Rope
Unbalance
Also called "wavy rope,"
unbalance is an indication
or result of abnormal movement
of strands in an operating
rope. It usually involves
two or more outer strands
of rope rising out of position,
standing higher than remaining
strands with no apparent cause
or evidence of external physical
force. This may cause vibration
during operation and unevenness
in the rate of wear.
Unbalance often shows up
in the middle of a rope system
where you don't expect it.
It's usually caused by "milking"
of the rope -- in other words,
a lay change in the rope.
The causes are many: swivels,
small diameter sheaves, improper-sized
or worn sheave grooves or
sheave misalignment, to name
a few.
Standard 6-strand regular
lay ropes are generally more
resistant to unbalance than
other ropes.
There are several practices
you can implement to minimize
rope unbalance problems. These
include:
- Eliminate swivels at
dead ends. A swivel
end termination will lengthen
the lay in the rope when
loaded, which can cause
an unbalance in the rope.
- Remove welded ends of
ropes. Where a
rope has been torch cut,
make sure the strands are
free to adjust before the
rope is clamped or seated
in an end termination. (Note:
Welded-ends must remain
on Flex-X 35)
- Look for any sheave
misalignment. Misalignment
of sheaves in multi-part
reevings and improperly
aligned idler sheaves can
also contribute to unbalance
problems.
- Assure proper groove
contours. Use a
groove gauge to inspect
sheave and drum grooves
for proper contour. If sheave
grooves are too small or
are worn deeper and narrower
by an old rope, they're
too tight for new ropes.
If grooves are too wide,
the ropes tend to flatten
out and become oval-shaped.
Any of these conditions
can restrict strand movement
and cause twist to build
up in the rope.
- Consider a 6-strand
rope construction.
Standard 6-strand regular
lay ropes are less susceptible
to unbalance than other
ropes.
- Remove any twist in
rope. See rope
installation guidelines
for details.
