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How obsolete?
Integration of the crushing and
screening plants within the ambit of mining activities is on the rise.
This is more so with in-pit crushing and on-site boulder handling and
eliminating blasting to a maximum extent on the face. Still the
involvement at middle and lower levels on these process equipment is not
as acute in drilling, blasting, loading and hauling. In many cases the
operations up to the crusher hopper and beyond are managed separately.
For a successful end to end operation awareness of the inter-dependence
is very necessary.
How much a new entrant is then aware of the constraints that could
affect the sequence of production functions? Perhaps the understanding
of issues that caused the stoppage or delays in earlier plant without
much protection or instrumentation could focus on the areas where things
have improved or still required more attention. The cycle times are not
meaningful if the hopper does not accommodate the input to the required
flow levels. This is even more pronounced when the operation is
scheduled as continuous and designed to run continuously without
interruption in which case the maintenance time calls for greater care
and understanding of the plant.
Everyone is aware that flow of material is the determining factor and
this is easily said than done on account of any number of variables in
the loading, hauling, dumping or crushing operations. This guideline or
rather a check point listing highlights some areas that cause
interruptions and need attention and precautions. The checklist covers
the crushing plants and conveyors since these are not under the scope of
mining in many cases.
SCREENING AND CRUSHING:
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Breakage of safety pins and replacement of pins and bushes
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Presence of external bodies coming out in
the system like metal plates etc.,
-
Bearing housing bolts failure
-
Damage to grate bars
-
Start up system delays
-
Boulder jams in the hopper
-
Chute jams
-
Improper unloading resulting in spillage
outside the crusher hoppers or passage
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Overloading of feeders
-
Flywheel alignment
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Voltage fluctuations
-
Holes in chute plates requiring welds
-
Mismatching of feeder and hopper
feeds
-
Mismatching of feeder and hopper
feeds
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Hammer failures including wear-outs
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Pitman collar requiring attention
-
Wet material
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Heating up of main bearings
-
Chute plates falling down
-
Push feeder shaft breakage
-
Flywheel bush failure
-
Secondary crusher sleeve bolt failure
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Secondary crusher tripping
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Alignment of motors
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Screen jamming
BELT CONVEYORS:
-
Condition of the belt and change cycle. Repairs requiring
stoppage of belt to prevent further damage
-
Slipping of belts
-
Overloading of belts bypassing feed
control
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Turning of belts
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Failure of “bold-backs”
-
Failure of roller sets
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Clearing drum spillage and accumulation
It would be an advantage to be present when the maintenance cycle is on
and also while the start up operations are on. It may be surprising to
note even where self lubricating and totally enclosed conveyor drives
and idlers are installed, the material flow gets retarded when care is
not taken around the tail drums, skirt-boards, chutes and screens. The
main hopper is being prominently visible and since the haul cycle is
directly affected, gets immediate attention generally but technology
brings in over confidence and then small accumulations develop forcing
attention and resulting stoppage.
While the objective of this note is not for discussing maintenance
points and detailed operational tune up, the above is a list of failures
actually observed at different locations and the analysis of these
points led to improvement and preventive maintenance as well as
strengthening. A budding mining engineer will do well to keep a starting
point as each plant has its own design, functions, and limitations as
seldom plants work to the design levels or theoretical available timings
in a mining related plant and the most practical available time is MAT
factor. This factor could be the starting point for analysis and would
yield startling facts often gone unnoticed and result in tangible
improvements and also generate interest in the overall working.
End Note:
It is prudent to go through the literature provided by the manufacturers
and recommendations.
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