Technical Foundation
What Is a Cylindrical Roller Bearing?
A cylindrical roller bearing carries radial load through line contact between straight cylindrical rollers and the bearing's inner and outer raceways, rather than the point contact a ball bearing makes — this line contact spreads load over a larger contact area, giving cylindrical roller bearings substantially higher radial load capacity than a ball bearing of the same bore size, at the cost of essentially no axial (thrust) load capacity in most configurations. ISO designations (NU, NJ, NUP, N) describe the flange arrangement on the inner and outer rings, which determines whether the bearing can locate the shaft axially at all, or purely floats radially while another bearing elsewhere on the shaft handles axial positioning.
NU-type bearings have no flanges on the inner ring, so the inner and outer rings can displace axially relative to each other — used as the 'floating' bearing in a shaft system to accommodate thermal expansion. NJ-type bearings have one flange, providing limited one-direction axial location, and NUP-type combines a fixed flange with a separate loose ring to provide axial location in both directions while remaining a predominantly radial-load bearing. Double row and full-complement (no cage, maximum roller count) configurations increase radial capacity further for the heaviest loads, at the cost of a somewhat lower maximum speed rating than a caged single-row bearing.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| ISO Series/Flange Type | NU, NJ, NUP, N — differ by inner/outer ring flange arrangement | Determines whether the bearing can axially locate the shaft or only floats radially |
| Bore Size | Metric, per ISO bearing bore/OD/width standard | Standard interchange sizing — must match shaft diameter exactly |
| Row Configuration | Single row, double row, full complement | More rows/full complement increase radial capacity but lower maximum speed rating |
| Radial Load Capacity | Dynamic and static load ratings, per manufacturer catalog | Cylindrical rollers give higher radial capacity than equivalent-bore ball bearings |
| Cage Material | Steel, brass, polymer (or cageless/full complement) | Affects maximum speed rating and lubrication requirements |
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Applications
Where Cylindrical Roller Bearings Get Used
Cylindrical roller bearings are specified wherever radial load capacity exceeds what an equivalent-bore ball bearing can support, and axial load is either absent or handled by a separate bearing on the shaft.
Gearbox & Speed Reducer Shafts
NU and NJ series bearings supporting high radial load gear shafts in industrial gearboxes.
Electric Motor & Generator Bearings
Cylindrical roller bearings on larger motor and generator shafts where radial load exceeds ball bearing capacity.
Rolling Mill & Heavy Machinery
Double row and full complement bearings carrying the extreme radial loads found in steel mill and heavy processing equipment.
Machine Tool Spindles
High-precision cylindrical roller bearings supporting radial loads on machine tool spindle assemblies.
Rail & Traction Equipment
Heavy-duty cylindrical roller bearings in railway axle and traction motor applications.
FAQ
Cylindrical Roller Bearings Questions, Answered
What's the difference between NU, NJ and NUP cylindrical roller bearings?
NU-type bearings have no flange on the inner ring, allowing the inner and outer rings to move axially relative to each other — used as a 'floating' bearing to accommodate shaft thermal expansion. NJ-type has one flange on the inner ring, providing axial location in one direction only. NUP-type combines a fixed flange with a separate loose locating ring, providing axial location in both directions, making it usable as a 'fixed' locating bearing while still primarily a radial-load bearing.
Why choose a cylindrical roller bearing over a ball bearing?
Cylindrical rollers make line contact with the raceway rather than the point contact of a ball, distributing load over a larger area — this gives significantly higher radial load capacity at the same bore size. The trade-off is that most cylindrical roller bearing types carry little to no axial (thrust) load, so where radial load dominates and axial load is minimal or handled by another bearing, cylindrical rollers are usually the better choice.
Can a cylindrical roller bearing handle axial (thrust) loads?
Generally no, or only very limited amounts, depending on the flange configuration — NU-type carries essentially none, while NJ and NUP types can handle light axial loads in one or both directions respectively due to their flange arrangement. Applications with significant combined radial and axial load typically use a cylindrical roller bearing paired with a separate bearing type (such as a ball or tapered roller bearing) dedicated to axial location.
What does 'full complement' mean, and when is it used?
A full complement bearing has no cage separating the rollers, packing in the maximum possible number of rollers around the raceway — this maximizes radial load capacity for a given bearing size, at the cost of a lower maximum speed rating and generally requiring more attentive lubrication since there's no cage to help distribute lubricant evenly between rollers. It's specified for slow-speed, very heavy radial load applications.
How do I select the right bore size?
Bore size must match the shaft diameter exactly per the standard ISO metric bearing dimension series — cylindrical roller bearings follow the same standardized bore/OD/width numbering as most other rolling element bearings, so a bearing's designation number can be cross-referenced to confirm exact bore, outside diameter and width before ordering.
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