Civil Engineering Reference
In-Depth Information
M rope ¼ M rev :
With that and the Eqs. ( 2.79 ) and ( 2.80 ) the mean rotary angle is
u 50 ¼ arcsin h 0 d c 1
r 1
ð 2 : 81 Þ
r 2
and the rotary angle that will not be exceeded in 90 % of the ropes (for untwisted
ropes, x 0 = 0) is
u 90 ¼ arcsin h 0
d ð c 1 þ 1 ; 282 s 1 Þ
r 1 r 2
:
ð 2 : 81a Þ
In addition a pre-twisting with a twist angle x 0 6 ¼ 0 can occur by wrong rope
mounting or rope running over sheaves with side deflection. Under the influence of
those pre-twisted ropes the total rotary angle is
:
f twi h 0 d ð c 1 þ 1 ; 282 s 1 Þ
r 1 r 2
u tot ¼ arcsin
ð 2 : 81b Þ
The twisting factor f twi is the ratio between the torque M out of the Eq. ( 2.77 )
for the pre-twisted ropes (x = x 0 ) and that without pre-twisting (x = 0)
f twi ¼ ð c 1 þ 1 ; 282 s 1 Þ d S þ c 2 d 2
S x þ c 3 G d 4
x
ð 2 : 82 Þ
ð c 1 þ 1 ; 282 s 1 Þ d S
with the rope tensile force
S ¼ Q 0 þ Q þ G rope = 2
z
:
ð 2 : 83 Þ
A pre-twisting angle should be estimated according the existing circumstances.
For example with two or four bearing rope traces (z = 2 or 4), a pre-twisting angle
x 0 = 20/100d may be exist.
The presented calculation method is not only valid for two rope traces. For all
number of bearing rope traces is
• r 1 is the mean distance between the upper end of all the rope traces to the load
rotation axis
• r 2 is the mean distance between the lower end of all the rope traces to the load
rotation axis.
An overlapping of the bearing rope traces will be prevented, if the rotary angle
is smaller than 90. The critical case is that for the load force out of the bottom
sheave mass only and for the biggest possible height h 0 .
Search WWH ::




Custom Search