Helical grooving does not employ a built in cross-over and does not work
as
well
for multiple layer spooling as a counterbalanced drum because
it does not have the
cross-over and does not consistently put the rope in the proper position at the
flanges to rise from one layer to the next layer.
Counterbalance grooving with two cross-overs is made so that each wrap
of
rope winds parallel to the drum flange for a distance less than half the circumfer-
ence around the drum, then follows a short cross-over to complete half the drum
circumference. The cross-over is at an angle with the drum flange and displaces
the rope laterally by half the pitch
of
grooving.
Around the other half
of
the drum circumference each wrap again winds paral-
lel to the flange for a distance, and then follows another short cross-over to a
point one full circumference from the start. At this point the lateral displacement
is equal to the full pitch
of
grooving.
The grooving for this type
of
winding is similar to the parallel grooving except
that half the drum circumference is laterally displaced from the other half
by
half
the pitch
of
grooving, and between these two halves the grooves make short
cross-overs to guide the rope properly. The two cross-over areas are on opposite
sides
of
the drum, or 180
0
apart.
Since the lateral displacement
of
each cross-over is one half the pitch
of
groov-
ing, or one
half
the displacement
of
the cross-overs encountered with other types
of
winding, "throw"
of
the rope is reduced, decreasing the Whipping action.
However,
if
the interval between these displacements happens to match the
rope's vibration cycle, whipping can still become severe because this action
is cumulative.
Since the cross-over areas are spaced opposite each other,
or
180
0
apart, raised
portions
of
the winding caused by vertical displacement at the cross-overs also
occur opposite each other. These raised sections become quite pronounced where
many layers are involved and the balancing effect
of
keeping them opposite gave
name to the method.
With counterbalance winding, the change
of
layers can be controlled better
than with other systems and is preferred when a rope must wind in many layers
on the drum.
48 • Wire Rope Technical Board - Wire Rope Users Manual, Fourth Edition
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