Page 60 - needle bearings

Technical Data
NTN

11.3.3 Outer ring strength 11.3.4 Stud strength of cam follower
Generally any outer ring never breaks down as long as
the load acting it is a usual operating load. This
Fr
paragraph describes hereunder the strength calculation
method to be used when the outer ring strength under
shock load and heavy load is reviewed. Shaft section view
The outer ring strength can be determined using the
formula given hereunder, assuming the respective outer
ring profiles as illustrated in Fig. 11.6. In this case, the
outer ring rupture strength means the bridged rupture
strength of roller. R A

Fig. 11.7
h2 h2

h Centroid h Centroid When load Fr acts on the center point of outer ring as
illustrated in Fig.11.7, bending moment FrɾRgenerates
and consequently bending stress М1 (deemed as tensile
Dʵ2h D Dʵ2h D stress) acts on the stud surface. In addition to this
bending stress, tensile stress М2 generates from screw
tightening because the stud itself is clamped to machine
body with nuts. The stud strength can be reviewed from
KR,KRV,NATR,NATV NUKR,NUTR
comparison of the sum (М1 + М2) of these two tensile
Fig. 11.6 stresses with allowable stress М for the stud material.
М 1 М2ʻМ
Regarding how to set up breaking stress, in general
FrɾR
2
1760MPa (180kg/mm ) can be set up as the breaking М1ʹʕʕʕʕ Fr ɿMaximum radial load
stress for bearing steel, but it is desirable to set up the Z Z ɿCoefficient of shaft section through Point-A
breaking strength with safety-side value (1170MPa М2˺98MPa (10kgf/mm )
2
2
[120kgf/mm ]), where stress concentration is taken into Tensile stress generating from maximum tightening
account. Generally any outer ring never break down as torque described in "Dimensions Table"
long as the load acting on it is usual operating load, but it МɿAllowable stress for material
necessary to check the rupture structure of outer ring, The following values are adopted from the repeated
where shock load and heavy load act on it. bending test result of the stud material.
Where the stud material is subjected to static
4К Dʵ2h
PʹʕʕʕʕʕʕʷʕʕʕʕʕʕʕʕʷIʷМ bending stress;
2
1ʴfʢЋʣ hʢDʵ2h ʣ 2
2
Мʹ1372MPa (140kgf/mm )
Where, Where the stud material is subjected to repeated
bending stress (single direction)
ʢКʵЋʣsinЋʵʢ1ʴcosЋʣ
fʢЋʣʹʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕ Мʹ784MPa (80kgf/mm )
2
2cosЋ
Where the stud material is subjected to repeated
bending stress (double directions)
К
Ћʹʕʕʢrad.ʣ Мʹ392MPa (40kgf/mm )
2
Z
Accordingly,
P ɿBreaking load (N)
Z
4
I ɿSecondary moment of outer ring section (mm ) FrʻʕʕʕʢМ М2ʣ
Z ɿNumber of rollers R
МʹBreaking stress (MPa)
Dɼhɼh2ɿper Fig. 11.6 (mm)

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