Shutting
down a primary gyratory crusher for relining requires careful planning. The
entire shutdown process—from cleaning out the pit to the final relining
steps—can take days and, in some cases, up to a week.
Many of the
tasks involve safety concerns that need to be examined and mitigated. To
mitigate some of these problems and speed up the overall relining process,
there are four solutions to consider. Each has advantages in terms of safety
improvements and reducing downtime, but they also carry certain costs that need
to be evaluated. Below is a quick overview of the benefits of these options.
Double tier concaves for quick gains in PG
relining
The outer
lining of a typical gyratory crusher consists of individual pieces
called concave segments; each one of these needs to be lifted separately during
installation and/or removal. A 60-89 gyratory crusher has a standard lining of 6 tiers of
concaves that need to be changed during a planned shutdown event. Normally, all
the concaves would be removed piece by piece and new concaves installed.
However,
switching to concave segments with a different design is a quick way to reduce
both downtime and maintenance. The double-tier concave segments are twice as
high as regular linings. This translates to 50% fewer consumable parts to be
changed, and ultimately reduces exposure to risks for the crews performing the
reline. The same relining methods are used for double tier concaves, so no
additional tooling is required. The double tier components can be slightly more
difficult to manipulate; however, the plusses often far outweigh any challenges
in handling the longer and heavier components.
Carousel and removal trays to cut installation
time
For further
improvements, using handling tools to manipulate both the worn and new concave
segments for removal and installation can bring even further gains. In a large
primary gyratory, there can easily be 80 concave segments to lift out and
replace (4 tiers with 20 segments per tier). Not only is each individual lift a
safety risk, but it is also time consuming as the pieces are lifted one by one.
For
removals of the older worn concaves, an entire tier of segments can be lifted
at the same time using concave removal trays. This significantly cuts down on
the number of lifts required. In the example with 80 concave segments, this
would cut the number of lifts from 80 to 4. The same logic applies to using a concave carousel for the installation of the new
tiers of concaves. The carousel can be used to install an entire tier of
replacement concaves, thereby also reducing the number of lifts from 80 to 4
for the entire installation sequence. By reducing the number of lifts, risk
exposure and maintenance times are reduced.
In terms of
overall time, using these two handling systems in combination typically cuts
reline time in half. Each carousel and removal tray is custom designed to fit
the specific PG model and chamber profile. Investing in these tools carries
initial investment costs but pays itself back with increased uptime as well as improving
safety thanks to the reduced number of lifts.
Maximizing primary gyratory uptime with rotable
top shells
For
customers who require the highest levels of availability from their Primary
Gyratory, there is a third option to consider. Rotable top shells are complete
shell segments relined in advance (either on or off-site) and ready to be
installed once the existing shell segments are removed with their worn concaves
still in place.
This
solution saves time as you do not need to install the concaves during the
planned shutdown, and fewer components are being manipulated during the outage
period. It is no longer necessary to transport and place work platforms in the
crusher and maintenance can be done in a more controlled and safer environment.
During the shutdown, the shells are separated and lifted (optionally with
hydraulic shell separators) and replaced with the relined shells.
Compared to
a typical shutdown period, using the rotable top shell concept can provide a
reduction in downtime. Using rotable top shells significantly reduces the time
needed to reline as well as requiring fewer labor hours and offering
improvements in safety by reducing the likelihood of incidents or risks to
personnel. However, the flip side of the coin is that additional shell segments
are needed which carry capital costs and also involve lifting capacity
considerations.
Tools are only as good as the crews using them
A final
factor to consider is whether hiring a reline crew to perform the shutdowns can
bring further benefits. Metso Life Cycle Services (LCS) contracts often make
use of the above solutions, while also utilizing tools such as SMED (Single
Minute Exchange of Dies) analysis, which looks at each task within a shutdown
to determine where delays are taking place to help determine where time savings
can be made. Over the course of the contract, shutdown times often continue to
decrease as the SMED is a continuous improvement process always looking for
delays to be eliminated.
Making the right choice
Each of the
above solutions can help to make significant improvements in reducing shutdown
times for concave replacement. Comparing the cost considerations for each
option versus the potential savings is an exercise that needs to be performed
in order to make the decision that will bring the highest operational gains for
your specific site and application.
(By Alex Merklein, Maintenance and Planning Engineer, Field Services, Metso)