Needle Roller Bearings - Ntn-snr.com

Shaft Bearing and Fits Housing Design
NTN
7.3 Shaft and housing accuracy
Because of its thin wall, the raceway surface accuracy
of needle roller bearing ring is influenced by the
respective fitting surface accuracy of a shaft /a housing
on/in which the needle roller bearing is installed. In the
case of general operating conditions, the fitting surfaces
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
and sound are strict.
Table 7.3 shows the fitting surface accuracy, profile
accuracy, surface roughness, and shoulder
perpendicularity to fitting surface of each of shaft and
housing under ordinary operating conditions.
Table 7.3 Shaft and housing accuracy
Characteristic item Shaft Housing
Dimensional accuracy
Roundness
(max)
cylindricality
Shoulder perpendicularity (max)
IT6IT5
IT3IT2
IT5IT4
IT7IT6
IT4IT3
IT5IT4
Fitting surface roughness
0.8a 1.6a
Remarks: The parenthesized values are applied to the bearings of accuracy
class 5 and higher.
Where a two-split housing is used, deformation of outer
ring by housing clamping can be minimized by providing a
relief on the mating surface at bore side.
7.4 Raceway surface accuracy
For needle roller bearings, shaft and housing are used
as the raceway surface on application. The raceway
dimensional accuracy, profile accuracy and surface
roughness of shaft/housing must be equivalent to the
raceway accuracy of bearing itself. Table 7.4 shows the
specified surface accuracy and surface roughness of
shaft/housing raceway.
Table 7.4 Raceway surface accuracy (recommendation)
Characteristic item Shaft Housing
Dimensional accuracy IT5IT4 IT6IT5
Roundness
(max)
cylindricality
IT3IT2 IT4IT3
Shoulder perpendicularity
(max)
Axial run-out
Thrust bearing
(max)
IT3IT2
IT5IT4
IT3IT2
7.5 Material and hardness of raceway surface
When the outer surface or bore surface of
shaft(hollowed) or housing is used as raceway, it must be
hardened to HRC58 to 64 for getting sufficient load
capacity. For that, the materials shown in Table 7.5 are
used after heat-treated properly.
Table 7.5 Materials used for raceway
When steel is surface-hardened by carburizing or
carbonitriding, JIS Standard as applicable defines the
depth from surface up to HV550 as an effective hardened
layer. The minimum value of effective hardened layer
depth is approximately expressed in formula (7.1).
Eht min0.8Dw0.1+0.002 Dw (7.1)
Where,
Kinds of steel
High carbon chrome bearing steel
Carbon tool steel
Nickel chrome molybdenum steel
Chrome steel
Chrome molybdenum steel
Nickel chrome steel
Representative
example
Related standards
SUJ2 JIS G 4805
SK3 JIS G 4401
SNCM420 JIS G 4103
SCr420 JIS G 4104
SCM420 JIS G 4105
SNC420 JIS G 4102
Eht min : Minimum effective hardened layer depth mm
Dw : Roller diameter mm
7.6 Allowable bearing inclination
The inner ring and outer ring of bearing incline a little
eventually against one another depending on shaft
deflection, shaft /housing machining accuracy, fitting
deviation, etc. Although this allowable inclination differs
depending on bearing type, bearing load, internal
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
and outer ring could cause reduction of bearing life and
damage of cage.
Table 7.6
Bearing type Allowable inclination
Radial needle roller bearing 1/2 000
Thrust bearing 1/10 000
Surface roughness
For shaft diameter of 80 and less :0.2a
For shaft diameter of over 80 to 120 :0.3a
For shaft diameter of over 120 :0.4a
Note) The parenthesized values are applied where high rotational accuracy is
required.
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