Wire Ropes, Elements and Definitions - Wire Ropes: Tension, Endurance, Reliability - page 12

free wire length l

1

2

ʴ . E
˃ b

C = K

3

6

7

5

4

5 control box
6 scale for distance
7 revolving wire clamp

1 machine case
2 wire guidance with disconnect
3 drive with wire clamp
4 counter

Fig. 1.8 Stuttgart rotary bending machine, Wolf ( 1987 )

outside of the wire to the wire axis. Therefore—as shown in Fig. 1.5 —the maximum
(nominal) stress exists only in a small ring zone. The advantage of rotary bending
tests is that it can be done very quickly with a frequency of 50 and more turns/second.
Older bending machines which rotate the wire are the Haigh/Robertson
machine, NN ( 1933 ), the Schenck machine, Erlinger ( 1942 ) and the Hunter testing
machine, Votta ( 1948 ). These machines have the disadvantage that of the whole
wire length only a small part is bent with the maximal (nominal) bending stress r a .
The newer Stuttgart rotary bending machine, Fig. 1.8 , avoids this disadvantage,
Wolf ( 1987 ). In this machine the wire has almost the same bending stress for the
whole bending length. The wire bow between the two parallel axes of the rotating
wire terminations with the distance C is nearly a circular arc. One of the two wire
terminations is driven.
One slight disadvantage of both the Hunter testing machine and the Stuttgart
testing machine is that the bending length is determined by the chosen bending stress.
The great advantage of these two machines is, however, that the bending stress is
determined by geometric dimensions only and these can be measured very simply.
For the Stuttgart rotary bending machine, the bending length (free wire length
between the terminations) l is only slightly larger than the circle bow length Cp/2.