Needle roller bearings (4703 /IE) - SKF Magnetic Bearings - #30

The roughness of bearing seating surfaces does not have the same degree of influence on bearing performance as the dimensional, form and running accuracies. However, a desired interference fit is much more accur­ately obtained the smoother the mating sur­faces. For less critical bearing arrangements relatively large surface roughnesses are per­mitted. For bearing arrangements where demands in respect of accuracy are high, guideline values for the mean surface rough­ness R_a are given in Table EE] for the differ­ent dimensional accuracies of the bearing seatings. These recommendations apply to ground seatings, which are normally as­sumed for shaft seatings.

Raceways machined in associated com­ponents for

• needle roller and cage assemblies,

• drawn cup needle roller bearings,

• needle roller bearings having only one ring,

• combined needle roller bearings without inner ring,

• needle roller and cage thrust assemblies and

• support rollers without inner ring

must have a hardness of between 58 and 64 HRC if the load carrying capacity of the bearing or assembly is to be fully exploited.

Influence of raceway hardness

Raceways having a hardness under 58 HRC reduce the load carrying capacity of the bearing arrangement. This is taken into account by multiplying the basic dynamic load rating by a reduction factor f_c from Table ED

Raceway surface finish and accuracy

The surface roughness should be R_a < 0,2 um or R_z < 1 um. For less demanding applica­tions, lower hardness and rougher surfaces may be used. For radial bearing arrangements,

• the out-of-round should not exceed 25 %, and

• the deviation from cylindrical form should not exceed 50 %,

of the actual diameter tolerance of the raceway.

The permissible axial runouts of race­ways for the needle roller and cage thrust assemblies are the same as for the shaft and housing washers of thrust bearings (-» Table EH, page 20).

Raceway materials

Suitable materials for the seatings include

• through-hardening steels to DIN 17 230: 1980, e.g. steel 100 Cr 6,

• case-hardening steels to DIN 17 210:1986 and 17 230:1980, e.g. 15CrNi6or

16 MnCr5, as well as

• steels for flame or induction hardening to DIN 17212:1972 or DIN 17230:1980, which can be partially hardened.

d (D) Diameter tolerance to

over ind. IT7 IT6 IT5

mm M^m

80 1,6 (N7) 0,8 (N6) 0,4 (N5)

80 500 1,6 (N7) 1,6 (N7) 0,8 (N6)

28

5KF