Sheave
Size & Wire Rope Strength |
|
Strength
Efficiency
Bending wire
rope reduces its strength. To account
for the effect of bend radius on wire rope strength when selecting a sheave, use the table
below:
Ratio A
|
Strength Efficiency
Compared to Catalog Strength in % |
40 |
95 |
30 |
93 |
20 |
91 |
15 |
89 |
10 |
86 |
8 |
83 |
6 |
79 |
4 |
75 |
2 |
65 |
1 |
50 |
| Ratio
A = |
|
Example:
To determine the strength efficiency of 1/2" diameter wire
rope using a 10" diameter sheave:
| Ratio
A = |
|
= 20 |
Refer to ratio A of 20 in the
table then check the column under the heading "Strength
Efficiency Compared to Catalog Strength in %"...91% strength
efficiency as compared to the catalog strength of wire rope. |
|
Fatigue Life
Repeated
bending and straightening of wire rope causes a cyclic change of
stress called “fatiguing.” Bend radius affects wire rope
fatigue life. A comparison of the relative effect of sheave
diameter on wire rope fatigue life can be determined as shown below:
Ratio B
|
Relative Fatigue
Bending Life |
30 |
10.0 |
25 |
6.6 |
20 |
3.8 |
18 |
2.9 |
16 |
2.1 |
14 |
1.5 |
12 |
1.1 |
|
Ratio
B = |
 |
 |
Example
To determine the extension of fatigue life for a 3/4"
wire rope using a 22.5" diameter sheave versus a 12"
diameter sheave:
|
|
|
Ratio
B = |
|
= 30 |
|
Ratio B = |
|
= 16 |
|
The relative fatigue bending
life for a ratio B of 16 is 2.1 (see above Table) and ratio
B of 30 is 10.
|
|
Relative
Fatigue
Bending Life |
=  |
=
4.7 |
|
Therefore, we expect extension
of fatigue life using a
22.5" diameter sheave to be 4.7 times greater than that
of a 12" diameter sheave.
|
|
