Needle Roller and Cage Assemblies

Needle roller and cage assemblies are ready-to-mount, self-contained bearing components. They are an excellent choice for applications that require a very rigid bearing arrangement as well as a high load carrying capacity. If the shaft and housing bore can serve as raceways, needle roller and cage assemblies require minimal radial space.

Standard needle roller and cage assemblies

SKF supplies needle roller and cage assemblies in single row and double row designs.

Needle roller and cage assembly, single row

Needle roller and cage assembly, double row

They are characterized by:

• a simple and rugged design
• accurate guidance of the rollers in the cage pockets
• good running performance

Other needle roller and cage assemblies

Only part of SKF’s comprehensive assortment of needle roller and cage assemblies is listed in the product tables. SKF also supplies other sizes and assemblies with cages that differ from the standard design, such as needle roller and cage assemblies with a split cage that can be used where raceways are recessed in the shaft.

Bearing arrangement incorporating needle roller and cage assemblies with a split cage

For connecting rods of internal combustion engines and compressors, SKF supplies special needle roller and cage assemblies for the gudgeon (wrist) pin

Needle roller and cage assembly for gudgeon pin bearing arrangements

and crank pin (crankshaft journal).

Needle roller and cage assembly for crank pin bearing arrangements

The assemblies for these applications can provide excellent service in spite of high accelerations, high temperatures, unfavourable load conditions or poor lubrication conditions.

SKF also supplies special sizes of needle roller and cage assemblies to special order. Details of these other needle roller and cage assemblies are available on request.

Dimensions The dimensions of needle roller and cage assemblies with an inside diameter up to and including 100 mm, where standardized, are in accordance with ISO 3030:1996.

Tolerances SKF needle roller and cage assemblies contain rollers of one gauge of grade G2 (ISO 3096:1996 Grade 2). The tolerance of each gauge is 2 µm. The deviation from the nominal dimensions of the needle rollers is printed on the package.

SKF needle roller and cage assemblies may comprise, as standard, assemblies of any standard gauge (table). If a specific gauge is required, it must be stated when ordering. Assemblies with rollers of a special gauge (table) are only available by special order on request.

The tolerances for the width U are −0,20/−0,80 mm for all needle roller and cage assemblies.

Paired mounting Needle roller and cage assemblies that are mounted immediately adjacent to each other must incorporate rollers of the same gauge. This will enable both assemblies to share the load equally.

Operational clearance The radial operational clearance of bearing arrangements incorporating needle roller and cage assemblies is determined by:

• the gauge of the needle rollers
• the shaft and housing raceway tolerances
• the operating temperature

Suitable raceway tolerance classes are listed in the table. If these tolerances are applied when using assemblies with standard gauge rollers (table), under normal conditions the operational clearance will reach a value in the range of C2 to Normal radial internal clearance (table).

If a specific radial internal clearance is required, the various components of the arrangement should be matched following a mounting scheme similar to the one shown in the table. The mean value of the needle roller gauge should be used to calculate the internal clearance, e.g. −6 µm for the gauge −5 to −7 µm.

Operational clearance The radial operational clearance of bearing arrangements incorporating needle roller and cage assemblies is determined by:

• the gauge of the needle rollers
• the shaft and housing raceway tolerances
• the operating temperature

Suitable raceway tolerance classes are listed in the table. If these tolerances are applied when using assemblies with standard gauge rollers (table), under normal conditions the operational clearance will reach a value in the range of C2 to Normal radial internal clearance (table).

If a specific radial internal clearance is required, the various components of the arrangement should be matched following a mounting scheme similar to the one shown in the table. The mean value of the needle roller gauge should be used to calculate the internal clearance, e.g. −6 µm for the gauge −5 to −7 µm.

Misalignment The ends of the needle rollers are relieved slightly to modify the line contact between the raceways and the rollers. This provides favourable load distribution in the needle roller and cage assembly and minimizes damaging edge stresses. It also enables single row needle roller and cage assemblies to accommodate a small amount of misalignment, approximately 1 min of arc between the shaft and housing.

The detrimental effects of misalignment increase with increasing bearing width and load. For additional information, contact the SKF application engineering service.

Cages SKF needle roller and cage assemblies are fitted, as standard, with a machined steelcage

Machined steel cage

or a sheet steel cage,

Sheet steel cage

with the exception of assemblies identified by the designation suffix TN. These have an injection moulded glass fibre reinforced polyamide 66 cage.

Polyamide 66 cage

Note Needle roller and cage assemblies with a polyamide 66 cage can be operated at temperatures up to 120 °C. The lubricants generally used for rolling bearings do not have a detrimental effect on cage properties. Exceptions are a few synthetic oils and greases with a synthetic oil base and lubricants containing a high proportion of EP additives when used at high temperatures.

For bearing arrangements that operate at continuously high temperatures or under arduous conditions, SKF recommends using assemblies with a steel cage.

For additional information about the temperature resistance and the applicability of cages, refer to the section Cage materials.

Raceways on shafts and in housings If the load carrying capacity of a needle roller and cage assembly in applications where the shaft and housing bore are used as raceways is to be fully exploited, both should have the same hardness and accuracy as a bearing raceway.

The running accuracy of the bearing arrangement also depends on the accuracy of the raceways. For additional information about accuracy, suitable materials, surface roughness and hardness, refer to the section Raceways on shafts and in housings.

Abutment dimensions Needle roller and cage assemblies should be axially guided. The lateral abutment surfaces should be fine turned and polished. For high speed operation they should be hardened and ground. Interruptions in the surface should be avoided. Snap rings can be used in less demanding applications, otherwise an intermediate ring, e.g. a spring steel washer, should be placed between the snap ring and the assembly. Appropriate values for the abutment diameters on the shaft are listed in the table.

Minimum load To achieve satisfactory operation, needle roller and cage assemblies must always be subjected to a requisite minimum load. Applying a requisite minimum load is especially important for cage assemblies that operate at high speeds or are subjected to high accelerations or rapid changes in the direction of load. Under these conditions, not applying the correct minimum load can result in damaging sliding movement between the rollers and raceways caused by the inertial forces of the needle rollers and cage, and friction in the lubricant.

The requisite minimum radial load to be applied to needle roller and cage assemblies can be estimated using

Frm = 0,02 C

where

Frm = minimum radial load [kN]

C = basic dynamic load rating [kN]

When starting up at low temperatures or when the lubricant is highly viscous, an even greater minimum load may be required. However, the weight of the components supported by the bearing, together with the external forces, generally exceeds the requisite minimum load. If this is not the case, the needle roller and cage assembly must be subjected to an additional radial load.

Equivalent dynamic bearing load

Needle roller and cage assemblies can only accommodate radial load. Therefore, the equivalent dynamic bearing load is equal to the calculated radial bearing load:

P = Fr

where

P = equivalent dynamic bearing load [kN]

Fr = actual radial bearing load [kN]

Equivalent static bearing load

Needle roller and cage assemblies can only accommodate radial load. Therefore, the equivalent static bearing load is equal to the calculated radial bearing load:

P0 = Fr

where

P0 = equivalent static bearing load [kN]

Fr = actual radial bearing load [kN]

Supplementary designations The designation suffixes used to identify certain features of SKF needle roller and cage assemblies are explained in the following:

Needle roller bearings | Needle roller and cage assemblies | Drawn cup needle roller bearings | Needle roller bearings with machined rings | Alignment needle roller bearings | Needle roller bearing inner rings | Universal joint bearings