Civil Engineering Reference
In-Depth Information
3.1.7 Pressure Between Rope and Sheave
The rope pressure is the imagined pressure between a rope which is entirely round
without any surface structure due to strands and wires and the groove. The line
pressure q is distributed lateral to the strands and the wires in contact with the
groove. In dimensioning wire ropes for mining hoistings and for elevators sim-
plified forms of rope pressure are used. The real pressure occurs between the most
prominent points of the wires and the sheave groove.
3.1.7.1 Global Rope Pressure
The global rope pressure p
0
is defined as the pressure between a limp-bending tape
with the rope diameter d as its width and a cylindrical sheave. The global rope
pressure is
p
0
¼
q
0
d
¼
2
S
ð
3
:
27a
Þ
D
d
with the global line pressure q
0
, the rope tensile force S, the rope diameter d and
the sheave diameter D measured from rope centre to rope centre of a rope wound
around the sheave. For sheaves with round grooves, the global rope pressure
represents all the working pressures between rope and groove. If round grooves
made of the same material are always used in combination with the same wire rope
surface, the global pressure is a dimensioning criterion. This is the case for mining
installations where the sheaves always have round grooves made of soft material
(small elasticity module).
3.1.7.2 Specific Pressure, Form Grooves
The specific pressure is a special form of rope pressure for use in elevators. For
traction sheaves in elevators, in particular for those with undercut grooves, the specific
pressure is used as a criterion for making sure that the rope and the traction sheave are
sufficiently durable and for calculating the friction force for driving the car.
Donandt (
1927
) and Hyman and Hellborn (
1927
) were the first to calculate the
specific pressure. They supposed that the pressure in the groove has a cosinus-like
distribution as shown in Fig.
3.22
for an undercut groove. With this supposition
the specific pressure is
k ¼ k
0
cos c
:
ð
3
:
30
Þ
The pressure k
0
is the pressure at the bottom of the groove (groove angle c = 0)
although this does not exist in undercut grooves. The groove angle is defined in
Fig.
3.22
. For traction sheaves where the specific pressure has to be considered,
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