Designs and variants
NNCL design bearings (fig. 1
) have three integral flanges on the inner ring and no flanges on the outer ring. A retaining ring inserted in the outer ring between the roller rows holds the bearing together. The retaining ring should not be loaded axially during operation. These bearings can accommodate axial displacement of the shaft relative to the housing in both directions.
NNCF design bearings (fig. 2
) have three integral flanges on the inner ring and one on the outer ring to locate the shaft axially in one direction. A retaining ring inserted in the outer ring on the side opposite the integral flange holds the bearing together. The retaining ring should not be loaded axially during operation. These bearings are used to locate the shaft axially in one direction and eventually to accommodate axial displacement of the shaft relative to the housing in the opposite direction.
NNC design bearings (fig. 3
) have the same inner ring as NNCL and NNCF design bearings. The twopiece outer ring is held together by retaining elements, which should never be loaded axially. Both parts of the outer ring are identical and have one integral flange. These bearings are used to locate the shaft axially in both directions.
NNF design (sealed bearings)
NNF design bearings (fig. 4
) in the 50 and 3194.. series have a two-piece inner ring, held together by a retaining ring. The inner ring has three integral flanges and the outer ring has one integral central flange. The bearings are used to locate a shaft axially in both directions. The distance between the two rows of rollers enables these bearings to accommodate tilting moments.
The outer ring of an NNF design bearing is 1 mm narrower than the inner ring. In applications with a rotating outer ring, there is no need for spacer rings between the inner ring and adjacent components. The outer ring has two snap ring grooves to simplify mounting and save space axially, when the bearing is mounted in/on an adjacent component, e.g. in rope sheaves (fig. 5
The bearings have a contact PUR seal on both sides. Each seal is fitted in a recess on the inner ring shoulder (fig. 4
). The seal lip exerts slight pressure against the outer ring raceway. The bearings are filled with a high-quality grease with good rust inhibiting properties table 1
. For additional information about greases, refer to Lubrication
For applications where oil lubrication is to be used, the bearings can be supplied open and without grease. If a small quantity of bearings without seals is required, the seals can be removed and the bearings can be washed prior to mounting.
Relubrication of sealed bearings
For many application conditions, sealed double row full complement cylindrical roller bearings do not require relubrication and can be considered relubrication-free (→ Relubrication). However, if they operate in a moist or contaminated environment, or if speeds are moderate to high, relubrication may be necessary. The bearings can be relubricated via lubrication holes in both the inner and outer rings.
SKF can supply matched bearings. To match bearings, SKF combines bearings so that the difference in cross-section height lies within a very small tolerance range. This reduced tolerance range is a precondition for equal load sharing between the bearings.
Matched bearings are identified by a designation suffix:
DR for a set of two bearings
TR for a set of three bearings
QR for a set of four bearings
For additional information, contact the SKF application engineering service.