JFK NK – NKI Needle Roller Bearings
NK / NKI series
- Reduced radial section
- With or without inner ring
NK and NKI needle roller bearings are radial bearings with a very low cross-section and high load capacity. Compared with ball bearings of the same bore diameter, the high number of rollers and the line contact with the raceways ensure significantly higher radial load capacity. The two versions differ in the inner ring: NK bearings are supplied without an inner ring and operate directly on the shaft, which must be hardened and ground; NKI bearings include a stamped inner ring and can also be mounted on untreated shafts.
JFK Group supplies both NK and NKI bearings with lubrication holes on the outer ring as standard. Each JFK needle roller cage is made of stamped steel and is available in a standard version and with specific suffixes for sealing and lubrication variants.
NK and NKI needle roller bearings are typically used in gearboxes, actuators, compact high-load systems, and applications where radial space is the primary constraint.
Versions
Two versions: how to choose the right NK or NKI needle roller bearing
The choice mainly depends on the shaft characteristics. The NK version requires a hardened and ground shaft surface that acts as the inner raceway; the NKI version includes an inner ring and can be used on untreated shafts.
NK Needle Roller Bearings
Without inner ring · Minimized cross-section · Hardened and ground shaftWithout inner ring. The rollers run directly on the shaft surface, which must be hardened and ground with suitable tolerances and surface roughness. The cross-section is minimized for a given bore diameter, maximizing load capacity within the available space. Supplied with lubrication holes on the outer ring as standard.
NKI Needle Roller Bearings
With inner ring · Untreated shafts · Simplified mountingWith stamped inner ring. They allow use on untreated cylindrical shafts, simplifying the design and reducing shaft machining costs. The cross-section is slightly larger than the NK version due to the inner ring. Supplied with lubrication holes on the outer ring as standard.
Performances
Design and performance features
Minimum cross-section and line contact between rollers and raceways for high radial load capacity in the smallest installation space.
High load capacity · High radial load capacity
The linear contact between rollers and raceways ensures significantly higher radial load capacity than ball bearings with the same bore diameter. Needle roller bearings are suitable for high radial loads even in limited installation spaces.
Low and medium rotational speeds
Needle roller bearings are suitable for low and medium speeds. For higher speeds, drawn cup needle roller bearings or ball bearings should be considered.
Minimum radial cross-section
The very low cross-sectional height makes them the ideal solution when radial space is the primary constraint. The NK version has an even smaller cross-section compared to the NKI version.
Hardened and ground · NK: hardened and ground · NKI: untreated
The NK version requires a hardened and ground shaft with suitable tolerances and surface roughness, acting as the inner raceway. The NKI version includes the inner ring and does not require shaft treatments.
Lubrication holes on the outer ring
Supplied with lubrication holes on the outer ring as standard for periodic relubrication. Lubrication is required to ensure the expected performance and service life.
Stamped steel
Pressed steel cages are standard on both versions.
Mounting
Mounting of NK and NKI Needle Roller Bearings
NK needle roller bearings are mounted directly on the shaft, which acts as the inner raceway. The shaft surface must be hardened and ground with suitable tolerances and surface roughness. NKI needle roller bearings are mounted with interference fit on the shaft through the inner ring. Lubrication must be ensured before commissioning and periodically during operation.
Mounting methods
- NK: Mounting on hardened and ground shaftThe outer ring with the roller and cage assembly is positioned directly on the treated shaft. Before mounting, verify that the shaft surface meets the required tolerances and surface roughness specifications.
- NKI: Mounting on the shaft through the inner ringThe stamped inner ring allows press fitting onto an untreated cylindrical shaft, using a mounting tool that applies the force directly to the inner ring. Never apply mounting force through the rollers.
Technical data
- Standard tolerance
- Normal (PN)
- Shaft for NK version
- Hardened and ground
- Shaft for NKI version
- No shaft treatments required
Applications
Applications
Components and application support for every industrial environment.
Industrial automation
Compact gearboxes and actuators with high radial loads and limited radial space. The NKI version simplifies the design by eliminating the need for shaft hardening and grinding.
Transmissions and axles
Transmission systems with high radial loads in compact spaces. Their higher load capacity compared with ball bearings makes them suitable also for applications with intermittent load cycles.
Metal Fabrication / Machining Industry
Machine tools and positioning systems with high radial loads in limited spaces. The minimum cross-section of the NK version maximizes load capacity within the available installation space.
Construction Equipment
Actuators and motion systems with high radial loads under demanding operating conditions. The robust design and higher load capacity compared with ball bearings ensure reliability even in the most severe applications.
Automotive / Motorcycles, Trucks & Buses
Components for suspension, transmission and linkage systems designed for intensive duty cycles, vibration and compact spaces.Technical documents
Contacts
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