Civil Engineering Reference
In-Depth Information
Fig. 3.77 Discarding
number of wire breaks B
A30
for parallel lay ropes
8 9 19 - FC - sZ
20
parallel lay ropes
8x19
−
FC-sZ
15
D/d=25
40
63
10
16
5
10
0
0
N/mm
2
specific tensile force S/d
2
100
200
300
made of steel or cast iron. For wire ropes with reverse bending cycles, Jahne
(
1992
) recommended calculating the discard number of wire breaks also with
(
3.83
) but with a DS/d
2
= 50 N/mm
2
higher specific tensile force than really
works.
Figure
3.77
shows the discard number of wire breaks B
A30
for parallel lay ropes
(Seale, Warrington and Filler) 8 9 19 - FC - sZ from (
3.83
). For wire ropes
with steel cores the discard number of wire breaks is always greater than for wire
ropes with fibre cores.
The lower the discard number of wire breaks from (
3.83
) and the shorter the
rope bending length, the less chance there is of detecting a dangerous rope situ-
ation by counting the wire breaks on the rope. Rope drives with a low discard
number of wire breaks should not be used in hoisting applications with safety
requirements.
In the case of lang lay ropes, multi-strand ropes and all kinds of ropes running
over sheaves out of soft material (small elasticity module), it is not possible to
detect the moment safely when a wire rope should be discarded by counting the
number of outside visible wire breaks, because wire breaks of those ropes more
often happen inside the rope. However lang lay ropes and multi-strand ropes show
outside damage as discard criteria if the ropes run over sheaves with undercut
grooves or V-grooves or if the ropes are wound in multi-layer spooling on drums.
Table
3.5
summarizes possible methods of rope inspection. If the numbers of wire
breaks are detected by magnetic devices, the discard number of wire breaks from
(
3.83
) can be used for all types of wire rope and all kinds of sheaves.
It may be remarked here briefly that, together with the magnetic detection of
wire breaks in special cases,
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