Needle roller bearings are radial bearings with very low section heights that have high load capacity . Needle roller bearings have the ability to mount inner and outer rings separately, the assembly becomes much simpler ,also in mass production conditions. In the case in which needle bearings work in a very limited space ( for example in adapters) are often used needle roller bearings without inner ring ( RNA ). In this case needle bearings work directly on the shaft surface . These surfaces running , however, must be designed with the same quality standards of the bearing rings ( hardened and ground ). Needle roller bearings are available in several designs , NK , NKI,…including variants without inner rings . The outer rings of the bearings ,together with needle bearings and with the cage form a single unit. To guide needle roller bearings , the outer rings have flanges . These bearings are integrated both with solid ribs, or in the case of small needle bearings they are separated with side plates . To facilitate an easy relubrication , the outer rings of needle roller bearings are produced with a groove and feature such as lubrication holes in their outer rings as standard. Needle roller bearings with machined rings are typically single row with the exception of needle roller bearings belong to the series NA 69 and RNA69 , which are double row ( only from a certain size onwards ). The series mentioned above are , respectively , available in the closed version ( identified with the suffix RSR ) or double seal ( identified with the suffix 2RSR ). These roller bearings are fitted with seals, upholster with a wear resistant synthetic rubber (NBR) , which prevents contamination by foreign particles and impurities . This seal material is suitable for operating temperatures of -30°C up to +120°C.
Needle roller bearings have a very low ability to compensate misalignment , due to the relatively long line of contact between the rollers and the raceways. Despite the geometry has been modified, it is recommended to avoid any misalignment since even small misalignments can generate a high operating noise . Also one must consider that the needle roller running in the presence of misalignments are subject to considerable additional forces that will reduce their lifespan.
ITS Italia provides roller wheels with steel cages as standard. Exceptions : needle roller bearings of small sizes that are equipped with polyamide cages, identified with the suffix TVP.
ITS Italia needle roller bearings are produced to normal tolerance class ( PN ) as standard. On request ITS Italia can provide, also , needle roller bearings with greater precision, in P6. Normally the diameter of the rollers , without inner rings ( series RNA ), it corresponds to the tolerance range P6 .
Needle roller bearings are produced with normal internal clearance , CN, as standard. ITS Italia can provide needle roller bearings with other internal clearances .
Needle roller bearings to operate correctly require a certain minimum load, to avoid excessive sliding friction . For ITS Italia the minimum load must be greater than 2 % of the basic dynamic load rating.