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.
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.
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.
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.
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.
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)