In a tandem cold mill, the exit section is equipped with carousel reels, installed to maintain continuous operations. As one of the mandrels has a coil wrapped around it and is then discharged, the next coil begins to wrap around the second mandrel. Each of these mandrels is subject to high loads and high rotational speeds as the coil is wrapped. Under these conditions, mandrels require regular maintenance and replacement of consumable parts.
Simplifying Maintenance
When looking at standard maintenance practices for mandrels, worn parts often need re-machining or even complete replacement. The process involves disassembling the casing or large portions of the carousel reel. Moreover, the placement of the reel above the coil car pit also places plant employees in difficult situations to perform such maintenance tasks. Additionally, during maintenance, the entire line is stopped, leading to a loss in productivity.
Thus, Primetals Technologies developed the “plug-in” type mandrel. The new mandrel design allows the mandrel to be inserted and removed from the casing without disassembly. The plug-in type mandrel uses a hollow shaft to create a dual structure, with gears and bearings mounted on it. This enables mandrel removal without casing disassembly. Removing the entire mandrel means maintenance tasks can be performed while spare mandrels are inserted, keeping production going. Moreover, this innovation improves maintenance time, improving production performance.
Safe Replacement
As the plug-in type mandrel brings significant benefits, concurrently, Primetals Technologies has also developed a motor-driven cart to move the mandrel into a position where it is accessible by an overhead crane. Given that the setup in and around the exit section of the tandem cold mill does not allow for the removal of the mandrel via crane, the motor-driven cart accesses the carousel when necessary. This is achieved through rails that come into play during replacement procedures, allowing the cart to move to the carousel and remove the mandrel.
Accommodating the newly designed mandrel, a transportation cart supports with the maintenance process.
Plug-in Innovation
The plug-in type mandrel improves on conventional maintenance practices for mandrel replacement and repair on tandem cold mills. This article introduced the application of the plug-in type mandrel to carousel reels in cold rolling. By replacing traditional mandrels with plug-in type mandrels, steel producers benefit from an estimated reduced downtime—from approximately 28 hours to 16 hours (estimated)—, including the ability to prepare and repair spare mandrels during regular operations. Furthermore, the plug-in type mandrel improves safety by allowing maintenance work to occur far from the coil car pit. Therefore, the plug-in type mandrel technology enhances operational reliability and contributes to more stable operations in tandem cold rolling mills.
