Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 312

Table 3.20 Constants c 0 in N/mm and c 1 (dimensionless) for calculating the loss of the specific
rope force, ( 3.97 ), steel sheave groove, Schraft et al. ( 1997 )
Wire rope Bright Zinc coated

FC WRC FC WRC

c 0 c 1 c 0 c 1 c 0 c 1 c 0 c 1

6 9 7 0.81 0.189 0.00 0.154 2.59 0.213 1.27 0.178

8 9 7 1.11 0.198 0.00 0.163 2.89 0.223 1.57 0.188

6 9 19 1.27 0.211 0.00 0.176 3.05 0.235 1.73 0.200

8 9 19 1.73 0.228 0.41 0.193 3.51 0.252 2.19 0.217

6 9 35 1.88 0.240 0.56 0.205 3.66 0.265 2.34 0.230

8 9 36 2.60 0.270 1.28 0.235 4.38 0.294 3.06 0.259

18 9 7 2.80 0.251 1.48 0.217 4.58 0.276 3.26 0.241

34 9 7 5.28 0.329 4.14 0.294 7.06 0.353 5.74 0.318

Standard deviation for c 0 is s 0 = 1.73. Standard deviation for c 1 is s 1 = 0.031

The constants c 0 (in N/mm 2 ) and c 1 (dimensionless) are evaluated from Schraft
and are listed in Table 3.20 for standardised round strand ropes with fibre or steel
core and bright or zinc coated. From different types of the two spiral round strand
rope constructions 18 9 7 and 34 9 7 mean constants have been calculated and
included in Table 3.20 . The constants relate to well-lubricated ropes. For de-
greased ropes, the constants c 0 have to be enlarged with 1.56 N/mm 2

and the

constants c K with 0.084.
The constant c 0 representing the force loss of wire ropes for the tensile force
S = 0, has a big standard deviation s 0 = 1.73 N/mm 2 . This big standard deviation
depends to a great extent on manufacturing conditions especially the pre-forming
of the strands. The constant c 1 , which depends mainly on dimension deviations,
has the relatively small standard deviation s 1 = 0.031.
The constants in Table 3.20 are only valid for a loss of force due to rope
friction. The entire force loss from rope friction, bearing friction and seal friction
is

DS tot
d 2

¼ DS

d 2 þ DS bear

þ DS seal
d 2

: ð 3 : 98 Þ

d 2

The force loss from the bearing is

¼ l bear d axle
D

2 sin # D
2

DS bear
d 2

S
d 2

: ð 3 : 99 Þ

In that l bear is the friction coefficient, d axle the axle diameter and # D the
deflection angle of the rope. According to the SKF catalogue for standard roller
bearings, the friction coefficient is l bear B 0.0024. With the general assumption
that the axle diameter is five times the rope diameter and that the deflection angle
is 180, the rope force loss from one or two roller bearings is