shown in Figure 6.
Impact Angle (IA) can be accurately measured and indi-
rectly indicates the liner wear as shown in Figures 8 to 11,
earlier in the paper. Figure 8, 40 ft. SAG mill, illustrates
Figure 13. High liner damage levels and pegging detection using trunnion sensor vibration differences
Figure 14. Detection of High and Low Grinding Media Operation through Jb/Jc Measurements
High and Low-Ball Charge (Jb/Jc) Ratios
One of the most important variables for optimizing the
performance of a grinding mill is the relationship between
the ball filling level (Jb) and the total charge (Jc) which
includes both the grinding media and slurry. Maintaining
a good Jb/Jc ratio is important for the following reasons: 1)
Reducing damage, wear and tear on the mechanical parts of
both the mill and grinding media. 2) Controlling and con-
serving energy consumption. 3) Optimizing mill through-
put. 4) Maximizing grinding efficiency.
Figure 14 shows the Jb/Jc ratio from a 22-foot SAG mill
where the baseline grinding media charge is approximately
12–13%. Under regular process operating conditions, the
Jb/Jc ratio is usually ~0.75 (high impact condition) as
shown initially in Figure 14. In the middle of the figure,
the Jb/Jc ratio increases to over 0.85 (very high impact con-
dition). During this period, the Jb (grinding media level)
was increased by the plant to approximately 15% and the
ore volume (feed) was slightly decreased to compensate for
the increased power draw to stay within mill motor limita-
tions. In this case, the ore portion of the total charge was
too low for the existing ball charge. On the right-hand side
of the figure, we then observe the opposite case where the
ball (Jb) drops to ~10%. The ore volume was then increased
to maintain regular motor power draw operation. In this
case, the ore portion of the total charge was too high for the
existing ball charge. The Jb/Jc ratio dropped to ~0.5 (very
low impact condition).
Hence the Jb/Jc ratio provides an excellent measure-
ment for how to detect when the balance between grind-
ing media and ore is not optimal. When the ideal Jb/Jc
ratio target is achieved, optimal grinding operating con-
ditions occur for current ball charge. Advanced Analytic
Measurements therefore can be used to measure and main-
tain a healthy ratio between media and total charge in real-
time avoiding poor operation.
CONCLUSIONS
Advances in high-volume data processing and Advanced
Analytics Measurements (AAM) allow us to benefit from
vibration sensors attached to grinding mills in new ways
not previously discovered. Examples are the avoiding high
levels is Liner Damage Level (LDL) as shown in Figure 6.
Impact Angle (IA) can be accurately measured and indi-
rectly indicates the liner wear as shown in Figures 8 to 11,
earlier in the paper. Figure 8, 40 ft. SAG mill, illustrates
Figure 13. High liner damage levels and pegging detection using trunnion sensor vibration differences
Figure 14. Detection of High and Low Grinding Media Operation through Jb/Jc Measurements