Cylindrical roller bearings give the highest radial capacity of the common separable designs. They consist of one outer ring, one inner ring and one roller and cage assembly, and in the basic form they cannot support axial load at all.
NU N NJ And NUP
The letter code describes which ring carries ribs, and therefore which axial loads the bearing can take.
- NU — ribs on the outer ring only. Purely radial, free to float axially.
- N — ribs on the inner ring only. Purely radial, free to float axially.
- NJ — locates the shaft in one direction.
- NUP — locates the shaft in both directions.
A common arrangement uses one NU as the floating bearing and one NUP or a separate thrust bearing as the located one.
Separability And Mounting
Because the roller and cage assembly separates from one ring, the two rings can be mounted independently. This is a real advantage on heavy shafts, and a real risk if the roller set is pushed into the ring off square, which scratches the raceway before the machine has ever run.
Full Complement And Double Row
Removing the cage and filling the annulus with rollers raises radial capacity substantially and lowers the speed limit just as substantially. The SL01, SL04, SL18 and SL19 series follow this principle, and are used where a caged bearing no longer carries the load in the available section.
Double row types such as the F- and Z- series appear in gear units and traction drives, where two rows share load in one housing.
Clearance
Cylindrical roller bearings are sensitive to residual clearance. Interference on the inner ring expands it and consumes clearance, and so does the temperature difference between inner and outer ring in service. C3 or C4 groups are specified in electric motors and gear units for exactly this reason.
