If
a change in construction is
being considered as a means
of
obtaining longer service
on
a rope
influenced principally
by
bending
stresses, this table
of
factors may
be useful.
For
example: a change
from a 6 x 25
FW
with a factor
of
1.00 to a 6 x 36 WS with a factor
of
1.15 would mean the service life
could be estimated to increase 1.15
times
or
15%.
These factors apply only for
bending stresses. There are other
factors, which are almost always
present
in
rope operation, that con-
tribute to rope deterioration. These
other factors are not considered in
this table.
Figure 34. This service life curve only
takes into account bending and tensile
stresses. This curve can
be
utilized to
predict comparative service life
of
a
specific wire rope with varying
DId
ratios. That resultant comparison is
illustrated by the following example: A
rope working with a
DId ratio
of
26
has a relative service life
of
17.
If
the
same rope works over a sheave that
increases its
DId
ratio to 35, the rela-
tive service life increases to 32. In
short, if this rope is used on the larger
sheave, one could estimate an increase
in its bending service life from 17 to
32 or an 88% increase.
TABLE
11
RELATIVE
BENDING
LIFE
FACTORS
Rope
Rope
Construction Factor
Constmction Factor
6 x 7 or 7 x 7 Aircraft
.60
7x25FW
19
x 7 or
18
x 7 R.R.
.70
6x29FW
6x
19
S
.80
6x36WS
1.15
6x
19W
6x36SFW
6x21
FW
6x43
FWS
6x26WS
7 x
31
WS
6x
25B
FS
.90
8x25FW
6x27HFS
6x41
WS
6x30GFS
6x41
SFW
1.25
6x31VFS
6x49SWS
7
x21FW
7x36FW
6x25FW
1.00
6x46SFW
6x31
WS
6x46WS
8 x
19S
8x36WS
1.35
8x21
FW
1.10
6x61
FWS
6x57
SFWS
*Note: This table, with some modifications,
is
based on outer wire diameter relationships. For rope
constructions not listed, consult the rope manufacturer.
SERVICE LIFE
CURVE
FOR
VARIOUS
Old
RATIOS
100
90
80
70
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tiso
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a:
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> 40
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30
20
10
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10
20
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,,-
i
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30
40
50
60
Old
RATIO
54 • Wire Rope Technical Board - Wire Rope Users Manual, Fourth Edition
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