In brief
A cylindrical roller bearing is a rolling bearing with cylindrical rollers that carries very high radial loads and permits high speeds.
Contents
What is Cylindrical roller bearing?
In a cylindrical roller bearing, cylindrical rollers roll in line contact between the inner and outer rings. As a result, they carry considerably higher radial loads than ball bearings of the same size. Most designs are separable: one ring with the roller set and cage can be separated from the other ring, which makes mounting and dismounting easier, for example with interference fits.
The designs differ in the position of the ribs. In type NU, the outer ring has two ribs and the inner ring none, so the shaft can move axially. The bearing is therefore suitable as a floating bearing. Types such as NJ or NUP have additional ribs and can accommodate limited axial forces in one or both directions. There are also full-complement bearings without a cage for very high loads at low speeds, as well as double-row and multi-row versions, for example for rolling mills. Key ratings are dimensions, load ratings, rib arrangement, cage material and clearance.
Typical applications are large electric motors, industrial gearboxes, machine tool spindles, rolls in paper and steel mills, and pumps. Damage is often caused by lack of lubricant, skidding under too light a load or edge running due to misalignment.
In practice: maintenance and procurement
In addition to the basic designation, the design, cage version and clearance are decisive, because an NU bearing cannot simply be replaced by an NJ bearing. For separable bearings, the inner and outer rings should be replaced together where possible, unless the manufacturer expressly identifies them as interchangeable.
Synonyms and abbreviations: CRB · NU roller bearing · cylindrical roller radial bearing · roller bearing NU/NJ/NUP
Frequently asked questions
What do NU, NJ and NUP mean for cylindrical roller bearings?
The codes describe which ring has ribs. NU: two ribs on the outer ring, inner ring without ribs, freely displaceable axially. NJ: additionally one rib on the inner ring, axial guidance in one direction. NUP: inner ring with a fixed rib and a loose rib washer, axial guidance in both directions. This determines whether the bearing works as a floating or locating bearing.
When is a cylindrical roller bearing used instead of a ball bearing?
When high radial forces have to be absorbed in a small installation space, for example on the drive end of large motors with belt or pinion drives, or in gearboxes. However, cylindrical roller bearings require a minimum load, otherwise the rollers can skid and damage the raceways. Under light loads, a ball bearing is often the better choice.
What information is needed to replace a cylindrical roller bearing?
The full designation with design, i.e. NU, NJ, NUP or N, dimension series and bore code, as well as all suffixes for cage, clearance and accuracy, is required. The installation location, speed and operating temperature are also helpful. For bearings from machine tool spindles, the accuracy class is particularly important.
Why does the cylindrical roller bearing have a brass cage?
Machined brass cages are robust against shocks, vibration and higher temperatures and are therefore preferred in heavy machinery. Polyamide cages are lighter and run with low friction but have temperature limits. Pressed steel cages are a common standard. A change of cage when procuring a replacement should only be made after checking the operating conditions.