Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 240

When sheave grooves are made of a soft material (small elasticity module), the
wire rope endurance increases. Müller ( 1961 ) carried out a series of comparative
bending fatigue tests with plastic and cast iron sheaves. The results are shown in
Fig. 3.50 .
The same tendency is also be found in the work done by other authors. The ratio
of the breaking number of bending cycles with sheave grooves made of plastic
material in comparison with those made of steel or cast iron shown in Fig. 3.51 has
been taken from all the known series of comparative tests. Only the very large
ratios Babel ( 1980 ) found in tests with degreased wire ropes have not been
included. The mean ratio of the breaking number with plastic groovesN pl and of
those with steel or cast iron N st is

N pl
N st

¼ 8 : 37 N 0 : 124
st

ð 3 : 58 Þ

50

or

2

0 : 75 þ 0 : 36 S = d 2

S = d 2
D = d

N pl
N st D = d 0 : 023

: ð 3 : 58a Þ

50

The lower the breaking cycles are with steel grooves, the higher the relation of
the number of bending cycles with plastic grooves to those with steel grooves is.
There is a tendency for rope endurance to be higher with very soft polyurethanes
than with the somewhat harder polyamides.

10,0

90%

5,0

3,0

2,0

10%

1,0

Müller (1961)
Paetzel (1969)
Oplatka (1977)

Babel (1980)
Jehmlich (1985)
Wiek (1989)

Feyrer (1982)

Feyrer

0,5

Vogel (2003)

10 4 10 5 10 6

5

23
number of bending cycles N steel,iron

5 2 3 5

Fig. 3.51 Ratio of breaking numbers with sheave grooves made of plastic and steel or cast iron