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Self Aligning Ball Bearings are non - separable double - row radial bearings. Both rows of balls rotate, in parallel, within the spherical outer ring. This allows excellent alignment compensation, caused by machining and mounting errors, between the shaft and housing.
Self aligning ball bearings are suitable for low to medium radial loads and low amounts of thrust forces.
Beside the standard design, (Abb. la), NKE Self aligning ball bearings with tapered bore, suffix K (i.e. taper 1:12), are available as standard, for ease of mounting (see b below). The facility of mounting these bearing types, using adaptor sleeves, enables mounting directly onto drawn or fine turned seats of shafts for applications where high running accuracy is not necessary. Some types of self aligning ball bearings are available with either cylindrical or tapered inner bores, these bearings incorporating contact rubbing seals (i.e. suffix .2RS, see c below and suffix K.2RS, see d and b respectively). The standard material used for contacting seals is a wear - resistant synthetic rubber (NBR) with integrated steel washers. NBR - seals are suitable for operating temperatures of -30 deg C up to + 120 deg C. When selecting self aligning ball bearing with contacting seals fitted consideration must be given to the reduction in achieving maximum speeds and their limited misalignment abilities.
Another design variant is self aligning ball bearings with extended inner rings, (Abb.3a). Unlike standard bearing bores, the bore diameter of self aligning ball bearings with extended inner rings have tolerances according to ISO - tolerance field J7.This tolerance J7 provides a loose sliding fit, of inner to shaft, for ease of mounting. As this fit provides adequate location on the shaft, the inner ring features a location slot to accept locator pins to prevent the inner ring rotating on the shaft. In the case of bearing arrangements consisting of two self aligning ball bearings with extended inner rings, the bearings must be mounted in such a way that the two location grooves on the inner rings either both face inwards (b) or both face outwards, (c).
Self Aligning Ball Bearings have excellent ability to compensate for misalignments. The maximum permissible misalignment from their centre axis ) is dependant upon the bearing design, series and actual operating conditions.
The following values are permissible: For bearings of series:
112 and 113 < 2.5 degrees for open bearing series 12 and 22 < 2.5 degrees for open bearing series
13 and 22 < degrees For sealed bearings (.2RS) <1.5 degrees NKE Self Aligning Ball Bearings are produced to normal tolerance class (PN) as standard. Speed Limitations for Self Sealed self aligning units Sealed self aligning ball bearings, suffix .2RS have limited speed ratings due to the additional heat generated by the rubbing of their sealing lips.
For this reason, the maximum speed must not exceed 2/3 of the speed rating recommended for open bearings with grease lubrication Cages
Small and medium sized NKE self aligning ball bearings are fitted with pressed steel cages as standard. Larger sizes are fitted with solid brass cages.
Several types and sizes of self aligning ball bearings are also produced with polyamide cages fitted.As there is an interactive internal design to cage type relationship, NKE request customer specify order preference. For the internal clearance group of self aligning ball bearings distinction is made between bearings with cylindrical or tapered bores. Because of the risk of applying accidental preloading to the bearing during mounting, bearings with tapered bore feature larger clearance when compared to cylindrical bore bearings even in the same clearance group.
NKE Self Aligning Ball Bearings with cylindrical or tapered bores are produced with normal internal clearance (CN) as standard. Other internal clearance groups are produced upon order request.
All informtion courtesy and copyright NKE Bearings Austria www.nke.at
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