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6-2. Tightening Torque
Figure 1 shows a comparison of tightening torque with the Model WH 22, C and B.
Bolt: M22 x 70 (F10T) high tension bolt
Steel plate: SS34P, 30 mm in thickness
Tightening time (S)
Fig. 1
WR 22SA
WH 22
B
C
6-3. Appropriate Tightening Torque for Bolts
Generally speaking, the appropriate tightening torque for a bolt can be determined by the strength grade of the
bolt or the material tightened. Tables 2, 3 and 4 below list data relative to the strength grade of various bolts and
the appropriate tightening torque. For further reference, appropriate tightening torque is calculated with the
following formula. Study and use this formula for accurate selection of tightening torque.
T = k
•
d
•
p
T: Tightening torque (kgf
•
cm)
d: Nominal diameter for the bolt (cm)
p: Recommended axial tightening force to be applied to the bolt (kg)
p=rated axial stress (kg•mm
2
) x 0.8 x effective sectional area of the bolt (mm
2
)
k: Torque coefficient (0.17)
Strength grade
Rated axial stress (kgf
.
mm
2
)
Material
Heat treatment
4.8 8.8 10.9 12.9
29.1 58.2 79.2 95
Carbon steel such as SS and SC
Special alloy steel such as SNC, SCM and SNCM
Not treated Treated
....
Hard material
<Table 2>
Strength grade and rated axial stress of bolts
6.8
43.7
Tightening torque (N
.
m)