The axial pretension of a screw connection often plays a decisive role for successful function, and must therefore be set with particular accuracy. However, in most assembly workshops, direct measurement of this variable is not possible, raising the need for indirect methods of setting. For this purpose the locknut pretensioning moment corresponding to the required pretensioning force is calculated.
Up to locknut size MSW 70.46
This factor can be determined using the following equation:
Mv
=
Pretensioning moment of the locknut [Nm]
Fv
=
Required axial pretension force of the screw connection [N]
B
=
Locknut-specific allowance [N], compensates face end relief due to the locking process (see table)
A
=
Constant [mm], includes the calculation factors for the respective thread diameter (see table)
ľA
=
Friction of coefficient for the end contact surface of the locknut. Approximate value ľA = 0,1 steel/steel
rA
=
Effective (middle) friction radius for the effective contact surface of the locknut [mm]
The locking process places the spindle thread under stress and in this case brings about intensive surface contact (=high axial rigidity). At the same time, this serves to relieve tension on the end contact surface of the locknut. This effect can be simply compensated by increasing pretensioning torque accordingly on mounting. This higher pretensioning torque is ascertained using the allowance B relative to the required pretensioning force Fv.
