Double row full complement cylindrical roller bearings (fig) incorporate a maximum number of rollers and are therefore suitable for very heavy radial loads. However, they cannot operate at the same high speeds as caged cylindrical roller bearings. SKF double row full complement cylindrical roller bearings are produced as standard in four designs, three open designs and one sealed. All the bearings are non-separable and have an annular groove and three lubrication holes in the outer ring to facilitate efficient lubrication.

NNCL design
NNCL design bearings (fig) have an inner ring with three integral flanges and a flangeless outer ring. A retaining ring, inserted in the outer ring between the roller rows, keeps all bearing components together. Axial displacement of the shaft relative to the housing in both directions can be accommodated within the bearing. The bearings are therefore suitable for non-locating bearing positions.

NNCF design
NNCF design bearings (fig) have three integral flanges on the inner ring and one integral flange on the outer ring enabling the bearing to provide axial location for a shaft in one direction. A retaining ring is inserted in the outer ring at the side opposite the integral flange and serves to hold the bearing together.

NNC design
NNC design bearings (fig) are equipped with the same inner ring as bearings of the NNCL and NNCF design. The outer ring is split and held together by retaining elements, which should not be loaded axially. Both parts of the outer ring are identical and carry one integral flange, enabling the bearing to locate the shaft axially in both directions.

NNF design
NNF design bearings (fig) in the NNF 50 and 3194(00) series are always sealed on both sides and filled with grease. The two-piece inner ring has three integral flanges and is held together by a retaining ring. The outer ring has an integral central flange. The bearings can be used to locate a shaft axially in both directions. Because of the large distance between the two rows of rollers, the bearings are also able to accommodate tilting moments.

The outer ring of an NNF bearing is 1 mm narrower than the inner ring and has two snap ring grooves in the outside diameter. Therefore it is possible to eliminate the need for spacer rings between the inner ring and adjacent components, for example, in rope sheaves (fig).

The bearings have a contact seal on both sides. The seals are retained on the inner ring shoulders, to provide efficient sealing at this position. The outer sealing lip exerts a slight pressure on the outer ring raceway. The operating temperature range for the seals is –40 to +80 °C.

The bearings are filled with greases, which have good rust inhibiting properties (table).

Under certain conditions, sealed NNF design bearings are maintenance-free, but if they operate in a moist or contaminated environment, or if speeds are moderate to high, they must be relubricated. This can be done through the inner as well as the outer ring.

If bearings with one or no seals are required, the seals may be removed easily with a screwdriver. For applications where oil lubrication is to be used, the bearings can be delivered without seals and grease if economic quantities are involved. Otherwise the seals should be removed and the bearings washed before use. If oil lubrication is used, the limiting speed quoted in the product tables can be increased by approximately 30%.

Special NNB design
These bearings have three integral flanges on the inner ring and a wide flangeless outer ring (fig). They are special bearings designed for non-locating bearing arrangements where large axial displacements have to be accommodated within the bearing.