Wire Breaks at
End
Termination
Crown wire breaks usually are due to normal wear and typically have square
ends. Valley breaks may indicate an abnormal condition, such as loss
of
core sup-
port, small sheave grooves
or
deterioration from unusually heavy rope loading.
When a wire has broken from excessive loading or a tensile overload, the ends
of
the wire will be pulled or necked down in diameter on each side
of
the break, in con-
trast to the typical square ends
of
crown wire breaks. In normal service, the wire
breaks will exhibit
characteristics
of
both axial loading and fatigue.
rt:
E
Figure 43. A wire broken under a tensile load that exceeds its strength is recognized
by
the "cup and
cone" configuration at the fracture point (a). The necking down
of
the wire at this point shows that fail-
ure occurred while the wire retained its ductility. Shear-tensile fracture
(b), usually exhibiting an angu-
Jar
flat plane failure surface, occurs in wire subjected to a combination
of
transverse and axial loads .
Fatigue breaks are usually characterized by squared-off ends perpendicular to the wire either straight
across
or
Z-shaped (c&d).
TYPES OF WIRE BREAKS
As a wire rope moves over sheaves and drums, each strand and each wire
in
every strand moves and adjusts. Bending the rope
or
observing
it
moving slowly
over a sheave can help the inspector find broken wires.
Once
wire breaks appear,
their
numbers will increase
if
the
rope
continues
in service.
Valley and strand-to-core contact point breaks are difficult to detect in a rope
and must be taken very seriously. These types
of
wire breaks are indicative
of
conditions that result in internal degradation occurring at a faster rate than exter-
nal degradation.
Wire breaks at rope terminations are also indicators
of
rope degradation. A single
broken wire at a termination is usually reason to question continued use
of
a rope;
more than one break is usually sufficient reason to remove the rope from service.
Flexing a rope can often expose broken wires hidden
in valleys between strands.
Wire Rope Technical Board - Wire Rope Users Manual, Fourth
Edition·
67
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