Page 43 - needle bearings

Shaft and Housing Design
Bearing Fits
NTN
NTN

7.3 Shaft and housing accuracy 7.5 Material and hardness of raceway surface
Because of its thin wall, the raceway surface accuracy When the outer surface or bore surface of
of needle roller bearing ring is influenced by the shaft(hollowed) or housing is used as raceway, it must be
respective fitting surface accuracy of a shaft /a housing hardened to HRC58 to 64 for getting sufficient load
on/in which the needle roller bearing is installed. In the capacity. For that, the materials shown in Table 7.5 are
case of general operating conditions, the fitting surfaces used after heat-treated properly.
of shaft and housing may be finished by lathe-turning, but
those must be finished by grinding where the acting load
is great and, in addition, the requirements for accuracy Table 7.5 Materials used for raceway
and sound are strict. Representative
Kinds of steel Related standards
Table 7.3 shows the fitting surface accuracy, profile example
accuracy, surface roughness, and shoulder High carbon chrome bearing steel SUJ2 JIS G 4805
perpendicularity to fitting surface of each of shaft and Carbon tool steel SK3 JIS G 4401
housing under ordinary operating conditions. Nickel chrome molybdenum steel SNCM420 JIS G 4103
Chrome steel SCr420 JIS G 4104
Chrome molybdenum steel SCM420 JIS G 4105
Table 7.3 Shaft and housing accuracy
Nickel chrome steel SNC420 JIS G 4102
Characteristic item Shaft Housing
Dimensional accuracy IT6ʢIT5ʣ IT7ʢIT6ʣ
When steel is surface-hardened by carburizing or
Roundness (max) IT3ʢIT2ʣ IT4ʢIT3ʣ
cylindricality carbonitriding, JIS Standard as applicable defines the
depth from surface up to HV550 as an effective hardened
Shoulder perpendicularity (max) IT5ʢIT4ʣ IT5ʢIT4ʣ
layer. The minimum value of effective hardened layer
Fitting surface roughness 0.8a 1.6a
depth is approximately expressed in formula (7.1).
Remarks: The parenthesized values are applied to the bearings of accuracy
class 5 and higher.
Eht minʾ0.8Dwʢ0.1+0.002 Dwʣ ʜʜʜʜʜʜʜʜʜ(7.1)
Where a two-split housing is used, deformation of outer Where,
ring by housing clamping can be minimized by providing a Eht min : Minimum effective hardened layer depth mm
relief on the mating surface at bore side.
Dw : Roller diameter mm

7.4 Raceway surface accuracy
7.6 Allowable bearing inclination
For needle roller bearings, shaft and housing are used
as the raceway surface on application. The raceway The inner ring and outer ring of bearing incline a little
dimensional accuracy, profile accuracy and surface eventually against one another depending on shaft
roughness of shaft/housing must be equivalent to the deflection, shaft /housing machining accuracy, fitting
raceway accuracy of bearing itself. Table 7.4 shows the deviation, etc. Although this allowable inclination differs
specified surface accuracy and surface roughness of depending on bearing type, bearing load, internal
shaft/housing raceway. clearance, etc., the inclination degree shown in Table 7.6
must be used as a guideline in the case of general
applications because even minor inclination of inner ring
Table 7.4 Raceway surface accuracy (recommendation)
and outer ring could cause reduction of bearing life and
Characteristic item Shaft Housing damage of cage.
Dimensional accuracy IT5ʢIT4ʣ IT6ʢIT5ʣ
Roundness (max) IT3ʢIT2ʣ IT4ʢIT3ʣ Table 7.6
cylindricality
Bearing type Allowable inclination
Shoulder perpendicularity
(max) IT3ʢIT2ʣ IT3ʢIT2ʣ Radial needle roller bearing 1/2 000
Thrust bearing 1/10 000
Axial run-out
(max) IT5ʢIT4ʣ
Thrust bearing
For shaft diameter of П80 and less :0.2a
Surface roughness For shaft diameter of over П80 to 120 :0.3a
For shaft diameter of over П120 :0.4a
Note) The parenthesized values are applied where high rotational accuracy is

required.

A-39