2
not just engineering excellence or design to a pro forma
arrangement.
Crushing and grinding circuits, like any other produc-
tion process, are greatly affected by changes over time since
they are continuous processes in which equipment is sub-
jected to variations in feed characteristics and/or changes
in equipment condition. The variations can be caused by
degrading equipment performance, reducing overall plant
capacity and thus decreasing product quality (Major, 2003
Bengtsson et al., 2009 Itavuo, 2009).
In flowsheet design, the impact of maintenance require-
ments is measured by estimating or calculating equipment
availability based on the planned maintenance of critical
components such as wear parts and lube systems. Major
mechanical and electrical components, such as drive sys-
tems, gear components, windings, etc., are expected to last
for an extended period if these components are monitored
and inspected periodically as part of a preventative mainte-
nance program.
Most primary crushing circuit designs are based on a
75% availability target, and grinding mills use, say, a 92%
availability target. The crushing circuit availability is lower
due, in part, to mine requirements and truck scheduling
rather than matters related to the crushing circuit. Based
on the throughput requirement of the project, the flow-
sheet and comminution equipment are selected and process
buffers, such as stockpiles, bins, and large tanks, are placed
so that stable and consistent production is maintained tar-
get. The sizes of the process buffers and the selection of
the comminution equipment in the flowsheet are mutu-
ally dependent. A small-capacity process buffer may require
the selection of duty standby equipment. In contrast,
the flowsheet may require a large-capacity process buffer
when selecting duty-only comminution equipment. The
optimum selection of the number of comminution equip-
ment and the size of process buffers in the flowsheet is a
function of:
• Incurred capital cost in the project—for junior min-
ing companies, where capital is constrained. A low
capital-cost flowsheet is often preferred.
• Available footprint to build the flowsheet—for
space-constrained areas, the layout of the flowsheet
is pertinent (e.g., Phu Kham)
• Impact on operating cost and greenhouse gas emis-
sions (GHGe)—additional equipment in the flow-
sheet may incur higher operating costs and, as a
result, incur higher scopes 2 and 3GHGe levels
• Commonality of spares and number of parts
required to maintain all equipment in the flowsheet.
Common spares minimize the need for large on-site
warehousing and reduce the risk of logistics-related
delay caused by unexpected circumstances (transpor-
tation risk, geopolitical, and environmental).
DESCRIPTION OF MAINTENANCE PARTS
The selection of the comminution equipment for the duty
in the selected flowsheet depends on its ability to process
ore with specific ore characteristics (competence, hardness
and abrasion index) at the desired throughput and the tar-
get product size distribution. A key factor in the selection of
the size of the equipment to achieve the duty is the equip-
ment availability based on the downtime for annualized
throughput rates. Maintenance of crushers and grinding
mills can be broken down into three types:
• Preventative—planned maintenance program to pre-
vent catastrophic failure of the equipment
• Predictive—requires continuous equipment moni-
toring while in operation to prevent unplanned
downtime.
• Reactive—Run to failure or ‘don’t fix it if it isn’t bro-
ken’ maintenance thinking. This type of maintenance
incurs unplanned downtime, impacting production.
Table 1 and Table 2 highlight the various components
of the crushers, grinding mills, classifiers and bulk handling
systems that require maintenance. Wear components are
parts in direct contact with the ore and slurry. The wear
rate of these parts differs based on the ore type and compo-
sition (such as competency/hardness, abrasiveness, particle
size distribution and moisture percentage). The operation
of various equipment’s mechanical, electrical, hydraulics,
and safety components are similar, such as in crushers,
mills, classifiers, and bulk handling systems. The expected
life-of-components are based on the runtimes (i.e., hours
of operation).
In greenfield design, the wear rates of various wear parts
are benchmarked using historical projects. Table 3 presents
the approximate life of major components for various com-
minution equipment as a function of ore abrasiveness. The
Table 1. Summary of major components in crushers and
grinding mills that require maintenance
Crushers Grinding Mills
Wear parts Liners, mantles,
concaves
Liners, pulp system,
trommel screens
Mechanical Gears, shafts, bearings, fasteners, gearboxes
Electrical Motors, control panels, wiring, exciters
Hydraulics Oil and filters, pumps, cylinders
Safety Guard rails, emergency stop buttons
not just engineering excellence or design to a pro forma
arrangement.
Crushing and grinding circuits, like any other produc-
tion process, are greatly affected by changes over time since
they are continuous processes in which equipment is sub-
jected to variations in feed characteristics and/or changes
in equipment condition. The variations can be caused by
degrading equipment performance, reducing overall plant
capacity and thus decreasing product quality (Major, 2003
Bengtsson et al., 2009 Itavuo, 2009).
In flowsheet design, the impact of maintenance require-
ments is measured by estimating or calculating equipment
availability based on the planned maintenance of critical
components such as wear parts and lube systems. Major
mechanical and electrical components, such as drive sys-
tems, gear components, windings, etc., are expected to last
for an extended period if these components are monitored
and inspected periodically as part of a preventative mainte-
nance program.
Most primary crushing circuit designs are based on a
75% availability target, and grinding mills use, say, a 92%
availability target. The crushing circuit availability is lower
due, in part, to mine requirements and truck scheduling
rather than matters related to the crushing circuit. Based
on the throughput requirement of the project, the flow-
sheet and comminution equipment are selected and process
buffers, such as stockpiles, bins, and large tanks, are placed
so that stable and consistent production is maintained tar-
get. The sizes of the process buffers and the selection of
the comminution equipment in the flowsheet are mutu-
ally dependent. A small-capacity process buffer may require
the selection of duty standby equipment. In contrast,
the flowsheet may require a large-capacity process buffer
when selecting duty-only comminution equipment. The
optimum selection of the number of comminution equip-
ment and the size of process buffers in the flowsheet is a
function of:
• Incurred capital cost in the project—for junior min-
ing companies, where capital is constrained. A low
capital-cost flowsheet is often preferred.
• Available footprint to build the flowsheet—for
space-constrained areas, the layout of the flowsheet
is pertinent (e.g., Phu Kham)
• Impact on operating cost and greenhouse gas emis-
sions (GHGe)—additional equipment in the flow-
sheet may incur higher operating costs and, as a
result, incur higher scopes 2 and 3GHGe levels
• Commonality of spares and number of parts
required to maintain all equipment in the flowsheet.
Common spares minimize the need for large on-site
warehousing and reduce the risk of logistics-related
delay caused by unexpected circumstances (transpor-
tation risk, geopolitical, and environmental).
DESCRIPTION OF MAINTENANCE PARTS
The selection of the comminution equipment for the duty
in the selected flowsheet depends on its ability to process
ore with specific ore characteristics (competence, hardness
and abrasion index) at the desired throughput and the tar-
get product size distribution. A key factor in the selection of
the size of the equipment to achieve the duty is the equip-
ment availability based on the downtime for annualized
throughput rates. Maintenance of crushers and grinding
mills can be broken down into three types:
• Preventative—planned maintenance program to pre-
vent catastrophic failure of the equipment
• Predictive—requires continuous equipment moni-
toring while in operation to prevent unplanned
downtime.
• Reactive—Run to failure or ‘don’t fix it if it isn’t bro-
ken’ maintenance thinking. This type of maintenance
incurs unplanned downtime, impacting production.
Table 1 and Table 2 highlight the various components
of the crushers, grinding mills, classifiers and bulk handling
systems that require maintenance. Wear components are
parts in direct contact with the ore and slurry. The wear
rate of these parts differs based on the ore type and compo-
sition (such as competency/hardness, abrasiveness, particle
size distribution and moisture percentage). The operation
of various equipment’s mechanical, electrical, hydraulics,
and safety components are similar, such as in crushers,
mills, classifiers, and bulk handling systems. The expected
life-of-components are based on the runtimes (i.e., hours
of operation).
In greenfield design, the wear rates of various wear parts
are benchmarked using historical projects. Table 3 presents
the approximate life of major components for various com-
minution equipment as a function of ore abrasiveness. The
Table 1. Summary of major components in crushers and
grinding mills that require maintenance
Crushers Grinding Mills
Wear parts Liners, mantles,
concaves
Liners, pulp system,
trommel screens
Mechanical Gears, shafts, bearings, fasteners, gearboxes
Electrical Motors, control panels, wiring, exciters
Hydraulics Oil and filters, pumps, cylinders
Safety Guard rails, emergency stop buttons