Needle Roller Bearings

Listing ID #4344866

Needle roller bearings can be considered a version of cylindrical roller bearings. As these small-sized bearings can take over heavy dynamic loads, they provide high stiffness in bearing units.

Needle roller bearings are manufactured in the follow-ing constructive versions:

Needle roller bearings with inner ring

In case of limited space needle roller bearings without inner rings (RNA type) can be used instead of needle roller bearings with inner rings. The shaft must be har-dened and ground.

The shaft raceway must have a hardness of 58…65 HRC and a minimum roughness Ra = 0,2 ?m for normal bearings. In case of less pretentious bearings, Ra = 0,3 ?m is allowed.

Minimum thickness of the case-hardened layer can be determined as a function of the rolling element diameter, using the equation:

tmin = (0,07…0,12)Dw, mm

where:

Dw = rolling element diameter, mm

Greater values are valid in case of materials with core low strength and heavy loads.

In case of heat treatment steels (e.g. 41 MoCM 1) which have been surface hardened and tempered, layer thick-ness can be calculated using the equation:

tmin = (0,1…0,15)Dw, mm

where:

Dw = rolling element diameter, mm

Layer thickness after grinding must be of minimum 0,3 mm.

If the hardness of the surface layer is less than 58 HRC, bearing cannot accommodate the initial basic dynamic load Cr and basic static load Cor, respectively. In this case, basic dynamic load will be decreased by factor fH and basic static load by factor foH, according to the equations:

Cr ef = fH Cr, kN

C0r ef = f0H C0r, kN

Factors fH and f0H are given in table 1.

The dimensions of needle roller bearings are stand-ardized only for dimension series NA48, NA49, NA69, in accordance with ISO 1206.

Tolerances

Needle roller bearings with one-piece rings are general-ly manufactured to the normal tolerance class (P0). At request, they can be manufactured to other tolerance classes (P6 and P5).

The values of tolerances are given in chapter 3 on page 24.

Radial clearance

Needle roller bearings with one-piece rings are general-ly manufactured with normal radial clearances and the values of clearance are the same with those of the cylindrical roller bearings, according to ISO 5753 and are given on page 159, table 2. At request, these bearingsare manufactured with other clearances (C2, C3 or C4).

If needle roller bearings are to be matched in pairs, radial clearance should be the same for both bearings so that loads should be uniformly distributed.

Cages

Needle roller bearings with one-piece rings are generally fitted with pressed sheet cages. At special request, when bearings are to be operated at high speeds and/or under heavy loads, machined steel cages are recommended to be used. Glass fibre reinforced polyamide 6.6 cages are also successfully used up to an operating temperature of+ 120?C.

??Cage design and some technical data are given intable2.

Fits

??Needle roller bearings are generally mounted with in-terference fits so that rings should not get deformed due to their low section. In case of large-sized bearings, heavy loads and shock loads, bearings are more tightly mounted. When determining the fit, the difference of temperature between the inner ring and the outer ring, respectively, should be considered. The manufacturing tolerance of the shaft should be in the tolerance class 6 (IT6) and of the housing in the tolerance class 7 (IT7). In case of bearings manufactured to more accurate tolerance classes, the manufacturing tolerance of the shaft should be in the tolerance class 5 (IT5 ) and of the housing in the tolerance class 6 (IT6). These classes are also compulsory for the raceway on shaft. Deviations of form and position should be in accordance with the stipulations on page 57.

??The shaft tolerances are given in table3. They depend on the radial clearance necessary for needle roller bearings without inner ringswhich are mounted into the housing, the housing bore being manufactured to the tolerance class K6.