Introduction
The most common task is replacing crushing hammers. This can be heavy work – depending on the size of the Rockertooth, hammers can range in weight from roughly 40lbs to 140lbs each (18kg to 163kg each). The front panel for accessing the crusher rotor can also be quite heavy. For this reason, it is highly advisable to incorporate some sort of overhead lifting arrangement in the area of the crusher to minimize the risk of injury to service personnel and to facilitate the replacement of hammers in general.
Safety first
With any equipment maintenance task, it cannot be stressed enough that the first and most important step is to follow proper lockout/tagout/tryout procedures. If there is any doubt regarding these procedures, contact your supervisor or safety officer.
The second – and also very important – step is to understand the task. Be sure you are aware of the process and parts involved with the service you are to complete, as well as the potential risks and how to minimize them.
Changing the hammers
Gaining access
Hammers are accessed through the front door assembly on Rockertooth Crushers. The front door assembly is opened by removing the bolts that secure the front door assembly to the upper enclosure. Once the door is free, it is rotated from its closed position to its open (horizontal) position. Depending on the options selected with the Rockertooth Crusher, it may have a manually operated hydraulic door opening arrangement, such as in the video below.
If such an opening system is not present, an overhead lifting system will be necessary to lower the door into its open position, as front door assemblies on Rockertooth Crushers are rather heavy due to the inherent robustness in design and are very difficult to move manually on smaller machines. It is not possible to move these front door assemblies manually on the larger machines.
Hammers and hammer rods
Once the front access door is open, the crusher rotor, along with one or two rows of hammers is visible. Each row of hammers is held in the rotor by two hammer rods. The first hammer rod serves as the pivot point for hammer movement (rocking). The second hammer rod sets the limit for how far out of the rotor that the hammer can extend. Hammers can be removed from the crusher rotor without removing the second hammer rod since the retaining notch on the hammer simply slides under the second hammer rod.
To remove a row of hammers, select the row of hammers to start with, and manually rotate the crusher rotor carefully into a position in which the hammer rod serving as the pivot for the row you will remove is oriented in the open area in the housing. Once the rotor is in position, it should be secured in this position until the row of hammers is removed.
With the rotor secured, a strap or similar device connected to the overhead lifting mechanism will need to be attached to the first hammer that will be removed. The first hammer removed should be the end hammer closest to the drive side to the machine, since the hammer rod will be withdrawn from the opposite drive side of the machine. Apply enough tension to the strap holding the hammer to prevent it from falling clear of the crusher rotor, and then remove the retaining caps from the pivot hammer rod corresponding to the row of hammers to be removed. Withdraw the hammer rod only far enough to clear the first hammer, which will now be entirely supported by the strap. Remove this hammer from the machine and maneuver it to a suitable location near the machine where it can be accessed for later disposal.
Return to the crusher and attach the strap to the next hammer in the row being removed and apply tension. Withdraw the hammer rod far enough to free the next hammer, and move this hammer to the used hammer collection point. Continue until all hammers in a row have been removed.
Next, manually rotate the crusher rotor until the next row of hammers to be removed is oriented in the opening, and re-secure the rotor. Hammers for this row are removed in the same manner as described for the first row. Continue until all rows of hammers have been removed from the machine.
Hammers are replaced in the opposite manner as described for removal. The crusher rotor will be secured in position from the last row of hammers that were removed, so this will be the first row of hammers that will be installed. A new hammer is connected to a strap and maneuvered into position at the crusher rotor. The first hammer to be installed will be the hammer at the end of the row opposite the drive side, since the hammer rod will be installed from that side. With the hammer in position, the hammer rod is inserted into the crusher rotor, passing through the eye of the hammer and through to the next section of rotor so that the hammer being installed will be fully supported on the pivot hammer rod. Be sure that the notch at the opposite side of the hammer is tucked under the second hammer rod so that the new hammer is captured within the rotor.
Continue positioning hammers and advancing the hammer rod until the entire row of hammers is installed. Rotate the rotor to the next hammer row and secure it in position. Install the next hammer row in the same manner as described for the first row, and continue until all hammer rows have been replaced.
Returning to service
Once all hammers have been replaced, verify that all tools and equipment are clear of the inside of the crusher and rotate the front access door up into its closed position. Replace the bolts that secure the door to the upper enclosure. Verify that the area around the crusher and its drive equipment is clear, and then re-energize the machine so that it can be restarted.
Changing the crushing screens and bars
Depending upon the configuration of the Rockertooth Crusher in question, the crushing deck may be comprised of either crushing screens (cassettes) or bars and racks. Regardless of the configuration, the basic procedure is the same.
Gaining access
Start by opening the front access door, as described above in the hammer replacement section. Since replacing screens and bars requires more access to the machine than replacing hammers, the upper rear potion of the crusher will also need to be removed. Remove the bolts from the upper rear enclosure section, attach a strap to the section and lift it away from the crusher. Place the upper rear section in a convenient location that will not interfere with work in the crusher until the machine will be reassembled.
Screens and bars
Screen and bar assemblies are held in position by retaining blocks. One retaining block is located on either end of the machine, and each retaining block is secured by two fasteners: one fastener on each side. Remove these fasteners, as well as the retaining blocks, and set both the fasteners and the retaining blocks aside until it is time for reassembly. At this point, the outermost screen or bar assembly is visible at both ends of the crusher. Attach a strap, hook, plate grab, etc. to a screen or bar assembly and pull it up out of the crusher using the overhead lifting arrangement. Continue connecting to and removing screen or bar assemblies until all screen or bar assemblies have been removed from the machine.
Install screen or bar assemblies by maneuvering them one by one into position at the crusher, and alternate tapping them on each side to work them down into the machine. Continue adding screen or bar assemblies until all assemblies have been installed. It should be noted that in the case of bar assemblies, individual bars will need to be placed into the racks (side pieces) as the bar assemblies are installed into the crusher.
After all screen or bar assemblies are installed, the retaining blocks can be fastened into place, securing the crushing deck components.
Returning to service
Once the crushing components have been secured with the retaining blocks, verify that all tools and equipment are clear of the inside of the crusher and reinstall the upper rear enclosure section. Then, rotate the front access door up into its closed position. Replace the bolts that secure the door to the upper enclosure. Verify that the area around the crusher and its drive equipment is clear, and then re-energize the machine so that it can be restarted.
Despite being heavy work, replacing hammers and/or crushing deck components is a relatively straightforward process. With some practice, a maintenance crew can safely and efficiently replace these components.
