Civil Engineering Reference
In-Depth Information
Fig. 3.17 Contact force
Q and line pressure q,
Example 3.2
ʴ
= 2mm
Q = 500 N
q = 25 N/mm
20mm
Q = 500 N
S = 10 000 N
R
0
= 400mm
S = 10 000 N
3.1.6.2 Line Pressure Between a Wire Rope and a Sheave
When a wire rope is stretched over a sheave, the contact force Q known from the
tape does not only work in a lateral line between rope and sheave. Because of the
deformation of the rope, the force in the contact point is more effective in a small
area. In any case, the pressure and the line pressure in this area are much higher
than in the remaining contact bow. The amount of this pressure depends on the
construction of the wire rope, as well as on the material and the shape of the
groove. In a steel sheave with a normal groove, Wiek (
1982b
) found a pressure
peak which was 50 % higher than in the remaining bow.
Partly due to the measuring devices used, Wiek's measurements (1982a,
b
)in
round grooves and Molkow (
1982
) in V-grooves give in their own opinion only first
rough results. Häberle (
1995
) made his measurements to evaluate the pressure and
the line pressure between a wire rope and a longer piece of sheave grooves con-
sisting only out of force measuring elements. Due to these measuring arrangements,
the resulting pressure and the line pressure evaluated here are reasonably precise.
Figure
3.18
from Häberle (
1995
) shows the line pressure measured while a wire
rope is running over the sheave. A high peak can be observed in the line pressure at
the point where the rope runs on and a lower peak where the rope runs off the
sheave. In addition, the global line pressure
q
0
¼
2
S
D
ð
3
:
27
Þ
is drawn as a dashed curve. The contact angle of the rope is about 3 smaller on
both sides than the calculated angle for a limp-bending yarn (that is equal to the
deflection angle
#
D
).
The line pressure measured for a wire rope running over a sheave under dif-
ferent tensile forces is shown in Fig.
3.19
. Häberle (
1995
) evaluated the ratio of
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