Fig. 12. Position (left) and surface of the cracks (right)
Fig. 13. The curve of shutting: vibration
2
n
of the shaft on the vertical turbine side,
with resonance on
n
2
/
2
maximum value of vibrational amplitude from previous 180 increased to
370.
No reason was found for this crack. Material of the shaft (dynamical
resistance) didn’t have any faults. At the exit point of the crack notch
factor was calculated and it was 3.7. If we take into consideration this and
decrease it due to roughness of the surface and effect of the dimensions
and probability of lower values of the material, then we allow alternating
tension of 52MPa. With nominal alternating tension
a
= 28
MPa, factor of
security is 52/28.
The crack has not appeared at the spot of the highest nominal tension,
which is 270 mm in axial direction toward the rotors center, and it has
nominal tension at 33MPa and factor of security is calculated at 1.8.
118 ISSN 0236-3941. Вестник МГТУ им. Н.Э. Баумана. Сер. “Машиностроение”. 2009. № 3
