MEASURING WIRE ROPE
Crushing strength is the strength necessary to
resist the compressive and squeezing forces that
distort the cross section of a wire rope, as it runs over
sheaves, rollers, and hoist drums when under a heavy
load. Regular lay rope distorts less in these situations
than lang lay.
Fatigue resistance is the ability to withstand the
constant bending and flexing of wire rope that runs
continuously on sheaves and hoist drums. Fatigue
resistance is important when the wire rope must be run
at high speeds. Such constant and rapid bending of the
rope can break individual wires in the strands. Lang
lay ropes are best for service requiring high fatigue
resistance. Ropes with smaller wires around the
outside of their strands also have greater fatigue
resistance, since these strands are more flexible.
Abrasion resistance is the ability to withstand the
gradual wearing away of the outer metal, as the rope
runs across sheaves and hoist drums. The rate of
abrasion depends mainly on the load carried by the
rope and the running speed. Generally, abrasion
resistance in a rope depends on the type of metal that
the rope is made of and the size of the individual outer
wires. Wire rope made of the harder steels, such as
improved plow steel, has considerable resistance to
abrasion. Ropes that have larger wires forming the
outside of their strands are more resistant to wear than
ropes having smaller wires that wear away more
Corrosion resistance is the ability to withstand the
dissolution of the wire metal that results from
chemical attack by moisture in the atmosphere or
elsewhere in the working environment. Ropes that are
put to static work, such as guy wires, maybe protected
from corrosive elements by paint or other special
dressings. Wire rope may also be galvanized for
corrosion protection. Most wire ropes used in crane
operations must rely on their lubricating dressing to
double as a corrosion preventive.
Wire rope is designated by its diameter, in inches.
The correct method of measuring the wire rope is to
measure from the top of one strand to the top of the
strand directly opposite it. The wrong way is to
measure across two strands side by side.
To ensure an accurate measurement of the
diameter of a wire rope, always measure the rope at
three places, at least 5 feet apart (fig. 5-7). Use the
average of the three measurements as the diameter of
NOTE: A crescent wrench can be used as an
expedient means to measure wire rope.
WIRE ROPE SAFE WORKING LOAD
The term safe working load (SWL) of wire rope is
used to define the load which can be applied that
allows the rope to provide efficient service and also
prolong the life of the rope.
The formula for computing the SWL of a wire
rope is the diameter of the rope squared, multiplied by
D x D x 8 = SWL (in tons)
Example: The wire rope is 1/2 inch in diameter.
Compute the SWL for the rope.
The first step is to convert the 1/2 into decimal
numbers by dividing the bottom number of the
fraction into the top number of the fraction: (1 divided
by 2 = .5.) Next, compute the SWL formula: (.5 x .5
x 8 = 2 tons.) The SWL of the 1/2-inch wire rope is 2
Figure 5-7.Correct and incorrect methods of measuring