Designs and variants
Needle roller bearings with machined inner and outer rings
Needle roller bearings with a machined outer ring, without an inner ring
- are an excellent choice for compact bearing arrangements if the shaft can be hardened and ground (fig. 3)
enable a larger shaft diameter and a stiffer bearing arrangement compared to arrangements with bearings with inner rings
Axial displacement of the shaft relative to the housing is only limited by the width of the raceway on the shaft. By machining the shaft raceways to the appropriate dimensional and geometrical tolerances, it is possible to obtain bearing arrangements with tighter geometrical tolerances. For additional information, refer to Raceways on shafts and in housings.
- are available open (without seals) or sealed on one or both sides
- are available with or without an inner ring
with D ≤ 17 mm (Fw ≤ 10 mm), are available with non-separable closure rings that act as flanges (fig. 4)
The flanges on larger bearings are an integral part of the outer ring, and the bearings have an annular groove and one or more lubrication holes in the outer ring (fig. 5).
are generally designed as single row bearings, with the exception of RNA 69 (fig. 6) and NA 69 series double row bearings with D ≥ 52 mm (Fw ≥ 40 mm)
The roller and cage assembly and outer ring of a needle roller bearing with flanges form a non-separable unit.
Needle roller bearings with machined rings, without flanges
are separable, i.e. the outer ring, needle roller and cage assembly, and inner ring, can all be mounted separately (fig. 7)
Needle roller and cage assemblies can, depending on the arrangement design, either be mounted:
- together with the outer ring
- together with the shaft
- together with the inner ring
- between the outer ring and shaft or inner ring as the final step
are generally designed with one needle roller and cage assembly
However, wide sizes incorporate two needle roller and cage assemblies immediately adjacent to each other and have an annular groove and a lubrication hole in the outer ring (fig. 8).
To accommodate combined radial and axial loads, needle roller bearings with machined rings can be combined with a needle roller thrust bearing with a centring flange, AXW series, if the outside diameter D of the radial bearing is equal to the flange diameter D1 of the thrust bearing (fig. 9, fig. 10).For additional information, refer to Needle roller thrust bearings.
- are available in the (R)NA 49 series with a contact seal made of NBR (effective at keeping the lubricant in and contaminants out of the bearing) on one (fig. 11) or both sides (fig. 12)
- have an inner ring that is 1 mm wider than the outer ring, which maintains the effectiveness of the seals and simplifies the bearing arrangements even when small axial displacements occur
When capped bearings must operate under certain conditions, such as very high speeds or high temperatures, some grease may leak. For bearing arrangements where this would be detrimental, appropriate actions could be taken.
Associated external seals
- can be used for needle roller bearing arrangements (without an inner ring)
can be supplied in various sizes (→ product table)
For information about associated power transmission seals, refer to Seals.
The relatively large quantity of grease in the bearings means they can be operated for long periods before relubrication is required (→ Perform calculations). SKF recommends SKF LGWA 2 grease (table 1), if relubrication is required.
SKF supplies needle roller bearings with different features to facilitate efficient lubrication and relubrication.
Needle roller bearings with machined rings:
with flanges and D ≥ 19 mm (F, Fw ≥ 12 mm)
- have an annular groove and, depending on the bearing size, one or more lubrication holes in the outer ring (fig. 5)
- with seal(s)
double row and without flanges
- have an annular groove with one lubrication hole in the outer ring (fig. 8)
without flanges and with an inner ring
- have one lubrication hole in the inner ring for certain sizes (→ product table)
SKF needle roller bearings with machined rings are fitted with one of the cages shown in table 2.
Double row needle roller bearings with machined rings are equipped with two cage assemblies (fig. 6).
When used at high temperatures, some lubricants can have a detrimental effect on polyamide cages. For additional information about the suitability of cages, refer to Cages.