SELF ALIGNING BALL BEARINGS
Self aligning ball bearings are non-separable double-row bearings, each set of balls rotate within a single outer ring spherical raceway.
There are various types of aligning ball bearings :
Self aligning ball bearings with tapered bore adapter sleeves
Self aligning ball bearings with extended inner rings
Both rows of balls rotate, in parallel, within the spherical outer ring. This allows an excellent alignment compensation caused by machining and mounting errors, between the shaft and housing. This gives the bearing a self aligning feature to overcome misalignments, shaft deflections and housing variations. They are suitable for medium radial loads and low axial forces. Self aligning ball bearings, between all the rolling bearings, it is the one that has the lowest friction and this allows the bearing to operate without heat even in the presence of high speeds.
The aligning ball bearings are available in cylindrical or conical inner holes, with contact seals incorporated, identifies with the suffix 2RS or K-2RS.
Bearings with the suffix 2RS have a limited speed index because of the additional heat generated by the rubbing of sealing lips. For this reason, the maximum speed should not exceed 2/3 of the recommended speed for open bearings lubricated with grease.
The standard material used for contacting seals is a wear-resistant synthetic rubber (NBR).
When selecting self aligning ball bearing with contacting seals fitted, consideration must be given to the reduction of their maximum operating speeds and their limited misalignment abilities.
Self aligning ball bearings are produced to normal tolerance class ( PN ) as standard.
For the internal clearance group of self aligning ball bearings distinction is made between bearings with cylindrical or tapered bores.
Because of the risk of applying a preload force to the bearing during mounting, bearings with tapered bore feature a larger radial internal clearance when compared to cylindrical bore bearings of the same clearance group.
Self aligning ball bearings with cylindrical or tapered bores are produced with normal internal clearance (CN) as standard.
Self aligning ball bearings to operate properly require a certain minimum load.
For ITS Italia the minimum load must be greater than 2% of the dynamic load coefficient.
Small and medium sized self aligning ball bearings are fitted with polyamide cages or rather pressed steel cages as standard. Larger sizes are fitted with solid brass cages.
Several types and sizes of self aligning ball bearings are also produced with polyamide cages fitted.
Self aligning ball bearings are used in the following application:
When should be fixed on a cylindrical shaft, bearings with tapered bore are used adapter sleeves , which facilitate the assembly and disassemble. The adapter sleeves do not require shaft axial anchoring devices. Sleeves are cut and are provided with lock rings and safety devices.
When using tapered bore bearings with adapter sleeves the time consuming and expensive fine machining of the bearing seats may be avoided for applications where less running accuracy is required. Adapter sleeves are equipped with washer that has a protrusion on the side of the bearing, which is necessary to avoid possible damage of the seal.
Using adapter sleeves aligning ball bearings may be mounted directly onto drawn or fine turned shaft seats. In applications where self aligning ball bearings are mounted on straight shafts without additional axial supports, their ability to accept thrust loads is limited by the amount of friction between adapter sleeve and shaft.
Another design is self aligning with extended inner rings. These bearings are use in applications with low requirements, where there are provided shafts obtained by wire drawing ( drawing - trafilatura). Special bore tolerances ensure easy assembly and disassemble.
Bearings are fixed axially on the shaft with a pin or a screw inserted in the hollow provided on an inner side of the ring and which also prevents the rotation on the shaft. When a shaft is mounted on two of these bearings,hollows obtain in the inner rings must be subjected opposite one another or in the opposite position.
Otherwise the shaft must be axially constrained in one direction only.