Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 236

200 . 10 3

cross lay 6 x 19
d = 16 mm

160

R 0 = 1270 N/mm 2

D = 500 mm
˃ z = 200 N/mm 2

120

80

ordinary lay

40

lang lay

0

= 20 ° = 32 ° 90 ° =45 ° ʳ = 60 °

r= 8mm

r = 50 mm

r = 0,53d

= 8,5 mm

Fig. 3.48 Breaking numbers of bending cycles for a ordinary and a lang lay rope in different
form grooves, Woernle ( 1934 )

actual measurement of the rope diameter d m . Below this ratio, the endurance of the
rope is strongly reduced and should be avoided.
Normally, the groove radius is r = 0.53d with d for the nominal rope diameter.
As the actual measurement of the rope diameter can be 5 % greater than the
nominal rope diameter, the wire rope will always be well-bedded and optimal rope
endurance can be more or less expected.

3.2.3.5 Special Form Grooves

Early bending fatigue tests with differently formed grooves have been carried out
by Woernle ( 1934 ). The results of these tests are shown in his frequently published
Fig. 3.48 . The cross lay ropes tested are no longer used in elevators and the test
conditions are very different from those found in practice with elevators. In
Woernle's tests which did not include traction forces, the rope tensile stress r z is
higher and the diameter ratio D/d is smaller. Furthermore, these tests were carried
out until the rope actually broke. However, the rope endurance up to its discarding
point is of especial interest for elevators. Figure 3.48 therefore only gives a first
impression.
To find out more about the influence of form grooves, Holeschak ( 1987 )
investigated rope endurance in existing elevators. His findings for undercut round
grooves and V-grooves are given in Fig. 3.49 as the ratio of the discarding
numbers of bending cycles with form grooves and with standard round grooves.