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Wire
ropes are manufactured in a great variety of constructions to meet
the varying demands of wire rope usage. Where abrasion is an important
factor, the rope must be made of a coarse construction containing
relatively large wires. In other cases, the great amount of bending
to which the rope is subjected is more important. Here, a more flexible
construction, containing many relatively small wires, is required.
In either case, however, if the rope operates over inadequate size
sheaves, the severe bending stresses imposed will cause the wires
to break from fatigue, even though actual wear is slight. The smaller
the diameter of the sheave, the sooner these fatigue breaks will
occur and the shorter rope life becomes.Another
undesirable effect of small sheaves is accelerated wear of both
rope and sheave groove. The pressure per unit area of rope on sheave
groove for a given load is inversely proportional to the size of
the sheave. In other words, the smaller the sheave the greater the
rope pressure per unit area on the groove. Using the proper diameter
sheave for the size and construction of rope can obviously prolong
both sheaves and rope life. Sheave
diameter can also influence rope strength. When a wire rope is bent
around a sheave, there is a loss of effective strength due to the
inability of the individual strands and wires to adjust themselves
entirely to their changed position. Tests show that rope strength
efficiency decreases to a marked degree as the sheave diameter is
reduced with respect to the diameter of the rope.Therefore,
it is evident that a definite relationship exists between rope service
and sheave size. As a guide to rope users, wire rope manufacturers
have established standards for sheave sizes to be used with various
rope constructions. To secure the most economical service, it is
important that the suggested size of sheaves given at right be used.
|
Proper Sheave and Drum Sizes
|
|
|
Suggested
|
Minimum
|
|
Construction
|
D/d* ratio
|
D/d* ratio
|
| 6x7 |
72
|
42
|
19x7 or 18x7
Rotation Resistant |
51
|
34
|
| 6x19 Seale |
51
|
34
|
| 6x27 H flattened strand
|
45
|
30
|
| 6x31 V flattened strand
|
45
|
30
|
| 6x21 filler wire |
45
|
30
|
| 6x25 filler wire |
39
|
26
|
| 6x31Warrington Seale |
39
|
26
|
| 6x36 Warrington Seale |
35
|
23
|
| 8x19 Seale |
41
|
27
|
| 8x25 filler wire |
32
|
21
|
| 6x41 Warrington Seale |
32
|
21
|
| 6x42 filler |
21
|
14
|
|
