NSK has introduced a range of full-complement cylindrical roller bearings for highly demanding steel industry applications. NUB series bearings are designed to be particularly effective when used on the non-driven side of strand guide rolls; for example, in the straightening section of continuous casting machines.
Located directly after the bending process, the straightening section of continuous casting machines facilitates transition to the roller tables for cooling newly-cast metal slabs before moving them along for additional processing. The clear principle of a continuous casting machine is to ‘keep moving’ so that yield, productivity and cost-efficiency can all be maximised. With this in mind, the conveyor keeps driving the strand forward, day-in, day-out, which is why the bearings are so process-critical.
Challenging environmental conditions are prevalent in steel industry applications such as these. For instance, not only are the bearings subjected to elevated mechanical stress, but they must be able to cope with cooling water in both liquid and mist form. In addition, the very low speeds (less than 10 rpm) of the roller table drives can be problematic for traditional spherical roller bearings as their design imposes very demanding lubrication requirements. Increased wear on rolling parts can be expected when speeds drop below a certain threshold.
Despite these challenges, steel plants demand long service life with no unplanned downtime and minimal maintenance costs, which is why NSK launched into developing its NUB series of cageless cylindrical roller bearings. To help maximise service life, the characteristics of these bearings include low friction and excellent rolling contact self-alignment. It is possible to compensate for any thermal expansion of the strand guide rolls, as misalignments as large as 12 angular minutes have no effect on the successful operation or service life of NUB series bearings.
In contrast to conventional spherical roller bearings, pure rolling friction occurs in NUB bearings thanks to predominant line contact in the raceway. Friction is therefore low and wear is reduced. Straightforward installation is another benefit whereby a simple snap-ring is used to attach the inner ring.
Compared with the previous product series, NSK’s NUB series bearings are able to treble service life, even when faced with the demanding environmental conditions of strand guide rolls in continuous casting machines. For this reason, the bearings help facilitate cost-effective, continuous and highly productive steel manufacturing.