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Multi-Row Full Complement Cylindrical Roller Bearings

Multi-Row Full Complement Cylindrical Roller Bearings

Multi-row full complement cylindrical roller bearings are mainly used in small cold rolling mills where very considerable rolling forces occur but where rolling speed is limited. Other applications for these bearings include straightening machines, shears and extruders. To facilitate efficient lubrication, all multi-row full complement cylindrical roller bearings have lubrication holes, or an annular groove and lubrication holes in the outer ring.

SKF multi-row cylindrical roller bearings are mainly produced to the NNU design described below. To special order, SKF can also produce three to five-row bearings of the NNCL and NNC designs. However, because of the large number of possible designs and sizes NNCL and NNC design bearings are not shown in the product tables. Further information on these bearings will be sent on request.

NNU design The bearings have two loose flange rings on the outer ring, a flangeless inner ring and four rows of rollers (fig) or eight rows of rollers (fig). The bearings are separable and enable a certain amount of axial displacement of the shaft relative to the housing in both directions to take place within the bearing.

NNCL design These bearings have four to six integral flanges on the inner ring and a flangeless outer ring (fig). Retaining rings at both sides of the outer ring raceway serve to hold the bearing together. A certain amount of axial displacement of the shaft relative to the housing can take place in both directions inside the bearing.

NNC design These bearings have four to six integral flanges on the inner ring and one integral flange ring and a loose flange ring on the outer ring (fig) attached to the outer ring which holds the bearing together. These bearings are able to axially locate a shaft in both directions.

Dimensions The boundary dimensions of the bearings of the NNU design conform to Dimension Series 69 or 60 as specified in ISO 15:1998.

The bore and outside diameters of the other multi-row bearings which are not shown in the product tables correspond to Diameter Series 9 of ISO 15:1998. The digit 9 in the designations of these bearings refers to this feature.

Tolerances SKF multi-row full complement cylindrical roller bearings are produced with Normal tolerances to ISO 492:2002 as standard.

Internal clearance Most SKF multi-row full complement cylindrical roller bearings are produced with C3 radial internal clearance to ISO 5753:1991. The clearance values apply to bearings before mounting and under zero measuring load.

Influence of operating temperature on bearing material

SKF multi-row full complement cylindrical roller bearings undergo a special heat treatment. They can therefore be used at temperatures of up to +150 C without inadmissible dimensional changes occurring.

Minimum load To achieve satisfactory operation, multi-row full complement cylindrical roller bearings, like all ball and roller bearings, must always be subjected to a given minimum load, especially if they are to operate at relatively high speeds (n > 0,5 times the speed rating) or are subjected to high accelerations or rapid changes in the direction of load. Under such conditions the inertia forces of the rollers, and the friction in the lubricant, can have a detrimental influence on the rolling conditions in the bearing arrangement and may cause damaging sliding movements to occur between the rollers and the raceways.

The requisite minimum load to be applied to multi-row full complement cylindrical roller bearings can be estimated using

where

Frm = minimum radial load [kN]

kr = minimum load factor (see product data)

n = rotational speed [r/min]

dm = mean diameter of bearing

= 0,5 (d + D) [mm]

When starting up at low temperatures or when the lubricant is highly viscous, even greater loads may be required. The weights of the components supported by the bearing, together with the external forces, generally exceed the requisite minimum load. If this is not the case, the multi-row full complement cylindrical roller bearing must be subjected to an additional radial load.

Equivalent dynamic bearing load

For multi-row full complement cylindrical roller bearings of the NNU design

P = Fr

Equivalent static bearing load

P0 = Fr


Cylindrical roller bearings | Single row cylindrical roller bearings | Double row cylindrical roller bearings | Multi-row cylindrical roller bearings | Single row full complement cylindrical roller bearings | Double row full complement cylindrical roller bearings | Multi-row full complement cylindrical roller bearings | Split cylindrical roller bearings