289 / 392
Figure 12. Contour, supports, and loading
Figure 13. Stress field of the bogie-wheel
Table 5. Percentual portions of stresses and deformation energy
Element
Membrane/Bending stress Deformation energy
Corona
0.8
0.5
2.3
Cone
14.1
2.5
7.4
Membrane
13.5
0.5
6.2
Hollow shaft
22.5
45.6
84.1
Sum
50.9
49.1
100
3.6. Diagnosed behaviour of the rotary excavator cantilever (C700S)
Fracture of some elements of the supporting cantilever of the bucket wheel excavator
SchRs 630 (Kolubara Metal Lazarevac) appeared in service, due to the appearance of
resonant frequencies with oscillation amplitudes up to 60 cm, disturbing the cantilever
dynamic behaviour.
The construction consists of one beam element and three bar elements: tie, yoke, and
cylinder, as modelled in Fig. 14. Strain energy is distributed as follows: beam 72.2%, tie
16.6%, cylinder 10.5%, and yoke 0.5% (Fig. 15).
tie
beam
yoke
cylinder
Figure 14. Plane model of the cantilever
Figure 15. Cantilever strain –
f
max
= 10.4 cm
Static computation reveals that declination of the beam is too big at the joint support;
the axial force in the tie and cylinder is high, but in the yoke is minor; bending moment in
the part of the beam linked to the yoke is high; and strain energy of the beam is dominant.
Dynamic computation has shown that the first two frequencies are low, close to each
other (Fig. 16) and coincide with the static deformation; the factor of dynamic amplifica-
tion is too large; both the imaginary part of frequency characteristic and strain energy
dominate in beam and in external masses (system is unstable), Tables 6–8, Figs. 17–19.
f
01
= 1.58 Hz
f
02
= 1.81 Hz
f
03
= 4.30 Hz
f
04
= 8.25 Hz
Figure 16. First four main modes of oscillations
285