Civil Engineering Reference
In-Depth Information
Example 2.8: Torque constant c of the open spiral rope in Fig.
2.4
According to (
2.74
), the torque constant is
c
1S
¼
ð
6
13
12
2
:
55
þ
18
3
:
8
Þ
1
:
227
0
:
970
2
0
:
242
8
:
85
½1
1
:
431
þð
6
þ
12
þ
18
Þ
1
:
227
0
:
970
3
c
1S
¼
12
:
74
369
:
45
¼ 0
:
0345
:
2.4.2 Torque of Twisted Round Strand Ropes
2.4.2.1 Measurements
The torque of twisted and not twisted round strand ropes has been investigated by
measurements. With the results of these measurements a simple calculation
method will be derived with that the customer can calculate the torque for a given
wire rope. This method will have the advantage that it can be used without
knowing the precise geometrical data of the rope.
Torque measurements with different tensile forces and different twist angles are
carried out with a series of ropes. The equipment of Feyrer and Schiffner (
1986
)
comprises a torque meter and a rope twisting device, mounted in a tensile testing
machine for carrying out the measurements. The torque meter, which measures the
torque by means of strain gauges, is because of the installed membranes nearly not
influenced by the tensile force. The entire equipment is shown in Fig.
2.21
. Rebel
and Chandler (
1996
) presented a measuring equipment with the opportunity to
measure in addition the rope elongation and the rope diameter reduction.
In all cases the wire rope is at both ends fixed in a rope socket so that a relative
motion of the wires and the strands are prevented strictly. The torques measured with
different twisted wire ropes (positive sign for turn off) are shown in Figs.
2.22
and
2.23
for ordinary lay ropes 6 9 7-FC and Warrington 8 9 19-FC. As for all wire ropes
with fibre core the torque increases nearly linear with the tensile force. The distance of
the lines for the different twist angles is for the wire rope 6 9 7-FC bigger than for the
Warrington rope 8 9 19-FC. That means the wire rope 6 9 7-FC with 42 wires is
more torsion rigid than the Warrington rope with 152 wires. The Warrington rope has
been measured lubricated and not lubricated with practically no different torque.
The torque for the increasing and decreasing tensile force shows nearly no hyster-
esis. In the following diagrams only the lines for the increasing tensile force are shown.
For wire ropes with independent made steel wire rope core IWRC the torque
also increases nearly linear with the tensile force. To demonstrate this, in addition
to the measured torque lines, straight lines are sketched in Fig.
2.24
for a Filler
rope 8 9 (19 + 6F)-IWRC-sZ.
Double parallel wire ropes (PWRC) have only a nearly linear relation between
torque and tensile force for small twist angles. Figure
2.25
shows the torque of a
Search WWH ::
Custom Search